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Sample records for absolute asymmetric synthesis

  1. Asymmetric total synthesis of (-)-lundurine B and determination of its absolute stereochemistry.

    PubMed

    Nakajima, Masaya; Arai, Shigeru; Nishida, Atsushi

    2015-04-01

    A total synthesis of the Kopsia tenuis alkaloid (-)-lundurine B has been achieved. A quaternary chiral carbon has been created by an asymmetric deprotonation using a symmetric spiro cyclohexanone intermediate with a chiral lithium amide. The hexacyclic skeleton was sequentially constructed through metal-mediated reactions. The absolute stereochemistry of intermediate 5 has been unambiguously established by X-ray crystallographic analysis. This is the first description of the absolute stereochemistry of Kopsia tenuis alkaloids based on chemical synthesis.

  2. Absolute asymmetric synthesis of enantiopure organozinc reagents, followed by highly enantioselective chlorination.

    PubMed

    Olsson, Susanne; Lennartson, Anders; Håkansson, Mikael

    2013-09-09

    We report the absolute asymmetric synthesis (AAS) of indenylzinc reagents by using total spontaneous resolution followed by enantiospecific conversion into 1-chloroindene. The chiral complex [Zn(dcp)(ind)(tmeda)] (dcp = 2,6-dichlorophenoxy and tmeda = N,N,N',N'-tetramethylethylenediamine) (3) was prepared from the achiral starting materials indene, potassium, zinc chloride, TMEDA, and 2,6-dichlorophenol. The reagent resolved spontaneously on crystallization, and single crystals of 3 react with N-chlorosuccinimide in the presence of benzoquinone in 2-propanol to give 1-chloroindene in >98 % enantiomeric excess. It was found that (R)-3 gave (R)-1-chloroindene upon reaction, indicating an SE 2'-mechanism. Since bulk samples of 3 gave optically active product upon chlorination, total spontaneous resolution must have occurred. This demonstrates that enantiopure products can be obtained through the absolute asymmetric synthesis of organometallic reagents starting from achiral materials. The general absolute asymmetric synthesis (AAS) method offers easy access to both enantiomers and an almost limitless variation in the design of the product.

  3. Stochastic and empirical models of the absolute asymmetric synthesis by the Soai-autocatalysis.

    PubMed

    Barabás, Béla; Zucchi, Claudia; Maioli, Marco; Micskei, Károly; Pályi, Gyula

    2015-02-01

    Absolute asymmetric synthesis (AAS) is the preparation of pure (or excess of one) enantiomer of a chiral compound from achiral precursor(s) by a chemical reaction, without enantiopure chiral additive and/or without applied asymmetric physical field. Only one well-characterized example of AAS is known today: the Soai-autocatalysis. In an attempt at clarification of the mechanism of this particular reaction we have undertaken empirical and stochastic analysis of several parallel AAS experiments. Our results show that the initial steps of the reaction might be controlled by simple normal distribution ("coin tossing") formalism. Advanced stages of the reaction, however, appear to be of a more complicated nature. Symmetric beta distribution formalism could not be brought into correspondence with the experimental observations. A bimodal beta distribution algorithm provided suitable agreement with the experimental data. The parameters of this bimodal beta function were determined by a Pólya-urn experiment (simulated by computer). Interestingly, parameters of the resulting bimodal beta function give a golden section ratio. These results show, that in this highly interesting autocatalysis two or even perhaps three catalytic cycles are cooperating. An attempt at constructing a "designed" Soai-type reaction system has also been made.

  4. Asymmetric Synthesis and Absolute Configuration Assignment of a New Type of Bedaquiline Analogue.

    PubMed

    Qiao, Chang-Jiang; Wang, Xiao-Kui; Xie, Fei; Zhong, Wu; Li, Song

    2015-12-11

    Bedaquiline is the first FDA-approved new chemical entity to fight multidrug-resistant tuberculosis in the last forty years. Our group replaced the quinoline ring with a naphthalene ring, leading to a new type of triarylbutanol skeleton. An asymmetric synthetic route was established for our bedaquiline analogues, and the goal of assigning their absolute configurations was achieved by comparison of experimental and calculated electronic circular dichroism spectra, and was confirmed by the combined use of circular dichroism and NMR spectroscopy.

  5. Asymmetric synthesis and absolute stereochemistry of a labdane-type diterpenoid isolated from the rhizomes of Isodan yuennanensis.

    PubMed

    Deng, Heping; Cao, Wei; Zhang, Zhijiang; Liu, Bo

    2016-07-14

    The first synthesis of a labdane-type diterpenoid isolated from Isodon yuennanensis was achieved in fourteen steps from commercially available starting material, (+)-sclareolide. The synthesis features the Barton nitrite ester reaction to introduce an oxime at the angular methyl group and the Jones oxidation to construct the lactone segment. By comparison of the optical rotation of our synthetic sample and the natural sample, the absolute stereochemistry of the natural diterpenoid has been determined.

  6. Concise asymmetric synthesis of (-)-sparteine.

    PubMed

    Hermet, Jean-Paul R; McGrath, Matthew J; O'Brien, Peter; Porter, David W; Gilday, John

    2004-08-21

    A six-step asymmetric synthesis of natural (-)-sparteine from ethyl 7-iodohept-2-enoate is reported, involving a connective Michael addition of an amino ester-derived enolate to an alpha,beta-unsaturated amino ester.

  7. Asymmetric Synthesis of (+)-anti- and (-)-syn-Mefloquine Hydrochloride.

    PubMed

    Rastelli, Ettore J; Coltart, Don M

    2016-10-21

    The asymmetric (er > 99:1) total synthesis of (+)-anti- and (-)-syn-mefloquine hydrochloride from a common intermediate is described. The Sharpless asymmetric dihydroxylation is the key asymmetric transformation used in the synthesis of this intermediate. It is carried out on an olefin that is accessed in three steps from commercially available materials, making the overall synthetic sequence very concise. The common diol intermediate derived from the Sharpless asymmetric dihydroxylation is converted into either a trans- or cis-epoxide, and these are subsequently converted to (+)-anti- and (-)-syn-mefloquine, respectively. X-ray crystallographic analysis of derivatives of (+)-anti- and (-)-syn-mefloquine is used to lay to rest a 40 year argument regarding the absolute stereochemistry of the mefloquines. A formal asymmetric (er > 99:1) synthesis of (+)-anti-mefloquine hydrochloride is also presented that uses a Sharpless asymmetric epoxidation as a key step.

  8. Organocatalyzed asymmetric synthesis of morphans.

    PubMed

    Bradshaw, Ben; Parra, Claudio; Bonjoch, Josep

    2013-05-17

    A general effective organocatalyzed synthesis of enantioenriched morphans with up to 92% ee was developed. The morphan scaffold was constructed in a one-pot tandem asymmetric organocatalyzed Michael addition followed by a domino Robinson annulation/aza-Michael intramolecular reaction sequence from easily available starting materials.

  9. Asymmetric synthesis of (-)-adaline.

    PubMed

    Itoh, Toshimasa; Yamazaki, Naoki; Kibayashi, Chihiro

    2002-07-25

    [reaction: see text] An enantioselective total synthesis of (-)-adaline has been achieved starting from a chiral 6,6-disubstituted piperidone derivative previously prepared by diastereoselective allylation of a chiral tricyclic N-acyl-N,O-acetal. The key steps include lithium ion-activated SN2-type alkynylation of the tricyclic N,O-acetal leading to exclusive formation of the (6S)-ethynylpiperidine and ring-closing olefin metathesis of the (2R,6S)-cis-2,6-dialkenylpiperidine for constructing the bridged azabicyclononane.

  10. Hydroxamic Acids in Asymmetric Synthesis

    PubMed Central

    Li, Zhi; Yamamoto, Hisashi

    2012-01-01

    Metal-catalyzed stereoselective reactions are a central theme in organic chemistry research. In these reactions, the stereoselection is achieved predominantly by introducing chiral ligands at the metal catalyst’s center. For decades, researchers have sought better chiral ligands for asymmetric catalysis and have made great progress. Nevertheless, to achieve optimal stereoselectivity and to catalyze new reactions, new chiral ligands are needed. Due to their high metal affinity, hydroxamic acids play major roles across a broad spectrum of fields from biochemistry to metal extraction. Dr. K. Barry Sharpless first revealed their potential as chiral ligands for asymmetric synthesis in 1977: He published the chiral vanadium-hydroxamic-acid-catalyzed, enantioselective epoxidation of allylic alcohols before his discovery of Sharpless Asymmetric Epoxidation, which uses titanium-tartrate complex as the chiral reagent. However, researchers have reported few highly enantioselective reactions using metal-hydroxamic acid as catalysts since then. This Account summarizes our research on metal-catalyzed asymmetric epoxidation using hydroxamic acids as chiral ligands. We designed and synthesized a series of new hydroxamic acids, most notably the C2-symmetric bis-hydroxamic acid (BHA) family. V-BHA-catalyzed epoxidation of allylic and homoallylic alcohols achieved higher activity and stereoselectivity than Sharpless Asymmetric Epoxidation in many cases. Changing the metal species led to a series of unprecedented asymmetric epoxidation reactions, such as (i) single olefins and sulfides with Mo-BHA, (ii) homoallylic and bishomoallylic alcohols with Zr- and Hf-BHA, and (iii) N-alkenyl sulfonamides and N-sulfonyl imines with Hf-BHA. These reactions produce uniquely functionalized chiral epoxides with good yields and enantioselectivities. PMID:23157425

  11. Asymmetric Synthesis (by Garry Procter)

    NASA Astrophysics Data System (ADS)

    Kesler, Brenda

    1998-05-01

    Oxford University Press: New York, 1996. vi + 237 pp. ISBN 0 19 855726 4 (cloth); 85.00. ISBN 0 19 855725 6 (paper); 37.00. This ever-expanding area of organic chemistry is indeed a daunting challenge for a book, both in terms of the breadth of material and the rapid change of events relative to the publishing time line. I feel the author has done an admirable job juggling these two issues. Following an introductory chapter on the principles of asymmetric induction are seven chapters on individual classes of reactions: additions to carbonyl compounds, alpha-substitution using chiral enolates, asymmetric aldol reactions, additions to C-C double bonds, reduction and oxidation, rearrangements, and hydrolysis and esterification. The vast majority of the references are from the mid-80s through the early 90s, including both general and seminal references. In particular, I feel a very solid balance has been achieved between content and clarity. The chapter on "Principles" at the beginning was very well thought out and organized and is a wonderful overview of asymmetric synthesis. This is balanced nicely in subsequent chapters on specific methods where very useful, practical generalizations are presented, such as the "best alpha-hydroxylation" method or the "best alpha-bromination" procedure. The chapters also have nicely integrated examples that show the power of the particular bond construction being examined as it applies to published total syntheses, my favorite being the ones in the chapter on asymmetric aldol reactions.

  12. A novel asymmetric synthesis of cinacalcet hydrochloride

    PubMed Central

    Gorentla, Laxminarasimhulu; Dubey, Pramod K

    2012-01-01

    Summary A novel route to asymmetric synthesis of cinacalcet hydrochloride by the application of (R)-tert-butanesulfinamide and regioselective N-alkylation of the naphthyl ethyl sulfinamide intermediate is described. PMID:23019473

  13. A Concise Asymmetric Total Synthesis of (+)-Brevisamide

    PubMed Central

    Herrmann, Aaron T.; Martinez, Steven R.; Zakarian, Armen

    2012-01-01

    A new protecting-group-free synthesis of the marine monocyclic ether (+)-brevisamide is reported. The enantioselective synthesis utilizes a key asymmetric Henry reaction and an Achmatowicz rearrangement for the formation of the tetrahydropyran ring. A penultimate Stille cross-coupling allows for an efficient installation of the conjugated (E,E)-diene side chain ultimately delivering (+)-brevisamide. PMID:21678904

  14. Enantiopure sulfoxides: recent applications in asymmetric synthesis.

    PubMed

    Carreño, M Carmen; Hernández-Torres, Gloria; Ribagorda, María; Urbano, Antonio

    2009-11-07

    Sulfoxides are nowadays recognised as powerful chiral auxiliaries that may participate in a wide range of asymmetric reactions. Their high configurational stability, the existence of several efficient methods allowing the access to both configurations as well as their synthetic versatility are characteristic features offering a tremendous potential to develop new applications. Significant recent advances leading to high asymmetric inductions in carbon-carbon and carbon-oxygen bond forming reactions, and applications of homochiral sulfoxides to atroposelective synthesis and asymmetric catalysis are discussed. New uses of sulfoxides in the design of chiroptical switches are also shown.

  15. Fluorous Mixture Synthesis of Asymmetric Dendrimers

    PubMed Central

    Jiang, Zhong-Xing; Yu, Yihua Bruce

    2010-01-01

    A divergent fluorous mixture synthesis (FMS) of asymmetric fluorinated dendrimers has been developed. Four generations of fluorinated dendrimers with the same fluorinated moiety were prepared with high efficiency, yield and purity. Comparison of the physicochemical properties of these dendrimers provided valuable information for their application and future optimization. This strategy has not only provided a practical method for the synthesis and purification of dendrimers, but also established the possibility of utilizing the same fluorinated moiety for FMS. PMID:20170088

  16. Asymmetric synthesis of tertiary thiols and thioethers

    PubMed Central

    MacLellan, Paul

    2011-01-01

    Summary Enantiomerically pure tertiary thiols provide a major synthetic challenge, and despite the importance of chiral sulfur-containing compounds in biological and medicinal chemistry, surprisingly few effective methods are suitable for the asymmetric synthesis of tertiary thiols. This review details the most practical of the methods available. PMID:21647256

  17. Studies Culminating in the Total Synthesis and Determination of the Absolute Configuration of (-)-Saudin

    PubMed Central

    Boeckman, Robert K.; del Rosario Ferreira, Maria Rico; Mitchell, Lorna H.; Shao, Pengcheng; Neeb, Michael J.; Fang, Yue

    2011-01-01

    A full account of studies that culminated in the total synthesis of both antipodes and the assignment of its absolute configuration of Saudin, a hypoglycemic natural product. Two approaches are described, the first proceeding though bicyclic lactone intermediates and related second monocyclic esters. The former was obtained via asymmetric Diels-Alder cycloaddition and the latter by an asymmetric annulation protocol. Both approaches employ a Lewis acid promoted Claisen rearrangement, with the successful approach taking advantage of bidentate chelation to control the facial selectivity of the key Claisen rearrangement PMID:22523435

  18. Asymmetric catalysis in organic synthesis

    SciTech Connect

    Reilly, S.D.; Click, D.R.; Grumbine, S.K.; Scott, B.L.; Watkins, J.G.

    1998-11-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The goal of the project was to prepare new catalyst systems, which would perform chemical reactions in an enantioselective manner so as to produce only one of the possible optical isomers of the product molecule. The authors have investigated the use of lanthanide metals bearing both diolate and Schiff-base ligands as catalysts for the enantioselective reduction of prochiral ketones to secondary alcohols. The ligands were prepared from cheap, readily available starting materials, and their synthesis was performed in a ''modular'' manner such that tailoring of specific groups within the ligand could be carried out without repeating the entire synthetic procedure. In addition, they have developed a new ligand system for Group IV and lanthanide-based olefin polymerization catalysts. The ligand system is easily prepared from readily available starting materials and offers the opportunity to rapidly prepare a wide range of closely related ligands that differ only in their substitution patterns at an aromatic ring. When attached to a metal center, the ligand system has the potential to carry out polymerization reactions in a stereocontrolled manner.

  19. Chiral-auxiliary-mediated asymmetric synthesis of ruthenium polypyridyl complexes.

    PubMed

    Gong, Lei; Wenzel, Marianne; Meggers, Eric

    2013-11-19

    An octahedral metal complex with 6 different monodentate ligands can form 15 diastereomers as pairs of enantiomers. As a result, the elaborate stereochemistry of octahedral coordination geometries provides tremendous opportunities in the fields of catalysis, the materials sciences, and the life sciences. The demand for enantiomerically pure coordination complexes for tasks related to the selective molecular recognition of biomacromolecules led us to develop synthetic methods to control the absolute stereochemistry at octahedral metal centers. A few years ago our laboratory therefore embarked on a project exploring new and general synthetic strategies for the asymmetric synthesis of inert octahedral transition metal complexes. We initially used the example of thermally inert ruthenium polypyridyl complexes and developed a family of chiral bidentate ligands, including salicyloxazolines, (mercaptophenyl)oxazolines, sulfinylphenols, N-acetylsulfinamides, a phosphinohydroxybinaphthyl, and even the amino acid proline to serve as chiral auxiliaries for asymmetric coordination chemistry. All these chiral auxiliaries strongly coordinate to ruthenium(II) in a bidentate, deprotonated fashion, allowing them to control the absolute metal-centered configuration in the course of subsequent ligand exchange reactions. Finally, we can remove them from the metal without any loss of chiral information and without leaving a chemical trace. A key feature of these chiral auxiliary ligands is their switchable binding strength. A chelate effect ensures that the chiral ligands coordinate very tightly to the metal center, placing their carbon-based, sulfur-based, or axial chirality in a well-defined position close to the metal center to efficiently establish the absolute metal-centered configuration. At the same time a coordinating phenolate, carboximidate, carboxylate, or thiophenolate moiety makes the coordination reversible by weakening the binding strength through protonation or

  20. Metal-Catalyzed Asymmetric Michael Addition in Natural Product Synthesis.

    PubMed

    Hui, Chunngai; Pu, Fan; Xu, Jing

    2016-12-19

    Asymmetric catalysis for chiral compound synthesis is a rapidly growing field in modern organic chemistry. Asymmetric catalytic processes have been indispensable for the synthesis of enantioselective materials to meet demands from various fields. Michael addition has been used extensively for the construction of C-C bonds under mild conditions. With the discovery and development of organo- and metal-catalyzed asymmetric Michael additions, the synthesis of enantioselective and/or diastereoselective Michael adducts has become possible and increasingly prevalent in the literature. In particular, metal-catalyzed asymmetric Michael addition has been employed as a key reaction in natural product synthesis for the construction of contiguous quaternary stereogenic center(s), which is still a difficult task in organic synthesis. Previously reported applications of metal-catalyzed asymmetric Michael additions in natural product synthesis are presented here and discussed in depth.

  1. Asymmetric total synthesis of Apocynaceae hydrocarbazole alkaloids (+)-deethylibophyllidine and (+)-limaspermidine.

    PubMed

    Du, Ji-Yuan; Zeng, Chao; Han, Xiao-Jie; Qu, Hu; Zhao, Xian-He; An, Xian-Tao; Fan, Chun-An

    2015-04-01

    An unprecedented asymmetric catalytic tandem aminolysis/aza-Michael addition reaction of spirocyclic para-dienoneimides has been designed and developed through organocatalytic enantioselective desymmetrization. A unified strategy based on this key tandem methodology has been divergently explored for the asymmetric total synthesis of two natural Apocynaceae alkaloids, (+)-deethylibophyllidine and (+)-limaspermidine. The present studies not only enrich the tandem reaction design concerning the asymmetric catalytic assembly of a chiral all-carbon quaternary stereocenter contained in the densely functionalized hydrocarbazole synthons but also manifest the potential for the application of the asymmetric catalysis based on the para-dienone chemistry in asymmetric synthesis of natural products.

  2. Microscale Synthesis of Chiral Alcohols via Asymmetric Catalytic Transfer Hydrogenation

    ERIC Educational Resources Information Center

    Peeters, Christine M.; Deliever, Rik; De Vos, Dirk

    2009-01-01

    Synthesis of pure enantiomers is a key issue in industry, especially in areas connected to life sciences. Catalytic asymmetric synthesis has emerged as a powerful and practical tool. Here we describe an experiment on racemic reduction and asymmetric reduction via a catalytic hydrogen transfer process. Acetophenone and substituted acetophenones are…

  3. Total Synthesis, Assignment of the Relative and Absolute Stereochemistry, and Structural Reassignment of Phostriecin (aka Sultriecin)

    PubMed Central

    Burke, Christopher P.; Haq, Nadia; Boger, Dale L.

    2010-01-01

    A total synthesis of phostriecin (2) previously known as sultriecin (1), its structural reassignment as a phosphate versus sulfate monoester, and the assignment of its relative and absolute stereochemistry are disclosed herein. Key elements of the work, which provided first the originally assigned sulfate monoester 1 and then the reassigned and renamed phosphate monoester 2, relied on diagnostic 1H NMR spectroscopic properties of the natural product for the assignment of relative and absolute stereochemistry as well as the subsequent structural reassignment, and a convergent asymmetric total synthesis to provide the unequivocal authentic materials. Key steps of the synthetic approach include a Brown allylation for diastereoselective introduction of the C9 stereochemistry, an asymmetric CBS reduction to establish the lactone C5-stereochemistry, diastereoselective oxidative ring expansion of an α-hydroxyfuran to access the pyran lactone precursor, and single-step installation of the sensitive Z,Z,E-triene unit through a chelation-controlled cuprate addition with installation of the C11 stereochemistry. The approach allows ready access to analogues that can now be used to probe important structural features required for PP2A inhibition, the mechanism of action defined herein. PMID:20108904

  4. Total synthesis, assignment of the relative and absolute stereochemistry, and structural reassignment of phostriecin (aka Sultriecin).

    PubMed

    Burke, Christopher P; Haq, Nadia; Boger, Dale L

    2010-02-24

    A total synthesis of phostriecin (2), previously known as sultriecin (1), its structural reassignment as a phosphate versus sulfate monoester, and the assignment of its relative and absolute stereochemistry are disclosed herein. Key elements of the work, which provided first the originally assigned sulfate monoester 1 and then the reassigned and renamed phosphate monoester 2, relied on diagnostic (1)H NMR spectroscopic properties of the natural product for the assignment of relative and absolute stereochemistry as well as the subsequent structural reassignment, and a convergent asymmetric total synthesis to provide the unequivocal authentic materials. Key steps of the synthetic approach include a Brown allylation for diastereoselective introduction of the C9 stereochemistry, an asymmetric CBS reduction to establish the lactone C5-stereochemistry, diastereoselective oxidative ring expansion of an alpha-hydroxyfuran to access the pyran lactone precursor, and single-step installation of the sensitive Z,Z,E-triene unit through a chelation-controlled cuprate addition with installation of the C11 stereochemistry. The approach allows ready access to analogues that can now be used to probe important structural features required for protein phosphatase 2A inhibition, the mechanism of action defined herein.

  5. A high-performance liquid chromatography-electronic circular dichroism online method for assessing the absolute enantiomeric excess and conversion ratio of asymmetric reactions.

    PubMed

    Zhang, Xiang; Wang, Mingchao; Li, Li; Yin, Dali

    2017-03-02

    Asymmetric reactions often need to be evaluated during the synthesis of chiral compounds. However, traditional evaluation methods require the isolation of the individual enantiomer, which is tedious and time-consuming. Thus, it is desirable to develop simple, practical online detection methods. We developed a method based on high-performance liquid chromatography-electronic circular dichroism (HPLC-ECD) that simultaneously analyzes the material conversion ratio and absolute optical purity of each enantiomer. In particular, only a reverse-phase C18 column instead of a chiral column is required in our method because the ECD measurement provides a g-factor that describes the ratio of each enantiomer in the mixtures. We used our method to analyze the asymmetric hydrosilylation of β-enamino esters, and we discussed the advantage, feasibility, and effectiveness of this new methodology.

  6. A high-performance liquid chromatography-electronic circular dichroism online method for assessing the absolute enantiomeric excess and conversion ratio of asymmetric reactions

    PubMed Central

    Zhang, Xiang; Wang, Mingchao; Li, Li; Yin, Dali

    2017-01-01

    Asymmetric reactions often need to be evaluated during the synthesis of chiral compounds. However, traditional evaluation methods require the isolation of the individual enantiomer, which is tedious and time-consuming. Thus, it is desirable to develop simple, practical online detection methods. We developed a method based on high-performance liquid chromatography-electronic circular dichroism (HPLC-ECD) that simultaneously analyzes the material conversion ratio and absolute optical purity of each enantiomer. In particular, only a reverse-phase C18 column instead of a chiral column is required in our method because the ECD measurement provides a g-factor that describes the ratio of each enantiomer in the mixtures. We used our method to analyze the asymmetric hydrosilylation of β-enamino esters, and we discussed the advantage, feasibility, and effectiveness of this new methodology. PMID:28252028

  7. A high-performance liquid chromatography-electronic circular dichroism online method for assessing the absolute enantiomeric excess and conversion ratio of asymmetric reactions

    NASA Astrophysics Data System (ADS)

    Zhang, Xiang; Wang, Mingchao; Li, Li; Yin, Dali

    2017-03-01

    Asymmetric reactions often need to be evaluated during the synthesis of chiral compounds. However, traditional evaluation methods require the isolation of the individual enantiomer, which is tedious and time-consuming. Thus, it is desirable to develop simple, practical online detection methods. We developed a method based on high-performance liquid chromatography-electronic circular dichroism (HPLC-ECD) that simultaneously analyzes the material conversion ratio and absolute optical purity of each enantiomer. In particular, only a reverse-phase C18 column instead of a chiral column is required in our method because the ECD measurement provides a g-factor that describes the ratio of each enantiomer in the mixtures. We used our method to analyze the asymmetric hydrosilylation of β-enamino esters, and we discussed the advantage, feasibility, and effectiveness of this new methodology.

  8. [Synthesis of asymmetric tetraarylporphyrins and its ytterbium complexes].

    PubMed

    Rumiantseva, V D; Roshchina, N V; Fedorova, L D; Mironov, A F; Markushev, V M; Shilov, I P

    2011-01-01

    The synthesis of asymmetric meso-aryl-substituted porphyrins containing three 4-methoxycarbonylphenyl groups, and as a forth substituent 4-hydroxyphenyl or 4-hydroxy-3- methoxyphenyl radicals, or the isomeric 3- and 4-pyridyl substituents is described. O-alkyl derivatives of 4-hydroxyl residue are obtained. The ytterbium complexes ofthese porphyrins were synthesized and studied their luminescence spectral properties were studied. A significant difference in the lifetimes of the excited state ofytterbium complexes of esters and acids of asymmetric porphyrins is demonstrated.

  9. Organocatalyzed Asymmetric Synthesis of Axially, Planar, and Helical Chiral Compounds.

    PubMed

    Shirakawa, Seiji; Liu, Shiyao; Kaneko, Shiho

    2016-02-04

    Axially, planar, and helical chiral compounds are indispensable building blocks in modern organic synthesis. A wide variety of chiral ligands and catalysts were designed based on these chiral scaffolds, and these chiral ligands and catalysts were used for various catalytic asymmetric transformations to produce important chiral compounds in an optically enriched form. Furthermore, these chiral skeletons are found in the structure of biologically active natural products. Thus, the development of efficient enantioselective methods for the synthesis of these chiral compounds is an important task in the field of organic chemistry. In the last few years, organocatalyzed approaches, which are one of the most reliable catalytic asymmetric methods, became a hot topic. This Focus Review summarizes asymmetric organocatalytic methods for the synthesis of axially, planar, and helical chiral compounds as useful chiral building blocks.

  10. Magnetically Retrievable Catalysts for Asymmetric Synthesis

    EPA Science Inventory

    Surface modification of magnetic nanoparticles with chiral scaffolds for asymmetric catalytic applications is an elegant way of providing a special pseudo homogenous phase which could be separated using an external magnet. In this review, we summarize the use of magnetic nanopart...

  11. The asymmetric total synthesis of cinbotolide: a revision of the original structure.

    PubMed

    Botubol, José Manuel; Durán-Peña, María Jesús; Macías-Sánchez, Antonio J; Hanson, James R; Collado, Isidro G; Hernández-Galán, Rosario

    2014-12-05

    The structure 3,4-dihydroxy-2,4,6,8-tetramethyldec-8-enolide (1) was assigned to a metabolite of Botrytis cinerea, but the spectra of several synthetic analogues had significant differences from that of 1. Examination of the constituents of a B. cinerea mutant that overproduces polyketides gave sufficient quantities of 1, now named cinbotolide, for chemical transformations. These led to a revised γ-butyrolactone structure for the metabolite. This structure has been confirmed by an asymmetric total synthesis, which also established its absolute configuration.

  12. Recent advances in rhodium-catalyzed asymmetric synthesis of heterocycles.

    PubMed

    Chen, Wen-Wen; Xu, Ming-Hua

    2017-02-01

    Heterocycles are crucial structural motifs that are ubiquitously present in biologically active natural products and pharmaceutically important compounds. Over the past few decades, great attention has been paid to develop efficient methodologies for the construction of diverse enantioenriched heterocyclic frameworks. This review focuses on the recent impressive progress and advances in the asymmetric synthesis of heterocycles under rhodium catalysis.

  13. Asymmetric Synthesis of Spiropyrazolones by Sequential Organo- and Silver Catalysis.

    PubMed

    Hack, Daniel; Dürr, Alexander B; Deckers, Kristina; Chauhan, Pankaj; Seling, Nico; Rübenach, Lukas; Mertens, Lucas; Raabe, Gerhard; Schoenebeck, Franziska; Enders, Dieter

    2016-01-26

    A stereoselective one-pot synthesis of spiropyrazolones through an organocatalytic asymmetric Michael addition and a formal Conia-ene reaction has been developed. Depending on the nitroalkene, the 5-exo-dig-cyclization could be achieved by silver-catalyzed alkyne activation or by oxidation of the intermediate enolate. The mechanistic pathways have been investigated using computational chemistry and mechanistic experiments.

  14. Short asymmetric synthesis of (-)- and (+)-cis-lauthisan.

    PubMed

    Carreño, M Carmen; Des Mazery, Renaud; Urbano, Antonio; Colobert, Françoise; Solladié, Guy

    2005-05-12

    The asymmetric synthesis of both enantiomers of cis-lauthisan (3) is achieved in only six steps from diethyl pimelate (4), the key steps being the diastereodivergent reduction of beta-ketosulfoxide 7 and the highly cis-stereoselective Et(3)SiH/TMSOTf-promoted reductive cyclization of enantiopure hydroxy sulfinyl ketones (S)-14 and (R)-14.

  15. Asymmetric Synthesis of Spiropyrazolones by Sequential Organo- and Silver Catalysis

    PubMed Central

    Hack, Daniel; Dürr, Alexander B; Deckers, Kristina; Chauhan, Pankaj; Seling, Nico; Rübenach, Lukas; Mertens, Lucas; Raabe, Gerhard; Schoenebeck, Franziska; Enders, Dieter

    2016-01-01

    A stereoselective one-pot synthesis of spiropyrazolones through an organocatalytic asymmetric Michael addition and a formal Conia-ene reaction has been developed. Depending on the nitroalkene, the 5-exo-dig-cyclization could be achieved by silver-catalyzed alkyne activation or by oxidation of the intermediate enolate. The mechanistic pathways have been investigated using computational chemistry and mechanistic experiments. PMID:26676875

  16. Asymmetric Total Synthesis of Ieodomycin B

    PubMed Central

    Lin, Shuangjie; Zhang, Jianting; Zhang, Zhibin; Xu, Tianxiang; Huang, Shuangping; Wang, Xiaoji

    2017-01-01

    Ieodomycin B, which shows in vitro antimicrobial activity, was isolated from a marine Bacillus species. A novel asymmetric total synthetic approach to ieodomycin B using commercially available geraniol was achieved. The approach involves the generation of 1,3-trans-dihydroxyl at C-3 and C-5 positions via a Crimmins-modified Evans aldol reaction and a chelation-controlled Mukaiyama aldol reaction of a p-methoxybenzyl-protected aldehyde, as well as the generation of a lactone ring in a deprotection–lactonization one-pot reaction. PMID:28106760

  17. Asymmetric synthesis using chiral-encoded metal

    PubMed Central

    Yutthalekha, Thittaya; Wattanakit, Chularat; Lapeyre, Veronique; Nokbin, Somkiat; Warakulwit, Chompunuch; Limtrakul, Jumras; Kuhn, Alexander

    2016-01-01

    The synthesis of chiral compounds is of crucial importance in many areas of society and science, including medicine, biology, chemistry, biotechnology and agriculture. Thus, there is a fundamental interest in developing new approaches for the selective production of enantiomers. Here we report the use of mesoporous metal structures with encoded geometric chiral information for inducing asymmetry in the electrochemical synthesis of mandelic acid as a model molecule. The chiral-encoded mesoporous metal, obtained by the electrochemical reduction of platinum salts in the presence of a liquid crystal phase and the chiral template molecule, perfectly retains the chiral information after removal of the template. Starting from a prochiral compound we demonstrate enantiomeric excess of the (R)-enantiomer when using (R)-imprinted electrodes and vice versa for the (S)-imprinted ones. Moreover, changing the amount of chiral cavities in the material allows tuning the enantioselectivity. PMID:27562028

  18. Asymmetric synthesis using chiral-encoded metal

    NASA Astrophysics Data System (ADS)

    Yutthalekha, Thittaya; Wattanakit, Chularat; Lapeyre, Veronique; Nokbin, Somkiat; Warakulwit, Chompunuch; Limtrakul, Jumras; Kuhn, Alexander

    2016-08-01

    The synthesis of chiral compounds is of crucial importance in many areas of society and science, including medicine, biology, chemistry, biotechnology and agriculture. Thus, there is a fundamental interest in developing new approaches for the selective production of enantiomers. Here we report the use of mesoporous metal structures with encoded geometric chiral information for inducing asymmetry in the electrochemical synthesis of mandelic acid as a model molecule. The chiral-encoded mesoporous metal, obtained by the electrochemical reduction of platinum salts in the presence of a liquid crystal phase and the chiral template molecule, perfectly retains the chiral information after removal of the template. Starting from a prochiral compound we demonstrate enantiomeric excess of the (R)-enantiomer when using (R)-imprinted electrodes and vice versa for the (S)-imprinted ones. Moreover, changing the amount of chiral cavities in the material allows tuning the enantioselectivity.

  19. Catalytic asymmetric synthesis of biologically important 3-hydroxyoxindoles: an update

    PubMed Central

    2016-01-01

    Summary Oxindole scaffolds are prevalent in natural products and have been recognized as privileged substructures in new drug discovery. Several oxindole-containing compounds have advanced into clinical trials for the treatment of different diseases. Among these compounds, enantioenriched 3-hydroxyoxindole scaffolds also exist in natural products and have proven to possess promising biological activities. A large number of catalytic asymmetric strategies toward the construction of 3-hydroxyoxindoles based on transition metal catalysis and organocatalysis have been reported in the last decades. Additionally, 3-hydroxyoxindoles as versatile precursors have also been used in the total synthesis of natural products and for constructing structurally novel scaffolds. In this review, we aim to provide an overview about the catalytic asymmetric synthesis of biologically important 3-substituted 3-hydroxyoxindoles and 3-hydroxyoxindole-based further transformations. PMID:27340490

  20. Synthesis and asymmetric resolution of α-azido-peroxides.

    PubMed

    Pramanik, Suman; Ghorai, Prasanta

    2013-08-02

    An unprecedented synthesis of α-azido-peroxides has been developed using an FeCl3-catalyst starting from carbonyl, TMS-azide, and hydroperoxide. Further, a base promoted decomposition of synthesized secondary α-azido-peroxides to provide the corresponding tert-butyl esters has been disclosed. Finally, an asymmetric kinetic resolution of such α-azido-peroxides has also been developed to provide chiral α-azido-peroxides in excellent enantiopurity.

  1. Catalytic asymmetric synthesis of {alpha}-amino phosphonates using lanthanoid-potassium-BINOL complexes

    SciTech Connect

    Sasai, Hiroaki; Arai, Shigeru; Shibasaki, Masakatsu

    1995-10-20

    {alpha}-Amino phosphonic acids 3 are interesting compounds in the design of enzyme inhibitors. The concept of mimicking tetrahedral transition states of enzyme-medicated peptide bond hydrolysis previously led to the successful design and synthesis of phosphonamide-containing peptides as a promising new class of proteinase inhibitors. It is not surprising that the absolute configuration of the {alpha}-carbon strongly influences the biological properties of 3. Several methods for the synthesis of optically active {alpha}-aminophosphonic acids have been published. The authors report here the first example of a catalytic asymmetric hydrophosphonylation to imines using lanthanoid-potassium-BINOL heterobimetallic complexes (LnPB, Ln = lanthanoid metal), which gives optically active {alpha}-amino phosphonates in modest to high enantiometric excess. 17 refs., 1 tab.

  2. Biomimetically inspired asymmetric total synthesis of (+)-19-dehydroxyl arisandilactone A

    NASA Astrophysics Data System (ADS)

    Han, Yi-Xin; Jiang, Yan-Long; Li, Yong; Yu, Hai-Xin; Tong, Bing-Qi; Niu, Zhe; Zhou, Shi-Jie; Liu, Song; Lan, Yu; Chen, Jia-Hua; Yang, Zhen

    2017-01-01

    Complex natural products are a proven and rich source of disease-modulating drugs and of efficient tools for the study of chemical biology and drug discovery. The architectures of complex natural products are generally considered to represent significant barriers to efficient chemical synthesis. Here we describe a concise and efficient asymmetric synthesis of 19-dehydroxyl arisandilactone A--which belongs to a family of architecturally unique, highly oxygenated nortriterpenoids isolated from the medicinal plant Schisandra arisanensis. This synthesis takes place by means of a homo-Michael reaction, a tandem retro-Michael/Michael reaction, and Cu-catalysed intramolecular cyclopropanation as key steps. The proposed mechanisms for the homo-Michael and tandem retro-Michael/Michael reactions are supported by density functional theory (DFT) calculation. The developed chemistry may find application for the synthesis of its other family members of Schisandraceae nortriterpenoids.

  3. Biomimetically inspired asymmetric total synthesis of (+)-19-dehydroxyl arisandilactone A

    PubMed Central

    Han, Yi-Xin; Jiang, Yan-Long; Li, Yong; Yu, Hai-Xin; Tong, Bing-Qi; Niu, Zhe; Zhou, Shi-Jie; Liu, Song; Lan, Yu; Chen, Jia-Hua; Yang, Zhen

    2017-01-01

    Complex natural products are a proven and rich source of disease-modulating drugs and of efficient tools for the study of chemical biology and drug discovery. The architectures of complex natural products are generally considered to represent significant barriers to efficient chemical synthesis. Here we describe a concise and efficient asymmetric synthesis of 19-dehydroxyl arisandilactone A—which belongs to a family of architecturally unique, highly oxygenated nortriterpenoids isolated from the medicinal plant Schisandra arisanensis. This synthesis takes place by means of a homo-Michael reaction, a tandem retro-Michael/Michael reaction, and Cu-catalysed intramolecular cyclopropanation as key steps. The proposed mechanisms for the homo-Michael and tandem retro-Michael/Michael reactions are supported by density functional theory (DFT) calculation. The developed chemistry may find application for the synthesis of its other family members of Schisandraceae nortriterpenoids. PMID:28139648

  4. Asymmetric synthesis of axially chiral anilides by Pd-catalyzed allylic substitutions with P/olefin ligands.

    PubMed

    Liu, Yilin; Feng, Xiangqing; Du, Haifeng

    2015-01-07

    As an attractive class of non-biaryl atropisomeric compounds, C-N axially chiral anilides have received considerable attention, and several methods have been successfully developed for their synthesis. Pd-catalyzed asymmetric allylic amination was proved to be an effective approach for the chiral anilide synthesis, although only moderate enantioselectivity and relatively narrow substrate scope have been achieved in the previous work. Searching for highly efficient methods for the synthesis of axially chiral anilides is therefore of great interest in synthetic and pharmaceutical chemistry. In this paper, a palladium-catalyzed asymmetric allylic substitution of ortho-substituted anilides using phosphorus amidite-olefin ligands was successfully achieved to afford a variety of axially chiral anilides in high yields with up to 84% ee. The absolute configurations of chiral anilides were also determined from X-ray and CD spectra.

  5. Enantiomeric separation and determination of absolute stereochemistry of asymmetric molecules in drug discovery: building chiral technology toolboxes.

    PubMed

    McConnell, Oliver; Bach, Alvin; Balibar, Carl; Byrne, Neal; Cai, Yanxuan; Carter, Guy; Chlenov, Michael; Di, Li; Fan, Kristi; Goljer, Igor; He, Yanan; Herold, Don; Kagan, Michael; Kerns, Edward; Koehn, Frank; Kraml, Christina; Marathias, Vasilios; Marquez, Brian; McDonald, Leonard; Nogle, Lisa; Petucci, Christopher; Schlingmann, Gerhard; Tawa, Gregory; Tischler, Mark; Williamson, R Thomas; Sutherland, Alan; Watts, William; Young, Mairead; Zhang, Mei-Yi; Zhang, Yingru; Zhou, Dahui; Ho, Douglas

    2007-09-01

    The application of Chiral Technology, or the (extensive) use of techniques or tools for the determination of absolute stereochemistry and the enantiomeric or chiral separation of racemic small molecule potential lead compounds, has been critical to successfully discovering and developing chiral drugs in the pharmaceutical industry. This has been due to the rapid increase over the past 10-15 years in potential drug candidates containing one or more asymmetric centers. Based on the experiences of one pharmaceutical company, a summary of the establishment of a Chiral Technology toolbox, including the implementation of known tools as well as the design, development, and implementation of new Chiral Technology tools, is provided.

  6. A 7-Step Formal Asymmetric Total Synthesis of Strictamine via an Asymmetric Propargylation and Metal-Mediated Cyclization.

    PubMed

    Smith, Myles W; Zhou, Zhiyao; Gao, Alison X; Shimbayashi, Takuya; Snyder, Scott A

    2017-03-03

    Herein is shown how a novel catalytic asymmetric propargylation of 3,4-dihydro-β-carboline, followed by a designed Au(I)/Ag(I)-mediated 6-endo-dig cyclization, can directly deliver the indolenine-fused methanoquinolizidine core of the akuammiline alkaloid strictamine in its native oxidation state, ultimately achieving a 7-step formal asymmetric total synthesis. Also demonstrated are how the cyclization products can rearrange into vincorine-type skeletons and a further use for the developed propargylation with the first catalytic asymmetric total synthesis of decarbomethoxydihydrogambirtannine.

  7. Asymmetric organic/metal(oxide) hybrid nanoparticles: synthesis and applications

    NASA Astrophysics Data System (ADS)

    He, Jie; Liu, Yijing; Hood, Taylor C.; Zhang, Peng; Gong, Jinlong; Nie, Zhihong

    2013-05-01

    Asymmetric particles (APs) with broken centrosymmetry are of great interest, due to the asymmetric surface properties and diverse functionalities. In particular, organic/metal(oxide) APs naturally combine the significantly different and complementary properties of organic and inorganic species, leading to their unique applications in various fields. In this review article, we highlighted recent advances in the synthesis and applications of organic/metal(oxide) APs. This type of APs is grounded on chemical or physical interactions between metal(oxide) NPs and organic small molecular or polymeric ligands. The synthetic methodologies were summarized in three categories, including the selective surface modifications, phase separation of mixed ligands on the surface of metal(oxide) NPs, and direct synthesis of APs. We further discussed the unique applications of organic/metal(oxide) APs in self-assembly, sensors, catalysis, and biomedicine, as a result of the distinctions between asymmetrically distributed organic and inorganic components. Finally, challenges and future directions are discussed in an outlook section.

  8. Asymmetric organic/metal(oxide) hybrid nanoparticles: synthesis and applications.

    PubMed

    He, Jie; Liu, Yijing; Hood, Taylor C; Zhang, Peng; Gong, Jinlong; Nie, Zhihong

    2013-06-21

    Asymmetric particles (APs) with broken centrosymmetry are of great interest, due to the asymmetric surface properties and diverse functionalities. In particular, organic/metal(oxide) APs naturally combine the significantly different and complementary properties of organic and inorganic species, leading to their unique applications in various fields. In this review article, we highlighted recent advances in the synthesis and applications of organic/metal(oxide) APs. This type of APs is grounded on chemical or physical interactions between metal(oxide) NPs and organic small molecular or polymeric ligands. The synthetic methodologies were summarized in three categories, including the selective surface modifications, phase separation of mixed ligands on the surface of metal(oxide) NPs, and direct synthesis of APs. We further discussed the unique applications of organic/metal(oxide) APs in self-assembly, sensors, catalysis, and biomedicine, as a result of the distinctions between asymmetrically distributed organic and inorganic components. Finally, challenges and future directions are discussed in an outlook section.

  9. Asymmetric organocatalytic methods for the synthesis of tetrahydropyrans and their application in total synthesis.

    PubMed

    Vetica, Fabrizio; Chauhan, Pankaj; Dochain, Simon; Enders, Dieter

    2017-03-21

    Recent advancement in the area of asymmetric organocatalysis led to the development of new methodologies for the construction of valuable enantiopure molecules, including various heterocycles. As one of the latter class of compounds tetrahydropyrans (THPs) constitute a core structure of a wide array of bioactive natural products. A noticeable growth has been observed in the asymmetric synthesis of THPs using small organic molecules as catalysts. This Tutorial Review describes the organocatalytic methods available to furnish THPs as well as the application of these methodologies in the total synthesis of THP-based natural products.

  10. The role of biocatalysis in the asymmetric synthesis of alkaloids

    PubMed Central

    2013-01-01

    Alkaloids are not only one of the most intensively studied classes of natural products, their wide spectrum of pharmacological activities also makes them indispensable drug ingredients in both traditional and modern medicine. Among the methods for their production, biotechnological approaches are gaining importance, and biocatalysis has emerged as an essential tool in this context. A number of chemo-enzymatic strategies for alkaloid synthesis have been developed over the years, in which the biotransformations nowadays take an increasingly ‘central’ role. This review summarises different applications of biocatalysis in the asymmetric synthesis of alkaloids and discusses how recent developments and novel enzymes render innovative and efficient chemo-enzymatic production routes possible. PMID:25580241

  11. Enantioselective synthesis of 5-epi-citreoviral using ruthenium-catalyzed asymmetric ring-closing metathesis.

    PubMed

    Funk, Timothy W

    2009-11-05

    Chiral ruthenium olefin metathesis catalysts can perform asymmetric ring-closing reactions in > or = 90% ee with low catalyst loadings. To illustrate the practicality of these reactions and the products they form, an enantioselective total synthesis of 5-epi-citreoviral was completed by using an asymmetric ring-closing olefin metathesis reaction as a key step early in the synthesis. All of the stereocenters in the final compound were set by using the chiral center generated by asymmetric olefin metathesis.

  12. Chiral alkynylcarbinols from marine sponges: asymmetric synthesis and biological relevance.

    PubMed

    Listunov, Dymytrii; Maraval, Valérie; Chauvin, Remi; Génisson, Yves

    2015-01-01

    Covering: up to March 2014. Previous review on the topic: B. W. Gung, C. R. Chim., 2009, 12, 489-505. Chiral α-functional lipidic propargylic alcohols extracted from marine sponges, in particular of the pacific genus Petrosia, constitute a class of acetylenic natural products exhibiting remarkable in vitro biological activities, especially anti-tumoral cytotoxicity. These properties, associated to functionalities that are uncommon among natural products, have prompted recent projects on asymmetric total synthesis. On the basis of a three-sector structural typology, three main sub-types of secondary alkynylcarbinols (with either alkyl, alkenyl, or alkynyl as the second substituent) can be identified as the minimal pharmacophoric units. Selected natural products containing these functionalities have been targeted using previously known or on purpose-designed procedures, where the stereo-determining step can be: (i) a C-C bond forming reaction (e.g. the Zn-mediated addition of alkynyl nucleophiles to aldehydes in the presence of chiral aminoalcohols), (ii) a functional layout (e.g. the asymmetric organo- or metallo-catalytic reduction of ynones), or (iii) an enantiomeric resolution (e.g. a lipase-mediated kinetic resolution via acetylation). The promising medicinal importance of these targets is finally surveyed, and future investigation prospects are proposed, such as: (i) further total synthesis of known or future extraction products; (ii) the synthesis of non-natural analogues, with simpler lipophilic environments of the alkynylcarbinol-based pharmacophoric units; (iii) the variation and optimization of both the pharmacophoric units and their lipophilic environment; and (iv) investigations into the biological mode of action of these unique structures.

  13. Asymmetric Total Syntheses of Two 3-Acyl-5,6- dihydro-2H-pyrones: (R)-Podoblastin-S and (R)- Lachnelluloic Acid with Verification of the Absolute Configuration of (-)-Lachnelluloic Acid.

    PubMed

    Fujiwara, Tetsuya; Tsutsumi, Takeshi; Nakata, Kohei; Nakatsuji, Hidefumi; Tanabe, Yoo

    2017-01-01

    Expedient asymmetric total syntheses of both (R)-podoblastin-S and (R)-lachnelluloic acid, representative of natural 3-acyl-5,6-dihydro-2H-pyran-2-ones, were performed. Compared with the reported total synthesis of (R)-podoblastin-S (14 steps, overall 5% yield), the present study was achieved in only five steps in an overall 40% yield and with 98% ee (HPLC analysis). In a similar strategy, the first asymmetric total synthesis of the relevant (R)-lachnelluloic acid was achieved in an overall 40% yield with 98% ee (HPLC analysis). The crucial step utilized readily accessible and reliable Soriente and Scettri's Ti(OiPr)₄/(S)-BINOL‒catalyzed asymmetric Mukaiyama aldol addition of 1,3-bis(trimethylsiloxy)diene, derived from ethyl acetoacetate with n-butanal for (R)- podoblastin-S and n-pentanal for (R)-lachnelluloic acid. With the comparison of the specific rotation values between the natural product and the synthetic specimen, the hitherto unknown absolute configuration at the C(6) position of (-)-lachnelluloic acid was unambiguously elucidated as 6R.

  14. De novo synthesis of natural products via the asymmetric hydration of polyenes.

    PubMed

    Wang, Yanping; Xing, Yalan; Zhang, Qi; O'Doherty, George A

    2011-08-14

    For the last ten years our group has been working toward the development of an asymmetric hydration approach to polyketide natural products based on the regioselective hydration of di- and tri-enoates. Key to the success of this approach is the recognition that both high regiocontrol and asymmetric induction could be obtained by the use of a Sharpless asymmetric dihydroxylation reaction. Herein we describe the development of the method and its application to natural product total synthesis.

  15. Catalytic asymmetric synthesis of O-acetyl cyanohydrins from KCN, Ac2O and aldehydes.

    PubMed

    Belokon, Yuri N; Gutnov, Andrey V; Moskalenko, Margarita A; Yashkina, Lidia V; Lesovoy, Denis E; Ikonnikov, Nicolai S; Larichev, Vladimir S; North, Michael

    2002-02-07

    A (salen)titanium catalyst has been found to induce the asymmetric addition of potassium cyanide and acetic anhydride to aldehydes, giving enantiomerically enriched cyanohydrin esters with up to 92% enantiomeric excess using just 1 mol% of the catalyst. This is the first report of the asymmetric synthesis of cyanohydrin derivatives using a cyanide source which is non-volatile and inexpensive.

  16. Total Synthesis and Absolute Stereochemistry of the Proteasome Inhibitors Cystargolides A and B

    PubMed Central

    Tello-Aburto, Rodolfo; Hallada, Liam P.; Niroula, Doleshwar; Rogelj, Snezna

    2015-01-01

    The absolute stereochemistry of the cystargolides was determined by total synthesis. Evaluation of synthetic cystargolides and derivatives showed that the natural (2S,3R) stereochemistry is essential for activity. Moreover, benzyl esters (−)-10 and (−)-15 were found to be about 100 times more potent, and to selectively kill MCF-7 cancerous cells. PMID:26400369

  17. Total synthesis and absolute stereochemistry of the proteasome inhibitors cystargolides A and B.

    PubMed

    Tello-Aburto, Rodolfo; Hallada, Liam P; Niroula, Doleshwar; Rogelj, Snezna

    2015-10-28

    The absolute stereochemistry of the cystargolides was determined by total synthesis. Evaluation of synthetic cystargolides and derivatives showed that the natural (2S,3R) stereochemistry is essential for activity. Moreover, benzyl esters (-)-10 and (-)-15 were found to be about 100 times more potent, and to selectively kill MCF-7 cancerous cells.

  18. Phase-transfer-catalyzed asymmetric synthesis of axially chiral anilides.

    PubMed

    Liu, Kun; Wu, Xiangfei; Kan, S B Jennifer; Shirakawa, Seiji; Maruoka, Keiji

    2013-12-01

    Catalytic asymmetric synthesis of axially chiral o-iodoanilides and o-tert-butylanilides as useful chiral building blocks was achieved by means of binaphthyl-modified chiral quaternary ammonium-salt-catalyzed N-alkylations under phase-transfer conditions. The synthetic utility of axially chiral products was demonstrated in various transformations. For example, axially chiral N-allyl-o-iodoanilide was transformed to 3-methylindoline by means of radical cyclization with high chirality transfer from axial chirality to C-centered chirality. Furthermore, stereochemical information on axial chirality in o-tert-butylanilides could be used as a template to control the stereochemistry of subsequent transformations. The transition-state structure of the present phase-transfer reaction was discussed on the basis of the X-ray crystal structure of ammonium anilide, which was prepared from binaphthyl-modified chiral ammonium bromide and o-iodoanilide. The chiral tetraalkylammonium bromide as a phase-transfer catalyst recognized the steric difference between the ortho substituents on anilide to obtain high enantioselectivity. The size and structural effects of the ortho substituents on anilide were investigated, and a wide variety of axially chiral anilides that possess various functional groups could be synthesized with high enantioselectivities. This method is the only general way to access a variety of axially chiral anilides in a highly enantioselective fashion reported to date.

  19. A Concise and Highly Enantioselective Total Synthesis of (+)-anti- and (-)-syn-Mefloquine Hydrochloride: Definitive Absolute Stereochemical Assignment of the Mefloquines.

    PubMed

    Rastelli, Ettore J; Coltart, Don M

    2015-11-16

    A concise asymmetric (>99:1 e.r.) total synthesis of (+)-anti- and (-)-syn-mefloquine hydrochloride from a common intermediate is described. The key asymmetric transformation is a Sharpless dihydroxylation of an olefin that is accessed in three steps from commercially available materials. The Sharpless-derived diol is converted into either a trans or cis epoxide, and these are subsequently converted into (+)-anti- and (-)-syn-mefloquine, respectively. The synthetic (+)-anti- and (-)-syn-mefloquine samples were derivatized with (S)-(+)-mandelic acid tert-butyldimethylsilyl ether, and a crystal structure of each derivative was obtained. These are the first X-ray structures for mefloquine derivatives that were obtained by coupling to a known chiral, nonracemic compound, and provide definitive confirmation of the absolute stereochemistry of (+)-anti- as well as (-)-syn-mefloquine.

  20. Synthesis of asymmetric tetracarboxylic acids and corresponding dianhydrides

    NASA Technical Reports Server (NTRS)

    Chuang, Chun-Hua (Inventor)

    2008-01-01

    This invention relates to processes for preparing asymmetrical biphenyl tetracarboxylic acids and the corresponding asymmetrical dianhydrides, namely 2,3,3',4'-biphenyl dianhydride (a-BPDA), 2,3,3',4'-benzophenone dianhydride (a-BTDA) and 3,4'-methylenediphthalic anhydride (-MDPA). By cross-coupling reactions of reactive metal substituted o-xylenes or by cross-coupling o-xylene derivatives in the presence of catalysts, this invention specifically produces asymmetrical biphenyl intermediates that are subsequently oxidized or hydrolyzed and oxidized to provide asymmetric biphenyl tetracarboxylic acids in comparatively high yields. These asymmetrical biphenyl tetracarboxylic acids are subsequently converted to the corresponding asymmetrical dianhydrides without contamination by symmetrical biphenyl dianhydrides.

  1. Concise and Practical Asymmetric Synthesis of a Challenging Atropisomeric HIV Integrase Inhibitor.

    PubMed

    Fandrick, Keith R; Li, Wenjie; Zhang, Yongda; Tang, Wenjun; Gao, Joe; Rodriguez, Sonia; Patel, Nitinchandra D; Reeves, Diana C; Wu, Jiang-Ping; Sanyal, Sanjit; Gonnella, Nina; Qu, Bo; Haddad, Nizar; Lorenz, Jon C; Sidhu, Kanwar; Wang, June; Ma, Shengli; Grinberg, Nelu; Lee, Heewon; Tsantrizos, Youla; Poupart, Marc-André; Busacca, Carl A; Yee, Nathan K; Lu, Bruce Z; Senanayake, Chris H

    2015-06-08

    A practical and efficient synthesis of a complex chiral atropisomeric HIV integrase inhibitor has been accomplished. The combination of a copper-catalyzed acylation along with the implementation of the BI-DIME ligands for a ligand-controlled Suzuki cross-coupling and an unprecedented bis(trifluoromethane)sulfonamide-catalyzed tert-butylation renders the synthesis of this complex molecule robust, safe, and economical. Furthermore, the overall synthesis was conducted in an asymmetric and diastereoselective fashion with respect to the imbedded atropisomer.

  2. Phosphonic Acid Functionalized Asymmetric Phthalocyanines: Synthesis, Modification of Indium Tin Oxide (ITO), and Charge Transfer

    SciTech Connect

    Polaske, Nathan W.; Lin, Hsiao-Chu; Tang, Anna; Mayukh, Mayank; Oquendo, Luis E.; Green, John; Ratcliff, Erin L.; Armstrong, Neal R.; Saavedra, S. Scott; McGrath, Dominic V.

    2011-12-20

    Metalated and free-base A₃B-type asymmetric phthalocyanines (Pcs) bearing, in the asymmetric quadrant, a flexible alkyl linker of varying chain lengths terminating in a phosphonic acid (PA) group have been synthesized. Two parallel series of asymmetric Pc derivatives bearing aryloxy and arylthio substituents are reported, and their synthesis and characterization through NMR, combustion analysis, and MALDI-MS are described. We also demonstrate the modification of indium tin oxide (ITO) substrates using the PA functionalized asymmetric Pc derivatives and monitoring their electrochemistry. The PA functionalized asymmetric Pcs were anchored to the ITO surface through chemisorption and their electrochemical properties characterized using cyclic voltammetry to investigate the effects of PA structure on the thermodynamics and kinetics of charge transfer. Ionization energies of the modified ITO surfaces were measured using ultraviolet photoemission spectroscopy.

  3. A convergent rhodium-catalysed asymmetric synthesis of tetrahydroquinolines.

    PubMed

    Li, Ho Yin; Horn, Joachim; Campbell, Amanda; House, David; Nelson, Adam; Marsden, Stephen P

    2014-09-14

    Rh-catalysed conjugate additions of 2-aminophenyl boronic acid derivatives were exploited in diastereoselective and asymmetric syntheses of tetrahydroquinolines. In both cases, combinatorial variation of the substitution of the tetrahydroquinoline ring system was possible.

  4. Total Synthesis of Chiral Biaryl Natural Products by Asymmetric Biaryl Coupling ‡

    PubMed Central

    Kozlowski, Marisa C.; Morgan, Barbara J.; Linton, Elizabeth C.

    2010-01-01

    This tutorial review highlights the use of catalytic asymmetric 2-naphthol couplings in total synthesis. The types of chirality, chiral biaryl natural products, prior approaches to chiral biaryl natural products, and other catalytic asymmetric biaryl couplings are outlined. The three main categories of chiral catalysts for 2-naphthol coupling (Cu, V, Fe) are described with discussion of their limitations and advantages. Applications of the copper catalyzed couplings in biomimetic syntheses are discussed including nigerone, hypocrellin, calphostin D, phleichrome, and cercosporin. PMID:19847351

  5. Total synthesis of chiral biaryl natural products by asymmetric biaryl coupling.

    PubMed

    Kozlowski, Marisa C; Morgan, Barbara J; Linton, Elizabeth C

    2009-11-01

    This tutorial review highlights the use of catalytic asymmetric 2-naphthol couplings in total synthesis. The types of chirality, chiral biaryl natural products, prior approaches to chiral biaryl natural products, and other catalytic asymmetric biaryl couplings are outlined. The three main categories of chiral catalysts for 2-naphthol coupling (Cu, V, Fe) are described with discussion of their limitations and advantages. Applications of the copper catalyzed couplings in biomimetic syntheses are discussed including nigerone, hypocrellin, calphostin D, phleichrome, and cercosporin.

  6. Asymmetric synthesis of H1 receptor antagonist (R,R)-clemastine.

    PubMed

    Lee, Sun Young; Jung, Jung Wha; Kim, Tae-Hyun; Kim, Hee-Doo

    2015-12-01

    The first asymmetric synthesis of (R,R)-clemastine (1) has been accomplished by the coupling of (R)-tertiary alcohol 2 and (R)-chloroethylpyrrolidine 3 via O-alkylation. (R)-Tertiary alcohol 2 was synthesized by stereoselective alkylation of chiral α-benzyloxy ketone with Grignard reagent via chelation-controlled 1,4-asymmetric induction. In the reaction, chiral benzyl group acts as a chiral auxiliary as well as a protecting group. (R)-Chloroethylpyrrolidine 3 was prepared by asymmetric transformation starting with L-homoserine lactone, in which racemization-minimized N-allylation and ring-closing metathesis were involved as key steps.

  7. Absolute configuration assignment by asymmetric syntheses of the homalium alkaloids (-)-(R,R,R)-hoprominol and (-)-(4'S,4″R,2‴R)-hopromalinol.

    PubMed

    Davies, Stephen G; Lee, James A; Roberts, Paul M; Stonehouse, Jeffrey P; Thomson, James E

    2012-11-02

    The conjugate addition of lithium (R)-N-(3-chloropropyl)-N-(α-methylbenzyl)amide to α,β-unsaturated esters was used as the key step in the syntheses of all possible diastereoisomers of the homalium alkaloids hoprominol and hopromalinol. Comparison of the specific rotation data for these synthetic samples with those of samples isolated from the natural source enabled the absolute configurations within these alkaloids to be confidently assigned for the first time as (-)-(R,R,R)-hoprominol and (-)-(4'S,4″R,2‴R)-hopromalinol. The asymmetric syntheses of (-)-(R,R,R)-hoprominol (in 10 steps and 4.0% overall yield) and (-)-(4'S,4″R,2‴R)-hopromalinol (in 10 steps and 9.3% overall yield), from commercially available starting materials in each case, therefore represent the first total asymmetric syntheses of these alkaloids to be reported.

  8. Asymmetric Synthesis of Chiral Atropisomeric Bis-Aryl Organophosphorus from Menthyl H-Phosphinate.

    PubMed

    Ma, Yan-Na; Yang, Shang-Dong

    2016-04-01

    This review describes new methods for the synthesis of chiral monophosphine ligands with menthyl phenylphosphinate as a chiral auxiliary through asymmetric Suzuki-Miyaura cross-coupling reactions and asymmetric C-H functionalization. The chiral menthyl phenylphosphinate as a chiral auxiliary is easy to prepare and the menthyl group can easily be transformed into other functional groups, with the chiral center synchronously remaining. These methodologies provide highly efficient and practical strategies for the synthesis of novel axially chiral biaryl monophosphine oxides and their corresponding phosphines. Meanwhile, these reactions are easy to handle and exhibit wide scope for substrates with excellent diastereomeric ratios.

  9. Synthesis of 3-Indolylglycine Derivatives via Dinuclear Zinc Catalytic Asymmetric Friedel-Crafts Alkylation Reaction.

    PubMed

    Wang, Xin-Wei; Hua, Yuan-Zhao; Wang, Min-Can

    2016-10-07

    A direct asymmetric Friedel-Crafts (F-C) alkylation reaction between a wide range of indoles and ethyl 2-(4-methoxyphenylimino)acetate catalyzed by Trost's dinuclear complex is reported. A series of 3-indolylglycine derivatives were synthesized in enantioselectivity of up to >99% enantiomeric excess (ee) using 10 mol% catalyst loading under mild conditions. This atom economic reaction could be run on a gram scale without impacting its enantioselectivity. The absolute stereochemistry of catalytic products was determined by correlation with a known configuration compound. A possible mechanism was proposed for the asymmetric induction.

  10. DNA vs. mirror-image DNA: a universal approach to tune the absolute configuration in DNA-based asymmetric catalysis.

    PubMed

    Wang, Jocelyn; Benedetti, Erica; Bethge, Lucas; Vonhoff, Stefan; Klussmann, Sven; Vasseur, Jean-Jacques; Cossy, Janine; Smietana, Michael; Arseniyadis, Stellios

    2013-10-25

    Mirror mirror on the wall: By taking advantage of the unique structural features of L-DNA, the first examples of left-helical enantioselective induction in the field of DNA-based asymmetric catalysis were realized. Most importantly, this approach is the only one that allows a reliable and predictable access to both enantiomers for any given reaction.

  11. Asymmetric synthesis of N-allylic indoles via regio- and enantioselective allylation of aryl hydrazines

    PubMed Central

    Xu, Kun; Gilles, Thomas; Breit, Bernhard

    2015-01-01

    The asymmetric synthesis of N-allylic indoles is important for natural product synthesis and pharmaceutical research. The regio- and enantioselective N-allylation of indoles is a true challenge due to the favourable C3-allylation. We develop here a new strategy to the asymmetric synthesis of N-allylic indoles via rhodium-catalysed N-selective coupling of aryl hydrazines with allenes followed by Fischer indolization. The exclusive N-selectivities and good to excellent enantioselectivities are achieved applying a rhodium(I)/DTBM-Segphos or rhodium(I)/DTBM-Binap catalyst. This method permits the practical synthesis of valuable chiral N-allylated indoles, and avoids the N- or C-selectivity issue. PMID:26137886

  12. Identification of (S)-selective transaminases for the asymmetric synthesis of bulky chiral amines

    NASA Astrophysics Data System (ADS)

    Pavlidis, Ioannis V.; Weiß, Martin S.; Genz, Maika; Spurr, Paul; Hanlon, Steven P.; Wirz, Beat; Iding, Hans; Bornscheuer, Uwe T.

    2016-11-01

    The use of transaminases to access pharmaceutically relevant chiral amines is an attractive alternative to transition-metal-catalysed asymmetric chemical synthesis. However, one major challenge is their limited substrate scope. Here we report the creation of highly active and stereoselective transaminases starting from fold class I. The transaminases were developed by extensive protein engineering followed by optimization of the identified motif. The resulting enzymes exhibited up to 8,900-fold higher activity than the starting scaffold and are highly stereoselective (up to >99.9% enantiomeric excess) in the asymmetric synthesis of a set of chiral amines bearing bulky substituents. These enzymes should therefore be suitable for use in the synthesis of a wide array of potential intermediates for pharmaceuticals. We also show that the motif can be engineered into other protein scaffolds with sequence identities as low as 70%, and as such should have a broad impact in the field of biocatalytic synthesis and enzyme engineering.

  13. Substrate specificity of FUT8 and chemoenzymatic synthesis of core-fucosylated asymmetric N-glycans.

    PubMed

    Calderon, Angie D; Liu, Yunpeng; Li, Xu; Wang, Xuan; Chen, Xi; Li, Lei; Wang, Peng G

    2016-04-26

    Substrate specificity studies of human FUT8 using 77 structurally-defined N-glycans as acceptors showed a strict requirement towards the α1,3-mannose branch, but a great promiscuity towards the α1,6-mannose branch. Accordingly, a chemoenzymatic strategy was developed for the efficient synthesis of core-fucosylated asymmetric N-glycans.

  14. Asymmetric synthesis of Crispine A: constructing tetrahydroisoquinoline scaffolds using pummerer cyclizations

    Technology Transfer Automated Retrieval System (TEKTRAN)

    For the first time, a concise, linear and protecting group-free stereoselective synthesis of both enantiomers of crispine A have been achieved in six steps with an overall yield of less than or equal to 20%,starting from commercially available veratraldehyde. Asymmetric Keck allylation and trifluoro...

  15. Asymmetric Co(II)-catalyzed cyclopropanation with succinimidyl diazoacetate: general synthesis of chiral cyclopropyl carboxamides.

    PubMed

    Ruppel, Joshua V; Gauthier, Ted J; Snyder, Nicole L; Perman, Jason A; Zhang, X Peter

    2009-06-04

    [Co(P1)] is an effective catalyst for asymmetric cyclopropanation with succinimidyl diazoacetate. The Co(II)-catalyzed reaction is suitable for various olefins, providing the desired cyclopropane succinimidyl esters in high yields and excellent diastereo- and enantioselectivity. The resulting enantioenriched cyclopropane succinimidyl esters can serve as convenient synthons for the general synthesis of optically active cyclopropyl carboxamides.

  16. Large-scale asymmetric synthesis of the bioprotective agent JP4-039 and analogs

    PubMed Central

    Frantz, Marie-Céline; Pierce, Joshua G.; Pierce, Joan M.; Kangying, Li; Qingwei, Wan; Johnson, Matthew; Wipf, Peter

    2011-01-01

    JP4-039 is a novel nitroxide conjugate capable of crossing lipid bilayer membranes and scavenging reactive oxygen species (ROS). An efficient and scalable one-pot hydrozirconation-transmetalation-imine addition methodology has been developed for its asymmetric preparation. Furthermore, this versatile methodology allows for the synthesis of cyclopropyl and fluorinated analogs of the parent lead structure. PMID:21452836

  17. Direct Catalytic Asymmetric Synthesis of β-Hydroxy Acids from Malonic Acid.

    PubMed

    Gao, Hang; Luo, Zhenli; Ge, Pingjin; He, Junqian; Zhou, Feng; Zheng, Peipei; Jiang, Jun

    2015-12-18

    A nickel(II) catalyzed asymmetric synthesis of β-hydroxy acids from malonic acid and ketones was developed, revealing for the first time the synthetic utility of malonic acid in the construction of chiral carboxyl acids; importantly, the synthetic potential of this strategy was further demonstrated by the rapid construction of cephalanthrin A, phaitanthrin B, cruciferane, and rice metabolites.

  18. Enantioselective Synthesis of (+)-Majusculone

    PubMed Central

    Taber, Douglass F.; Sikkander, M. Inthikhab; Storck, Pierre H.

    2011-01-01

    The first enantioselective synthesis of a chamigrane sesquiterpene, (+)-majusculone, has been completed. The quaternary center was generated asymmetrically by alkylidene carbene insertion, with retention of absolute configuration, from a diastereomerically pure ketal. PMID:17447815

  19. Synthesis of helical and supplementary chirally doped PMO materials. Suitable catalysts for asymmetric synthesis.

    PubMed

    García-Muñoz, Rafael A; Morales, Victoria; Linares, María; Rico-Oller, Beatriz

    2014-01-28

    Exciting helical mesoporous organosilicas including supplementary chirally doped moieties into their spiral walls were one-pot successfully synthesized with good structural order for, to the best of our knowledge, the first time. This one-step direct synthesis of helical chirally doped periodic mesoporous organosilica (PMO) materials was carried out by combination of a tartrate-based bis-organosilicon precursor with tetraethyl orthosilicate (TEOS) and two surfactants, cetyltrimethylammonium bromide and perfluoroctanoic acid (CTAB and PFOA). For comparison purposes, a conventional two-step postsynthetic grafting methodology was carried out. In this method, the chiral tartrate-based moieties were grafted onto the helical silica mesoporous materials previously prepared by the dual-templating approach (CTAB and PFOA). The chirally doped materials prepared by both methodologies exhibited helical structure and high BET surface area, pore size distributions, and total pore volume in the range of mesopores. Solid-state (13)C and (29)Si MAS NMR experiments confirmed the presence of the chiral organic precursor in the silica wall covalently bonded to silicon atoms. Nevertheless, one-pot direct synthesis led to a greater control of surface properties and presented larger incorporation of organic species compared with the two-step postsynthetic methodology. To further prove the potential feasibility of these materials in enantiomeric applications, Mannich diastereoselective asymmetric synthesis was chosen as catalytic test. In the case of the one-pot PMO material, the rigidity of the chiral ligand backbone provided by its integration into the inorganic helical wall in combination with the steric impediments supplied by the twisted geometry led to the reagents to adopt specific orientations. These geometrical constrictions resulted in an outstanding diastereomeric induction toward the preferred enantiomer.

  20. Asymmetric Synthesis of Octahydroindoles via a Domino Robinson Annulation/5-Endo Intramolecular Aza-Michael Reaction.

    PubMed

    Parra, Claudio; Bosch, Caroline; Gómez-Bengoa, Enrique; Bonjoch, Josep; Bradshaw, Ben

    2016-11-04

    A straightforward, two-step asymmetric synthesis of octahydroindoles has been developed on the basis of two complementary strategies: (i) an organocatalyzed Michael reaction followed by a tandem Robinson-aza-Michael double cyclization catalyzed by PS-BEMP, and (ii) a diastereoselective cyclization, which formally constitutes a remote 1,6 asymmetric induction mediated by PS-BEMP. This allowed the construction of complex octahydroindoles with up to four stereocenters, excellent enantioselectivities (up to 95% ee), and complete diastereoselective control in a single-pot operation. DFT calculations were performed to understand the origin of this effect.

  1. Asymmetric Total Synthesis of the Indole Diterpene Alkaloid Paspaline

    PubMed Central

    Sharpe, Robert J.; Johnson, Jeffrey S.

    2015-01-01

    An enantioselective synthesis of the indole diterpenoid natural product paspaline is disclosed. Critical to this approach was the implementation of stereoselective desymmetrization reactions to assemble key stereocenters of the molecule. The design and execution of these tactics are described in detail, and a thorough analysis of observed outcomes is presented, ultimately providing the title compound in high stereopurity. This synthesis provides a novel template for preparing key stereocenters in this family of molecules, and the reactions developed en route to paspaline present a series of new synthetic disconnections in preparing steroidal natural products. PMID:26398568

  2. Organocatalytic asymmetric synthesis of 3,3-disubstituted oxindoles featuring two heteroatoms at the C3 position.

    PubMed

    Zhou, Feng; Zeng, Xing-Ping; Wang, Chao; Zhao, Xiao-Li; Zhou, Jian

    2013-03-11

    We report the first organocatalytic asymmetric synthesis of 3,3-disubstituted oxindoles featuring two heteroatoms at the C3 position. Importantly, 3-thiooxindoles and 3-alkoxyoxindoles are demonstrated to be reactive nucleophiles for the development of catalytic asymmetric reactions for the first time.

  3. Asymmetric Synthesis of d-ribo-Phytosphingosine from 1-Tetradecyne and (4-Methoxyphenoxy)acetaldehyde

    PubMed Central

    Liu, Zheng; Byun, Hoe-Sup

    2010-01-01

    An asymmetric synthesis of d-ribo-phytosphingosine (1) was achieved by utilizing the ProPhenol-catalyzed alkynylation of aldehyde 8 to afford allylic propargylic alcohol (S)-6 followed by asymmetric epoxidation and opening of propargylic epoxy alcohol anti-5 with NaN3/NH4Cl. Deprotection and reduction of the resulting acyclic azide 3 then gave 1. Alkyne-azide 3 was subjected to an intramolecular click reaction, generating a bicyclic triazole, which was found to have unexpected vicinal coupling constants. Application of the advanced Mosher method verified the configurations of the three contiguous stereogenic centers of 1. An alkynyl-azide analogue of 1, which may be useful as a glycosyl acceptor in the synthesis of α-galactosylceramide derivatives, was also readily prepared by this route. PMID:20527744

  4. Asymmetric synthesis of D-ribo-phytosphingosine from 1-tetradecyne and (4-methoxyphenoxy)acetaldehyde.

    PubMed

    Liu, Zheng; Byun, Hoe-Sup; Bittman, Robert

    2010-07-02

    An asymmetric synthesis of d-ribo-phytosphingosine (1) was achieved by utilizing the ProPhenol (12)-catalyzed alkynylation of unsaturated aldehyde 8 to afford allylic propargylic alcohol (S)-6 followed by asymmetric epoxidation and opening of propargylic epoxy alcohol anti-5 with NaN(3)/NH(4)Cl. Deprotection and reduction of the resulting acyclic azide 3 then gave 1. Alkyne-azide 3 was subjected to an intramolecular click reaction, generating a bicyclic triazole, which was found to have unexpected vicinal coupling constants. Application of the advanced Mosher method verified the configurations of the three contiguous stereogenic centers of 1. An alkynyl azide analogue of 1, which may be useful as a glycosyl acceptor in the synthesis of alpha-galactosylceramide derivatives, was also readily prepared by this route.

  5. Catalytic asymmetric synthesis of enantioenriched heterocycles bearing a C-CF3 stereogenic center.

    PubMed

    Huang, Yi-Yong; Yang, Xing; Chen, Zhuo; Verpoort, Francis; Shibata, Norio

    2015-06-08

    Given the important agricultural and medicinal application of optically pure heterocycles bearing a trifluoromethyl group at the stereogenic carbon center in the heterocyclic framework, the exploration of efficient and practical synthetic strategies to such types of molecules remains highly desirable. Catalytic enantioselective synthesis has one clear advantage that it is more cost-effective than other synthetic methods, but remains limited by challenges in achieving excellent yield and stereoselectivities with a low catalyst loading. Thus far, numerous models of organo- and organometal-catalyzed asymmetric reactions have been exploited to achieve this elusive goal over the past decade. This review article describes recent progress on this research topic, and focuses on an understanding of the catalytic asymmetric protocols exemplified in the catalytic enantioselective synthesis of a wide range of complex enantioenriched trifluoromethylated heterocycles.

  6. Synthesis of axially chiral heterobiaryl alkynes via dynamic kinetic asymmetric alkynylation.

    PubMed

    Hornillos, Valentín; Ros, Abel; Ramírez-López, Pedro; Iglesias-Sigüenza, Javier; Fernández, Rosario; Lassaletta, José M

    2016-12-01

    The dynamic kinetic Pd(0)-catalyzed alkynylation of racemic heterobiaryl sulfonates was used for the asymmetric synthesis of axially chiral heterobiaryl alkynes with a broad scope. The use of Pd(OAc)2/(S)-QUINAP as the precatalyst provides products in excellent yields and enantioselectivities under mild conditions (DMSO, 40 °C). Semireduction, 1,3-dipolar cycladdition or N-oxidation served to illustrate the synthetic potential of the methodology.

  7. C2-Symmetric diamines and their derivatives as promising organocatalysts for asymmetric synthesis

    NASA Astrophysics Data System (ADS)

    Zlotin, S. G.; Kochetkov, S. V.

    2015-11-01

    The review is devoted to the application of C2-symmetric diamines and their derivatives as organocatalysts for asymmetric reactions (aldol, Michael, Mannich, Diels-Alder reactions, desymmetrization, allylation, etc.). Amino acid derivatives, di- and polyamides (sulfamides), bisureas, bisthioureas, bisamidines and bisguanidines are considered. Significant attention is given to the effect of the catalyst structure on the mechanism of catalytic action. Successful applications of such catalysts in enantioselective synthesis of chiral biologically active compounds are summarized. The bibliography includes 181 references.

  8. Concise, Asymmetric, Stereocontrolled Total Synthesis of Stephacidins A, B and Notoamide B

    PubMed Central

    Artman, Gerald D.; Grubbs, Alan W.; Williams, Robert M.

    2007-01-01

    Concise asymmetric total syntheses of the fungal metabolites (−)-stephacidin A, (+)-stephacidin B, and (+)-notoamide B are described. Key features of these total syntheses include (1) a facile synthesis of (R)-allyl proline methyl ester, (2) a revised route toward the pyranoindole ring system, (3) a novel cross-metathesis strategy for the introduction of important functional groups, and (4) an SN2′ cyclization to form the [2.2.2] bridged bicyclic ring system. Furthermore, our synthesis has taken advantage of microwave heating to shorten reaction times as well as increase yields for the preparation of vital intermediates. PMID:17455936

  9. Bifunctional phase-transfer catalysis in the asymmetric synthesis of biologically active isoindolinones

    PubMed Central

    Di Mola, Antonia; Tiffner, Maximilian; Scorzelli, Francesco; Palombi, Laura; Filosa, Rosanna; De Caprariis, Paolo

    2015-01-01

    Summary New bifunctional chiral ammonium salts were investigated in an asymmetric cascade synthesis of a key building block for a variety of biologically relevant isoindolinones. With this chiral compound in hand, the development of further transformations allowed for the synthesis of diverse derivatives of high pharmaceutical value, such as the Belliotti (S)-PD172938 and arylated analogues with hypnotic sedative activity, obtained in good overall total yield (50%) and high enantiomeric purity (95% ee). The synthetic routes developed herein are particularly convenient in comparison with the current methods available in literature and are particularly promising for large scale applications. PMID:26734105

  10. Rational design and asymmetric synthesis of potent and neurotrophic ligands for FK506-binding proteins (FKBPs).

    PubMed

    Pomplun, Sebastian; Wang, Yansong; Kirschner, Alexander; Kozany, Christian; Bracher, Andreas; Hausch, Felix

    2015-01-02

    To create highly efficient inhibitors for FK506-binding proteins, a new asymmetric synthesis for pro-(S)-C(5) -branched [4.3.1] aza-amide bicycles was developed. The key step of the synthesis is an HF-driven N-acyliminium cyclization. Functionalization of the C(5)  moiety resulted in novel protein contacts with the psychiatric risk factor FKBP51, which led to a more than 280-fold enhancement in affinity. The most potent ligands facilitated the differentiation of N2a neuroblastoma cells with low nanomolar potency.

  11. Synthesis and spectroscopic properties of novel asymmetric Schiff bases.

    PubMed

    Güngör, Ozlem; Gürkan, Perihan

    2010-09-15

    Three novel diimine Schiff bases including two asymmetric imines (2-OH)R-CHN-C(6)H(4)-CHN-R'(2-OH) type [where R=R'=phenyl for H(2)L(1); R=naphthyl, R'=phenyl for H(2)L(2) and R=R'=naphthyl for H(2)L(3)] have been synthesized with a new two step method. For this purpose, the starting Schiff bases 4-nitrobenzylidene-2-hydroxyaniline (SB(1)-NO(2)) and 4-nitrobenzylidene-2-hydroxy-3-naphthylamine (SB(2)-NO(2)) have been synthesized, previously. Nitro groups of them have been reduced into their amino derivatives (SB(1)-NH(2) and SB(2)-NH(2)) with sodium dithionite as selective reductant and the other imino groups have been formed by adding salicylaldehyde or 2-hydroxy-1-naphthaldehyde to the same solutions. The structures of the diimine Schiff bases were confirmed by elemental analyses, ESI-MS, FT-IR, (1)H NMR and (13)C NMR spectroscopy. The phenol-imine and keto-amine tautomerism of the Schiff bases were investigated by FT-IR, (1)H NMR, (13)C NMR techniques and UV-vis spectra in different solvents (DMSO, methanol, chloroform, toluene and cyclohexane). The effects of acidic and basic media on the tautomeric equilibria were discussed.

  12. Practical Catalytic Asymmetric Synthesis of Diaryl-, Aryl Heteroaryl- and Diheteroarylmethanols

    PubMed Central

    Salvi, Luca; Kim, Jeung Gon; Walsh, Patrick J.

    2009-01-01

    Enantioenriched diaryl-, aryl heteroaryl- and diheteroarylmethanols exhibit important biological and medicinal properties. One-pot catalytic asymmetric syntheses of these compounds beginning from readily available aryl bromides are introduced. Thus, lithium-bromide exchange with commercially available aryl bromides and n-BuLi was followed by salt metathesis with ZnCl2 to generate ArZnCl. A second equivalent of n-BuLi was added to form the mixed organozinc, ArZnBu. In the presence of enantioenriched amino alcohol-based catalysts, ArZnBu adds to aldehydes to afford essentially racemic diarylmethanols. The low enantioselectivities were attributed to a LiCl-promoted background reaction. To inhibit this background reaction, the chelating diamine TEEDA (tetraethylethylene diamine) was introduced prior to aldehyde addition. Under these conditions, enantioenriched diarylmethanols were obtained with >90% ee. Arylations of enals generated allylic alcohols with 81–90% ee. This procedure was unsuccessful, however, when applied to heteraryl bromides, which was attributed to decomposition of the heteroaryl lithium under the salt metathesis conditions. To avoid this problem, the metathesis was conducted with EtZnCl, which enabled the salt metathesis to proceed at low temperatures. The resulting EtZn(ArHetero) intermediates (ArHetero=2- and 3-thiophenyl, 2-benzothiophenyl, 3-furyl, and 5-indolyl) were successfully added to aldehydes and heteroaryl aldehydes with enantioselectivities between 81–99%. These are the first examples of catalytic and highly enantioselective syntheses of diheteroarylmethanols. In a similar fashion, ferrocenyl bromide was used to generate FcZnEt and the ferrocenyl group added to benzaldehyde and heteroaromatic aldehydes to form ferrocene-based ligand precursors in 86–95% yield with 96–98% ee. It was also found that the arylation and heteroarylation of enals could be followed by diastereoselective epoxidations to provide epoxy alcohols with high

  13. Chemo-Enzymatic Synthesis of (13)C Labeled Complex N-Glycans As Internal Standards for the Absolute Glycan Quantification by Mass Spectrometry.

    PubMed

    Echeverria, Begoña; Etxebarria, Juan; Ruiz, Nerea; Hernandez, Álvaro; Calvo, Javier; Haberger, Markus; Reusch, Dietmar; Reichardt, Niels-Christian

    2015-11-17

    Methods for the absolute quantification of glycans are needed in glycoproteomics, during development and production of biopharmaceuticals and for the clinical analysis of glycan disease markers. Here we present a strategy for the chemo-enzymatic synthesis of (13)C labeled N-glycan libraries and provide an example for their use as internal standards in the profiling and absolute quantification of mAb glycans by matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry. A synthetic biantennary glycan precursor was (13)C-labeled on all four amino sugar residues and enzymatically derivatized to produce a library of 15 glycan isotopologues with a mass increment of 8 Da over the natural products. Asymmetrically elongated glycans were accessible by performing enzymatic reactions on partially protected UV-absorbing intermediates, subsequent fractionation by preparative HPLC, and final hydrogenation. Using a preformulated mixture of eight internal standards, we quantified the glycans in a monoclonal therapeutic antibody with excellent precision and speed.

  14. Total Synthesis of (-)-Conolutinine.

    PubMed

    Feng, Xiangyang; Jiang, Guangde; Xia, Zilei; Hu, Jiadong; Wan, Xiaolong; Gao, Jin-Ming; Lai, Yisheng; Xie, Weiqing

    2015-09-18

    The first enantioselective synthesis of (-)-conolutinine was achieved in 10 steps. The synthesis featured a catalytic asymmetric bromocyclization of tryptamine to forge the tricycle intermediate. Hydration of an alkene catalyzed by Co(acac)2 was also employed as a key step to diastereoselectively introduce the tertiary alcohol moiety. The absolute configuration of (-)-conolutinine was established to be (2S,5aS,8aS,13aR) based on this asymmetric total synthesis.

  15. Asymmetric synthesis of 3-substituted tetrahydro-2-benzazepines.

    PubMed

    Quick, Matthias P; Fröhlich, Roland; Schepmann, Dirk; Wünsch, Bernhard

    2015-07-14

    The enantiomerically and diastereomerically pure tricyclic oxazolidine cis-10 was prepared in a five step synthesis starting with 1-bromo-2-iodobenzene. Me3SiCN and allylSiMe3 reacted with cis-10 in the presence of TiCl4 to form the nitrile (3S)-11 and the allyl derivative (3S)-12 with high diastereoselectivity. The hydrogenolytic removal of the chiral auxiliary failed, since the endocyclic benzyl-N-bond was cleaved simultaneously. Therefore the N-(hydroxyethyl)amide of (3S)-12 was transformed into the enamide 27, which was hydrolyzed to afford the secondary amide 28. The enamide strategy to remove the chiral auxiliary from (3S)-11 led to complete racemization due to fast deprotonation in α-position of the cyano moiety. Two pairs of enantiomers 30a-b/ent-30a-b with prototypical σ substituents at the N-atom were prepared. The low σ1 affinity of the tetrahydro-2-benzazepines (ent-30b, Ki = 407 nM) is attributed to the short distance between the two lipophilic aromatic moieties.

  16. Synthesis of functionalized asymmetric star polymers containing conductive polyacetylene segments by living anionic polymerization.

    PubMed

    Zhao, Youliang; Higashihara, Tomoya; Sugiyama, Kenji; Hirao, Akira

    2005-10-19

    Novel 3-arm ABC, 4-arm ABCD, and 5-arm ABCDE asymmetric star polymers comprising the conductive polyacetylene precursor, poly(4-methylphenyl vinyl sulfoxide) (PMePVSO), and other segments, such as polystyrene, poly(alpha-methylstyrene), poly(4-methoxystyrene), poly(4-trimethylsilylstyrene), and poly(4-methylstyrene), were synthesized by the methodology based on living anionic polymerization using DPE-functionalized polymers. This methodology involves the addition reaction of a DPE-functionalized polymer to a living anionic polymer followed by the living anionic polymerization of MePVSO initiated from the in situ formed polymer anion with two, three, or four polymer segments. The resultant asymmetric star polymers possessed predetermined molecular weights, narrow molecular weight distributions (Mw/Mn < 1.03), and desired compositions as confirmed by SEC, 1H NMR, SLS, and elemental analysis. After thermal treatment, the PMePVSO segment in the star polymer could be completely converted into a conductive polyacetylene segment, evident from TGA and elemental analysis. These asymmetric star polymers are expected to exhibit interesting solution properties and unique microphase-separated morphological suprastructures with potential applications in nanoscopic conductive materials. Moreover, this methodology can afford the target asymmetric star polymers with arm segments varying in a wide range and enables the synthesis of more complex macromolecular architectures.

  17. Chiral salicyloxazolines as auxiliaries for the asymmetric synthesis of ruthenium polypyridyl complexes.

    PubMed

    Gong, Lei; Mulcahy, Seann P; Devarajan, Deepa; Harms, Klaus; Frenking, Gernot; Meggers, Eric

    2010-09-06

    Chiral auxiliaries are promising emerging tools for the asymmetric synthesis of octahedral metal complexes. We recently introduced chiral salicyloxazolines as coordinating bidentate chiral ligands which provide excellent control over the metal-centered configuration in the course of ligand substitution reactions and can be removed afterward in an acid-induced fashion under complete retention of configuration (J. Am. Chem. Soc. 2009, 131, 9602-9603). Here reported is our detailed investigation of this sequence of reactions, affording virtually enantiopure ruthenium polypyridyl complexes. The control of the metal-centered chirality by the coordinated chiral salicyloxazolinate ligand was evaluated as a function of reaction conditions, the employed bidentate 2,2'-bipyridine and 1,10-phenanthroline ligands, and the substituent at the asymmetric 5-position of the oxazoline heterocycle. Most striking was the strong influence of the reaction solvent, with aprotic solvents of lower polarity providing the most favorable diastereoselectivities. Through a combination of computational and experimental results, it was revealed that the observed stereoselectivities are under thermodynamic control. The removal of the chiral salicyloxazoline auxiliary under retention of the configuration requires acidic conditions and a coordinating solvent such as MeCN or THF in order to prevent partial racemization. This method represents the first general strategy for the asymmetric synthesis of enantiopure heteroleptic ruthenium polypyridyl complexes.

  18. Asymmetric Synthesis of Ramariolides A and C through Bimetallic Cascade Cyclization and Z-E Isomerization Reaction.

    PubMed

    Pal, Pratik; Nanda, Samik

    2017-03-03

    A short and flexible asymmetric synthesis of ramariolides A and C was accomplished. A bimetallic catalytic system consisting of Pd-Cu-mediated cascade cyclization, unprecedented Z-E isomerization by a Ru-based metathesis catalyst, and late-stage stereoselective epoxidation are the key steps involved in the synthesis.

  19. Biocatalytic asymmetric synthesis of chiral amines from ketones applied to sitagliptin manufacture.

    PubMed

    Savile, Christopher K; Janey, Jacob M; Mundorff, Emily C; Moore, Jeffrey C; Tam, Sarena; Jarvis, William R; Colbeck, Jeffrey C; Krebber, Anke; Fleitz, Fred J; Brands, Jos; Devine, Paul N; Huisman, Gjalt W; Hughes, Gregory J

    2010-07-16

    Pharmaceutical synthesis can benefit greatly from the selectivity gains associated with enzymatic catalysis. Here, we report an efficient biocatalytic process to replace a recently implemented rhodium-catalyzed asymmetric enamine hydrogenation for the large-scale manufacture of the antidiabetic compound sitagliptin. Starting from an enzyme that had the catalytic machinery to perform the desired chemistry but lacked any activity toward the prositagliptin ketone, we applied a substrate walking, modeling, and mutation approach to create a transaminase with marginal activity for the synthesis of the chiral amine; this variant was then further engineered via directed evolution for practical application in a manufacturing setting. The resultant biocatalysts showed broad applicability toward the synthesis of chiral amines that previously were accessible only via resolution. This work underscores the maturation of biocatalysis to enable efficient, economical, and environmentally benign processes for the manufacture of pharmaceuticals.

  20. Recent Advances in Substrate-Controlled Asymmetric Induction Derived from Chiral Pool α-Amino Acids for Natural Product Synthesis.

    PubMed

    Paek, Seung-Mann; Jeong, Myeonggyo; Jo, Jeyun; Heo, Yu Mi; Han, Young Taek; Yun, Hwayoung

    2016-07-21

    Chiral pool α-amino acids have been used as powerful tools for the total synthesis of structurally diverse natural products. Some common naturally occurring α-amino acids are readily available in both enantiomerically pure forms. The applications of the chiral pool in asymmetric synthesis can be categorized prudently as chiral sources, devices, and inducers. This review specifically examines recent advances in substrate-controlled asymmetric reactions induced by the chirality of α-amino acid templates in natural product synthesis research and related areas.

  1. Memory of chirality generated by spontaneous crystallization and asymmetric synthesis using the frozen chirality.

    PubMed

    Sakamoto, Masami; Iwamoto, Takuya; Nono, Naoyuki; Ando, Masaru; Arai, Wataru; Mino, Takashi; Fujita, Tsutomu

    2003-02-07

    Asymmetric synthesis using frozen chirality generated by spontaneous crystallization was performed. Achiral asymmetrically substituted imide with a tetrahydronaphthyl group on the nitrogen atom crystallized in a chiral fashion, with space group P2(1)2(1)2(1). The molecular chirality generated by spontaneous crystallization was retained in cold THF. The half-life determined on the basis of decreasing optical activity followed by CD spectrometer was 7.8, 33.1, and 150.0 min at -20, -30, -40 degrees C, respectively. The energy barrier (DeltaG()) of racemization was calculated with the temperature dependence of the kinetic constant to be 18.24-18.36 kcal mol(-)(1) at 233-253 K. The memorized frozen chirality was transferred to permanent optically active alcohols by nucleophilic addition with n-buthyllithium.

  2. Catalytic asymmetric synthesis of 3-aminooxindoles: enantiofacial selectivity switch in bimetallic vs monometallic Schiff base catalysis.

    PubMed

    Mouri, Shinsuke; Chen, Zhihua; Mitsunuma, Harunobu; Furutachi, Makoto; Matsunaga, Shigeki; Shibasaki, Masakatsu

    2010-02-03

    A highly enantioselective catalytic asymmetric access to 3-aminooxindoles with a tetrasubstituted carbon stereocenter is described. 1-2 mol % of homobimetallic (R)-Ni(2)-Schiff base 1 catalyzed the asymmetric amination of 3-substituted oxindoles with azodicarboxylates to give (R)-products in 99-89% yield and 99-87% ee. Reversal of enantiofacial selectivity was observed between bimetallic and monometallic Schiff base complexes, and monometallic (R)-Ni-Schiff base 2c gave (S)-products in 98-80% ee. Transformation of the products into an optically active oxindole with a spiro-beta-lactam unit and a known key intermediate for AG-041R synthesis is also described.

  3. Efficient asymmetric synthesis of novel gastrin receptor antagonist AG-041R via highly stereoselective alkylation of oxindole enolates.

    PubMed

    Emura, Takashi; Esaki, Toru; Tachibana, Kazutaka; Shimizu, Makoto

    2006-10-27

    An efficient method for asymmetric synthesis of the potent Gastrin/CCK-B receptor antagonist AG-041R was developed. Core oxindole stereochemistry was established by asymmetric alkylation of oxindole enolates with bromoacetic acid esters, using l-menthol as a chiral auxiliary. The key alkylation reaction of the oxindole enolates generated tetrasubstituted chiral intermediates with high diastereoselectivity. The stereoselective alkylation reactions are described in detail.

  4. Multicomponent synthesis of chiral bidentate unsymmetrical unsaturated N-heterocyclic carbenes: copper-catalyzed asymmetric C-C bond formation.

    PubMed

    Jahier-Diallo, Claire; Morin, Marie S T; Queval, Pierre; Rouen, Mathieu; Artur, Isabelle; Querard, Pierre; Toupet, Loic; Crévisy, Christophe; Baslé, Olivier; Mauduit, Marc

    2015-01-12

    A multicomponent strategy was applied to the synthesis of chiral bidentate unsaturated hydroxyalkyl- and carboxyalkyl-N-heterocyclic carbene (NHC) precursors. The newly developed low-cost chiral ligands derived from amino alcohols and amino acids were evaluated in copper-catalyzed asymmetric conjugated addition and asymmetric allylic alkylation, which afforded the desired tertiary and quaternary carbon stereocenters with excellent regio- and enantioselectivities (up to 99:1 e.r.).

  5. New Organocatalytic Asymmetric Synthesis of Highly Substituted Chiral 2-Oxospiro-[indole-3,4'- (1',4'-dihydropyridine)] Derivatives.

    PubMed

    Auria-Luna, Fernando; Marqués-López, Eugenia; Mohammadi, Somayeh; Heiran, Roghayeh; Herrera, Raquel P

    2015-08-31

    Herein, we report our preliminary results concerning the first promising asymmetric synthesis of highly functionalized 2-oxospiro-[indole-3,4'-(1',4'-dihydropyridine)] via the reaction of an enamine with isatylidene malononitrile derivatives in the presence of a chiral base organocatalyst. The moderate, but promising, enantioselectivity observed (30%-58% ee (enantiomeric excess)) opens the door to a new area of research for the asymmetric construction of these appealing spirooxindole skeletons, whose enantioselective syntheses are still very limited.

  6. Asymmetric synthesis of syn-propargylamines and unsaturated β-amino acids under Brønsted base catalysis

    PubMed Central

    Wang, Yingcheng; Mo, Mingjie; Zhu, Kongxi; Zheng, Chao; Zhang, Hongbin; Wang, Wei; Shao, Zhihui

    2015-01-01

    Propargylamines are important intermediates for the synthesis of polyfunctional amino derivatives and natural products and biologically active compounds. The classic method of synthesizing chiral propargylamines involves the asymmetric alkynylation of imines. Here, we report a significant advance in the catalytic asymmetric Mannich-type synthesis of propargylamines through catalytic asymmetric addition of carbon nucleophiles to C-alkynyl imines, culminating in a highly syn-selective catalytic asymmetric Mannich reaction of C-alkynyl imines that provide syn-configured propargylamines with two adjacent stereogenic centres and a transition metal-free organocatalytic asymmetric approach to β-alkynyl-β-amino acids with high efficiency and practicality, via a chiral Brønsted base-catalysed asymmetric Mannich-type reaction of in situ generated challenging N-Boc C-alkynyl imines from previously unreported C-alkynyl N-Boc-N,O-acetals, with α-substituted β-keto esters and less-acidic malonate (thio)esters as nucleophiles, respectively. A catalytic activation strategy is also disclosed, which may have broad implications for use in catalysis and synthesis. PMID:26423837

  7. Multi-component Cycloaddition Approaches in the Catalytic Asymmetric Synthesis of Alkaloid Targets†

    PubMed Central

    Perreault, Stéphane; Rovis, Tomislav

    2010-01-01

    Cycloaddition reactions are attractive strategies for rapid formation of molecular complexity in organic synthesis as multiple bonds are formed in a single process. To this end, several research groups have been actively involved in the development of catalytic methods to activate readily accessible π-components to achieve cycloadditions. However, the use of C-N π-components for the formation of heterocycles by these processes is less well developed. It has been previously demonstrated that the combination of different isocyanates with two alkynes yields pyridones of several types by metal-catalyzed [2+2+2] cycloadditions. The potential of this chemistry has been extended to alkenes as C-C π-components, allowing the formation of sp3-stereocenters. In this tutorial review directed towards [n+2+2] cycloaddition of heterocumulenes, alkynes and alkenes, the recent advances in catalytic asymmetric synthesis of indolizidine, quinolizidine and azocine skeletons are discussed. PMID:19847348

  8. Engineering methylaspartate ammonia lyase for the asymmetric synthesis of unnatural amino acids

    NASA Astrophysics Data System (ADS)

    Raj, Hans; Szymański, Wiktor; de Villiers, Jandré; Rozeboom, Henriëtte J.; Veetil, Vinod Puthan; Reis, Carlos R.; de Villiers, Marianne; Dekker, Frank J.; de Wildeman, Stefaan; Quax, Wim J.; Thunnissen, Andy-Mark W. H.; Feringa, Ben L.; Janssen, Dick B.; Poelarends, Gerrit J.

    2012-06-01

    The redesign of enzymes to produce catalysts for a predefined transformation remains a major challenge in protein engineering. Here, we describe the structure-based engineering of methylaspartate ammonia lyase (which in nature catalyses the conversion of 3-methylaspartate to ammonia and 2-methylfumarate) to accept a variety of substituted amines and fumarates and catalyse the asymmetric synthesis of aspartic acid derivatives. We obtained two single-active-site mutants, one exhibiting a wide nucleophile scope including structurally diverse linear and cyclic alkylamines and one with broad electrophile scope including fumarate derivatives with alkyl, aryl, alkoxy, aryloxy, alkylthio and arylthio substituents at the C2 position. Both mutants have an enlarged active site that accommodates the new substrates while retaining the high stereo- and regioselectivity of the wild-type enzyme. As an example, we demonstrate a highly enantio- and diastereoselective synthesis of threo-3-benzyloxyaspartate (an important inhibitor of neuronal excitatory glutamate transporters in the brain).

  9. Investigation of Lewis acid versus Lewis base catalysis in asymmetric cyanohydrin synthesis.

    PubMed

    North, Michael; Omedes-Pujol, Marta; Williamson, Courtney

    2010-10-04

    The asymmetric addition of trimethylsilyl cyanide to aldehydes can be catalysed by Lewis acids and/or Lewis bases, which activate the aldehyde and trimethylsilyl cyanide, respectively. It is not always apparent from the structure of the catalyst whether Lewis acid or Lewis base catalysis predominates. To investigate this in the context of using salen complexes of titanium, vanadium and aluminium as catalysts, a Hammett analysis of asymmetric cyanohydrin synthesis was undertaken. When Lewis acid catalysis is dominant, a significantly positive reaction constant is observed, whereas reactions dominated by Lewis base catalysis give much smaller reaction constants. [{Ti(salen)O}(2)] was found to show the highest degree of Lewis acid catalysis, whereas two [VO(salen)X] (X=EtOSO(3) or NCS) complexes both displayed lower degrees of Lewis acid catalysis. In the case of reactions catalysed by [{Al(salen)}(2)O] and triphenylphosphine oxide, a non-linear Hammett plot was observed, which is indicative of a change in mechanism with increasing Lewis base catalysis as the carbonyl compound becomes more electron-deficient. These results suggested that the aluminium complex/triphenylphosphine oxide catalyst system should also catalyse the asymmetric addition of trimethylsilyl cyanide to ketones and this was found to be the case.

  10. Synthesis and photophysicochemical studies of poly(ethylene glycol) conjugated symmetrical and asymmetrical zinc phthalocyanines

    NASA Astrophysics Data System (ADS)

    Dinçer, Hatice; Mert, Humeyra; Çalışkan, Emel; Atmaca, Göknur Yaşa; Erdoğmuş, Ali

    2015-12-01

    Synthesis and characterization of poly(ethylene glycol) conjugated symmetrical and asymmetrical zinc phthalocyanines (ZnPcs) is described. Copper (I) catalyzed azide-alkyne cycloaddition (CuAAC) click reaction between azide functional methoxypoly(ethylene glycol) (mPEG-N3) and tetra terminal alkynyl substituted ZnPc yields star polymer with ZnPc core. Furthermore, CuAAC click reaction between asymmetrically terminal alkynyl substituted zinc phthalocyanine (aZnPc) and mPEG-N3 yields aZnPc end functionalized PEG. Spectral, photophysical (fluorescence quantum yield), photochemical (singlet oxygen (ΦΔ), and photodegradation quantum yield (Φd) properties of the symmetrically, and asymmetrically PEGylated ZnPcs are investigated to be used as sensitizers in photodynamic therapy (PDT). The quantum yield values of fluorescence (ΦF) and singlet oxygen generation (ΦΔ) for water soluble symmetrically PEGylated ZnPc in aqueous solution are calculated as 0.01 and 0.14 respectively, suggesting its potential as photosensitizer in PDT treatment.

  11. Synthesis and application of arylmonophosphinoferrocene ligands: ultrafast asymmetric hydrosilylation of styrene.

    PubMed

    Pedersen, Henriette Lodberg; Johannsen, Mogens

    2002-11-15

    A short and efficient synthetic route to a novel class of atropisomeric and planar chiral 2-aryl-1-diphenylphosphanylferrocene ligands is presented. The modular design of the ligands allows a synthetic approach in which both the aromatic moiety and the phosphino substituent can be varied easily. This permits fine-tuning of steric and electronic properties. The ligands have been tested in the asymmetric hydrosilylation of styrene where enantioselectivities up to 90% are obtained. Optimization of the palladium-to-ligand ratio resulted in hitherto unparalleled turnover frequencies (TOF) exceeding 180 000 h(-1). The absolute stereochemistry of the ligands was determined from an X-ray structure. 2D NMR experiments in combination with ab initio calculations were used to assign the conformation of the atropisomeric biarylic scaffold.

  12. A tailor-made chimeric thiamine diphosphate dependent enzyme for the direct asymmetric synthesis of (S)-benzoins.

    PubMed

    Westphal, Robert; Vogel, Constantin; Schmitz, Carlo; Pleiss, Jürgen; Müller, Michael; Pohl, Martina; Rother, Dörte

    2014-08-25

    Thiamine diphosphate dependent enzymes are well known for catalyzing the asymmetric synthesis of chiral α-hydroxy ketones from simple prochiral substrates. The steric and chemical properties of the enzyme active site define the product spectrum. Enzymes catalyzing the carboligation of aromatic aldehydes to (S)-benzoins have not so far been identified. We were able to close this gap by constructing a chimeric enzyme, which catalyzes the synthesis of various (S)-benzoins with excellent enantiomeric excess (>99%) and very good conversion.

  13. Catalytic asymmetric assembly of octahydroindolones: divergent synthesis of lycorine-type amaryllidaceae alkaloids (+)-α-lycorane and (+)-lycorine.

    PubMed

    Sun, Zhongwen; Zhou, Mingtao; Li, Xiang; Meng, Xueling; Peng, Fangzhi; Zhang, Hongbin; Shao, Zhihui

    2014-05-12

    We report the first catalytic asymmetric approach to octahydroindolones and a divergent enantioselective synthesis of perhydroindole alkaloids, as exemplified by lycorine-type Amaryllidaceae alkaloids (+)-α-lycorane and (+)-lycorine, from a common intermediate by using a highly concise route. The assembly of octahydroindolones employs a catalytic enantioselective 1,4-conjugate addition of nitro dienynes, followed by a TsOH-catalyzed cascade synthesis of highly functionalized enones, and a diastereoselective intramolecular Michael addition.

  14. Asymmetric Synthesis of (-)-Incarvillateine Employing an Intramolecular Alkylation via Rh-Catalyzed Olefinic C-H Bond Activation

    SciTech Connect

    Tsai, Andy; Bergman, Robert; Ellman, Jonathan

    2008-02-18

    An asymmetric total synthesis of (-)-incarvillateine, a natural product having potent analgesic properties, has been achieved in 11 steps and 15.4% overall yield. The key step is a rhodium-catalyzed intramolecular alkylation of an olefinic C-H bond to set two stereocenters. Additionally, this transformation produces an exocyclic, tetrasubstituted alkene through which the bicyclic piperidine moiety can readily be accessed.

  15. A direct organocatalytic entry to sphingoids: asymmetric synthesis of D-arabino- and L-ribo-phytosphingosine.

    PubMed

    Enders, Dieter; Palecek, Jirí; Grondal, Christoph

    2006-02-14

    The organocatalytic asymmetric synthesis of D-arabino- and L-ribo-phytosphingosine is described employing a diastereo- and enantioselective (S)-proline-catalyzed aldol reaction of 2,2-dimethyl-1,3-dioxan-5-one and pentadecanal as the key step.

  16. Asymmetric allylation/Pauson-Khand reaction: a simple entry to polycyclic amines. Application to the synthesis of aminosteroid analogues.

    PubMed

    Fustero, Santos; Lázaro, Rubén; Aiguabella, Nuria; Riera, Antoni; Simón-Fuentes, Antonio; Barrio, Pablo

    2014-02-21

    Asymmetric allylation of o-iodoarylsulfinylimines has been achieved in high diastereoselectivities. The thus-obtained o-iodoarylhomoallylic sulfinamides participate in a subsequent Sonogashira coupling followed by a diastereoselective intramolecular Pauson-Khand reaction. In this way, tricyclic amines showing a unique benzo-fused indenyl backbone were obtained. The methodology has been applied to the synthesis of amino steroid analogues.

  17. A Simple Synthesis of Alliin and allo-Alliin: X-ray Diffraction Analysis and Determination of Their Absolute Configurations.

    PubMed

    Hakamata, Wataru; Koyama, Ryosuke; Tanida, Mizuki; Haga, Tomomi; Hirano, Takako; Akao, Makoto; Kumagai, Hitomi; Nishio, Toshiyuki

    2015-12-23

    A simple method for the isolation of the bioactive compound alliin from garlic, as well as a method for the synthesis of diastereomerically pure alliin and allo-alliin on a preparative laboratory scale, was developed. The absolute configuration of the sulfur atom in alliin and allo-alliin was assigned on the basis of enzyme reactivity, optical rotatory dispersion, and circular dichroism analyses. A comparison of the results from these analyses, in combination with an X-ray diffraction study on a protected allo-alliin derivative, revealed S and R configurations of the sulfur atoms in alliin and allo-alliin, respectively. In addition, the same (1)H NMR spectrum was observed for synthetic and natural alliin. The absolute configuration of natural alliin was assigned for the first time on the basis of the NMR spectrum and X-ray coordinates.

  18. Synthesis and odor description of both enantiomers of methyl 4,5-didehydrojasmonate, a component of jasmin absolute.

    PubMed

    Asamitsu, Yuko; Nakamura, Yoko; Ueda, Minoru; Kuwahara, Shigefumi; Kiyota, Hiromasa

    2006-06-01

    Synthesis of both enantiomers of methyl 4,5-didehydrojasmonate (1, Delta(4,5)-MJA; >99.8% ee), a constituent of jasmin absolute, established the absolute configuration of the natural product, and their odor quality was evaluated. The fragrance of the natural (3S,7R)-enantiomer (a fresh natural, sweet floral fruity odor, reminiscent of Jasmin and Ylang Ylang flower, more intensive and tenacious) was superior to that of the unnatural (3R,7S)-enantiomer (a floral green odor with slight metallic green aspect, less intensive than the natural form) and the racemate (green-floral note, having weak and less volume than methyl jasmonate). Odor difference between natural and unnatural enantiomers of methyl jasmonate (2) is also reported.

  19. Preferential synthesis of asymmetric antibodies in rats immunized with paternal particulate antigens. Effect on pregnancy.

    PubMed

    Gentile, T; Borel, I M; Angelucci, J; Miranda, S; Margni, R A

    1992-08-01

    The effect of immunization of female Fischer rats with particulate (spleen cells) (group I) or soluble (supernatant of disintegrated spleen cells) (group II) paternal antigens previous to mating with Buffalo rats was investigated. The percentage of asymmetric IgG molecules in the serum of rats inoculated with particulate antigens was 38% while in those injected with soluble antigens it was 29% and 28% in non-immunized animals. These percentages further increased during pregnancy to 45%, 38% and 37%, respectively. The antipaternal antibody titres, as determined by indirect immunofluorescence (IIF), was much higher in the animals immunized with particulate antigens but the effector activity, judged by complement fixation, was similar in both groups. The same values were observed at the time of mating (after 3 months of immunization) and at day 17 of pregnancy. Fetus and placenta weights and offspring survival were equally greater in group I than in group II or non-immunized rats (group III). The results obtained indicate the preferential synthesis of antipaternal IgG asymmetric antibodies in rats injected with particulate antigens previous to mating and suggests a beneficial effect of these antibodies in pregnancy.

  20. Thiophenyl-substituted triazolyl-thione L-alanine: asymmetric synthesis, aggregation and biological properties.

    PubMed

    Saghyan, Ashot S; Simonyan, Hayarpi M; Petrosyan, Satenik G; Geolchanyan, Arpine V; Roviello, Giovanni N; Musumeci, Domenica; Roviello, Valentina

    2014-10-01

    In this work, we report the asymmetric synthesis and characterization of an artificial amino acid based on triazolyl-thione L-alanine, which was modified with a thiophenyl-substituted moiety, as well as in vitro studies of its nucleic acid-binding ability. We found, by dynamic light scattering studies, that the synthetic amino acid was able to form supramolecular aggregates having a hydrodynamic diameter higher than 200 nm. Furthermore, we demonstrated, by UV and CD experiments, that the heteroaromatic amino acid, whose enzymatic stability was demonstrated by HPLC analysis also after 24 h of incubation in human serum, was able to bind a RNA complex, which is a feature of biomedical interest in view of innovative antiviral strategies based on modulation of RNA-RNA molecular recognition.

  1. Asymmetric Synthesis of Chiral Bimetallic [Ag28Cu12(SR)24](4-) Nanoclusters via Ion Pairing.

    PubMed

    Yan, Juanzhu; Su, Haifeng; Yang, Huayan; Hu, Chengyi; Malola, Sami; Lin, Shuichao; Teo, Boon K; Häkkinen, Hannu; Zheng, Nanfeng

    2016-10-05

    In this work, a facile ion-pairing strategy for asymmetric synthesis of optically active negatively charged chiral metal nanoparticles using chiral ammonium cations is demonstrated. A new thiolated chiral three-concentric-shell cluster, [Ag28Cu12(SR)24](4-), was first synthesized as a racemic mixture and characterized by single-crystal X-ray structure determination. Mass spectrometric measurements revealed relatively strong ion-pairing interactions between the anionic nanocluster and ammonium cations. Inspired by this observation, the as-prepared racemic mixture was separated into enantiomers by employing chiral quaternary ammonium salts as chiral resolution agents. Subsequently, direct asymmetric synthesis of optically active enantiomers of [Ag28Cu12(SR)24](4-) was achieved by using appropriate chiral ammonium cations (such as N-benzylcinchoninium vs N-benzylcinchonidinium) in the cluster synthesis. These simple strategies, ion-pairing enantioseparation and direct asymmetric synthesis using chiral counterions, may be of general use in preparing chiral metal nanoparticles.

  2. New enantiomeric fluorine-containing derivatives of sulforaphane: synthesis, absolute configurations and biological activity.

    PubMed

    Kiełbasiński, Piotr; Łuczak, Jerzy; Cierpiał, Tomasz; Błaszczyk, Jarosław; Sieroń, Lesław; Wiktorska, Katarzyna; Lubelska, Katarzyna; Milczarek, Małgorzata; Chilmończyk, Zdzisław

    2014-04-09

    Three pairs of enantiomers of the unknown sulforaphane analogs bearing organofluorine substituents bonded to the sulfinyl sulfur atom and having different number of methylene groups in the central carbon chain were synthesized and fully characterized, including determination of their absolute configurations. All the new compounds were tested in vitro for their cytotoxicity against melanoma cells to show increased activity in comparison with the natural sulforaphane. The influence of the particular structural changes in the molecule on the cytotoxicity is discussed.

  3. Asymmetric Friedel-Crafts alkylations of indoles with dialkyl 3-oxoprop-1-enylphosphonates: organocatalytic enantioselective synthesis of alpha-indolyl phosphonates.

    PubMed

    Guo, Ying-Cen; Li, Dong-Ping; Li, Yu-Ling; Wang, Hong-Mei; Xiao, Wen-Jing

    2009-08-01

    Organocatalytic enantioselective synthesis of alpha-indolyl phosphonates has been successfully carried out via asymmetric Friedel-Crafts alkylation of substituted indoles with (E)-dialkyl 3-oxoprop-1-enylphosphonates in 48-82% yield and 73-96% ee.

  4. Easy Absolute Values? Absolutely

    ERIC Educational Resources Information Center

    Taylor, Sharon E.; Mittag, Kathleen Cage

    2015-01-01

    The authors teach a problem-solving course for preservice middle-grades education majors that includes concepts dealing with absolute-value computations, equations, and inequalities. Many of these students like mathematics and plan to teach it, so they are adept at symbolic manipulations. Getting them to think differently about a concept that they…

  5. Organocatalytic Asymmetric Synthesis of Functionalized 1,3,5-Triarylpyrrolidin-2-ones via an Aza-Michael/Aldol Domino Reaction

    PubMed Central

    Joie, Céline; Deckers, Kristina; Enders, Dieter

    2014-01-01

    The organocatalytic asymmetric synthesis of functionalized 1,3,5-triarylpyrrolidin-2-ones bearing three contiguous stereocenters through an aza-Michael/aldol domino reaction of α-ketoamides with α,β-unsaturated aldehydes is described. The domino products were further derivatized by aldehyde olefination under one-pot conditions. The reaction proceeds with excellent diastereoselectivities (>20:1) and good to excellent enantioselectivities (60–96% ee). PMID:25278634

  6. Highly regio- and enantioselective synthesis of N-substituted 2-pyridones: iridium-catalyzed intermolecular asymmetric allylic amination.

    PubMed

    Zhang, Xiao; Yang, Ze-Peng; Huang, Lin; You, Shu-Li

    2015-02-02

    The first iridium-catalyzed intermolecular asymmetric allylic amination reaction with 2-hydroxypyridines has been developed, thus providing a highly efficient synthesis of enantioenriched N-substituted 2-pyridone derivatives from readily available starting materials. This protocol features a good tolerance of functional groups in both the allylic carbonates and 2-hydroxypyridines, thereby delivering multifunctionalized heterocyclic products with up to 98% yield and 99% ee.

  7. Asymmetric Synthesis of (-)-Pterocarine and (-)-Galeon via Chiral Phase Transfer-Catalyzed Atropselective Formation of Diarylether Cyclophane Skeleton.

    PubMed

    Ding, Qiang; Wang, Qiuyan; He, Huan; Cai, Qian

    2017-04-07

    Pterocarine and galeon are typical examples of diarylether heptanoids (DAEHs) with planar chirality due to the strictly constrained conformations in their molecular skeletons. The characterized oxa[1,7]metapara-cyclophane motifs in DAEHs impose great challenges for their enantioselective synthesis. The asymmetric syntheses of (-)-pterocarine and (-)-galeon are demonstrated by employing a chiral phase transfer-catalyzed highly enantioselective SNAr cyclization as the key step for the formation of a diarylether cyclophane skeleton.

  8. Total synthesis of (R,R,R)-α-tocopherol through asymmetric Cu-catalyzed 1,4-addition.

    PubMed

    Termath, Andreas Ole; Sebode, Hanna; Schlundt, Waldemar; Stemmler, René T; Netscher, Thomas; Bonrath, Werner; Schmalz, Hans-Günther

    2014-09-15

    By introducing a disposable activating substituent at C-3, the asymmetric 1,4-addition to a notoriously unreactive 2-substituted chromenone was achieved with high levels of (2R)-stereoselectivity in the presence of a chiral Cu(I)-phosphoramidite complex as a catalyst. This paved the way for an efficient and conceptually novel synthesis of (R,R,R)-α-tocopherol from readily available starting materials.

  9. [Development of asymmetric synthesis of optically active compounds including fluoroorganic molecules].

    PubMed

    Iseki, K

    1999-11-01

    The synthesis of chiral fluorinated molecules is important in the biological and medicinal chemistry fields in view of the influence of fluorine's unique properties on biological activity. In recent years, we have studied asymmetric synthesis focussing on such optically active compounds. This review describes 1) diastereoselective trifluoromethylation of chiral N-acyloxazolidinones, 2) catalytic enantioselective aldol reactions of fluorine-substituted ketene silyl acetals, and 3) catalytic enantioselective allylation of aldehydes mediated by chiral Lewis bases. The trifluoromethylation of lithium enolates of N-acyloxazolidinones with iodotrifluoromethane is mediated by triethylborane to give the corresponding trifluoromethylated products with up to 86% diastereomeric excess. The stereoselective reaction is considered to proceed through the attack of the trifluoromethyl radical on the less hindered face of the lithium imide. Difluoroketene and bromofluoroketene trimethylsilyl ethyl acetals react with various aldehydes in the presence of chiral Lewis acids to afford the corresponding desired aldols with up to 99% enantiomeric excess (ee). It is noteworthy that the aldol reactions of the fluorine-substituted acetals at -78 degrees C and at higher temperatures (-45 or -20 degrees C) provide the (+)- and (-)-aldols, respectively, with excellent-to-good enantioselectivity. Chiral phosphoramides newly prepared from (S)-proline were found to catalyze the allylation and crotylation of aromatic aldehydes with allylic trichlorosilanes in good enantioselective yields (up to 90% ee). (S,S)-Bis(alpha-methylbenzyl)formamide developed as an efficient catalyst for the allylation and crotylation of aliphatic aldehydes mediates the enantioselective addition with the assistance of hexamethylphosphoramide (HMPA) to afford the corresponding homoallylic alcohols in up to 98% ee.

  10. Highly asymmetrical glycerol diether bolalipids: synthesis and temperature-dependent aggregation behavior.

    PubMed

    Markowski, Thomas; Drescher, Simon; Förster, Günter; Lechner, Bob-Dan; Meister, Annette; Blume, Alfred; Dobner, Bodo

    2015-10-06

    In the present work, we describe the synthesis and temperature-dependent aggregation behavior of two examples of a new class of highly asymmetrical glycerol diether bolaphospholipids. The bolalipids contain a long alkyl chain (C32) bound to glycerol in the sn-3 position, carrying a hydroxyl group at the ω position. The C16 alkyl chain in the sn-2 position either possesses a racemic methyl branch at the 10 position of the short alkyl chain (lipid II) or does not (lipid I). The sn-1 position of the glycerol is linked to a zwitterionic phosphocholine moiety. The temperature-dependent aggregation behavior of both bolalipids was studied using differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy, and X-ray scattering. Aggregate structures were visualized by transmission electron microscopy (TEM). We show that both bolalipids self-assemble into large lamellar sheetlike aggregates. Closed lipid vesicles or other aggregate structures such as tubes or nanofibers, as usually found for diglycerol tetraether lipids, were not observed. Within the lamellae the bolalipid molecules are arranged in an antiparallel (interdigitated) orientation. Lipid I, without an additional methyl moiety in the short alkyl chain, shows a lamellar phase with high crystallinity up to a temperature of 34 °C, which was not observed before for other phospholipids.

  11. Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate

    PubMed Central

    Omedes-Pujol, Marta

    2010-01-01

    Summary Propylene carbonate can be used as a green solvent for the asymmetric synthesis of cyanohydrin trimethylsilyl ethers from aldehydes and trimethylsilyl cyanide catalysed by VO(salen)NCS, though reactions are slower in this solvent than the corresponding reactions carried out in dichloromethane. A mechanistic study has been undertaken, comparing the catalytic activity of VO(salen)NCS in propylene carbonate and dichloromethane. Reactions in both solvents obey overall second-order kinetics, the rate of reaction being dependent on the concentration of both the aldehyde and trimethylsilyl cyanide. The order with respect to VO(salen)NCS was determined and found to decrease from 1.2 in dichloromethane to 1.0 in propylene carbonate, indicating that in propylene carbonate, VO(salen)NCS is present only as a mononuclear species, whereas in dichloromethane dinuclear species are present which have previously been shown to be responsible for most of the catalytic activity. Evidence from 51V NMR spectroscopy suggested that propylene carbonate coordinates to VO(salen)NCS, blocking the free coordination site, thus inhibiting its Lewis acidity and accounting for the reduction in catalytic activity. This explanation was further supported by a Hammett analysis study, which indicated that Lewis base catalysis made a much greater contribution to the overall catalytic activity of VO(salen)NCS in propylene carbonate than in dichloromethane. PMID:21085513

  12. Catalytic asymmetric synthesis of spirocyclic azlactones by a double Michael-addition approach.

    PubMed

    Weber, Manuel; Frey, Wolfgang; Peters, René

    2013-06-17

    Spirocyclic azlactones are shown to be useful precursors of cyclic quaternary amino acids, such as the constrained cyclohexane analogues of phenylalanine. These compounds are of interest as building blocks for the synthesis of artificial peptide analogues with controlled folds in the peptide backbone. They were prepared in the present study by a step- and atom-economic catalytic asymmetric tandem approach, requiring two steps starting from N-benzoyl glycine and divinylketones. The key of this protocol is the enantioselective formation of the azlactone spirocycles, which involves a PdII-catalyzed double 1,4-addition of an in situ generated azlactone intermediate to the dienone (a formal [5+1] cycloaddition). As the catalyst, a planar chiral ferrocene bispalladacycle was used. Mechanistic studies suggest a monometallic reaction pathway. Although the diastereoselectivity was found to be moderate, the enantioselectivity is usually high for the formation of the azlactone spirocycles, which contain up to three contiguous stereocenters. Spectroscopic studies have shown that the spirocycles often prefer a twist over a chair conformation of the cyclohexanone moiety.

  13. Chemoenzymatic asymmetric synthesis of 1,4-benzoxazine derivatives: application in the synthesis of a levofloxacin precursor.

    PubMed

    López-Iglesias, María; Busto, Eduardo; Gotor, Vicente; Gotor-Fernández, Vicente

    2015-04-17

    A versatile and general route has been developed for the asymmetric synthesis of a wide family of 3-methyl-3,4-dihydro-2H-benzo[b][1,4]oxazines bearing different pattern substitutions in the aromatic ring. Whereas hydrolases were not suitable for resolution of these racemic cyclic nitrogenated amines, alternative chemoenzymatic strategies were designed through independent pathways leading to both amine antipodes. On one hand, bioreduction of 1-(2-nitrophenoxy)propan-2-ones allowed the recovery of the enantiopure (S)-alcohols in high yields using the alcohol dehydrogenase from Rhodococcus ruber (ADH-A), whereas evo-1.1.200 ADH led to their counterpart (R)-enantiomers also with complete selectivity and quantitative conversion. Alternatively, lipase-catalyzed acetylation of these racemic alcohols, and the complementary hydrolysis of the acetate analogues, gave access to the corresponding optically enriched products with high stereodiscrimination. Particularly attractive was the design of a chemoenzymatic strategy in six steps for the production of (S)-(-)-7,8-difluoro-3-methyl-3,4-dihydro-2H-benzo-[b][1,4]oxazine, which is a key precursor of the antimicrobial agent Levofloxacin.

  14. [Development of highly stereoselective reactions utilizing heteroatoms--asymmetric synthesis of alpha-substituted serines].

    PubMed

    Sano, S

    2000-01-01

    the Isaria sinclairii metabolite) is described. Asymmetric total synthesis of ISP-I has been achieved in a highly stereoselective manner by utilizing the Mg(II)-promoted aldol-type reaction with ethyl (5R)-3,6-diethoxy-2,5-dihydro-5-isopropyl-2-pyrazinecarboxylate and Schlosser modification of the Wittig reaction.

  15. Carotenoids and related polyenes, part 12. First total synthesis and absolute configuration of 3'-deoxycapsanthin and 3,4-didehydroxy-3'-deoxycapsanthin.

    PubMed

    Yamano, Yumiko; Chary, Mahankhali Venu; Wada, Akimori

    2010-10-01

    The synthesis of 3'-deoxycapsanthin (1) and 3,4-didehydroxy-3'-deoxycapsanthin (2), carotenoids of paprika, has been achieved by employing Lewis acid-promoted regio- and stereoselective rearrangement of the C(15)-epoxy dienal 5a. The absolute stereochemistry of the newly formed C-5 chiral center of rearrangement product 6a was determined to be (R) from its alternative synthesis derived from (+)-(R)-camphonanic acid (11).

  16. Can the analyte-triggered asymmetric autocatalytic Soai reaction serve as a universal analytical tool for measuring enantiopurity and assigning absolute configuration?

    PubMed

    Welch, Christopher J; Zawatzky, Kerstin; Makarov, Alexey A; Fujiwara, Satoshi; Matsumoto, Arimasa; Soai, Kenso

    2016-12-20

    An investigation is reported on the use of the autocatalytic enantioselective Soai reaction, known to be influenced by the presence of a wide variety of chiral materials, as a generic tool for measuring the enantiopurity and absolute configuration of any substance. Good generality for the reaction across a small group of test analytes was observed, consistent with literature reports suggesting a diversity of compound types that can influence the stereochemical outcome of this reaction. Some trends in the absolute sense of stereochemical enrichment were noted, suggesting the possible utility of the approach for assigning absolute configuration to unknown compounds, by analogy to closely related species with known outcomes. Considerable variation was observed in the triggering strength of different enantiopure materials, an undesirable characteristic when dealing with mixtures containing minor impurities with strong triggering strength in the presence of major components with weak triggering strength. A strong tendency of the reaction toward an 'all or none' type of behavior makes the reaction most sensitive for detecting enantioenrichment close to zero. Consequently, the ability to discern modest from excellent enantioselectivity was relatively poor. While these properties limit the ability to obtain precise enantiopurity measurements in a simple single addition experiment, prospects may exist for more complex experimental setups that may potentially offer improved performance.

  17. Chiral N-phosphonyl imine chemistry: asymmetric synthesis of alpha-alkyl beta-amino ketones by reacting phosphonyl imines with ketone-derived enolates.

    PubMed

    Ai, Teng; Han, Jianlin; Chen, Zhong-Xiu; Li, Guigen

    2009-02-01

    A series of new chiral syn-alpha-branched beta-amino ketones has been synthesized by reacting chiral phosphonyl imines with ketone-derived enolates. The N-protection group on imine auxiliary was found to be crucial to the asymmetric induction. The absolute stereochemistry has been unambiguously determined by converting a product to a known sample.

  18. De novo asymmetric synthesis and biological analysis of the daumone pheromones in Caenorhabditis elegans and in the soybean cyst nematode Heterodera glycines

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The de novo asymmetric total syntheses of daumone 1, daumone 2 and analogs are described. The key steps of our approach are the diastereoselective palladium catalyzed glycosylation reaction, the Noyori reduction of a acetylfuran and a propargyl ketone, which introduce the absolute stereochemistry of...

  19. Synthesis of novel chiral phosphinocyrhetrenyloxazoline ligands and their application in asymmetric catalysis.

    PubMed

    Bolm, Carsten; Xiao, Li; Kesselgruber, Martin

    2003-01-07

    Several novel planar chiral phosphinocyrhetrenyloxazolines have been synthesized, and their catalytic activities have been evaluated in a variety of asymmetric catalytic reactions. Preferable effects as compared to their ferrocenyl analogues have been observed in asymmetric allylic amination and asymmetric hydrosilylation, and up to 97% ee and 72% ee were reached, respectively. The Lewis basicity of the phosphorus on the ferrocene and the cyrhetrene, which contributes to their different behavior in catalysis, has been deduced by 31P NMR spectroscopy analysis, as indicated by 1J(77Se-31P) in the corresponding phosphine selenides.

  20. Conjugate addition of lithium N-phenyl-N-(α-methylbenzyl)amide: application to the asymmetric synthesis of (R)-(-)-angustureine.

    PubMed

    Bentley, Scott A; Davies, Stephen G; Lee, James A; Roberts, Paul M; Thomson, James E

    2011-05-20

    The conjugate addition of lithium (R)-N-phenyl-N-(α-methylbenzyl)amide to a range of α,β-unsaturated 4-methoxyphenyl esters proceeds with excellent levels of diastereoselectivity to give the corresponding β-amino esters in good yield and as single diastereoisomers (>99:1 dr). The synthetic utility of this methodology has been demonstrated via the short and concise asymmetric synthesis of the tetrahydroquinoline alkaloid (R)-(-)-angustureine in six steps and 32% overall yield from commercially available oct-2-enoic acid.

  1. Preparation of anti-Vicinal Amino Alcohols: Asymmetric Synthesis of d-erythro-Sphinganine, (+)-Spisulosine, and d-ribo-Phytosphingosine

    PubMed Central

    2013-01-01

    Two variations of the Overman rearrangement have been developed for the highly selective synthesis of anti-vicinal amino alcohol natural products. A MOM ether-directed palladium(II)-catalyzed rearrangement of an allylic trichloroacetimidate was used as the key step for the preparation of the protein kinase C inhibitor d-erythro-sphinganine and the antitumor agent (+)-spisulosine, whereas the Overman rearrangement of chiral allylic trichloroacetimidates generated by the asymmetric reduction of an α,β-unsaturated methyl ketone allowed rapid access both to d-ribo-phytosphingosine and l-arabino-phytosphingosine. PMID:23795558

  2. Preparation of anti-vicinal amino alcohols: asymmetric synthesis of D-erythro-sphinganine, (+)-spisulosine, and D-ribo-phytosphingosine.

    PubMed

    Calder, Ewen D D; Zaed, Ahmed M; Sutherland, Andrew

    2013-07-19

    Two variations of the Overman rearrangement have been developed for the highly selective synthesis of anti-vicinal amino alcohol natural products. A MOM ether-directed palladium(II)-catalyzed rearrangement of an allylic trichloroacetimidate was used as the key step for the preparation of the protein kinase C inhibitor D-erythro-sphinganine and the antitumor agent (+)-spisulosine, whereas the Overman rearrangement of chiral allylic trichloroacetimidates generated by the asymmetric reduction of an α,β-unsaturated methyl ketone allowed rapid access both to D-ribo-phytosphingosine and L-arabino-phytosphingosine.

  3. Asymmetric synthesis and biological evaluation of natural or bioinspired cytotoxic C2-symmetrical lipids with two terminal chiral alkynylcarbinol pharmacophores.

    PubMed

    Listunov, Dymytrii; Fabing, Isabelle; Saffon-Merceron, Nathalie; Gaspard, Hafida; Volovenko, Yulian; Maraval, Valérie; Chauvin, Remi; Génisson, Yves

    2015-06-05

    Bidirectional syntheses of C2-symmetrical lipids embedding two terminal alkynylcarbinol pharmacophores are reported. Naturally occurring chiral alkenylalkynylcarbinol units were generated using Pu's procedure for enantioselective addition of terminal alkynes to aldehydes, allowing the first asymmetric synthesis of (3R,4E,16E,18R)-icosa-4,16-diene-1,19-diyne-3,18-diol, isolated from Callyspongia pseudoreticulata. Two synthetic analogues embedding the recently uncovered (S)-dialkynylcarbinol pharmacophore were secured using Carreira's procedure adapted to ynal substrates. The dramatic effect of the carbinol configuration on cytotoxicity was confirmed with submicromolar IC50 values against HCT116 cells.

  4. Core-structure-inspired asymmetric addition reactions: enantioselective synthesis of dihydrobenzoxazinone- and dihydroquinazolinone-based anti-HIV agents.

    PubMed

    Li, Shen; Ma, Jun-An

    2015-11-07

    Dihydrobenzoxazinones and dihydroquinazolinones are the core units present in many anti-HIV agents, such as Efavirenz, DPC 961, DPC 963, and DPC 083. All these molecules contain a trifluoromethyl moiety at the quaternary stereogenic carbon center with S configuration. The enantioselective addition of carbon nucleophiles to ketones or cyclic ketimines could serve as a key step to access these molecules. This tutorial review provides an overview of significant advances in the synthesis of dihydrobenzoxazinone- and dihydroquinazolinone-based anti-HIV agents and relative analogues, with an emphasis on asymmetric addition reactions for the establishment of the CF3-containing quaternary carbon centers.

  5. Highly enantioselective synthesis of γ-, δ-, and ε-chiral 1-alkanols via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA)-Cu- or Pd-catalyzed cross-coupling.

    PubMed

    Xu, Shiqing; Oda, Akimichi; Kamada, Hirofumi; Negishi, Ei-ichi

    2014-06-10

    Despite recent advances of asymmetric synthesis, the preparation of enantiomerically pure (≥99% ee) compounds remains a challenge in modern organic chemistry. We report here a strategy for a highly enantioselective (≥99% ee) and catalytic synthesis of various γ- and more-remotely chiral alcohols from terminal alkenes via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA reaction)-Cu- or Pd-catalyzed cross-coupling. ZACA-in situ oxidation of tert-butyldimethylsilyl (TBS)-protected ω-alkene-1-ols produced both (R)- and (S)-α,ω-dioxyfunctional intermediates (3) in 80-88% ee, which were readily purified to the ≥99% ee level by lipase-catalyzed acetylation through exploitation of their high selectivity factors. These α,ω-dioxyfunctional intermediates serve as versatile synthons for the construction of various chiral compounds. Their subsequent Cu-catalyzed cross-coupling with various alkyl (primary, secondary, tertiary, cyclic) Grignard reagents and Pd-catalyzed cross-coupling with aryl and alkenyl halides proceeded smoothly with essentially complete retention of stereochemical configuration to produce a wide variety of γ-, δ-, and ε-chiral 1-alkanols of ≥99% ee. The MαNP ester analysis has been applied to the determination of the enantiomeric purities of δ- and ε-chiral primary alkanols, which sheds light on the relatively undeveloped area of determination of enantiomeric purity and/or absolute configuration of remotely chiral primary alcohols.

  6. Asymmetric synthesis of both the enantiomers of trans-3-hydroxypipecolic acid.

    PubMed

    Kumar, Pradeep; Bodas, Mandar S

    2005-01-07

    Both the enantiomers of trans-3-hydroxypipecolic acid have been synthesized employing the Sharpless asymmetric dihydroxylation and epoxidation as the key steps starting from a commercially available starting material 1,4-butanediol.

  7. Cascade Biocatalysis for Sustainable Asymmetric Synthesis: From Biobased l-Phenylalanine to High-Value Chiral Chemicals.

    PubMed

    Zhou, Yi; Wu, Shuke; Li, Zhi

    2016-09-12

    Sustainable synthesis of useful and valuable chiral fine chemicals from renewable feedstocks is highly desirable but remains challenging. Reported herein is a designed and engineered set of unique non-natural biocatalytic cascades to achieve the asymmetric synthesis of chiral epoxide, diols, hydroxy acid, and amino acid in high yield and with excellent ee values from the easily available biobased l-phenylalanine. Each of the cascades was efficiently performed in one pot by using the cells of a single recombinant strain over-expressing 4-10 different enzymes. The cascade biocatalysis approach is promising for upgrading biobased bulk chemicals to high-value chiral chemicals. In addition, combining the non-natural enzyme cascades with the natural metabolic pathway of the host strain enabled the fermentative production of the chiral fine chemicals from glucose.

  8. Enantiodivergent Atroposelective Synthesis of Chiral Biaryls by Asymmetric Transfer Hydrogenation: Chiral Phosphoric Acid Catalyzed Dynamic Kinetic Resolution.

    PubMed

    Mori, Keiji; Itakura, Tsubasa; Akiyama, Takahiko

    2016-09-12

    Reported herein is an enantiodivergent synthesis of chiral biaryls by a chiral phosphoric acid catalyzed asymmetric transfer hydrogenation reaction. Upon treatment of biaryl lactols with aromatic amines and a Hantzsch ester in the presence of chiral phosphoric acid, dynamic kinetic resolution (DKR) involving a reductive amination reaction proceeded smoothly to furnish both R and S isomers of chiral biaryls with excellent enantioselectivities by proper choice of hydroxyaniline derivative. This trend was observed in wide variety of substrates, and various chiral biphenyl and phenyl naphthyl adducts were synthesized with satisfactory enantioselectivities in enantiodivergent fashion. The enantiodivergent synthesis of synthetically challenging, chiral o-tetrasubstituted biaryls were also accomplished, and suggests high synthetic potential of the present method.

  9. Asymmetric reactions in continuous flow

    PubMed Central

    Mak, Xiao Yin; Laurino, Paola

    2009-01-01

    Summary An overview of asymmetric synthesis in continuous flow and microreactors is presented in this review. Applications of homogeneous and heterogeneous asymmetric catalysis as well as biocatalysis in flow are discussed. PMID:19478913

  10. The Construction of All-Carbon Quaternary Stereocenters by Use of Pd-Catalyzed Asymmetric Allylic Alkylation Reactions in Total Synthesis

    PubMed Central

    Hong, Allen Y.

    2014-01-01

    All-carbon quaternary stereocenters have posed significant challenges in the synthesis of complex natural products. These important structural motifs have inspired the development of broadly applicable palladium-catalyzed asymmetric allylic alkylation reactions of unstabilized non-biased enolates for the synthesis of enantioenriched α-quaternary products. This microreview outlines key considerations in the application of palladium-catalyzed asymmetric allylic alkylation reactions and presents recent total syntheses of complex natural products that have employed these powerful transformations for the direct, catalytic, enantioselective construction of all-carbon quaternary stereocenters. PMID:24944521

  11. Synthesis and characterization of asymmetric polymer/inorganic nanocomposites with pH/temperature sensitivity

    NASA Astrophysics Data System (ADS)

    Zhang, Xinjie; Gao, Chunmei; Liu, Mingzhu; Huang, Yinjuan; Yu, Xiyong; Ding, Enyong

    2013-01-01

    An easy, comprehensive and inexpensive method is demonstrated to produce asymmetric polymer/inorganic nanocomposites in a large quantity. With the aid of Pickering emulsion, unmodified particles aggregate on the surface of emulsion droplets and are fixed in place when the wax solidifies. The exposed surfaces of immobilized SiO2 particles are modified chemically by 2-(dimethylamino) ethylmethacrylate (DMAEMA). With the removal of wax, the exposed side of particles can be further modified chemically by N-isopropylacrylamide (NIPAAm). Based on these procedures, dual responsive asymmetric nanocomposite particles are achieved with both pH and temperature sensitivities. Due to their dual-stimuli and asymmetric structure, these particles have potential applications in molecule targeting, drug delivery and as building blocks for the assembly of complex nanostructure.

  12. Asymmetric Total Syntheses of Megacerotonic Acid and Shimobashiric Acid A

    PubMed Central

    Krabbe, Scott W.; Johnson, Jeffrey S.

    2015-01-01

    The asymmetric total syntheses of the α-benzylidene-γ-butyrolactone natural products megacerotonic acid and shimobashiric acid A have been accomplished in nine and 11 steps, respectively, from simple, commercially available starting materials. The key step for each synthesis is the (arene)RuCl(monosulfonamide)-catalyzed dynamic kinetic resolution-asymmetric transfer hydrogenation (DKR-ATH) of racemic α,δ-diketo-β-aryl esters to establish the absolute stereochemistry. Intramolecular diastereoselective Dieckmann cyclization forms the lactone core, and ketone reduction/alcohol elimination installs the α-arylidene. PMID:25699999

  13. Asymmetric Synthesis of Axially Chiral Isoquinolones: Nickel-Catalyzed Denitrogenative Transannulation.

    PubMed

    Fang, Zhi-Jia; Zheng, Sheng-Cai; Guo, Zhen; Guo, Jing-Yao; Tan, Bin; Liu, Xin-Yuan

    2015-08-10

    The first Ni(0)/bis(oxazoline)-catalyzed asymmetric denitrogenative transannulation of 1,2,3-benzotriazin-4(3H)-ones with bulky internal alkynes to form novel axially chiral isoquinolones in an atroposelective manner has been developed. This method provides direct asymmetric access to axially chiral isoquinolones with excellent functional-group tolerance in excellent yields and stereoselectivities from readily available starting materials under mild reaction conditions. These axially chiral isoquinolones exhibit high cytotoxicity against a number of human cancer cell lines. DFT calculations reveal the nature of the transition state in the key annulation step.

  14. Mechanism-guided development of VO(salen)X complexes as catalysts for the asymmetric synthesis of cyanohydrin trimethylsilyl ethers.

    PubMed

    Belokon, Yuri N; Clegg, William; Harrington, Ross W; Maleev, Victor I; North, Michael; Pujol, Marta Omedes; Usanov, Dmitry L; Young, Carl

    2009-01-01

    Catalyze this! Detailed study of the mechanism of asymmetric cyanohydrin synthesis catalyzed by VO(salen)X complexes (see figure) led to the development of VO(salen)NCS, as the most active vanadium-based catalyst yet developed for this reaction.The mechanism by which oxovanadium(V)(salen) complexes(1) VO(salen)X catalyze the asymmetric addition of trimethylsilyl cyanide to benzaldehyde has been studied. The reaction kinetics indicated that the structure of the counterion (X) had a significant influence on the rate, but not on the enantioselectivity of the reaction. The less coordinating the counterion, the lower the catalytic activity; a trend that was confirmed by a Hammett analysis. Variable temperature kinetics allowed the enthalpies and entropies of activation to be determined for some catalysts, and showed that, for others, the overall reaction order changes from second order to zero order as the temperature is reduced. The order with respect to the catalyst was determined for nine of the VO(salen)X complexes and showed that the less active catalysts were active predominantly as mononuclear species whilst the more active catalysts were active predominantly as dinuclear species. Mass spectrometry confirmed the formation of dinuclear species in situ from all of the VO(salen)X complexes and indicated that the dinuclear complexes contained one vanadium(V) and one vanadium(IV) ion. The latter conclusion was supported by cyclic voltammetry of the complexes, by fluorescence measurements and by the fact that catalyst deactivation occurs when reactions are carried out under an inert atmosphere. Based on this evidence, it has been deduced that the catalysis involves two catalytic cycles: one for catalysis by mononuclear VO(salen)X species and the other for catalysis by dinuclear species. The catalytic cycle involving dinuclear species involves activation of both the cyanide and aldehyde, whereas the catalytic cycle involving mononuclear species activates only the

  15. Applications of helical-chiral pyridines as organocatalysts in asymmetric synthesis.

    PubMed

    Peng, Zhili; Takenaka, Norito

    2013-02-01

    A new family of chiral pyridines has been designed and synthesized for use in asymmetric organocatalysis. Thus, helical-chiral pyridines induce high enantioselectivity in a range of mechanistically unrelated, synthetically significant transformations, including Friedel-Crafts alkylation with nitroalkenes, periselective Diels-Alder reactions with nitroalkenes, the ring-opening of epoxides with a chloride nucleophile, and the propargylation of aldehydes.

  16. Enantioselective synthesis of β-substituted chiral allylic amines via Rh-catalyzed asymmetric hydrogenation.

    PubMed

    Wang, Qingli; Gao, Wenchao; Lv, Hui; Zhang, Xumu

    2016-09-27

    An asymmetric mono-hydrogenation of 2-acetamido-1,3-dienes catalyzed by a Rh-DuanPhos complex has been developed. This approach provides easy access to chiral allylic amines with excellent enantioselectivities and high regioselectivities. The products are valuable chiral building blocks for pharmaceuticals.

  17. Asymmetric bromine-lithium exchange: application toward the synthesis of natural product.

    PubMed

    Graff, Julien; Debande, Thibaut; Praz, Jézabel; Guénée, Laure; Alexakis, Alexandre

    2013-08-16

    Asymmetric bromine-lithium exchange has been successfully employed to synthesize bicoumarin chiral building blocks of (+)-isokotanin A and (-)-kotanin in good yields and with an excellent level of enantioselectivity. This is the first reported example of formal syntheses, using this direct methodology, leading to the single (M)-atropoisomer of (+)-isokotanin A and (-)-kotanin building blocks, without any resolution step.

  18. Catalytic Asymmetric Synthesis of Chiral 2-Vinylindole Scaffolds by Friedel-Crafts Reaction.

    PubMed

    Arai, Takayoshi; Tsuchida, Akiko; Miyazaki, Tomoya; Awata, Atsuko

    2017-02-17

    A chiral bis(imidazolidine)pyridine (PyBidine)-Ni(OTf)2 complex smoothly catalyzed an asymmetric Friedel-Crafts reaction of 2-vinylindoles with nitroalkenes to give chiral indoles in a highly enantioselective manner while maintaining the 2-vinyl functionality. The chiral 2-vinylindoles offer unique chiral scaffolds for diverse transformations.

  19. Synthesis of Asymmetrical Organic Carbonates using CO2 as a Feedstock in AgCl/Ionic Liquid System at Ambient Conditions.

    PubMed

    Hu, Jiayin; Ma, Jun; Lu, Lu; Qian, Qingli; Zhang, Zhaofu; Xie, Chao; Han, Buxing

    2017-03-22

    Synthesis of asymmetrical organic carbonates from the renewable and inexpensive CO2 is of great importance but also challenging, especially at ambient conditions. Herein, we found that some metal salt/ionic liquid catalyst systems were highly active for the synthesis of asymmetrical organic carbonates from CO2 , propargylic alcohols, and primary alcohols. Especially, the AgCl/1-butyl-3-methylimidazolium acetate ([Bmim][OAc]) system was very efficient for the reactions of a wide range of substrates at room temperature and atmospheric pressure, and the yields of the asymmetrical organic carbonates could approach 100 %. The catalyst system could be reused at least five times without changing its catalytic performance, and could be easily recovered and reused. A detailed study indicated that AgCl and [Bmim][OAc] catalyzed the reactions cooperatively, resulting in unique catalytic performance.

  20. Asymmetric synthesis of dihydropyranones from ynones by sequential copper(I)-catalyzed direct aldol and silver(I)-catalyzed oxy-Michael reactions.

    PubMed

    Shi, Shi-Liang; Kanai, Motomu; Shibasaki, Masakatsu

    2012-04-16

    Ynones as diene surrogates: the asymmetric synthesis of enantiomerically enriched substituted dihydropyranones is described. The products are obtained in two steps by a copper(I)-catalyzed direct aldol reaction of ynones followed by a silver-catalyzed oxy-Michael reaction. This easy method is compatible with both aromatic and aliphatic substrates, and provides excellent chemoselectivity under mild reaction conditions.

  1. Asymmetric synthesis of the HMG-CoA reductase inhibitor atorvastatin calcium: an organocatalytic anhydride desymmetrization and cyanide-free side chain elongation approach.

    PubMed

    Chen, Xiaofei; Xiong, Fangjun; Chen, Wenxue; He, Qiuqin; Chen, Fener

    2014-03-21

    An efficient asymmetric synthesis of atorvastatin calcium has been achieved from commercially available diethyl 3-hydroxyglutarate through a novel approach that involves an organocatalytic enantioselective cyclic anhydride desymmetrization to establish C(3) stereogenicity and cyanide-free assembly of C7 amino type side chain via C5+C2 strategy as the key transformations.

  2. Asymmetric synthesis of tetrahydroquinolin-3-ols via CoCl2-catalyzed reductive cyclization of nitro cyclic sulfites with NaBH4.

    PubMed

    Jagdale, Arun R; Reddy, R Santhosh; Sudalai, Arumugam

    2009-02-19

    A new method for the construction of chiral 3-substituted tetrahydroquinoline derivatives based on asymmetric dihydroxylation and CoCl(2)-catalyzed reductive cyclization of nitro cyclic sulfites with NaBH(4) has been described with high optical purities. This method has been successfully applied in the formal synthesis of PNU 95666E and anachelin H chromophore.

  3. Asymmetric aza-[2,3]-Wittig sigmatropic rearrangements: chiral auxiliary control and formal asymmetric synthesis of (2S, 3R, 4R)-4-hydroxy-3-methylproline and (-)-kainic acid.

    PubMed

    Anderson, James C; O'Loughlin, Julian M A; Tornos, James A

    2005-08-07

    A survey of 16 different chiral auxiliaries and a variety of strategies found that an (-)-8-phenylmenthol ester of a glycine derived migrating group can control the absolute stereochemistry of aza-[2,3]-Wittig sigmatropic rearrangements with diastereoselectivities of ca. 3 : 1 with respect to the auxiliary. In two specific examples, ca. 50% yields of enantiomerically pure products were obtained after chromatographic purification. These were synthetically manipulated with no erosion of stereochemistry into intermediates that completed formal asymmetric syntheses of (+)-HyMePro and (-)-kainic acid.

  4. Divergent Chemoenzymatic Synthesis of Asymmetrical-Core-Fucosylated and Core-Unmodified N-Glycans.

    PubMed

    Li, Tiehai; Huang, Min; Liu, Lin; Wang, Shuo; Moremen, Kelley W; Boons, Geert-Jan

    2016-12-23

    A divergent chemoenzymaytic approach for the preparation of core-fucosylated and core-unmodified asymmetrical N-glycans from a common advances precursor is described. An undecasaccharide was synthesized by sequential chemical glycosylations of an orthogonally protected core fucosylated hexasaccharide that is common to all mammalian core fucosylated N-glycans. Antennae-selective enzymatic extension of the undecasaccharide using a panel of glycosyl transferases afforded core fucosylated asymmetrical triantennary N-glycan isomers, which are potential biomarkers for breast cancer. A unique aspect of our approach is that a fucosidase (FucA1) has been identified that selectively can cleave a core-fucoside without affecting the fucoside of a sialyl Lewis(X) epitope to give easy access to core-unmodified compounds.

  5. Spiro-fused carbohydrate oxazoline ligands: Synthesis and application as enantio-discrimination agents in asymmetric allylic alkylation

    PubMed Central

    Kraft, Jochen; Golkowski, Martin

    2016-01-01

    Summary In the present work, we describe a convenient synthesis of spiro-fused D-fructo- and D-psico-configurated oxazoline ligands and their application in asymmetric catalysis. The ligands were synthesized from readily available 3,4,5-tri-O-benzyl-1,2-O-isopropylidene-β-D-fructopyranose and 3,4,5-tri-O-benzyl-1,2-O-isopropylidene-β-D-psicopyranose, respectively. The latter compounds were partially deprotected under acidic conditions followed by condensation with thiocyanic acid to give an anomeric mixture of the corresponding 1,3-oxazolidine-2-thiones. The anomeric 1,3-oxazolidine-2-thiones were separated after successive benzylation, fully characterized and subjected to palladium catalyzed Suzuki–Miyaura coupling with 2-pyridineboronic acid N-phenyldiethanolamine ester to give the corresponding 2-pyridyl spiro-oxazoline (PyOx) ligands. The spiro-oxazoline ligands showed high asymmetric induction (up to 93% ee) when applied as chiral ligands in palladium-catalyzed allylic alkylation of 1,3-diphenylallyl acetate with dimethyl malonate. The D-fructo-PyOx ligand provided mainly the (R)-enantiomer while the D-psico-configurated ligand gave the (S)-enantiomer with a lower enantiomeric excess. PMID:26877819

  6. Synthesis and characterisation of self-assembled and self-adjuvanting asymmetric multi-epitope lipopeptides of ovalbumin.

    PubMed

    Eskandari, Sharareh; Stephenson, Rachel J; Fuaad, Abdullah Ahmad; Apte, Simon H; Doolan, Denise L; Toth, Istvan

    2015-01-12

    Designing a lipopeptide (LP) vaccine with a specific asymmetric arrangement of epitopes may result in an improved display of antigens, increasing host-cell recognition and immunogenicity. This study aimed to synthesise and characterise the physicochemical properties of a library of asymmetric LP-based vaccine candidates that contained multiple CD4(+) and CD8(+) T-cell epitopes from the model protein antigen, ovalbumin. These fully synthetic vaccine candidates were prepared by microwave-assisted solid phase peptide synthesis. The C12 or C16 lipoamino acids were coupled to the N or C terminus of the OVA CD4 peptide epitope. The OVA CD4 LPs and OVA CD8 peptide constructs were then conjugated using azide-alkyne Huisgen cycloaddition to give multivalent synthetic vaccines. Physiochemical characterisation of these vaccines showed a tendency to self-assemble in aqueous media. Changes in lipid length and position induced self-assembly with significant changes to their morphology and secondary structure as shown by transmission electron microscopy and circular dichroism.

  7. Asymmetric Allylic C-H Oxidation for the Synthesis of Chromans.

    PubMed

    Wang, Pu-Sheng; Liu, Peng; Zhai, Yu-Jia; Lin, Hua-Chen; Han, Zhi-Yong; Gong, Liu-Zhu

    2015-10-14

    An enantioselective intramolecular allylic C-H oxidation to generate optically active chromans has been accomplished under the cooperative catalysis of a palladium complex of chiral phosphoramidite ligand and 2-fluorobenzoic acid. Mechanistic studies suggest that this reaction commences with a Pd-catalyzed allylic C-H activation event and then undergoes asymmetric allylic alkoxylation. The synthetic significance of the method has been embodied by concisely building up a key chiral intermediate to access (+)-diversonol.

  8. Stereodivergent organocatalytic intramolecular Michael addition/lactonization for the asymmetric synthesis of substituted dihydrobenzofurans and tetrahydrofurans.

    PubMed

    Belmessieri, Dorine; de la Houpliere, Alix; Calder, Ewen D D; Taylor, James E; Smith, Andrew D

    2014-07-28

    A stereodivergent asymmetric Lewis base catalyzed Michael addition/lactonization of enone acids into substituted dihydrobenzofuran and tetrahydrofuran derivatives is reported. Commercially available (S)-(-)-tetramisole hydrochloride gives products with high syn diastereoselectivity in excellent enantioselectivity (up to 99:1 d.r.syn/anti , 99 % eesyn ), whereas using a cinchona alkaloid derived catalyst gives the corresponding anti-diastereoisomers as the major product (up to 10:90 d.r.syn/anti , 99 % eeanti ).

  9. Asymmetric Synthesis of Medium-Sized Rings by Intramolecular Au(I)-Catalyzed Cyclopropanation

    PubMed Central

    Watson, Iain D. G.; Ritter, Stefanie; Toste, F. Dean

    2009-01-01

    An efficient method for the asymmetric gold(I)-catalyzed preparation of medium sized rings has been developed. The method provides 7- to 9-membered rings in excellent yield. High enantioselectivities can be achieved for 7- and 8-membered ring products employing chiral gold(I) complexes. The results provide insight into the mechanism, showing the fluxional nature of gold(I)-stabilized vinyl carbenoid intermediates. PMID:19161306

  10. Synthesis of trifluoromethyl-containing vicinal diamines by asymmetric decarboxylative mannich addition reactions.

    PubMed

    Wu, Lingmin; Xie, Chen; Mei, Haibo; Dai, Yanling; Han, Jianlin; Soloshonok, Vadim A; Pan, Yi

    2015-03-20

    Herein is reported a study of asymmetric decarboxylative Mannich addition reactions between (Ss)-N-t-butylsulfinyl-3,3,3-trifluoroacetaldimine and Schiff bases derived from various aldehydes and lithium 2,2-diphenylglycinate. These reactions proceed with excellent diastereoselectivities and good chemical yields, providing a practical method for preparation of trifluoromethyl-containing vicinal diamines. The procedures can be conducted under convenient conditions, rendering this approach of high synthetic value.

  11. A Petal-type Chiral NADH Model: Design, Synthesis and its Asymmetric Reduction

    PubMed Central

    Bai, Cui-Bing; Wang, Nai-Xing; Wang, Yan-Jing; Xing, Yalan; Zhang, Wei; Lan, Xing-Wang

    2015-01-01

    A new type of NADH model compound has been synthesized by an efficient and convenient method. This model compound exhibits high reactivity and enantioselectivity in asymmetric reduction reactions. The results show that chiral NADH model S could be effectively combined with Mg2+ to form ternary complexes. This novel C3 symmetrical NADH model is capable of fluorescence emission at 460 nm when excited at 377 nm. PMID:26648413

  12. Asymmetric Synthesis of a CBI-Based Cyclic N-Acyl O-Amino Phenol Duocarmycin Prodrug

    PubMed Central

    2015-01-01

    A short, asymmetric synthesis of a cyclic N-acyl O-amino phenol duocarmycin prodrug subject to reductive activation based on the simplified 1,2,9,9a-tetrahydrocyclopropa[c]benz[e]indol-4-one (CBI) DNA alkylation subunit is described. A key element of the approach entailed treatment of iodo-epoxide 7, prepared by N-alkylation of 6 with (S)-glycidal 3-nosylate, with EtMgBr at room temperature to directly provide the optically pure alcohol 8 in 78% yield (99% ee) derived from an effective metal–halogen exchange and subsequent regioselective intramolecular 6-endo-tet cyclization. Following O-debenzylation, introduction of a protected N-methylhydroxamic acid, direct trannannular spirocyclization, and subsequent stereoelectronically controlled acid-catalyzed cleavage of the resulting cyclopropane (HCl), further improvements in a unique intramolecular cyclization with N–O bond formation originally introduced for formation of the reductively labile prodrug functionality are detailed. PMID:25247380

  13. Asymmetric Synthesis of α-Amino 1,3-Dithianes via Chiral N-Phosphonyl Imine-based Umpolung Reaction

    PubMed Central

    Kattamuri, Padmanabha V.; Ai, Teng; Pindi, Suresh; Sun, Yinwei; Gu, Peng; Shi, Min; Li, Guigen

    2011-01-01

    A series of α-amino-1,3-dithianes have been synthesized via the asymmetric Umpolung reaction of 2-lithio-1,3-dithianes with chiral N-phosphonyl imines in good chemical yields (up to 82%) and good to excellent diastereoselectivities (>99:1). The addition manner by which chiral N-phosphonyl imines are slowly added into the solution of 2-lithio-1,3-dithiane was found to be crucial for achieving excellent diastereoselectivity. The current synthesis was proven to follow the GAP chemistry (Group-Assistant-Purification chemistry) process which avoids traditional purification techniques of chromatography or recrystallization, i.e., the pure chiral α-amino-1,3-dithianes attached with the chiral N-phosphonyl group were readily obtained by washing the solid crude products with hexane or the mixture of hexane-ethyl acetate. PMID:21405041

  14. Asymmetric silica encapsulation toward colloidal Janus nanoparticles: a concave nanoreactor for template-synthesis of an electocatalytic hollow Pt nanodendrite

    NASA Astrophysics Data System (ADS)

    Koo, Jung Hun; Kim, Daun; Kim, Jin Goo; Jeong, Hwakyeung; Kim, Jongwon; Lee, In Su

    2016-07-01

    A novel reverse microemulsion strategy was developed to asymmetrically encapsulate metal-oxide nanoparticles in silica by exploiting the self-catalytic growth of aminosilane-containing silica at a single surface site. This strategy produced various colloidal Janus nanoparticles, including Au/Fe3O4@asy-SiO2, which were converted to an Au-containing silica nanosphere, Au@con-SiO2, by reductive Fe3O4 dissolution. The use of Au@con-SiO2 as a metal-growing nanoreactor allowed the templated synthesis of various noble-metal nanocrystals, including a hollow dendritic Pt nanoshell which exhibits significantly better electrocatalytic activities for the oxygen reduction reaction than commercial Pt/C catalysts.A novel reverse microemulsion strategy was developed to asymmetrically encapsulate metal-oxide nanoparticles in silica by exploiting the self-catalytic growth of aminosilane-containing silica at a single surface site. This strategy produced various colloidal Janus nanoparticles, including Au/Fe3O4@asy-SiO2, which were converted to an Au-containing silica nanosphere, Au@con-SiO2, by reductive Fe3O4 dissolution. The use of Au@con-SiO2 as a metal-growing nanoreactor allowed the templated synthesis of various noble-metal nanocrystals, including a hollow dendritic Pt nanoshell which exhibits significantly better electrocatalytic activities for the oxygen reduction reaction than commercial Pt/C catalysts. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr03557d

  15. Asymmetric syntheses and transformations--tools for chirality multiplication in drug synthesis.

    PubMed

    Gawroński, Jacek

    2006-01-01

    A review of currently used methods for the synthesis and resolution of enantiomers of drugs and their precursors is presented. For the synthesis part the methods of diastereoselective as well as enantioselective synthesis are discussed, with particular consideration given to enantioselective catalysis with either metal complexes or biocatalysts. Desymmetrization processes are also included as methods to access enantiomerically pure compounds. Racemate resolution still remains an important method to obtain pure enantiomers and methods involving kinetic resolution in enzymatic or chemical systems, and particularly in connection with racemization (dynamic kinetic resolution) are on the rise in fine chemical industry, when applicable.

  16. Cyclic sulfamidates as lactam precursors. An efficient asymmetric synthesis of (-)-aphanorphine.

    PubMed

    Bower, John F; Szeto, Peter; Gallagher, Timothy

    2005-12-14

    A short and efficient enantioselective synthesis of (-)-aphanorphine is described based on the use of a cyclic sulfamidate to provide a suitably functionalised lactam that allows for construction of the tricyclic 3-benzazepine scaffold.

  17. Enantioselective synthesis of cyclic sulfamidates by using chiral rhodium-catalyzed asymmetric transfer hydrogenation.

    PubMed

    Kang, Soyeong; Han, Juae; Lee, Eun Sil; Choi, Eun Bok; Lee, Hyeon-Kyu

    2010-09-17

    Asymmetric transfer hydrogenation (ATH) of cyclic sulfamidate imines 4 and 9, using a HCO(2)H/Et(3)N mixture as the hydrogen source and well-defined chiral Rh catalysts (S,S)- or (R,R)-2, Cp*RhCl(TsDPEN), effectively produces the corresponding cyclic sulfamidates with excellent yields and enantioselectivities at room temperature within 0.5 h. ATH of 4,5-disubstituted imines 9, having preexisting stereogenic centers, is shown to take place with dynamic kinetic resolution.

  18. Stereoselective synthesis of norephedrine and norpseudoephedrine by using asymmetric transfer hydrogenation accompanied by dynamic kinetic resolution.

    PubMed

    Lee, Hyeon-Kyu; Kang, Soyeong; Choi, Eun Bok

    2012-06-15

    Each of the enantiomers of both norephedrine and norpseudoephedrine were stereoselectively prepared from the common, prochiral cyclic sulfamidate imine of racemic 1-hydroxy-1-phenyl-propan-2-one by employing asymmetric transfer hydrogenation (ATH) catalyzed by the well-defined chiral Rh-complexes, (S,S)- or (R,R)-Cp*RhCl(TsDPEN), and HCO(2)H/Et(3)N as the hydrogen source. The ATH processes are carried out under mild conditions (rt, 15 min) and are accompanied by dynamic kinetic resolution.

  19. Flexible and Asymmetric Ligand in Constructing Coordinated Complexes: Synthesis, Crystal Structures and Fluorescent Characterization

    PubMed Central

    Chen, Peng; Lin, Jianhua

    2011-01-01

    Flexible and asymmetric ligand L [L = 1-((pyridin-3-yl)methyl)-1H-benzotriazole], is used as a basic backbone to construct complicated metal-organic frameworks. Two new polymers, namely, [Ag2(L)2(NO3)2]n (1) and [Ag(L)(ClO4)]n (2), were synthesized and characterized by X-ray structure analysis and fluorescent spectroscopy. The complex 1 gives an “S” type double helical conformation, whereas complex 2 exhibits a 1D zigzag configuration. Different anions affect the silver coordination geometry and crystal packing topology. PMID:21339976

  20. Facile Synthesis of Hierarchical Mesoporous Honeycomb-like NiO for Aqueous Asymmetric Supercapacitors.

    PubMed

    Ren, Xiaochuan; Guo, Chunli; Xu, Liqiang; Li, Taotao; Hou, Lifeng; Wei, Yinghui

    2015-09-16

    Three-dimensional (3D) hierarchical nanostructures have been demonstrated as one of the most ideal electrode materials in energy storage systems due to the synergistic combination of the advantages of both nanostructures and microstructures. In this study, the honeycomb-like mesoporous NiO microspheres as promising cathode materials for supercapacitors have been achieved using a hydrothermal reaction, followed by an annealing process. The electrochemical tests demonstrate the highest specific capacitance of 1250 F g(-1) at 1 A g(-1). Even at 5 A g(-1), a specific capacitance of 945 F g(-1) with 88.4% retention after 3500 cycles was obtained. In addition, the 3D porous graphene (reduced graphene oxide, rGO) has been prepared as an anode material for supercapacitors, which displays a good capacitance performance of 302 F g(-1) at 1 A g(-1). An asymmetric supercapacitor has been successfully fabricated based on the honeycomb-like NiO and rGO. The asymmetric supercapacitor achieves a remarkable performance with a specific capacitance of 74.4 F g(-1), an energy density of 23.25 Wh kg(-1), and a power density of 9.3 kW kg(-1), which is able to light up a light-emitting diode.

  1. Facile synthesis of polyester dendrimers from sequential click coupling of asymmetrical monomers.

    PubMed

    Ma, Xinpeng; Tang, Jianbin; Shen, Youqing; Fan, Maohong; Tang, Huadong; Radosz, Maciej

    2009-10-21

    Polyester dendrimers are attractive for in vivo delivery of bioactive molecules due to their biodegradability, but their synthesis generally requires multistep reactions with intensive purifications. A highly efficient approach to the synthesis of dendrimers by simply "sticking" generation by generation together is achieved by combining kinetic or mechanistic chemoselectivity with click reactions between the monomers. In each generation, the targeted molecules are the major reaction product as detected by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). The only separation needed is to remove the little unreacted monomer by simple precipitation or washing. This simple clicklike process without complicated purification is particularly suitable for the synthesis of custom-made polyester dendrimers.

  2. Asymmetric stereodivergent strategy towards aminocyclitols.

    PubMed

    Trost, Barry M; Malhotra, Sushant

    2014-07-01

    A concise asymmetric synthesis of aminocyclitols, such as diastereomeric 2-deoxystreptamine analogues and conduramine A, is described. The Pd-catalyzed asymmetric desymmetrization of meso 1,4-dibenzolate enables the synthesis of highly oxidized cyclohexane architectures. These scaffolds can potentially be used to access new aminoglycoside antibiotics and enantiomerically pure α-glucosidase inhibitors.

  3. Total Synthesis and Stereochemical Assignment of Delavatine A: Rh-Catalyzed Asymmetric Hydrogenation of Indene-Type Tetrasubstituted Olefins and Kinetic Resolution through Pd-Catalyzed Triflamide-Directed C-H Olefination.

    PubMed

    Zhang, Zhongyin; Wang, Jinxin; Li, Jian; Yang, Fan; Liu, Guodu; Tang, Wenjun; He, Weiwei; Fu, Jian-Jun; Shen, Yun-Heng; Li, Ang; Zhang, Wei-Dong

    2017-03-08

    Delavatine A (1) is a structurally unusual isoquinoline alkaloid isolated from Incarvillea delavayi. The first and gram-scale total synthesis of 1 was accomplished in 13 steps (the longest linear sequence) from commercially available starting materials. We exploited an isoquinoline construction strategy and developed two reactions, namely Rh-catalyzed asymmetric hydrogenation of indene-type tetrasubstituted olefins and kinetic resolution of β-alkyl phenylethylamine derivatives through Pd-catalyzed triflamide-directed C-H olefination. The substrate scope of the first reaction covered unfunctionalized olefins and those containing polar functionalities such as sulfonamides. The kinetic resolution provided a collection of enantioenriched indane and tetralin-based triflamides, including those bearing quaternary chiral centers. The selectivity factor (s) exceeded 100 for a number of substrates. These reactions enabled two different yet related approaches to a key intermediate 28 in excellent enantiopurity. In the synthesis, the triflamide served as not only an effective directing group for C-H bond activation but also a versatile functional group for further elaborations. The relative and absolute configurations of delavatine A were unambiguously assigned by the syntheses of the natural product and its three stereoisomers. Their cytotoxicity against a series of cancer cell lines were evaluated.

  4. cis-Decahydroquinolines via asymmetric organocatalysis: application to the total synthesis of lycoposerramine Z.

    PubMed

    Bradshaw, Ben; Luque-Corredera, Carlos; Bonjoch, Josep

    2013-01-18

    A concise synthesis of the Lycopodium alkaloid lycoposerramine Z is reported. Key to the strategy is a one-pot organocatalyzed Michael reaction followed by a domino Robinson annulation/intramolecular aza-Michael reaction promoted by LiOH, leading to enantiopure cis-decahydroquinolines.

  5. Large Scale Synthesis of NiCo Layered Double Hydroxides for Superior Asymmetric Electrochemical Capacitor

    PubMed Central

    Li, Ruchun; Hu, Zhaoxia; Shao, Xiaofeng; Cheng, Pengpeng; Li, Shoushou; Yu, Wendan; Lin, Worong; Yuan, Dingsheng

    2016-01-01

    We report a new environmentally-friendly synthetic strategy for large-scale preparation of 16 nm-ultrathin NiCo based layered double hydroxides (LDH). The Ni50Co50-LDH electrode exhibited excellent specific capacitance of 1537 F g−1 at 0.5 A g−1 and 1181 F g−1 even at current density as high as 10 A g−1, which 50% cobalt doped enhances the electrical conductivity and porous and ultrathin structure is helpful with electrolyte diffusion to improve the material utilization. An asymmetric ultracapacitor was assembled with the N-doped graphitic ordered mesoporous carbon as negative electrode and the NiCo LDH as positive electrode. The device achieves a high energy density of 33.7 Wh kg−1 (at power density of 551 W kg−1) with a 1.5 V operating voltage. PMID:26754281

  6. Asymmetric total synthesis of 6-Tuliposide B and its biological activities against tulip pathogenic fungi.

    PubMed

    Shigetomi, Kengo; Omoto, Shoko; Kato, Yasuo; Ubukata, Makoto

    2011-01-01

    The structure-activity relationship was investigated to evaluate the antifungal activities of tuliposides and tulipalins against tulip pathogenic fungi. 6-Tuliposide B was effectively synthesized via the asymmetric Baylis-Hillman reaction. Tuliposides and tulipalins showed antifungal activities against most of the strains tested at high concentrations (2.5 mM), while Botrytis tulipae was resistant to tuliposides. Tulipalin formation was involved in the antifungal activity, tulipalin A showed higher inhibitory activity than 6-tuliposide B and tulipalin B. Both the tuliposides and tulipalins showed pigment-inducing activity against Gibberella zeae and inhibitory activity against Fusarium oxysporum f. sp tulipae. These activities were induced at a much lower concentration (0.05 mM) than the antifungal MIC values.

  7. Synthesis of new macrocyclic chiral manganese(III) Schiff bases as catalysts for asymmetric epoxidation.

    PubMed

    Martinez, Alexandre; Hemmert, Catherine; Loup, Christophe; Barré, Guillaume; Meunier, Bernard

    2006-02-17

    We describe a general synthetic strategy for the preparation of a series of macrocyclic chiral manganese(III) salen complexes. The developed reaction pathway allows the modulation of the different key groups, namely, the chiral diimine, the bulky substituents in positions 3 and 3', and the linker used in the macrocyclization of the Schiff base. The different complexes presented here illustrate these readily available structural variations. The catalytic properties of the catalysts (5 mol %) were improved for the asymmetric epoxidation of 2,2'-dimethylchromene with NaOCl or H2O2 as oxygen atom donor. A large range of enantiomeric excesses was obtained (ee values from 30% to 96%), depending on the features and the stability of the complexes. The most efficient catalyst, in terms of stereoinduction (ee value = 96%), contains a diiminocyclohexyl moiety, ethyl groups in positions 3 and 3', and a short polyether junction arm.

  8. Large Scale Synthesis of NiCo Layered Double Hydroxides for Superior Asymmetric Electrochemical Capacitor

    NASA Astrophysics Data System (ADS)

    Li, Ruchun; Hu, Zhaoxia; Shao, Xiaofeng; Cheng, Pengpeng; Li, Shoushou; Yu, Wendan; Lin, Worong; Yuan, Dingsheng

    2016-01-01

    We report a new environmentally-friendly synthetic strategy for large-scale preparation of 16 nm-ultrathin NiCo based layered double hydroxides (LDH). The Ni50Co50-LDH electrode exhibited excellent specific capacitance of 1537 F g‑1 at 0.5 A g‑1 and 1181 F g‑1 even at current density as high as 10 A g‑1, which 50% cobalt doped enhances the electrical conductivity and porous and ultrathin structure is helpful with electrolyte diffusion to improve the material utilization. An asymmetric ultracapacitor was assembled with the N-doped graphitic ordered mesoporous carbon as negative electrode and the NiCo LDH as positive electrode. The device achieves a high energy density of 33.7 Wh kg‑1 (at power density of 551 W kg‑1) with a 1.5 V operating voltage.

  9. Asymmetric Desymmetrization via Metal-Free C-F Bond Activation: Synthesis of 3,5-Diaryl-5-fluoromethyloxazolidin-2-ones with Quaternary Carbon Centers.

    PubMed

    Tanaka, Junki; Suzuki, Satoru; Tokunaga, Etsuko; Haufe, Günter; Shibata, Norio

    2016-08-01

    We disclose the first asymmetric activation of a non-activated aliphatic C-F bond in which a conceptually new desymmetrization of 1,3-difluorides by silicon-induced selective C-F bond scission is a key step. The combination of a cinchona alkaloid based chiral ammonium bifluoride catalyst and N,O-bis(trimethylsilyl)acetoamide (BSA) as the silicon reagent enabled the efficient catalytic cycle of asymmetric Csp3 -F bond cleavage under mild conditions with high enantioselectivities. The ortho effect of the aryl group at the prostereogenic center is remarkable. This concept was applied for the asymmetric synthesis of promising agrochemical compounds, 3,5-diaryl-5-fluoromethyloxazolidin-2-ones bearing a quaternary carbon center.

  10. An enantioselective strategy for the total synthesis of (S)-tylophorine via catalytic asymmetric allylation and a one-pot DMAP-promoted isocyanate formation/Lewis acid catalyzed cyclization sequence.

    PubMed

    Su, Bo; Zhang, Hui; Deng, Meng; Wang, Qingmin

    2014-06-14

    A new asymmetric total synthesis of a phenanthroindolizidine alkaloid (S)-tylophorine is reported, which features a catalytic asymmetric allylation of aldehydes and an unexpected one-pot DMAP promoted isocyanate formation and Lewis acid catalyzed intramolecular cyclization reaction. In addition, White's direct C-H oxidation catalyst system converting monosubstituted olefins to linear allylic acetates was also employed for late-stage transformation.

  11. Asymmetric synthesis of aromatic β-amino acids using ω-transaminase: Optimizing the lipase concentration to obtain thermodynamically unstable β-keto acids.

    PubMed

    Mathew, Sam; Jeong, Seong-Su; Chung, Taeowan; Lee, Sang-Hyeup; Yun, Hyungdon

    2016-01-01

    Synthesized aromatic β-amino acids have recently attracted considerable attention for their application as precursors in many pharmacologically relevant compounds. Previous studies on asymmetric synthesis of aromatic β-amino acids using ω-transaminases could not be done efficiently due to the instability of β-keto acids. In this study, a strategy to circumvent the instability problem of β-keto acids was utilized to generate β-amino acids efficiently via asymmetric synthesis. In this work, thermodynamically stable β-ketoesters were initially converted to β-keto acids using lipase, and the β-keto acids were subsequently aminated using ω-transaminase. By optimizing the lipase concentration, we successfully overcame the instability problem of β-keto acids and enhanced the production of β-amino acids. This strategy can be used as a general approach to efficiently generate β-amino acids from β-ketoesters.

  12. Catalytic asymmetric synthesis of pyrroloindolines via a rhodium(II)-catalyzed annulation of indoles.

    PubMed

    Spangler, Jillian E; Davies, Huw M L

    2013-05-08

    Herein we report the synthesis of pyrroloindolines via a catalytic enantioselective formal [3+2] cycloaddition of C(3)-substituted indoles. This methodology utilizes 4-aryl-1-sulfonyl-1,2,3-triazoles as carbenoid precursors and the rhodium(II)-tetracarboxylate catalyst Rh2(S-PTAD)4. A variety of aryl-substituted pyrroloindolines were prepared in good yields and with high levels of enantioinduction.

  13. Synthesis and use of an asymmetric transfer hydrogenation catalyst based on iron(II) for the synthesis of enantioenriched alcohols and amines.

    PubMed

    Zuo, Weiwei; Morris, Robert H

    2015-02-01

    The catalytic hydrogenation of prochiral ketones and imines is an advantageous approach to the synthesis of enantioenriched alcohols and amines, respectively, which are two classes of compounds that are highly prized in pharmaceutical, fragrance and flavoring chemistry. This hydrogenation reaction is generally carried out using ruthenium-based catalysts. Our group has developed an alternative synthetic route that is based on the environmentally friendlier iron-based catalysis. This protocol describes the three-part synthesis of trans-[amine(imine)diphosphine]chlorocarbonyliron(II) tetrafluoroborate templated by iron salts and starting from commercially available chemicals, which provides the precatalyst for the efficient asymmetric transfer hydrogenation of ketones and imines. The use of the enantiopure (S,S) catalyst to reduce prochiral ketones to the (R)-alcohol in good to excellent yields and enantioenrichment is also detailed, as well as the reduction to the amine in very high yield and enantiopurity of imines substituted at the nitrogen with the N-(diphenylphosphinoyl) group (-P(O)Ph2). Although the best ruthenium catalysts provide alcohols in higher enantiomeric excess (ee) than the iron complex catalyst used in this protocol, they do so on much longer time scales or at higher catalyst loadings. This protocol can be completed in 2 weeks.

  14. Asymmetric total synthesis of (+)-bermudenynol, a C15 Laurencia metabolite with a vinyl chloride containing oxocene skeleton, through intramolecular amide enolate alkylation.

    PubMed

    Kim, Gyudong; Sohn, Te-Ik; Kim, Deukjoon; Paton, Robert S

    2014-01-03

    A substrate-controlled asymmetric total synthesis of (+)-bermudenynol, a compact and synthetically challenging C15 Laurencia metabolite that contains several halogen atoms, is reported. The oxocene core, which contains a vinyl chloride, was constructed by an efficient and highly stereoselective intramolecular amide enolate alkylation (IAEA). This result showcases the broad utility of the IAEA methodology as a useful alternative for cases in which the ring-closing metathesis is inefficient.

  15. Possibilities of synthesis of unknown isotopes of superheavy nuclei with charge numbers Z > 108 in asymmetric actinide-based complete fusion reactions

    NASA Astrophysics Data System (ADS)

    Hong, Juhee; Adamian, G. G.; Antonenko, N. V.

    2016-10-01

    The possibilities of production of new isotopes of superheavy nuclei with charge numbers Z = 109-114 in various asymmetric hot fusion reactions are studied for the first time. The excitation functions of the formation of these isotopes in the xn evaporation channels are predicted and the optimal conditions for the synthesis are proposed. The products of the suggested reactions can fill a gap of unknown isotopes between the isotopes of the heaviest nuclei obtained in cold and hot complete fusion reactions.

  16. Asymmetric [4 + 3] cycloadditions between vinylcarbenoids and dienes: application to the total synthesis of the natural product (-)-5-epi-vibsanin E.

    PubMed

    Schwartz, Brett D; Denton, Justin R; Lian, Yajing; Davies, Huw M L; Williams, Craig M

    2009-06-17

    The total synthesis of (-)-5-epi-vibsanin E (2) has been achieved in 18 steps. The synthesis combines the rhodium-catalyzed [4 + 3] cycloaddition between a vinylcarbenoid and a diene to rapidly generate the tricyclic core with an effective end game strategy to introduce the remaining side-chains. The [4 + 3] cycloaddition occurs by a cyclopropanation to form a divinylcyclopropane followed by a Cope rearrangement to form a cycloheptadiene. The quaternary stereogenic center generated in the process can be obtained with high asymmetric induction when the reaction is catalyzed by the chiral dirhodium complex, Rh(2)(S-PTAD)(4).

  17. Synthesis, Annealing and Performance of Pd-Au Asymmetric Composite Membranes for Hydrogen Purification

    SciTech Connect

    Ma, Yi Hua; Chen, Chao-Huang; Catalano, Jacopo; Guazzone, Federico; Payzant, E Andrew

    2013-01-01

    Composite asymmetric Pd-Au membranes, based on porous Inconel and Hastelloy tubular supports, were prepared by means of electroless deposition and galvanic displacement techniques and tested, before and after Au deposition, in pure H2 atmosphere. The final membranes, with Au average bulk composition up to 16.7 wt%, were 9 15 m thick and showed, for the entire duration of characterization, H2/He ideal selectivity in excess of 900. The annealing of the as-prepared membranes was conducted through the coating and diffusion mechanism in He and H2 atmospheres at 500 C. The annealing conditions were chosen after non-isothermal and isothermal HT-XRD studies on coupons synthetized with similar preparation methods. After the formation of the Pd-Au layer, the membranes showed steady flux and a stable Au gradient on the membrane top layer. Comparisons between permeance for Pd/Au and pure Pd membranes indicated that the membranes with an Au average bulk composition of 4.5 and 5.4 wt% had an enhancement, up to 20%, of the H2 permeability in the temperature range 250 450 C with respect to pure Pd membranes. On the other hand, the membrane having the highest Au composition, 16.7 wt%, even though characterized by a lower H2 permeability (77% of pure Pd) had a rather high surface Au composition (approximately 46 wt%), which might provide good H2S poisoning tolerance.

  18. Enantioselective Synthesis of β-Arylamines via Chiral Phosphoric Acid-Catalyzed Asymmetric Reductive Amination.

    PubMed

    Kim, Kyung-Hee; Lee, Chun-Young; Cheon, Cheol-Hong

    2015-06-19

    A new method for the synthesis of chiral β-aryl amines via chiral phosphoric acid-catalyzed enantioselective reductive amination of benzyl methyl ketone derivatives with Hantzsch ester was developed. Various chiral β-aryl amines were obtained in high yields and with good to high enantioselectivities. This transformation is applicable to gram-scale reactions, and the catalyst loading can be reduced to 1 mol % without sacrificing any catalytic efficacy. Furthermore, the resulting β-aryl amine was successfully converted into a tetrahydroisoquinoline compound without any loss of enantioselectivity.

  19. Directed ortho,ortho'-dimetalation of hydrobenzoin: Rapid access to hydrobenzoin derivatives useful for asymmetric synthesis.

    PubMed

    Cho, Inhee; Meimetis, Labros; Belding, Lee; Katz, Michael J; Dudding, Travis; Britton, Robert

    2011-01-01

    A variety of ortho,ortho'-disubstituted hydrobenzoin derivatives are readily accessible through a directed ortho,ortho'-dimetalation strategy in which the alcohol functions in hydrobenzoin are deprotonated by n-BuLi and the resulting lithium benzyl alkoxides serve as directed metalation groups. The optimization and scope of this reaction are discussed, and the utility of this process is demonstrated in the one-pot preparation of a number of chiral diols as well as a short synthesis of the chiral ligand Vivol.

  20. Absolute Zero

    NASA Astrophysics Data System (ADS)

    Donnelly, Russell J.; Sheibley, D.; Belloni, M.; Stamper-Kurn, D.; Vinen, W. F.

    2006-12-01

    Absolute Zero is a two hour PBS special attempting to bring to the general public some of the advances made in 400 years of thermodynamics. It is based on the book “Absolute Zero and the Conquest of Cold” by Tom Shachtman. Absolute Zero will call long-overdue attention to the remarkable strides that have been made in low-temperature physics, a field that has produced 27 Nobel Prizes. It will explore the ongoing interplay between science and technology through historical examples including refrigerators, ice machines, frozen foods, liquid oxygen and nitrogen as well as much colder fluids such as liquid hydrogen and liquid helium. A website has been established to promote the series: www.absolutezerocampaign.org. It contains information on the series, aimed primarily at students at the middle school level. There is a wealth of material here and we hope interested teachers will draw their student’s attention to this website and its substantial contents, which have been carefully vetted for accuracy.

  1. Asymmetric synthesis of highly substituted azapolycyclic compounds via 2-alkenyl sulfoximines: potential scaffolds for peptide mimetics.

    PubMed

    Reggelin, Michael; Junker, Bernd; Heinrich, Timo; Slavik, Stefan; Bühle, Philipp

    2006-03-29

    The application of metalated, enantiomerically pure acyclic and cyclic 2-alkenyl sulfoximines for the synthesis of highly substituted aza(poly)cyclic ring systems is described. The method relies on a one-pot combination of a reagent-controlled allyl transfer reaction to alpha- or beta-amino aldehydes, followed by a Michael-type cyclization of the intermediate vinyl sulfoximines generated in the first step. The sulfur-free target compounds are preferentially obtained by samarium iodide treatment of the sulfonimidoyl substituted heterocycles. In addition to this methodological work, initial results on the biological activity of selected examples are reported. Furthermore, a concept for the transformation of peptidic lead structures into non-peptide mimetics is described, and the relevance of the new approach to highly substituted azaheterocycles in this context is discussed.

  2. Asymmetric synthesis from terminal alkenes by cascades of diboration and cross-coupling.

    PubMed

    Mlynarski, Scott N; Schuster, Christopher H; Morken, James P

    2014-01-16

    Terminal, monosubstituted alkenes are ideal prospective starting materials for organic synthesis because they are manufactured on very large scales and can be functionalized via a broad range of chemical transformations. Alkenes also have the attractive feature of being stable in the presence of many acids, bases, oxidants and reductants. In spite of these attributes, relatively few catalytic enantioselective transformations have been developed that transform aliphatic α-olefins into chiral products with an enantiomeric excess greater then 90 per cent. With the exception of site-controlled isotactic polymerization of α-olefins, none of these catalytic enantioselective processes results in chain-extending carbon-carbon bond formation to the terminal carbon. Here we describe a strategy that directly addresses this gap in synthetic methodology, and present a single-flask, catalytic enantioselective conversion of terminal alkenes into a number of chiral products. These reactions are facilitated by a neighbouring functional group that accelerates palladium-catalysed cross-coupling of 1,2-bis(boronates) relative to non-functionalized alkyl boronate analogues. In tandem with enantioselective diboration, this reactivity feature transforms alkene starting materials into a diverse array of chiral products. We note that the tandem diboration/cross-coupling reaction generally provides products in high yield and high selectivity (>95:5 enantiomer ratio), uses low loadings (1-2 mol per cent) of commercially available catalysts and reagents, offers an expansive substrate scope, and can address a broad range of alcohol and amine synthesis targets, many of which cannot be easily addressed with current technology.

  3. Asymmetric synthesis from terminal alkenes by cascades of diboration and cross-coupling

    NASA Astrophysics Data System (ADS)

    Mlynarski, Scott N.; Schuster, Christopher H.; Morken, James P.

    2014-01-01

    Terminal, monosubstituted alkenes are ideal prospective starting materials for organic synthesis because they are manufactured on very large scales and can be functionalized via a broad range of chemical transformations. Alkenes also have the attractive feature of being stable in the presence of many acids, bases, oxidants and reductants. In spite of these attributes, relatively few catalytic enantioselective transformations have been developed that transform aliphatic α-olefins into chiral products with an enantiomeric excess greater then 90 per cent. With the exception of site-controlled isotactic polymerization of α-olefins, none of these catalytic enantioselective processes results in chain-extending carbon-carbon bond formation to the terminal carbon. Here we describe a strategy that directly addresses this gap in synthetic methodology, and present a single-flask, catalytic enantioselective conversion of terminal alkenes into a number of chiral products. These reactions are facilitated by a neighbouring functional group that accelerates palladium-catalysed cross-coupling of 1,2-bis(boronates) relative to non-functionalized alkyl boronate analogues. In tandem with enantioselective diboration, this reactivity feature transforms alkene starting materials into a diverse array of chiral products. We note that the tandem diboration/cross-coupling reaction generally provides products in high yield and high selectivity (>95:5 enantiomer ratio), uses low loadings (1-2 mol per cent) of commercially available catalysts and reagents, offers an expansive substrate scope, and can address a broad range of alcohol and amine synthesis targets, many of which cannot be easily addressed with current technology.

  4. Asymmetric synthesis of rubiginones A(2) and C(2) and their 11-methoxy regioisomers.

    PubMed

    Carreño, M Carmen; Somoza, Alvaro; Ribagorda, María; Urbano, Antonio

    2007-01-01

    Convergent enantioselective syntheses of angucyclinone-type natural products rubiginones A(2) (2) and C(2) (1) and their 11-methoxy regioisomers 3 a and 3 b have been achieved by using two domino processes from a common enantiomerically pure 1-vinylcyclohexene 4. Key steps in the synthesis of this diene were the stereoselective conjugate addition of AlMe(3) on (SS)-[(p-tolylsulfinyl)methyl]-p-quinol (9) and the elimination of the beta-hydroxy sulfoxide fragment, after oxidation to sulfone, to recover a carbonyl group. The first domino sequence comprised Diels-Alder reaction with a sulfinyl naphthoquinone followed by sulfoxide elimination. An efficient opposite regioselection in the cycloaddition step was achieved in the convergent construction of the tetracyclic skeleton using a sulfoxide at C-2 or C-3 of the dienophiles 5 or 6, derived from 5-methoxy-1,4-naphthoquinone. The second domino process, triggered by oxygen and sunlight, allowed the transformation of the initial tetracyclic adducts into the final products after B ring aromatization, silyl deprotection and C-1 oxidation.

  5. Asymmetric chemoenzymatic synthesis of miconazole and econazole enantiomers. The importance of chirality in their biological evaluation.

    PubMed

    Mangas-Sánchez, Juan; Busto, Eduardo; Gotor-Fernández, Vicente; Malpartida, Francisco; Gotor, Vicente

    2011-04-01

    A simple and novel chemoenzymatic route has been applied for the first time in the synthesis of miconazole and econazole single enantiomers. Lipases and oxidoreductases have been tested in stereoselective processes; the best results were attained with oxidoreductases for the introduction of chirality in an adequate intermediate. The behaviors of a series of ketones and racemic alcohols in bioreductions and acetylation procedures, respectively, have been investigated; the best results were found with alcohol dehydrogenases A and T, which allowed the production of (R)-2-chloro-1-(2,4-dichlorophenyl)ethanol in enantiopure form under very mild reaction conditions. Final chemical modifications have been performed in order to isolate the target fungicides miconazole and econazole both as racemates and as single enantiomers. Biological evaluation of the racemates and single enantiomers has shown remarkable differences against the growth of several microorganisms; while (R)-miconazole seemed to account for most of the biological activity of racemic miconazole on all the strains tested, both enantiomers of econazole showed considerable biological activities. In this manner, (R)-econazole showed higher values against Candida krusei , while higher values were observed for (S)-econazole against Cryptococcus neoformans, Penicillium chrysogenum, and Aspergillus niger.

  6. Asymmetric syntheses of the homalium alkaloids (-)-(S,S)-homaline and (-)-(R,R)-hopromine.

    PubMed

    Davies, Stephen G; Lee, James A; Roberts, Paul M; Stonehouse, Jeffrey P; Thomson, James E

    2012-08-17

    The highly diastereoselective conjugate additions of the novel lithium amide reagents lithium (R)-N-(3-chloropropyl)-N-(α-methylbenzyl)amide and lithium (R)-N-(3-chloropropyl)-N-(α-methyl-p-methoxybenzyl)amide to α,β-unsaturated esters were used as the key steps in syntheses of the homalium alkaloids (-)-(S,S)-homaline and (-)-(R,R)-hopromine. The asymmetric synthesis of (-)-(S,S)-homaline was achieved in 8 steps and 18% overall yield, and the asymmetric synthesis of (-)-(R,R)-hopromine was achieved in 9 steps and 23% overall yield, from commercially available starting materials in each case. These syntheses therefore represent by far the most efficient total asymmetric syntheses of these alkaloids reported to date. A sample of the (4'R,4''S)-epimer of hopromine was also produced using this approach, which provided the first unambiguous confirmation of its absolute configuration and therefore that of natural (-)-(R,R)-hopromine.

  7. Absolute Summ

    NASA Astrophysics Data System (ADS)

    Phillips, Alfred, Jr.

    Summ means the entirety of the multiverse. It seems clear, from the inflation theories of A. Guth and others, that the creation of many universes is plausible. We argue that Absolute cosmological ideas, not unlike those of I. Newton, may be consistent with dynamic multiverse creations. As suggested in W. Heisenberg's uncertainty principle, and with the Anthropic Principle defended by S. Hawking, et al., human consciousness, buttressed by findings of neuroscience, may have to be considered in our models. Predictability, as A. Einstein realized with Invariants and General Relativity, may be required for new ideas to be part of physics. We present here a two postulate model geared to an Absolute Summ. The seedbed of this work is part of Akhnaton's philosophy (see S. Freud, Moses and Monotheism). Most important, however, is that the structure of human consciousness, manifest in Kenya's Rift Valley 200,000 years ago as Homo sapiens, who were the culmination of the six million year co-creation process of Hominins and Nature in Africa, allows us to do the physics that we do. .

  8. Asymmetric Synthesis of Spirocyclic 2-Benzopyrans for Positron Emission Tomography of σ1 Receptors in the Brain

    PubMed Central

    Holl, Katharina; Schepmann, Dirk; Fischer, Steffen; Ludwig, Friedrich-Alexander; Hiller, Achim; Donat, Cornelius K.; Deuther-Conrad, Winnie; Brust, Peter; Wünsch, Bernhard

    2014-01-01

    Sharpless asymmetric dihydroxylation of styrene derivative 6 afforded chiral triols (R)-7 and (S)-7, which were cyclized with tosyl chloride in the presence of Bu2SnO to provide 2-benzopyrans (R)-4 and (S)-4 with high regioselectivity. The additional hydroxy moiety in the 4-position was exploited for the introduction of various substituents. Williamson ether synthesis and replacement of the Boc protective group with a benzyl moiety led to potent σ1 ligands with high σ1/σ2-selectivity. With exception of the ethoxy derivative 16, the (R)-configured enantiomers represent eutomers with eudismic ratios of up to 29 for the ester (R)-18. The methyl ether (R)-15 represents the most potent σ1 ligand of this series of compounds, with a Ki value of 1.2 nM and an eudismic ratio of 7. Tosylate (R)-21 was used as precursor for the radiosynthesis of [18F]-(R)-20, which was available by nucleophilic substitution with K[18F]F K222 carbonate complex. The radiochemical yield of [18F]-(R)-20 was 18%–20%, the radiochemical purity greater than 97% and the specific radioactivity 175–300 GBq/µmol. Although radiometabolites were detected in plasma, urine and liver samples, radiometabolites were not found in brain samples. After 30 min, the uptake of the radiotracer in the brain was 3.4% of injected dose per gram of tissue and could be reduced by coadministration of the σ1 antagonist haloperidol. [18F]-(R)-20 was able to label those regions of the brain, which were reported to have high density of σ1 receptors. PMID:24451404

  9. Asymmetric Schiff bases derived from diaminomaleonitrile and their metal complexes

    NASA Astrophysics Data System (ADS)

    Yang, Jianjie; Shi, Rufei; Zhou, Pei; Qiu, Qiming; Li, Hui

    2016-02-01

    Asymmetric Schiff bases, due to its asymmetric structure, can be used as asymmetric catalyst, antibacterial, and mimic molecules during simulate biological processes, etc. In recent years, research on synthesis and properties of asymmetric Schiff bases have become an increase interest of chemists. This review summarizes asymmetric Schiff bases derived from diaminomaleonitrile (DAMN) and DAMN-based asymmetric Schiff bases metal complexes. Applications of DAMN-based asymmetric Schiff bases are also discussed in this review.

  10. Practical asymmetric synthesis of a potent PDE4 inhibitor via stereoselective enolate alkylation of a chiral aryl-heteroaryl secondary tosylate.

    PubMed

    O'Shea, Paul D; Chen, Cheng-yi; Chen, Weirong; Dagneau, Philippe; Frey, Lisa F; Grabowski, Edward J J; Marcantonio, Karen M; Reamer, Robert A; Tan, Lushi; Tillyer, Richard D; Roy, Amélie; Wang, Xin; Zhao, Dalian

    2005-04-15

    A practical, chromatography-free catalytic asymmetric synthesis of a potent and selective PDE4 inhibitor (L-869,298, 1) is described. Catalytic asymmetric hydrogenation of thiazole ketone 5a afforded the corresponding alcohol 3b in excellent enantioselectivity (up to 99.4% ee). Activation of alcohol 3b via formation of the corresponding p-toluenesulfonate followed by an unprecedented displacement with the lithium enolate of ethyl 3-pyridylacetate N-oxide 4a generated the required chiral trisubstituted methane. The displacement reaction proceeded with inversion of configuration and without loss of optical purity. Conversion of esters 2b to 1 was accomplished via a one-pot deprotection, saponification, and decarboxylation sequence in excellent overall yield.

  11. Chiral Bidentate NHC Ligands Based on the 1,1'-Binaphthyl Scaffold: Synthesis and Application in Transition-Metal-Catalyzed Asymmetric Reactions.

    PubMed

    Xu, Qin; Gu, Peng; Jiang, Hanchun; Wei, Yin; Shi, Min

    2016-12-01

    The use of the chiral 1,1'-binaphthyl scaffold to construct chiral ligands can be traced back for a long time. However, the development of bidentate NHC ligands based on the same backbone has only appeared recently. In this account, we describe the design and synthesis of a new family of chiral NHC ligands based on the 1,1'-binaphthyl scaffold and demonstrate the applications of these chiral NHC-metal complexes in the catalyzed oxidative kinetic resolution of secondary alcohols, asymmetric carbon-carbon bond formations, hydrosilylations, and cyclizations of 1,6-enynes. The chiral NHC ligands containing the 1,1'-binaphthyl backbone can be synthesized in good yields from enantiomerically pure 1,1'-binaphthyl-2,2'-diamine. These transition metals coordinated with chiral bidentate NHC ligands exhibit high catalytic activities and good enantioselectivities for a wide range of metal-catalyzed asymmetric reactions.

  12. Absolute Photometry

    NASA Astrophysics Data System (ADS)

    Hartig, George

    1990-12-01

    The absolute sensitivity of the FOS will be determined in SV by observing 2 stars at 3 epochs, first in 3 apertures (1.0", 0.5", and 0.3" circular) and then in 1 aperture (1.0" circular). In cycle 1, one star, BD+28D4211 will be observed in the 1.0" aperture to establish the stability of the sensitivity and flat field characteristics and improve the accuracy obtained in SV. This star will also be observed through the paired apertures since these are not calibrated in SV. The stars will be observed in most detector/grating combinations. The data will be averaged to form the inverse sensitivity functions required by RSDP.

  13. Synthesis and absolute configuration of a new 3,4-dihydro-beta-carboline-type alkaloid, 3,4-dehydro-5(S)-5-carboxystrictosidine, isolated from Peruvian Uña de Gato (Uncaria tomentosa).

    PubMed

    Kitajima, Mariko; Yokoya, Masashi; Takayama, Hiromitsu; Aimi, Norio

    2002-10-01

    The structure including the absolute configuration of a new glucoalkaloid, 3,4-dehydro-5(S)-5-carboxystrictosidine, isolated from Peruvian Uña de Gato (Cat's Claw, original plant: Uncaria tomentosa), was confirmed by synthesis starting from secologanin and L-tryptophan.

  14. Kinetic Resolution Driven Diastereo- and Enantioselective Synthesis of cis-β-Heteroaryl Amino Cycloalkanols by Ruthenium-Catalyzed Asymmetric Transfer Hydrogenation.

    PubMed

    Vyas, Vijyesh K; Bhanage, Bhalchandra M

    2016-12-16

    The utility of tethered Ru-TsDPEN catalyst has been demonstrated for the asymmetric transfer hydrogenation of rac-α-heteroaryl amino cycloalkanones to construct biologically important cis-β-heteroaryl amino cycloalkanols with two contiguous chiral centers via dynamic kinetic resolution. The stated (R,R)-Teth-TsDPEN-Ru-catalyzed transformation is carried out under mild conditions using formic acid/triethylamine as a hydrogen source with excellent diastereo- and enantioselectivities. Further, this methodology has been applied for the synthesis of an antileishmanial agent and chiral ionic liquid.

  15. Asymmetric Synthesis of N-Boc-(R)-Silaproline via Rh-Catalyzed Intramolecular Hydrosilylation of Dehydroalanine and Continuous Flow N-Alkylation.

    PubMed

    Chung, John Y L; Shevlin, Michael; Klapars, Artis; Journet, Michel

    2016-04-15

    An asymmetric synthesis of a silicon-containing proline surrogate, N-Boc-(R)-silaproline (1), is described. Starting from N-Boc-dehydroalanine ester, deprotonation, followed by N-alkylation with chloromethyldimethylsilane under flow conditions, afforded the N-alkylated product 8 in 91% yield. An unprecedented enantioselective (NBD)2RhBF4/Josiphos 404-1 catalyzed 5-endo-trig hydrosilylation afforded the silaproline ester in 85-90% yield and >95% ee. Subsequent saponification and salt formation upgraded 1 to >99% ee.

  16. Chiral bidentate [N,S]-ferrocene ligands based on a thiazoline framework. Synthesis and use in palladium-catalyzed asymmetric allylic alkylation.

    PubMed

    Sánchez-Rodríguez, E P; Hochberger-Roa, F; Corona-Sánchez, R; Barquera-Lozada, J E; Toscano, R A; Urrutigoïty, M; Gouygou, M; Ortega-Alfaro, M C; López-Cortés, J G

    2017-01-31

    An efficient method to obtain chiral 1,2-disubstituted ferrocenyl ligands has been developed. The introduction of planar chirality was accomplished by using 2-thiazoline as an ortho-directing lithiation group, and moreover, these kinds of ligands possess a central chirality from the amino alcohol used in their synthesis. The X-ray analysis and DFT calculations confirmed the diastereoselectivity of ortho-lithiation and the configuration of the planar chirality. The ability of these new bidentate [N,S]-ferrocene ligands to act in Pd-catalyzed asymmetric allylic alkylation has also been demonstrated and compared with their oxazoline counterparts.

  17. Asymmetric synthesis and biological evaluations of (+)- and (-)-6-dimethoxymethyl-1,4-dihydropyridine-3-carboxylic acid derivatives blocking N-type calcium channels.

    PubMed

    Yamamoto, Takashi; Ohno, Seiji; Niwa, Seiji; Tokumasu, Munetaka; Hagihara, Masako; Koganei, Hajime; Fujita, Shin-ichi; Takeda, Tomoko; Saitou, Yuki; Iwayama, Satoshi; Takahara, Akira; Iwata, Seinosuke; Shoji, Masataka

    2011-06-01

    An efficient asymmetric synthesis of 1,4-dihydropyridine derivatives is described. The key step is the stereoselective Michael addition using t-butyl ester of L-valine as a chiral auxiliary to achieve good ee (>95% for all the tested experiments) and moderate yield. With this method, (+)-4-(3-chlorophenyl)-6-dimethoxymethyl-2-methyl-1,4-dihydropyridine-3,5-dicarboxylic acid cinnamyl ester was obtained and was characterized as a promising N-type calcium channel blocker with improved selectivity over L-type compared to its (-)- and racemic isomers.

  18. Brønsted-acid-catalyzed asymmetric multicomponent reactions for the facile synthesis of highly enantioenriched structurally diverse nitrogenous heterocycles.

    PubMed

    Yu, Jie; Shi, Feng; Gong, Liu-Zhu

    2011-11-15

    Optically pure nitrogenous compounds, and especially nitrogen-containing heterocycles, have drawn intense research attention because of their frequent isolation as natural products. These compounds have wide-ranging biological and pharmaceutical activities, offering potential as new drug candidates. Among the various synthetic approaches to nitrogenous heterocycles, the use of asymmetric multicomponent reactions (MCRs) catalyzed by chiral phosphoric acids has recently emerged as a particularly robust tool. This method combines the prominent merits of MCRs with organocatalysis, thus affording enantio-enriched nitrogenous heterocyclic compounds with excellent enantioselectivity, atom economy, bond-forming efficiency, structural diversity, and complexity. In this Account, we discuss a variety of asymmetric MCRs catalyzed by chiral phosphoric acids that lead to the production of structurally diverse nitrogenous heterocycles. In MCRs, three or more reagents are combined simultaneously to produce a single product containing structural contributions from all the components. These one-pot processes are especially useful in the construction of heterocyclic cores: they can provide a high degree of both complexity and diversity for a targeted set of scaffolds while minimizing the number of synthetic operations. Unfortunately, enantioselective MCRs have thus far been relatively underdeveloped. Particularly lacking are reactions that proceed through imine intermediates, which are formed from the condensation of carbonyls and amines. The concomitant generation of water in the condensation reaction can deactivate some Lewis acid catalysts, resulting in premature termination of the reaction. Thus, chiral catalysts typically must be compatible with water for MCRs to generate nitrogenous compounds. Recently, organocatalytic MCRs have proven valuable in this respect. Brønsted acids, an important class of organocatalysts, are highly compatible with water and thereby offer great

  19. Synthesis of Enantiomerically Pure Anthracyclinones

    NASA Astrophysics Data System (ADS)

    Achmatowicz, Osman; Szechner, Barbara

    The anthracycline antibiotics are among the most important clinical drugs used in the treatment of human cancer. The search for new agents with improved therapeutic efficacy and reduced cardiotoxicity stimulated considerable efforts in the synthesis of new analogues. Since the biological activity of anthracyclines depends on their natural absolute configuration, various strategies for the synthesis of enantiomerically pure anthracyclinones (aglycones) have been developed. They comprise: resolution of racemic intermediate, incorporation of a chiral fragment derived from natural and non-natural chiral pools, asymmetric synthesis with the use of a chiral auxiliary or a chiral reagent, and enantioselective catalysis. Synthetic advances towards enantiopure anthracyclinones reported over the last 17 years are reviewed.

  20. Asymmetric Synthesis of Substituted Thiolanes through Domino Thia-Michael-Henry Dynamic Covalent Systemic Resolution using Lipase Catalysis.

    PubMed

    Zhang, Yan; Vongvilai, Pornrapee; Sakulsombat, Morakot; Fischer, Andreas; Ramström, Olof

    2014-03-24

    Dynamic systems based on consecutive thia-Michael and Henry reactions were generated and transformed using lipase-catalyzed asymmetric transformation. Substituted thiolane structures with three contiguous stereocenters were resolved in the process in high yields and high enantiomeric excesses.

  1. Asymmetric synthesis of gem-diaryl substituted cyclic sulfamidates and sulfamides by rhodium-catalyzed arylation of cyclic ketimines.

    PubMed

    Nishimura, Takahiro; Ebe, Yusuke; Fujimoto, Hiroto; Hayashi, Tamio

    2013-06-18

    Asymmetric addition of arylboronates to aryl-substituted cyclic ketimines proceeded in the presence of a rhodium catalyst coordinated with a chiral diene ligand to give high yields of sulfamidates and sulfamides with high enantioselectivity (up to 99% ee).

  2. Enantioselective Synthesis of (−)-Acetylapoaranotin

    PubMed Central

    2017-01-01

    The first enantioselective total synthesis of the epipolythiodiketopiperazine (ETP) natural product (−)-acetylapoaranotin (3) is reported. The concise synthesis was enabled by an eight-step synthesis of a key cyclohexadienol-containing amino ester building block. The absolute stereochemistry of both amino ester building blocks used in the synthesis is set through catalytic asymmetric (1,3)-dipolar cycloaddition reactions. The formal syntheses of (−)-emethallicin E and (−)-haemotocin are also achieved through the preparation of a symmetric cyclohexadienol-containing diketopiperazine. PMID:28349698

  3. Synthesis and Application of Chiral Spiro Cp Ligands in Rhodium-Catalyzed Asymmetric Oxidative Coupling of Biaryl Compounds with Alkenes.

    PubMed

    Zheng, Jun; Cui, Wen-Jun; Zheng, Chao; You, Shu-Li

    2016-04-27

    The vastly increasing application of chiral Cp ligands in asymmetric catalysis results in growing demand for novel chiral Cp ligands. Herein, we report a new class of chiral Cp ligands based on 1,1'-spirobiindane, a privileged scaffold for chiral ligands and catalysts. The corresponding Rh complexes are shown to be excellent catalysts in asymmetric oxidative coupling reactions, providing axially chiral biaryls in 19-97% yields with up to 98:2 er.

  4. Synthesis of 3,3-Disubstituted Oxindoles by Palladium-Catalyzed Asymmetric Intramolecular α-Arylation of Amides: Reaction Development and Mechanistic Studies.

    PubMed

    Katayev, Dmitry; Jia, Yi-Xia; Sharma, Akhilesh K; Banerjee, Dipshikha; Besnard, Céline; Sunoj, Raghavan B; Kündig, E Peter

    2013-09-02

    Palladium complexes incorporating chiral N-heterocyclic carbene (NHC) ligands catalyze the asymmetric intramolecular α-arylation of amides producing 3,3-disubstituted oxindoles. Comprehensive DFT studies have been performed to gain insight into the mechanism of this transformation. Oxidative addition is shown to be rate-determining and reductive elimination to be enantioselectivity-determining. The synthesis of seven new NHC ligands is detailed and their performance is compared. One of them, L8, containing a tBu and a 1-naphthyl group at the stereogenic centre, proved superior and was very efficient in the asymmetric synthesis of fifteen new spiro-oxindoles and three azaspiro-oxindoles often in high yields (up to 99 %) and enantioselectivities (up to 97 % ee; ee=enantiomeric excess). Three palladacycle intermediates resulting from the oxidative addition of [Pd(NHC)] into the aryl halide bond were isolated and structurally characterized (X-ray). Using these intermediates as catalysts showed alkene additives to play an important role in increasing turnover number and frequency.

  5. New chiral phosphinephosphinite ligands: Application to stereoselective synthesis of a key intermediate of 1{beta}-methyl carbapenems by Rh(I)-catalyzed asymmetric hydroformylation

    SciTech Connect

    Saito, Takao; Yoshida, Akifumi; Matsumura, Kazuhiko

    1995-12-31

    Transition metal catalyzed asymmetric hydroformylation is an attractive and highly useful homologation process for organic synthesis. Recently, the authors reported that the Rh(I) complexes of phosphinephosphite BINAPHOS are highly efficient catalysts for enantioselective hydroformylation of a variety of olefins. This time, the authors have designed and synthesized new chiral phosphinephosphinite ligands having binaphthyl backbone, (R)-2-diarylphosphino-2{prime}-diarylphosphinoxy-1,1{prime}-binaphthy1 (hereafter abbreviated (R)-BIPNITE). The Rh(I) complexes of these ligands are effective catalysts for the asymmetric hydroformylation of 4-vinylazetidin-2-one to give the corresponding oxo-aldehyde 3{beta} as the major product in very high diastereoselectivities and in good regioselectivities. Interestingly, modifications of the aryl substituents in phosphine and phosphinite moieties afforded higher selectivities. Aldehyde 3{beta} was easily oxidized with NaClO{sub 2} to 4, a key intermediate of 1{beta}-methyl carbapenems. Thus, the present method provides a new practical route to a versatile key intermediate for the synthesis of carbapenem antibiotics.

  6. Stereoselective α-fluoroamide and α-fluoro-γ-lactone synthesis by an asymmetric zwitterionic aza-Claisen rearrangement

    PubMed Central

    Tenza, Kenny; Northen, Julian S; O'Hagan, David; Slawin, Alexandra MZ

    2005-01-01

    Background Asymmetric introduction of fluorine α-to a carbonyl has become popular recently, largely because the direct fluorination of enolates by asymmetric electrophilic fluorinating reagents has improved, and as a result such compounds are becoming attractive synthons. We have sought an alternative but straightforward asymmetric method to this class of compounds, utilising the zwitterionic aza-Claisen rearrangement by reacting α-fluoroacid chlorides and homochiral N-allylpyrrolidines as starting materials. Results Treatment of N-allylmorpholine with 2-fluoropropionyl chloride under Yb(OTf)3 catalysis generated the zwitterionic aza-Claisen rearrangement product in good yield and demonstrated the chemical feasibility of the approach. For the asymmetric reaction, N-allyl-(S)-2-(methoxymethyl)pyrrolidine was treated with either 2-fluoropropionyl chloride or 2-fluorophenylacetic acid chloride under similar conditions and resulted in N-(α-fluoro-γ-vinylamide)pyrrolidine products as homochiral materials in 99% de. These products were readily converted to their corresponding α-fluoro-γ-lactones by iodolactonisation and in good diastereoselectivity. Conclusion Molecules which have fluorine at a stereogeneic centre are finding increasing utility in pharmaceutical, fine chemicals and materials research. The zwitterionic aza-Claisen rearrangement proved to be an effective and competitive complement to asymmetric electrophilic fluorination strategies and provides access to versatile synthetic intermediates with fluorine at the stereogenic centre. PMID:16542024

  7. Highly Stereoselective Synthesis of Anti, Anti-Dipropionate Stereotriads: A Solution to the Long-Standing Problem of Challenging Mismatched Double Asymmetric Crotylboration Reactions#

    PubMed Central

    Chen, Ming; Roush, William R.

    2012-01-01

    The stereocontrolled synthesis of the β-branched anti, anti-dipropionate stereotriad 4 via aldol or crotylmetal chemistry represents a historical challenge to the organic synthesis community. Here we describe a general solution to the long-standing problem associated with the synthesis of 4 by utilizing mismatched double asymmetric crotylboration reactions of enantioenriched α-methyl substituted aldehydes with the chiral, nonracemic crotylborane reagent (S)-(E)-22 (or its enantiomer). This method not only provides direct access to anti, anti-dipropionate stereotriads 24 [a synthetic equivalent of 4] with very good (5-8:1) if not excellent (≥15:1) diastereoselectivity from β-branched chiral aldehydes with ≤50:1 intrinsic diastereofacial selectivity preferences, but also provides a vinylstannane unit in the products that is properly functionalized for use in subsequent C-C bond forming events. We anticipate that this method will be widely applicable and will lead to substantial simplification of strategies for synthesis of polyketide natural products. PMID:22332989

  8. Synthesis and the absolute configuration of both enantiomers of 4,5-dihydroxy-3-(formyl)cyclopent-2-enone acetonide as a new chiral building block for prostanoid synthesis.

    PubMed

    Łukasik, Beata; Mikołajczyk, Marian; Bujacz, Grzegorz; Żurawiński, Remigiusz

    2015-01-21

    The synthesis of both enantiomers of 4,5-dihydroxy-3-(formyl)cyclopent-2-enone acetonide (5) was accomplished in five steps starting from meso-tartaric acid (6). The key steps involved are preparation of the isopropylidene protected 3-[(dimethoxyphosphoryl)methyl]-4,5-dihydroxycyclopent-2-enone (9), resolution of the diastereoisomeric products 10 of the Horner reaction of racemic 9 with (R)-glyceraldehyde acetonide and the final regioselective ozonolysis of the exocyclic carbon–carbon double bond of the separated dienones 10 leading to both enantiomeric title compounds 5. The absolute configuration of both enantiomers was initially assigned based on the comparison of the chiroptical properties obtained from the DFT calculations with the experimental data and finally confirmed by X-ray analysis.

  9. Asymmetric Synthesis of α-Branched Amines via Rh(III)-Catalyzed C–H Bond Functionalization

    PubMed Central

    2015-01-01

    The first asymmetric intermolecular addition of non-acidic C–H bonds to imines is reported. The use of the activating N-perfluorobutanesulfinyl imine substituent is essential for achieving sufficient reactivity and provides outstanding diastereoselectivity (>98:2 dr). Straightforward removal of the sulfinyl group with HCl yields the highly enantiomerically enriched amine hydrochlorides. PMID:24901217

  10. Diastereoselective Allylation of "N"-"Tert"-Butanesulfinyl Imines: An Asymmetric Synthesis Experiment for the Undergraduate Organic Laboratory

    ERIC Educational Resources Information Center

    Chen, Xiao-Yang; Sun, Li-Sen; Gao, Xiang; Sun, Xing-Wen

    2015-01-01

    An asymmetric synthetic experiment that encompasses both diastereoselectivity and enantioselectivity is described. In this experiment, Zn-mediated allylation of an ("R")-"N"-"tert"-butanesulfinyl imine is first performed to obtain either diastereomer using two different solvent systems, followed by oxidation of the…

  11. Rapid Asymmetric Synthesis of Disubstituted Allenes by Coupling of Flow‐Generated Diazo Compounds and Propargylated Amines

    PubMed Central

    Poh, Jian‐Siang; Makai, Szabolcs; von Keutz, Timo; Tran, Duc N.; Battilocchio, Claudio; Pasau, Patrick

    2017-01-01

    Abstract We report herein the asymmetric coupling of flow‐generated unstabilized diazo compounds and propargylated amine derivatives, using a new pyridinebis(imidazoline) ligand, a copper catalyst and base. The reaction proceeds rapidly, generating chiral allenes in 10–20 minutes with high enantioselectivity (89–98 % de/ee), moderate yields and a wide functional group tolerance. PMID:28075518

  12. Enantioselective synthesis of tunable chiral Clickphine P,N-ligands and their application in Ir-catalyzed asymmetric hydrogenation.

    PubMed

    Wassenaar, Jeroen; Detz, Remko J; de Boer, Sandra Y; Lutz, Martin; van Maarseveen, Jan H; Hiemstra, Henk; Reek, Joost N H

    2015-04-03

    A small library of highly tunable chiral Clickphine P,N-ligands has been prepared in an enantioselective fashion by Cu(I)-catalyzed asymmetric propargylic amination using a single chiral complex and a subsequent in situ cycloaddition click reaction. The scope of the propargylic amination to yield optically active triazolyl amines is described. The amines are transformed in a one-pot procedure to the corresponding Ir-Clickphine complexes, which serve as catalysts for the asymmetric hydrogenation of di-, tri-, and tetrasubstituted unfunctionalized alkenes. Enantioselectivities of up to 90% ee were obtained in these hydrogenations, which are among the best reported in the case of the tetrasubstituted substrate 2-(4'-methoxyphenyl)-3-methylbut-2-ene (9) (87% ee). This is a demonstration of the effective use of the chiral pool, as from one chiral catalyst a library of chiral Ir complexes has been synthesized that can hydrogenate various alkenes with high selectivity.

  13. Green synthesis of asymmetrically textured silver meso-flowers (AgMFs) as highly sensitive SERS substrates.

    PubMed

    Nhung, Tran Thi; Lee, Sang-Wha

    2014-12-10

    Highly asymmetrical "flower-like" micron silver particles, so-called hierarchical silver meso-flowers (AgMFs), were facilely synthesized using ascorbic acid at room temperature in the presence of chitosan biopolymer. The time-evolution of TEM images and XRD analysis confirmed the anisotropic growth of AgMFs with single crystalline phase of which the formation mechanism was described in detail. The morphology and size of as-prepared AgMFs were tunable simply by changing the concentration of chitosan biopolymer and/or AgNO3 precursor under otherwise identical conditions. The asymmetrically textured AgMFs dramatically enhanced Raman signals of probe molecules (2-chlorothiophenol, 4-aminothiophenol) even at a single particle level because of their surface morphologies consisting of numerous nanoedges and crevices.

  14. Crystallography of magnetite plaquettes and their significance as asymmetric catalysts for the synthesis of chiral organics in carbonaceous chondrites

    NASA Astrophysics Data System (ADS)

    Chan, Q. H. S.; Zolensky, M. E.

    2015-10-01

    We have previously observed the magnetite plaquettes in carbonaceous chondrites using scanning electron microscope (SEM) imaging, examined the crystal orientation of the polished surfaces of magnetite plaquettes in CI Orgueil using electron backscattered diffraction (EBSD) analysis, and concluded that these magnetite plaquettes are likely naturally asymmetric materials [1]. In this study, we expanded our EBSD observation to other magnetite plaquettes in Orgueil, and further examined the internal structure of these remarkable crystals with the use of X-ray computed microtomography.

  15. Enantioselective synthesis of binaphthyl polymers using chiral asymmetric phenolic coupling catalysts: oxidative coupling and tandem glaser/oxidative coupling.

    PubMed

    Morgan, Barbara J; Xie, Xu; Phuan, Puay-Wah; Kozlowski, Marisa C

    2007-08-03

    A series of functionalized and optically active polybinaphthyls have been synthesized from achiral substrates by asymmetric oxidative phenolic coupling using a chiral 1,5-diaza-cis-decalin copper catalyst. In most cases, a copper tetrafluoroborate catalyst was found to be superior to the copper iodide catalyst, as ortho-iodination of the substrates could be prevented. Three methods for the formation of chiral polymers are described. In the first method, two 2-naphthols linked together at C-6 are subjected to the optimized asymmetric oxidative phenolic coupling conditions to form chiral polynaphthyls. A combination of NMR and HPLC measurements secured the selectivity of the asymmetric coupling. In the second method, substrates containing only one naphthalene were utilized. By incorporating a 2-naphthol and a terminal alkyne, the chiral copper catalysts effect both Glaser-Hay coupling of the alkyne and oxidative asymmetric coupling of the 2-naphthol with remarkable chemoselectivity. The relative reaction rates of various moieties with the chiral catalysts follows the order: benzyl cyanides > aryl alkynes > electron-rich 2-naphthols > electron-deficient 2-naphthols > alkyl alkynes. Because of high chemoselectivity, this approach is useful for the organized assembly of multifunctional substrates in a single operation. In all cases, no cross-coupling is observed between the alkyne and the 2-naphthol. This approach was thus applied to a set of highly functionalized precursors. In this third case, the biaryl coupling was performed first and a Glaser-Hay coupling was performed in a separate step to generate a highly functionalized polymer. In some cases, the resultant chiral polymers exhibit very large optical rotations.

  16. Crystallography of Magnetite Plaquettes and their Significance as Asymmetric Catalysts for the Synthesis of Chiral Organics in Carbonaceous Chondrites

    NASA Technical Reports Server (NTRS)

    Chan, Q. H. S.; Zolensky, M. E.

    2015-01-01

    We have previously observed the magnetite plaquettes in carbonaceous chondrites using scanning electron microscope (SEM) imaging, examined the crystal orientation of the polished surfaces of magnetite plaquettes in CI Orgueil using electron backscattered diffraction (EBSD) analysis, and concluded that these magnetite plaquettes are likely naturally asymmetric materials. In this study, we expanded our EBSD observation to other magnetite plaquettes in Orgueil, and further examined the internal structure of these remarkable crystals with the use of X-ray computed microtomography.

  17. Total synthesis of (R,R,R)-γ-tocopherol through Cu-catalyzed asymmetric 1,2-addition.

    PubMed

    Wu, Zhongtao; Harutyunyan, Syuzanna R; Minnaard, Adriaan J

    2014-10-27

    Based on the asymmetric copper-catalyzed 1,2-addition of Grignard reagents to ketones, (R,R,R)-γ-tocopherol has been synthesized in 36 % yield over 12 steps (longest linear sequence). The chiral center in the chroman ring was constructed with 73 % ee by the 1,2-addition of a phytol-derived Grignard reagent to an α-bromo enone prepared from 2,3-dimethylquinone.

  18. Chemoenzymatic one-pot synthesis in an aqueous medium: combination of metal-catalysed allylic alcohol isomerisation-asymmetric bioamination.

    PubMed

    Ríos-Lombardía, Nicolás; Vidal, Cristian; Cocina, María; Morís, Francisco; García-Álvarez, Joaquín; González-Sabín, Javier

    2015-07-11

    The ruthenium-catalysed isomerisation of allylic alcohols was coupled, for the first time, with asymmetric bioamination in a one-pot process in an aqueous medium. In the cases involving prochiral ketones, the ω-TA exhibited excellent enantioselectivity, identical to that observed in the single step. As a result, amines were obtained from allylic alcohols with high overall yields and excellent enantiomeric excesses.

  19. Cu(II)-catalyzed asymmetric hydrosilylation of diaryl- and aryl heteroaryl ketones: application in the enantioselective synthesis of orphenadrine and neobenodine.

    PubMed

    Sui, Yao-Zong; Zhang, Xi-Chang; Wu, Jun-Wen; Li, Shijun; Zhou, Ji-Ning; Li, Min; Fang, Wenjun; Chan, Albert S C; Wu, Jing

    2012-06-11

    With certain amounts of sodium tert-butoxide and tert-butanol as additives, catalytic amounts of an inexpensive and easy-to-handle copper source Cu(OAc)(2)⋅H(2)O, a commercially available and air-stable non-racemic dipyridylphosphine ligand, as well as the stoichiometric desirable hydride donor polymethylhydrosiloxane (PMHS), formed a versatile in situ catalyst system for the enantioselective reduction of a broad spectrum of prochiral diaryl and aryl heteroarylketones in air, in high yields and with good to excellent enantioselectivities (up to 96 %). In particular, the practical viability of this process was evinced by its successful applications in the asymmetric synthesis of optically enriched potent antihistaminic drugs orphenadrine and neobenodine.

  20. Highly diastereoselective and stereodivergent dihydroxylations of acyclic allylic amines: application to the asymmetric synthesis of 3,6-dideoxy-3-amino-L-talose.

    PubMed

    Csatayová, Kristína; Davies, Stephen G; Lee, James A; Roberts, Paul M; Russell, Angela J; Thomson, James E; Wilson, David L

    2011-05-20

    Aminohydroxylation of tert-butyl sorbate [tert-butyl (E,E)-hexa-2,4-dienoate] using enantiopure lithium (R)-N-benzyl-N-(α-methylbenzyl)amide and (-)-camphorsulfonyloxaziridine gives tert-butyl (R,R,R,E)-2-hydroxy-3-[N-benzyl-N-(α-methylbenzyl)amino]hex-4-enoate in >99:1 dr. Subsequent dihydroxylation under Upjohn conditions (OsO(4)/NMO) gives tert-butyl (2R,3R,4S,5S,αR)-2,4,5-trihydroxy-3-[N-benzyl-N-(α-methylbenzyl)amino]hexanoate (in 95:5 dr) while dihydroxylation under Donohoe conditions (OsO(4)/TMEDA) proceeds with antipodal diastereofacial selectivity to give the (R,R,R,R,R)-diastereoisomer (in 95:5 dr). The amino triols resulting from these dihydroxylation reactions are useful for further elaboration, as demonstrated by the asymmetric synthesis of 3,6-dideoxy-3-amino-L-talose.

  1. Asymmetric synthesis of α-amino acids via homologation of Ni(II) complexes of glycine Schiff bases. Part 3: Michael addition reactions and miscellaneous transformations.

    PubMed

    Aceña, José Luis; Sorochinsky, Alexander E; Soloshonok, Vadim

    2014-09-01

    The major goal of this review is a critical discussion of the literature data on asymmetric synthesis of α-amino acids via Michael addition reactions involving Ni(II)-complexes of amino acids. The material covered is divided into two conceptually different groups dealing with applications of: (a) Ni(II)-complexes of glycine as C-nucleophiles and (b) Ni(II)-complexes of dehydroalanine as Michael acceptors. The first group is significantly larger and consequently subdivided into four chapters based on the source of stereocontrolling element. Thus, a chiral auxiliary can be used as a part of nucleophilic glycine Ni(II) complex, Michael acceptor or both, leading to the conditions of matching vs. mismatching stereochemical preferences. The particular focus of the review is made on the practical aspects of the methodology under discussion and mechanistic considerations.

  2. Zn-catalyzed enantio- and diastereoselective formal [4 + 2] cycloaddition involving two electron-deficient partners: asymmetric synthesis of piperidines from 1-azadienes and nitro-alkenes.

    PubMed

    Chu, John C K; Dalton, Derek M; Rovis, Tomislav

    2015-04-08

    We report a catalytic asymmetric synthesis of piperidines through [4 + 2] cycloaddition of 1-azadienes and nitro-alkenes. The reaction uses earth abundant Zn as catalyst and is highly diastereo- and regioselective. A novel BOPA ligand (F-BOPA) confers high reactivity and enantioselectivity in the process. The presence of ortho substitution on the arenes adjacent to the bis(oxazolines) was found to be particularly impactful, due to limiting the undesired coordination of 1-azadiene to the Lewis acid and thus allowing the reaction to be carried out at lower temperature. A series of secondary kinetic isotope effect studies using a range of ligands implicates a stepwise mechanism for the transformation, involving an initial Michael-type addition of the imine to the nitro-alkene followed by a cyclization event. The stepwise mechanism obviates the electronic requirement inherent to a concerted mechanism, explaining the successful cycloaddition between two electron-deficient partners.

  3. One-step synthesis of graphene nanoribbon-MnO₂ hybrids and their all-solid-state asymmetric supercapacitors.

    PubMed

    Liu, Mingkai; Tjiu, Weng Weei; Pan, Jisheng; Zhang, Chao; Gao, Wei; Liu, Tianxi

    2014-04-21

    Three-dimensional (3D) hierarchical hybrid nanomaterials (GNR-MnO₂) of graphene nanoribbons (GNR) and MnO₂ nanoparticles have been prepared via a one-step method. GNR, with unique features such as high aspect ratio and plane integrity, has been obtained by longitudinal unzipping of multi-walled carbon nanotubes (CNTs). By tuning the amount of oxidant used, different mass loadings of MnO₂ nanoparticles have been uniformly deposited on the surface of GNRs. Asymmetric supercapacitors have been fabricated with the GNR-MnO₂ hybrid as the positive electrode and GNR sheets as the negative electrode. Due to the desirable porous structure, excellent electrical conductivity, as well as high rate capability and specific capacitances of both the GNR and GNR-MnO₂ hybrid, the optimized GNR//GNR-MnO₂ asymmetric supercapacitor can be cycled reversibly in an enlarged potential window of 0-2.0 V. In addition, the fabricated GNR//GNR-MnO₂ asymmetric supercapacitor exhibits a significantly enhanced maximum energy density of 29.4 W h kg(-1) (at a power density of 12.1 kW kg(-1)), compared with that of the symmetric cells based on GNR-MnO₂ hybrids or GNR sheets. This greatly enhanced energy storage ability and high rate capability can be attributed to the homogeneous dispersion and excellent pseudocapacitive performance of MnO₂ nanoparticles and the high electrical conductivity of the GNRs.

  4. Chiral hydroxy phosphonates: synthesis, configuration and biological properties

    NASA Astrophysics Data System (ADS)

    Kolodiazhnyi, Oleg I.

    2006-03-01

    Published data on the synthesis, absolute configurations and biological properties of chiral hydroxy phosphonates are generalised and described systematically. Examples of asymmetric synthesis of hydroxy phosphonates by the phospho-aldol reaction, reduction of keto phosphonates, chemo-enzymatic approach, and so on are discussed. Methods for determination of the optical purity and absolute configuration of hydroxy phosphonates using modification by chiral reagents, NMR, circular dichroism, GLC and HPLC on columns with chiral sorbents are considered. The significance of hydroxy phosphonates as promising compounds for the development of new drugs and bioregulators is demonstrated.

  5. Asymmetric Ion-Pairing Catalysis

    PubMed Central

    Brak, Katrien

    2014-01-01

    Charged intermediates and reagents are ubiquitous in organic transformations. The interaction of these ionic species with chiral neutral, anionic, or cationic small molecules has emerged as a powerful strategy for catalytic, enantioselective synthesis. This review describes developments in the burgeoning field of asymmetric ion-pairing catalysis with an emphasis on the insights that have been gleaned into the structural and mechanistic features that contribute to high asymmetric induction. PMID:23192886

  6. Asymmetric Formal Total Synthesis of the Stemofoline Alkaloids: The Evolution, Development and Application of a Catalytic Dipolar Cycloaddition Cascade

    PubMed Central

    Shanahan, Charles S.; Fang, Chao; Paull, Daniel H.; Martin, Stephen F.

    2013-01-01

    A formal synthesis of didehydrostemofoline and isodidehydrostemofoline has been accomplished by preparing an intermediate in the Overman synthesis of these alkaloids from commercially available 2-deoxy-D-ribose. The work presented in this account chronicles the evolution of our explorations to identify the optimal steric and electronic control elements necessary to generate the tricyclic core structure of these alkaloids in a single operation from an acyclic precursor. The key step in the synthesis is a novel dipolar cycloaddition cascade sequence that is initiated by cyclization of a rhodium-derived carbene onto the nitrogen atom of a proximal imine group to generate an azomethine ylide that then undergoes spontaneous cyclization via dipolar cycloaddition. The synthesis features several other interesting reactions, including a Boord elimination to prepare a chiral allylic alcohol, a highly diastereoselective Hirama-Itô cyclization, and a useful modification of the Barton decarboxylation protocol. PMID:24072939

  7. Teaching Absolute Value Meaningfully

    ERIC Educational Resources Information Center

    Wade, Angela

    2012-01-01

    What is the meaning of absolute value? And why do teachers teach students how to solve absolute value equations? Absolute value is a concept introduced in first-year algebra and then reinforced in later courses. Various authors have suggested instructional methods for teaching absolute value to high school students (Wei 2005; Stallings-Roberts…

  8. Synthesis of chiral diether and tetraether phospholipids: Regiospecific ring opening of epoxy alcohol intermediates derived from asymmetric epoxidation

    SciTech Connect

    Thompson, D.H.; Svendsen, C.B.; Di Meglio, C.; Anderson, V.C.

    1994-06-03

    Diether and tetraether phospholipids have been synthesized using chiral epoxy alcohol starting materials (e.g. glycidol 3-nitrobenzenesulfonate esters or tert-butyldiphenylsilyl ethers). These chiral precursors provide control over the stereochemistry, substitution patterns, and steric properties of the phosphoglycerol backbone. Configuration at the sn-2 glycerol carbon was controlled by asymmetric epoxidation of allyl alcohol followed by acid-catalyzed, regioselective opening of the oxirane ring using excess aliphatic n-alcohols to give mono-O-alkylated glycerol intermediates in good yields. 9 figs., 5 tabs.

  9. Calcium-catalyzed asymmetric synthesis of 3-tetrasubstituted oxindoles: efficient construction of adjacent quaternary and tertiary chiral centers.

    PubMed

    Shimizu, Shota; Tsubogo, Tetsu; Xu, Pengyu; Kobayashi, Shū

    2015-04-17

    Chiral Ca-catalyzed asymmetric addition reactions of 3-substituted oxindoles with N-Boc-imines afford 3-tetrasubstituted oxindole derivatives bearing adjacent quaternary and tertiary chiral centers, which are key structures for biological activities. Ubiquitous and nontoxic Ca catalysts (1-10 mol %) work well in this reaction, and high yields (up to 99%) and selectivities (up to >99% ee) of the products with wide substrate scope have been attained. The structures of the chiral Ca catalysts and intermediary Ca enolates are also discussed.

  10. Organocatalytic Domino Oxa-Michael/1,6-Addition Reactions: Asymmetric Synthesis of Chromans Bearing Oxindole Scaffolds.

    PubMed

    Zhao, Kun; Zhi, Ying; Shu, Tao; Valkonen, Arto; Rissanen, Kari; Enders, Dieter

    2016-09-19

    An asymmetric organocatalytic domino oxa-Michael/1,6-addition reaction of ortho-hydroxyphenyl-substituted para-quinone methides and isatin-derived enoates has been developed. In the presence of 5 mol % of a bifunctional thiourea organocatalyst, this scalable domino reaction affords 4-phenyl-substituted chromans bearing spiro-connected oxindole scaffolds and three adjacent stereogenic centers in good to excellent yields (up to 98 %) and with very high stereoselectivities (up to >20:1 d.r., >99 % ee).

  11. Exploring the Scope of Asymmetric Synthesis of β-Hydroxy-γ-lactams via Noyori-type Reductions.

    PubMed

    Lynch, Denis; Deasy, Rebecca E; Clarke, Leslie-Ann; Slattery, Catherine N; Khandavilli, U B Rao; Lawrence, Simon E; Maguire, Anita R; Magnus, Nicholas A; Moynihan, Humphrey A

    2016-10-07

    Enantio- and diastereoselective hydrogenation of β-keto-γ-lactams with a ruthenium-BINAP catalyst, involving dynamic kinetic resolution, has been employed to provide a general, asymmetric approach to β-hydroxy-γ-lactams, a structural motif common to several bioactive compounds. Full conversion to the desired β-hydroxy-γ-lactams was achieved with high diastereoselectivity (up to >98% de) by addition of catalytic HCl and LiCl, while β-branching of the ketone substituent demonstrated a pronounced effect on the modest to excellent enantioselectivity (up to 97% ee) obtained.

  12. The synthesis of chiral β-aryl-α,β-unsaturated amino alcohols via a Pd-catalyzed asymmetric allylic amination.

    PubMed

    Quan, Mao; Butt, Nicholas; Shen, Jiefeng; Shen, Kaiji; Liu, Delong; Zhang, Wanbin

    2013-11-14

    Chiral β-aryl-α,β-unsaturated amino alcohols were synthesized via a Pd-catalyzed asymmetric allylic amination of 4-aryl-1,3-dioxolan-2-one using planar chiral 1,2-disubstituted ferrocene-based phosphinooxazolines as ligands. Under the optimized reaction conditions, a series of substrates were examined and the products were obtained in good to excellent yields (up to 92%) and enantioselectivities (up to 98% ee) under mild reaction conditions. The desired products were determined to be of (R)-configuration and could subsequently be transformed into compounds with interesting biological activity using simple transformations.

  13. N-phosphinyl imine chemistry (I): design and synthesis of novel N-phosphinyl imines and their application to asymmetric aza-Henry reaction.

    PubMed

    Pindi, Suresh; Kaur, Parminder; Shakya, Gaurav; Li, Guigen

    2011-01-01

    Novel chiral N-phosphinamide and N-phosphinyl imines have been designed, synthesized and applied to asymmetric aza-Henry reaction to give excellent chemical yields (92%- quant.) and diastereoselectivity (91% to >99%de). The reaction showed a great substrate scope in which aromatic/aliphatic aldehyde- and ketone-derived N-phosphinyl imines can be employed as electrophiles. The chiral N-phosphinamide can be stored at room temperature for more than 2 months without inert gas protection, and chiral N-phosphinyl imines were also proven to be highly stable at room temperature for a long period under inert gas protection. The N-phosphinyl group enabled the product purification to be performed simply by washing crude product with EtOAc and hexane. This reaction joined other eight GAP (Group-Assistant-Purification) chemistry processes that were developed in our laboratories. The absolute configuration has been unambiguously determined by converting a β-nitroamine product into a known N-Boc sample.

  14. Application of an intramolecular dipolar cycloaddition to an asymmetric synthesis of the fully oxygenated tricyclic core of the stemofoline alkaloids

    PubMed Central

    Carra, Ryan J.; Epperson, Matthew T.; Gin, David Y.

    2008-01-01

    An intramolecular non-stabilized azomethine ylide dipolar cycloaddition was applied toward the first non-racemic synthesis of the fully-oxygenated bridged pyrrolizidine core (45) of (+)-stemofoline (1) in eleven steps from a commercially available starting material. PMID:18443655

  15. Acylation, Diastereoselective Alkylation, and Cleavage of an Oxazolidinone Chiral Auxiliary: A Multistep Asymmetric Synthesis Experiment for Advanced Undergraduates

    ERIC Educational Resources Information Center

    Smith, Thomas E.; Richardson, David P.; Truran, George A.; Belecki, Katherine; Onishi, Megumi

    2008-01-01

    An introduction to the concepts and experimental techniques of diastereoselective synthesis using a chiral auxiliary is described. The 4-benzyl-2-oxazolidinone chiral auxiliary developed by Evans is acylated with propionic anhydride under mild conditions using DMAP as an acyl transfer catalyst. Deprotonation with NaN(TMS)[subscript 2] at -78…

  16. Asymmetric Synthesis of the C1-C6 Portion of the Psymberin Using an Evans Chiral Auxiliary

    PubMed Central

    Pal, Ashutosh; Peng, Zhenghong; Schuber, Paul T.; Bhanu Prasad, Basvoju A.; Bornmann, William G.

    2014-01-01

    The C1-C6 region of the potent cytotoxic agent psymberin has been synthesized. The key transformations of the synthesis are an auxiliary-controlled addition of a Sn(II)-glycolate enolate to an aldehyde to yield the anti aldol product and transforming the primary alcohol into a terminal olefin utilizing organoselenium chemistry. PMID:25110364

  17. Asymmetric synthesis of allylic sulfonic acids: enantio- and regioselective iridium-catalyzed allylations of Na2SO3.

    PubMed

    Liu, Wei; Zhao, Xiao-ming; Zhang, Hong-bo; Zhang, Liang; Zhao, Ming-zhu

    2014-12-15

    An enantioselective allylation reaction of allylic carbonates with sodium sulfite (Na2 SO3 ) catalyzed by Ir complex was accomplished, providing allylic sulfonic acids in good to excellent yields with a high level of enantio- and regioselectivities. (R)-2-Phenyl-2-sulfoacetic acid, a key intermediate for the synthesis of Cefsulodin and Sulbenicillin, was synthesized as well.

  18. Asymmetric Donor-π-Acceptor-Type Benzo-Fused Aza-BODIPYs: Facile Synthesis and Colorimetric Properties.

    PubMed

    Zheng, Wei; Wang, Bei-Bei; Li, Cheng-Hui; Zhang, Jing-Xuan; Wan, Cheng-Zhang; Huang, Jia-Hao; Liu, Jian; Shen, Zhen; You, Xiao-Zeng

    2015-07-27

    Novel aza-diisoindolylmethene and their BF2 -chelating complexes (benzo-fused aza-BODIPYs) were synthesized on a large scale and in a facile manner from phthalonitrile in tBuOK-DMF solution. The unique asymmetric donor-π-acceptor structure facilitates B-N bond detachment in the presence of trifluoroacetic acid (TFA) in dichloromethane, resulting in sharp color change from red to colorless, with over 250 nm hypsochromic shift in the absorption maximum. This colorimetric process can be reversed by adding a very small amount of proton-accepting solvents or compounds. A (1) H and (11) B NMR spectroscopy study and also density functional theory (DFT) calculations suggest that TFA-induced B-N bond cleavage may disrupt the whole π-conjugation of the BODIPY molecule, resulting in significant colorimetric behavior.

  19. Rational Design and Synthesis of [5]Helicene-Derived Phosphine Ligands and Their Application in Pd-Catalyzed Asymmetric Reactions

    NASA Astrophysics Data System (ADS)

    Yamamoto, Kosuke; Shimizu, Takashi; Igawa, Kazunobu; Tomooka, Katsuhiko; Hirai, Go; Suemune, Hiroshi; Usui, Kazuteru

    2016-11-01

    A series of novel optically active [5]helicene-derived phosphine ligands (L1, with a 7,8-dihydro[5]helicene core structure- and L2, with a fully aromatic [5]helicene core structure) were synthesized. Despite their structural similarities, L1 and L2 exhibit particularly different characteristics in their use as chiral ligands. L1 was highly effective in the asymmetric allylation of indoles with 1,3-diphenylallyl acetate (up to 99% ee), and in the etherification of alcohols (up to 96% ee). In contrast, L2 was highly effective in the stereocontrol of helical chirality in Suzuki–Miyaura coupling (SMC) reaction (up to 99% ee). Density functional theory analysis was employed to propose a model that accounts for the origin of the enantioselectivity in these reactions.

  20. Synthesis of asymmetric zinc(II) phthalocyanines with two different functional groups & spectroscopic properties and photodynamic activity for photodynamic therapy.

    PubMed

    Göksel, Meltem

    2016-09-15

    Zinc(II) phthalocyanine containing [2-(tert-butoxycarbonyl)amino]ethoxy and iodine groups (A and B), as well as their deprotected mono-amino and tri-iodine zinc(II) phthalocyanine (2) were obtained. This structure surrounds by substituents with functional groups. From this perspective it can be used a starting material for many reactions and applications, such as sonogashira coupling, carbodiimide coupling. An example of a first diversification reaction of this compound was obtained with conjugation of a biotin. Asymmetrically biotin conjugated and heavy atom bearing zinc(II) phthalocyanine (3) were synthesized characterized for the first time and photophysical, photochemical and photobiological properties of these phthalocyanines were compared in this study.

  1. Asymmetric 1,3,4-oxadiazole derivatives containing naphthalene and stilbene units: synthesis, optical and electrochemical properties.

    PubMed

    Lu, Huixiong; He, Daohang

    2014-04-24

    Six novel asymmetric 1,3,4-oxadiazole derivatives containing naphthalene and stilbene units have been efficiently synthesized and characterized by FT-IR, (1)H NMR, (13)C NMR, mass spectrometry and elemental analysis. The UV-vis absorption maximum wavelength, fluorescence excitation wavelength, fluorescence emission wavelength and fluorescence quantum yield were measured in dilute tetrahydrofuran solution. The solvent effect was also studied. The HOMO and LUMO levels of these compounds were calculated by density functional theory (DFT) (B3LYP, 6-31G(*)) method and cyclic voltammetry. They emit bright violet to blue emission with high fluorescence quantum yields (0.23-0.94) and large Stokes shifts (53-102 nm). These compounds possess high HOMO levels (-5.03 to -5.17 eV) and suitable band gaps, indicating that they could be benefit for hole injection. The results show that they have a potential for application in optoelectronic materials.

  2. Organocatalytic Friedel-Crafts Alkylation/Lactonization Reaction of Naphthols with 3-Trifluoroethylidene Oxindoles: The Asymmetric Synthesis of Dihydrocoumarins.

    PubMed

    Zhao, Yun-Long; Lou, Qin-Xin; Wang, Long-Sheng; Hu, Wen-Hui; Zhao, Jun-Ling

    2017-01-02

    Naphthols and 3-trifluoroethylidene oxindoles were found to undergo an asymmetric Friedel-Crafts alkylation/lactonization reaction, catalyzed by only 2.5 mol % of a quinine-derived squaramide catalyst, to afford the corresponding α-aryl-β-trifluoromethyl dihydrocoumarin derivatives in high yields (up to 99 %) with excellent enantio- and diastereoselectivities (up to 98 % ee, >20:1 d.r.). Importantly, the lactonization proceeded by nucleophilic attack of the naphthol hydroxy group at the amide motif of the oxindoles under mild reaction conditions. This protocol represents a new strategy for the formation of dihydrocoumarins by an efficient intramolecular amide C-N bond-cleavage and esterification process.

  3. Rational Design and Synthesis of [5]Helicene-Derived Phosphine Ligands and Their Application in Pd-Catalyzed Asymmetric Reactions

    PubMed Central

    Yamamoto, Kosuke; Shimizu, Takashi; Igawa, Kazunobu; Tomooka, Katsuhiko; Hirai, Go; Suemune, Hiroshi; Usui, Kazuteru

    2016-01-01

    A series of novel optically active [5]helicene-derived phosphine ligands (L1, with a 7,8-dihydro[5]helicene core structure- and L2, with a fully aromatic [5]helicene core structure) were synthesized. Despite their structural similarities, L1 and L2 exhibit particularly different characteristics in their use as chiral ligands. L1 was highly effective in the asymmetric allylation of indoles with 1,3-diphenylallyl acetate (up to 99% ee), and in the etherification of alcohols (up to 96% ee). In contrast, L2 was highly effective in the stereocontrol of helical chirality in Suzuki–Miyaura coupling (SMC) reaction (up to 99% ee). Density functional theory analysis was employed to propose a model that accounts for the origin of the enantioselectivity in these reactions. PMID:27824074

  4. Absolute Stereochemistry of the β-Hydroxy Acid Unit in Hantupeptins and Trungapeptins.

    PubMed

    Gupta, Deepak Kumar; Ding, Gary Chi Ying; Teo, Yong Chua; Tan, Lik Tong

    2016-01-01

    The β-hydroxy/amino acid unit is a common structural feature of many bioactive marine cyanobacterial depsipeptides. In this study, the absolute stereochemistry of the β-hydroxy acid moieties in hantupeptins and trungapeptins were determined through their synthesis and HPLC analysis of the Mosher ester derivatives. Synthesis of two3-hydroxy-2-methyloctanoic acid (Hmoa) stereoisomers, (2S,3R)-Hmoa and (2S,3S)-Hmoa, were achieved using diastereoselective asymmetric method and the retention times of all four Hmoa isomers were established indirectly by RPLC-MS analysis of their Mosher ester derivative standards. Based on the retention times of the standards, the absolute configuration of the Hmoa unit in hantupeptin C (3) and trungapeptin C (6) was assigned as (2R,3S)- and (2S,3R)-Hmoa, respectively. The use of the Mosher's reagents, coupled with HPLC analysis, provided a viable alternative to the absolute stereochemical determination of β-hydroxy acid units in depsipeptides.

  5. Advanced asymmetric synthesis of (1R,2S)-1-amino-2-vinylcyclopropanecarboxylic acid by alkylation/cyclization of newly designed axially chiral Ni(II) complex of glycine Schiff base.

    PubMed

    Kawashima, Aki; Shu, Shuangjie; Takeda, Ryosuke; Kawamura, Akie; Sato, Tatsunori; Moriwaki, Hiroki; Wang, Jiang; Izawa, Kunisuke; Aceña, José Luis; Soloshonok, Vadim A; Liu, Hong

    2016-04-01

    Asymmetric synthesis of (1R,2S)-1-amino-2-vinylcyclopropanecarboxylic acid (vinyl-ACCA) is in extremely high demand due to the pharmaceutical importance of this tailor-made, sterically constrained α-amino acid. Here we report the development of an advanced procedure for preparation of the target amino acid via two-step SN2 and SN2' alkylation of novel axially chiral nucleophilic glycine equivalent. Excellent yields and diastereoselectivity coupled with reliable and easy scalability render this method of immediate use for practical synthesis of (1R,2S)-vinyl-ACCA.

  6. Design, synthesis, and evaluation of asymmetric EF24 analogues as potential anti-cancer agents for lung cancer.

    PubMed

    Wu, Jianzhang; Wu, Shoubiao; Shi, Lingyi; Zhang, Shanshan; Ren, Jiye; Yao, Song; Yun, Di; Huang, Lili; Wang, Jiabing; Li, Wulan; Wu, Xiaoping; Qiu, Peihong; Liang, Guang

    2017-01-05

    The nuclear factor-kappa B (NF-κB) signaling pathway has been targeted for the therapy of various cancers, including lung cancer. EF24 was considered as a potent inhibitor of NF-κB signaling pathway. In this study, a series of asymmetric EF24 analogues were synthesized and evaluated for their anti-cancer activity against three lung cancer cell lines (A549, LLC, H1650). Most of the compounds exhibited good anti-tumor activity. Among them, compound 81 showed greater cytotoxicity than EF24. Compound 81 also possessed a potent anti-migration and anti-proliferative ability against A549 cells in a concentration-dependent manner. Moreover, compound 81 induced lung cancer cells death by inhibiting NF-κB signaling pathway, and activated the JNK-mitochondrial apoptotic pathway by increasing reactive oxygen species (ROS) generation resulting in apoptosis. In summary, compound 81 is a valuable candidate for anti-lung cancer therapy.

  7. Synthesis and characterization of mesoporous spinel NiCo2O4 using surfactant-assembled dispersion for asymmetric supercapacitors

    NASA Astrophysics Data System (ADS)

    Hsu, Chun-Tsung; Hu, Chi-Chang

    2013-11-01

    A simple and scalable process has been developed for synthesizing spinel NiCo2O4 nanocrystals through a thermal decomposition method. The introduction of hexadecyltrimethylammonium bromide (CTAB, (C16H33)N(CH3)3Br) into precursor solutions significantly enhances the homogeneity and porosity of spinel NiCo2O4. The porosity and high specific surface area of NiCo2O4 preserves the brilliant pseudo-capacitive performances due to providing smooth paths for electrolyte penetration and ion diffusion into inner active sites. Morphologies and microstructures of the active materials are examined by transmission electron microscopic (TEM) and X-ray diffraction (XRD) analyses. Thermogravimetric analysis (TGA) is used to evaluate the thermal properties of precursor solutions. The electrochemical performances of NiCo2O4 are systematically characterized by cyclic voltammetry and charge-discharge tests. Asymmetric supercapacitors are assembled with these brilliant binary oxides as the positive electrode and activated carbon as the negative electrode. The highly porous NiCo2O4 exhibits superior capacitive performances, i.e., high specific capacitance (764 F g-1 at 2 mV s-1) and long cycle life.

  8. Synthesis and aggregation behaviour of luminescent mesomorphic zinc(II) complexes with 'salen' type asymmetric Schiff base ligands.

    PubMed

    Chakraborty, Sutapa; Bhattacharjee, Chira R; Mondal, Paritosh; Prasad, S Krishna; Rao, D S Shankar

    2015-04-28

    A new series of photoluminescent Zn(II)-salen type asymmetric Schiff base complexes, [ZnL], H2L = [N,N'-bis-(4-n-alkoxysalicylidene)-1,2-diaminopropane] (n = 12, 14 and 16) have been accessed and their mesomorphic and photophysical properties investigated. Though the ligands are non-mesomorphic, coordination to Zn(2+) ion induces liquid crystalline behaviour. The complexes exhibited a lamello-columnar phase (Coll) as characterized by a variable temperature powder X-ray diffraction (XRD) study. Intense blue emissions were observed for the complexes at room temperature in solution, in the solid state and in the mesophase. Aggregation properties of the complexes were explored in different solvents through absorption and photoluminescence studies. While de-aggregation to monomers occurred in coordinating solvents due to axial coordination to Zn(II), aggregates were formed in the solution of non-coordinating solvents. Density functional theory (DFT) computation carried out on a representative complex using a GAUSSIAN 09 program at the B3LYP level suggested a distorted square planar geometry. The results of a time-dependent DFT (TD-DFT) spectral correlative study showed the electronic properties of the complex molecule to be in compliance with the spectral data.

  9. 1: Mass asymmetric fission barriers for {sup 98}Mo; 2: Synthesis and characterization of actinide-specific chelating agents

    SciTech Connect

    Veeck, A.C. ||

    1996-08-01

    Excitation functions have been measured for complex fragment emission from the compound nucleus {sup 98}Mo, produced by the reaction of {sup 86}Kr with {sup 12}C. Mass asymmetric fission barriers have been obtained by fitting the excitation functions with a transition state formalism. The extracted barriers are {approximately} 5.7 MeV higher, on average, than the calculations of the Rotating Finite Range Model (RFRM). These data clearly show an isospin dependence of the conditional barriers when compared with the extracted barriers from {sup 90}Mo and {sup 94}Mo. Eleven different liquid/liquid extractants were synthesized based upon the chelating moieties 3,2-HOPO and 3,4-HOPO; additionally, two liquid/liquid extractants based upon the 1,2-HOPO chelating moiety were obtained for extraction studies. The Pu(IV) extractions, quite surprisingly, yielded results that were very different from the Fe(III) extractions. The first trend remained the same: the 1,2-HOPOs were the best extractants, followed closely by the 3,2-HOPOs, followed by the 3,4-HOPOs; but in these Pu(IV) extractions the 3,4-HOPOs performed much better than in the Fe(III) extractions. 129 refs.

  10. PEG mediated synthesis and biological evaluation of asymmetrical pyrazole curcumin analogues as potential analgesic, anti-inflammatory and antioxidant agents.

    PubMed

    Jadhav, Shravan Y; Bhosale, Raghunath B; Shirame, Sachin P; Patil, Sandeep B; Kulkarni, Suresh D

    2015-03-01

    The new series of asymmetrical pyrazole curcumin analogues 4a-g were synthesized by using polyethylene glycol (PEG-400) as a green reaction medium and evaluated for their in vivo analgesic and in vitro antioxidant (H2 O2 , DPPH, Ferrous reducing power and Nitric oxide scavenging activity) and anti-inflammatory activities. All the compounds synthesized 4a-g showed the potential to demonstrate analgesic activity as compared to the standard ibuprofen. Among the tested series, compounds 4e and 4b exhibited good hydrogen peroxide scavenging activity as compared to the standard butylated hydroxy toluene (BHT). Compounds 4b, 4d, 4f, and 4g showed good DPPH free radical scavenging activity. Compounds 4b, 4c, 4d, 4e and 4g showed excellent ferrous-reducing power activity, whereas all the compounds showed better nitric oxide scavenging activity than standard ascorbic acid. Additionally, all the synthesized compounds were also screened for their in vitro anti-inflammatory activity. Compounds 4b, 4d, 4f and 4g showed good anti-inflammatory activity as compared to standard diclofenac sodium.

  11. One-pot synthesis of γ-MnS/reduced graphene oxide with enhanced performance for aqueous asymmetric supercapacitors

    NASA Astrophysics Data System (ADS)

    Zhang, Guanggao; Kong, Menglai; Yao, Yadong; Long, Lu; Yan, Minglei; Liao, Xiaoming; Yin, Guangfu; Huang, Zhongbing; Asiri, Abdullah M.; Sun, Xuping

    2017-02-01

    In this work, γ-MnS/reduced graphene oxide composites (γ-MnS/rGO) were prepared using a facile one-pot hydrothermal method. As an electrode material for supercapacitors, the γ-MnS/rGO-60 composite obtained under dosages of graphene oxide was 60 mg and exhibited an enhanced specific capacitance of 547.6 F g-1 at a current density of 1 A g-1, and outstanding rate capability (65% capacitance retention at 20 A g-1), with superior cycling stability and electrochemical reversibility. An asymmetric supercapacitor assembled from γ-MnS/rGO-60 composite and rGO (γ-MnS/rGO-60//rGO) showed a voltage window of 0-1.6 V and delivered a high energy density of 23.1 W h kg-1 at a power density of 798.8 W kg-1, and 15.9 W h kg-1 at 4.5 kW kg-1. Moreover, two such 1.0 × 1.0 cm2 devices connected together in series easily light up a group of LED lights, showing its potential practical application as an attractive energy storage device.

  12. An organocatalytic Mannich/denitration reaction for the asymmetric synthesis of 3-ethylacetate-substitued 3-amino-2-oxindoles: formal synthesis of AG-041R.

    PubMed

    Zhao, Kun; Shu, Tao; Jia, Jiaqi; Raabe, Gerhard; Enders, Dieter

    2015-03-02

    The highly enantioselective organocatalytic addition of ethyl nitroacetate to isatin-derived N-Boc ketimines (Boc = tert-butoxycarbonyl), followed by the removal of the nitro group, is described. The scalable reaction sequence leads to the title compounds as important intermediates of pyrroloindoline alkaloids and related drugs in excellent yields and enantioselectivities. The synthesis of the hexahydrofurano[2,3-b]indole skeleton, the spirocarbamate oxindole unit, and the formal synthesis of AG-041R have been carried out to demonstrate the synthetic utility of this protocol.

  13. Absolutely classical spin states

    NASA Astrophysics Data System (ADS)

    Bohnet-Waldraff, F.; Giraud, O.; Braun, D.

    2017-01-01

    We introduce the concept of "absolutely classical" spin states, in analogy to absolutely separable states of bipartite quantum systems. Absolutely classical states are states that remain classical (i.e., a convex sum of projectors on coherent states of a spin j ) under any unitary transformation applied to them. We investigate the maximal size of the ball of absolutely classical states centered on the maximally mixed state and derive a lower bound for its radius as a function of the total spin quantum number. We also obtain a numerical estimate of this maximal radius and compare it to the case of absolutely separable states.

  14. Rhodium-catalyzed asymmetric addition of arylboronic acids to β-nitroolefins: formal synthesis of (S)-SKF 38393.

    PubMed

    Huang, Kung-Chih; Gopula, Balraj; Kuo, Ting-Shen; Chiang, Chien-Wei; Wu, Ping-Yu; Henschke, Julian P; Wu, Hsyueh-Liang

    2013-11-15

    An efficient enantioselective addition of an array of arylboronic acids to various β-nitrostyrenes catalyzed by a novel and reactive rhodium-diene catalyst (S/C up to 1000) was developed, providing β,β-diarylnitroethanes in good to high yields (62-99%) with excellent enantioselectivities (85-97% ee). The method was extended to 2-heteroarylnitroolefins and 2-alkylnitroolefins similarly providing the desired products with high enantioselectivities and yields. The usefulness of this method was demonstrated in the formal synthesis of the enantiomer of the dopamine receptor agonist and antagonist, SKF 38393.

  15. Absolute configuration of sex pheromone for tea tussock moth,Euproctis pseudoconspersa (strand)via synthesis of (R)- and (S)-10, 14-dimethyl-1-pentadecyl isobutyrates.

    PubMed

    Ichikawa, A; Yasuda, T; Wakamura, S

    1995-05-01

    (R)- and (S)-10,14-dimethyl-1-pentadecyl isobutyrates were synthesized from (S)- and (R)-citronellols, respectively. TheR enantiomer was as active as the natural pheromone but theS enantiomer was less active in the electrophysiological analyses, which provided conclusive proof that the absolute configuration of the natural pheromone isR.

  16. Asymmetric synthesis of α-amino acids via homologation of Ni(II) complexes of glycine Schiff bases; Part 1: alkyl halide alkylations.

    PubMed

    Sorochinsky, Alexander E; Aceña, José Luis; Moriwaki, Hiroki; Sato, Tatsunori; Soloshonok, Vadim A

    2013-10-01

    Alkylations of chiral or achiral Ni(II) complexes of glycine Schiff bases constitute a landmark in the development of practical methodology for asymmetric synthesis of α-amino acids. Straightforward, easy preparation as well as high reactivity of these Ni(II) complexes render them ready available and inexpensive glycine equivalents for preparing a wide variety of α-amino acids, in particular on a relatively large scale. In the case of Ni(II) complexes containing benzylproline moiety as a chiral auxiliary, their alkylation proceeds with high thermodynamically controlled diastereoselectivity. Similar type of Ni(II) complexes derived from alanine can also be used for alkylation providing convenient access to quaternary, α,α-disubstituted α-amino acids. Achiral type of Ni(II) complexes can be prepared from picolinic acid or via recently developed modular approach using simple secondary or primary amines. These Ni(II) complexes can be easily mono/bis-alkylated under homogeneous or phase-transfer catalysis conditions. Origin of diastereo-/enantioselectivity in the alkylations reactions, aspects of practicality, generality and limitations of this methodology is critically discussed.

  17. Studies on an (S)-2-Amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic Acid (AMPA) Receptor Antagonist IKM-159: Asymmetric Synthesis, Neuroactivity, and Structural Characterization

    PubMed Central

    Juknaitė, Lina; Sugamata, Yutaro; Tokiwa, Kazuya; Ishikawa, Yuichi; Takamizawa, Satoshi; Eng, Andrew; Sakai, Ryuichi; Pickering, Darryl S.; Frydenvang, Karla; Swanson, Geoffrey T.; Kastrup, Jette S.; Oikawa, Masato

    2015-01-01

    IKM-159 was developed and identified as a member of a new class of heterotricyclic glutamate analogues that act as AMPA receptor-selective antagonists. However, it was not known which enantiomer of IKM-159 was responsible for its pharmacological activities. Here, we report in vivo and in vitro neuronal activities of both enantiomers of IKM-159 prepared by enantioselective asymmetric synthesis. By employment of (R)-2-amino-2-(4-methoxyphenyl)ethanol as a chiral auxiliary, (2R)-IKM-159 and the (2S)-counterpart were successfully synthesized in 0.70% and 1.5% yields, respectively, over a total of 18 steps. Both behavioral and electrophysiological assays showed that the biological activity observed for the racemic mixture was reproduced only with (2R)-IKM-159, whereas the (2S)-counterpart was inactive in both assays. Racemic IKM-159 was crystallized with the ligand-binding domain of GluA2, and the structure revealed a complex containing (2R)-IKM-159 at the glutamate binding site. (2R)-IKM-159 locks the GluA2 in an open form, consistent with a pharmacological action as competitive antagonist of AMPA receptors. PMID:23432124

  18. Asymmetric organocatalytic synthesis of tertiary azomethyl alcohols: key intermediates towards azoxy compounds and α-hydroxy-β-amino esters.

    PubMed

    Carmona, José A; Gonzalo, Gonzalo de; Serrano, Inmaculada; Crespo-Peña, Ana M; Šimek, Michal; Monge, David; Fernández, Rosario; Lassaletta, José M

    2017-04-05

    A series of peracylated glycosamine-derived thioureas have been synthesized and their behavior as bifunctional organocatalysts has been tested in the enantioselective nucleophilic addition of formaldehyde tert-butyl hydrazone to aliphatic α-keto esters for the synthesis of tertiary azomethyl alcohols. Using the 1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy-β-d-glucosamine derived 3,5-bis-(trifluoromethyl)phenyl thiourea the reaction could be accomplished with high yields (75-98%) and moderate enantioselectivities (50-64% ee). Subsequent high-yielding and racemization-free tranformations of both aromatic- and aliphatic-substituted diazene products in a one pot fashion provide a direct entry to valuable azoxy compounds and α-hydroxy-β-amino esters.

  19. Organocatalytic Asymmetric Biginelli-like Reaction Involving Isatin.

    PubMed

    Stucchi, Mattia; Lesma, Giordano; Meneghetti, Fiorella; Rainoldi, Giulia; Sacchetti, Alessandro; Silvani, Alessandra

    2016-03-04

    The first asymmetric, Brønsted acid catalyzed Biginelli-like reaction of a ketone has been developed, employing N-substituted isatins as carbonyl substrates, and urea and alkyl acetoacetates as further components. BINOL-derived phosphoric acid catalysts have been used to achieve the synthesis of a small library of chiral, enantioenriched spiro(indoline-pyrimidine)-diones derivatives. The absolute configuration of the new spiro stereocenter was assessed on diastereoisomeric derivatives through computer-assisted NMR spectroscopy. X-ray diffractometry allowed the disclosure of the overall molecular conformation in the solid state and the characterization of the crystal packing of a Br-substituted Biginelli-like derivative, while computational studies on the reaction transition state allowed us to rationalize the stereochemical outcome.

  20. Absolute nuclear material assay

    DOEpatents

    Prasad, Manoj K [Pleasanton, CA; Snyderman, Neal J [Berkeley, CA; Rowland, Mark S [Alamo, CA

    2012-05-15

    A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

  1. Absolute nuclear material assay

    DOEpatents

    Prasad, Manoj K.; Snyderman, Neal J.; Rowland, Mark S.

    2010-07-13

    A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

  2. Origin of stereocontrol in guanidine-bisurea bifunctional organocatalyst that promotes α-hydroxylation of tetralone-derived β-ketoesters: asymmetric synthesis of β- and γ-substituted tetralone derivatives via organocatalytic oxidative kinetic resolution.

    PubMed

    Odagi, Minami; Furukori, Kota; Yamamoto, Yoshiharu; Sato, Makoto; Iida, Keisuke; Yamanaka, Masahiro; Nagasawa, Kazuo

    2015-02-11

    The mechanism of asymmetric α-hydroxylation of tetralone-derived β-ketoesters with guanidine-bisurea bifunctional organocatalyst in the presence of cumene hydroperoxide (CHP) was examined by means of DFT calculations to understand the origin of the stereocontrol in the reaction. The identified transition-state model was utilized to design an enantioselective synthesis of β- or γ-substituted tetralones by catalytic oxidative kinetic resolution reaction of tetralone-derived β-ketoesters. This kinetic resolution reaction proceeded with high selectivity, and selectivity factors (s value) of up to 99 were obtained. The potential utility of this oxidative kinetic resolution method for synthesis of natural products was confirmed by applying it to achieve an enantioselective synthesis of (+)-linoxepin (13) from β-substituted tetralone rac-7 in only six steps.

  3. Synthesis and anti-HIV activity of lupane and olean-18-ene derivatives. Absolute configuration of 19,20-epoxylupanes by VCD.

    PubMed

    Gutiérrez-Nicolás, Fátima; Gordillo-Román, Bárbara; Oberti, Juan C; Estévez-Braun, Ana; Ravelo, Angel G; Joseph-Nathan, Pedro

    2012-04-27

    Lupane triterpenoids 2 and 5-12 and oleanene derivatives 13 and 14 were prepared from lupeol (1), betulin (3), and germanicol (4). They were tested for anti-HIV activity, and some structure-activity relationships were outlined. The 20-(S) absolute configuration of epoxylupenone (8) was assessed by comparison of the observed and DFT-calculated vibrational circular dichroism spectra. The CompareVOA algorithm was employed to support the C-20 configuration assignment. The 20,29 double bond in lupenone (2) and 3-epilupeol (15) was stereoselectively epoxidized to produce 20-(S)-8 and 20-(S)-16, respectively, an assignment in agreement with their X-ray diffraction structures.

  4. The Origin of Remarkable Chromatographic Differences in Novel Azulenyl-1,5-diols; & Synthesis and Use of Phosphinine and Phosphabarrelene Ligands for Asymmetric Catalysis

    NASA Astrophysics Data System (ADS)

    Horgen, Dana Ann

    The synthesis, characterization and analysis of novel chiral molecules advance many areas of synthetic organic chemistry, both industrially and academically. This work touches on three of the major methods for obtaining enantiomerically pure compounds. Based on the observation of a remarkably large difference in the silica TLC mobility of a pair of azulene 1,5-diol diastereomers, a series of such azulene 1,5-diols were prepared. Every pair of diastereomers was especially well separated, and X-ray crystallography revealed a conformational explanation of the large differences in mobility. The separation of the diol enantiomers was then studied on two chiral HLPC columns. The enantiomers were well-resolved, the separation appearing to benefit from the presence of the azulene ring. In addition, the more polar diastereomers on silica TLC gave dramatically better enantiomer separations on a Chiralcel-OD-H column. Very few chiral phosphinine and phosphabarrelene ligands have been reported in the literature but have shown promise as good ligands for asymmetric catalysis. Our group had previously synthesized a C2-symmetric chiral bis-camphorphosphinine and the derived bis-camphorphosphabarrelene but neither had been tested as ligands for hydroformylation. In this work, optimization of the synthesis of these two compounds was undertaken. In addition, modifications to the structure of these molecules that incorporated electron donating (N,N-dimethylaminophenyl-) or electron withdrawing (trifluoromethyl-) substituents were made in an attempt to affect the electronic nature of the phosphorus atom. Steric modifications were also done to create a more hindered environment around the phosphorus atom. The activity and selectivity of bis-camphorphosphinine, bis-camphorphosphabarrelene and other chiral phosphinine molecules serving as ligands in the rhodiumcatalyzed hydroformylation of styrene were compared to other phosphorus ligands recently published in the literature. All of

  5. Revision of absolute configuration of enantiomeric (methylenecyclopropyl)carbinols obtained from (R)-(-)- and (S)-(+)-epichlorohydrin and methylenetriphenylphosphorane. Implications for reaction mechanism and improved synthesis of antiviral methylenecyclopropane analogues of nucleosides.

    PubMed

    Chen, Xinchao; Zemlicka, Jiri

    2002-01-11

    Absolute configurations of enantiomeric methylenecyclopropanecarbinols obtained by reaction of (R)- and (S)-epichlorohydrin 5 with methylenetriphenylphosphorane or resolution of the corresponding oxaphospholane 6 via a salt with L-(+)-tartaric acid and subsequent Wittig transformation with formaldehyde were revised. The (-)-oxaphospholane 6 has the S,S and (-)-(methylenecyclopropyl)carbinol (4) the R configuration. The configurations of (+)-6 and (+)-4 are then R,R and S, respectively. These assignments are in accord with an initial attack of phosphorane at the oxirane ring of epichlorohydrin. An improved preparation of key enantiomeric intermediates (R)-1a and (S)-1a, important for synthesis of antiviral purine methylenecyclopropane analogues of nucleosides, is also described.

  6. Enantioselective synthesis of beta-aryl-gamma-amino acid derivatives via Cu-catalyzed asymmetric 1,4-reductions of gamma-phthalimido-substituted alpha,beta-unsaturated carboxylic acid esters.

    PubMed

    Deng, Jun; Hu, Xiang-Ping; Huang, Jia-Di; Yu, Sai-Bo; Wang, Dao-Yong; Duan, Zheng-Chao; Zheng, Zhuo

    2008-08-01

    A series of chiral beta-aryl-substituted gamma-amino butyric acid derivatives were synthesized in good enantioselectivities via the Cu-catalyzed asymmetric conjugate reduction of gamma-phthalimido-alpha,beta-unsaturated carboxylic acid esters using Cu(OAc)2 x H2O as a catalyst precursor, (S)-BINAP as a ligand, PMHS as a hydride source, and t-BuOH as an additive. The methodology has been applied successfully to the enantioselective synthesis of a chiral pharmaceutical, (R)-baclofen.

  7. Applications of organocatalytic asymmetric synthesis to drug prototypes--dual action and selective inhibitors of n-nitric oxide synthase with activity against the 5-HT1D/1B subreceptors.

    PubMed

    Hanessian, Stephen; Stoffman, Eli; Mi, Xueling; Renton, Paul

    2011-03-04

    The scope of MacMillan's organocatalytic asymmetric conjugate addition reaction of indoles and electron-rich aromatics to α,β-unsaturated aldehydes has been extended to the use of 3-amino crotonaldehydes as substrates. The aromatics used include indoles as well as an aniline and a furan. The scope and effect of the groups on nitrogen (R, R') has also been studied. The method has been applied to the concise synthesis of an advanced precursor to S-(+)-1, a drug prototype for the treatment of migraine headaches.

  8. Asymmetric synthesis of N,O,O,O-tetra-acetyl d-lyxo-phytosphingosine, jaspine B (pachastrissamine), 2-epi-jaspine B, and deoxoprosophylline via lithium amide conjugate addition.

    PubMed

    Abraham, Elin; Brock, E Anne; Candela-Lena, José I; Davies, Stephen G; Georgiou, Matthew; Nicholson, Rebecca L; Perkins, James H; Roberts, Paul M; Russell, Angela J; Sánchez-Fernández, Elena M; Scott, Philip M; Smith, Andrew D; Thomson, James E

    2008-05-07

    The highly diastereoselective anti-aminohydroxylation of (E)-gamma-tri-iso-propylsilyloxy-alpha,beta-unsaturated esters, via conjugate addition of lithium (S)-N-benzyl-N-(alpha-methylbenzyl)amide and subsequent in situ enolate oxidation with (+)-(camphorsulfonyl)oxaziridine, has been used as the key step in the asymmetric synthesis of N,O,O,O-tetra-acetyl d-lyxo-phytosphingosine (20% yield over 7 steps), the anhydrophytosphingosine jaspine B (10% yield over 9 steps), 2-epi-jaspine B (14% yield over 9 steps), and the Prosopis alkaloid deoxoprosophylline (26% yield over 7 steps).

  9. Combinatorial synthesis of functionalized chiral and doubly chiral ionic liquids and their applications as asymmetric covalent/non-covalent bifunctional organocatalysts.

    PubMed

    Zhang, Long; Luo, Sanzhong; Mi, Xueling; Liu, Song; Qiao, Yupu; Xu, Hui; Cheng, Jin-Pei

    2008-02-07

    A facile combinatorial strategy was developed for the construction of libraries of functionalized chiral ionic liquids (FCILs) including doubly chiral ionic liquids and bis-functional chiral ionic liquids. These FCIL libraries have the potential to be used as asymmetric catalysts or chiral ligands. As an example, novel asymmetric bifunctional catalysts were developed by simultaneously incorporating functional groups onto the cation and anion. The resultant bis-functionalized CILs showed significantly improved stereoselectivity over the mono-functionalized parent CILs.

  10. "Marking" the nitrogen atoms of phenyl-(2-pyridyl)-(3-pyridyl)-(4-pyridyl)-methane. Synthesis and absolute configuration of the corresponding tris(pyridine N-oxide).

    PubMed

    Matsumoto, Kouzou; Miki, Kaori; Inagaki, Takuya; Nehira, Tatsuo; Pescitelli, Gennaro; Hirao, Yasukazu; Kurata, Hiroyuki; Kawase, Takeshi; Kubo, Takashi

    2011-08-01

    To "mark" the nitrogen atoms in phenyl-(2-pyridyl)-(3-pyridyl)-(4-pyridyl)methane (1), we have synthesized the corresponding tris(pyridine N-oxide) 2 by oxidation of 1 with m-chloroperbenzoic acid. The nitrogen atoms of 2 are unequivocally determined by the X-ray crystal analysis of a single crystal of rac-2 whereas the nitrogen atoms cannot be assigned at all in the case of rac-1. N-Oxide 2 can be resolved by chiral high-performance liquid chromatography under similar conditions to those used for the resolution of 1. The calculated circular dichroism (CD) curve for (R)-2 on the basis of time-dependent density functional theory reproduces the experimental spectra very well to suggest that the second-eluted fraction ([CD(+)283]-2) is the R isomer, namely (R)-[CD(+)283]-2. The independent absolute configuration determinations for 1 and 2 are in keeping with the chemical correlation between the two compounds by oxidation of (R)-1 into (R)-2.

  11. Gold(I)-catalyzed asymmetric induction of planar chirality by intramolecular nucleophilic addition to chromium-complexed alkynylarenes: asymmetric synthesis of planar chiral (1H-isochromene and 1,2-dihydroisoquinoline)chromium complexes.

    PubMed

    Murai, Masato; Sota, Yumi; Onohara, Yuki; Uenishi, Jun'ichi; Uemura, Motokazu

    2013-11-01

    Gold(I)-catalyzed asymmetric intramolecular cyclization of prochiral 1,3-dihydroxymethyl-2-alkynylbenzene or 1,3-bis(carbamate)-2-alkynylbenzene tricarbonylchromium complexes with axially chiral diphosphine ligand gave planar chiral tricarbonylchromium complexes of 1H-isochromene or 1,2-dihydroisoquinoline with high enantioselectivity. An enantiomeric excess of the planar chiral arene chromium complexes was largely affected by a combination of axially chiral diphosphine(AuCl)2 precatalysts and silver salts. In the case of 1,3-dihydroxymethyl-2-alkynylbenzene chromium complexes, a system of segphos(AuCl)2 with AgBF4 resulted in the formation of the corresponding antipode.

  12. Absolute and relative blindsight.

    PubMed

    Balsdon, Tarryn; Azzopardi, Paul

    2015-03-01

    The concept of relative blindsight, referring to a difference in conscious awareness between conditions otherwise matched for performance, was introduced by Lau and Passingham (2006) as a way of identifying the neural correlates of consciousness (NCC) in fMRI experiments. By analogy, absolute blindsight refers to a difference between performance and awareness regardless of whether it is possible to match performance across conditions. Here, we address the question of whether relative and absolute blindsight in normal observers can be accounted for by response bias. In our replication of Lau and Passingham's experiment, the relative blindsight effect was abolished when performance was assessed by means of a bias-free 2AFC task or when the criterion for awareness was varied. Furthermore, there was no evidence of either relative or absolute blindsight when both performance and awareness were assessed with bias-free measures derived from confidence ratings using signal detection theory. This suggests that both relative and absolute blindsight in normal observers amount to no more than variations in response bias in the assessment of performance and awareness. Consideration of the properties of psychometric functions reveals a number of ways in which relative and absolute blindsight could arise trivially and elucidates a basis for the distinction between Type 1 and Type 2 blindsight.

  13. β,γ-CHF- and β,γ-CHCl-dGTP diastereomers: synthesis, discrete 31P NMR signatures and absolute configurations of new stereochemical probes for DNA polymerases

    PubMed Central

    Wu, Yue; Zakharova, Valeria M.; Kashemirov, Boris A.; Goodman, Myron F.; Batra, Vinod K.; Wilson, Samuel H.; McKenna, Charles E.

    2012-01-01

    Deoxynucleoside 5′-triphosphate analogues in which the β,γ-bridging oxygen has been replaced with a CXY group are useful chemical probes to investigate DNA polymerase catalytic and base selection mechanisms. A limitation of such probes has been that conventional synthetic methods generate a mixture of diastereomers when the bridging carbon substitution is non-equivalent (X ≠ Y). We report here a general solution to this long-standing problem with four examples of individual β,γ-CXY dNTP diastereomers: (S)- and (R)-β,γ-CHCl dGTP (12a-1, 12a-2) and (S)- and (R)-β,γ-CHF dGTP (12b-1, 12b-2). Central to their preparation was conversion of the achiral parent bisphosphonic acids to P,C-dimorpholinamide derivatives (7) of their (R)-mandelic acid monoesters (6), which provided access to the individual diastereomers 7a-1, 7a-2, 7b-1, and 7b-2 by preparative HPLC. Selective acidic hydrolysis of the P-N bond then afforded the “ portal ” diastereomers 10, which were readily coupled to morpholine-activated dGMP. Removal of the chiral auxiliary by H2 (Pd/C) afforded the four individual diastereomeric nucleotides (12), which were characterized by 31P, 1H and 19F NMR, and by MS. After treatment with Chelex®-100 to remove traces of paramagnetic ions, at pH ~10 the diastereomer pairs 12a and 12b exhibit discrete Pα and Pβ 31P resonances. The more upfield Pα and more downfield Pβ resonances (and also the more upfield 19F NMR resonance in 12b) are assigned to the (R) configuration at the Pβ-CHX-Pγ carbons, based on the absolute configurations of the individual diastereomers as determined by X-ray crystallographic structures of their ternary complexes with DNA-pol β. PMID:22397499

  14. Asymmetric Earth

    NASA Astrophysics Data System (ADS)

    Doglioni, Carlo; Carminati, Eugenio; Crespi, Mattia; Cuffaro, Marco; Ismail-Zadeh, Alik; Levshin, Anatoli; Panza, Giuliano F.; Riguzzi, Federica

    2010-05-01

    The net rotation, or so-called W-ward drift of the lithosphere, implies a decoupling of the plates relative to the underlying asthenosphere, and a relative "E-ward" mantle flow. This polarized flow can account for a number of asymmetries. When comparing the W-directed versus the E- to NE-directed subduction zones, as a general observation, they have the subduction hinge diverging versus converging relative to the upper plate; low versus high topography and structural elevation respectively; deep versus shallow trenches and foreland basins; shallow versus deep decollement; low versus high basement involvement; high versus low heat flow and gravity anomaly; shallow versus deep asthenosphere; etc. The western limbs of rift zones show S-waves faster in the lithosphere and slower in the asthenosphere with respect to the eastern limb. The asymmetry can be recognized when moving along the "tectonic equator", which describes the fastest flow of plates relative to the mantle, and it undulates relative to the geographic equator. In our reconstructions, the best fit for the tectonic equator has a pole of rotation at latitude -56.4° and longitude 136.7°, with an angular velocity of 1.2036°/Ma. Shear-wave splitting alignments tend to parallel the tectonic flow, apart along the subduction zones where they become orthogonal, as a flow encountering an obstacle. The tectonic equator lies close to the revolution plane of the Moon about the Earth. All these data and interpretations point for an asymmetric Earth, whose nature appears to be related to the rotation and its tidal despinning, combined with the thermal cooling of the planet. However, this model has been questioned on the basis of the high viscosity so far inferred in the asthenosphere. Preliminary modelling shows that the tidal oscillation can generate gravitational wave propagation in the lithosphere, and the wave velocity can increase with the decrease of the asthenospheric viscosity.

  15. Chemoenzymatic asymmetric total syntheses of antitumor agents (3R,9R,10R)- and (3S,9R,10R)-Panaxytriol and (R)- and (S)-Falcarinol from Panax ginseng using an enantioconvergent enzyme-triggered cascade reaction.

    PubMed

    Mayer, Sandra F; Steinreiber, Andreas; Orru, Romano V A; Faber, Kurt

    2002-12-27

    Total asymmetric synthesis of two components of Panax ginseng showing antitumor activity, i.e., (3R,9R,10R)- and (3S,9R,10R)-Panaxytriol and of both enantiomers of Falcarinol was accomplished. Due to the fact that the synthetic strategy was based on enantioconvergent biotransformations, the occurrence of any undesired stereoisomer was entirely avoided. The absolute configuration of naturally occurring Panaxytriol was confirmed to be (3R,9R,10R) on the basis of optical rotation values. It was shown that enzyme-triggered cascade reactions represent a valuable tool for the synthesis of natural products.

  16. Absolute neutrino mass scale

    NASA Astrophysics Data System (ADS)

    Capelli, Silvia; Di Bari, Pasquale

    2013-04-01

    Neutrino oscillation experiments firmly established non-vanishing neutrino masses, a result that can be regarded as a strong motivation to extend the Standard Model. In spite of being the lightest massive particles, neutrinos likely represent an important bridge to new physics at very high energies and offer new opportunities to address some of the current cosmological puzzles, such as the matter-antimatter asymmetry of the Universe and Dark Matter. In this context, the determination of the absolute neutrino mass scale is a key issue within modern High Energy Physics. The talks in this parallel session well describe the current exciting experimental activity aiming to determining the absolute neutrino mass scale and offer an overview of a few models beyond the Standard Model that have been proposed in order to explain the neutrino masses giving a prediction for the absolute neutrino mass scale and solving the cosmological puzzles.

  17. The absolute path command

    SciTech Connect

    Moody, A.

    2012-05-11

    The ap command traveres all symlinks in a given file, directory, or executable name to identify the final absolute path. It can print just the final path, each intermediate link along with the symlink chan, and the permissions and ownership of each directory component in the final path. It has functionality similar to "which", except that it shows the final path instead of the first path. It is also similar to "pwd", but it can provide the absolute path to a relative directory from the current working directory.

  18. Bimetallic Gold(I)/Chiral N,N'-Dioxide Nickel(II) Asymmetric Relay Catalysis: Chemo- and Enantioselective Synthesis of Spiroketals and Spiroaminals.

    PubMed

    Li, Jun; Lin, Lili; Hu, Bowen; Lian, Xiangjin; Wang, Gang; Liu, Xiaohua; Feng, Xiaoming

    2016-05-10

    A highly efficient asymmetric cascade reaction between keto esters and alkynyl alcohols and amides is reported. The success of the reaction was attributed to the combination of chiral Lewis acid N,N'-dioxide nickel(II) catalysis with achiral π-acid gold(I) catalysis working as an asymmetric relay catalytic system. The corresponding spiroketals and spiroaminals were synthesized in up to 99 % yield, 19:1 d.r., and more than 99 % ee under mild reaction conditions. Control experiments suggest that the N,N'-dioxide ligand was essential for the formation of the spiro products.

  19. Efficient and selective synthesis of 6,7-Dehydrostipiamide via Zr-catalyzed asymmetric carboalumination and Pd-catalyzed cross-coupling of organozincs.

    PubMed

    Zeng, Xingzhong; Zeng, Fanxing; Negishi, Ei-ichi

    2004-09-16

    [structure: see text] 6,7-Dehydrostipiamide has been synthesized in 23% yield in 15 steps in the longest linear sequence through the application of the Zr-catalyzed asymmetric carboalumination and the Pd-catalyzed organozinc cross-coupling in addition to the Brown crotylboration, the Corey-Peterson olefination, and the Corey-Fuchs reaction for carbon-carbon bond formation.

  20. Dual metal and Lewis base catalysis approach for asymmetric synthesis of dihydroquinolines and the α-arylation of aldehydes via N-acyliminium ions.

    PubMed

    Volla, Chandra M R; Fava, Eleonora; Atodiresei, Iuliana; Rueping, Magnus

    2015-11-11

    A dual catalytic system consisting of indium triflate and a chiral imidazolidinone catalyzes the asymmetric addition of aldehydes to N-acyl quinoliniums furnishing optically active dihydroquinolines in good yields and excellent selectivities. The products were further functionalized into optically active tetrahydroquinolines, quinolines and 6-oxa-2-aza-bicyclo[3.3.1]nonanes.

  1. Rhodium-catalyzed asymmetric addition of arylboronic acids to cyclic N-sulfonyl ketimines towards the synthesis of α,α-diaryl-α-amino acid derivatives.

    PubMed

    Takechi, Ryosuke; Nishimura, Takahiro

    2015-05-07

    Rhodium/chiral diene complex-catalyzed asymmetric addition of arylboronic acids to cyclic ketimines having an ester group proceeded to give the corresponding α-amino acid derivatives in high yields with high enantioselectivity. The cyclic amino acid derivative was transformed into a linear α,α-diaryl-substituted α-N-methylamino acid ester.

  2. Asymmetric synthesis of 3-oxa-15-Deoxy-16-(m-tolyl)-17,18,19,20-tetranorisocarbacyclin and its neuroprotective analogue 15-Deoxy-16-(m-tolyl)-17,18,19,20-tetranorisocarbacyclin based on the conjugate addition-azoalkene-asymmetric olefination strategy.

    PubMed

    van de Sande, Marc; Gais, Hans-Joachim

    2007-01-01

    A fully stereocontrolled synthesis of 3-oxa-15-deoxy-16-(m-tolyl)-17,18,19,20-tetranorisocarbacyclin (3-oxa-15-deoxy-TIC, 7 b) and a formal one of 15-deoxy-16-(m-tolyl)-17,18,19,20-tetranorisocarbacyclin (15-deoxy-TIC, 7 a) are described. 15-Deoxy-TIC is specific for the neuronal prostacyclin receptor (IP2) and exhibits neuroprotective activities, and the new 3-oxa-15-deoxy-TIC is expected to be metabolically more stable than 15-deoxy-TIC. The syntheses of 7 a and 7 b are based on the convergent conjugate addition-azoalkene-asymmetric olefination strategy. Key building blocks are the readily available bicyclic azoalkene 14 and the alkenylcopper derivative 15. The stereoselective conjugate addition of 15 to 14 gave hydrazone 13, which was stereoselectively converted to the bicyclic ketone 11. The key steps for the construction of the alpha side chain of 7 a and 7 b and the regioselective introduction of the endocyclic Delta6,6a double bond are: 1) a highly selective asymmetric olefination of ketone 11 with the chiral Horner-Wadsworth-Emmons reagent 28 and 2) a regioselective deconjugation of the alpha,beta-unsaturated ester (E)-10 with the chiral lithium amide 29, which gave the beta,gamma-unsaturated ester anti-9 with high selectivity. The homoallylic alcohol 8 served at a late stage as the joint intermediate in the syntheses of 7 a and 7 b. While an etherification of 8 furnished, after hydrolysis and deprotection, 3-oxa-15-deoxy-TIC, its alkylation afforded alcohol 37, the known precursor for the synthesis of 15-deoxy-TIC.

  3. Asymmetric Ashes

    NASA Astrophysics Data System (ADS)

    2006-11-01

    that oscillate in certain directions. Reflection or scattering of light favours certain orientations of the electric and magnetic fields over others. This is why polarising sunglasses can filter out the glint of sunlight reflected off a pond. When light scatters through the expanding debris of a supernova, it retains information about the orientation of the scattering layers. If the supernova is spherically symmetric, all orientations will be present equally and will average out, so there will be no net polarisation. If, however, the gas shell is not round, a slight net polarisation will be imprinted on the light. This is what broad-band polarimetry can accomplish. If additional spectral information is available ('spectro-polarimetry'), one can determine whether the asymmetry is in the continuum light or in some spectral lines. In the case of the Type Ia supernovae, the astronomers found that the continuum polarisation is very small so that the overall shape of the explosion is crudely spherical. But the much larger polarization in strongly blue-shifted spectral lines evidences the presence, in the outer regions, of fast moving clumps with peculiar chemical composition. "Our study reveals that explosions of Type Ia supernovae are really three-dimensional phenomena," says Dietrich Baade. "The outer regions of the blast cloud is asymmetric, with different materials found in 'clumps', while the inner regions are smooth." "This study was possible because polarimetry could unfold its full strength thanks to the light-collecting power of the Very Large Telescope and the very precise calibration of the FORS instrument," he adds. The research team first spotted this asymmetry in 2003, as part of the same observational campaign (ESO PR 23/03 and ESO PR Photo 26/05). The new, more extensive results show that the degree of polarisation and, hence, the asphericity, correlates with the intrinsic brightness of the explosion. The brighter the supernova, the smoother, or less clumpy

  4. Enantioselective Cyclopropanation with α-Alkyl-α-diazoesters Catalyzed by Chiral Oxazaborolidinium Ion: Total Synthesis of (+)-Hamavellone B.

    PubMed

    Shim, Su Yong; Kim, Jae Yeon; Nam, Miso; Hwang, Geum-Sook; Ryu, Do Hyun

    2016-01-15

    Chiral oxazaborolidinium ion-catalyzed asymmetric cyclopropanation of α- or α,β-substituted acroleins with α-alkyl-α-diazoesters has been developed. With this methodology, chiral functionalized cyclopropanes containing a quaternary stereogenic center were obtained with high to excellent enantioselectivities (up to >99% ee). The synthetic utility of optically enriched functionalized cyclopropane was demonstrated in the first total synthesis of (+)-hamavellone B, which establishes the absolute configuration of natural (+)-hamavellone B.

  5. Asymmetric Redox-Annulation of Cyclic Amines

    PubMed Central

    2015-01-01

    Cyclic amines such as 1,2,3,4-tetrahydroisoquinoline undergo regiodivergent annulation reactions with 4-nitrobutyraldehydes. These redox-neutral transformations enable the asymmetric synthesis of highly substituted polycyclic ring systems in just two steps from commercial materials. The utility of this process is illustrated in a rapid synthesis of (−)-protoemetinol. Computational studies provide mechanistic insights and implicate the elimination of acetic acid from an ammonium nitronate intermediate as the rate-determining step. PMID:26348653

  6. Asymmetric dark matter

    SciTech Connect

    Kumar, Jason

    2014-06-24

    We review the theoretical framework underlying models of asymmetric dark matter, describe astrophysical constraints which arise from observations of neutron stars, and discuss the prospects for detecting asymmetric dark matter.

  7. Nucleophilic Chiral Phosphines: Powerful and Versatile Catalysts for Asymmetric Annulations

    PubMed Central

    Xiao, Yumei; Guo, Hongchao; Kwon, Ohyun

    2016-01-01

    Recent advances in chiral-phosphine-catalyzed asymmetric annulation reactions; including annulations of allenes, alkynes, Morita–Baylis–Hillman (MBH) carbonates, and ketenes; and their applications in the synthesis of bioactive molecules and natural products are reviewed. PMID:28077882

  8. Asymmetric AB3 Miktoarm Star Polymers: Synthesis, Self-Assembly, and Study of Micelle Stability Using AF4 for Efficient Drug Delivery.

    PubMed

    Moquin, Alexandre; Sharma, Anjali; Cui, Yiming; Lau, Anthony; Maysinger, Dusica; Kakkar, Ashok

    2015-12-01

    A simple and versatile methodology, which employs a combination of ring-opening polymerization and alkyne-azide click chemistry to synthesize amphiphilic AB3 miktoarm stars, is reported. Their aqueous self-assembly behavior was studied using dynamic light scattering, fluorescence, and asymmetrical flow field-flow fractionation (AF4). AB3 miktoarm stars form micelles which incorporate curcumin with high efficiency, and significantly reduce the viability of glioblastoma cells in spheroids. We demonstrate that AF4 is an effective technique to determine the size distribution of self-assembled structures exposed to a biological medium. The ease, with which asymmetric AB3 miktoarm polymers are constructed, provides a platform that can be widely employed to deliver a variety of lipophilic drugs.

  9. Dynamic kinetic resolution in the stereoselective synthesis of 4,5-diaryl cyclic sulfamidates by using chiral rhodium-catalyzed asymmetric transfer hydrogenation.

    PubMed

    Han, Juae; Kang, Soyeong; Lee, Hyeon-Kyu

    2011-04-07

    The dynamic kinetic resolution of 4,5-diaryl cyclic sulfamidate imines was achieved via asymmetric transfer hydrogenation using a HCO(2)H/Et(3)N mixture as the hydrogen source and chiral Rh catalysts (R,R)- or (S,S)-RhCl(TsDPEN)Cp* affording the corresponding cyclic sulfamidates in good yields with up to >20 : 1 dr and up to >99% ee.

  10. Stereoselective Synthesis of 4-Substituted Cyclic Sulfamidate-5-Phosphonates by Using Rh-Catalyzed, Asymmetric Transfer Hydrogenation with Accompanying Dynamic Kinetic Resolution.

    PubMed

    Seo, Yeon Ji; Kim, Jin-ah; Lee, Hyeon-Kyu

    2015-09-04

    Dynamic kinetic resolution driven, asymmetric transfer hydrogenation of 4-substituted cyclic sulfamidate imine-5-phosphonates produces the corresponding cyclic sulfamidate-5-phosphonates. The process employs a HCO2H/Et3N mixture as the hydrogen source and the chiral Rh catalysts, (R,R)- or (S,S)-Cp*RhCl(TsDPEN), and it takes place at room temperature within 1 h with high yields and high levels of stereoselectivity.

  11. Asymmetric organocatalyzed Michael addition of nitromethane to a 2-oxoindoline-3-ylidene acetaldehyde and the three one-pot sequential synthesis of (-)-horsfiline and (-)-coerulescine.

    PubMed

    Mukaiyama, Takasuke; Ogata, Kento; Sato, Itaru; Hayashi, Yujiro

    2014-10-13

    (-)-Horsfiline and (-)-coerulescine were synthesized through three one-pot operations in 33 and 46% overall yield, respectively. Key to the success was the efficient use of a diarylprolinol silyl ether to catalyze the asymmetric Michael addition of nitromethane to a 2-oxoindoline-3-ylidene acetaldehyde. This allowed the all-carbon quaternary, spirocyclic carbon stereocenter to be constructed in good yield with excellent enantioselectivity.

  12. Enantioselective Friedel-Crafts alkylation of indoles with alkylidene malonates catalyzed by N,N'-dioxide-scandium(III) complexes: asymmetric synthesis of beta-carbolines.

    PubMed

    Liu, Yanling; Shang, Deju; Zhou, Xin; Liu, Xiaohua; Feng, Xiaoming

    2009-01-01

    An efficient catalytic asymmetric Friedel-Crafts alkylation of indoles with alkylidene malonates has been developed by using a chiral N,N'-dioxide-Sc(OTf)(3) complex as the catalyst (see scheme). Some optically active intermediates containing the indole skeleton have been synthesized, such as indolepropionic acid, tryptamines, and beta-carbolines. The coordination between the scandium atom and the chiral N,N'-dioxide compound has been revealed by X-ray structure analysis.

  13. Terminating Catalytic Asymmetric Heck Cyclizations by Stereoselective Intramolecular Capture of η3-Allylpalladium Intermediates: Total Synthesis of (−)-Spirotryprostatin B and Three Stereoisomers

    PubMed Central

    Overman, Larry E.; Rosen, Mark D.

    2010-01-01

    A catalytic intramolecular Heck reaction, followed by capture of the resulting η3-allylpalladium intermediate by a tethered diketopiperazine, is the central step in a concise synthetic route to (−)-spirotryprostatin B and three stereoisomers. This study demonstrates that an acyclic, chiral η3-allylpalladium fragment generated in a catalytic asymmetric Heck cyclization can be trapped by even a weakly nucleophilic diketopiperazine more rapidly than it undergoes diastereomeric equilibration. PMID:20725641

  14. Ru-TsDPEN with formic acid/Hunig's base for asymmetric transfer hydrogenation, a practical synthesis of optically enriched N-propyl pantolactam.

    PubMed

    Zhang, Ji; Blazecka, Peter G; Bruendl, Michelle M; Huang, Yun

    2009-02-06

    The Noyori-Ikariya catalysts, Ru-TsDPEN 1 or 2, in combination with HCOOH/Hunig's base (5:2) have been successfully utilized for catalytic asymmetric transfer hydrogenation of alpha-ketopantolactam, and optically enriched N-substituted pantolactam was prepared (S/C = 500, up to 95% ee and 99% conversion in HCOOH/Hunig's base condition). More than 2 kg of this key intermediate 9 has been synthesized efficiently with excellent chemical yield and chiral purity.

  15. Asymmetric Catalytic aza-Morita-Baylis-Hillman Reaction for the Synthesis of 3-Substituted-3-Aminooxindoles with Chiral Quaternary Carbon Centers

    PubMed Central

    Hu, Fang-Le; Wei, Yin; Shi, Min; Pindi, Suresh; Li, Guigen

    2013-01-01

    Asymmetric catalytic aza-Morita-Baylis-Hillman (aza-MBH) reaction of isatin-derived ketimines with MVK has been established by using chiral amino and phosphino catalysts. The reaction resulted in biomedically important 3-substituted 3-amino-2-oxindoles in good yields (>80% for most cases) and excellent enantioselectivity (90–99%ee). Twenty-eight cases assembled with chiral quaternary stereogenic centers have been examined under convenient systems. PMID:23407608

  16. Asymmetric synthesis of α-amino acids via homologation of Ni(II) complexes of glycine Schiff bases. Part 2: aldol, Mannich addition reactions, deracemization and (S) to (R) interconversion of α-amino acids.

    PubMed

    Sorochinsky, Alexander E; Aceña, José Luis; Moriwaki, Hiroki; Sato, Tatsunori; Soloshonok, Vadim

    2013-11-01

    This review provides a comprehensive treatment of literature data dealing with asymmetric synthesis of α-amino-β-hydroxy and α,β-diamino acids via homologation of chiral Ni(II) complexes of glycine Schiff bases using aldol and Mannich-type reactions. These reactions proceed with synthetically useful chemical yields and thermodynamically controlled stereoselectivity and allow direct introduction of two stereogenic centers in a single operation with predictable stereochemical outcome. Furthermore, new application of Ni(II) complexes of α-amino acids Schiff bases for deracemization of racemic α-amino acids and (S) to (R) interconversion providing additional synthetic opportunities for preparation of enantiomerically pure α-amino acids, is also reviewed. Origin of observed diastereo-/enantioselectivity in the aldol, Mannich-type and deracemization reactions, generality and limitations of these methodologies are critically discussed.

  17. Microwave Assisted Synthesis of Porous NiCo2O4 Microspheres: Application as High Performance Asymmetric and Symmetric Supercapacitors with Large Areal Capacitance

    NASA Astrophysics Data System (ADS)

    Khalid, Syed; Cao, Chuanbao; Wang, Lin; Zhu, Youqi

    2016-03-01

    Large areal capacitance is essentially required to integrate the energy storage devices at the microscale electronic appliances. Energy storage devices based on metal oxides are mostly fabricated with low mass loading per unit area which demonstrated low areal capacitance. It is still a challenge to fabricate supercapacitor devices of porous metal oxides with large areal capacitance. Herein we report microwave method followed by a pyrolysis of the as-prepared precursor is used to synthesize porous nickel cobaltite microspheres. Porous NiCo2O4 microspheres are capable to deliver large areal capacitance due to their high specific surface area and small crystallite size. The facile strategy is successfully demonstrated to fabricate aqueous-based asymmetric & symmetric supercapacitor devices of porous NiCo2O4 microspheres with high mass loading of electroactive materials. The asymmetric & symmetric devices exhibit maximum areal capacitance and energy density of 380 mF cm‑2 & 19.1 Wh Kg‑1 and 194 mF cm‑2 & 4.5 Wh Kg‑1 (based on total mass loading of 6.25 & 6.0 mg) respectively at current density of 1 mA cm‑2. The successful fabrication of symmetric device also indicates that NiCo2O4 can also be used as the negative electrode material for futuristic asymmetric devices.

  18. Microwave Assisted Synthesis of Porous NiCo2O4 Microspheres: Application as High Performance Asymmetric and Symmetric Supercapacitors with Large Areal Capacitance

    PubMed Central

    Khalid, Syed; Cao, Chuanbao; Wang, Lin; Zhu, Youqi

    2016-01-01

    Large areal capacitance is essentially required to integrate the energy storage devices at the microscale electronic appliances. Energy storage devices based on metal oxides are mostly fabricated with low mass loading per unit area which demonstrated low areal capacitance. It is still a challenge to fabricate supercapacitor devices of porous metal oxides with large areal capacitance. Herein we report microwave method followed by a pyrolysis of the as-prepared precursor is used to synthesize porous nickel cobaltite microspheres. Porous NiCo2O4 microspheres are capable to deliver large areal capacitance due to their high specific surface area and small crystallite size. The facile strategy is successfully demonstrated to fabricate aqueous-based asymmetric & symmetric supercapacitor devices of porous NiCo2O4 microspheres with high mass loading of electroactive materials. The asymmetric & symmetric devices exhibit maximum areal capacitance and energy density of 380 mF cm−2 & 19.1 Wh Kg−1 and 194 mF cm−2 & 4.5 Wh Kg−1 (based on total mass loading of 6.25 & 6.0 mg) respectively at current density of 1 mA cm−2. The successful fabrication of symmetric device also indicates that NiCo2O4 can also be used as the negative electrode material for futuristic asymmetric devices. PMID:26936283

  19. Microwave Assisted Synthesis of Porous NiCo2O4 Microspheres: Application as High Performance Asymmetric and Symmetric Supercapacitors with Large Areal Capacitance.

    PubMed

    Khalid, Syed; Cao, Chuanbao; Wang, Lin; Zhu, Youqi

    2016-03-03

    Large areal capacitance is essentially required to integrate the energy storage devices at the microscale electronic appliances. Energy storage devices based on metal oxides are mostly fabricated with low mass loading per unit area which demonstrated low areal capacitance. It is still a challenge to fabricate supercapacitor devices of porous metal oxides with large areal capacitance. Herein we report microwave method followed by a pyrolysis of the as-prepared precursor is used to synthesize porous nickel cobaltite microspheres. Porous NiCo2O4 microspheres are capable to deliver large areal capacitance due to their high specific surface area and small crystallite size. The facile strategy is successfully demonstrated to fabricate aqueous-based asymmetric &symmetric supercapacitor devices of porous NiCo2O4 microspheres with high mass loading of electroactive materials. The asymmetric &symmetric devices exhibit maximum areal capacitance and energy density of 380 mF cm(-2) &19.1 Wh Kg(-1) and 194 mF cm(-2) &4.5 Wh Kg(-1) (based on total mass loading of 6.25 &6.0 mg) respectively at current density of 1 mA cm(-2). The successful fabrication of symmetric device also indicates that NiCo2O4 can also be used as the negative electrode material for futuristic asymmetric devices.

  20. Electronic Absolute Cartesian Autocollimator

    NASA Technical Reports Server (NTRS)

    Leviton, Douglas B.

    2006-01-01

    An electronic absolute Cartesian autocollimator performs the same basic optical function as does a conventional all-optical or a conventional electronic autocollimator but differs in the nature of its optical target and the manner in which the position of the image of the target is measured. The term absolute in the name of this apparatus reflects the nature of the position measurement, which, unlike in a conventional electronic autocollimator, is based absolutely on the position of the image rather than on an assumed proportionality between the position and the levels of processed analog electronic signals. The term Cartesian in the name of this apparatus reflects the nature of its optical target. Figure 1 depicts the electronic functional blocks of an electronic absolute Cartesian autocollimator along with its basic optical layout, which is the same as that of a conventional autocollimator. Referring first to the optical layout and functions only, this or any autocollimator is used to measure the compound angular deviation of a flat datum mirror with respect to the optical axis of the autocollimator itself. The optical components include an illuminated target, a beam splitter, an objective or collimating lens, and a viewer or detector (described in more detail below) at a viewing plane. The target and the viewing planes are focal planes of the lens. Target light reflected by the datum mirror is imaged on the viewing plane at unit magnification by the collimating lens. If the normal to the datum mirror is parallel to the optical axis of the autocollimator, then the target image is centered on the viewing plane. Any angular deviation of the normal from the optical axis manifests itself as a lateral displacement of the target image from the center. The magnitude of the displacement is proportional to the focal length and to the magnitude (assumed to be small) of the angular deviation. The direction of the displacement is perpendicular to the axis about which the

  1. Absolute airborne gravimetry

    NASA Astrophysics Data System (ADS)

    Baumann, Henri

    This work consists of a feasibility study of a first stage prototype airborne absolute gravimeter system. In contrast to relative systems, which are using spring gravimeters, the measurements acquired by absolute systems are uncorrelated and the instrument is not suffering from problems like instrumental drift, frequency response of the spring and possible variation of the calibration factor. The major problem we had to resolve were to reduce the influence of the non-gravitational accelerations included in the measurements. We studied two different approaches to resolve it: direct mechanical filtering, and post-processing digital compensation. The first part of the work describes in detail the different mechanical passive filters of vibrations, which were studied and tested in the laboratory and later in a small truck in movement. For these tests as well as for the airborne measurements an absolute gravimeter FG5-L from Micro-G Ltd was used together with an Inertial navigation system Litton-200, a vertical accelerometer EpiSensor, and GPS receivers for positioning. These tests showed that only the use of an optical table gives acceptable results. However, it is unable to compensate for the effects of the accelerations of the drag free chamber. The second part describes the strategy of the data processing. It is based on modeling the perturbing accelerations by means of GPS, EpiSensor and INS data. In the third part the airborne experiment is described in detail, from the mounting in the aircraft and data processing to the different problems encountered during the evaluation of the quality and accuracy of the results. In the part of data processing the different steps conducted from the raw apparent gravity data and the trajectories to the estimation of the true gravity are explained. A comparison between the estimated airborne data and those obtained by ground upward continuation at flight altitude allows to state that airborne absolute gravimetry is feasible and

  2. Absolute-structure reports.

    PubMed

    Flack, Howard D

    2013-08-01

    All the 139 noncentrosymmetric crystal structures published in Acta Crystallographica Section C between January 2011 and November 2012 inclusive have been used as the basis of a detailed study of the reporting of absolute structure. These structure determinations cover a wide range of space groups, chemical composition and resonant-scattering contribution. Defining A and D as the average and difference of the intensities of Friedel opposites, their level of fit has been examined using 2AD and selected-D plots. It was found, regardless of the expected resonant-scattering contribution to Friedel opposites, that the Friedel-difference intensities are often dominated by random uncertainty and systematic error. An analysis of data collection strategy is provided. It is found that crystal-structure determinations resulting in a Flack parameter close to 0.5 may not necessarily be from crystals twinned by inversion. Friedifstat is shown to be a robust estimator of the resonant-scattering contribution to Friedel opposites, very little affected by the particular space group of a structure nor by the occupation of special positions. There is considerable confusion in the text of papers presenting achiral noncentrosymmetric crystal structures. Recommendations are provided for the optimal way of treating noncentrosymmetric crystal structures for which the experimenter has no interest in determining the absolute structure.

  3. Chiral N-phosphonyl imine chemistry: asymmetric synthesis of alpha,beta-diamino esters by reacting phosphonyl imines with glycine enolates.

    PubMed

    Ai, Teng; Li, Guigen

    2009-07-15

    Chiral phosphonyl imines attached with N-isopropyl protection group were found to react with lithium glycine enolates under convenient conditions to give alpha,beta-diamino esters. Thirteen examples have been examined in good to excellent chemical yields (85-97%) diastereoselectivity (up to 99% de). By treating with HBr at room temperature, the chiral auxiliary can be readily removed and recycled. The absolute structure has been unambiguously determined by converting a product to a known sample.

  4. Synthesis of Chiral γ-Lactams via in Situ Elimination/Iridium-Catalyzed Asymmetric Hydrogenation of Racemic γ-Hydroxy γ-Lactams.

    PubMed

    Yuan, Qianjia; Liu, Delong; Zhang, Wanbin

    2017-04-07

    Chiral γ-lactams have been synthesized in excellent yields and enantioselectivities (up to 99% yield and 96% ee) from easily accessible racemic γ-hydroxy γ-lactams via an iridium-phosphoramidite catalyzed asymmetric hydrogenation. The reaction was designed based on insight into the reaction mechanism demonstrated in previous work and can be carried out at a reduced catalyst loading of 0.1 mol % on a gram scale. Several potential bioactive compounds can be synthesized from the reduced products. Mechanistic studies indicated that the reduced products were obtained via the hydrogenation of the N-acyliminium cations, generated from γ-hydroxy γ-lactams.

  5. Enantio- and diastereoselective synthesis of piperidines by coupling of four components in a "one-pot" sequence involving diphenylprolinol silyl ether mediated Michael reaction.

    PubMed

    Urushima, Tatsuya; Sakamoto, Daisuke; Ishikawa, Hayato; Hayashi, Yujiro

    2010-10-15

    An efficient, asymmetric, four-component, one-pot synthesis of highly substituted piperidines with excellent diastereo- and enantioselectivity was established through the diphenylprolinol silyl ether mediated Michael reaction of aldehyde and nitroalkene, followed by the domino aza-Henry reaction/hemiaminalization reaction and a Lewis acid mediated allylation or cyanation reaction. All carbons of the piperidine ring are substituted with different groups, and its five contiguous stereocenters are completely controlled in both relative and absolute senses.

  6. Strength by joining methods: combining synthesis with NMR, IR, and vibrational circular dichroism spectroscopy for the determination of the relative configuration in hemicalide.

    PubMed

    De Gussem, Ewoud; Herrebout, Wouter; Specklin, Simon; Meyer, Christophe; Cossy, Janine; Bultinck, Patrick

    2014-12-22

    The relative configuration of a key subunit of hemicalide, a recently isolated, highly bioactive marine natural product having potent antiproliferative activity against a panel of human cancer cell lines, was assigned by combining stereocontrolled synthesis of model substrates with NMR, IR, and vibrational circular dichroism (VCD) spectroscopy. The assignment of the absolute configuration of asymmetric carbon center C42 in two structurally complex epimeric substructures containing six stereocenters by VCD analysis illustrates the power and reliability of combining methods.

  7. Absolute Equilibrium Entropy

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    1997-01-01

    The entropy associated with absolute equilibrium ensemble theories of ideal, homogeneous, fluid and magneto-fluid turbulence is discussed and the three-dimensional fluid case is examined in detail. A sigma-function is defined, whose minimum value with respect to global parameters is the entropy. A comparison is made between the use of global functions sigma and phase functions H (associated with the development of various H-theorems of ideal turbulence). It is shown that the two approaches are complimentary though conceptually different: H-theorems show that an isolated system tends to equilibrium while sigma-functions allow the demonstration that entropy never decreases when two previously isolated systems are combined. This provides a more complete picture of entropy in the statistical mechanics of ideal fluids.

  8. Absolute multilateration between spheres

    NASA Astrophysics Data System (ADS)

    Muelaner, Jody; Wadsworth, William; Azini, Maria; Mullineux, Glen; Hughes, Ben; Reichold, Armin

    2017-04-01

    Environmental effects typically limit the accuracy of large scale coordinate measurements in applications such as aircraft production and particle accelerator alignment. This paper presents an initial design for a novel measurement technique with analysis and simulation showing that that it could overcome the environmental limitations to provide a step change in large scale coordinate measurement accuracy. Referred to as absolute multilateration between spheres (AMS), it involves using absolute distance interferometry to directly measure the distances between pairs of plain steel spheres. A large portion of each sphere remains accessible as a reference datum, while the laser path can be shielded from environmental disturbances. As a single scale bar this can provide accurate scale information to be used for instrument verification or network measurement scaling. Since spheres can be simultaneously measured from multiple directions, it also allows highly accurate multilateration-based coordinate measurements to act as a large scale datum structure for localized measurements, or to be integrated within assembly tooling, coordinate measurement machines or robotic machinery. Analysis and simulation show that AMS can be self-aligned to achieve a theoretical combined standard uncertainty for the independent uncertainties of an individual 1 m scale bar of approximately 0.49 µm. It is also shown that combined with a 1 µm m‑1 standard uncertainty in the central reference system this could result in coordinate standard uncertainty magnitudes of 42 µm over a slender 1 m by 20 m network. This would be a sufficient step change in accuracy to enable next generation aerospace structures with natural laminar flow and part-to-part interchangeability.

  9. New chiral didehydroamino acid derivatives from a cyclic glycine template with 3,6-dihydro-2H-1,4-oxazin-2-one structure: applications to the asymmetric synthesis of nonproteinogenic alpha-amino acids.

    PubMed

    Chinchilla, R; Falvello, L R; Galindo, N; Nájera, C

    2000-05-19

    New chiral (Z)-alpha,beta-didehydroamino acid (DDAA) derivatives with 3,5-dihydro-2H-1,4-oxazin-2-one structure 11a-f have been stereoselectively prepared after condensation of chiral glycine equivalent 7 with aldehydes in the presence of K(2)CO(3) under mild solid-liquid phase-transfer catalysis reaction conditions. These new systems have been used in diastereoselective cyclopropanation reactions using Corey's ylide for the asymmetric synthesis of 1-aminocyclopropane-1-carboxylic acids (ACCs) such as allo-corononamic and allo-norcoronamic acids. The hydrogenation reaction of these systems at ambient pressure in the presence of formaldehyde affords saturated oxazinones and N-methylated oxazinones which have been transformed into the N-methyl-alpha-amino acids (N-MAAs) (S)-2-(methylamino)butanoic acid and (S)-N-methylleucine. In addition, the parent alpha, beta-didehydroalanine derivative 11g has been prepared by a direct aminomethylation-elimination sequence from 7 and Eschenmoser's salt and has been used in Diels-Alder cycloaddition with endo selectivity for the synthesis of the enantiomerically pure bicyclic alpha-amino acids (-)-2-aminobicyclo[2.2.1]heptane-2-carboxylic and (-)-2-aminobicyclo[2.2.2]octane-2-carboxylic acids.

  10. Tunable synthesis of hierarchical NiCo2O4 nanosheets-decorated Cu/CuOx nanowires architectures for asymmetric electrochemical capacitors

    NASA Astrophysics Data System (ADS)

    Kuang, Min; Zhang, Yu Xin; Li, Tong Tao; Li, Kai Feng; Zhang, Sheng Mao; Li, Gang; Zhang, Wei

    2015-06-01

    We demonstrate a facile and tunable preparative strategy of porous NiCo2O4 nanosheets-decorated Cu-based nanowires hybrids as high-performance supercapacitor electrodes. A fast faradic reaction has been realized by inducing elementary copper core in the composite, which assists in high electric conductivity of the cell and creates intimate channels for fast charge collection and electron transfer. As a result, this hybrid composite electrode displays high specific capacitance (578 F g-1 at current density of 1.0 A g-1) and rate capability (80.1% capacitance retention from 1 A g-1 to 10 A g-1). Additionally, asymmetric device is constructed from NiCo2O4/Cu-based NWs and activated graphene (AG) with an operation potential from 0 to 1.4 V. The asymmetric device exhibits an energy density of 12.6 Wh kg-1 at a power density of 344 W kg-1 and excellent long-term cycling stability (only 1.8% loss of its initial capacitance after 10,000 cycles). These attractive findings suggest that such unique NiCo2O4/Cu-based NWs hybrid architecture is promising for electrochemical applications as efficient electrode material.

  11. Determination of absolute configuration of chiral molecules using vibrational optical activity: a review.

    PubMed

    He, Yanan; Wang, Bo; Dukor, Rina K; Nafie, Laurence A

    2011-07-01

    Determination of the absolute handedness, known as absolute configuration (AC), of chiral molecules is an important step in any field related to chirality, especially in the pharmaceutical industry. Vibrational optical activity (VOA) has become a powerful tool for the determination of the AC of chiral molecules in the solution state after nearly forty years of evolution. VOA offers a novel alternative, or supplement, to X-ray crystallography, permitting AC determinations on neat liquid, oil, and solution samples without the need to grow single crystals of the pure chiral sample molecules as required for X-ray analysis. By comparing the sign and intensity of the measured VOA spectrum with the corresponding ab initio density functional theory (DFT) calculated VOA spectrum of a chosen configuration, one can unambiguously assign the AC of a chiral molecule. Comparing measured VOA spectra with calculated VOA spectra of all the conformers can also provide solution-state conformational populations. VOA consists of infrared vibrational circular dichroism (VCD) and vibrational Raman optical activity (ROA). Currently, VCD is used routinely by researchers in a variety of backgrounds, including molecular chirality, asymmetric synthesis, chiral catalysis, drug screening, pharmacology, and natural products. Although the application of ROA in AC determination lags behind that of VCD, with the recent implementation of ROA subroutines in commercial quantum chemistry software, ROA will in the future complement VCD for AC determination. In this review, the basic principles of the application of VCD to the determination of absolute configuration in chiral molecules are described. The steps required for VCD spectral measurement and calculation are outlined, followed by brief descriptions of recently published papers reporting the determination of AC in small organic, pharmaceutical, and natural product molecules.

  12. Asymmetric catalysis with short-chain peptides.

    PubMed

    Lewandowski, Bartosz; Wennemers, Helma

    2014-10-01

    Within this review article we describe recent developments in asymmetric catalysis with peptides. Numerous peptides have been established in the past two decades that catalyze a wide variety of transformations with high stereoselectivities and yields, as well as broad substrate scope. We highlight here catalytically active peptides, which have addressed challenges that had thus far remained elusive in asymmetric catalysis: enantioselective synthesis of atropoisomers and quaternary stereogenic centers, regioselective transformations of polyfunctional substrates, chemoselective transformations, catalysis in-flow and reactions in aqueous environments.

  13. Absolute Rate Theories of Epigenetic Stability

    NASA Astrophysics Data System (ADS)

    Walczak, Aleksandra M.; Onuchic, Jose N.; Wolynes, Peter G.

    2006-03-01

    Spontaneous switching events in most characterized genetic switches are rare, resulting in extremely stable epigenetic properties. We show how simple arguments lead to theories of the rate of such events much like the absolute rate theory of chemical reactions corrected by a transmission factor. Both the probability of the rare cellular states that allow epigenetic escape, and the transmission factor, depend on the rates of DNA binding and unbinding events and on the rates of protein synthesis and degradation. Different mechanisms of escape from the stable attractors occur in the nonadiabatic, weakly adiabatic and strictly adiabatic regimes, characterized by the relative values of those input rates.

  14. Absolute rate theories of epigenetic stability

    NASA Astrophysics Data System (ADS)

    Walczak, Aleksandra M.; Onuchic, José N.; Wolynes, Peter G.

    2005-12-01

    Spontaneous switching events in most characterized genetic switches are rare, resulting in extremely stable epigenetic properties. We show how simple arguments lead to theories of the rate of such events much like the absolute rate theory of chemical reactions corrected by a transmission factor. Both the probability of the rare cellular states that allow epigenetic escape and the transmission factor depend on the rates of DNA binding and unbinding events and on the rates of protein synthesis and degradation. Different mechanisms of escape from the stable attractors occur in the nonadiabatic, weakly adiabatic, and strictly adiabatic regimes, characterized by the relative values of those input rates. rate theory | stochastic gene expression | gene switches

  15. Cell-sized asymmetric lipid vesicles facilitate the investigation of asymmetric membranes

    NASA Astrophysics Data System (ADS)

    Kamiya, Koki; Kawano, Ryuji; Osaki, Toshihisa; Akiyoshi, Kazunari; Takeuchi, Shoji

    2016-09-01

    Asymmetric lipid giant vesicles have been used to model the biochemical reactions in cell membranes. However, methods for producing asymmetric giant vesicles lead to the inclusion of an organic solvent layer that affects the mechanical and physical characteristics of the membrane. Here we describe the formation of asymmetric giant vesicles that include little organic solvent, and use them to investigate the dynamic responses of lipid molecules in the vesicle membrane. We formed the giant vesicles via the inhomogeneous break-up of a lipid microtube generated by applying a jet flow to an asymmetric planar lipid bilayer. The asymmetric giant vesicles showed a lipid flip-flop behaviour in the membrane, superficially similar to the lipid flip-flop activity observed in apoptotic cells. In vitro synthesis of membrane proteins into the asymmetric giant vesicles revealed that the lipid asymmetry in bilayer membranes improves the reconstitution ratio of membrane proteins. Our asymmetric giant vesicles will be useful in elucidating lipid-lipid and lipid-membrane protein interactions involved in the regulation of cellular functions.

  16. Effect of high pressure on the organocatalytic asymmetric Michael reaction: highly enantioselective synthesis of γ-nitroketones with quaternary stereogenic centers.

    PubMed

    Kwiatkowski, Piotr; Dudziński, Krzysztof; Łyżwa, Dawid

    2011-07-15

    The significant effect of hydrostatic pressure on the difficult organocatalytic 1,4-conjugate addition of nitroalkanes to prochiral sterically congested β,β-disubstituted enones is demonstrated. This approach allows for the synthesis of γ-nitroketones containing quaternary stereogenic centers with good yields, excellent enantioselectivity, and low loading (1-5 mol %) of simple chiral primary amine catalysts.

  17. Enantioselective Synthesis of Anti-β-Substituted γ,δ-Unsaturated Amino Acids: A Highly Selective Asymmetric Thio-Claisen Rearrangement

    PubMed Central

    Liu, Zhihua; Qu, Hongchang; Gu, Xuyuan; Min, Byoung J.; Nyberg, Joel; Hruby, Victor J.

    2009-01-01

    A novel synthesis of optically active anti-1β-substituted γ,δ-unsaturated amino acids via a thio-Claisen rearrangement has been achieved. A 2,5-diphenylpyrrolidine was used as a C2-symmetric chiral auxiliary to control the stereochemistry, giving good yields and excellent diastereoselectivities and enantioselectivities. PMID:18702500

  18. Synthesis, spectral, photolysis and electrochemical studies of mononuclear copper(II) complex with a new asymmetric tetradentate ligand: Application as copper nanoparticle precursor

    NASA Astrophysics Data System (ADS)

    Habibi, Mohammad Hossein; Mikhak, Maryam

    2012-10-01

    A copper(II) complex with asymmetric tetradentate Schiff base ligand, obtained by the single condensation of 1,2-diaminopropane with 2-hydroxy-5-methoxy benzaldehyde was prepared. The ligand and complex were characterized by their IR, UV-Vis, FT-IR, NMR spectra and CV. Crystal structures of the mononuclear copper complex have been obtained by X-ray diffraction studies which revealed to be distorted square planner coordination geometry. The spectral data confirm coordination of ligand to copper ion center. The redox properties of complex at different scan rates exhibit grossly similar features consisting of an electrochemically pseudo-reversible Cu(II)/Cu(I) reduction at ca. -0.97 V and pseudo-reversible Cu(I)/Cu(II) oxidation at ca. -0.81 V. The copper nanoparticles with average size of 73 nm were formed by thermal reduction of copper complex in the presence of triphenylphosphine.

  19. Diastereodivergent Asymmetric Michael Addition of Cyclic Azomethine Ylides to Nitroalkenes: Direct Approach for the Synthesis of 1,7-Diazaspiro[4.4]nonane Diastereoisomers.

    PubMed

    Li, Chun-Yan; Yang, Wu-Lin; Luo, Xiaoyan; Deng, Wei-Ping

    2015-12-21

    The first highly diastereoselective and enantioselective catalytic asymmetric Michael addition of cyclic azomethine ylides with nitroalkenes have been developed to diastereodivergently generate either the syn or anti adducts by employing N,O-ligand/Cu(OAc)2 and N,P-ligand/Cu(OAc)2 catalytic systems. Both catalytic systems exhibit broad substrate applicability to afford the corresponding Michael adducts in good to excellent yields, with excellent levels of diastereo- (up to 99:1 diastereomeric ratio) and enantioselectivities (up to >99% enantiomeric excess). Importantly, the chiral 1,7-diazaspiro[4.4]nonane diastereomer derivatives can be easily obtained in good yields through facile NaBH4 reduction of the Michael adducts.

  20. Controlled synthesis, asymmetrical transport behavior and luminescence properties of lanthanide doped ZnO mushroom-like 3D hierarchical structures

    NASA Astrophysics Data System (ADS)

    Yue, Dan; Lu, Wei; Jin, Lin; Li, Chunyang; Luo, Wen; Wang, Mengnan; Wang, Zhenling; Hao, Jianhua

    2014-10-01

    Lanthanide doped ZnO mushroom-like 3D hierarchical structures have been fabricated by polyol-mediated method and characterized by various microstructural and optical techniques. The results indicate that the as-prepared ZnO:Ln3+ (Ln = Tb, Eu) samples have a hexagonal phase structure and possess a mushroom-like 3D hierarchical morphology. The length of the whole mushroom from stipe bottom to pileus top is about 1.0 μm, and the diameters of pileus and stipe are about 0.8 μm and 0.4 μm, respectively. It is found that the flow of N2 is the key parameter for the formation of the novel ZnO structure and the addition of (NH4)2HPO4 has a prominent effect on the phase structure and the growth of mushroom-like morphology. The potential mechanism of forming this morphology is proposed. The pileus of the formed mushroom is assembled by several radial ZnO:Ln3+ nanorods, whereas the stipe is composed of over layered ZnO:Ln3+ nanosheets. Moreover, asymmetrical I-V characteristic curves of ZnO:Ln3+ mushrooms indicate that the texture composition of the 3D hierarchical morphology might lead to the asymmetrical transport behavior of electrical conductivity. Lanthanide doped ZnO samples can exhibit red or green emission under the excitation of UV light.Lanthanide doped ZnO mushroom-like 3D hierarchical structures have been fabricated by polyol-mediated method and characterized by various microstructural and optical techniques. The results indicate that the as-prepared ZnO:Ln3+ (Ln = Tb, Eu) samples have a hexagonal phase structure and possess a mushroom-like 3D hierarchical morphology. The length of the whole mushroom from stipe bottom to pileus top is about 1.0 μm, and the diameters of pileus and stipe are about 0.8 μm and 0.4 μm, respectively. It is found that the flow of N2 is the key parameter for the formation of the novel ZnO structure and the addition of (NH4)2HPO4 has a prominent effect on the phase structure and the growth of mushroom-like morphology. The potential

  1. Synthesis, spectral, photolysis and electrochemical studies of mononuclear copper(II) complex with a new asymmetric tetradentate ligand: application as copper nanoparticle precursor.

    PubMed

    Habibi, Mohammad Hossein; Mikhak, Maryam

    2012-10-01

    A copper(II) complex with asymmetric tetradentate Schiff base ligand, obtained by the single condensation of 1,2-diaminopropane with 2-hydroxy-5-methoxy benzaldehyde was prepared. The ligand and complex were characterized by their IR, UV-Vis, FT-IR, NMR spectra and CV. Crystal structures of the mononuclear copper complex have been obtained by X-ray diffraction studies which revealed to be distorted square planner coordination geometry. The spectral data confirm coordination of ligand to copper ion center. The redox properties of complex at different scan rates exhibit grossly similar features consisting of an electrochemically pseudo-reversible Cu(II)/Cu(I) reduction at ca. -0.97 V and pseudo-reversible Cu(I)/Cu(II) oxidation at ca. -0.81 V. The copper nanoparticles with average size of 73 nm were formed by thermal reduction of copper complex in the presence of triphenylphosphine.

  2. Zn(II), Ni(II), Cu(II) and Pb(II) complexes of tridentate asymmetrical Schiff base ligands: Synthesis, characterization, properties and biological activity

    NASA Astrophysics Data System (ADS)

    Şahin, Mustafa; Koçak, Nuriye; Erdenay, Damla; Arslan, Uğur

    2013-02-01

    New asymmetrical tridentate Schiff base ligands were synthesized using 1,2-phenylenediamine, 4-methyl-1,2-phenylenediamine, 2-hydroxy-1-napthaldehyde, 9-anthracenecarboxaldehyde. Schiff base ligands and their metal complexes were synthesised and characterized by using FT-IR, 1H NMR, 13C NMR, UV-Vis, XRD, ESR, elemental analysis and fluorescence studies. The antimicrobial activity of the ligands and their metal complexes were studied against Staphylococcus aureus ATCC 29213, S. aureus ATCC 25923, Streptococcus mutans RSHM 676, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853. The determination of the antibacterial activity was done using the broth microdilution methods. In general, it has been determined that the studied compounds have MIC values similar to Gram-positive and Gram-negative bacteria. It has been found that Ni, Pb, Zn derivatives of HL1A and ZnL2A has lower MIC values than ampicillin for P. aeruginosa ATCC 27853 strain.

  3. Asymmetric PTC C-alkylation catalyzed by chiral derivatives of tartaric acid and aminophenols. Synthesis Of (R)- and (S)-alpha-methyl amino acids

    PubMed

    Belokon; Kochetkov; Churkina; Ikonnikov; Chesnokov; Larionov; Singh; Parmar; Vyskocil; Kagan

    2000-10-20

    A new type of efficient chiral catalyst has been elaborated for asymmetric C-alkylation of CH acids under PTC conditions. Sodium alkoxides formed from chiral derivatives of tartaric acid and aminophenols (TADDOL's 2a-e and NOBIN's 3a-h) can be used as chiral catalysts in the enantioselective alkylation, as exemplified by the reaction of Schiff's bases 1a-e derived from alanine esters and benzaldehydes with active alkyl halides. Acid-catalyzed hydrolysis of the products formed in the reaction afforded (R)-alpha-methylphenylalanine, (R)-alpha-naphthylmethylalanine, and (R)-alpha-allylalanine in 61-93% yields and with ee 69-93%. The procedure could be successfully scaled up to 6 g of substrate 1b. When (S,S)-TADDOL or (R)-NOBIN are used, the (S)-amino acids are formed. A mechanism rationalizing the observed features of the reaction has been suggested.

  4. Zn(II), Ni(II), Cu(II) and Pb(II) complexes of tridentate asymmetrical Schiff base ligands: synthesis, characterization, properties and biological activity.

    PubMed

    Şahin, Mustafa; Koçak, Nuriye; Erdenay, Damla; Arslan, Uğur

    2013-02-15

    New asymmetrical tridentate Schiff base ligands were synthesized using 1,2-phenylenediamine, 4-methyl-1,2-phenylenediamine, 2-hydroxy-1-napthaldehyde, 9-anthracenecarboxaldehyde. Schiff base ligands and their metal complexes were synthesised and characterized by using FT-IR, (1)H NMR, (13)C NMR, UV-Vis, XRD, ESR, elemental analysis and fluorescence studies. The antimicrobial activity of the ligands and their metal complexes were studied against Staphylococcus aureus ATCC 29213, S. aureus ATCC 25923, Streptococcus mutans RSHM 676, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853. The determination of the antibacterial activity was done using the broth microdilution methods. In general, it has been determined that the studied compounds have MIC values similar to Gram-positive and Gram-negative bacteria. It has been found that Ni, Pb, Zn derivatives of HL1A and ZnL(2)A has lower MIC values than ampicillin for P. aeruginosa ATCC 27853 strain.

  5. Asymmetric synthesis of anti- and syn-beta-amino alcohols by reductive cross-coupling of transition metal-coordinated planar chiral arylaldehydes with aldimines.

    PubMed

    Tanaka, Yoshie; Taniguchi, Nobukazu; Kimura, Takayuki; Uemura, Motokazu

    2002-12-27

    Samarium iodide-mediated cross-coupling of N-tosyl ferrocenylideneamine with planar chiral ferrocenecarboxaldehydes or benzaldehyde chromium complexes gave diastereoselectively the corresponding anti-beta-amino alcohol derivatives in good yields, while N-tosyl benzylideneamine produced syn-beta-amino alcohols by coupling with planar chiral arylaldehydes. Dynamic kinetic resolution of a configurationally equilibrated reactive species generated from achiral N-tosyl ferrocenilideneamine and benzylideneamine by reduction with samarium iodide was observed in the cross-coupling with planar chiral arylaldehydes giving both antipodes of beta-amino alcohols depending on the planar chirality. The obtained anti-beta-amino alcohol with the ferrocene ring was utilized as a chiral ligand for catalytic asymmetric reduction of acetophenone.

  6. Design and synthesis of a new type of ferrocene-based planar chiral DMAP analogues. A new catalyst system for asymmetric nucleophilic catalysis.

    PubMed

    Seitzberg, Jimmi Gerner; Dissing, Carsten; Søtofte, Inger; Norrby, Per-Ola; Johannsen, Mogens

    2005-10-14

    A new first-generation catalyst system for nucleophilic catalysis has been developed. It is based on a planar chiral ferrocene skeleton with either the potent nucleophile 4-(dimethylamino)pyridine (DMAP) or the related 4-nitropyridine N-oxide attached in either the 2- or the 3-position. The syntheses are short, efficient, and enantioselective and X-ray crystal structures of both DMAP-derived catalysts are presented. The DMAP-based catalysts were tested in asymmetric reactions and the 3-derivative 14 showed good activity and a moderate level of enantioselectivity. The sense of induction (selectivity) was studied using molecular modeling and the results pointed at new directions for future generations of catalysts based on this design.

  7. Solvothermal Synthesis of Three-Dimensional Hierarchical CuS Microspheres from a Cu-Based Ionic Liquid Precursor for High-Performance Asymmetric Supercapacitors.

    PubMed

    Zhang, Jing; Feng, Huijie; Yang, Jiaqin; Qin, Qing; Fan, Hongmin; Wei, Caiying; Zheng, Wenjun

    2015-10-07

    It is meaningful to exploit copper sulfide materials with desired structure as well as potential application due to their cheapness and low toxicity. A low-temperature and facile solvothermal method for preparing three-dimensional (3D) hierarchical covellite (CuS) microspheres from an ionic liquid precursor [Bmim]2Cu2Cl6 (Bmim = 1-butyl-3-methylimidazolium) is reported. The formation of CuS nanostructures was achieved by decomposition of intermediate complex Cu(Tu)3Cl (thiourea = Tu), which produced CuS microspheres with diameters of 2.5-4 μm assembled by nanosheets with thicknesses of 10-15 nm. The ionic liquid, as an "all-in-one" medium, played a key role for the fabrication and self-assembly of CuS nanosheets. The alkylimidazolium rings ([Bmim](+)) were found to adsorb onto the (001) facets of CuS crystals, which inhibited the crystal growth along the [001] direction, while the alkyl chain had influence on the assembly of CuS nanosheets. The CuS microspheres showed enhanced electrochemical performance and high stability for the application in supercapacitors due to intriguing structural design and large specific surface area. When this well-defined CuS electrode was assembled into an asymmetric supercapacitor (ASC) with an activated carbon (AC) electrode, the CuS//AC-ASC demonstrated good cycle performance (∼88% capacitance after 4000 cycles) and high energy density (15.06 W h kg(-1) at a power density of 392.9 W kg(-1)). This work provides new insights into the use of copper sulfide electrode materials for asymmetric supercapacitors and other electrochemical devices.

  8. Combination of an anionic terminator multifunctional initiator and divergent carbanionic polymerization: application to the synthesis of dendrimer-like polymers and of asymmetric and miktoarm stars.

    PubMed

    Matmour, Rachid; Gnanou, Yves

    2008-01-30

    A new and versatile synthetic strategy that provides access to precisely defined and totally soluble multicarbanionic initiators has been implemented to obtain by divergent growth dendrimer-like samples of polystyrene (PS) (up to the seventh generation) or polybutadiene (PB) (up to the third generation) and also asymmetric and miktoarm stars. This strategy rests on lithium-halide exchange reactions to generate multicarbanionic species and on the design of an original reagent that can concomitantly react with living carbanionic chains/arms to deactivate them and produce multicarbanionic sites after exchange of its bromides against lithium. This reagent, 4,4'-dibromodiphenylethylene (1), functions as a TERminating agent and a Multifunctional INItiator (TERMINI), according to a concept first proposed by Percec in another context. Upon using this anionic TERMINI in living carbanionic polymerization and repeating the two steps of chain end derivatization by 1 and divergent arm growth from the multifunctional sites generated, perfectly defined dendrimer-like polystyrene and polybutadiene could be obtained up to the seventh generation for the former and up to the third generation for the latter. Each step, i.e., chain end modification and arm growth, was carefully monitored, and the dendrimer-like samples of PS and PB were all characterized by size exclusion chromatography equipped with a multiangle laser light scattering detector (SEC/LS) and high-temperature size exclusion chromatography equipped with a viscometric detector (HT-SEC). The viscosity behavior of these dendrimer-like polystyrenes--bell-shaped variation versus the number of generation--was found to be similar to that reported for regular dendrimers. This chemistry, namely this anionic TERMINI, was also exploited to derive three-arm asymmetric and miktoarm stars.

  9. Asymmetric Black Diholes

    SciTech Connect

    Manko, V. S.; Sanchez-Mondragon, J.; Ruiz, E.

    2009-05-01

    In the present paper we enlarge the list of black dihole spacetimes by introducing the notion of asymmetric black diholes which describe configurations composed of two static charged black holes endowed with unequal masses and equal but opposite charges. The asymmetric dihole solutions are considered both in the Einstein-Maxwell and Einstein-Maxwell-dilaton theories.

  10. Estimating Absolute Site Effects

    SciTech Connect

    Malagnini, L; Mayeda, K M; Akinci, A; Bragato, P L

    2004-07-15

    The authors use previously determined direct-wave attenuation functions as well as stable, coda-derived source excitation spectra to isolate the absolute S-wave site effect for the horizontal and vertical components of weak ground motion. They used selected stations in the seismic network of the eastern Alps, and find the following: (1) all ''hard rock'' sites exhibited deamplification phenomena due to absorption at frequencies ranging between 0.5 and 12 Hz (the available bandwidth), on both the horizontal and vertical components; (2) ''hard rock'' site transfer functions showed large variability at high-frequency; (3) vertical-motion site transfer functions show strong frequency-dependence, and (4) H/V spectral ratios do not reproduce the characteristics of the true horizontal site transfer functions; (5) traditional, relative site terms obtained by using reference ''rock sites'' can be misleading in inferring the behaviors of true site transfer functions, since most rock sites have non-flat responses due to shallow heterogeneities resulting from varying degrees of weathering. They also use their stable source spectra to estimate total radiated seismic energy and compare against previous results. they find that the earthquakes in this region exhibit non-constant dynamic stress drop scaling which gives further support for a fundamental difference in rupture dynamics between small and large earthquakes. To correct the vertical and horizontal S-wave spectra for attenuation, they used detailed regional attenuation functions derived by Malagnini et al. (2002) who determined frequency-dependent geometrical spreading and Q for the region. These corrections account for the gross path effects (i.e., all distance-dependent effects), although the source and site effects are still present in the distance-corrected spectra. The main goal of this study is to isolate the absolute site effect (as a function of frequency) by removing the source spectrum (moment-rate spectrum) from

  11. Synthesis, photophysical and charge-transporting properties of a novel asymmetric indolo [3,2-b]carbazole derivative containing benzothiazole and diphenylamino moieties

    NASA Astrophysics Data System (ADS)

    Shi, Heping; Yuan, Jiandong; Dong, Xiuqing; Cheng, Fangqin

    2014-12-01

    A novel asymmetric donor-π-donor-π-acceptor compound, 2-benzothiazolyl-8-diphenylamino-5,11-dihexylindolo[3,2-b]carbazole (BDDAICZ), has been successfully synthesized by introducing a benzothiazole moiety (as an electron-acceptor) and a diphenylamino moiety (as an electron-donor) to 2-position and 8-position of indolo[3,2-b]carbazole moiety (as a skeleton and an electron-donor), and characterized by elemental analysis, 1H NMR, 13C NMR and MS. The thermal, electrochemical properties of BDDAICZ were characterized by thermogravimetric analysis combined with electrochemistry. The absorption and emission spectra of BDDAICZ was experimentally determined in several solvents and computed using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The calculated absorption and emission wavelengths are coincident with the measured data. The ionization potential (IP), the electron affinity (EA) and reorganization energy of BDDAICZ were also investigated using density functional theory (DFT). Charge-transporting properties of BDDAICZ were characterized by OLEDs devices fabricated by using it as charge-transport layers. The results show that BDDAICZ has excellent thermal stability, electrochemical stability and hole-transporting properties, indicating its potential application as a hole-transporting material in OLEDs devices.

  12. Synthesis, photophysical and charge-transporting properties of a novel asymmetric indolo [3,2-b]carbazole derivative containing benzothiazole and diphenylamino moieties.

    PubMed

    Shi, Heping; Yuan, Jiandong; Dong, Xiuqing; Cheng, Fangqin

    2014-12-10

    A novel asymmetric donor-π-donor-π-acceptor compound, 2-benzothiazolyl-8-diphenylamino-5,11-dihexylindolo[3,2-b]carbazole (BDDAICZ), has been successfully synthesized by introducing a benzothiazole moiety (as an electron-acceptor) and a diphenylamino moiety (as an electron-donor) to 2-position and 8-position of indolo[3,2-b]carbazole moiety (as a skeleton and an electron-donor), and characterized by elemental analysis, (1)H NMR, (13)C NMR and MS. The thermal, electrochemical properties of BDDAICZ were characterized by thermogravimetric analysis combined with electrochemistry. The absorption and emission spectra of BDDAICZ was experimentally determined in several solvents and computed using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The calculated absorption and emission wavelengths are coincident with the measured data. The ionization potential (IP), the electron affinity (EA) and reorganization energy of BDDAICZ were also investigated using density functional theory (DFT). Charge-transporting properties of BDDAICZ were characterized by OLEDs devices fabricated by using it as charge-transport layers. The results show that BDDAICZ has excellent thermal stability, electrochemical stability and hole-transporting properties, indicating its potential application as a hole-transporting material in OLEDs devices.

  13. Two 2D Cd(II) coordination polymers based on asymmetrical Schiff-base ligand: synthesis, crystal structures and luminescent properties.

    PubMed

    Dang, Dong-Bin; Li, Meng-Meng; Bai, Yan; Zhou, Rui-Min

    2013-02-15

    Two new two-dimensional coordination polymers [Cd(3)L(2)(SCN)(6)](n) (1) and [CdLI(2)](n) (2) have been synthesized and characterized by IR spectroscopy, elemental analysis, TG technique, XRPD and complete single crystal structure analysis, where L is 4-(pyridine-2-yl)methyleneamino-1,2,4-trizaole. Asymmetrical Schiff-base ligand L with five- and six-membered N-containing heterocyclic rings acts as a tridentate bridging ligand to bind two Cd(II) centers through one terminal N(triazolyl) and one pyridylimine chelate unit in 1 and 2. For polymer 1, tridentate bridging ligands link Cd-(1,3-μ-SCN(-)) 1D inorganic chains to form a 2D layer network. The existence of C-H···π and π-π stacking interactions between 2D hybrid layers further gives rise to a 3D supramolecular network. In comparison with 1, polymer 2 shows a 2D layer network containing hexanuclear macrometallacyclic units. The 2D layers are staggered together through the combination of C-H···π and π-π stacking interactions and forming a 3D supramolecular structure. The luminescent properties of the polymers 1 and 2 were investigated in the solid state at room temperature.

  14. A new copper(II) Schiff base complex containing asymmetrical tetradentate N2O2 Schiff base ligand: Synthesis, characterization, crystal structure and DFT study

    NASA Astrophysics Data System (ADS)

    Grivani, Gholamhossein; Baghan, Sara Husseinzadeh; Vakili, Mohammad; Khalaji, Aliakbar Dehno; Tahmasebi, Vida; Eigner, Václav; Dušek, Michal

    2015-02-01

    A new copper (II) Schiff base complex, CuL1, was prepared from the reaction of asymmetrical Schiff base ligand of L1 and Cu(OAC)2 (L1 = salicylidene imino-ethylimino-pentan-2-one). The Schiff base ligand, L1, and its copper (II) complex, CuL1, have been characterized by elemental analysis (CHN) and FT-IR and UV-vis spectroscopy. In addition, 1H NMR was employed for characterization of the ligand. Thermogrametric analysis of the CuL1 reveals its thermal stability and its decomposition pattern shows that it is finally decomposed to the copper oxide (CuO). The crystal structure of CuL1 was determined by the single crystal X-ray analysis. The CuL1 complex crystallizes in the monoclinic system, with space group P21/n and distorted square planar coordination around the metal ion. The Schiff base ligand of L1 acts as a chelating ligand and coordinates via two nitrogen and two oxygen atoms to the copper (II) ion with C1 symmetry. The structure of the CuL1 complex was also studied theoretically at different levels of DFT and basis sets. According to calculated results the Csbnd O bond length of the salicylate fragment is slightly higher than that in the acetylacetonate fragment of ligand, which could be interpreted by resonance increasing between phenyl and chelated rings in ligand in relative to the acetylacetonate fragment.

  15. Chiral phosphinoferrocene carboxamides with amino acid substituents as ligands for Pd-catalysed asymmetric allylic substitutions. Synthesis and structural characterisation of catalytically relevant Pd complexes.

    PubMed

    Tauchman, Jiří; Císařová, Ivana; Stěpnička, Petr

    2011-11-28

    An extensive series of chiral amino acid amides prepared from 1'-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) or its planar-chiral isomer, 2-(diphenylphosphino)ferrocene-1-carboxylic acid, have been tested as ligands for Pd-catalysed asymmetric allylic substitution reactions. In alkylation of 1,3-diphenylallyl acetate as a model substrate with dimethyl malonate the ligands performed well in terms of both reaction rate and enantioselectivity, achieving up to 98% ee. In contrast, the reactions of the same substrate with other nucleophiles proceeded either slowly and with poor ee's (amination with benzylamine) or not at all (etherification with benzyl alcohol). In order to rationalise the influence of the ligand structure on the reaction course, three model complexes, viz. [(η(3)-methallyl)PdCl(L-κP)], [(η(3)-methallyl)Pd(L-κ(2)O,P)]ClO(4) and [(η(3)-methallyl)Pd(L-κP)(2)]ClO(4) have been prepared from the achiral amide Ph(2)PfcCONHCH(2)CO(2)Me (L; fc = ferrocene-1,1'-diyl) and structurally characterised. The coordination study showed that the amido-phosphines readily form 1 : 1 complexes as O,P-chelates where the amino acid chirality is brought close to the Pd atom. At higher ligand-to-metal ratios, however, simple P-monodentate coordination prevails, minimising the influence of the chiral amino acid pendant.

  16. Hydrodehalogenation of Alkyl Iodides with Base-Mediated Hydrogenation and Catalytic Transfer Hydrogenation: Application to the Asymmetric Synthesis of N-Protected α-Methylamines

    PubMed Central

    2015-01-01

    We report a very mild synthesis of N-protected α-methylamines from the corresponding amino acids. Carboxyl groups of amino acids are reduced to iodomethyl groups via hydroxymethyl intermediates. Reductive deiodination to methyl groups is achieved by hydrogenation or catalytic transfer hydrogenation under alkaline conditions. Basic hydrodehalogenation is selective for the iodomethyl group over hydrogenolysis-labile protecting groups, such as benzyloxycarbonyl, benzyl ester, benzyl ether, and 9-fluorenyloxymethyl, thus allowing the conversion of virtually any protected amino acid into the corresponding N-protected α-methylamine. PMID:25116734

  17. Rh2 (S-1,2-NTTL)4 : A novel Rh2 (S-PTTL)4 analog with lower ligand symmetry for asymmetric synthesis of chiral cyclopropylphosphonates.

    PubMed

    Adly, Frady G; Maddalena, Johncarlo; Ghanem, Ashraf

    2014-11-01

    A new series of dirhodium(II) tetracarboxylate was derived from N-1,2-naphthaloyl-(S)-amino acid ligands. In terms of enantioselectivity, Rh2 (S-1,2-NTTL)4 () derived from N-1,2-naphthaloyl-(S)-tert-leucine, was the best-performing catalyst among the new series in the enantioselective synthesis of cyclopropylphosphonate derivatives (up to >99% enantiomeric excess). A predictive model was proposed to justify the observed high enantiomeric induction exhibited by Rh2 (S-1,2-NTTL)4 with donor-acceptor phosphonate carbenoids.

  18. Hydrodehalogenation of alkyl iodides with base-mediated hydrogenation and catalytic transfer hydrogenation: application to the asymmetric synthesis of N-protected α-methylamines.

    PubMed

    Mandal, Pijus K; Birtwistle, J Sanderson; McMurray, John S

    2014-09-05

    We report a very mild synthesis of N-protected α-methylamines from the corresponding amino acids. Carboxyl groups of amino acids are reduced to iodomethyl groups via hydroxymethyl intermediates. Reductive deiodination to methyl groups is achieved by hydrogenation or catalytic transfer hydrogenation under alkaline conditions. Basic hydrodehalogenation is selective for the iodomethyl group over hydrogenolysis-labile protecting groups, such as benzyloxycarbonyl, benzyl ester, benzyl ether, and 9-fluorenyloxymethyl, thus allowing the conversion of virtually any protected amino acid into the corresponding N-protected α-methylamine.

  19. [4+2] Cycloaddition of 2-substituted 1,2-dihydropyridines with nitrosobenzene: asymmetric synthesis of trans-2-substituted 3-amino-1,2,3,6-tetrahydropyridines.

    PubMed

    Lemire, Alexandre; Beaudoin, Daniel; Grenon, Michel; Charette, André B

    2005-03-18

    [reaction: see text] A new methodology for the stereoselective synthesis of trans-2-substituted 3-amino-1,2,3,6-tetrahydropyridines is reported. The preparation of these 3-aminopiperidines is achieved by cycloaddition of nitrosobenzene with 2-substituted 1,2-dihydropyridines followed by chemoselective reduction of the cycloadducts. Enantioenriched 1,2-dihydropyridine derivatives are easily prepared from pyridine and a chiral amide following a previous report from our laboratories. Moreover, the in situ hydrogenation of these cycloadducts over palladium in a solution of hydrogen chloride in methanol led to tetrahydropyrroloimidazoles.

  20. Widely applicable synthesis of enantiomerically pure tertiary alkyl-containing 1-alkanols by zirconium-catalyzed asymmetric carboalumination of alkenes and palladium- or copper-catalyzed cross-coupling.

    PubMed

    Xu, Shiqing; Lee, Ching-Tien; Wang, Guangwei; Negishi, Ei-ichi

    2013-08-01

    A highly enantioselective and widely applicable method for the synthesis of various chiral 2-alkyl-1-alkanols, especially those of feeble chirality, has been developed. It consists of zirconium-catalyzed asymmetric carboalumination of alkenes (ZACA), lipase-catalyzed acetylation, and palladium- or copper-catalyzed cross-coupling. By virtue of the high selectivity factor (E) associated with iodine, either (S)- or (R)-enantiomer of 3-iodo-2-alkyl-1-alkanols (1), prepared by ZACA reaction of allyl alcohol, can be readily purified to the level of ≥99% ee by lipase-catalyzed acetylation. A variety of chiral tertiary alkyl-containing alcohols, including those that have been otherwise difficult to prepare, can now be synthesized in high enantiomeric purity by Pd- or Cu-catalyzed cross-coupling of (S)-1 or (R)-2 for introduction of various primary, secondary, and tertiary carbon groups with retention of all carbon skeletal features. These chiral tertiary alkyl-containing alcohols can be further converted into the corresponding acids with full retention of the stereochemistry. The synthetic utility of this method has been demonstrated in the highly enantioselective (≥99% ee) and efficient syntheses of (R)-2-methyl-1-butanol and (R)- and (S)-arundic acids.

  1. Asymmetric gas separation membranes

    SciTech Connect

    Malon, R. F.; Zampini, A.

    1984-12-04

    Asymmetric gas separation membranes of materials having selective permeation of at least one gas of a gaseous mixture over that of one or more remaining gases of the gaseous mixture, exhibit significantly improved permeation selectivities for the at least one gas when the asymmetric membrane is contacted on one or both surfaces with an effective amount of a Lewis acid. The improved asymmetric gas separation membranes, process for producing the improved membrane, and processes utilizing such membranes for selectively separating at least one gas from a gaseous mixture by permeation are disclosed.

  2. Asymmetric gas separation membranes

    SciTech Connect

    Malon, R. F.; Zampini, A.

    1984-09-18

    Asymmetric gas separation membranes of materials having selective permeation of at least one gas of a gaseous mixture over that of one or more remaining gases of the gaseous mixture, exhibit significantly improved permeation selectivities for the at least one gas when the asymmetric membrane is contacted on one or both surfaces with an effective amount of a Br nsted-Lowry acid. The improved asymmetric gas separation membranes, process for producing the improved membrane, and processes utilizing such membranes for selectively separating at least one gas from a gaseous mixture by permeation are disclosed.

  3. Asymmetric catalysis: An enabling science

    PubMed Central

    Trost, Barry M.

    2004-01-01

    Chirality of organic molecules plays an enormous role in areas ranging from medicine to material science, yet the synthesis of such entities in one enantiomeric form is one of the most difficult challenges. The advances being made stem from the convergence of a broader understanding of theory and how structure begets function, the developments in the interface between organic and inorganic chemistry and, most notably, the organic chemistry of the transition metals, and the continuing advancements in the tools to help define structure, especially in solution. General themes for designing catalysts to effect asymmetric induction are helping to make this strategy more useful, in general, with the resultant effect of a marked enhancement of synthetic efficiency. PMID:14990801

  4. Asymmetric Peptide Nanoribbons.

    PubMed

    Yu, Zhilin; Tantakitti, Faifan; Palmer, Liam C; Stupp, Samuel I

    2016-11-09

    Asymmetry in chemical structure or shape at molecular, nanoscale, or microscopic levels is essential to a vast number of functionalities in both natural and artificial systems. Bottom-up approaches to create asymmetric supramolecular nanostructures are considered promising but this strategy suffers from the potentially dynamic nature of noncovalent interactions. We report here on supramolecular self-assembly of asymmetric peptide amphiphiles consisting of two different molecularly linked domains. We found that strong noncovalent interactions and a high degree of internal order among the asymmetric amphiphiles lead to nanoribbons with asymmetric faces due to the preferential self-association of the two domains. The capture of gold nanoparticles on only one face of the nanoribbons demonstrates symmetry breaking in these supramolecular structures.

  5. Asymmetric Boltzmann machines.

    PubMed

    Apolloni, B; Bertoni, A; Campadelli, P; de Falco, D

    1991-01-01

    We study asymmetric stochastic networks from two points of view: combinatorial optimization and learning algorithms based on relative entropy minimization. We show that there are non trivial classes of asymmetric networks which admit a Lyapunov function L under deterministic parallel evolution and prove that the stochastic augmentation of such networks amounts to a stochastic search for global minima of L. The problem of minimizing L for a totally antisymmetric parallel network is shown to be associated to an NP-complete decision problem. The study of entropic learning for general asymmetric networks, performed in the non equilibrium, time dependent formalism, leads to a Hebbian rule based on time averages over the past history of the system. The general algorithm for asymmetric networks is tested on a feed-forward architecture.

  6. Correlation after Asymmetrical Clipping,

    DTIC Science & Technology

    1987-02-01

    A general formula is derived for the correlation coefficient between clipped waveforms or among detection sequences, for the case where the clipping is asymmetric or the detection probability departs from 50%. The analytic arcsine law for symmetrical clipping is rehearsed and new analytic forms are found for asymmetrical clipping with high positive correlation, numerically low correlation and high negative correlation. Keywords: Sonar; Detection; Probability; Great Britain.

  7. Asymmetric block copolymers for supramolecular templating of inorganic nanospace materials.

    PubMed

    Bastakoti, Bishnu Prasad; Li, Yunqi; Kimura, Tatsuo; Yamauchi, Yusuke

    2015-05-06

    This review focuses on polymeric micelles consisting of asymmetric block copolymers as designed templates for several inorganic nanospace materials with a wide variety of compositions. The presence of chemically distinct domains of asymmetric triblock and diblock copolymers provide self-assemblies with more diverse morphological and functional features than those constructed by EOn POm EOn type symmetric triblock copolymers, thereby affording well-designed nanospace materials. This strategy can produce unprecedented nanospace materials, which are very difficult to prepare through other conventional organic templating approaches. Here, the recent development on the synthesis of inorganic nanospace materials are mainly focused on, such as hollow spheres, tubes, and porous oxides, using asymmetric triblock copolymers.

  8. Generic approach for synthesizing asymmetric nanoparticles and nanoassemblies

    DOEpatents

    Sun, Yugang; Hu, Yongxing

    2015-05-26

    A generic route for synthesis of asymmetric nanostructures. This approach utilizes submicron magnetic particles (Fe.sub.3O.sub.4--SiO.sub.2) as recyclable solid substrates for the assembly of asymmetric nanostructures and purification of the final product. Importantly, an additional SiO.sub.2 layer is employed as a mediation layer to allow for selective modification of target nanoparticles. The partially patched nanoparticles are used as building blocks for different kinds of complex asymmetric nanostructures that cannot be fabricated by conventional approaches. The potential applications such as ultra-sensitive substrates for surface enhanced Raman scattering (SERS) have been included.

  9. Asymmetric Michael Addition of Aldimino Esters with Chalcones Catalyzed by Silver/Xing-Phos: Mechanism-Oriented Divergent Synthesis of Chiral Pyrrolines.

    PubMed

    Bai, Xing-Feng; Li, Li; Xu, Zheng; Zheng, Zhan-Jiang; Xia, Chun-Gu; Cui, Yu-Ming; Xu, Li-Wen

    2016-07-18

    The mechanism-oriented reaction design for the divergent synthesis of chiral molecules from simple starting materials is highly desirable. In this work, aromatic amide-derived nonbiarylatropisomer/silver (silver/Xing-Phos) complex was used to catalyze the Michael addition of glycine aldimino esters to chalcones and successfully applied to the subsequent cyclocondensation to afford substituted cis-Δ(1)-pyrroline derivatives with up to 98 % ee. Besides the inherent performance of the chiral Ag/Xing-Phos catalyst system, it was found that the workup of such reactions played an important role for the stereoselective construction of stereodivergent Δ(1)-pyrrolines, in which an epimerization of the cis-Δ(1)-pyrrolines to the trans-isomers during was revealed.

  10. Cryogenic, Absolute, High Pressure Sensor

    NASA Technical Reports Server (NTRS)

    Chapman, John J. (Inventor); Shams. Qamar A. (Inventor); Powers, William T. (Inventor)

    2001-01-01

    A pressure sensor is provided for cryogenic, high pressure applications. A highly doped silicon piezoresistive pressure sensor is bonded to a silicon substrate in an absolute pressure sensing configuration. The absolute pressure sensor is bonded to an aluminum nitride substrate. Aluminum nitride has appropriate coefficient of thermal expansion for use with highly doped silicon at cryogenic temperatures. A group of sensors, either two sensors on two substrates or four sensors on a single substrate are packaged in a pressure vessel.

  11. Asymmetric synthesis of cyclopentanes bearing four contiguous stereocenters via an NHC-catalyzed Michael/Michael/esterification domino reaction† †Electronic supplementary information (ESI) available: Experimental procedures and characterization date (NMR, IR, MS, HPLC). CCDC 1437686. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5cc09581f Click here for additional data file. Click here for additional data file.

    PubMed Central

    Shu, Tao; Ni, Qijian; Song, Xiaoxiao; Zhao, Kun; Wu, Tianyu; Puttreddy, Rakesh; Rissanen, Kari

    2016-01-01

    An NHC-catalyzed Michael/Michael/esterification domino reaction via homoenolate/enolate intermediates for the asymmetric synthesis of tetrasubstituted cyclopentanes bearing four contiguous stereocenters is described. A variety of α,β-unsaturated aldehydes and 2-nitroallylic acetates react well with good domino yields and high stereoselectivities. PMID:26750327

  12. Determination of the Absolute Stereochemistry of Secondary Alcohols: An Advanced Organic Chemistry Experiment for Undergraduate Students.

    ERIC Educational Resources Information Center

    Bandaranayake, Wickramasinghe M.

    1980-01-01

    Describes experiments which can be completed in five four-hour laboratory sessions, including two synthesis (alpha-phenylbutyric and alpha-phenylbutyric acid anhydride) and determining the absolute stereochemistry of secondary alcohols using the synthetic products. (JN)

  13. Prediction of Multi-Target Networks of Neuroprotective Compounds with Entropy Indices and Synthesis, Assay, and Theoretical Study of New Asymmetric 1,2-Rasagiline Carbamates

    PubMed Central

    Romero Durán, Francisco J.; Alonso, Nerea; Caamaño, Olga; García-Mera, Xerardo; Yañez, Matilde; Prado-Prado, Francisco J.; González-Díaz, Humberto

    2014-01-01

    In a multi-target complex network, the links (Lij) represent the interactions between the drug (di) and the target (tj), characterized by different experimental measures (Ki, Km, IC50, etc.) obtained in pharmacological assays under diverse boundary conditions (cj). In this work, we handle Shannon entropy measures for developing a model encompassing a multi-target network of neuroprotective/neurotoxic compounds reported in the CHEMBL database. The model predicts correctly >8300 experimental outcomes with Accuracy, Specificity, and Sensitivity above 80%–90% on training and external validation series. Indeed, the model can calculate different outcomes for >30 experimental measures in >400 different experimental protocolsin relation with >150 molecular and cellular targets on 11 different organisms (including human). Hereafter, we reported by the first time the synthesis, characterization, and experimental assays of a new series of chiral 1,2-rasagiline carbamate derivatives not reported in previous works. The experimental tests included: (1) assay in absence of neurotoxic agents; (2) in the presence of glutamate; and (3) in the presence of H2O2. Lastly, we used the new Assessing Links with Moving Averages (ALMA)-entropy model to predict possible outcomes for the new compounds in a high number of pharmacological tests not carried out experimentally. PMID:25255029

  14. Asymmetric Synthesis, Structure, and Reactivity of Unexpectedly Stable Spiroepoxy-β-Lactones Including Facile Conversion to Tetronic Acids: Application to (+)-Maculalactone A

    PubMed Central

    Duffy, Richard J.; Morris, Kay A.; Vallakati, Ravikrishna; Zhang, Wei; Romo, Daniel

    2009-01-01

    A novel class of small spirocyclic heterocycles, spiroepoxy-β-lactones (1,4-dioxaspiro[2.3]-hexan-5-ones), is described that exhibit a number of interesting reactivity patterns. These spiroheterocycles, including an optically active series, are readily synthesized by epoxidation of ketene dimers (4-alkylidene-2-oxetanones) available from homo- or heteroketene dimerization. An analysis of bond lengths in these systems by X-ray crystallography and comparison to data for known spirocycles and those determined computationally, suggest that anomeric effects in these systems may be more pronounced due to their rigidity and may contribute to their surprising stability. The synthetic utility of spiroepoxy-β-lactones was explored and one facile rearrangement identified under several conditions provides a 3-step route from acid chlorides to optically active tetronic acids, ubiquitous heterocycles in bioactive natural products. The addition of various nucleophiles to these spirocycles leads primarily to addition at C5 and C2. The utility of an optically active spiroepoxy-β-lactone was demonstrated in the concise, enantioselective synthesis of the anti-fouling agent, (+)-maculalactone A, which proceeds in 5 steps from hydrocinnamoyl chloride by way of a tetronic acid intermediate. PMID:19453152

  15. Catalyst control in sequential asymmetric allylic substitution: stereodivergent access to N,N-diprotected unnatural amino acids.

    PubMed

    Tosatti, Paolo; Campbell, Amanda J; House, David; Nelson, Adam; Marsden, Stephen P

    2011-07-01

    The sequential use of Cu-catalyzed asymmetric allylic alkylation, olefin cross-metathesis, and Ir-catalyzed asymmetric allylic amination allows the concise, stereodivergent synthesis of complex chiral amines with complete regiocontrol and good diastereoselectivity, exemplified by the synthesis of a pair of diastereoisomeric unnatural branched amino acid derivatives.

  16. Asymmetrical field emitter

    DOEpatents

    Fleming, J.G.; Smith, B.K.

    1995-10-10

    A method is disclosed for providing a field emitter with an asymmetrical emitter structure having a very sharp tip in close proximity to its gate. One preferred embodiment of the present invention includes an asymmetrical emitter and a gate. The emitter having a tip and a side is coupled to a substrate. The gate is connected to a step in the substrate. The step has a top surface and a side wall that is substantially parallel to the side of the emitter. The tip of the emitter is in close proximity to the gate. The emitter is at an emitter potential, and the gate is at a gate potential such that with the two potentials at appropriate values, electrons are emitted from the emitter. In one embodiment, the gate is separated from the emitter by an oxide layer, and the emitter is etched anisotropically to form its tip and its asymmetrical structure. 17 figs.

  17. Asymmetrical field emitter

    DOEpatents

    Fleming, James G.; Smith, Bradley K.

    1995-01-01

    Providing a field emitter with an asymmetrical emitter structure having a very sharp tip in close proximity to its gate. One preferred embodiment of the present invention includes an asymmetrical emitter and a gate. The emitter having a tip and a side is coupled to a substrate. The gate is connected to a step in the substrate. The step has a top surface and a side wall that is substantially parallel to the side of the emitter. The tip of the emitter is in close proximity to the gate. The emitter is at an emitter potential, and the gate is at a gate potential such that with the two potentials at appropriate values, electrons are emitted from the emitter. In one embodiment, the gate is separated from the emitter by an oxide layer, and the emitter is etched anisotropically to form its tip and its asymmetrical structure.

  18. Database applicaton for absolute spectrophotometry

    NASA Astrophysics Data System (ADS)

    Bochkov, Valery V.; Shumko, Sergiy

    2002-12-01

    32-bit database application with multidocument interface for Windows has been developed to calculate absolute energy distributions of observed spectra. The original database contains wavelength calibrated observed spectra which had been already passed through apparatus reductions such as flatfielding, background and apparatus noise subtracting. Absolute energy distributions of observed spectra are defined in unique scale by means of registering them simultaneously with artificial intensity standard. Observations of sequence of spectrophotometric standards are used to define absolute energy of the artificial standard. Observations of spectrophotometric standards are used to define optical extinction in selected moments. FFT algorithm implemented in the application allows performing convolution (deconvolution) spectra with user-defined PSF. The object-oriented interface has been created using facilities of C++ libraries. Client/server model with Windows Socket functionality based on TCP/IP protocol is used to develop the application. It supports Dynamic Data Exchange conversation in server mode and uses Microsoft Exchange communication facilities.

  19. Recent progress in asymmetric bifunctional catalysis using multimetallic systems.

    PubMed

    Shibasaki, Masakatsu; Kanai, Motomu; Matsunaga, Shigeki; Kumagai, Naoya

    2009-08-18

    The concept of bifunctional catalysis, wherein both partners of a bimolecular reaction are simultaneously activated, is very powerful for designing efficient asymmetric catalysts. Catalytic asymmetric processes are indispensable for producing enantiomerically enriched compounds in modern organic synthesis, providing more economical and environmentally benign results than methods requiring stoichiometric amounts of chiral reagents. Extensive efforts in this field have produced many asymmetric catalysts, and now a number of reactions can be rendered asymmetric. We have focused on the development of asymmetric catalysts that exhibit high activity, selectivity, and broad substrate generality under mild reaction conditions. Asymmetric catalysts based on the concept of bifunctional catalysis have emerged as a particularly effective class, enabling simultaneous activation of multiple reaction components. Compared with conventional catalysts, bifunctional catalysts generally exhibit enhanced catalytic activity and higher levels of stereodifferentiation under milder reaction conditions, attracting much attention as next-generation catalysts for prospective practical applications. In this Account, we describe recent advances in enantioselective catalysis with bifunctional catalysts. Since our identification of heterobimetallic rare earth-alkali metal-BINOL (REMB) complexes, we have developed various types of bifunctional multimetallic catalysts. The REMB catalytic system is effective for catalytic asymmetric Corey-Chaykovsky epoxidation and cyclopropanation. A dinucleating Schiff base has emerged as a suitable multidentate ligand for bimetallic catalysts, promoting catalytic syn-selective nitro-Mannich, anti-selective nitroaldol, and Mannich-type reactions. The sugar-based ligand GluCAPO provides a suitable platform for polymetallic catalysts; structural elucidation revealed that their higher order polymetallic structures are a determining factor for their function in the

  20. Asymmetric ion trap

    DOEpatents

    Barlow, S.E.; Alexander, M.L.; Follansbee, J.C.

    1997-12-02

    An ion trap having two end cap electrodes disposed asymmetrically about a center of a ring electrode is disclosed. The inner surface of the end cap electrodes are conformed to an asymmetric pair of equipotential lines of the harmonic formed by the application of voltages to the electrodes. The asymmetry of the end cap electrodes allows ejection of charged species through the closer of the two electrodes which in turn allows for simultaneously detecting anions and cations expelled from the ion trap through the use of two detectors charged with opposite polarity. 4 figs.

  1. Asymmetric ion trap

    DOEpatents

    Barlow, Stephan E.; Alexander, Michael L.; Follansbee, James C.

    1997-01-01

    An ion trap having two end cap electrodes disposed asymmetrically about a center of a ring electrode. The inner surface of the end cap electrodes are conformed to an asymmetric pair of equipotential lines of the harmonic formed by the application of voltages to the electrodes. The asymmetry of the end cap electrodes allows ejection of charged species through the closer of the two electrodes which in turn allows for simultaneously detecting anions and cations expelled from the ion trap through the use of two detectors charged with opposite polarity.

  2. Absolute classification with unsupervised clustering

    NASA Technical Reports Server (NTRS)

    Jeon, Byeungwoo; Landgrebe, D. A.

    1992-01-01

    An absolute classification algorithm is proposed in which the class definition through training samples or otherwise is required only for a particular class of interest. The absolute classification is considered as a problem of unsupervised clustering when one cluster is known initially. The definitions and statistics of the other classes are automatically developed through the weighted unsupervised clustering procedure, which is developed to keep the cluster corresponding to the class of interest from losing its identity as the class of interest. Once all the classes are developed, a conventional relative classifier such as the maximum-likelihood classifier is used in the classification.

  3. Total synthesis of fostriecin: via a regio- and stereoselective polyene hydration, oxidation, and hydroboration sequence.

    PubMed

    Gao, Dong; O'Doherty, George A

    2010-09-03

    A total synthesis of the fostriecin has been achieved in 24 steps from enyne 11. The lactone moiety was installed by a Leighton allylation and Grubbs ring-closing metathesis reaction. The highly reactive Z,Z,E-triene moiety was installed via a late-stage Suzuki-Miyaura cross-coupling of a remarkably stable Z-vinyl boronate. The relative and absolute stereocenters of the C-8,9,11 triol were generated with a regio- and stereoselective asymmetric hydration/oxidation sequence.

  4. Absolute transition probabilities of phosphorus.

    NASA Technical Reports Server (NTRS)

    Miller, M. H.; Roig, R. A.; Bengtson, R. D.

    1971-01-01

    Use of a gas-driven shock tube to measure the absolute strengths of 21 P I lines and 126 P II lines (from 3300 to 6900 A). Accuracy for prominent, isolated neutral and ionic lines is estimated to be 28 to 40% and 18 to 30%, respectively. The data and the corresponding theoretical predictions are examined for conformity with the sum rules.-

  5. Relativistic Absolutism in Moral Education.

    ERIC Educational Resources Information Center

    Vogt, W. Paul

    1982-01-01

    Discusses Emile Durkheim's "Moral Education: A Study in the Theory and Application of the Sociology of Education," which holds that morally healthy societies may vary in culture and organization but must possess absolute rules of moral behavior. Compares this moral theory with current theory and practice of American educators. (MJL)

  6. Absolute Standards for Climate Measurements

    NASA Astrophysics Data System (ADS)

    Leckey, J.

    2016-10-01

    In a world of changing climate, political uncertainty, and ever-changing budgets, the benefit of measurements traceable to SI standards increases by the day. To truly resolve climate change trends on a decadal time scale, on-orbit measurements need to be referenced to something that is both absolute and unchanging. One such mission is the Climate Absolute Radiance and Refractivity Observatory (CLARREO) that will measure a variety of climate variables with an unprecedented accuracy to definitively quantify climate change. In the CLARREO mission, we will utilize phase change cells in which a material is melted to calibrate the temperature of a blackbody that can then be observed by a spectrometer. A material's melting point is an unchanging physical constant that, through a series of transfers, can ultimately calibrate a spectrometer on an absolute scale. CLARREO consists of two primary instruments: an infrared (IR) spectrometer and a reflected solar (RS) spectrometer. The mission will contain orbiting radiometers with sufficient accuracy to calibrate other space-based instrumentation and thus transferring the absolute traceability. The status of various mission options will be presented.

  7. Potential Skin Regeneration Activity and Chemical Composition of Absolute from Pueraria thunbergiana Flower.

    PubMed

    Kim, Do-Yoon; Won, Kyung-Jong; Hwang, Dae-Il; Yoon, Seok Won; Lee, Su Jin; Park, Joo-Hoon; Yoon, Myeong Sik; Kim, Bokyung; Lee, Hwan Myung

    2015-11-01

    The flower of Pueraria thunbergiana BENTH (PTBF) contains isoflavonoids and essential oil components. It has many biological and pharmacological activities, including anti-diabetes, anti-oxidant, and weight loss. However, its effect on skin regeneration remains unknown. In the present study, we isolated the absolute from PTBF through solvent extraction and determined the role of the absolute on skin regeneration-associated responses in human epidermal-keratinocytes (HaCats). The PTBF absolute, which contained 10 compounds, stimulated migration and proliferation and increased the phosphorylation of serine/threonine-specific protein kinase and extracellular signal-regulated kinasel/2 in HaCats. It induced type I and IV collagen synthesis in HaCats. In addition, treatment with PTBF absolute resulted in increased sprout outgrowth in HaCats. These findings suggest that PTBF absolute may participate in skin regeneration, probably through promotion of migration, proliferation, and collagen synthesis.

  8. Asymmetric catalysis for the construction of quaternary carbon centres: nucleophilic addition on ketones and ketimines.

    PubMed

    Riant, Olivier; Hannedouche, Jérôme

    2007-03-21

    There is a growing need in organic synthesis for efficient methodologies for the asymmetric synthesis of quaternary carbon centres. One of the most attractive and straightforward methods focuses on the use of asymmetric catalysis for the addition of various types of nucleophiles on prochiral ketones and ketimines. A view of the literature from this growing area of research will be presented in this review, with an emphasis on the pioneer works and milestones brought by the main players in this field.

  9. Rh-Catalyzed Asymmetric Hydrogenation of 1,2-Dicyanoalkenes.

    PubMed

    Li, Meina; Kong, Duanyang; Zi, Guofu; Hou, Guohua

    2017-01-06

    A highly efficient enantioselective hydrogenation of 1,2-dicyanoalkenes catalyzed by the complex of rhodium and f-spiroPhos has been developed. A series of 1,2-dicyanoalkenes were successfully hydrogenated to the corresponding chiral 1,2-dicyanoalkanes under mild conditions with excellent enantioselectivities (up to 98% ee). This methodology provides efficient access to the asymmetric synthesis of chiral diamines.

  10. New advances in dual stereocontrol for asymmetric reactions.

    PubMed

    Escorihuela, Jorge; Burguete, M Isabel; Luis, Santiago V

    2013-06-21

    Achieving dual stereocontrol in asymmetric reactions using a single enantiomer for the building of the chiral catalyst or auxiliary is a very important goal in enantioselective synthesis as it eliminates the need for having available the two enantiomers of the auxiliary or catalyst designed. Recent strategies and advances towards this goal during the last four years will be discussed throughout this review.

  11. One-step catalytic asymmetric synthesis of all-syn deoxypropionate motif from propylene: Total synthesis of (2R,4R,6R,8R)-2,4,6,8-tetramethyldecanoic acid

    PubMed Central

    Ota, Yusuke; Murayama, Toshiki; Nozaki, Kyoko

    2016-01-01

    In nature, many complex structures are assembled from simple molecules by a series of tailored enzyme-catalyzed reactions. One representative example is the deoxypropionate motif, an alternately methylated alkyl chain containing multiple stereogenic centers, which is biosynthesized by a series of enzymatic reactions from simple building blocks. In organic synthesis, however, the majority of the reported routes require the syntheses of complex building blocks. Furthermore, multistep reactions with individual purifications are required at each elongation. Here we show the construction of the deoxypropionate structure from propylene in a single step to achieve a three-step synthesis of (2R,4R,6R,8R)-2,4,6,8-tetramethyldecanoic acid, a major acid component of a preen-gland wax of the graylag goose. To realize this strategy, we focused on the coordinative chain transfer polymerization and optimized the reaction condition to afford a stereo-controlled oligomer, which is contrastive to the other synthetic strategies developed to date that require 3–6 steps per unit, with unavoidable byproduct generation. Furthermore, multiple oligomers with different number of deoxypropionate units were isolated from one batch, showing application to the construction of library. Our strategy opens the door for facile synthetic routes toward other natural products that share the deoxypropionate motif. PMID:26908873

  12. Stereoselective synthesis of 4-substituted-cyclic sulfamidate-5-carboxylates by asymmetric transfer hydrogenation accompanied by dynamic kinetic resolution and applications to concise stereoselective syntheses of (-)-epi-cytoxazone and the taxotere side-chain.

    PubMed

    Kim, Jin-ah; Seo, Yeon Ji; Kang, Soyeong; Han, Juae; Lee, Hyeon-Kyu

    2014-11-18

    Dynamic kinetic resolution driven, asymmetric transfer hydrogenation reactions of cyclic sulfamidate imine-5-carboxylate esters were developed. Applications of the new methodology to stereoselective syntheses of the taxotere side-chain and (-)-epi-cytoxazone are described.

  13. Absolute calibration of optical flats

    DOEpatents

    Sommargren, Gary E.

    2005-04-05

    The invention uses the phase shifting diffraction interferometer (PSDI) to provide a true point-by-point measurement of absolute flatness over the surface of optical flats. Beams exiting the fiber optics in a PSDI have perfect spherical wavefronts. The measurement beam is reflected from the optical flat and passed through an auxiliary optic to then be combined with the reference beam on a CCD. The combined beams include phase errors due to both the optic under test and the auxiliary optic. Standard phase extraction algorithms are used to calculate this combined phase error. The optical flat is then removed from the system and the measurement fiber is moved to recombine the two beams. The newly combined beams include only the phase errors due to the auxiliary optic. When the second phase measurement is subtracted from the first phase measurement, the absolute phase error of the optical flat is obtained.

  14. The Absolute Spectrum Polarimeter (ASP)

    NASA Technical Reports Server (NTRS)

    Kogut, A. J.

    2010-01-01

    The Absolute Spectrum Polarimeter (ASP) is an Explorer-class mission to map the absolute intensity and linear polarization of the cosmic microwave background and diffuse astrophysical foregrounds over the full sky from 30 GHz to 5 THz. The principal science goal is the detection and characterization of linear polarization from an inflationary epoch in the early universe, with tensor-to-scalar ratio r much greater than 1O(raised to the power of { -3}) and Compton distortion y < 10 (raised to the power of{-6}). We describe the ASP instrument and mission architecture needed to detect the signature of an inflationary epoch in the early universe using only 4 semiconductor bolometers.

  15. Physics of negative absolute temperatures

    NASA Astrophysics Data System (ADS)

    Abraham, Eitan; Penrose, Oliver

    2017-01-01

    Negative absolute temperatures were introduced into experimental physics by Purcell and Pound, who successfully applied this concept to nuclear spins; nevertheless, the concept has proved controversial: a recent article aroused considerable interest by its claim, based on a classical entropy formula (the "volume entropy") due to Gibbs, that negative temperatures violated basic principles of statistical thermodynamics. Here we give a thermodynamic analysis that confirms the negative-temperature interpretation of the Purcell-Pound experiments. We also examine the principal arguments that have been advanced against the negative temperature concept; we find that these arguments are not logically compelling, and moreover that the underlying "volume" entropy formula leads to predictions inconsistent with existing experimental results on nuclear spins. We conclude that, despite the counterarguments, negative absolute temperatures make good theoretical sense and did occur in the experiments designed to produce them.

  16. Optomechanics for absolute rotation detection

    NASA Astrophysics Data System (ADS)

    Davuluri, Sankar

    2016-07-01

    In this article, we present an application of optomechanical cavity for the absolute rotation detection. The optomechanical cavity is arranged in a Michelson interferometer in such a way that the classical centrifugal force due to rotation changes the length of the optomechanical cavity. The change in the cavity length induces a shift in the frequency of the cavity mode. The phase shift corresponding to the frequency shift in the cavity mode is measured at the interferometer output to estimate the angular velocity of absolute rotation. We derived an analytic expression to estimate the minimum detectable rotation rate in our scheme for a given optomechanical cavity. Temperature dependence of the rotation detection sensitivity is studied.

  17. cis-2,5-Diaminobicyclo[2.2.2]octane, a New Chiral Scaffold for Asymmetric Catalysis.

    PubMed

    Shaw, Subrata; White, James D

    2016-09-20

    synthesis of the cyclopropane-containing drug candidate Synosutine. Reduction of the pair of imine functions of the ligand to secondary amines permitted formation of a copper(I)-salen complex that catalyzed asymmetric Henry ("nitroaldol") condensation with excellent efficiency; this catalyst was applied in an economical synthesis of three drugs of the "beta-blocker" family including (S)-Propanolol. Chromium(II) and chromium(III) complexes were prepared from our bicyclooctane-salen ligand bearing a pair of tert-butyl groups in each benzenoid ring. These complexes were found to catalyze, respectively, enantioselective formation of homoallylic alcohols from Nozaki-Hiyama-Kishi allylation of aromatic aldehydes and dihydropyranones from hetero-Diels-Alder cycloaddition. Plausible reaction models emerging from knowledge of the absolute configuration of products from each of these reactions place the metal-coordinated substrate in a quadrant beneath the bicyclooctane scaffold so that one face of the substrate is blocked by an aryl ring of the salen ligand while the opposite face is left open to attack. The consistent and predictable stereochemical outcome from reactions catalyzed by salen-metal complexes derived from our diaminobicyclo[2.2.2]octane scaffold adds a valuable new dimension to asymmetric synthesis.

  18. Multipartite asymmetric quantum cloning

    SciTech Connect

    Iblisdir, S.; Gisin, N.; Acin, A.; Cerf, N.J.; Filip, R.; Fiurasek, J.

    2005-10-15

    We investigate the optimal distribution of quantum information over multipartite systems in asymmetric settings. We introduce cloning transformations that take N identical replicas of a pure state in any dimension as input and yield a collection of clones with nonidentical fidelities. As an example, if the clones are partitioned into a set of M{sub A} clones with fidelity F{sup A} and another set of M{sub B} clones with fidelity F{sup B}, the trade-off between these fidelities is analyzed, and particular cases of optimal N{yields}M{sub A}+M{sub B} cloning machines are exhibited. We also present an optimal 1{yields}1+1+1 cloning machine, which is an example of a tripartite fully asymmetric cloner. Finally, it is shown how these cloning machines can be optically realized.

  19. Asymmetric hydrogenations (Nobel lecture).

    PubMed

    Knowles, William S

    2002-06-17

    The start of the development of catalysts for asymmetric hydrogenation was the concept of replacing the triphenylphosphane ligand of the Wilkinson catalyst with a chiral ligand. With the new catalysts, it should be possible to hydrogenate prochiral olefins. Knowles and his co-workers were convinced that the phosphorus atom played a central role in this selectivity, as only chiral phosphorus ligands such as (R,R)-DIPAMP, whose stereogenic center lies directly on the phosphorus atom, lead to high enantiomeric excesses when used as catalysts in asymmetric hydrogenation reactions. This hypothesis was disproven by the development of ligands with chiral carbon backbones. Although the exact mechanism of action of the phosphane ligands is not incontrovertibly determined to this day, they provide a simple entry to a large number of chiral compounds.

  20. Advances in Stereoconvergent Catalysis from 2005 to 2015: Transition-Metal-Mediated Stereoablative Reactions, Dynamic Kinetic Resolutions, and Dynamic Kinetic Asymmetric Transformations.

    PubMed

    Bhat, Vikram; Welin, Eric R; Guo, Xuelei; Stoltz, Brian M

    2017-03-08

    Stereoconvergent catalysis is an important subset of asymmetric synthesis that encompasses stereoablative transformations, dynamic kinetic resolutions, and dynamic kinetic asymmetric transformations. Initially, only enzymes were known to catalyze dynamic kinetic processes, but recently various synthetic catalysts have been developed. This Review summarizes major advances in nonenzymatic, transition-metal-promoted dynamic asymmetric transformations reported between 2005 and 2015.

  1. Asymmetric information and economics

    NASA Astrophysics Data System (ADS)

    Frieden, B. Roy; Hawkins, Raymond J.

    2010-01-01

    We present an expression of the economic concept of asymmetric information with which it is possible to derive the dynamical laws of an economy. To illustrate the utility of this approach we show how the assumption of optimal information flow leads to a general class of investment strategies including the well-known Q theory of Tobin. Novel consequences of this formalism include a natural definition of market efficiency and an uncertainty principle relating capital stock and investment flow.

  2. Asymmetric dipolar ring

    DOEpatents

    Prosandeev, Sergey A.; Ponomareva, Inna V.; Kornev, Igor A.; Bellaiche, Laurent M.

    2010-11-16

    A device having a dipolar ring surrounding an interior region that is disposed asymmetrically on the ring. The dipolar ring generates a toroidal moment switchable between at least two stable states by a homogeneous field applied to the dipolar ring in the plane of the ring. The ring may be made of ferroelectric or magnetic material. In the former case, the homogeneous field is an electric field and in the latter case, the homogeneous field is a magnetic field.

  3. Oscillating asymmetric dark matter

    SciTech Connect

    Tulin, Sean; Yu, Hai-Bo; Zurek, Kathryn M. E-mail: haiboyu@umich.edu

    2012-05-01

    We study the dynamics of dark matter (DM) particle-antiparticle oscillations within the context of asymmetric DM. Oscillations arise due to small DM number-violating Majorana-type mass terms, and can lead to recoupling of annihilation after freeze-out and washout of the DM density. Asymmetric DM oscillations 'interpolate' between symmetric and asymmetric DM freeze-out scenarios, and allow for a larger DM model-building parameter space. We derive the density matrix equations for DM oscillations and freeze-out from first principles using nonequilibrium field theory, and our results are qualitatively different than in previous studies. DM dynamics exhibits particle-vs-antiparticle 'flavor' effects, depending on the interaction type, analogous to neutrino oscillations in a medium. 'Flavor-sensitive' DM interactions include scattering or annihilation through a new vector boson, while 'flavor-blind' interactions include scattering or s-channel annihilation through a new scalar boson. In particular, we find that flavor-sensitive annihilation does not recouple when coherent oscillations begin, and that flavor-blind scattering does not lead to decoherence.

  4. Asymmetrical Capacitors for Propulsion

    NASA Technical Reports Server (NTRS)

    Canning, Francis X.; Melcher, Cory; Winet, Edwin

    2004-01-01

    Asymmetrical Capacitor Thrusters have been proposed as a source of propulsion. For over eighty years, it has been known that a thrust results when a high voltage is placed across an asymmetrical capacitor, when that voltage causes a leakage current to flow. However, there is surprisingly little experimental or theoretical data explaining this effect. This paper reports on the results of tests of several Asymmetrical Capacitor Thrusters (ACTs). The thrust they produce has been measured for various voltages, polarities, and ground configurations and their radiation in the VHF range has been recorded. These tests were performed at atmospheric pressure and at various reduced pressures. A simple model for the thrust was developed. The model assumed the thrust was due to electrostatic forces on the leakage current flowing across the capacitor. It was further assumed that this current involves charged ions which undergo multiple collisions with air. These collisions transfer momentum. All of the measured data was consistent with this model. Many configurations were tested, and the results suggest general design principles for ACTs to be used for a variety of purposes.

  5. Oscillating asymmetric dark matter

    NASA Astrophysics Data System (ADS)

    Tulin, Sean; Yu, Hai-Bo; Zurek, Kathryn M.

    2012-05-01

    We study the dynamics of dark matter (DM) particle-antiparticle oscillations within the context of asymmetric DM. Oscillations arise due to small DM number-violating Majorana-type mass terms, and can lead to recoupling of annihilation after freeze-out and washout of the DM density. Asymmetric DM oscillations "interpolate" between symmetric and asymmetric DM freeze-out scenarios, and allow for a larger DM model-building parameter space. We derive the density matrix equations for DM oscillations and freeze-out from first principles using nonequilibrium field theory, and our results are qualitatively different than in previous studies. DM dynamics exhibits particle-vs-antiparticle "flavor" effects, depending on the interaction type, analogous to neutrino oscillations in a medium. "Flavor-sensitive" DM interactions include scattering or annihilation through a new vector boson, while "flavor-blind" interactions include scattering or s-channel annihilation through a new scalar boson. In particular, we find that flavor-sensitive annihilation does not recouple when coherent oscillations begin, and that flavor-blind scattering does not lead to decoherence.

  6. Asymmetric Synthesis of Tertiary Benzylic Alcohols

    PubMed Central

    Antczak, Monika I.; Cai, Feng; Ready, Joseph M.

    2010-01-01

    Vinyl, aryl and alkynyl organometallics add to ketones containing a stereogenic sulfoxide. Tertiary alcohols are generated in diastereomerically and enantiomerically pure form. Reductive lithiation converts the sulfoxide into a variety of useful functional groups. PMID:21142190

  7. Efficient asymmetric synthesis of [7]helicene bisquinones.

    PubMed

    Carreño, M Carmen; González-López, Marcos; Urbano, Antonio

    2005-02-07

    The efficient one-pot six-step domino process which occurs when (SS)-2-(p-tolylsulfinyl)-1,4-benzoquinone (1) reacts with 3,6-divinyl-1,2,7,8-tetrahydrophenanthrenes 2a-c allowed enantioselective access to [7]helicene bisquinones 3a-c with excellent optical purities (96 to > 99% ee).

  8. Asymmetric multiscale detrended fluctuation analysis of California electricity spot price

    NASA Astrophysics Data System (ADS)

    Fan, Qingju

    2016-01-01

    In this paper, we develop a new method called asymmetric multiscale detrended fluctuation analysis, which is an extension of asymmetric detrended fluctuation analysis (A-DFA) and can assess the asymmetry correlation properties of series with a variable scale range. We investigate the asymmetric correlations in California 1999-2000 power market after filtering some periodic trends by empirical mode decomposition (EMD). Our findings show the coexistence of symmetric and asymmetric correlations in the price series of 1999 and strong asymmetric correlations in 2000. What is more, we detect subtle correlation properties of the upward and downward price series for most larger scale intervals in 2000. Meanwhile, the fluctuations of Δα(s) (asymmetry) and | Δα(s) | (absolute asymmetry) are more significant in 2000 than that in 1999 for larger scale intervals, and they have similar characteristics for smaller scale intervals. We conclude that the strong asymmetry property and different correlation properties of upward and downward price series for larger scale intervals in 2000 have important implications on the collapse of California power market, and our findings shed a new light on the underlying mechanisms of power price.

  9. Absolute calibration of optical tweezers

    SciTech Connect

    Viana, N.B.; Mazolli, A.; Maia Neto, P.A.; Nussenzveig, H.M.; Rocha, M.S.; Mesquita, O.N.

    2006-03-27

    As a step toward absolute calibration of optical tweezers, a first-principles theory of trapping forces with no adjustable parameters, corrected for spherical aberration, is experimentally tested. Employing two very different setups, we find generally very good agreement for the transverse trap stiffness as a function of microsphere radius for a broad range of radii, including the values employed in practice, and at different sample chamber depths. The domain of validity of the WKB ('geometrical optics') approximation to the theory is verified. Theoretical predictions for the trapping threshold, peak position, depth variation, multiple equilibria, and 'jump' effects are also confirmed.

  10. Switching control of linear systems subject to asymmetric actuator saturation

    NASA Astrophysics Data System (ADS)

    Yuan, Chengzhi; Wu, Fen

    2015-01-01

    In this paper, we study the saturation control problem for linear time-invariant (LTI) systems subject to asymmetric actuator saturation under a switching control framework. The LTI plant with asymmetric saturation is first transformed to an equivalent switched linear model with each subsystem subject to symmetric actuator saturation, based on which a dwell-time switching controller augmented with a controller state reset is then developed by using multiple Lyapunov functions. The controller synthesis conditions are formulated as linear matrix inequalities (LMIs), which can be solved efficiently. Simulation results are also included to illustrate the effectiveness and advantages of the proposed approach.

  11. Phosphorothioate analogs of P1,P3-di(nucleosid-5'-yl) triphosphates: Synthesis, assignment of the absolute configuration at P-atoms and P-stereodependent recognition by Fhit hydrolase.

    PubMed

    Kaczmarek, Renata; Krakowiak, Agnieszka; Korczyński, Dariusz; Baraniak, Janina; Nawrot, Barbara

    2016-11-01

    Di(nucleosid-5'-yl) polyphosphates (NPnN) are involved in various biological processes, and constitute signaling molecules in the intermolecular purinergic systems. They exert tumor suppression function and are substrates for specific hydrolases (e.g., HIT proteins). Their structural analogs may serve as molecular probes and potential therapeutic agents. Three P1,P3-bis-thio-analogs of symmetrical di(nucleosid-5'-yl) triphosphates (NP3N) bearing adenosine, guanosine or ribavirin residues (6, 7 and 8, respectively), were obtained by direct condensation of corresponding base-protected nucleoside-5'-O-(2-thio-1,3,2-oxathiaphospholane) with anhydrous phosphoric acid in the presence of DBU. Deprotected products 6 and 8 were separated into individual P-diastereoisomers, whereas 7 was partially separated to yield diastereomerically enriched fractions. The absolute configuration at P-stereogenic centers in the separated diastereoisomers was assigned by RP-HPLC analysis of the products of enzymatic digestion with snake venom phosphodiesterase. The Fhit-assisted hydrolysis rates for 6 and 7 are by 2-3 orders of magnitude lower than that for the reference AP3A, and depend on the configuration of the stereogenic phosphorus atoms, while 8 occurred to be resistant to this cleavage.

  12. Cosmology with negative absolute temperatures

    NASA Astrophysics Data System (ADS)

    Vieira, J. P. P.; Byrnes, Christian T.; Lewis, Antony

    2016-08-01

    Negative absolute temperatures (NAT) are an exotic thermodynamical consequence of quantum physics which has been known since the 1950's (having been achieved in the lab on a number of occasions). Recently, the work of Braun et al. [1] has rekindled interest in negative temperatures and hinted at a possibility of using NAT systems in the lab as dark energy analogues. This paper goes one step further, looking into the cosmological consequences of the existence of a NAT component in the Universe. NAT-dominated expanding Universes experience a borderline phantom expansion (w < -1) with no Big Rip, and their contracting counterparts are forced to bounce after the energy density becomes sufficiently large. Both scenarios might be used to solve horizon and flatness problems analogously to standard inflation and bouncing cosmologies. We discuss the difficulties in obtaining and ending a NAT-dominated epoch, and possible ways of obtaining density perturbations with an acceptable spectrum.

  13. Preparation of asymmetric porous materials

    DOEpatents

    Coker, Eric N [Albuquerque, NM

    2012-08-07

    A method for preparing an asymmetric porous material by depositing a porous material film on a flexible substrate, and applying an anisotropic stress to the porous media on the flexible substrate, where the anisotropic stress results from a stress such as an applied mechanical force, a thermal gradient, and an applied voltage, to form an asymmetric porous material.

  14. Additive Effects on Asymmetric Catalysis.

    PubMed

    Hong, Liang; Sun, Wangsheng; Yang, Dongxu; Li, Guofeng; Wang, Rui

    2016-03-23

    This review highlights a number of additives that can be used to make asymmetric reactions perfect. Without changing other reaction conditions, simply adding additives can lead to improved asymmetric catalysis, such as reduced reaction time, improved yield, or/and increased selectivity.

  15. Asymmetric twin Dark Matter

    SciTech Connect

    Farina, Marco

    2015-11-09

    We study a natural implementation of Asymmetric Dark Matter in Twin Higgs models. The mirroring of the Standard Model strong sector suggests that a twin baryon with mass around 5 GeV is a natural Dark Matter candidate once a twin baryon number asymmetry comparable to the SM asymmetry is generated. We explore twin baryon Dark Matter in two different scenarios, one with minimal content in the twin sector and one with a complete copy of the SM, including a light twin photon. The essential requirements for successful thermal history are presented, and in doing so we address some of the cosmological issues common to many Twin Higgs models. The required interactions we introduce predict signatures at direct detection experiments and at the LHC.

  16. Asymmetric twin Dark Matter

    SciTech Connect

    Farina, Marco

    2015-11-01

    We study a natural implementation of Asymmetric Dark Matter in Twin Higgs models. The mirroring of the Standard Model strong sector suggests that a twin baryon with mass around 5 GeV is a natural Dark Matter candidate once a twin baryon number asymmetry comparable to the SM asymmetry is generated. We explore twin baryon Dark Matter in two different scenarios, one with minimal content in the twin sector and one with a complete copy of the SM, including a light twin photon. The essential requirements for successful thermal history are presented, and in doing so we address some of the cosmological issues common to many Twin Higgs models. The required interactions we introduce predict signatures at direct detection experiments and at the LHC.

  17. Allenes in Asymmetric Catalysis. Asymmetric Ring-Opening of Meso-Epoxides Catalyzed by Allene-Containing Phosphine Oxides

    PubMed Central

    Pu, Xiaotao; Qi, Xiangbing; Ready, Joseph M.

    2009-01-01

    Unsymmetrically substituted allenes (1,2 dienes) are inherently chiral and can be prepared in optically pure form. Nonetheless, to date the allene framework has not been incorporated into ligands for asymmetric catalysis. Since allenes project functionality differently than either tetrahedral carbon or chiral biaryls, they may create complementary chiral environments. This study demonstrates that optically active C2 symmetric allene-containing bisphosphine oxides can catalyze the addition of SiCl4 to meso epoxides with high enantioselectivity. The epoxide-opening likely involves generation of a Lewis acidic, cationic (bisphosphine oxide)SiCl3 complex. The fact that high asymmetric induction is observed suggests that allenes may represent a new platform for the development of ligands and catalysts for asymmetric synthesis. PMID:19722613

  18. Asymmetric photoredox transition-metal catalysis activated by visible light

    NASA Astrophysics Data System (ADS)

    Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Röse, Philipp; Chen, Liang-An; Harms, Klaus; Marsch, Michael; Hilt, Gerhard; Meggers, Eric

    2014-11-01

    Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the `green' synthesis of non-racemic chiral molecules.

  19. Asymmetric Palladium-Catalyzed Directed Intermolecular Fluoroarylation of Styrenes

    PubMed Central

    2015-01-01

    A mild catalytic asymmetric direct fluoro-arylation of styrenes has been developed. The palladium-catalyzed three-component coupling of Selectfluor, a styrene and a boronic acid, provides chiral monofluorinated compounds in good yield and in high enantiomeric excess. A mechanism proceeding through a Pd(IV)-fluoride intermediate is proposed for the transformation and synthesis of an sp3 C–F bond. PMID:24617344

  20. Tectonically Asymmetric Earth

    NASA Astrophysics Data System (ADS)

    Doglioni, C.; Carminati, E.; Crespi, M.; Cuffaro, M.; Panza, G. F.; Riguzzi, F.

    2011-12-01

    The net rotation, or so-called W-ward drift of the lithosphere, implies a decoupling of the plates relative to the underlying asthenosphere, and a relative "E-ward" mantle flow. This polarized flow can account for a number of asymmetries. When comparing the W-directed versus the E- to NE-directed subduction zones, as a general observation, they have the subduction hinge diverging versus converging relative to the upper plate; low versus high topography and structural elevation respectively; deep versus shallow trenches and foreland basins; shallow versus deep decollement; low versus high basement involvement; high versus low heat flow and gravity anomaly; shallow versus deep asthenosphere; etc. The western limbs of rift zones have in average a deeper bathymetry, and show S-waves faster in the lithosphere and slower in the asthenosphere with respect to the eastern limb. These asymmetries can be recognized when moving along the "tectonic equator", which describes the fastest flow of plates relative to the mantle, and it undulates relative to the geographic equator, with an angle of about 30°. Shear-wave splitting alignments tend to parallel the tectonic flow, apart along the subduction zones where they become orthogonal, as a flow encountering an obstacle. The estimates of the net rotation span from 0.2° to 1.2° Ma. However, only a net rotation >1° Ma is required in order to satisfy the aforementioned tectonically asymmetric Earth. In our reconstructions, the best fit for the tectonic equator has a pole of rotation at latitude 56.4° and longitude 136.7°, with an angular velocity of 1.2036°/Ma. This velocity can be obtained only if the source of the so-called volcanic trails or plumes are sourced from the middle of the low-velocity layer, at the top of the asthenosphere, i.e., within the decoupling layer of the plates relative to the underlying mantle. The tectonic equator lies close to the revolution plane of the Moon about the Earth. All these data and

  1. Asymmetric AgPd-AuNR heterostructure with enhanced photothermal performance and SERS activity.

    PubMed

    Zhang, Han; Liu, Zeke; Kang, Xiaolin; Guo, Jun; Ma, Wanli; Cheng, Si

    2016-01-28

    Most as-reported nanostructures through galvanic replacement reactions are still symmetric hollow structures, until now. Asymmetric structures fabricated through a galvanic replacement reaction have been rarely reported. However, asymmetric heterostructures can generally lead to new intriguing properties through asymmetric synergistic coupling. Here, we report a simple synthesis of an asymmetric one-ended AgPd bimetal on Au nanorods (AuNR) by combining a galvanic replacement reaction with an Ostwald ripening process. The morphological evolution from a nanodumbbell to a dandelion structure is thoroughly investigated. The unique asymmetric AgPd-AuNR heterostructures possess the required plasmonic performance and avoid strong damping caused by the poor plasmonic metal Pd, resulting in a superior photothermal heating performance and enhanced SERS sensitivity for in situ monitoring of a catalytic reaction compared with the symmetric counterparts.

  2. Activation of carboxylic acids in asymmetric organocatalysis.

    PubMed

    Monaco, Mattia Riccardo; Poladura, Belén; Diaz de Los Bernardos, Miriam; Leutzsch, Markus; Goddard, Richard; List, Benjamin

    2014-07-01

    Organocatalysis, catalysis using small organic molecules, has recently evolved into a general approach for asymmetric synthesis, complementing both metal catalysis and biocatalysis. Its success relies to a large extent upon the introduction of novel and generic activation modes. Remarkably though, while carboxylic acids have been used as catalyst directing groups in supramolecular transition-metal catalysis, a general and well-defined activation mode for this useful and abundant substance class is still lacking. Herein we propose the heterodimeric association of carboxylic acids with chiral phosphoric acid catalysts as a new activation principle for organocatalysis. This self-assembly increases both the acidity of the phosphoric acid catalyst and the reactivity of the carboxylic acid. To illustrate this principle, we apply our concept in a general and highly enantioselective catalytic aziridine-opening reaction with carboxylic acids as nucleophiles.

  3. Catalytic asymmetric umpolung reactions of imines.

    PubMed

    Wu, Yongwei; Hu, Lin; Li, Zhe; Deng, Li

    2015-07-23

    The carbon-nitrogen double bonds in imines are fundamentally important functional groups in organic chemistry. This is largely due to the fact that imines act as electrophiles towards carbon nucleophiles in reactions that form carbon-carbon bonds, thereby serving as one of the most widely used precursors for the formation of amines in both synthetic and biosynthetic settings. If the carbon atom of the imine could be rendered electron-rich, the imine could react as a nucleophile instead of as an electrophile. Such a reversal in the electronic characteristics of the imine functionality would facilitate the development of new chemical transformations that convert imines into amines via carbon-carbon bond-forming reactions with carbon electrophiles, thereby creating new opportunities for the efficient synthesis of amines. The development of asymmetric umpolung reactions of imines (in which the imines act as nucleophiles) remains uncharted territory, in spite of the far-reaching impact such reactions would have in organic synthesis. Here we report the discovery and development of new chiral phase-transfer catalysts that promote the highly efficient asymmetric umpolung reactions of imines with the carbon electrophile enals. These catalysts mediate the deprotonation of imines and direct the 2-azaallyl anions thus formed to react with enals in a highly chemoselective, regioselective, diastereoselective and enantioselective fashion. The reaction tolerates a broad range of imines and enals, and can be carried out in high yield with as little as 0.01 mole per cent catalyst with a moisture- and air-tolerant operational protocol. These umpolung reactions provide a conceptually new and practical approach to chiral amino compounds.

  4. Catalytic asymmetric umpolung reactions of imines

    NASA Astrophysics Data System (ADS)

    Wu, Yongwei; Hu, Lin; Li, Zhe; Deng, Li

    2015-07-01

    The carbon-nitrogen double bonds in imines are fundamentally important functional groups in organic chemistry. This is largely due to the fact that imines act as electrophiles towards carbon nucleophiles in reactions that form carbon-carbon bonds, thereby serving as one of the most widely used precursors for the formation of amines in both synthetic and biosynthetic settings. If the carbon atom of the imine could be rendered electron-rich, the imine could react as a nucleophile instead of as an electrophile. Such a reversal in the electronic characteristics of the imine functionality would facilitate the development of new chemical transformations that convert imines into amines via carbon-carbon bond-forming reactions with carbon electrophiles, thereby creating new opportunities for the efficient synthesis of amines. The development of asymmetric umpolung reactions of imines (in which the imines act as nucleophiles) remains uncharted territory, in spite of the far-reaching impact such reactions would have in organic synthesis. Here we report the discovery and development of new chiral phase-transfer catalysts that promote the highly efficient asymmetric umpolung reactions of imines with the carbon electrophile enals. These catalysts mediate the deprotonation of imines and direct the 2-azaallyl anions thus formed to react with enals in a highly chemoselective, regioselective, diastereoselective and enantioselective fashion. The reaction tolerates a broad range of imines and enals, and can be carried out in high yield with as little as 0.01 mole per cent catalyst with a moisture- and air-tolerant operational protocol. These umpolung reactions provide a conceptually new and practical approach to chiral amino compounds.

  5. Synthesis of taurospongin A.

    PubMed

    Wu, Boshen; Mallinger, Aurélie; Robertson, Jeremy

    2010-06-18

    Two new routes to the C(1-10) carboxylic acid core of taurospongin A are presented. In the first route, overall asymmetric hydration of a C(2)-C(3) alkene is achieved by Sharpless AD and selective deoxygenation at C(2); in the second route, the C(3) stereogenic center is set by Tietze asymmetric allylation. A short synthesis of the C(1'-25') fatty acid combines with the product from the first route to complete the total synthesis of taurospongin A.

  6. Asymmetric synthesis of chiral β-alkynyl carbonyl and sulfonyl derivatives via sequential palladium and copper catalysis† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c6sc01724j Click here for additional data file.

    PubMed Central

    Masters, James T.; Taft, Benjamin R.; Lumb, Jean-Philip

    2016-01-01

    We present a full account detailing the development of a sequential catalysis strategy for the synthesis of chiral β-alkynyl carbonyl and sulfonyl derivatives. A palladium-catalyzed cross coupling of terminal alkyne donors with acetylenic ester, ketone, and sulfone acceptors generates stereodefined enynes in high yield. These compounds are engaged in an unprecedented, regio- and enantioselective copper-catalyzed conjugate reduction. The process exhibits a high functional group tolerance, and this enables the synthesis of a broad range of chiral products from simple, readily available alkyne precursors. The utility of the method is demonstrated through the elaboration of the chiral β-alkynyl products into a variety of different molecular scaffolds. Its value in complex molecule synthesis is further validated through a concise, enantioselective synthesis of AMG 837, a potent GPR40 receptor agonist. PMID:27746892

  7. Absolute optical metrology : nanometers to kilometers

    NASA Technical Reports Server (NTRS)

    Dubovitsky, Serge; Lay, O. P.; Peters, R. D.; Liebe, C. C.

    2005-01-01

    We provide and overview of the developments in the field of high-accuracy absolute optical metrology with emphasis on space-based applications. Specific work on the Modulation Sideband Technology for Absolute Ranging (MSTAR) sensor is described along with novel applications of the sensor.

  8. ON A SUFFICIENT CONDITION FOR ABSOLUTE CONTINUITY.

    DTIC Science & Technology

    The formulation of a condition which yields absolute continuity when combined with continuity and bounded variation is the problem considered in the...Briefly, the formulation is achieved through a discussion which develops a proof by contradiction of a sufficiently theorem for absolute continuity which uses in its hypothesis the condition of continuity and bounded variation .

  9. Introducing the Mean Absolute Deviation "Effect" Size

    ERIC Educational Resources Information Center

    Gorard, Stephen

    2015-01-01

    This paper revisits the use of effect sizes in the analysis of experimental and similar results, and reminds readers of the relative advantages of the mean absolute deviation as a measure of variation, as opposed to the more complex standard deviation. The mean absolute deviation is easier to use and understand, and more tolerant of extreme…

  10. Monolithically integrated absolute frequency comb laser system

    SciTech Connect

    Wanke, Michael C.

    2016-07-12

    Rather than down-convert optical frequencies, a QCL laser system directly generates a THz frequency comb in a compact monolithically integrated chip that can be locked to an absolute frequency without the need of a frequency-comb synthesizer. The monolithic, absolute frequency comb can provide a THz frequency reference and tool for high-resolution broad band spectroscopy.

  11. Asymmetric Hybrid Nanoparticles

    SciTech Connect

    Chumanov, George

    2015-11-05

    Hybrid Nanoparticles (AHNs) are rationally-designed multifunctional nanostructures and novel building blocks for the next generation of advanced materials and devices. Nanoscale materials attract considerable interest because of their unusual properties and potential for practical applications. Most of the activity in this field is focused on the synthesis of homogeneous nanoparticles from metals, metal oxides, semiconductors, and polymers. It is well recognized that properties of nanoparticles can be further enhanced if they are made as hybrid structures. This program is concerned with the synthesis, characterization, and application of such hybrid structures termed AHNs. AHNs are composed of a homogeneous core and several caps of different materials deposited on its surface (Fig. 1). Combined properties of the core and the caps as well as new properties that arise from core-cap and cap-cap interactions render AHNs multifunctional. In addition, specific chemical reactivity of the caps enables directional self-assembly of AHNs into complex architectures that are not possible with only spherical nanoparticles.

  12. Absolute instability of the Gaussian wake profile

    NASA Technical Reports Server (NTRS)

    Hultgren, Lennart S.; Aggarwal, Arun K.

    1987-01-01

    Linear parallel-flow stability theory has been used to investigate the effect of viscosity on the local absolute instability of a family of wake profiles with a Gaussian velocity distribution. The type of local instability, i.e., convective or absolute, is determined by the location of a branch-point singularity with zero group velocity of the complex dispersion relation for the instability waves. The effects of viscosity were found to be weak for values of the wake Reynolds number, based on the center-line velocity defect and the wake half-width, larger than about 400. Absolute instability occurs only for sufficiently large values of the center-line wake defect. The critical value of this parameter increases with decreasing wake Reynolds number, thereby indicating a shrinking region of absolute instability with decreasing wake Reynolds number. If backflow is not allowed, absolute instability does not occur for wake Reynolds numbers smaller than about 38.

  13. Alkaline earth metal catalysts for asymmetric reactions.

    PubMed

    Kobayashi, Shū; Yamashita, Yasuhiro

    2011-01-18

    The group 2 alkaline earth metals calcium (Ca), strontium (Sr), and barium (Ba) are among the most common elements on Earth, abundant in both the sea and the Earth's crust. Although they are familiar in our daily lives, their application to organic synthesis has, so far, been limited. Some particularly useful properties of these elements include (i) low electronegativity, (ii) a stable oxidation state of +2, meaning that they can potentially form two covalent bonds with anions, and (iii) the ability to occupy a variety of coordination sites due to their large ionic radius. Furthermore, the alkaline earth metals, found between the group 1 and group 3 elements, show mild but significant Lewis acidity, which can be harnessed to control coordinative molecules via a Lewis acid-base interaction. Taken together, these characteristics make the metals Ca, Sr, and Ba very promising components of highly functionalized acid-base catalysts. In this Account, we describe the development of chiral alkaline earth metal catalysts for asymmetric carbon-carbon bond-forming reactions. Recently prepared chiral alkaline earth metal complexes have shown high diastereo- and enantioselectivities in fundamental and important chemical transformations. We chose chiral bisoxazoline (Box) derivatives bearing a methylene tether as a ligand for chiral modification. These molecules are very useful because they can covalently coordinate to alkaline earth metals in a bidentate fashion through deprotonation of the tether portion. It was found that chiral calcium-Box complexes could successfully promote catalytic asymmetric 1,4-addition and [3 + 2] cycloaddition reactions with high diastereo- and enantioselectivities. Both the calcium-Box complexes and chiral strontium-bis-sulfonamide and chiral barium-BINOLate complexes could catalyze asymmetric 1,4-addition reactions with high enantioselectivities. Furthermore, we designed a calcium-neutral coordinative ligand complex as a new type of chiral alkaline

  14. Cinchona Alkaloid Squaramide-Catalyzed Asymmetric Michael Addition of α-Aryl Isocyanoacetates to β-Trifluoromethylated Enones and Its Applications in the Synthesis of Chiral β-Trifluoromethylated Pyrrolines.

    PubMed

    Zhao, Mei-Xin; Zhu, Hui-Kai; Dai, Tong-Lei; Shi, Min

    2015-11-20

    Cinchona alkaloid squaramide can effectively catalyze the asymmetric Michael addition of α-aryl isocyanoacetates to β-trifluoromethylated enones, affording the corresponding adducts with an adjacent chiral tertiary carbon center bearing a CF3 group and a quaternary carbon center in moderate to good yields along with excellent stereoselectivities. The adduct can be easily transformed into biologically attractive chiral β-trifluoromethylated pyrroline carboxylate in high yield via an isocyano group hydrolysis/cyclization/dehydration cascade reaction by treating with acid. The one-pot enantioselective Michael addition/isocyano group hydrolysis/cyclization/dehydration sequential protocol has also been investigated.

  15. Absolute quantitation of protein posttranslational modification isoform.

    PubMed

    Yang, Zhu; Li, Ning

    2015-01-01

    Mass spectrometry has been widely applied in characterization and quantification of proteins from complex biological samples. Because the numbers of absolute amounts of proteins are needed in construction of mathematical models for molecular systems of various biological phenotypes and phenomena, a number of quantitative proteomic methods have been adopted to measure absolute quantities of proteins using mass spectrometry. The liquid chromatography-tandem mass spectrometry (LC-MS/MS) coupled with internal peptide standards, i.e., the stable isotope-coded peptide dilution series, which was originated from the field of analytical chemistry, becomes a widely applied method in absolute quantitative proteomics research. This approach provides more and more absolute protein quantitation results of high confidence. As quantitative study of posttranslational modification (PTM) that modulates the biological activity of proteins is crucial for biological science and each isoform may contribute a unique biological function, degradation, and/or subcellular location, the absolute quantitation of protein PTM isoforms has become more relevant to its biological significance. In order to obtain the absolute cellular amount of a PTM isoform of a protein accurately, impacts of protein fractionation, protein enrichment, and proteolytic digestion yield should be taken into consideration and those effects before differentially stable isotope-coded PTM peptide standards are spiked into sample peptides have to be corrected. Assisted with stable isotope-labeled peptide standards, the absolute quantitation of isoforms of posttranslationally modified protein (AQUIP) method takes all these factors into account and determines the absolute amount of a protein PTM isoform from the absolute amount of the protein of interest and the PTM occupancy at the site of the protein. The absolute amount of the protein of interest is inferred by quantifying both the absolute amounts of a few PTM

  16. Enantioselective synthesis of (-)-basiliskamide A.

    PubMed

    Chen, Ming; Roush, William R

    2012-03-16

    Basiliskamide A is an antifungal polyketide natural product isolated by Andersen and co-workers from a Bacillus laterosporus isolate, PNG-276. A nine-step enantioselective synthesis of (-)-basiliskamide A is reported, starting from commercially available β-hydroxy ester 7. The synthesis features a highly diastereoselective mismatched double asymmetric δ-stannylallylboration reaction of aldehyde 5 with the bifunctional allylborane reagent 4.

  17. Absolute realization of low BRDF value

    NASA Astrophysics Data System (ADS)

    Liu, Zilong; Liao, Ningfang; Li, Ping; Wang, Yu

    2010-10-01

    Low BRDF value is widespread used in many critical domains such as space and military fairs. These values below 0.1 Sr-1 . So the Absolute realization of these value is the most critical issue in the absolute measurement of BRDF. To develop the Absolute value realization theory of BRDF , defining an arithmetic operators of BRDF , achieving an absolute measurement Eq. of BRDF based on radiance. This is a new theory method to solve the realization problem of low BRDF value. This theory method is realized on a self-designed common double orientation structure in space. By designing an adding structure to extend the range of the measurement system and a control and processing software, Absolute realization of low BRDF value is achieved. A material of low BRDF value is measured in this measurement system and the spectral BRDF value are showed within different angles allover the space. All these values are below 0.4 Sr-1 . This process is a representative procedure about the measurement of low BRDF value. A corresponding uncertainty analysis of this measurement data is given depend on the new theory of absolute realization and the performance of the measurement system. The relative expand uncertainty of the measurement data is 0.078. This uncertainty analysis is suitable for all measurements using the new theory of absolute realization and the corresponding measurement system.

  18. A Synergistic Combinatorial and Chiroptical Study of Peptide Catalysts for Asymmetric Baeyer–Villiger Oxidation

    PubMed Central

    Giuliano, Michael W.; Lin, Chung-Yon; Romney, David K.

    2015-01-01

    We report an approach to the asymmetric Baeyer–Villiger oxidation utilizing bioinformatics-inspired combinatorial screening for catalyst discovery. Scaled-up validation of our on-bead efforts with a circular dichroism-based assay of alcohols derived from the products of solution-phase reactions established the absolute configuration of lactone products; this assay proved equivalent to HPLC in its ability to evaluate catalyst performance, but was far superior in its speed of analysis. Further solution-phase screening of a focused library suggested a mode of asymmetric induction that draws distinct parallels with the mechanism of Baeyer–Villiger monooxygenases. PMID:26543444

  19. A New Gimmick for Assigning Absolute Configuration.

    ERIC Educational Resources Information Center

    Ayorinde, F. O.

    1983-01-01

    A five-step procedure is provided to help students in making the assignment absolute configuration less bothersome. Examples for both single (2-butanol) and multi-chiral carbon (3-chloro-2-butanol) molecules are included. (JN)

  20. Magnifying absolute instruments for optically homogeneous regions

    SciTech Connect

    Tyc, Tomas

    2011-09-15

    We propose a class of magnifying absolute optical instruments with a positive isotropic refractive index. They create magnified stigmatic images, either virtual or real, of optically homogeneous three-dimensional spatial regions within geometrical optics.

  1. The Simplicity Argument and Absolute Morality

    ERIC Educational Resources Information Center

    Mijuskovic, Ben

    1975-01-01

    In this paper the author has maintained that there is a similarity of thought to be found in the writings of Cudworth, Emerson, and Husserl in his investigation of an absolute system of morality. (Author/RK)

  2. Absolute cross sections of compound nucleus reactions

    NASA Astrophysics Data System (ADS)

    Capurro, O. A.

    1993-11-01

    The program SEEF is a Fortran IV computer code for the extraction of absolute cross sections of compound nucleus reactions. When the evaporation residue is fed by its parents, only cumulative cross sections will be obtained from off-line gamma ray measurements. But, if one has the parent excitation function (experimental or calculated), this code will make it possible to determine absolute cross sections of any exit channel.

  3. Kelvin and the absolute temperature scale

    NASA Astrophysics Data System (ADS)

    Erlichson, Herman

    2001-07-01

    This paper describes the absolute temperature scale of Kelvin (William Thomson). Kelvin found that Carnot's axiom about heat being a conserved quantity had to be abandoned. Nevertheless, he found that Carnot's fundamental work on heat engines was correct. Using the concept of a Carnot engine Kelvin found that Q1/Q2 = T1/T2. Thermometers are not used to obtain absolute temperatures since they are calculated temperatures.

  4. Copper(II) coordination chain complex with the 2,5-bis(2-pyridyl)-1,3,4-thiadiazole ligand and an asymmetric μ2-1,1-azido double-bridged: Synthesis, crystal structure and magnetic properties

    NASA Astrophysics Data System (ADS)

    Laachir, Abdelhakim; Guesmi, Salaheddine; Saadi, Mohamed; El Ammari, Lahcen; Mentré, Olivier; Vezin, Hervé; Colis, Silviu; Bentiss, Fouad

    2016-11-01

    A new asymmetric μ2-1,1-azido double bridged cooper (II), with 2,5-bis(2-pyridyl)-1,3,4-thiadiazole (L), has been synthesized and characterized using single crystal X-ray diffraction, FT-IR, UV-Visible spectroscopic and magnetic measurements. The asymmetric unit of the title compound contains half molecule of formula, C12H8CuN10S, which crystallizes in the triclinic system, space group P 1 bar , with a = 6.5916 (4)Å, b = 10.6905 (7) Å, c = 11.5037 (7) Å, α = 106.508 (3)°, β = 105.538 (3)°, γ = 90.233 (4)°, V = 745.99 (8) Å3 and Z = 2. The structure consists of two [CuN5] prismatic polyhedra linked together by edge-sharing to build up a [Cu2N8] dimer arranged in chain. The connectivity along the chain is performed by Nsbnd N edge sharing between dimers. In the crystal, the molecules are linked together by Csbnd H⋯N hydrogen bonds and by π---π interactions between parallel pyridyl rings of neighboring molecules. The interpretation of FT-IR and UV-Vis spectra is consistent with the crystal structure determined by X-ray diffraction. The magnetic properties of the complex confirm the picture of an alternated … Cu-J1-Cu ….J2 … Cu-J1-Cu … magnetic chains. We found in the dimers weak antiferromagnetic exchange interactions J1/k = -5.9 (1) k and between them J2/k = -2.3 k.

  5. Asymmetric counterpropagating fronts without flow

    NASA Astrophysics Data System (ADS)

    Andrade-Silva, I.; Clerc, M. G.; Odent, V.

    2015-06-01

    Out-of-equilibrium systems exhibit domain walls between different states. These walls, depending on the type of connected states, can display rich spatiotemporal dynamics. In this Rapid Communication, we investigate the asymmetrical counterpropagation of fronts in an in-plane-switching cell filled with a nematic liquid crystal. Experimentally, we characterize the different front shapes and propagation speeds. These fronts present dissimilar elastic deformations that are responsible for their asymmetric speeds. Theoretically, using a phenomenological model, we describe the observed dynamics with fair agreement.

  6. Asymmetric counterpropagating fronts without flow.

    PubMed

    Andrade-Silva, I; Clerc, M G; Odent, V

    2015-06-01

    Out-of-equilibrium systems exhibit domain walls between different states. These walls, depending on the type of connected states, can display rich spatiotemporal dynamics. In this Rapid Communication, we investigate the asymmetrical counterpropagation of fronts in an in-plane-switching cell filled with a nematic liquid crystal. Experimentally, we characterize the different front shapes and propagation speeds. These fronts present dissimilar elastic deformations that are responsible for their asymmetric speeds. Theoretically, using a phenomenological model, we describe the observed dynamics with fair agreement.

  7. Miniature high-throughput chemosensing of yield, ee, and absolute configuration from crude reaction mixtures

    PubMed Central

    Bentley, Keith W.; Zhang, Peng; Wolf, Christian

    2016-01-01

    High-throughput experimentation (HTE) has emerged as a widely used technology that accelerates discovery and optimization processes with parallel small-scale reaction setups. A high-throughput screening (HTS) method capable of comprehensive analysis of crude asymmetric reaction mixtures (eliminating product derivatization or isolation) would provide transformative impact by matching the pace of HTE. We report how spontaneous in situ construction of stereodynamic metal probes from readily available, inexpensive starting materials can be applied to chiroptical chemosensing of the total amount, enantiomeric excess (ee), and absolute configuration of a wide variety of amines, diamines, amino alcohols, amino acids, carboxylic acids, α-hydroxy acids, and diols. This advance and HTS potential are highlighted with the analysis of 1 mg of crude reaction mixtures of a catalytic asymmetric reaction. This operationally simple assay uses a robust mix-and-measure protocol, is amenable to microscale platforms and automation, and provides critical time efficiency and sustainability advantages over traditional serial methods. PMID:26933684

  8. Development of chiral sulfoxide ligands for asymmetric catalysis.

    PubMed

    Trost, Barry M; Rao, Meera

    2015-04-20

    Nitrogen-, phosphorus-, and oxygen-based ligands with chiral backbones have been the historic workhorses of asymmetric transition-metal-catalyzed reactions. On the contrary, sulfoxides containing chirality at the sulfur atom have mainly been used as chiral auxiliaries for diastereoselective reactions. Despite several distinct advantages over traditional ligand scaffolds, such as the proximity of the chiral information to the metal center and the ability to switch between S and O coordination, these compounds have only recently emerged as a versatile class of chiral ligands. In this Review, we detail the history of the development of chiral sulfoxide ligands for asymmetric catalysis. We also provide brief descriptions of metal-sulfoxide bonding and strategies for the synthesis of enantiopure sulfoxides. Finally, insights into the future development of this underutilized ligand class are discussed.

  9. Asymmetric Allylboration of Acyl Imines Catalyzed by Chiral Diols

    PubMed Central

    Lou, Sha; Moquist, Philip N.; Schaus, Scott E.

    2008-01-01

    Chiral BINOL-derived diols catalyze the enantioselective asymmetric allylboration of acyl imines. The reaction requires 15 mol% of (S)-3,3′-Ph2-BINOL as the catalyst and allyldiisopropoxyborane as the nucleophile. The reaction products are obtained in good yields (75 – 94%) and high enantiomeric ratios (95:5 – 99.5:0.5) for aromatic and aliphatic imines. High diastereoselectivities (dr > 98:2) and enantioselectivities (er > 98:2) are obtained in the reactions of acyl imines with crotyldiisopropoxyboranes. This asymmetric transformation is directly applied to the synthesis of maraviroc, the selective CCR5 antagonist with potent activity against HIV-1 infection. Mechanistic investigations of the allylboration reaction including IR, NMR, and mass spectrometry study indicate that acyclic boronates are activated by chiral diols via exchange of one of the boronate alkoxy groups with activation of the acyl imine via hydrogen bonding. PMID:18020334

  10. Self-assembled Chiral Nanostructure as Scaffold for Asymmetric Reaction.

    PubMed

    Jiang, Jian; Ouyang, Guanghui; Zhang, Li; Liu, Minghua

    2017-03-25

    Asymmetric reaction is one of the most important reactions in organic synthesis. While large amount of efficient molecular catalysts have been developed and applied, supramolecular and nanostructured catalysts have been attracting recent interest. In this mini review, we focused on the self-assembled chiral nanostructures and reviewed their possibility and feasibility as the enantioselective catalyst. The design concept and the requirement of the chiral scaffold as the catalysts are discussed. Based on the chirality and catalytic performance of the building molecules and the supramolecular nanostructures, the nanocatalyst is divided into chiral nanostructure driven (CND) and chiral nanostructure enhanced (CNE) enantioselective catalysts. Then, several typical self-assembled chiral nanostructures such as nanocage, nanotube, nanorod, micelles and vesicles are selected as the chiral scaffold and their catalytic behaviors for the asymmetric reactions were demonstrated. Finally, the future development of the field is also outlooked.

  11. Measurement of the absolute branching fraction of D0-->K-pi+.

    PubMed

    Aubert, B; Bona, M; Boutigny, D; Karyotakis, Y; Lees, J P; Poireau, V; Prudent, X; Tisserand, V; Zghiche, A; Garra Tico, J; Grauges, E; Lopez, L; Palano, A; Eigen, G; Ofte, I; Stugu, B; Sun, L; Abrams, G S; Battaglia, M; Brown, D N; Button-Shafer, J; Cahn, R N; Groysman, Y; Jacobsen, R G; Kadyk, J A; Kerth, L T; Kolomensky, Yu G; Kukartsev, G; Lopes Pegna, D; Lynch, G; Mir, L M; Orimoto, T J; Pripstein, M; Roe, N A; Ronan, M T; Tackmann, K; Wenzel, W A; Del Amo Sanchez, P; Hawkes, C M; Watson, A T; Held, T; Koch, H; Lewandowski, B; Pelizaeus, M; Schroeder, T; Steinke, M; Cottingham, W N; Walker, D; Asgeirsson, D J; Cuhadar-Donszelmann, T; Fulsom, B G; Hearty, C; Knecht, N S; Mattison, T S; McKenna, J A; Khan, A; Saleem, M; Teodorescu, L; Blinov, V E; Bukin, A D; Druzhinin, V P; Golubev, V B; Onuchin, A P; Serednyakov, S I; Skovpen, Yu I; Solodov, E P; Todyshev, K Yu; Bondioli, M; Curry, S; Eschrich, I; Kirkby, D; Lankford, A J; Lund, P; Mandelkern, M; Martin, E C; Stoker, D P; Abachi, S; Buchanan, C; Foulkes, S D; Gary, J W; Liu, F; Long, O; Shen, B C; Zhang, L; Paar, H P; Rahatlou, S; Sharma, V; Berryhill, J W; Campagnari, C; Cunha, A; Dahmes, B; Hong, T M; Kovalskyi, D; Richman, J D; Beck, T W; Eisner, A M; Flacco, C J; Heusch, C A; Kroseberg, J; Lockman, W S; Schalk, T; Schumm, B A; Seiden, A; Williams, D C; Wilson, M G; Winstrom, L O; Chen, E; Cheng, C H; Dvoretskii, A; Fang, F; Hitlin, D G; Narsky, I; Piatenko, T; Porter, F C; Mancinelli, G; Meadows, B T; Mishra, K; Sokoloff, M D; Blanc, F; Bloom, P C; Chen, S; Ford, W T; Hirschauer, J F; Kreisel, A; Nagel, M; Nauenberg, U; Olivas, A; Smith, J G; Ulmer, K A; Wagner, S R; Zhang, J; Gabareen, A M; Soffer, A; Toki, W H; Wilson, R J; Winklmeier, F; Zeng, Q; Altenburg, D D; Feltresi, E; Hauke, A; Jasper, H; Merkel, J; Petzold, A; Spaan, B; Wacker, K; Brandt, T; Klose, V; Lacker, H M; Mader, W F; Nogowski, R; Schubert, J; Schubert, K R; Schwierz, R; Sundermann, J E; Volk, A; Bernard, D; Bonneaud, G R; Latour, E; Lombardo, V; Thiebaux, Ch; Verderi, M; Clark, P J; Gradl, W; Muheim, F; Playfer, S; Robertson, A I; Xie, Y; Andreotti, M; Bettoni, D; Bozzi, C; Calabrese, R; Cecchi, A; Cibinetto, G; Franchini, P; Luppi, E; Negrini, M; Petrella, A; Piemontese, L; Prencipe, E; Santoro, V; Anulli, F; Baldini-Ferroli, R; Calcaterra, A; de Sangro, R; Finocchiaro, G; Pacetti, S; Patteri, P; Peruzzi, I M; Piccolo, M; Rama, M; Zallo, A; Buzzo, A; Contri, R; Lo Vetere, M; Macri, M M; Monge, M R; Passaggio, S; Patrignani, C; Robutti, E; Santroni, A; Tosi, S; Chaisanguanthum, K S; Morii, M; Wu, J; Dubitzky, R S; Marks, J; Schenk, S; Uwer, U; Bard, D J; Dauncey, P D; Flack, R L; Nash, J A; Nikolich, M B; Panduro Vazquez, W; Behera, P K; Chai, X; Charles, M J; Mallik, U; Meyer, N T; Ziegler, V; Cochran, J; Crawley, H B; Dong, L; Eyges, V; Meyer, W T; Prell, S; Rosenberg, E I; Rubin, A E; Gritsan, A V; Guo, Z J; Lae, C K; Denig, A G; Fritsch, M; Schott, G; Arnaud, N; Béquilleux, J; Davier, M; Grosdidier, G; Höcker, A; Lepeltier, V; Le Diberder, F; Lutz, A M; Pruvot, S; Rodier, S; Roudeau, P; Schune, M H; Serrano, J; Sordini, V; Stocchi, A; Wang, W F; Wormser, G; Lange, D J; Wright, D M; Chavez, C A; Forster, I J; Fry, J R; Gabathuler, E; Gamet, R; Hutchcroft, D E; Payne, D J; Schofield, K C; Touramanis, C; Bevan, A J; George, K A; Di Lodovico, F; Menges, W; Sacco, R; Cowan, G; Flaecher, H U; Hopkins, D A; Jackson, P S; McMahon, T R; Salvatore, F; Wren, A C; Brown, D N; Davis, C L; Allison, J; Barlow, N R; Barlow, R J; Chia, Y M; Edgar, C L; Lafferty, G D; West, T J; Yi, J I; Anderson, J; Chen, C; Jawahery, A; Roberts, D A; Simi, G; Tuggle, J M; Blaylock, G; Dallapiccola, C; Hertzbach, S S; Li, X; Moore, T B; Salvati, E; Saremi, S; Cowan, R; Fisher, P H; Sciolla, G; Sekula, S J; Spitznagel, M; Taylor, F; Yamamoto, R K; McLachlin, S E; Patel, P M; Robertson, S H; Lazzaro, A; Palombo, F; Bauer, J M; Cremaldi, L; Eschenburg, V; Godang, R; Kroeger, R; Sanders, D A; Summers, D J; Zhao, H W; Brunet, S; Côté, D; Simard, M; Taras, P; Viaud, F B; Nicholson, H; De Nardo, G; Fabozzi, F; Lista, L; Monorchio, D; Sciacca, C; Baak, M A; Raven, G; Snoek, H L; Jessop, C P; Losecco, J M; Benelli, G; Corwin, L A; Gan, K K; Honscheid, K; Hufnagel, D; Kagan, H; Kass, R; Morris, J P; Rahimi, A M; Regensburger, J J; Ter-Antonyan, R; Wong, Q K; Blount, N L; Brau, J; Frey, R; Igonkina, O; Kolb, J A; Lu, M; Rahmat, R; Sinev, N B; Strom, D; Strube, J; Torrence, E; Gagliardi, N; Gaz, A; Margoni, M; Morandin, M; Pompili, A; Posocco, M; Rotondo, M; Simonetto, F; Stroili, R; Voci, C; Ben-Haim, E; Briand, H; Chauveau, J; David, P; Del Buono, L; de la Vaissière, Ch; Hamon, O; Hartfiel, B L; Leruste, Ph; Malclès, J; Ocariz, J; Perez, A; Gladney, L; Biasini, M; Covarelli, R; Manoni, E; Angelini, C; Batignani, G; Bettarini, S; Calderini, G; Carpinelli, M; Cenci, R; Cervelli, A; Forti, F; Giorgi, M A; Lusiani, A; Marchiori, G; Mazur, M A; Morganti, M; Neri, N; Paoloni, E; Rizzo, G; Walsh, J J; Haire, M; Biesiada, J; Elmer, P; Lau, Y P; Lu, C; Olsen, J; Smith, A J S; Telnov, A V; Baracchini, E; Bellini, F; Cavoto, G; D'Orazio, A; Del Re, D; Di Marco, E; Faccini, R; Ferrarotto, F; Ferroni, F; Gaspero, M; Jackson, P D; Li Gioi, L; Mazzoni, M A; Morganti, S; Piredda, G; Polci, F; Renga, F; Voena, C; Ebert, M; Schröder, H; Waldi, R; Adye, T; Castelli, G; Franek, B; Olaiya, E O; Ricciardi, S; Roethel, W; Wilson, F F; Aleksan, R; Emery, S; Escalier, M; Gaidot, A; Ganzhur, S F; de Monchenault, G Hamel; Kozanecki, W; Legendre, M; Vasseur, G; Yèche, Ch; Zito, M; Chen, X R; Liu, H; Park, W; Purohit, M V; Wilson, J R; Allen, M T; Aston, D; Bartoldus, R; Bechtle, P; Berger, N; Claus, R; Coleman, J P; Convery, M R; Dingfelder, J C; Dorfan, J; Dubois-Felsmann, G P; Dujmic, D; Dunwoodie, W; Field, R C; Glanzman, T; Gowdy, S J; Graham, M T; Grenier, P; Hast, C; Hryn'ova, T; Innes, W R; Kelsey, M H; Kim, H; Kim, P; Leith, D W G S; Li, S; Luitz, S; Luth, V; Lynch, H L; Macfarlane, D B; Marsiske, H; Messner, R; Muller, D R; O'Grady, C P; Perazzo, A; Perl, M; Pulliam, T; Ratcliff, B N; Roodman, A; Salnikov, A A; Schindler, R H; Schwiening, J; Snyder, A; Stelzer, J; Su, D; Sullivan, M K; Suzuki, K; Swain, S K; Thompson, J M; Va'vra, J; van Bakel, N; Wagner, A P; Weaver, M; Wisniewski, W J; Wittgen, M; Wright, D H; Yarritu, A K; Yi, K; Young, C C; Burchat, P R; Edwards, A J; Majewski, S A; Petersen, B A; Wilden, L; Ahmed, S; Alam, M S; Bula, R; Ernst, J A; Jain, V; Pan, B; Saeed, M A; Wappler, F R; Zain, S B; Bugg, W; Krishnamurthy, M; Spanier, S M; Eckmann, R; Ritchie, J L; Ruland, A M; Schilling, C J; Schwitters, R F; Izen, J M; Lou, X C; Ye, S; Bianchi, F; Gallo, F; Gamba, D; Pelliccioni, M; Bomben, M; Bosisio, L; Cartaro, C; Cossutti, F; Della Ricca, G; Lanceri, L; Vitale, L; Azzolini, V; Lopez-March, N; Martinez-Vidal, F; Milanes, D A; Oyanguren, A; Albert, J; Banerjee, Sw; Bhuyan, B; Hamano, K; Kowalewski, R; Nugent, I M; Roney, J M; Sobie, R J; Back, J J; Harrison, P F; Latham, T E; Mohanty, G B; Pappagallo, M; Band, H R; Chen, X; Dasu, S; Flood, K T; Hollar, J J; Kutter, P E; Pan, Y; Pierini, M; Prepost, R; Wu, S L; Yu, Z; Neal, H

    2008-02-08

    We measure the absolute branching fraction for D(0)-->K(-)pi(+) using partial reconstruction of B(0)-->D(*+)Xl(-)nu(l) decays, in which only the charged lepton and the pion from the decay D(*+)-->D(0)pi(+) are used. Based on a data sample of 230 x 10(6) BB pairs collected at the Upsilon(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC, we obtain B(D(0)-->K(-)pi(+)) = (4.007+/-0.037+/-0.072)%, where the first uncertainty is statistical and the second is systematic.

  12. Asymmetrical Switch Costs in Children

    ERIC Educational Resources Information Center

    Ellefson, Michelle R.; Shapiron, Laura R.; Chater, Nick

    2006-01-01

    Switching between tasks produces decreases in performance as compared to repeating the same task. Asymmetrical switch costs occur when switching between two tasks of unequal difficulty. This asymmetry occurs because the cost is greater when switching to the less difficult task than when switching to the more difficult task. Various theories about…

  13. Asymmetric Penning trap coherent states

    SciTech Connect

    Contreras-Astorga, Alonso; Fernandez, David J.

    2010-07-12

    By using a matrix technique, which allows to identify directly the ladder operators, the coherent states of the asymmetric Penning trap are derived as eigenstates of the appropriate annihilation operators. They are compared with those obtained through the displacement operator method.

  14. Catalytic Asymmetric Bromocyclization of Polyenes.

    PubMed

    Samanta, Ramesh C; Yamamoto, Hisashi

    2017-02-01

    The first catalytic asymmetric bromonium ion-induced polyene cyclization has been achieved by using a chiral BINOL-derived thiophosphoramide catalyst and 1,3-dibromo-5,5-dimethylhydantoin as an electrophilic bromine source. Bromocyclization products are obtained in high yields, with good enantiomeric ratios and high diastereoselectivity, and are abundantly found as scaffolds in natural products.

  15. Jasminum flexile flower absolute from India--a detailed comparison with three other jasmine absolutes.

    PubMed

    Braun, Norbert A; Kohlenberg, Birgit; Sim, Sherina; Meier, Manfred; Hammerschmidt, Franz-Josef

    2009-09-01

    Jasminum flexile flower absolute from the south of India and the corresponding vacuum headspace (VHS) sample of the absolute were analyzed using GC and GC-MS. Three other commercially available Indian jasmine absolutes from the species: J. sambac, J. officinale subsp. grandiflorum, and J. auriculatum and the respective VHS samples were used for comparison purposes. One hundred and twenty-one compounds were characterized in J. flexile flower absolute, with methyl linolate, benzyl salicylate, benzyl benzoate, (2E,6E)-farnesol, and benzyl acetate as the main constituents. A detailed olfactory evaluation was also performed.

  16. Asymmetric allylation of α-ketoester-derived N-benzoylhydrazones promoted by chiral sulfoxides/N-oxides Lewis bases: highly enantioselective synthesis of quaternary α-substituted α-allyl-α-amino acids.

    PubMed

    Reyes-Rangel, Gloria; Bandala, Yamir; García-Flores, Fred; Juaristi, Eusebio

    2013-09-01

    Chiral sulfoxides/N-oxides (R)-1 and (R,R)-2 are effective chiral promoters in the enantioselective allylation of α-keto ester N-benzoylhydrazone derivatives 3a-g to generate the corresponding N-benzoylhydrazine derivatives 4a-g, with enantiomeric excesses as high as 98%. Representative hydrazine derivatives 4a-b were subsequently treated with SmI2, and the resulting amino esters 5a-b with LiOH to obtain quaternary α-substituted α-allyl α-amino acids 6a-b, whose absolute configuration was assigned as (S), with fundament on chemical correlation and electronic circular dichroism (ECD) data.

  17. Universal Cosmic Absolute and Modern Science

    NASA Astrophysics Data System (ADS)

    Kostro, Ludwik

    The official Sciences, especially all natural sciences, respect in their researches the principle of methodic naturalism i.e. they consider all phenomena as entirely natural and therefore in their scientific explanations they do never adduce or cite supernatural entities and forces. The purpose of this paper is to show that Modern Science has its own self-existent, self-acting, and self-sufficient Natural All-in Being or Omni-Being i.e. the entire Nature as a Whole that justifies the scientific methodic naturalism. Since this Natural All-in Being is one and only It should be considered as the own scientifically justified Natural Absolute of Science and should be called, in my opinion, the Universal Cosmic Absolute of Modern Science. It will be also shown that the Universal Cosmic Absolute is ontologically enormously stratified and is in its ultimate i.e. in its most fundamental stratum trans-reistic and trans-personal. It means that in its basic stratum. It is neither a Thing or a Person although It contains in Itself all things and persons with all other sentient and conscious individuals as well, On the turn of the 20th century the Science has begun to look for a theory of everything, for a final theory, for a master theory. In my opinion the natural Universal Cosmic Absolute will constitute in such a theory the radical all penetrating Ultimate Basic Reality and will substitute step by step the traditional supernatural personal Absolute.

  18. A Palladium-Catalyzed Asymmetric Allylic Alkylation Approach to α-Quaternary γ-Butyrolactones.

    PubMed

    Nascimento de Oliveira, Marllon; Fournier, Jeremy; Arseniyadis, Stellios; Cossy, Janine

    2017-01-06

    The Pd-catalyzed asymmetric allylic alkylation (Pd-AAA) of enol carbonates derived from γ-butyrolactones is reported, affording the corresponding enantioenriched α,α'-disubstituted γ-butyrolactones in both high yields and high enantioselectivities (up to 94% ee). This method was eventually applied to the synthesis of chiral spirocyclic compounds.

  19. Helical chiral pyridine N-oxides: a new family of asymmetric catalysts.

    PubMed

    Chen, Jinshui; Takenaka, Norito

    2009-07-27

    Optically active chiral alkyl chlorides are valuable compounds because of their bioactivity and versatile synthetic utility. Accordingly, the ring opening of epoxides with a chloride nucleophile stands as an important goal in asymmetric catalysis. We describe herein recent advances in the design and development of chiral pyridine N-oxide catalysts for the enantioselective synthesis of chlorohydrins.

  20. Quantitative standards for absolute linguistic universals.

    PubMed

    Piantadosi, Steven T; Gibson, Edward

    2014-01-01

    Absolute linguistic universals are often justified by cross-linguistic analysis: If all observed languages exhibit a property, the property is taken to be a likely universal, perhaps specified in the cognitive or linguistic systems of language learners and users. In many cases, these patterns are then taken to motivate linguistic theory. Here, we show that cross-linguistic analysis will very rarely be able to statistically justify absolute, inviolable patterns in language. We formalize two statistical methods--frequentist and Bayesian--and show that in both it is possible to find strict linguistic universals, but that the numbers of independent languages necessary to do so is generally unachievable. This suggests that methods other than typological statistics are necessary to establish absolute properties of human language, and thus that many of the purported universals in linguistics have not received sufficient empirical justification.

  1. Mechanochemical organic synthesis.

    PubMed

    Wang, Guan-Wu

    2013-09-21

    Recently, mechanical milling using a mixer mill or planetary mill has been fruitfully utilized in organic synthesis under solvent-free conditions. This review article provides a comprehensive overview of various solvent-free mechanochemical organic reactions, including metal-mediated or -catalyzed reactions, condensation reactions, nucleophilic additions, cascade reactions, Diels-Alder reactions, oxidations, reductions, halogenation/aminohalogenation, etc. The ball milling technique has also been applied to the synthesis of calixarenes, rotaxanes and cage compounds, asymmetric synthesis as well as the transformation of biologically active compounds.

  2. Absolute Distance Measurement with the MSTAR Sensor

    NASA Technical Reports Server (NTRS)

    Lay, Oliver P.; Dubovitsky, Serge; Peters, Robert; Burger, Johan; Ahn, Seh-Won; Steier, William H.; Fetterman, Harrold R.; Chang, Yian

    2003-01-01

    The MSTAR sensor (Modulation Sideband Technology for Absolute Ranging) is a new system for measuring absolute distance, capable of resolving the integer cycle ambiguity of standard interferometers, and making it possible to measure distance with sub-nanometer accuracy. The sensor uses a single laser in conjunction with fast phase modulators and low frequency detectors. We describe the design of the system - the principle of operation, the metrology source, beamlaunching optics, and signal processing - and show results for target distances up to 1 meter. We then demonstrate how the system can be scaled to kilometer-scale distances.

  3. Absolutely relative or relatively absolute: violations of value invariance in human decision making.

    PubMed

    Teodorescu, Andrei R; Moran, Rani; Usher, Marius

    2016-02-01

    Making decisions based on relative rather than absolute information processing is tied to choice optimality via the accumulation of evidence differences and to canonical neural processing via accumulation of evidence ratios. These theoretical frameworks predict invariance of decision latencies to absolute intensities that maintain differences and ratios, respectively. While information about the absolute values of the choice alternatives is not necessary for choosing the best alternative, it may nevertheless hold valuable information about the context of the decision. To test the sensitivity of human decision making to absolute values, we manipulated the intensities of brightness stimuli pairs while preserving either their differences or their ratios. Although asked to choose the brighter alternative relative to the other, participants responded faster to higher absolute values. Thus, our results provide empirical evidence for human sensitivity to task irrelevant absolute values indicating a hard-wired mechanism that precedes executive control. Computational investigations of several modelling architectures reveal two alternative accounts for this phenomenon, which combine absolute and relative processing. One account involves accumulation of differences with activation dependent processing noise and the other emerges from accumulation of absolute values subject to the temporal dynamics of lateral inhibition. The potential adaptive role of such choice mechanisms is discussed.

  4. A Biomimetic Route for the Construction of the [4+2] and [3+2] Core Skeletons of the Dimeric Pyrrole-Imidazole Alkaloids and the Asymmetric Synthesis of Ageliferins

    PubMed Central

    Wang, Xiao; Wang, Xiaolei; Tan, Xianghui; Lu, Jianming; Cormier, Kevin W.; Ma, Zhiqiang

    2012-01-01

    The pyrrole-imidazole alkaloids have fascinated chemists for decades because of their unique structures. The high nitrogen and halogen contents and the densely functionalized skeletons make their laboratory synthesis challenging. We describe herein an oxidative method for accessing the core skeletons of two classes of pyrrole-imidazole dimers. This synthetic strategy was inspired by the putative biosynthesis pathways and its development was facilitated by computational studies. Using this method, we have successfully prepared ageliferin, bromoageliferin, and dibromoageliferin in their natural enantiomeric form. PMID:23072663

  5. Trienamine catalyzed asymmetric synthesis and biological investigation of a cytochalasin B-inspired compound collection† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5ob02272j Click here for additional data file.

    PubMed Central

    Sellstedt, Magnus; Schwalfenberg, Melanie; Ziegler, Slava; Antonchick, Andrey P.

    2016-01-01

    Due to their enhanced metabolic needs many cancers need a sufficient supply of glucose, and novel inhibitors of glucose import are in high demand. Cytochalasin B (CB) is a potent natural glucose import inhibitor which also impairs the actin cytoskeleton leading to undesired toxicity. With a view to identifying selective glucose import inhibitors we have developed an enantioselective trienamine catalyzed synthesis of a CB-inspired compound collection. Biological analysis revealed that indeed actin impairment can be distinguished from glucose import inhibition and led to the identification of the first selective glucose import inhibitor based on the basic structural architecture of cytochalasin B. PMID:26606903

  6. Asymmetric Organocatalysis at the Service of Medicinal Chemistry

    PubMed Central

    2014-01-01

    The application of the most representative and up-to-date examples of homogeneous asymmetric organocatalysis to the synthesis of molecules of interest in medicinal chemistry is reported. The use of different types of organocatalysts operative via noncovalent and covalent interactions is critically reviewed and the possibility of running some of these reactions on large or industrial scale is described. A comparison between the organo- and metal-catalysed methodologies is offered in several cases, thus highlighting the merits and drawbacks of these two complementary approaches to the obtainment of very popular on market drugs or of related key scaffolds. PMID:24971178

  7. A novel and versatile entry to asymmetrically substituted pyrazines.

    PubMed

    Mehta, Vaibhav Pravinchandra; Sharma, Anuj; Hecke, Kristof Van; Meervelt, Luc Van; Eycken, Erik Van der

    2008-03-21

    A novel and convenient procedure for the synthesis of asymmetrically tri- and tetrasubstituted pyrazines starting from para-methoxybenzyl-protected 3,5-dichloro-2(1H)-pyrazinones was elaborated. The key step is the conversion of the intermediate para-methoxybenzyl-protected thiopyrazinone upon treatment with MeI/I(2), into a pyrazine, rendering the chlorine in the C5-position susceptible to substitution. This approach entails the orthogonal introduction of the four substituents of the pyrazine scaffold. The application of microwave irradiation during different steps of the sequence has been shown to be highly valuable for speeding up reactions.

  8. Electron jet of asymmetric reconnection

    NASA Astrophysics Data System (ADS)

    Khotyaintsev, Yu. V.; Graham, D. B.; Norgren, C.; Eriksson, E.; Li, W.; Johlander, A.; Vaivads, A.; André, M.; Pritchett, P. L.; Retinò, A.; Phan, T. D.; Ergun, R. E.; Goodrich, K.; Lindqvist, P.-A.; Marklund, G. T.; Le Contel, O.; Plaschke, F.; Magnes, W.; Strangeway, R. J.; Russell, C. T.; Vaith, H.; Argall, M. R.; Kletzing, C. A.; Nakamura, R.; Torbert, R. B.; Paterson, W. R.; Gershman, D. J.; Dorelli, J. C.; Avanov, L. A.; Lavraud, B.; Saito, Y.; Giles, B. L.; Pollock, C. J.; Turner, D. L.; Blake, J. D.; Fennell, J. F.; Jaynes, A.; Mauk, B. H.; Burch, J. L.

    2016-06-01

    We present Magnetospheric Multiscale observations of an electron-scale current sheet and electron outflow jet for asymmetric reconnection with guide field at the subsolar magnetopause. The electron jet observed within the reconnection region has an electron Mach number of 0.35 and is associated with electron agyrotropy. The jet is unstable to an electrostatic instability which generates intense waves with E∥ amplitudes reaching up to 300 mV m-1 and potentials up to 20% of the electron thermal energy. We see evidence of interaction between the waves and the electron beam, leading to quick thermalization of the beam and stabilization of the instability. The wave phase speed is comparable to the ion thermal speed, suggesting that the instability is of Buneman type, and therefore introduces electron-ion drag and leads to braking of the electron flow. Our observations demonstrate that electrostatic turbulence plays an important role in the electron-scale physics of asymmetric reconnection.

  9. Synthesis, Characterization, and Crystal Structure of a Novel Copper(II) Complex with an Asymmetric Coordinated 2,2'-Bipyridine Derivative: A Model for the Associative Complex in the Ligand-Substitution Reactions of [Cu(tren)L](2+)?

    PubMed

    Lu Zl, Zhong-lin; Duan Cy, Chun-ying; Tian Yp, Yu-peng; You Xz, Xiao-zeng; Huang Xy, Xiao-ying

    1996-04-10

    The titled compound, (tris(2-aminoethyl)amine)(4,5-diazafluoren-9-one) copper(II) perchlorate, [Cu(C(6)H(18)N(4))(C(11)H(6)N(2)O)(ClO(4))(2)], 1, has been designed, synthesized, and characterized. The electronic and ESR spectra are very different from those of [Cu(tren)L](2+) complexes where L is monodentate ligand. The X-ray analysis revealed that the complex crystallizes in the monoclinic space group P2(1)/c, with a = 10.726(6) Å, b = 14.921(7) Å, c = 14.649(4) Å, beta = 95.13(3) degrees, and Z = 4. The copper(II) ion is coordinated by four nitrogen atoms from tris(2-aminoethyl)amine (tren) and two nitrogen atoms from 4,5-diazafluoren-9-one (dzf) to form an unusual six-coordinate (4 + 1 + 1') geometry. The structure is very rare, and to our knowledge, it is the first example of an asymmetric bidentate phenanthroline derivative metal complex. The structure could be used as a model of the associative complex in the ligand-exchange and ligand-substitution reactions of [Cu(tren)L](2+) and the catalytic mechanisms of enzymes involving copper sites. From the electronic and variable-temperature ESR spectra in solution, the possible mechanism of these reactions has also been proposed. As a comparison, the complex [Cu(tren)(ImH)(ClO(4))(2)], 2, was also synthesized and characterized, where ImH is imidazole.

  10. Stereodivergent Synthesis of Chiral Fullerenes by [3 + 2] Cycloadditions to C60

    PubMed Central

    2013-01-01

    A wide range of new dipoles and catalysts have been used in 1,3-dipolar cycloadditions of N-metalated azomethine ylides onto C60 yielding a full stereodivergent synthesis of pyrrolidino[60]fullerenes with complete diastereoselectivities and very high enantioselectivities. The use of less-explored chiral α-iminoamides as starting 1,3-dipoles leads to an interesting double asymmetric induction resulting in a matching/mismatching effect depending upon the absolute configuration of the stereocenter in the starting α-iminoamide. An enantioselective process was also found in the retrocycloaddition reaction as revealed by mass spectrometry analysis on quasi-enantiomeric pyrrolidino[60]fullerenes. Theoretical DFT calculations are in very good agreement with the experimental data. On the basis of this agreement, a plausible reaction mechanism is proposed. PMID:24359021

  11. Organocatalytic asymmetric hydrophosphination of nitroalkenes.

    PubMed

    Bartoli, Giuseppe; Bosco, Marcella; Carlone, Armando; Locatelli, Manuela; Mazzanti, Andrea; Sambri, Letizia; Melchiorre, Paolo

    2007-02-21

    The use of a bifunctional Cinchona alkaloid catalyst has provided a new organocatalytic strategy for the enantioselective addition of diphenylphosphine to a range of nitroalkenes, affording optically active beta-nitrophosphines (up to 99% ee after crystallization); this organocatalytic approach, providing a direct route to a new class of potentially useful enantiopure P,N-ligands, constitutes a bridge between the two complementary areas of asymmetric catalysis: organo- and metal-catalyzed transformations.

  12. Defeating the Modern Asymmetric Threat

    DTIC Science & Technology

    2002-06-01

    prolific use of suicide bombers by the LTTE: one strategic, one operational, one psychological and one religious. Chapter V conducts an analysis of...and responsive government) are the applicable variables in defeating the modern asymmetric threat, even those that employ suicide bombers. I...future. 15. NUMBER OF PAGES 171 14. SUBJECT TERMS Sri Lanka, LTTE, Ethnic Conflict, Asymmetry, Suicide Terrorism, Foreign Internal Defense

  13. Asymmetric information and macroeconomic dynamics

    NASA Astrophysics Data System (ADS)

    Hawkins, Raymond J.; Aoki, Masanao; Roy Frieden, B.

    2010-09-01

    We show how macroeconomic dynamics can be derived from asymmetric information. As an illustration of the utility of this approach we derive the equilibrium density, non-equilibrium densities and the equation of motion for the response to a demand shock for productivity in a simple economy. Novel consequences of this approach include a natural incorporation of time dependence into macroeconomics and a common information-theoretic basis for economics and other fields seeking to link micro-dynamics and macro-observables.

  14. Comparative vs. Absolute Judgments of Trait Desirability

    ERIC Educational Resources Information Center

    Hofstee, Willem K. B.

    1970-01-01

    Reversals of trait desirability are studied. Terms indicating conservativw behavior appeared to be judged relatively desirable in comparative judgement, while traits indicating dynamic and expansive behavior benefited from absolute judgement. The reversal effect was shown to be a general one, i.e. reversals were not dependent upon the specific…

  15. New Techniques for Absolute Gravity Measurements.

    DTIC Science & Technology

    1983-01-07

    Hammond, J.A. (1978) Bollettino Di Geofisica Teorica ed Applicata Vol. XX. 8. Hammond, J. A., and Iliff, R. L. (1979) The AFGL absolute gravity system...International Gravimetric Bureau, No. L:I-43. 7. Hammond. J.A. (1978) Bollettino Di Geofisica Teorica ed Applicata Vol. XX. 8. Hammond, J.A., and

  16. An Absolute Electrometer for the Physics Laboratory

    ERIC Educational Resources Information Center

    Straulino, S.; Cartacci, A.

    2009-01-01

    A low-cost, easy-to-use absolute electrometer is presented: two thin metallic plates and an electronic balance, usually available in a laboratory, are used. We report on the very good performance of the device that allows precise measurements of the force acting between two charged plates. (Contains 5 footnotes, 2 tables, and 6 figures.)

  17. Stimulus Probability Effects in Absolute Identification

    ERIC Educational Resources Information Center

    Kent, Christopher; Lamberts, Koen

    2016-01-01

    This study investigated the effect of stimulus presentation probability on accuracy and response times in an absolute identification task. Three schedules of presentation were used to investigate the interaction between presentation probability and stimulus position within the set. Data from individual participants indicated strong effects of…

  18. Absolute Positioning Using the Global Positioning System

    DTIC Science & Technology

    1994-04-01

    Global Positioning System ( GPS ) has becom a useful tool In providing relativ survey...Includes the development of a low cost navigator for wheeled vehicles. ABSTRACT The Global Positioning System ( GPS ) has become a useful tool In providing...technique of absolute or point positioning involves the use of a single Global Positioning System ( GPS ) receiver to determine the three-dimenslonal

  19. Asymmetric Wettability Directs Leidenfrost Droplets

    SciTech Connect

    Agapov, Rebecca L; Boreyko, Jonathan B; Briggs, Dayrl P; Srijanto, Bernadeta R; Retterer, Scott T; Collier, Pat; Lavrik, Nickolay V

    2014-01-01

    Leidenfrost phenomena on nano- and microstructured surfaces are of great importance for increasing control over heat transfer in high power density systems utilizing boiling phenomena. They also provide an elegant means to direct droplet motion in a variety of recently emerging fluidic systems. Here, we report the fabrication and characterization of tilted nanopillar arrays (TNPAs) that exhibit directional Leidenfrost water droplets under dynamic conditions, namely on impact with Weber numbers 40 at T 325 C. The batch fabrication of the TNPAs was achieved by glancing-angle anisotropic reactive ion etching of a thermally dewet platinum mask, with mean pillar diameters of 100 nm and heights of 200-500 nm. In contrast to previously implemented macro- and microscopic Leidenfrost ratchets, our TNPAs induce no preferential directional movement of Leidenfrost droplets under conditions approaching steady-state film boiling, suggesting that the observed droplet directionality is not a result of asymmetric vapor flow. Using high-speed imaging, phase diagrams were constructed for the boiling behavior upon impact for droplets falling onto TNPAs, straight nanopillar arrays, and smooth silicon surfaces. The asymmetric impact and directional trajectory of droplets was exclusive to the TNPAs for impacts corresponding to the transition boiling regime, revealing that asymmetric wettability upon impact is the mechanism for the droplet directionality.

  20. Asymmetric Dimethylarginine, Endothelial Dysfunction and Renal Disease

    PubMed Central

    Aldámiz-Echevarría, Luis; Andrade, Fernando

    2012-01-01

    l-Arginine (Arg) is oxidized to l-citrulline and nitric oxide (NO) by the action of endothelial nitric oxide synthase (NOS). In contrast, protein-incorporated Arg residues can be methylated with subsequent proteolysis giving rise to methylarginine compounds, such as asymmetric dimethylarginine (ADMA) that competes with Arg for binding to NOS. Most ADMA is degraded by dimethylarginine dimethyaminohydrolase (DDAH), distributed widely throughout the body and regulates ADMA levels and, therefore, NO synthesis. In recent years, several studies have suggested that increased ADMA levels are a marker of atherosclerotic change, and can be used to assess cardiovascular risk, consistent with ADMA being predominantly absorbed by endothelial cells. NO is an important messenger molecule involved in numerous biological processes, and its activity is essential to understand both pathogenic and therapeutic mechanisms in kidney disease and renal transplantation. NO production is reduced in renal patients because of their elevated ADMA levels with associated reduced DDAH activity. These factors contribute to endothelial dysfunction, oxidative stress and the progression of renal damage, but there are treatments that may effectively reduce ADMA levels in patients with kidney disease. Available data on ADMA levels in controls and renal patients, both in adults and children, also are summarized in this review. PMID:23109853

  1. Absolute Radiation Thermometry in the NIR

    NASA Astrophysics Data System (ADS)

    Bünger, L.; Taubert, R. D.; Gutschwager, B.; Anhalt, K.; Briaudeau, S.; Sadli, M.

    2017-04-01

    A near infrared (NIR) radiation thermometer (RT) for temperature measurements in the range from 773 K up to 1235 K was characterized and calibrated in terms of the "Mise en Pratique for the definition of the Kelvin" (MeP-K) by measuring its absolute spectral radiance responsivity. Using Planck's law of thermal radiation allows the direct measurement of the thermodynamic temperature independently of any ITS-90 fixed-point. To determine the absolute spectral radiance responsivity of the radiation thermometer in the NIR spectral region, an existing PTB monochromator-based calibration setup was upgraded with a supercontinuum laser system (0.45 μm to 2.4 μm) resulting in a significantly improved signal-to-noise ratio. The RT was characterized with respect to its nonlinearity, size-of-source effect, distance effect, and the consistency of its individual temperature measuring ranges. To further improve the calibration setup, a new tool for the aperture alignment and distance measurement was developed. Furthermore, the diffraction correction as well as the impedance correction of the current-to-voltage converter is considered. The calibration scheme and the corresponding uncertainty budget of the absolute spectral responsivity are presented. A relative standard uncertainty of 0.1 % (k=1) for the absolute spectral radiance responsivity was achieved. The absolute radiometric calibration was validated at four temperature values with respect to the ITS-90 via a variable temperature heatpipe blackbody (773 K ...1235 K) and at a gold fixed-point blackbody radiator (1337.33 K).

  2. Asymmetric aminolytic kinetic resolution of racemic epoxides using recyclable chiral polymeric Co(III)-salen complexes: a protocol for total utilization of racemic epoxide in the synthesis of (R)-Naftopidil and (S)-Propranolol.

    PubMed

    Kumar, Manish; Kureshy, Rukhsana I; Shah, Arpan K; Das, Anjan; Khan, Noor-ul H; Abdi, Sayed H R; Bajaj, Hari C

    2013-09-20

    Chiral polymeric Co(III) salen complexes with chiral ((R)/(S)-BINOL, diethyl tartrate) and achiral (piperazine and trigol) linkers with varying stereogenic centers were synthesized for the first time and used as catalysts for aminolytic kinetic resolution (AKR) of a variety of terminal epoxides and glycidyl ethers to get enantio-pure epoxides (ee, 99%) and N-protected β-amino alcohols (ee, 99%) with quantitative yield in 16 h at RT under optimized reaction conditions. This protocol was also used for the synthesis of two enantiomerically pure drug molecules (R)-Naftopidil (α1-blocker) and (S)-Propranolol (β-blocker) as a key step via AKR of single racemic naphthylglycidyl ether with Boc-protected isoproylamine with 100% epoxide utilization at 1 g level. The catalyst 1 was successfully recycled for a number of times.

  3. Mechanistic insights on cooperative asymmetric multicatalysis using chiral counterions.

    PubMed

    Jindal, Garima; Sunoj, Raghavan B

    2014-08-15

    Cooperative multicatalytic methods are steadily gaining popularity in asymmetric catalysis. The use of chiral Brønsted acids such as phosphoric acids in conjunction with a range of transition metals has been proven to be effective in asymmetric synthesis. However, the lack of molecular-level understanding and the accompanying ambiguity on the role of the chiral species in stereoinduction continues to remain an unresolved puzzle. Herein, we intend to disclose some novel transition state models obtained through DFT(B3LYP and M06) computations for a quintessential reaction in this family, namely, palladium-catalyzed asymmetric Tsuji-Trost allylation of aldehydes. The aldehyde is activated as an enamine by the action of a secondary amine (organocatalysis), which then adds to an activated Pd-allylic species (transition metal catalysis) generated through the protonation of allyic alcohol by chiral BINOL-phosphoric acid (Brønsted acid catalysis). We aim to decipher the nature of chiral BINOL-phosphates and their role in creating a quaternary chiral carbon atom in this triple catalytic system. The study reports the first transition state model capable of rationalizing chiral counterion-induced enantioselectivity. It is found that the chiral phosphate acts as a counterion in the stereocontrolling event rather than the conventional ligand mode.

  4. Quinap and congeners: atropos PN ligands for asymmetric catalysis.

    PubMed

    Fernández, Elena; Guiry, Patrick J; Connole, Kieran P T; Brown, John M

    2014-06-20

    Among the range of P,N-chelating ligands that have been employed in asymmetric catalysis, those relying on atropisomerism for the stability of individual enantiomers form a definable class. These APN (atropos P,N) ligands require a specific type of biaryl, with one component carrying a pendant phosphine unit, most commonly diaryl substituted, and the other bearing an sp(2)-nitrogen adjacent to the biaryl link. When substituents in the biaryl inhibit rotation about the linking bond, stable nonracemizing six-membered ring chelates can be formed. This Perspective relates the background to the initial synthesis in 1993 of Quinap, the original member of the series, and initial observations on its effectiveness in asymmetric catalysis. The current state of play in development of syntheses of this and other members of the APN ligand family is assessed, and their applications in asymmetric catalysis are presented. These include hydroboration and diboration of alkenes, 1,3-dipolar cycloadditions, alkynylation of iminium salts in a three-component (A(3)) condensation, and conjugate additions of Cu acetylides.

  5. Determination of the Absolute Configuration of Gliomasolide D through Total Syntheses of the C-17 Epimers.

    PubMed

    Seetharamsingh, B; Ganesh, Routholla; Reddy, D Srinivasa

    2017-02-24

    The absolute configuration at C-17, the carbon bearing the distal hydroxy group of the 14-membered natural product gliomasolide D, was assigned as R by comparison of (13)C NMR shifts and specific rotation values of the epimers at C-17. The first total synthesis of gliomasolide D along with its C-17 epimer, regioselective macrocyclization (18 membered vs 14 membered), and regioselective Wacker oxidation are highlights of the present work.

  6. Catalytic enantioselective synthesis of naturally occurring butenolides via hetero-allylic alkylation and ring closing metathesis.

    PubMed

    Mao, Bin; Geurts, Koen; Fañanás-Mastral, Martín; van Zijl, Anthoni W; Fletcher, Stephen P; Minnaard, Adriaan J; Feringa, Ben L

    2011-03-04

    An efficient catalytic asymmetric synthesis of chiral γ-butenolides was developed based on the hetero-allylic asymmetric alkylation (h-AAA) in combination with ring closing metathesis (RCM). The synthetic potential of the h-AAA-RCM protocol was illustrated with the facile synthesis of (-)-whiskey lactone, (-)-cognac lactone, (-)-nephrosteranic acid, and (-)-roccellaric acid.

  7. From Hubble's NGSL to Absolute Fluxes

    NASA Technical Reports Server (NTRS)

    Heap, Sara R.; Lindler, Don

    2012-01-01

    Hubble's Next Generation Spectral Library (NGSL) consists of R-l000 spectra of 374 stars of assorted temperature, gravity, and metallicity. Each spectrum covers the wavelength range, 0.18-1.00 microns. The library can be viewed and/or downloaded from the website, http://archive.stsci.edu/prepds/stisngsll. Stars in the NGSL are now being used as absolute flux standards at ground-based observatories. However, the uncertainty in the absolute flux is about 2%, which does not meet the requirements of dark-energy surveys. We are therefore developing an observing procedure that should yield fluxes with uncertainties less than 1 % and will take part in an HST proposal to observe up to 15 stars using this new procedure.

  8. Consistent thermostatistics forbids negative absolute temperatures

    NASA Astrophysics Data System (ADS)

    Dunkel, Jörn; Hilbert, Stefan

    2014-01-01

    Over the past 60 years, a considerable number of theories and experiments have claimed the existence of negative absolute temperature in spin systems and ultracold quantum gases. This has led to speculation that ultracold gases may be dark-energy analogues and also suggests the feasibility of heat engines with efficiencies larger than one. Here, we prove that all previous negative temperature claims and their implications are invalid as they arise from the use of an entropy definition that is inconsistent both mathematically and thermodynamically. We show that the underlying conceptual deficiencies can be overcome if one adopts a microcanonical entropy functional originally derived by Gibbs. The resulting thermodynamic framework is self-consistent and implies that absolute temperature remains positive even for systems with a bounded spectrum. In addition, we propose a minimal quantum thermometer that can be implemented with available experimental techniques.

  9. Absolute measurement of length with nanometric resolution

    NASA Astrophysics Data System (ADS)

    Apostol, D.; Garoi, F.; Timcu, A.; Damian, V.; Logofatu, P. C.; Nascov, V.

    2005-08-01

    Laser interferometer displacement measuring transducers have a well-defined traceability route to the definition of the meter. The laser interferometer is de-facto length scale for applications in micro and nano technologies. However their physical unit -half lambda is too large for nanometric resolution. Fringe interpolation-usual technique to improve the resolution-lack of reproducibility could be avoided using the principles of absolute distance measurement. Absolute distance refers to the use of interferometric techniques for determining the position of an object without the necessity of measuring continuous displacements between points. The interference pattern as produced by the interference of two point-like coherent sources is fitted to a geometric model so as to determine the longitudinal location of the target by minimizing least square errors. The longitudinal coordinate of the target was measured with accuracy better than 1 nm, for a target position range of 0.4μm.

  10. Asteroid absolute magnitudes and slope parameters

    NASA Technical Reports Server (NTRS)

    Tedesco, Edward F.

    1991-01-01

    A new listing of absolute magnitudes (H) and slope parameters (G) has been created and published in the Minor Planet Circulars; this same listing will appear in the 1992 Ephemerides of Minor Planets. Unlike previous listings, the values of the current list were derived from fits of data at the V band. All observations were reduced in the same fashion using, where appropriate, a single basis default value of 0.15 for the slope parameter. Distances and phase angles were computed for each observation. The data for 113 asteroids was of sufficiently high quality to permit derivation of their H and G. These improved absolute magnitudes and slope parameters will be used to deduce the most reliable bias-corrected asteroid size-frequency distribution yet made.

  11. Computer processing of spectrograms for absolute intensities.

    PubMed

    Guttman, A; Golden, J; Galbraith, H J

    1967-09-01

    A computer program was developed to process photographically recorded spectra for absolute intensity. Test and calibration films are subjected to densitometric scans that provide digitally recorded densities on magnetic tapes. The nonlinear calibration data are fitted by least-squares cubic polynomials to yield a good approximation to the monochromatic H&D curves for commonly used emulsions (2475 recording film, Royal-X, Tri-X, 4-X). Several test cases were made. Results of these cases show that the machine processed absolute intensities are accurate to within 15%o. Arbitrarily raising the sensitivity threshold by 0.1 density units above gross fog yields cubic polynomial fits to the H&D curves that are radiometrically accurate within 10%. In addition, curves of gamma vs wavelength for 2475, Tri-X, and 4-X emulsions were made. These data show slight evidence of the photographic Purkinje effect in the 2475 emulsion.

  12. An absolute measure for a key currency

    NASA Astrophysics Data System (ADS)

    Oya, Shunsuke; Aihara, Kazuyuki; Hirata, Yoshito

    It is generally considered that the US dollar and the euro are the key currencies in the world and in Europe, respectively. However, there is no absolute general measure for a key currency. Here, we investigate the 24-hour periodicity of foreign exchange markets using a recurrence plot, and define an absolute measure for a key currency based on the strength of the periodicity. Moreover, we analyze the time evolution of this measure. The results show that the credibility of the US dollar has not decreased significantly since the Lehman shock, when the Lehman Brothers bankrupted and influenced the economic markets, and has increased even relatively better than that of the euro and that of the Japanese yen.

  13. Probing absolute spin polarization at the nanoscale.

    PubMed

    Eltschka, Matthias; Jäck, Berthold; Assig, Maximilian; Kondrashov, Oleg V; Skvortsov, Mikhail A; Etzkorn, Markus; Ast, Christian R; Kern, Klaus

    2014-12-10

    Probing absolute values of spin polarization at the nanoscale offers insight into the fundamental mechanisms of spin-dependent transport. Employing the Zeeman splitting in superconducting tips (Meservey-Tedrow-Fulde effect), we introduce a novel spin-polarized scanning tunneling microscopy that combines the probing capability of the absolute values of spin polarization with precise control at the atomic scale. We utilize our novel approach to measure the locally resolved spin polarization of magnetic Co nanoislands on Cu(111). We find that the spin polarization is enhanced by 65% when increasing the width of the tunnel barrier by only 2.3 Å due to the different decay of the electron orbitals into vacuum.

  14. Absolute and relative dosimetry for ELIMED

    NASA Astrophysics Data System (ADS)

    Cirrone, G. A. P.; Cuttone, G.; Candiano, G.; Carpinelli, M.; Leonora, E.; Lo Presti, D.; Musumarra, A.; Pisciotta, P.; Raffaele, L.; Randazzo, N.; Romano, F.; Schillaci, F.; Scuderi, V.; Tramontana, A.; Cirio, R.; Marchetto, F.; Sacchi, R.; Giordanengo, S.; Monaco, V.

    2013-07-01

    The definition of detectors, methods and procedures for the absolute and relative dosimetry of laser-driven proton beams is a crucial step toward the clinical use of this new kind of beams. Hence, one of the ELIMED task, will be the definition of procedures aiming to obtain an absolute dose measure at the end of the transport beamline with an accuracy as close as possible to the one required for clinical applications (i.e. of the order of 5% or less). Relative dosimetry procedures must be established, as well: they are necessary in order to determine and verify the beam dose distributions and to monitor the beam fluence and the energetic spectra during irradiations. Radiochromic films, CR39, Faraday Cup, Secondary Emission Monitor (SEM) and transmission ionization chamber will be considered, designed and studied in order to perform a fully dosimetric characterization of the ELIMED proton beam.

  15. Asymmetric gold nanoparticle reduction into polydimethylsiloxane thin films

    NASA Astrophysics Data System (ADS)

    Dunklin, Jeremy R.; Forcherio, Gregory T.; Berry, Keith R.; Roper, D. Keith

    2014-09-01

    Polymer thin films embedded with plasmonic gold nanoparticles (AuNPs) are of significant interest in biomedicine, optics, photovoltaic, and nanoelectromechanical systems. Thin polydimethylsiloxane (PDMS) films containing 3-7 micron layers of AuNPs that were fabricated with a novel diffusive-reduction synthesis technique attenuated up to 85% of incoming laser light at the plasmon resonance. Rapid diffusive reduction of AuNPs into asymmetric PDMS thin films provided superior optothermal capabilities relative to thicker films in which AuNPs were reduced throughout. A photonto- heat conversion of up to 3000°C/watt was demonstrated, which represents a 3-230-fold increase over previous AuNPfunctionalized systems. Optical attenuation and thermal response increased in proportion to order of magnitude increases in tetrachloroaurate (TCA) solution concentration. Optical and thermoplasmonic responses were observed with and without an adjacent mesh support, which increased attenuation but decreased thermal response. Morphological, optical, and thermoplasmonic properties of asymmetric AuNP-PDMS films varied significantly with diffusive TCA concentration. Gold nanoparticles, networks, and conglomerates were formed via reduction as the amount of dissolved TCA increased across a log10-scale. Increasing TCA concentrations caused polymer surface cratering, leading to a larger effective surface area. This method, utilizing the diffusion of TCA into a single exposed partially cured PDMS interface, could be used to replace expensive lithographic or solution synthesis of plasmon-functionalized systems.

  16. Mechanistic Insights into Homogeneous and Heterogeneous Asymmetric Iron Catalysis

    NASA Astrophysics Data System (ADS)

    Sonnenberg, Jessica

    Our group has been focused on replacing toxic and expensive precious metal catalysts with iron for the synthesis of enantiopure compounds for industrial applications. During an investigation into the mechanism of asymmetric transfer hydrogenation with our first generation iron-(P-N-N-P) catalysts we found substantial evidence for zero-valent iron nanoparticles coated in chiral ligand acting as the active site. Extensive experimental and computational experiments were undertaken which included NMR, DFT, reaction profile analysis, substoichiometric poisoning, electron microscope imaging, XPS and multiphasic analysis, all of which supported the fact that NPs were the active species in catalysis. Reversibility of this asymmetric reaction on the nanoparticle surface was then probed using oxidative kinetic resolution of racemic alcohols, yielding modest enantiopurity and high turnover frequencies (TOF) for a range of aromatic alcohols. Efficient dehydrogenation of ammonia-borane for hydrogen evolution and the formation of B-N oligomers was also shown using the NP system, yielding highly active systems, with a maximum TOF of 3.66 H2/s-1 . We have also begun to focus on the development of iron catalysts for asymmetric direct hydrogenation of ketones using hydrogen gas. New chiral iron-(P-N-P) catalysts were developed and shown to be quite active and selective for a wide range of substrates. Mechanistic investigations primarily using NMR and DFT indicated that a highly active trans-dihydride species was being formed during catalyst activation. Lastly, a new library of chiral P-N-P and P-NH-P ligands were developed, as well as their corresponding iron complexes, some of which show promise for the development of future generations of active asymmetric direct hydrogenation catalysts.

  17. Asymmetric Walkway: A Novel Behavioral Assay for Studying Asymmetric Locomotion

    PubMed Central

    Tuntevski, Kiril; Ellison, Ryan; Yakovenko, Sergiy

    2016-01-01

    Behavioral assays are commonly used for the assessment of sensorimotor impairment in the central nervous system (CNS). The most sophisticated methods for quantifying locomotor deficits in rodents is to measure minute disturbances of unconstrained gait overground (e.g., manual BBB score or automated CatWalk). However, cortical inputs are not required for the generation of basic locomotion produced by the spinal central pattern generator (CPG). Thus, unconstrained walking tasks test locomotor deficits due to motor cortical impairment only indirectly. In this study, we propose a novel, precise foot-placement locomotor task that evaluates cortical inputs to the spinal CPG. An instrumented peg-way was used to impose symmetrical and asymmetrical locomotor tasks mimicking lateralized movement deficits. We demonstrate that shifts from equidistant inter-stride lengths of 20% produce changes in the forelimb stance phase characteristics during locomotion with preferred stride length. Furthermore, we propose that the asymmetric walkway allows for measurements of behavioral outcomes produced by cortical control signals. These measures are relevant for the assessment of impairment after cortical damage. PMID:26863182

  18. Silicon Absolute X-Ray Detectors

    SciTech Connect

    Seely, John F.; Korde, Raj; Sprunck, Jacob; Medjoubi, Kadda; Hustache, Stephanie

    2010-06-23

    The responsivity of silicon photodiodes having no loss in the entrance window, measured using synchrotron radiation in the 1.75 to 60 keV range, was compared to the responsivity calculated using the silicon thickness measured using near-infrared light. The measured and calculated responsivities agree with an average difference of 1.3%. This enables their use as absolute x-ray detectors.

  19. Pd-catalyzed asymmetric allylic amination using easily accessible metallocenyl P,N-ligands.

    PubMed

    Wu, Hongwei; Xie, Fang; Wang, Yanlan; Zhao, Xiaohu; Liu, Delong; Zhang, Wanbin

    2015-04-14

    Compared to their C1-symmetric counterparts, planar chiral C2-symmetric metallocenyl P,N-ligands are efficient chiral ligands for Pd-catalyzed asymmetric allylic aminations, providing a number of amination products with high enantioselectivities. A non-C2-symmetric ferrocenyl P,N-ligand (a by-product obtained during the synthesis of the above C2-symmetric species) was also found to be an efficient ligand for asymmetric allylic aminations. A mixed ligand system consisting of both C2- and non-C2-symmetric ferrocene complexes was examined and showed high catalytic activity with the amination products being obtained with excellent enantioselectivities.

  20. LG tools for asymmetric wargaming

    NASA Astrophysics Data System (ADS)

    Stilman, Boris; Yakhnis, Alex; Yakhnis, Vladimir

    2002-07-01

    Asymmetric operations represent conflict where one of the sides would apply military power to influence the political and civil environment, to facilitate diplomacy, and to interrupt specified illegal activities. This is a special type of conflict where the participants do not initiate full-scale war. Instead, the sides may be engaged in a limited open conflict or one or several sides may covertly engage another side using unconventional or less conventional methods of engagement. They may include peace operations, combating terrorism, counterdrug operations, arms control, support of insurgencies or counterinsurgencies, show of force. An asymmetric conflict can be represented as several concurrent interlinked games of various kinds: military, transportation, economic, political, etc. Thus, various actions of peace violators, terrorists, drug traffickers, etc., can be expressed via moves in different interlinked games. LG tools allow us to fully capture the specificity of asymmetric conflicts employing the major LG concept of hypergame. Hypergame allows modeling concurrent interlinked processes taking place in geographically remote locations at different levels of resolution and time scale. For example, it allows us to model an antiterrorist operation taking place simultaneously in a number of countries around the globe and involving wide range of entities from individuals to combat units to governments. Additionally, LG allows us to model all sides of the conflict at their level of sophistication. Intelligent stakeholders are represented by means of LG generated intelligent strategies. TO generate those strategies, in addition to its own mathematical intelligence, the LG algorithm may incorporate the intelligence of the top-level experts in the respective problem domains. LG models the individual differences between intelligent stakeholders. The LG tools make it possible to incorporate most of the known traits of a stakeholder, i.e., real personalities involved in