Sample records for absolute asymmetric synthesis

  1. Asymmetric synthesis of (+)- and (-)-pauciflorol F: confirmation of absolute stereochemistry.

    PubMed

    Kerr, Daniel J; Miletic, Michael; Manchala, Narasimhulu; White, Jonathan M; Flynn, Bernard L

    2013-08-16

    An efficient, formal enantioselective synthesis of (+)- and (-)-pauciflorol F has been achieved using a recently introduced oxazolidinone controlled torquoselective Nazarov reaction. The absolute stereochemistry of pauciflorol F and its biosynthetic precursors has been unambiguously confirmed using X-ray crystallography. PMID:23899350

  2. 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. PMID:25601233

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

    PubMed

    Olsson, Susanne; Lennartson, Anders; Håkansson, Mikael

    2013-09-01

    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. PMID:23881740

  4. Absolute asymmetric synthesis in enantioselective autocatalytic reaction networks: theoretical games, speculations on chemical evolution and perhaps a synthetic option.

    PubMed

    Ribó, Josep M; Blanco, Celia; Crusats, Joaquim; El-Hachemi, Zoubir; Hochberg, David; Moyano, Albert

    2014-12-22

    The Soai reaction and the Viedma deracemization of racemic conglomerate crystal mixtures are experimental pieces of evidence of the ability of enantioselective autocatalytic coupled networks to yield absolute asymmetric synthesis. Thermodynamically open systems or systems with non-uniform energy distributions may lead to chiral final states and, in systems able to come into thermodynamic equilibrium with their surroundings, to kinetically controlled absolute asymmetric synthesis. The understanding of network parameters and of the thermodynamic scenarios that may lead to spontaneous mirror symmetry breaking (SMSB) could assist in the development of new methods for asymmetric synthesis and enantioselective polymerizations (e.g., replicators), and to frame reasonable speculations on the origin of biological homochirality. PMID:25352056

  5. 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. PMID:25644371

  6. Absolute asymmetric synthesis from an isotropic racemic mixture of chiral molecules with the help of their laser orientation-dependent selection

    NASA Astrophysics Data System (ADS)

    Zhdanov, Dmitry V.; Zadkov, Victor N.

    2007-12-01

    We analyzed the absolute asymmetric synthesis (AAS) of enantiomers from an isotropic racemic mixture of chiral molecules, which employs the laser electrodipole interaction, and revealed a set of basic symmetry-based conditions on the parameters of field-molecule interaction. Using these conditions, we developed a novel scenario of the AAS (through selective photodestruction of the enantiomers of a given type) based on the joint action of the strong multicomponent femtosecond and picosecond laser pulses. Key mechanism of this scenario is the partly modified scheme of laser orientation-dependent selection of molecules proposed by us earlier [D. V. Zhdanov et al., JETP 130, 387 (2006)]. Calculations made on example of chiral molecule SiHNaClF show rather high efficiency and stability of the proposed AAS scenario with respect to the parameters of the incident laser pulses and even feasibility of its realization at room temperature.

  7. Asymmetric total synthesis of (+)-dragmacidin d reveals unexpected stereocomplexity.

    PubMed

    Zhang, Fengying; Wang, Bin; Prasad, Pritesh; Capon, Robert J; Jia, Yanxing

    2015-03-20

    The first asymmetric total synthesis of the bis-indole marine alkaloid (+)-dragmacidin D (1) has been achieved. This synthesis revises an earlier configurational assignment based on biosynthetic considerations and assigns an R absolute configuration to (+)-1. The current studies reveal that natural dragmacidin D is isolated as either a racemate or a scalemic mixture (39% ee). PMID:25730523

  8. Asymmetric total synthesis of rollicosin.

    PubMed

    Quinn, Kevin J; Isaacs, André K; DeChristopher, Brian A; Szklarz, Stephanie C; Arvary, Rebecca A

    2005-03-31

    [structure: see text] The first total synthesis of rollicosin, a member of a rare subgroup of Annonaceous acetogenins containing two terminal gamma-lactones, is reported. The approach features a highly regio- and stereoselective tandem ring-closing/cross-metathesis reaction for construction of the east-wing lactone and incorporation of the alkyl spacer. Establishment of the C4 stereocenter and addition of the west-wing lactone were achieved by Sharpless asymmetric dihydroxylation and enolate alkylation. PMID:15787477

  9. 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

  10. Photochirogenesis: Photochemical models on the absolute asymmetric formation of amino acids in interstellar space

    NASA Astrophysics Data System (ADS)

    Meinert, Cornelia; de Marcellus, Pierre; Le Sergeant D'Hendecourt, Louis; Nahon, Laurent; Jones, Nykola C.; Hoffmann, Søren V.; Bredehöft, Jan Hendrik; Meierhenrich, Uwe J.

    2011-10-01

    Proteins of all living organisms including plants, animals, and humans are made up of amino acid monomers that show identical stereochemical L-configuration. Hypotheses for the origin of this symmetry breaking in biomolecules include the absolute asymmetric photochemistry model by which interstellar ultraviolet (UV) circularly polarized light (CPL) induces an enantiomeric excess in chiral organic molecules in the interstellar/circumstellar media. This scenario is supported by a) the detection of amino acids in the organic residues of UV-photo-processed interstellar ice analogues, b) the occurrence of L-enantiomer-enriched amino acids in carbonaceous meteorites, and c) the observation of CPL of the same helicity over large distance scales in the massive star-forming region of Orion. These topics are of high importance in topical biophysical research and will be discussed in this review. Further evidence that amino acids and other molecules of prebiotic interest are asymmetrically formed in space comes from studies on the enantioselective photolysis of amino acids by UV-CPL. Also, experiments have been performed on the absolute asymmetric photochemical synthesis of enantiomer-enriched amino acids from mixtures of astrophysically relevant achiral precursor molecules using UV-circularly polarized photons. Both approaches are based on circular dichroic transitions of amino acids that will be highlighted here as well. These results have strong implications on our current understanding of how life's precursor molecules were possibly built and how life selected the left-handed form of proteinogenic amino acids.

  11. Absolute asymmetric synthesis: protected substrate oxidation.

    PubMed

    Olsson, Susanne; Björemark, Per Martin; Kokoli, Theonitsa; Sundberg, Jonas; Lennartson, Anders; McKenzie, Christine J; Håkansson, Mikael

    2015-03-23

    Three new conglomerates incorporating bidentate sulfide ligands coordinated by Ru(II) centers have been prepared. Total spontaneous resolution by slow crystallization gives highly enantioenriched crystal batches, which are used in enantioselective oxidation of the sulfide ligands to give chiral sulfoxide complexes with >98?%?ee. All relevant stereoisomers have been characterized by single-crystal X-ray diffraction, CD spectroscopy, and chiral HPLC. If the ligand range can be extended to monodentate sulfides, a large-scale and recyclable process for enantioselective oxidation of sulfides can be designed. PMID:25677197

  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. 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

  14. Organocatalytic Asymmetric Assembly Reactions: Synthesis of Spirooxindoles via Organocascade Strategies

    E-print Network

    Barbas III, Carlos F.

    Organocatalytic Asymmetric Assembly Reactions: Synthesis of Spirooxindoles via Organocascade in the enantioselective synthesis of spirooxindoles via organocascade strategies. Various organocatalysts with distinct on the enantioselective synthesis of spirooxindoles via organocascade strategies and is organized on the basis of three

  15. 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

  16. Enantioselective synthesis of indoloquinolizidines via asymmetric catalytic hydrogenation/lactamization of imino diesters.

    PubMed

    Liu, Yong; Wang, Qun; Zhang, Ying; Huang, Jianbiao; Nie, Linlin; Chen, Jie; Cao, Weiguo; Wu, Xiaoyu

    2013-12-01

    We have developed a highly efficient cascade sequence for asymmetric synthesis of indoloquinolizidines with absolute control of cis-H2/H12b relative geometry in good to excellent yields and excellent enantioselectivities. This cascade was triggered by the Ru(II)-TsDPEN-catalyzed asymmetric transfer hydrogenation of imino diesters, with subsequent spontaneous lactamization with discrimination between the two diastereotopic 2-alkoxy-2-oxoethyl groups. The synthetic utility of this strategy was demonstrated by the asymmetric preparation of dihydrocorynantheol, geissoschizol, and isogeissoschizol. PMID:24195678

  17. 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.

  18. Asymmetric total synthesis of (+)-attenol B.

    PubMed

    Ren, Jingyun; Wang, Jian; Tong, Rongbiao

    2015-02-01

    The more cytotoxic, thermodynamically less stable (+)-attenol B was isolated as a minor isomer of the spiroketal attenol A and synthesized previously as a minor product. Herein, we report a new strategy that for the first time led to asymmetric synthesis of (+)-attenol B as an exclusive product, featuring sequential Achmatowicz rearrangement/bicycloketalization to efficiently construct the 6,8-dioxabicyclo[3.2.1]octane core. In addition, (-)-attenol A was obtained with 91% yield by isomerization of (+)-attenol B in CDCl3. PMID:25627786

  19. 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. PMID:25767939

  20. Total Synthesis and Absolute Configuration of the Marine Norditerpenoid Xestenone

    PubMed Central

    Ota, Koichiro; Kurokawa, Takao; Kawashima, Etsuko; Miyaoka, Hiroaki

    2009-01-01

    Xestenone is a marine norditerpenoid found in the northeastern Pacific sponge Xestospongia vanilla. The relative configuration of C-3 and C-7 in xestenone was determined by NOESY spectral analysis. However the relative configuration of C-12 and the absolute configuration of this compound were not determined. The authors have now achieved the total synthesis of xestenone using their developed one-pot synthesis of cyclopentane derivatives employing allyl phenyl sulfone and an epoxy iodide as a key step. The relative and absolute configurations of xestenone were thus successfully determined by this synthesis. PMID:20098605

  1. 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…

  2. Double asymmetric induction as a mechanistic probe: conjugate addition for the asymmetric synthesis of a pseudotripeptide.

    PubMed

    Davies, Stephen G; Hermann, Gesine J; Sweet, Miles J; Smith, Andrew D

    2004-05-01

    Double asymmetric induction as a mechanistic probe indicates that, for the conjugate addition of (R)- and (S)-lithium N-benzyl-N--alpha-methylbenzylamide to (S)-3'-phenylprop-2'-enoyl-4-benzyloxazolidinone, the reactive conformation of the N-acyl oxazolidinone is the anti-s-cis form, facilitating the asymmetric synthesis of a pseudotripeptide. PMID:15116218

  3. Enzyme-Assisted Asymmetric Total Synthesis of (-)-Podophyllotoxin and (-)-Picropodophyllin

    E-print Network

    Berkowitz, David

    , Nebraska 68588-0304 Received October 11, 1999 Described is the first catalytic, asymmetric synthesis neat dimethyl acetylene dicarboxylate as the dienophile, followed by catalytic hydrogenation. Reduction is converted to (-)- picropodophyllin in two steps (lactonization, SEM deprotection) or to (-)-podophyllotoxin

  4. Catalytic Asymmetric Synthesis of Hydroxy Enol Ethers: Approach to a

    E-print Network

    Walsh, Patrick J.

    Catalytic Asymmetric Synthesis of Hydroxy Enol Ethers: Approach to a Two-Carbon Homologation. The resultant enantiomerically enriched hydroxy enol ethers were converted to protected hydroxy aldehydes the catalytic asymmetric allylation of aldehydes followed by oxidative cleavage of the allyl group (Scheme 1, A

  5. Transition Metal Catalysed Heterocycle Synthesis Asymmetric Processes and Catalysis

    E-print Network

    Takada, Shoji

    are interested in all aspects of catalysis relevant to organic synthesis. One area interest is the activationTransition Metal Catalysed Heterocycle Synthesis Asymmetric Processes and Catalysis New Reaction Organic Chemistry Seminar University of Oxford Exploring New Reactivity and Selectivity Using Rhodium

  6. 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

    2014-12-01

    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 ?-butyrolactone structure for the metabolite. This structure has been confirmed by an asymmetric total synthesis, which also established its absolute configuration. PMID:25372296

  7. 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...

  8. Asymmetric synthesis of amines using tert-butanesulfinamide.

    PubMed

    Xu, Hai-Chao; Chowdhury, Somenath; Ellman, Jonathan A

    2013-11-01

    Chiral amines are prevalent in many bioactive molecules, including amino acids and pharmaceutical agents. tert-Butanesulfinamide (tBS) is a chiral amine reagent that has enabled the reliable asymmetric synthesis of a very broad range of different amine structures from simple, readily available starting materials. Three steps are commonly applied to the asymmetric synthesis of amines: (i) condensation of tBS with a carbonyl compound, (ii) nucleophile addition and (iii) tert-butanesulfinyl group cleavage. Here we demonstrate these steps with the preparation of a propargylic tertiary carbinamine, one of a class of amines that have been used for many different biological purposes, including click chemistry applications, diversity-oriented synthesis, the preparation of peptide isosteres and the development of protease inhibitors as drug candidates and imaging agents. The process described here can be performed in 3-4 d. PMID:24157547

  9. Total synthesis, structure revision, and absolute configuration of (-)-brevenal.

    PubMed

    Fuwa, Haruhiko; Ebine, Makoto; Bourdelais, Andrea J; Baden, Daniel G; Sasaki, Makoto

    2006-12-27

    Total synthesis of structure 1 originally proposed for brevenal, a nontoxic polycyclic ether natural product isolated from the Florida red tide dinoflagellate, Karenia brevis, was accomplished. The key features of the synthesis involved (i) convergent assembly of the pentacyclic polyether skeleton based on our developed Suzuki-Miyaura coupling chemistry and (ii) stereoselective construction of the multi-substituted (E,E)-dienal side chain by using copper(I) thiophen-2-carboxylate (CuTC)-promoted modified Stille coupling. The disparity of NMR spectra between the synthetic material and the natural product required a revision of the proposed structure. Detailed spectroscopic comparison of synthetic 1 with natural brevenal, coupled with the postulated biosynthetic pathway for marine polyether natural products, suggested that the natural product was most likely represented by 2, the C26 epimer of the proposed structure 1. The revised structure was finally validated by completing the first total synthesis of (-)-2, which also unambiguously established the absolute configuration of the natural product. PMID:17177450

  10. Asymmetric total synthesis of fredericamycin A: an intramolecular cycloaddition pathway.

    PubMed

    Akai, Shuji; Tsujino, Toshiaki; Fukuda, Nobuhisa; Iio, Kiyosei; Takeda, Yoshifumi; Kawaguchi, Ken-ichi; Naka, Tadaatsu; Higuchi, Kazuhiro; Akiyama, Emi; Fujioka, Hiromichi; Kita, Yasuyuki

    2005-10-21

    The asymmetric total synthesis of the potent antitumor antibiotic fredericamycin A ((S)-1) was achieved by the intramolecular [4+2] cycloaddition of the silylene-protected styrene derivative (S)-7 followed by the aromatic Pummerer-type reaction of the sulfoxide (S)-5. Although we had already succeeded in the total synthesis of racemic 1 by the same approach, synthesis of its asymmetric version was more complicated than we had expected due to the difficulties involved in constructing the quaternary carbon center and the tendency of this center to undergo facile racemization. Racemization of this center during the installation of the acetylene moiety on the dione (R)-8 was the most serious aspect. Systematic studies of its DE-ring analogue (R)-25 revealed that racemization of the quaternary carbon center proceeded by a retro-aldol-aldol reaction of the initial adduct, (1R)-39 a-Li, and that the degree of racemization was dependent on the reaction temperature. The racemization process could be completely depressed by keeping the reaction temperature at -78 degrees C. The construction of the stereogenic quaternary carbon center was achieved by the lipase-catalyzed desymmetrization of the prochiral 1,3-diol 9 a bearing the DEF-ring moiety. These studies enabled us to attain the asymmetric total synthesis of (S)-1 while completely retaining the chiral integrity created by the enzymatic reactions. PMID:16075440

  11. 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

  12. Stereoselective total synthesis of (-)-perrottetinene and assignment of its absolute configuration.

    PubMed

    Song, Yanling; Hwang, Soonho; Gong, Ping; Kim, Deukjoon; Kim, Sanghee

    2008-01-17

    The first stereoselective total synthesis of the bibenzyl tetrahydrocannabinol, (-)-perrottetinene, has been achieved from readily available starting materials. The absolute stereochemistry is derived from a chiral gamma-hydroxy vinylstannane. The key reaction is the synthesis of the cis-disubstituted cyclohexene ring of perrottetinene by diastereoselective Ireland-Claisen rearrangement and a ring-closing metathesis reaction. The absolute configuration of (-)-perrottetinene is proposed. PMID:18085788

  13. Asymmetric synthesis of gem-difluoromethylenated dihydroxypyrrolizidines and indolizidines.

    PubMed

    Thaharn, Watcharaporn; Bootwicha, Teerawut; Soorukram, Darunee; Kuhakarn, Chutima; Prabpai, Samran; Kongsaeree, Palangpon; Tuchinda, Patoomratana; Reutrakul, Vichai; Pohmakotr, Manat

    2012-10-01

    An asymmetric synthesis of gem-difluoromethylenated dihydroxypyrrolizidines and indolizidines is described. The fluoride-catalyzed nucleophilic addition of PhSCF(2)SiMe(3) (1) to chiral imides was achieved in satisfactory yields to provide mixtures of syn- and anti-isomers 6-9 with moderate to good diastereoselectivities. Reductive cleavage of the phenylsulfanyl group followed by intramolecular radical cyclization of the syn-isomers 6-9 occurred under refluxing conditions to afford the corresponding gem-difluoromethylenated 1-azabicyclic compounds 10-13 in moderate yields as a separable mixture of cis- and trans-isomers. The cis-isomers of compounds 10 and 12 and trans-13 were readily transformed to gem-difluoromethylenated dihydroxypyrrolizidines 20 and 27 and indolizidine 28, respectively, by reductive cleavage of the hydroxyl group and organometallic addition followed by hydrogenolysis. PMID:22946770

  14. High-turnover hypoiodite catalysis for asymmetric synthesis of tocopherols.

    PubMed

    Uyanik, Muhammet; Hayashi, Hiroki; Ishihara, Kazuaki

    2014-07-18

    The diverse biological activities of tocopherols and their analogs have inspired considerable interest in the development of routes for their efficient asymmetric synthesis. Here, we report that chiral ammonium hypoiodite salts catalyze highly chemo- and enantioselective oxidative cyclization of ?-(2-hydroxyphenyl)ketones to 2-acyl chromans bearing a quaternary stereocenter, which serve as productive synthetic intermediates for tocopherols. Raman spectroscopic analysis of a solution of tetrabutylammonium iodide and tert-butyl hydroperoxide revealed the in situ generation of the hypoiodite salt as an unstable catalytic active species and triiodide salt as a stable inert species. A high-performance catalytic oxidation system (turnover number of ~200) has been achieved through reversible equilibration between hypoiodite and triiodide in the presence of potassium carbonate base. We anticipate that these findings will open further prospects for the development of high-turnover redox organocatalysis. PMID:25035486

  15. Formal synthesis of the anti-angiogenic polyketide (-)-borrelidin under asymmetric catalytic control.

    PubMed

    Madduri, Ashoka V R; Minnaard, Adriaan J

    2010-10-11

    Borrelidin (1) is a polyketide that possesses extremely potent anti-angiogenesis activity. This paper describes its formal total synthesis by the most efficient route to date. This modular approach takes optimal benefit of asymmetric catalysis and permits the synthesis of analogues; in addition, the high yields and selectivities obtained eliminate the need for separation of stereoisomers. The upper half of borrelidin has been accessed by iterative copper-catalysed asymmetric conjugate addition of methylmagnesium bromide, whereas synthesis of the lower half of the molecule was achieved by relying on asymmetric hydrogenation and cross-methathesis as key steps. PMID:20734306

  16. Asymmetric Synthesis of Ampelomin A and ent-Epiampelomin A.

    PubMed

    Koyanagi, Yuji; Hamada, Toshiyuki; Iwagawa, Tetsuo; Okamura, Hiroaki

    2015-01-01

    We synthesized the naturally occurring carbasugar ampelomin A and its epimer from a common starting material. The enantiomerically pure starting material was obtained by base-catalyzed asymmetric Diels-Alder reaction of 3-hydroxy-2-pyrone and chiral acrylate. The total yield of ampelomin A was 14% in seven synthetic steps. The key step of the synthesis of ampelomin A was inversion of the stereochemistry at the C-6 position, which was achieved by stereoselective catalytic hydrogenation of the corresponding methylidene group. Further synthesis of the epimer was straightforward, because all stereogenic centers had already been introduced on the starting material; the total yield was 44% in four synthetic steps. Both the final products were obtained in pure form without contamination with undesired isomers. The reported (1)H NMR chemical shift of the C-7 methyl protons and the H-5axial coupling pattern of natural ampelomin A were inconsistent with those of our synthetic product. After careful comparison of the spectra and examination of the stable conformation obtained through MM2 calculations, we present revised NMR data for ampelomin A. PMID:25833454

  17. Chiral 1,3,2-oxazaborolidines in asymmetric synthesis: recent advances

    NASA Astrophysics Data System (ADS)

    Glushkov, Vladimir A.; Tolstikov, Alexander G.

    2004-06-01

    The use of chiral 1,3,2-oxazaborolidines in asymmetric organic synthesis, particularly, in enantioselective reduction of ketones, imines and oxime ethers, asymmetric Diels-Alder reactions, aldol condensation and atroposelective reduction of lactones is reviewed. Reactions of immobilised 1,3,2-oxazaborolidines are also considered.

  18. Asymmetric total synthesis of smyrindiol employing an organocatalytic aldol key step

    PubMed Central

    Fronert, Jeanne; Bisschops, Tom; Boeck, Florian

    2012-01-01

    Summary The first organocatalytic asymmetric synthesis of smyrindiol, by using an (S)-proline catalyzed enantioselective intramolecular aldol reaction as the key step, is described. Smyrindiol was synthesized from commercially available 2,4-dihydroxybenzaldehyde in 15 steps, with excellent stereoselectivity (de = 99%, ee = 99%). In the course of this total synthesis a new and mild coumarin assembly was developed. PMID:23019438

  19. 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.

  20. A combined continuous microflow photochemistry and asymmetric organocatalysis approach for the enantioselective synthesis of tetrahydroquinolines

    PubMed Central

    2013-01-01

    Summary A continuous-flow asymmetric organocatalytic photocyclization–transfer hydrogenation cascade reaction has been developed. The new protocol allows the synthesis of tetrahydroquinolines from readily available 2-aminochalcones using a combination of photochemistry and asymmetric Brønsted acid catalysis. The photocylization and subsequent reduction was performed with catalytic amount of chiral BINOL derived phosphoric acid diester and Hantzsch dihydropyridine as hydrogen source providing the desired products in good yields and with excellent enantioselectivities. PMID:24367413

  1. Asymmetric Synthesis of 2,4,5-Trisubstituted ?2-Thiazolines

    PubMed Central

    Bengtsson, Christoffer; Nelander, Hanna; Almqvist, Fredrik

    2013-01-01

    ?2-Thiazolines are interesting heterocycles that display a wide variety of biological characteristics. They are also common in chiral ligands used for asymmetric syntheses and as synthetic intermediates. Herein, we present asymmetric routes to 2,4,5-trisubstituted ?2-thiazolines. These ?2-thiazolines were synthesized from readily accessible/commercially available ?,?-unsaturated methyl esters through a Sharpless asymmetric dihydroxylation and an O?N acyl migration reaction as key steps. The final products were obtained in good yields with up to 97% enantiomeric excess. PMID:23776083

  2. Totally asymmetric exclusion process with extended objects: A model for protein synthesis Leah B. Shaw,1,2,

    E-print Network

    Shaw, Leah B.

    Totally asymmetric exclusion process with extended objects: A model for protein synthesis Leah B lattice site. We expand the well studied totally asymmetric exclusion process, in which particles concentrate on protein synthesis in prokary- otes, particularly Escherichia coli, because it is relatively

  3. Catalytic asymmetric synthesis of all-carbon quaternary stereocenters

    PubMed Central

    Douglas, Christopher J.; Overman, Larry E.

    2004-01-01

    Only a few catalytic asymmetric C—C bond-forming reactions have been shown to be useful for constructing all-carbon quaternary stereocenters. This Perspective examines the current state of such methods. PMID:14724294

  4. 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. PMID:25052422

  5. Palladium and organocatalysis: an excellent recipe for asymmetric synthesis.

    PubMed

    Fernández-Ibañez, M Angeles; Maciá, Beatriz; Alonso, Diego A; Pastor, Isidro M

    2013-01-01

    The dual activation of simple substrates by the combination of organocatalysis and palladium catalysis has been successfully applied in a variety of different asymmetric transformations. Thus, the asymmetric a-allylation of carbonyl compounds, a-fluorination of acyl derivatives, decarboxylative protonation of ?-dicarbonyl compounds, cyclization reactions of alkynyl carbonyl compounds and ?-functionalization of aldehydes have been efficiently achieved employing this double-catalytic methodology. PMID:23973988

  6. A SuperQuat glycolate aldol approach to the asymmetric synthesis of hexose monosaccharides.

    PubMed

    Davies, Stephen G; Nicholson, Rebecca L; Smith, Andrew D

    2005-01-21

    A stereoselective two-carbon homologation protocol has been developed and applied to the asymmetric synthesis of the hexose monosaccharides D-galactose, D-fucose, D-idose, D-6-deoxyidose, D-talose and D-6-deoxytalose. PMID:15632978

  7. Asymmetric total synthesis of (-)-leuconoxine via chiral phosphoric acid catalyzed desymmetrization of a prochiral diester.

    PubMed

    Higuchi, Kazuhiro; Suzuki, Shin; Ueda, Reeko; Oshima, Norifumi; Kobayashi, Emiko; Tayu, Masanori; Kawasaki, Tomomi

    2015-01-01

    The asymmetric total synthesis of (-)-leuconoxine has been achieved. The desymmetrization of a prochiral diester using a chiral phosphoric acid catalyst produced a highly enantioenriched lactam with excellent yield. The ring construction featuring an intramolecular N-acyliminium cyclization and the one-step pyrrolidone formation using Bestmann's ylide was successfully accomplished. PMID:25522825

  8. Asymmetric Catalytic Synthesis of P-Stereogenic Phosphines via a Nucleophilic Ruthenium Phosphido Complex

    E-print Network

    Toste, Dean

    Asymmetric Catalytic Synthesis of P-Stereogenic Phosphines via a Nucleophilic Ruthenium Phosphido reaction. On the basis of the strong basicity and nucleophilicity of previously reported iron and ruthenium cationic phosphine complex 2-BPh4. Deprotonation of this complex with KHMDS afforded ruthenium phosphido

  9. An alternative stereoselective synthesis of (R)- and (S)-Rosaphen® via asymmetric catalytic hydrogenation.

    PubMed

    Matteoli, Ugo; Beghetto, Valentina; Scrivanti, Alberto; Aversa, Manuela; Bertoldini, Matteo; Bovo, Sara

    2011-10-01

    We report an alternative synthesis of the two enantiomers of the floral fragrance Rosaphen®. The key intermediate 2-methyl-5-phenylpentanoic acid 3 is synthesized via asymmetric hydrogenation (ee up to 99%) in the presence of an in situ prepared ruthenium catalyst containing the chiral ferrocenyl phosphine Mandyphos-4. PMID:22135807

  10. Asymmetric Total Synthesis of Dendrobatid Alkaloids: Preparation of Indolizidine 251F and Its 3-Desmethyl

    E-print Network

    Taber, Douglass

    Asymmetric Total Synthesis of Dendrobatid Alkaloids: Preparation of Indolizidine 251F and Its 3-mail: jaube@ku.edu Abstract: Total syntheses of alkaloid 251F (1), a natural product detected from the skin array of natural product targets, particularly alkaloids, unprecedented in other biological systems.1

  11. Enantioselective Organocatalytic Intramolecular Diels-Alder Reactions. The Asymmetric Synthesis of Solanapyrone D

    E-print Network

    MacMillan, David W. C.

    Enantioselective Organocatalytic Intramolecular Diels-Alder Reactions. The Asymmetric Synthesis the development of enantioselective catalytic variants of the Diels-Alder reaction.1 During this time, remarkable levels of enantiocontrol in the intramolecular Diels-Alder (IMDA) reaction,2,3 a notable deficiency

  12. 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...

  13. An efficient single-enzymatic cascade for asymmetric synthesis of chiral amines catalyzed by ?-transaminase.

    PubMed

    Wang, Bo; Land, Henrik; Berglund, Per

    2013-01-01

    An efficient single-enzymatic cascade approach for the asymmetric synthesis of chiral amines has been developed, which applies the amino donor 3-aminocyclohexa-1,5-dienecarboxylic acid spontaneously tautomerizing to reach reaction completion with excellent ee values. PMID:23169388

  14. Multistep One-Pot Reactions Combining Biocatalysts and Chemical Catalysts for Asymmetric Synthesis

    E-print Network

    Zhao, Huimin

    Multistep One-Pot Reactions Combining Biocatalysts and Chemical Catalysts for Asymmetric Synthesis Carl A. Denard, John F. Hartwig,*, and Huimin Zhao*,,§ Department of Chemical and Biomolecular of chemical catalysts. Over the last 20 years, research in this area has provided us with proof of concept

  15. Catalytic asymmetric claisen rearrangement in natural product synthesis: synthetic studies toward (-)-xeniolide F.

    PubMed

    Pollex, Annett; Hiersemann, Martin

    2005-12-01

    [chemical reaction: see text]. The catalytic asymmetric Claisen rearrangement (CAC) of a highly substituted and functionalized alpha-alkoxycarbonyl-substituted allyl vinyl ether has been exploited to gain access to an advanced building block for the projected total synthesis of (-)-xeniolide F, the enantiomer of a xenicane diterpene isolated from a coral of the genus Xenia. PMID:16321027

  16. Chemoenzymatic Asymmetric Synthesis of Pregabalin Precursors via Asymmetric Bioreduction of ?-Cyanoacrylate Esters Using Ene-Reductases

    PubMed Central

    2013-01-01

    The asymmetric bioreduction of a library of ?-cyanoacrylate esters using ene-reductases was studied with the aim to provide a biocatalytic route to precursors for GABA analogues, such as pregabalin. The stereochemical outcome could be controlled by substrate-engineering through size-variation of the ester moiety and by employing stereochemically pure (E)- or (Z)-isomers, which allowed to access both enantiomers of each product in up to quantitative conversion in enantiomerically pure form. In addition, stereoselectivities and conversions could be improved by mutant variants of OPR1, and the utility of the system was demonstrated by preparative-scale applications. PMID:23316696

  17. Asymmetric multibranched conjugated molecules: synthesis, structure and photophysical properties.

    PubMed

    Zhao, Li; Wang, Wenji; Yuan, Mao-Sen

    2015-01-25

    The symmetric multibranched ?-conjugated compounds with C3 or C6 configuration have been intensively studied. The reports on asymmetric multibranched compounds are very limited. In this work, we designed and synthesized two asymmetric multibranched ?-conjugated molecules using truxene as the central core, diphenylamino and thiophenyl (or thiophenylethynyl) groups as the different branches respectively: 2,7-di(N,N-diphenylamino)-12-(2-thiophenyl)-5,5',10,10',15,15'-hexaethyltruxene and 2,7-di(N,N-diphenylamino)-12-(2-thiophenylethynyl)-5,5',10,10',15,15'-hexaethyltruxene. Their photophysical properties have been explored combining with their theoretical calculation and X-ray single-crystal structure of a key intermediate. Though their different ?-conjugation length of branches, the two title compounds exhibit almost same absorption maxima. However, their emission peaks behave a gradual red-shift with the increase of the conjugation length. The theoretical calculation results indicate that the two asymmetric compounds behave a main transition from the HOMO-1 to the LUMO or from the HOMO to the LUMO+1 upon excited. PMID:25062050

  18. Inherently Chiral Calixarenes: Synthesis, Optical Resolution, Chiral Recognition and Asymmetric Catalysis

    PubMed Central

    Li, Shao-Yong; Xu, Yao-Wei; Liu, Jun-Min; Su, Cheng-Yong

    2011-01-01

    Inherently chiral calixarenes, whose chirality is based on the absence of a planar symmetry or an inversion center in the molecules as a whole through the asymmetric array of several achiral groups upon the three-dimensional calix-skeletons, are challenging and attractive chiral molecules, because of their potential in supramolecular chemistry. The synthesis and optical resolution of all varieties of inherently chiral calixarenes are systematically discussed and classified, and their applications in chiral recognition and asymmetric catalysis are thoroughly illustrated in this review. PMID:21339996

  19. Synthesis and Application of New Ligands Derived from N-Heterocyclic Carbenes, Phosphines and Phosphites for Asymmetric Hydrogenations

    E-print Network

    Khumsubdee, Sakunchai

    2013-11-05

    , especially on hydrogenation of "largely unfunctionalized" alkenes, for more than a decade. These substrates, however, could not be easily modified leading to limited applications for organic synthesis. As a result, asymmetric hydrogenations of substrates...

  20. Rhodium-catalyzed asymmetric synthesis of silicon-stereogenic dibenzosiloles by enantioselective [2+2+2] cycloaddition.

    PubMed

    Shintani, Ryo; Takagi, Chihiro; Ito, Tomoaki; Naito, Masanobu; Nozaki, Kyoko

    2015-01-26

    A rhodium-catalyzed asymmetric synthesis of silicon-stereogenic dibenzosiloles has been developed through a [2+2+2] cycloaddition of silicon-containing prochiral triynes with internal alkynes. High yields and enantioselectivities have been achieved by employing an axially chiral monophosphine ligand, and the present catalysis is also applicable to the asymmetric synthesis of a germanium-stereogenic dibenzogermole. Preliminary studies on the optical properties of these compounds are also described. PMID:25491349

  1. Asymmetric Synthesis of gem-Difluoromethylenated Linear Triquinanes via Cascade gem-Difluoroalkyl Radical Cyclization.

    PubMed

    Thaharn, Watcharaporn; Soorukram, Darunee; Kuhakarn, Chutima; Tuchinda, Patoomratana; Pakawatchai, Chaveng; Saithong, Saowanit; Reutrakul, Vichai; Pohmakotr, Manat

    2015-01-16

    An asymmetric synthesis of gem-difluoromethylenated linear triquinanes is described exploiting the synthetic utilities of PhSCF2TMS (5) as a "(•)CF2(-)'' building block. The strategy involves fluoride-catalyzed nucleophilic addition of PhSCF2TMS (5) to chiral ketocyclopentenes 6 to provide silylated adducts 9 or alcohol derivatives 10 and 11. Subsequent cascade radical cyclization of the gem-difluoroalkyl radical generated from silylated adducts 9 or alcohols 10 and 11 afforded gem-difluoromethylenated linear triquinanes 16 as an approximate 1:1 mixture of two diastereomers (16A and 16B). Alternatively, a convenient asymmetric synthesis of gem-difluoromethylenated linear triquinanes 16A can be accomplished by oxidation of 16a (R = H) to provide ketotriquinane 17 followed by a highly stereoselective nucleophilic addition to 17 employing DIBAL, NaBH4, and various Grignard reagents. PMID:25517014

  2. Supported liquid membrane as a novel tool for driving the equilibrium of ?-transaminase catalyzed asymmetric synthesis.

    PubMed

    Rehn, Gustav; Adlercreutz, Patrick; Grey, Carl

    2014-06-10

    An attractive option to produce chiral amines of industrial importance is through asymmetric synthesis using ?-transaminase. However, reaching high yields often requires a strategy for shifting the equilibrium position. This paper describes a novel strategy for handling this problem. It involves the use of a supported liquid membrane (SLM) together with a packed bed reactor. The reactor contains Escherichia coli cells with ?-transaminase from Arthrobacter citreus, immobilized by flocculation with chitosan. The SLM consists of a hollow fibre membrane contactor in which the pores contain undecane. The system enables continuous extraction of the amine product and was used to successfully shift the equilibrium in asymmetric synthesis of (S)-?-methylbenzylamine (MBA). A conversion of 98% was reached, compared to 50% without product extraction. Moreover, a selective extraction of the produced MBA was realized. A high product concentration of 55g/l was reached after 80h, and the system showed promising potential for continuous operation. PMID:24675224

  3. Organocatalytic asymmetric cascade reactions of 7-vinylindoles: diastereo- and enantioselective synthesis of C7-functionalized indoles.

    PubMed

    Shi, Feng; Zhang, Hong-Hao; Sun, Xiao-Xue; Liang, Jing; Fan, Tao; Tu, Shu-Jiang

    2015-02-16

    The first catalytic asymmetric cascade reaction of 7-vinylindoles has been established by the rational design of such substrates. Cascade reactions with isatin-derived 3-indolylmethanols in the presence of a chiral phosphoric acid derivative allow the diastereo- and enantioselective synthesis of C7-functionalized indoles as well as the construction of cyclopenta[b]indole and spirooxindole frameworks (all >95:5 d.r., 94->99?% ee). This approach not only addresses the great challenge of the catalytic asymmetric synthesis of C7-functionalized indoles, but also provides an efficient method for constructing biologically important cyclopenta[b]indole and spirooxindole scaffolds with excellent optical purity. Investigation of the reaction pathway and activation mode has suggested that this cascade reaction proceeds through a vinylogous Michael addition/Friedel-Crafts process, in which dual H-bonding activation of the two reactants plays a crucial role. PMID:25521722

  4. Asymmetric disulfonimide-catalyzed synthesis of ?-amino-?-ketoester derivatives by vinylogous Mukaiyama-Mannich reactions.

    PubMed

    Wang, Qinggang; van Gemmeren, Manuel; List, Benjamin

    2014-12-01

    An organocatalytic asymmetric synthesis of ?-amino-?-ketoester derivatives has been developed. A chiral disulfonimide (DSI) serves as a highly efficient precatalyst for a vinylogous Mukaiyama-Mannich reaction of readily available dioxinone-derived silyloxydienes with N-Boc-protected imines, delivering products in excellent yields and enantioselectivities. The synthetic utility of this reaction is illustrated in various transformations, including a new C?C bond-forming reaction, which provide useful enantioenriched building blocks. The methodology is applied in a formal synthesis of (-)-lasubin. PMID:25348924

  5. 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

  6. Chemoenzymatic Synthesis of Vitamin B5-Intermediate (R)-Pantolactone via Combined Asymmetric Organo- and Biocatalysis.

    PubMed

    Heidlindemann, Marcel; Hammel, Matthias; Scheffler, Ulf; Mahrwald, Rainer; Hummel, Werner; Berkessel, Albrecht; Gröger, Harald

    2015-04-01

    The combination of an asymmetric organocatalytic aldol reaction with a subsequent biotransformation toward a "one-pot-like" process for the synthesis of (R)-pantolactone, which to date is industrially produced by a resolution process, is demonstrated. This process consists of an initial aldol reaction catalyzed by readily available l-histidine followed by biotransformation of the aldol adduct by an alcohol dehydrogenase without the need for intermediate isolation. Employing the industrially attractive starting material isobutanal, a chemoenzymatic three-step process without intermediate purification is established allowing the synthesis of (R)-pantolactone in an overall yield of 55% (three steps) and high enantiomeric excess of 95%. PMID:25710713

  7. Highly Efficient Synthesis of Chiral ?-CF3 Amines via Rh-Catalyzed Asymmetric Hydrogenation.

    PubMed

    Jiang, Jun; Lu, Wenxin; Lv, Hui; Zhang, Xumu

    2015-03-01

    Highly enantioselective catalytic asymmetric hydrogenation of ?-CF3-enamides has been achieved by employing rhodium-DuanPhos as the catalyst, which provides a readily accessible method for the synthesis of chiral trifluoromethylated amines. The reaction has a broad substrate scope; both aryl- and alkyl-substituted ?-CF3-enamides worked smoothly and afford the corresponding chiral amines in high yields and excellent enantioselectivities (up to 99% ee). PMID:25685874

  8. Asymmetric synthesis of vicinal amino alcohols: xestoaminol C, sphinganine and sphingosine.

    PubMed

    Abraham, Elin; Davies, Stephen G; Millican, Nicholas L; Nicholson, Rebecca L; Roberts, Paul M; Smith, Andrew D

    2008-05-01

    The highly diastereoselective anti-aminohydroxylation of 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-diacetyl xestoaminol C (41% yield over 8 steps), N,O,O-triacetyl sphinganine (30% yield over 8 steps) and N,O,O-triacetyl sphingosine (30% yield over 7 steps). PMID:18421400

  9. Enantioselective total synthesis of (?)-pseudophrynaminol through tandem olefination, isomerization and asymmetric Claisen rearrangement

    Microsoft Academic Search

    Tomomi Kawasaki; Atsuyo Ogawa; Yasuyuki Takashima; Masanori Sakamoto

    2003-01-01

    A new and efficient total synthesis of (?)-pseudophrynaminol, the pyrrolo[2,3-b]indole alkaloid bearing the allylic moiety at the 3a-position, has been achieved by a sequence involving 3-allylindol-2-one 8 as a key intermediate. The enantioselective construction of the quaternary carbon in 8 was performed through a tandem cascade reaction of 2-allyloxyindolin-3-one 4, olefination, isomerization, and asymmetric Claisen rearrangement.

  10. Catalytic asymmetric crotylation of aldehydes: application in total synthesis of (-)-elisabethadione.

    PubMed

    O'Hora, Paul S; Incerti-Pradillos, Celia A; Kabeshov, Mikhail A; Shipilovskikh, Sergei A; Rubtsov, Aleksandr E; Elsegood, Mark R J; Malkov, Andrei V

    2015-03-16

    A new, highly efficient Lewis base catalyst for a practical enantio- and diastereoselective crotylation of unsaturated aldehydes with E- and Z-crotyltrichlorosilanes has been developed. The method was employed as a key step in a novel asymmetric synthesis of bioactive serrulatane diterpene (-)-elisabethadione. Other strategic reactions for setting up the stereogenic centers included anionic oxy-Cope rearrangement and cationic cyclization. The synthetic route relies on simple, high yielding reactions and avoids use of protecting groups or chiral auxiliaries. PMID:25663158

  11. Asymmetric synthesis of (-)-aurantioclavine via palladium-catalyzed intramolecular allylic amination.

    PubMed

    Suetsugu, Satoshi; Nishiguchi, Hiromi; Tsukano, Chihiro; Takemoto, Yoshiji

    2014-02-01

    The total synthesis of (-)-aurantioclavine (1) was accomplished based on an intramolecular asymmetric amination of allyl carbonate 3 containing a p-tosylamide group. The reaction using tris(dibenzylideneacetone)dipalladium(0), tBu-phosphinooxazoline, and Bu4NCl in CH2Cl2 gave azepane 2 in 77% yield with 95% enantiomeric excess. The obtained azepane 2 was also converted to a substructure of communesin F. PMID:24460216

  12. Hydroxynitrile lyase from Passiflora edulis: Purification, characteristics and application in asymmetric synthesis of ( R)-mandelonitrile

    Microsoft Academic Search

    Techawaree Ueatrongchit; Ken’ichirou Tamura; Tohru Ohmiya; Aran H-Kittikun; Yasuhisa Asano

    2010-01-01

    A hydroxynitrile lyase from leaves of Passiflora edulis (PeHNL) was purified and characterized for the first time. The enzyme is a monomer of 15kDa and 18kDa by SDS-PAGE, and gel filtration, respectively. Asymmetric synthesis of (R)-mandelonitrile from benzaldehyde and acetone cyanohydrin in a biphasic system employing the PeHNL from rinds of P. edulis was carried out. Several parameters influenced the

  13. Asymmetric synthesis of fully substituted cyclopentane-oxindoles through an organocatalytic triple Michael domino reaction.

    PubMed

    Zou, Liang-Hua; Philipps, Arne R; Raabe, Gerhard; Enders, Dieter

    2015-01-12

    An efficient, highly stereoselective asymmetric synthesis of fully functionalized cyclopentanes bearing an oxindole moiety and several other functional groups in one pot has been developed. Key step is an organocatalytic triple Michael domino reaction forming three C-C bonds and six stereocenters, including a quaternary one. Starting from equimolar amounts of simple substrates, a high molecular complexity can be reached after a Wittig olefination in one pot. The new protocol can easily be scaled up to gram amounts. PMID:25470781

  14. Asymmetric Synthesis of 1,2-dioxanes: Approaches to the Peroxyplakoric Acids

    PubMed Central

    Xu, Chunping; Schwartz, Chris; Raible, Joseph; Dussault, Patrick H.

    2009-01-01

    The stereospecific intramolecular alkylation of a hydroperoxyacetal provides the basis for the first asymmetric synthesis of the dioxane propionate core of the peroxyplakorates. Chemoselective hydrometallation of an alkyne in the presence of a peroxide is used to introduce a synthon for the polyunsaturated side chains of the peroxyplakorates. The route suggests a general solution for the 1,2-dioxane unit in many peroxide natural products. PMID:20160918

  15. 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. PMID:24030985

  16. Total synthesis of (-)-bitungolide F and determination of its absolute stereochemistry.

    PubMed

    Ghosh, Subhash; Kumar, Soma Uday; Shashidhar, J

    2008-02-15

    A highly convergent total synthesis of bitungolide F leading to the assignment of its absolute stereochemistry is described. The key steps include a Horner-Wadsworth-Emmons olefination to construct the C7-C8 bond, a Wittig reaction to introduce the conjugate E,E-olefinic moiety in the molecule, and finally a ring-closing metathesis reaction to construct the six-membered alpha,beta-unsaturated delta-lactone of the molecule. Modified Evans's syn-aldol reaction, using Crimmins's protocol, was used to install the stereochemistries at the C4 and C5 centers. The stereochemistry at C9 was introduced by means of hydroxy-directed reduction of the C9 keto using Evans's protocol. PMID:18201100

  17. Synthesis, chiral resolution, and absolute configuration of dissymmetric 4,15-difunctionalized [2.2]paracyclophanes.

    PubMed

    Meyer-Eppler, Georg; Sure, Rebecca; Schneider, Andreas; Schnakenburg, Gregor; Grimme, Stefan; Lützen, Arne

    2014-07-18

    Despite the fact that functionalized planar chiral [2.2]paracyclophanes have received a lot of attention, the chemistry of pseudo-meta 4,15-distubstituted [2.2]paracyclophanes is largely unexplored. This is mainly due to the fact that the 4,5-dibromo-functionalized [2.2]paracyclophane is much less prone to halogen-metal exchange reactions than its constitutional pseudo-ortho or pseudo-para isomers. Here, we give an account of an efficient protocol to achieve this, which allows the synthesis of a broad variety of 4,15-disubstituted [2.2]paracyclophanes. Furthermore, we were able to resolve several of the racemic compounds via chiral HPLC and assign the absolute configurations of the isolated enantiomers by X-ray diffraction and/or by the comparison of calculated and measured CD-spectra. PMID:24971748

  18. Short synthesis of berkeleyamide D and determination of the absolute configuration by the vibrational circular dichroism exciton chirality method.

    PubMed

    Komori, Kenta; Taniguchi, Tohru; Mizutani, Shoma; Monde, Kenji; Kuramochi, Kouji; Tsubaki, Kazunori

    2014-03-01

    The first synthesis of (±)-berkeleyamide D has been accomplished. The key features of this synthesis include the formation of an ?,?-epoxy-?-lactam via a Darzens reaction and the construction of a spirocyclic ring system by a C-acylation reaction followed by an intramolecular spirocyclization via an epoxide-opening reaction. Following optical resolution by chiral HPLC, the absolute configurations of both enantiomers of berkeleyamide D were determined by the vibrational circular dichroism exciton chirality method. PMID:24527805

  19. Synthesis of Non-racemic ?-Hydroxyphosphonates via Asymmetric Phospho-Aldol Reaction.

    PubMed

    Spilling, Christopher D; Malla, Raj K

    2015-01-01

    It has been more than 50 years since the first phospho-aldol reactions of dialkyl phosphites were reported. These efficient P-C bond-forming reactions have become the cornerstone of methods for the synthesis of ?-hydroxyphosphonates and, by numerous available substitution reactions, the synthesis of other ?- and ?-substituted phosphonates and phosphonic acids. Much of the interest in ?- and ?-substituted phosphonates and phosphonic acids has been stimulated by reports of their biological activity, which is often dependent upon their absolute and relative stereochemistry. In this chapter, we review diastereoselective and enantioselective additions of dialkyl phosphites to aldehydes and ketones, otherwise called the phospho-aldol, Pudovik or Abramov reactions. PMID:25467537

  20. Asymmetric Autocatalysis with Amplification of Chirality

    NASA Astrophysics Data System (ADS)

    Soai, Kenso; Kawasaki, Tsuneomi

    We found that chiral 5-pyrimidyl alkanols are highly enantioselective asymmetric autocatalysts for the addition of i-Pr2Zn to the corresponding aldehyde. Asymmetric autocatalysis with amplification of ee from extremely low (0.00005%) ee to >99.5% ee was realized for the first time by consecutive asymmetric autocatalysis. The chirality of CPL was directly correlated with the chirality of the pyrimidyl alkanol with high ee by asymmetric photodegradation of the racemic pyrimidyl alkanol in combination with asymmetric autocatalysis. Chiral inorganic crystals such as quartz act as chiral triggers and regulate the sense of the asymmetric autocatalysis. Chiral organic crystals composed of an achiral compound such as hippuric acid act as the initial source of chirality for asymmetric autocatalysis to produce the nearly enantiomerically pure product. Highly sensitive chiral discrimination of amino acids with low ee is described. Direct examination of extraterrestrial chirality was performed on meteorites by applying asymmetric autocatalysis as the chiral sensor. Spontaneous absolute asymmetric synthesis is described in the formation of enantiomerically enriched pyrimidyl alkanol from the reaction of pyrimidine-5-carbaldehyde and i-Pr2Zn without adding any chiral substance in combination with asymmetric autocatalysis. Asymmetric autocatalysis of a chiral pyrimidyl alkanol is the only possible method to discriminate a cryptochiral quaternary saturated hydrocarbon, whose chirality is not capable of determination by any current method. The discrimination of chirality due to deuterium substitution is also accessible by the highly sensitive asymmetric autocatalysis.

  1. Development of an Asymmetric Synthesis of a Chiral Quaternary FLAP Inhibitor.

    PubMed

    Fandrick, Keith R; Mulder, Jason A; Patel, Nitinchandra D; Gao, Joe; Konrad, Michael; Archer, Elizabeth; Buono, Frederic G; Duran, Adil; Schmid, Rolf; Daeubler, Juergen; Desrosiers, Jean-Nicolas; Zeng, Xingzhong; Rodriguez, Sonia; Ma, Shengli; Qu, Bo; Li, Zhibin; Fandrick, Daniel R; Grinberg, Nelu; Lee, Heewon; Bosanac, Todd; Takahashi, Hidenori; Chen, Zhidong; Bartolozzi, Alessandra; Nemoto, Peter; Busacca, Carl A; Song, Jinhua J; Yee, Nathan K; Mahaney, Paige E; Senanayake, Chris H

    2015-02-01

    A practical sequence involving a noncryogenic stereospecific boronate rearrangement followed by a robust formylation with an in situ generated DCM anion has been developed for the asymmetric construction of an all-carbon quaternary stereogenic center of a FLAP inhibitor. The key boronate rearrangement was rendered noncryogenic and robust by using LDA as the base and instituting an in situ trapping of the unstable lithiated benzylic carbamate with the boronic ester. A similar strategy was implemented for the DCM formylation reaction. It was found that the 1,2-boronate rearrangement for the formylation reaction could be temperature-controlled, thus preventing overaddition of the DCM anion and rendering the process reproducible. The robust stereospecific boronate rearrangement and formylation were utilized for the practical asymmetric synthesis of a chiral quaternary FLAP inhibitor. PMID:25562342

  2. Highly enantioselective synthesis of ?-, ?-, and ?-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 ?- 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 ?-alkene-1-ols produced both (R)- and (S)-?,?-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 ?,?-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 ?-, ?-, and ?-chiral 1-alkanols of ?99% ee. The M?NP ester analysis has been applied to the determination of the enantiomeric purities of ?- and ?-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. PMID:24912191

  3. Highly enantioselective synthesis of ?-, ?-, and ?-chiral 1-alkanols via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA)–Cu- or Pd-catalyzed cross-coupling

    PubMed Central

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

    2014-01-01

    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 ?- 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 ?-alkene-1-ols produced both (R)- and (S)-?,?-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 ?,?-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 ?-, ?-, and ?-chiral 1-alkanols of ?99% ee. The M?NP ester analysis has been applied to the determination of the enantiomeric purities of ?- and ?-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. PMID:24912191

  4. Asymmetric catalytic synthesis of enantiopure N-protected 1,2-amino alcohols.

    PubMed

    Bartoli, Giuseppe; Bosco, Marcella; Carlone, Armando; Locatelli, Manuela; Melchiorre, Paolo; Sambri, Letizia

    2004-10-28

    [reaction: see text] The asymmetric aminolytic kinetic resolution (AKR) of racemic terminal epoxides using carbamates as the nucleophile catalyzed by (salen)Co(III) complex provides a practical and straightforward method for the synthesis of both aliphatic and aromatic N-Boc- or N-Cbz-protected 1,2-amino alcohols in almost enantiomerically pure form (ee >/= 99%). The AKR uses an easily accessible catalyst and inexpensive starting materials, and the reactions are conveniently carried out at room temperature under an air atmosphere. PMID:15496077

  5. Recent contributions from the asymmetric aza-Michael reaction to alkaloids total synthesis.

    PubMed

    Amara, Zacharias; Caron, Joachim; Joseph, Delphine

    2013-09-01

    This review focuses on recent applications of the aza-Michael reaction in alkaloids total synthesis with a special emphasis on stereoselectivity. The report highlights achievements and challenges over the past five years and describes stereoselective intra- and inter-molecular conjugate addition of nitrogen-containing nucleophiles, including tandem and cascade processes. Total asymmetric syntheses of natural scaffolds, such as pyrrolidine, piperidine and "izidine" families, are depicted. Multi-step syntheses of highly challenging natural products are further detailed, assessing the scope of the stereocontrolled aza-Michael reaction as a powerful tool in alkaloid chemistry. PMID:23896828

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

    NASA Astrophysics Data System (ADS)

    Raj, Hans; Szyma?ski, 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).

  7. Asymmetric total synthesis of sperabillins B and D via lithium amide conjugate addition.

    PubMed

    Davies, Stephen G; Haggitt, Jane R; Ichihara, Osamu; Kelly, Richard J; Leech, Michael A; Price Mortimer, Anne J; Roberts, Paul M; Smith, Andrew D

    2004-09-21

    Diastereoselective conjugate addition of homochiral lithium (R)-N-allyl-N-alpha-methylbenzylamide to methyl (2E,5E)-hepatadienoate, followed by protecting group manipulation and subsequent iodocyclocarbamation allows a concise route to the core fragment, methyl (3R,5R,6R)-3,6-diamino-5-hydroxyheptanoate, of sperabillins B and D. Differentiation between the C-3 and C-6 primary amino groups of this core amino acid was readily achieved by treatment with acetone, giving the 5,6-isopropylidene and C-3-imine protected diamine, with subsequent regioselective acylation of the C-6-nitrogen facilitating the total synthesis of sperabillin D in 10.8% overall yield, and the first asymmetric synthesis of sperabillin B in 5.8% overall yield. PMID:15351828

  8. 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 ?-components to achieve cycloadditions. However, the use of C-N ?-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 ?-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

  9. Symmetry Breaking in Asymmetric Autocatalysis of Pyrimidyl Alkanol

    NASA Astrophysics Data System (ADS)

    Soai, Kenso; Kawasaki, Tsuneomi

    2008-03-01

    Asymmetric autocatalysis is a reaction in which chiral product acts as a chiral catalyst for its own production. Pyrimidyl alkanol was found to act as asymmetric autocatalysts with significant amplification of enantiopurity in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde. Symmetry breaking is observed in the reaction between the aldehyde and diisopropylzinc without adding chiral substance. Enantioenriched pyrimidyl alkanol was obtained with stochastic distribution of R and S-enantiomers. This is a unique example of spontaneous absolute asymmetric synthesis. Asymmetric autocatalysis is also described using chiral initiators such as circularly polarized light, quartz, chiral crystal of achiral cytosine.

  10. Symmetry Breaking in Asymmetric Autocatalysis of Pyrimidyl Alkanol

    SciTech Connect

    Soai, Kenso; Kawasaki, Tsuneomi [Department of Applied Chemistry, Tokyo University of Science, Kagurazaka, Shinjuku-ku, Tokyo 162-8601 (Japan)

    2008-03-05

    Asymmetric autocatalysis is a reaction in which chiral product acts as a chiral catalyst for its own production. Pyrimidyl alkanol was found to act as asymmetric autocatalysts with significant amplification of enantiopurity in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde. Symmetry breaking is observed in the reaction between the aldehyde and diisopropylzinc without adding chiral substance. Enantioenriched pyrimidyl alkanol was obtained with stochastic distribution of R and S-enantiomers. This is a unique example of spontaneous absolute asymmetric synthesis. Asymmetric autocatalysis is also described using chiral initiators such as circularly polarized light, quartz, chiral crystal of achiral cytosine.

  11. The ever-expanding role of asymmetric covalent organocatalysis in scalable, natural product synthesis.

    PubMed

    Abbasov, Mikail E; Romo, Daniel

    2014-10-01

    Following the turn of the millennium, the role of asymmetric covalent organocatalysis has developed into a scalable, synthetic paradigm galvanizing the synthetic community toward utilization of these methods toward more practical, metal-free syntheses of natural products. A myriad of reports on asymmetric organocatalytic modes of substrate activation relying on small, exclusively organic molecules are delineating what has now become the multifaceted field of organocatalysis. In covalent catalysis, the catalyst and substrate combine to first form a covalent, activated intermediate that enters the catalytic cycle. Following asymmetric bond formation, the chiral catalyst is recycled through hydrolysis or displacement by a pendant group on the newly formed product. Amine- and phosphine-based organocatalysts are the most common examples that have led to a vast array of reaction types. This Highlight provides a brief overview of covalent modes of organocatalysis and applications of scalable versions of these methods applied to the total synthesis of natural products including examples from our own laboratory. PMID:25042097

  12. Synthesis, structure revision, and absolute configuration of (+)-didemniserinolipid B, a serinol marine natural product from a tunicate Didemnum sp.

    PubMed

    Kiyota, Hiromasa; Dixon, Darren J; Luscombe, Christine K; Hettstedt, Stephan; Ley, Steven V

    2002-09-19

    [structure: see text] En route to proving the absolute and relative stereochemistry, through synthesis, of (+)-didemniserinolipid B (1), the first natural serinolipid isolated from a tunicate Didemnum sp., it was discovered that the isolated natural product was in fact the 31-sulfate configured 8R,9R,10R,13S,30S. This structural reassignment was only possible after the development of a microwave-assisted method for the sulfation of unreactive hydroxyl groups. PMID:12227754

  13. Nickel-catalyzed asymmetric cross-couplings of secondary allylic chlorides and planar-chiral compounds in asymmetric synthesis

    E-print Network

    Son, Sunghee

    2008-01-01

    In Part I, nickel-catalyzed asymmetric carbon-carbon bond-forming reactions are described. A nickel/Pybox system effectively catalyzes regio- and enantioselective cross-couplings between racemic secondary allylic chlorides ...

  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. Bifunctional thiourea-catalyzed enantioselective double Michael reaction of ?,?-unsaturated ?-ketoester to nitroalkene: asymmetric synthesis of (?)-epibatidine

    Microsoft Academic Search

    Yasutaka Hoashi; Takaya Yabuta; Yoshiji Takemoto

    2004-01-01

    The asymmetric synthesis of 4-nitrocyclohexanone derivatives has been accomplished by enantioselective double Michael additions of ?,?-unsaturated ?-ketoesters to nitroalkenes using a catalytic amount of bifunctional thiourea and TMG. The three contiguous stereogenic centers of the obtained products were constructed with good to high diastereoselectivity and up to 92% ee. The biologically active natural product, (?)-epibatidine, has been synthesized from the

  16. Synthesis of enantiomerically enriched 3-amino-2-oxindoles through a palladium-mediated asymmetric intramolecular arylation of ?-ketimino amides.

    PubMed

    Tolstoy, Päivi; Lee, Samantha X Y; Sparr, Christof; Ley, Steven V

    2012-09-21

    A highly efficient and enantioselective synthesis of 3-amino-2-oxindoles through a palladium-catalyzed asymmetric intramolecular arylation of ?-ketimino amides using (R)-DiFluorPhos as the coordinating ligand is reported. This report constitutes the first enantioselective palladium-catalyzed arylation of ketimines. PMID:22946713

  17. 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. PMID:24952728

  18. Development of an Asymmetric Trimethylenemethane Cycloaddition Reaction: Application in the Enantioselective Synthesis of Highly Substituted Carbocycles

    PubMed Central

    Trost, Barry M.; Silverman, Steven M.; Stambuli, James P.

    2011-01-01

    A protocol for the enantioselective [3+2] cycloaddition of trimethylenemethane with electron-deficient olefins has been developed. The synthesis of novel phosphoramidite ligands was critical in this effort, and the preparation and reactivity of these ligands is detailed. The evolution of the ligand design, commencing with acyclic amine-derived phosphoramidites and leading to cyclic pyrrolidine and azetidine structures is discussed. The conditions developed to effect an asymmetric TMM reaction using 2-trimethylsilylmethyl allyl acetate were shown to be tolerant of a wide variety of alkene acceptors, providing the desired methylenecyclopentanes with high levels of enantioselectivity. The donor scope was also explored and substituted systems were tolerated, including one bearing a nitrile moiety. These donors were reactive with unsaturated acylpyrroles, giving the product cyclopentane rings bearing three stereocenters in high enantioselectivity and complete diastereoselectivity. PMID:21936576

  19. Catalytic Asymmetric Synthesis of Secondary Nitriles via Stereoconvergent Negishi Arylations and Alkenylations of Racemic ?-Bromonitriles

    PubMed Central

    Choi, Junwon; Fu, Gregory C.

    2012-01-01

    The first method for the stereoconvergent cross-coupling of racemic ?-halonitriles is described, specifically, nickel-catalyzed Negishi arylations and alkenylations that furnish an array of enantioenriched ?-arylnitriles and allylic nitriles, respectively. Noteworthy features of this investigation include: the highly enantioselective synthesis of ?-alkyl-?-aryl nitriles that bear secondary ?-alkyl substituents; the first examples of the use of alkenylzinc reagents in stereoconvergent Negishi reactions of alkyl electrophiles; demonstration of the utility of a new family of ligands for asymmetric Negishi cross-couplings (a bidentate bis(oxazoline), rather than a tridentate pybox); in the case of arylzinc reagents, carbon–carbon bond formation at a remarkably low temperature (?78 °C), the lowest reported to date for an enantioselective cross-coupling of an alkyl electrophile; a mechanistic dichotomy between Negishi reactions of an unactivated versus an activated secondary alkyl bromide. PMID:22612264

  20. N-silyl oxyketene imines are underused yet highly versatile reagents for catalytic asymmetric synthesis

    NASA Astrophysics Data System (ADS)

    Denmark, Scott E.; Wilson, Tyler W.

    2010-11-01

    The reactions of acyl anion equivalents (d1 synthons) with carbonyl electrophiles allow for the construction of a wide range of molecules useful for the synthesis of biologically active compounds, natural products and chiral ligands. Despite their utility, significant challenges still exist for developing catalytic, enantioselective variants of these reactions. For example, the asymmetric benzoin process, arguably the most characteristic reaction of d synthetic equivalents, finds no general solution for reactions involving aliphatic acyl anions. In this Article, we introduce a new class of stable, isolable silyl ketene imines derived from protected cyanohydrins. These nucleophiles serve as acyl anion equivalents in Lewis base catalysed aldol addition reactions and allow for the preparation of cross-benzoin and glycolate-aldol products in high yield and with exceptional diastereo- and enantioselectivities.

  1. Haloperidol metabolite II prodrug: asymmetric synthesis and biological evaluation on rat C6 glioma cells.

    PubMed

    Sozio, Piera; Fiorito, Jole; Di Giacomo, Viviana; Di Stefano, Antonio; Marinelli, Lisa; Cacciatore, Ivana; Cataldi, Amelia; Pacella, Stephanie; Turkez, Hasan; Parenti, Carmela; Rescifina, Antonio; Marrazzo, Agostino

    2015-01-27

    In a previous work we reported the antiproliferative effects of (±)-MRJF4, a novel haloperidol metabolite II (HP-mII) (a sigma-1 antagonist and sigma-2 agonist) prodrug, obtained through conjugation to 4-phenylbutyric acid (PhBA) [a histone deacetylase inhibitor (HDACi)] via an ester bond. As a continuation of this work, here we report the asymmetric synthesis of compounds (R)-(+)-MRJF4 and (S)-(-)-MRJF4 and the evaluation of their biological activity on rat C6 glioma cells, derived from glioblastoma multiforme (GBM), which is the most common and deadliest central nervous system (CNS) invasive malignancy. Favourable physicochemical properties, high permeability in the parallel artificial membrane permeability assay (PAMPA), good enzymatic and chemical stability, in vivo anticancer activity, associated with the capacity to reduce cell viability and to increase cell death by apoptosis, render compound (R)-(+)-MRJF4 a promising candidate for the development of a useful therapeutic for gliomas therapy. PMID:25461306

  2. Asymmetric Hydrogenations of Chiral Acyclic Alkenes for Important Chiron Syntheses

    E-print Network

    Zhu, Ye

    2012-07-16

    Page 6.2.2 Syntheses of the triads T-W via asymmetric hydrogenations 82 6.2.3 Relative and absolute configuration determination ............... 85 6.2.4 Total synthesis................................. 91 7.2. Some natural products prepared via hydrogenation reactions ................ 92 7.3. Ir-hydride intermediates in catalytic hydrogenations have markedly different acidities...

  3. Asymmetric synthesis of enantiopure isoxazolidinone monomers for the synthesis of ?3-oligopeptides by chemoselective amide ligation

    PubMed Central

    Juarez-Garcia, M. Elisa; Yu, Shouyun; Bode, Jeffrey W.

    2010-01-01

    The design and general synthesis of enantiopure isoxazolidinone monomers as precursors for the preparation of enantiopure N-terminal hydroxylamine—?3-oligopeptides, which may be used as reaction partners with ?-ketoacids in the decarboxylative amide ligation reaction, is described. PMID:21499500

  4. Asymmetric triple relay catalysis: enantioselective synthesis of spirocyclic indolines through a one-pot process featuring an asymmetric 6? electrocyclization.

    PubMed

    Yin, Xiao-Ping; Zeng, Xing-Ping; Liu, Yun-Lin; Liao, Fu-Min; Yu, Jin-Sheng; Zhou, Feng; Zhou, Jian

    2014-12-01

    A rare example of a one-pot process that involves asymmetric triple relay catalysis is reported. The key step is an asymmetric [1,5] electrocyclic reaction of functionalized ketimines. The substrates for this process were obtained in?situ in a two-step process that involved the hydrogenation of nitroarenes with a Pd/C catalyst to yield aryl amines and their subsequent coupling with isatin derivatives in a Brønsted acid catalyzed ketimine formation reaction. The electrocyclization was catalyzed by a bifunctional chiral Brønsted base/hydrogen bond donor catalyst. The one-pot process gave the desired products in good yields and with excellent enantioselectivity. PMID:25313907

  5. 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. PMID:17193299

  6. Collective asymmetric synthesis of (-)-antofine, (-)-cryptopleurine, (-)-tylophorine, and (-)-tylocrebrine with tert-butanesulfinamide as a chiral auxiliary.

    PubMed

    Zheng, Yanlong; Liu, Yuxiu; Wang, Qingmin

    2014-04-18

    A collective asymmetric synthesis of phenanthroindolizidine and phenanthroquinolizidine alkaloids (-)-antofine, (-)-cryptopleurine, (-)-tylophorine, and (-)-tylocrebrine was achieved by means of a reaction sequence involving efficient generation of chiral homoallylic amine intermediates by asymmetric allylation of the corresponding tert-butanesulfinyl imine. From these intermediates, the pyrrolidine and piperidine rings were constructed by means of an intramolecular SN2 substitution reaction and a ring-closing metathesis reaction, respectively. The unusual C5-methoxy-substituted phenanthrene moiety of (-)-tylocrebrine was generated by means of an InCl3-catalyzed cycloisomerization reaction of an o-propargylbiaryl compound. PMID:24679059

  7. Synthesis and absolute configuration assignment of 5-amino-1,3,5-triphenyl-pentane-1,3-diol stereoisomers.

    PubMed

    Uncuta, Cornelia; Caraman, George B; Tanase, Catalin I; Bartha, Emeric; Kravtsov, Victor Ch; Simonov, Yurii A; Lipkowski, Janus; Vanthuyne, Nicolas; Roussel, Christian

    2005-01-01

    Starting from 2,4,6-triphenylpyrylium perchlorate, 5-amino-1,3,5-triphenyl-pentane-1,3-diol stereoisomers 4 were obtained in a simple two-step synthesis: reaction with hydroxylamine, and reduction with LAH of the resulting 2-isoxazoline ketone derivative 2. The eight stereoisomers of 4 were separated in a single shot on a chiral stationary phase cellulose tris(3,5-dimethylphenylcarbamate) (Chiralcel OD-H). The absolute configuration of the title compounds, intermediate 2-isoxazoline ketone 2 and isoxazoline alcohol derivative 3 were determined using a combination of diastereoselective synthesis, affiliation of the sign in chemical interconversion method, and X-ray determination. 2-Isoxazoline ketone 2 enantiomers and isoxazoline alcohol 3 enantiomers were obtained by chiral HPLC on Chiralpak AD column. 2-Isoxazoline ketone 2 enantiomers can be racemized via a retro Michael addition. PMID:15549713

  8. Radical cyclization/ipso-1,4-aryl migration cascade: asymmetric synthesis of 3,3-difluoro-2-propanoylbicyclo[3.3.0]octanes.

    PubMed

    Thaharn, Watcharaporn; Soorukram, Darunee; Kuhakarn, Chutima; Tuchinda, Patoomratana; Reutrakul, Vichai; Pohmakotr, Manat

    2014-02-17

    A novel method for the asymmetric synthesis of 3,3-difluoro-2-propanoylbicyclo-[3.3.0]octanes involves an unprecedented intramolecular radical cyclization/ipso-1,4-aryl migration cascade. PMID:24478184

  9. Versatile, diastereoselective additions of silyl ketene acetals, allyl tributylstannane, and Me(3)SiCN to N-acyl pyrazolines: asymmetric synthesis of densely functionalized pyrazolidines

    PubMed

    Guerra; Mish; Carreira

    2000-12-28

    We report the diastereoselective addition of a wide range of nucleophiles to chiral pyrazolines to provide facile access to a range of useful densely functionalized building blocks for asymmetric synthesis. Coupled with the asymmetric cycloaddition reaction of Me(3)SiCHN(2) to chiral acrylates, access to these chiral heterocycles is considerably expanded. PMID:11150215

  10. Controlling the Facial Selectivity of Asymmetric [4+2] Cyclo-additions: A Concise Synthesis of the cis-Decalin Core Structure of Superstolides A and B

    PubMed Central

    Chen, Lei; Hua, Zhengmao; Li, Gangqin; Jin, Zhendong

    2011-01-01

    Regio, stereo and facial selective [4+2] cycloadditions between highly activated vinyl sulfones and 1,3-dienes derived from (R)-4-t-butyldimethyl-silyloxy-2-cyclohexen-1-one provide a powerful approach for the asymmetric synthesis of compounds containing the bicyclo[2.2.2]octanone carbon skeleton. This new methodology has been successfully applied to the asymmetric synthesis of the cis-decalin core structure of the potent anticancer marine natural products superstolides A and B. PMID:21671636

  11. Asymmetric Total Synthesis of (?)-Plicatic Acid via a Highly Enantioselective and Diastereoselective Nucleophilic Epoxidation of Acyclic Trisubstitued Olefins

    PubMed Central

    Sun, Bing-Feng; Hong, Ran; Kang, Yan-Biao; Deng, Li

    2009-01-01

    The first total synthesis of (?)-plicatic acid has been achieved by a concise and enantioselective route. In this synthesis, a conceptually new strategy featuring an asymmetric epoxidation-intramolecular epoxy-ring-opening Friedel-Crafts reaction sequence was developed for the stereoselective construction of the 2,7’-cyclolignane skeleton bearing contiguous quaternary-quaternary-tertiary stereocenters. The implementation of this strategy was enabled by the development of a modified protocol for the Seebach epoxidation with TADOOH, which affords an unprecedented, highly enantioselective and diastereoselective epoxidation with a range of ?-carbonyl-?-substituted acrylates 3. PMID:19601599

  12. Synthesis, resolution, and determination of absolute configuration of protected ?-ethynylphenylalanine enantiomers.

    PubMed

    Benfodda, Z; Bénimélis, D; Jean, M; Naubron, J-V; Rolland, V; Meffre, P

    2015-05-01

    Racemic-protected ?-ethynylphenylalanine was synthesized from DL-2-benzylserine using ?-benzylserinal as key intermediate and was successfully resolved by HPLC on a chiral stationary phase at a semipreparative scale. The absolute configuration of both enantiomers was determined by vibrational circular dichroism. PMID:25618753

  13. 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

    2015-02-01

    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. PMID:25504907

  14. 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 ?-ketoamides with ?,?-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

  15. The synthesis and applications of a biaryl-based asymmetric phosphine ligand

    E-print Network

    Hirai, Satoko

    2005-01-01

    The asymmetric biaryl backbone of a dialkylbiphenyl phosphine ligand was developed, synthesized, and resolved. The application of the chiral phosphine ligand to the asymmetric Suzuki-Miyaura cross-coupling reaction was ...

  16. Synthesis of phosphorescent asymmetrically ?-extended porphyrins for two-photon applications.

    PubMed

    Esipova, Tatiana V; Vinogradov, Sergei A

    2014-09-19

    Significant effort has been directed in recent years toward porphyrins with enhanced two-photon absorption (2PA). However, the properties of their triplet states, which are central to many applications, have rarely been examined in parallel. Here we report the synthesis of asymmetrically ?-extended platinum(II) and palladium(II) porphyrins, whose 2PA into single-photon-absorbing states is enhanced as a result of the broken center-of-inversion symmetry and whose triplet states can be monitored by room-temperature phosphorescence. 5,15-Diaryl-syn-dibenzoporphyrins (DBPs) and syn-dinaphthoporphyrins (DNPs) were synthesized by [2 + 2] condensation of the corresponding dipyrromethanes and subsequent oxidative aromatization. Butoxycarbonyl groups on the meso-aryl rings render these porphyrins well-soluble in a range of organic solvents, while 5,15-meso-aryl substitution causes minimal nonplanar distortion of the macrocycle, ensuring high triplet emissivity. A syn-DBP bearing four alkoxycarbonyl groups in the benzo rings and possessing a large static dipole moment was also synthesized. Photophysical properties (2PA brightness and phosphorescence quantum yields and lifetimes) of the new porphyrins were measured, and their ground-state structures were determined by DFT calculations and/or X-ray analysis. The developed synthetic methods should facilitate the construction of ?-extended porphyrins for applications requiring high two-photon triplet action cross sections. PMID:25157580

  17. Molecular Models of Reactants and Products from an Asymmetric Synthesis of a Chiral Carboxylic Acid

    NSDL National Science Digital Library

    Our JCE Featured Molecules for this month come from the paper by Thomas E. Smith, David P. Richardson, George A. Truran, Katherine Belecki, and Megumi Onishi (1). The authors describe the use of a chiral auxiliary, 4-benzyl-2-oxazolidinone, in the synthesis of a chiral carboxylic acid. The majority of the molecules used in the experiment, together with several of the pharmaceuticals mentioned in the paper, have been added to our molecule collection. In many instances multiple enantiomeric and diastereomeric forms of the molecules have been included. This experiment could easily be extended to incorporate various aspects of computation for use in an advanced organic or integrated laboratory. Here are some possible exercises using the R and S forms of the 4-benzyl-2-oxazolidinone as the authors point out that both forms are available commercially. Calculation of the optimized structures and energies of the enantiomers at the HF/631-G(d) level using Gaussian03 (2) produces the results shown in Table 1. Evaluation of the vibrational frequencies results in no imaginary frequencies and the 66 real frequencies are identical for the two forms. Examination of the computed IR spectra also shows them to be identical. Additionally, the Raman and NMR spectra can be calculated for the enantiomers and compared to experimental values and spectral patterns. A tool that is becoming increasingly important for assigning absolute configuration is vibrational circular dichroism (VCD). Although the vibrational spectra of an enantiomeric pair are identical, the VCD spectra show opposite signs, as shown in Figure 1. One can imagine a synthesis, using an unknown enantiomer of the chiral auxiliary, followed by calculations of the electronic and vibrational properties of all of the intermediates and the product, and determination of absolute configuration of reactants and products by comparison of experimental and computed VCD spectra. Using a viewer capable of displaying two molecules that can be moved independently, students could more easily visualize the origin of the enantiomeric preference in the reaction between the chelated enolate and allyl iodide.

  18. Solid-phase asymmetric synthesis using a polymer-supported chiral Evans'-type oxazolidin-2-one.

    PubMed

    Green, Rachel; Peed, Jennifer; Taylor, James E; Blackburn, Richard A R; Bull, Steven D

    2013-10-01

    This protocol describes the synthesis of (S)-4-(4-hydroxybenzyl)-oxazolidin-2-one, its attachment to a Merrifield-Cl resin and its use for asymmetric synthesis. The chiral auxiliary is prepared in four steps from N-Boc-L-tyrosine on a multigram scale in high yield and attached to Merrifield-Cl resin via its phenolic group to afford a solid-supported chiral auxiliary for asymmetric synthesis that takes ?7 d to prepare. A procedure for its N-acylation is reported and a method for carrying out diastereoselective solid-supported Evans' syn-aldol reactions is described, with aldol products being cleaved from the polymer by either hydrolysis or reduction. The use of the supported auxiliary for two sequential 'on-bead' reactions has been demonstrated for the synthesis of a chiral cyclopropane aldol and a ?-lactone in a >95:5 diastereomeric ratio. These polymer-supported reactions are carried out in IRORI Kan resin capsules to protect the polymer support from mechanical degradation, thus allowing multiple on-bead reactions to be performed. PMID:24030439

  19. Intermolecular Asymmetric Carboesterification of Alkenes by Using Chiral Amine Auxiliaries under O2 : Synthesis of Enantioenriched ?-Methylene-?-Lactones through Chloropalladation of Alkynes.

    PubMed

    Zhang, Zhenming; Wu, Wanqing; Liao, Jianhua; Li, Jianxiao; Jiang, Huanfeng

    2015-04-27

    Herein, the first example of chloropalladation-initiated asymmetric intermolecular carboesterification of alkenes with alkynes by using chiral amine auxiliaries is reported. The use of (1S,2S)-N(1) ,N(1) -dimethylcyclohexane-1,2-diamine auxiliaries is essential for providing ?-methylene-?-lactones products in moderate to high yields and excellent enantioselectivities at room temperature. Moreover, the chiral amine auxiliaries can be readily removed by hydrolysis during the reaction process to keep the absolute configuration. This oxygen- and water-promoted asymmetric reaction opens a new window to study asymmetric processes in halopalladation reactions. PMID:25760781

  20. Stereodivergent strategy for neurofuran synthesis via palladium-catalyzed asymmetric allylic cyclization: total synthesis of 7-epi-ST-?(8)-10-neurofuran.

    PubMed

    Valli, Matteo; Bruno, Paolo; Sbarbada, Davide; Porta, Alessio; Vidari, Giovanni; Zanoni, Giuseppe

    2013-06-01

    Neurofurans are formed in vivo in the human brain as a consequence of an increased oxidative stress, and they could be valuable biomarkers of the neuronal oxidative stress. In this paper, an enantioselective stereodivergent approach to two key neurofuran precursors, belonging to the AC and ST classes, has been developed starting from a single achiral precursor, the meso-diol 11. The absolute configuration of the THF cores was secured by a Pd-catalyzed asymmetric allylic alkylation using (S,S)-L1 and (R,R)-L2 ligands, respectively. PMID:23641720

  1. Asymmetric Synthesis of Spirocyclic 2-Benzopyrans for Positron Emission Tomography of ?1 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 ?1 ligands with high ?1/?2-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 ?1 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 ?1 antagonist haloperidol. [18F]-(R)-20 was able to label those regions of the brain, which were reported to have high density of ?1 receptors. PMID:24451404

  2. Asymmetric Syntheses of Nakinadine D, Nakinadine E, and Nakinadine F: Confirmation of Their Relative (RS,SR)-Configurations and Proposal of Their Absolute (2S,3R)-Configurations.

    PubMed

    Davies, Stephen G; Fletcher, Ai M; Shah, Rushabh S; Roberts, Paul M; Thomson, James E

    2015-04-17

    The syn- and anti-diastereoisomeric forms of the reported structures of the marine alkaloids nakinadines D-F have been synthesized, for the first time in all cases, via an approach involving asymmetric Mannich-type (imino-aldol) reactions of methyl phenylacetate with N-tert-butylsulfinyl imines as the key steps to control the stereochemistry. Comparison of the (1)H and (13)C NMR spectroscopic data reported for the natural materials with those acquired for these synthetic samples confirms the initially assigned relative (RS,SR)-configurations of these three alkaloids. In the absence of specific rotation (or other diagnostic) data for the natural materials, it is not possible to unambiguously assign their absolute configurations, although given the absolute (2S)-configurations assigned to nakinadines B and C, and the absolute (2S,3R)-configuration previously established for nakinadine A, the data herein uphold our proposal that nakinadines D-F share the absolute (2S,3R)-configuration. PMID:25790266

  3. Synthesis of the tetracyclic core of Illicium sesqui-terpenes using an organocatalyzed asymmetric

    E-print Network

    Theodorakis, Emmanuel

    asymmetric Robinson annulation Lynnie Trzoss, Jing Xu, Michelle H. Lacoske and Emmanuel A. Theodorakis* Full here. This strategy is based on an organocatalyzed asymmetric Robinson annulation and provides concentrations. Thus, to develop an efficient synthetic approach toward the complex core skeleton

  4. Determination of absolute configuration using vibrational circular dichroism spectroscopy: phenyl glycidic acid derivatives obtained via asymmetric epoxidation using oxone and a keto bile acid

    Microsoft Academic Search

    Frank J. Devlin; Philip J. Stephens; Olga Bortolini

    2005-01-01

    The (+)-enantiomers of the o-Br, m-F and p-CH3 derivatives of trans phenyl glycidic acid have been obtained from the corresponding trans cinnamic acid derivatives using Oxone and the tri-keto bile acid dehydrocholic acid. Vibrational circular dichroism (VCD) spectroscopy of their methyl esters has been used to determine their absolute configurations. In each case, the absolute configurations of both methyl ester

  5. 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 ?,?-unsaturated methyl ketone allowed rapid access both to d-ribo-phytosphingosine and l-arabino-phytosphingosine. PMID:23795558

  6. A Fully Synthetic and Biochemically Validated Phosphatidyl Inositol-3-Phosphate Hapten via Asymmetric Synthesis and Native Chemical Ligation

    PubMed Central

    Chandler, Brent D.; Burkhardt, Anne L.; Foley, Klaudia; Cullis, Courtney; Driscoll, Denise; D’Amore, Natalie Roy; Miller, Scott J.

    2014-01-01

    We report the synthesis and biochemical validation of a phosphatidyl inositol-3 phosphate (PI3P) immunogen. The inositol stereochemistry was secured through peptide-catalyzed asymmetric phosphorylation catalysis, and the subsequent incorporation of a cysteine residue was achieved by native chemical ligation (NCL). Conjugation of the PI3P hapten to maleimide activated keyhole limpet hemocyanin (KLH) provided a PI3P immunogen, which was successfully used to generate selective PI3P antibodies. The incorporation of a sulfhydryl nucleophile into a phosphoinositide hapten demonstrates a general strategy to reliably access phosphoinositide immunogens. PMID:24344932

  7. Synthesis and asymmetric hydrogenation of (3E)-1-benzyl-3-[(2-oxopyridin-1(2H)-yl)methylidene]piperidine-2,6-dione.

    PubMed

    Bisset, Alexander A; Shiibashi, Akira; Desmond, Jasmine L; Dishington, Allan; Jones, Teyrnon; Clarkson, Guy J; Ikariya, Takao; Wills, Martin

    2012-12-21

    The synthesis of (3E)-1-benzyl-3-[(2-oxopyridin-1(2H)-yl)methylidene]piperidine-2,6-dione 5 from N-benzylglutarimide was achieved in three steps. The asymmetric hydrogenation of 4 gave either the product of partial reduction (10) or full reduction (13), depending on the catalyst which was employed, in high ee in each case. Attempts at asymmetric transfer hydrogenation (ATH) of resulted in formation of a racemic product. PMID:23128555

  8. An enantioselective formal synthesis of 4-demethoxydaunomycin using the catalytic asymmetric ring opening reaction of meso-epoxide with p-anisidine

    Microsoft Academic Search

    Akihiro Sekine; Takashi Ohshima; Masakatsu Shibasaki

    2002-01-01

    A catalytic asymmetric formal synthesis of 4-demethoxydaunomycin (3) was achieved using a catalytic asymmetric ring opening reaction of meso-epoxide 9 as a key step. The epoxide opening reaction was promoted by 10mol% of Pr-(R)-BINOL–Ph3P?O complex to give the ?-amino alcohol 11 in 80% yield with 65% enantiomeric excess (ee). Single recrystallization enhanced the enantiomeric purity of the ?-amino alcohol 11

  9. Absolute enantioselective separation: optical activity ex machina.

    PubMed

    Bielski, Roman; Tencer, Michal

    2005-11-01

    The paper describes methodology of using three independent macroscopic factors affecting molecular orientation to accomplish separation of a racemic mixture without the presence of any other chiral compounds, i. e., absolute enantioselective separation (AES) which is an extension of a concept of applying these factors to absolute asymmetric synthesis. The three factors may be applied simultaneously or, if their effects can be retained, consecutively. The resulting three mutually orthogonal or near orthogonal directors constitute a true chiral influence and their scalar triple product is the measure of the chirality of the system. AES can be executed in a chromatography-like microfluidic process in the presence of an electric field. It may be carried out on a chemically modified flat surface, a monolithic polymer column made of a mesoporous material, each having imparted directional properties. Separation parameters were estimated for these media and possible implications for the natural homochirality are discussed. PMID:16342798

  10. Chiral-Auxiliary-Mediated Asymmetric Synthesis of Tris-Heteroleptic Ruthenium Polypyridyl Complexes

    E-print Network

    Meggers, Eric

    as bidentate ligands that provide excellent asymmetric induction in the course of the coordination chemistry ligands, all of which are accessible for substitution. Accordingly, heating of (S)-4 with 1 equiv of bpy

  11. A catalytic asymmetric protocol for the enantioselective synthesis of 3(2H)-furanones.

    PubMed

    Marson, Charles M; Edaan, Esra; Morrell, James M; Coles, Simon J; Hursthouse, Michael B; Davies, David T

    2007-06-28

    3(2H)-Furanones can be prepared by a catalytic asymmetric protocol from enynones, which, if electron-rich, require only one reagent and involve two reactions in a single operation--a domino process. PMID:17563807

  12. Phosphine-Catalyzed Formation of Carbon-Sulfur Bonds: Catalytic Asymmetric Synthesis of gamma-Thioesters

    E-print Network

    Sun, Jianwei

    A method for catalytic asymmetric ? sulfenylation of carbonyl compounds has been developed. In the presence of an appropriate catalyst, thiols not only add to the ? position of allenoates, overcoming their propensity to ...

  13. 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 ?-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

  14. Synthesis of NH006--a photostable fungicide effective against Botrytis cinerea--according to the asymmetric total synthesis of MK8383.

    PubMed

    Hayashi, Nobuyuki; Yamamoto, Kentaro; Minowa, Nobuto; Mitomi, Masaaki; Nakada, Masahisa

    2010-04-21

    MK8383, isolated from Phoma sp. T2526 in 1993, exhibits potent antibiotic activities against a variety of phytopathogens and has been considered a promising fungicide against Botrytis cinerea. Unfortunately, MK8383 is a photosensitive compound and it undergoes irreversible decomposition. Although much effort has been devoted to improving the photostability of MK8383 by chemical modification of its structure by a research group organized by Meiji Seika Kaishya, Ltd. and Mitsubishi Chemical Corporation, a photostable MK8383 derivative has never been prepared. We have found that a C13-14 double bond of MK8383 and (+)-phomopsidin is responsible for the photosensitivity, and herein, we report the synthesis of NH006, an MK8383 derivative with a saturated C13-14 double bond and (S) configuration at C14, based on the asymmetric total synthesis of MK8383. NH006 exhibits good photostability and potent antifungal activity against B. cinerea. PMID:20449485

  15. Asymmetric reactions in continuous flow.

    PubMed

    Mak, Xiao Yin; Laurino, Paola; Seeberger, Peter H

    2009-01-01

    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

  16. 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

  17. 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.

  18. Design, synthesis, and applications of chiral N-2-phenyl-2-propyl sulfinyl imines for group-assisted purification (GAP) asymmetric synthesis.

    PubMed

    Pindi, Suresh; Wu, Jianbin; Li, Guigen

    2013-04-19

    A new chiral (Rs)-2-phenyl-2-propyl sulfinamide has been designed and synthesized; its derived aldimines and ketimines have been applied for asymmetric addition reaction with allylmagnesium bromide. The reaction was conveniently performed at room temperature to give a series of homoallylic amines in high yields (up to quant) and diastereoselectivity (up to >99% de). The pure products were obtained by relying on group-assisted purification (GAP) chemistry to avoid traditional purification methods of column chromatography or recrystallization. The conversion of disulfide to (R(s))-thiosulfinate which contains a newly generated polar group was also confirmed to be of the GAP chemistry in which washing crude product can generate pure enantiomer. The absolute stereochemistry has been determined by X-ray analysis. PMID:23496279

  19. A room-temperature catalytic asymmetric synthesis of allenes with ECNU-Phos.

    PubMed

    Wang, Yuli; Zhang, Wanli; Ma, Shengming

    2013-08-01

    Three-carbon axial chirality has been asymmetrically established from racemic one-carbon central chirality efficiently at room temperature: we report here the discovery of the first catalytic asymmetric carbonylation of readily available racemic propargylic carbonates to access optically active 2,3-allenoates with fairly high ee. The combination of [(?-allyl)PdCl]2 with [(R)-ECNU-Phos], a new chiral bisphosphine ligand based on a biphenyl skeleton, demonstrates high enantioselectivity. Both enantiomers of allenoates can be obtained at room temperature by applying either (R)- or (S)-ECNU-Phos. PMID:23869750

  20. A Stereoselective Synthesis of (?)-Viridiofungin A Utilizing a TiCl4-Promoted Asymmetric Multicomponent Reaction

    PubMed Central

    Ghosh, Arun K.; Kass, Jorden

    2012-01-01

    A stereoselective synthesis of (?)-Viridiofungin A is described. The convergent synthesis utilized a unique highly diastereoselective multicomponent reaction between optically active phenyldihydrofuran and an ?-ketoester to provide two chiral centers including a quarternary carbon center in a single step. Other key steps include an acyloxycarbonum ion-mediated tetrahydrofuran ring-opening reaction and a Julia-Kocienski olefination. PMID:22195730

  1. Asymmetric total synthesis of (-)-scabronine G via intramolecular double Michael reaction and Prins cyclization.

    PubMed

    Kanoh, Naoki; Sakanishi, Kohei; Iimori, Emiko; Nishimura, Ken'ichi; Iwabuchi, Yoshiharu

    2011-06-01

    The enantioselective total synthesis of (-)-scabronine G is described. The key features of the present synthesis include the construction of a 5-6 ring system containing two quaternary carbon centers via a diastereoselective intramolecular double Michael reaction and the formation of a seven-membered ring using a Prins cyclization. PMID:21548644

  2. The cobalt way to angucyclinones: asymmetric total synthesis of the antibiotics (+)-rubiginone B2, (-)-tetrangomycin, and (-)-8-O-methyltetrangomycin.

    PubMed

    Kesenheimer, Christian; Kalogerakis, Aris; Meissner, Anja; Groth, Ulrich

    2010-08-01

    A cobalt(I)-mediated convergent and asymmetric total synthesis of angucyclinones with an aromatic B ring has been developed. In the course of our research, we synthesized three naturally occurring anguclinone derivatives, namely, (+)-rubiginone B(2) (1), (-)-8-O-methyltetrangomycin (2), and (-)-tetrangomycin (3). By combining 3-hydroxybenzoic acid, 3-methoxybenzoic acid, citronellal, and geraniol as starting materials in a convergent way, we were able to synthesize chiral triyne chains, which were cyclized with [CpCo(C(2)H(4))(2)] (Cp=cyclopentadienyl) by means of an intramolecular [2+2+2] cycloaddition to their corresponding tetrahydrobenzo[a]anthracenes. Successive oxidation and deprotection steps led to the above-mentioned natural products 1-3. PMID:20575121

  3. 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. PMID:25399845

  4. Total synthesis of gobiusxanthin stereoisomers and their application to determination of absolute configurations of natural products: revision of reported absolute configuration of epigobiusxanthin.

    PubMed

    Yamano, Yumiko; Ematsu, Kotaro; Kurimoto, Hiromasa; Maoka, Takashi; Wada, Akimori

    2015-01-01

    (3R)-Gobiusxanthin stereoisomers (1a-d) were synthesized by stereoselective Wittig reaction of the (3R)-C15-acetylenic tri-n-butylphosphonium salt 7 with C25-apocarotenal stereoisomers 5a,b and 14a,b bearing four kinds of 3,6-dihydroxy-?-end groups. The validity of the reported stereochemistry of gobiusxanthin was demonstrated by the fact that the reported spectral data of natural gobiusxanthin were in agreement with those of synthetic (3R,3'S,6'R)-gobiusxanthin (1a). On the other hand, the reported CD spectral data of natural epigobiusxanthin, which has been assigned as (3R,3'R,6'R)-isomer (3'-epigobiusxanthin), were identical with those of synthetic (3R,3'S,6'S)-isomer 1d (6'-epigobiusxanthin) rather than those of the corresponding synthetic 3'-epi-isomer 1b. It was found that the stereochemistry at C3-position has little effect on the shape of their CD spectra. Thus, in order to reinforce the validity of the absolute configurations at C3-position of natural specimens, (3S,3'S,6'R)- and (3S,3'S,6'S)-stereoisomers 1e and 1f were also synthesized and a HPLC analytical method for four stereoisomers was established by using a column carrying a chiral stationary phase. The HPLC analysis has proven that the stereochemistry of the natural epigobiusxanthin is 3R,3'S,6'S. PMID:25561412

  5. Enantioselective Synthesis of Tryptophan Derivatives by a Tandem Friedel – Crafts Conjugate Addition/Asymmetric Protonation Reaction

    PubMed Central

    Kieffer, Madeleine E.; Repka, Lindsay M.; Reisman, Sarah E.

    2012-01-01

    The tandem Friedel–Crafts conjugate addition/asymmetric protonation reaction between 2-substituted indoles and methyl 2-acetamidoacrylate is reported. The reaction is catalyzed by (R)-3,3?-dibromo-BINOL in the presence of stoichiometric SnCl4, and is the first example of a tandem conjugate addition/asymmetric protonation reaction using a BINOL•SnCl4 complex as the catalyst. A range of indoles furnished synthetic tryptophan derivatives in good yields and high levels of enantioselectivity, even on preparative scale. The convergent nature of this transformation should lend itself to the preparation of unnatural tryptophan derivatives for use in a broad array of synthetic and biological applications. PMID:22390403

  6. A General Strategy for the Chemoenzymatic Synthesis of Asymmetrically Branched N-Glycans

    PubMed Central

    Wang, Zhen; Chinoy, Zoeisha S.; Ambre, Shailesh G.; Peng, Wenjie; McBride, Ryan; de Vries, Robert P.; Glushka, John; Paulson, James C.; Boons, Geert-Jan

    2013-01-01

    A systematic, efficient means of producing diverse libraries of asymmetrically branched N-glycans is needed to investigate the specificities and biology of glycan binding proteins. To that end, we describe a core pentasaccharide that at potential branching positions is modified by orthogonal protecting groups to allow selective attachment of unique saccharide moieties by chemical glycosylation. The appendages were selected in such a way that the antenna of the resulting deprotected compounds could be selectively extended by glycosyltransferases to give libraries of asymmetrical multi-antennary glycans. The power of the methodology was demonstrated by the preparation of a series of complex oligosaccharides that were printed as microarrays and screened for binding to lectins and influenza-virus hemagglutinins, which showed that recognition is modulated by presentation of minimal epitopes in the context of complex N-glycans. PMID:23888036

  7. 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. PMID:25714116

  8. 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

  9. Synthesis and assessment of the antioxidant and antitumor properties of asymmetric curcumin analogues.

    PubMed

    Li, Qingyong; Chen, Jian; Luo, Shuyue; Xu, Jialin; Huang, Qiaoxian; Liu, Tianyu

    2015-03-26

    In this study, 12 asymmetric curcumin (CUR) analogues and 5 symmetric curcumin derivatives were synthesized, the antioxidant activity of these derivatives were evaluated by radicals 1,1-diphenyl-2-picryl-hydrazyl (DPPH) assay, 2,2-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) assay, ROO (TRAP) assay and O(2-) (NET) assay and anti-proliferative activities of these analogues were assessed against the human hepatoma cell line (SMMC-7721), the human breast cancer cell line (MCF-7) and the human prostate cancer cell lines (PC-3). Most of the asymmetric compounds showed stronger antioxidant activities than Vitamin C (Vc). Curcumin analogues reducing free radicals contain two reaction mechanisms: H-atom and electron transfer mechanisms. Compound 14 showed the most significant antioxidant activity compared with curcumin and other derivatives. Shorted the carbon chain of 14 can reduce the O-H bond dissociation enthalpy (BED) to improve the antioxidant activity. The antioxidant activity of 25 was similar to curcumin. All of the compounds performed better in an anti-proliferate assay than curcumin, especially compound 25, which exhibited the preferential cytotoxic activity against MCF-7 cells(25, IC50 = 9.11 ?M, curcumin, IC50 = 70.2 ?M). Considering these data, future studies should be performed to assess the therapeutic values of these asymmetric curcumin analogues. PMID:25728027

  10. Necessary and Sufficient Conditions for the Asymmetric Synthesis of Chiral Amines Using

    E-print Network

    Lee, Jooyoung

    higher affinity to benzene ring of acetophenone than v-ATVf were computationally screened using synthesis reaction rate of (S)- a-MBA and lower (S)-a-MBA degradation reaction rate than v-ATVf. To verify

  11. Asymmetric reduction of 4-hydroxy-2-butanone to (R)-1,3-butanediol with absolute stereochemical selectivity by a newly isolated strain of Pichia jadinii.

    PubMed

    Yang, Taowei; Man, Zaiwei; Rao, Zhiming; Xu, Meijuan; Zhang, Xian; Xu, Zhenghong

    2014-12-01

    In this study, a novel strain of Pichia jadinii, HBY61, capable of the biocatalysis of 4-hydroxy-2-butanone (4H2B) to (R)-1,3-BD was isolated. HBY61 produced (R)-1,3-BD with high activity and absolute stereochemical selectivity (100 % e.e). Glucose and beef extract were found to be the key factors governing the fermentation, and their optimal concentrations were determined to be 84.2 and 43.7 g/L, respectively. The optimal bioconversion conditions of 4H2B catalyzed by HBY61 were pH 7.4, 30 °C, and 250 rpm with 6 % (v/v) glucose as the co-substrate. Accordingly, when 45 g/L of 4H2B was divided into three equal parts and added successively into the system at set time intervals, the maximum (R)-1,3-BD concentration reached 38.3 g/L with high yield (85.1 %) and strict 100 % enantioselectivity. Compared with previously reported yields for the biocatalytic production of (R)-1,3-BD, the use of strain HBY61 provided a high yield with excellent stereoselectivity. PMID:25306883

  12. 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. PMID:23270499

  13. ?,?-Unsaturated ?,?-diamino acids as building blocks for the asymmetric synthesis of diverse ?,?-diamino acids.

    PubMed

    Saha, Nemai; Chatterjee, Bhaskar; Chattopadhyay, Shital K

    2015-02-01

    A building block approach for the synthesis of ?,?-diamino acids is described, which involves the diastereodivergent preparation of two sets of orthogonally protected ?,?-unsaturated ?,?-diamino acids as templates for the preparation of 12 new ?,?-diamino acids of biological relevance using simple techniques. PMID:25562112

  14. An asymmetric route to total synthesis of the furano lignan (+)-veraguensin

    Microsoft Academic Search

    Kiran Matcha; Subrata Ghosh

    2010-01-01

    Total synthesis of the furano lignan (+)-veraguensin is described. The key steps involve a diastereoselective aldol-type condensation of an ester enolate having an ?-chiral center with an aromatic aldehyde and a novel isomerization of the syn vicinal substituents on the furan ring via a ring opening–ring closing protocol.

  15. Multigramme synthesis and asymmetric dihydroxylation of a 4-fluorobut-2E-enoate.

    PubMed

    Laurenson, James A B; Parkinson, John A; Percy, Jonathan M; Rinaudo, Giuseppe; Roig, Ricard

    2013-01-01

    Esters of crotonic acid were brominated on a multigramme scale using a free radical procedure. A phase transfer catalysed fluorination transformed these species to the 4-fluorobut-2E-enoates reproducibly and at scale (48-53%, ca. 300 mmol). Asymmetric dihydroxylation reactions were then used to transform the butenoate, ultimately into all four diastereoisomers of a versatile fluorinated C4 building block at high enantiomeric-enrichment. The (DHQ)2AQN and (DHQD)2AQN ligands described by Sharpless were the most effective. The development and optimisation of a new and facile method for the determination of ee is also described; (19)F{(1)H} spectra recorded in d-chloroform/diisopropyl tartrate showed distinct baseline separated signals for different enantiomers. PMID:24367430

  16. Asymmetric three- and [2 + 1]-component conjugate addition reactions for the stereoselective synthesis of polysubstituted piperidinones.

    PubMed

    Davies, Stephen G; Roberts, Paul M; Smith, Andrew D

    2007-05-01

    The efficiency and stereoselectivity of the conjugate addition of lithium (Z)- or (E)-beta-amino ester enolates, generated by lithium amide conjugate addition to an alpha,beta-unsaturated ester or deprotonation of a beta-amino ester, respectively, to a range of alpha,beta-unsaturated acceptors has been investigated. Deprotonation of a beta-amino ester with LDA, followed by conjugate addition to a chiral alpha,beta-unsaturated oxazolidinone gives high 2,3-anti selectivity ( approximately 90% d.e.), with hydrogenolysis and purification to homogeneity generating stereodefined trisubstituted piperidinones as single stereoisomers. Asymmetric three-component couplings of alpha,beta-unsaturated esters and alkylidene malonates initiated by lithium amide conjugate addition proceeds with high levels of 2,3-anti stereoselectivity, with hydrogenolysis giving tetrasubstituted piperidinones. PMID:17464410

  17. Synthesis of Optically Active Vasicinone Based on Intramolecular Aza-Wittig Reaction and Asymmetric Oxidation(1).

    PubMed

    Eguchi, Shoji; Suzuki, Toshio; Okawa, Tomohiro; Matsushita, Yuji; Yashima, Eiji; Okamoto, Yoshio

    1996-10-18

    Both optical isomers of a quinazoline alkaloid, vasicinone, were synthesized by two different methods. The first method used (3S)-3-hydroxy-gamma-lactam as a chiral synthon, which was, after O-TBDMS protection, o-azidobenzoylated followed by treatment with tri-n-butylphosphine to afford (S)-(-)-vasicinone via the tandem Staudinger/intramolecualr aza-Wittig reaction. The second method utilized asymmetric oxygenation of deoxyvasicinone with (1S)-(+)- or (1R)-(-)-(10-camphorsulfonyl)oxaziridine (the Davis reagent), respectively. The aza-enolate anion of deoxyvasicinone was treated with (S)-(+)-reagent to afford (R)-(+)-vasicinone in 71% ee, while the reaction with (R)-(-)-reagent gave (S)-(-)-vasicinone in 62% ee. The optical purity was analyzed by HPLC on specially modified cellulose as a stationary phase. These results provided a facile method to prepare both optical isomers of vasicinone and confirmed the recently reversed stereochemistry of natural (-)-vasicinone. PMID:11667656

  18. 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. PMID:21512240

  19. Synthesis of axially chiral gold complexes and their applications in asymmetric catalyses

    PubMed Central

    Sun, Yin-wei

    2013-01-01

    Summary Several novel chiral N-heterocyclic carbene and phosphine ligands were prepared from (S)-BINOL. Moreover, their ligated Au complexes were also successfully synthesized and characterized by X-ray crystal diffraction. A weak gold-? interaction between the Au atom and the aromatic ring in these gold complexes was identified. Furthermore, we confirmed the formation of a pair of diastereomeric isomers in NHC gold complexes bearing an axially chiral binaphthyl moiety derived from the hindered rotation around C–C and C–N bonds. In the asymmetric intramolecular hydroamination reaction most of these chiral Au(I) complexes showed good catalytic activities towards olefins tethered with a NHTs functional group to give the corresponding product in moderate yields and up to 29% ee. PMID:24204435

  20. Asymmetric synthesis of the tricyclic core of NGF-inducing cyathane diterpenes via a transition-metal-catalyzed [5 + 2] cycloaddition.

    PubMed

    Wender, P A; Bi, F C; Brodney, M A; Gosselin, F

    2001-06-28

    [reaction: see text] A concise asymmetric synthesis of the tricyclic core of cyathane diterpenes is described, based on a novel transition-metal-catalyzed intramolecular [5 + 2] cycloaddition of ynone-vinylcyclopropane 10 (assembled from commercially available (S)-(-)-limonene), which proceeds in 90% yield with >95% selectivity. This strategy provides efficient access (14 steps and 13% overall yield) to potential analogues as well as precursors of nerve growth factor (NGF)-inducing diterpenes. PMID:11418060

  1. Asymmetric noncovalent synthesis of self-assembled one-dimensional stacks by a chiral supramolecular auxiliary approach.

    PubMed

    George, Subi J; de Bruijn, Robin; Tomovi?, Željko; Van Averbeke, Bernard; Beljonne, David; Lazzaroni, Roberto; Schenning, Albertus P H J; Meijer, E W

    2012-10-24

    Stereoselective noncovalent synthesis of one-dimensional helical self-assembled stacks of achiral oligo(p-phenylenevinylene) ureidotriazine (AOPV3) monomers is obtained by a chiral supramolecular auxiliary approach. The racemic mixture of helical stacks of achiral AOPV3 molecules is converted into homochiral helical stacks, as shown by both spectroscopic measurements and molecular modeling simulations. The conversion is promoted by an orthogonal two-point ion-pair interaction with the chiral auxiliary dibenzoyl tartaric acid (D- or L-TA) molecules, which biases the angle population distribution and thereby the stack helicity. The induced preferred helicity is maintained by the OPV stacks even after the removal of the chiral auxiliary by extraction with ethylenediamine (EDA), due to the kinetic stability of the OPV stacks at room temperature. Spectroscopic probing of the helical self-assembly and the racemization process of these ?-conjugated OPV chromophores shed further light into the mechanistic pathways of this chiral asymmetric noncovalent synthesis and the kinetic stability of the stacks produced. The racemization of the stacks follows first-order kinetics and no switch in mechanism is observed as a result of a temperature change; therefore, a racemization via disassembly assembly is proposed. Remarkably, the preferred helicity of the stacks of achiral AOPV3 can be retained almost completely after a heating-cooling cycle where the stacks first partially depolymerize and then polymerize again with the still existing stacks being the seeds for self-assembly of achiral AOPV3. Only after a fully dissociated state is obtained at high temperatures, the optical activity of the supramolecular stack self-assembled at room temperature is lost. PMID:23030496

  2. 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.

  3. De Novo Asymmetric Synthesis of all D-, all L- and D-/L-Oligosaccharides Using Atom-less Protecting Groups

    PubMed Central

    Babu, Ravula Satheesh; Chen, Qian; Kang, Sang-Woo; Zhou, Maoquan; O’Doherty, George A.

    2012-01-01

    Oligosaccharide synthesis is hindered by the need for multiple steps as well as numerous selective protections and deprotections. Herein we report a highly efficient de novo route to various oligosaccharide motifs, of use for biological and medicinal structure activity studies. The key to the overall efficiency is the judicious use of asymmetric catalysis and synthetic design. These green principles include the bidirectional use of highly stereoselective catalysis (Pd(0)-glycosylation/post-glycosylation). In addition, the chemoselective use of C-C and C-O ?-bonds functionality, as atom-less protecting groups as well as an anomeric directing group (via a Pd-?-allyl), highlights the atom economical aspects of the route to a divergent set of natural and unnatural oligosaccharides (i.e., various D-/L-diastereomers of oligosaccharide as well as deoxysugars which lack C-2 anomeric directing groups). For example, in only 12 steps, the construction of a highly branched hepta-saccharide with 35 stereocenters was accomplished from an achiral acylfuran. PMID:22780712

  4. Asymmetric synthesis from terminal alkenes by diboration/cross-coupling cascades

    PubMed Central

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

    2013-01-01

    Amongst prospective starting materials for organic synthesis, terminal (monosubstituted) alkenes are ideal. In the form of ?-olefins, they are manufactured on enormous scale and they are the core product features from many organic chemical reactions. While their latent reactivity can easily enable hydrocarbon chain extension, alkenes also have the attractive feature of being stable in the presence of many acids, bases, oxidants and reductants. In spite of these impressive attributes, relatively few catalytic enantioselective transformations have been developed that transform aliphatic ?-olefins in >90% ee and, with the exception of site-controlled isotactic polymerization of ?-olefins,1 none of these processes result in chain-extending C-C bond formation to the terminal carbon.2, 3, 4, 5, 6 Herein, 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 range of chiral products. These reactions are enabled by an unusual neighboring group participation effect that accelerates Pd-catalyzed cross-coupling of 1,2-bis(boronates) relative to nonfunctionalized alkyl boronate analogs. In tandem with enantioselective diboration, this reactivity feature connects abundant alkene starting materials to a diverse array of chiral products. Importantly with respect to synthesis utility, the tandem diboration/cross-coupling reaction (DCC reaction) generally provides products in high yield and high selectivity (>95:5 enantiomer ratio), employs low loadings (1–2 mol %) of commercially available catalysts and reagents, it 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. PMID:24352229

  5. CAL-B catalyzed desymmetrization of 3-alkylglutarate: "olefin effect" and asymmetric synthesis of pregabalin.

    PubMed

    Jung, Jae-Hoon; Yoon, Doo-Ha; Kang, Philjun; Lee, Won Koo; Eum, Heesung; Ha, Hyun-Joon

    2013-06-14

    CAL-B catalyzed desymmetrization of prochiral 3-alkylglutaric acid diesters was performed to prepare optically active 3-alkylglutaric acid monoesters bearing various alkyl substituents, including methyl, ethyl, propyl and allyl groups. Allyl esters showed far better stereoselectivity among the alkyl esters, suggesting possible ?-? interactions between the olefin of the substrate and the Trp104 or His224 side chains at the enzyme active site. Based on this reaction, the synthesis of (S)-(+)-3-aminomethyl-5-methylhexanoic acid (pregabalin) was achieved with a 70% overall yield. PMID:23525234

  6. Optimising the feedback loop of a millimetre-wave absolute photoacoustic power meter using H-infinity control synthesis

    NASA Astrophysics Data System (ADS)

    Hadjiloucas, S.; Franklin, T.; Becerra, V. M.; Walker, G. C.; Bowen, J. W.

    2009-07-01

    An H-infinity control strategy has been developed for the design of controllers used in feedback controlled electrical substitution measurements (FCESM). The methodology has the potential to provide substantial improvements in both response time and resolution of a millimetre-wave absolute photoacoustic power meter.

  7. Stereoselective Synthesis of ?-Hydroxy Enamines, Amino Cyclopropanes and 1,3-Amino Alcohols via Asymmetric Catalysis

    PubMed Central

    Valenta, Petr; Carroll, Patrick J.; Walsh, Patrick J.

    2010-01-01

    Tandem methods for the catalytic asymmetric preparation of enantioenriched ?-hydroxy (E)-enamines and cyclopropylamines are presented. The diastereoselective hydrogenation of enantioenriched (E)-trisubstituted hydroxy enamines to generate 1,2-disubstituted 1,3-amino alcohols is also outlined. These methods are initiated by highly regioselective hydroboration of N-tosyl substituted ynamides with diethylborane to generate ?-amino alkenyl boranes. In situ boron to zinc transmetalation generates ?-amino alkenyl zinc reagents. These functionalized vinylzinc intermediates were subsequently added to aldehydes in the presence of catalyst derived from an enantioenriched amino alcohol (morpholino isoborneol, MIB). The catalyst promotes highly enantioselective C–C bond-formation to provide ?-hydroxy enamines in good isolated yields (68–86%) with 54–98% enantioselectivity. The intermediate zinc ?-alkoxy enamines can be subjected to a tandem cyclopropanation to afford amino cyclopropyl carbinols with three continuous stereocenters in a one-pot procedure with good yields (72–82%), enantioselectivities of 76–94% and diastereomeric ratios >20:1. Diastereoselective hydrogenation of isolated enantioenriched ?-hydroxy enamines over Pd/C furnished syn-1,2-disubstituted-1,3-amino alcohols with high yields (82–90%) and moderate to excellent diastereoselectivities. These methods were used in an efficient preparation of the enantioenriched precursor to PRC200-SS derivatives, which are potent serotonin-norepinephrine-dopamine reuptake inhibitors. PMID:20853837

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

    SciTech Connect

    Ma, Yi Hua [Worcester Polytechnic Institute; Chen, Chao-Huang [Worcester Polytechnic Institute; Catalano, Jacopo [Worcester Polytechnic Institute; Guazzone, Federico [Worcester Polytechnic Institute; Payzant, E Andrew [ORNL

    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.

  9. 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 ?-olefins into chiral products with an enantiomeric excess greater then 90 per cent. With the exception of site-controlled isotactic polymerization of ?-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.

  10. Asymmetric Catalysis Special Feature Part I: Solidphase synthesis of chiral 3,4-diazaphospholanes and their application to catalytic asymmetric allylic alkylation

    Microsoft Academic Search

    Clark R. Landis; Thomas P. Clark

    2004-01-01

    Functionalized chiral diazaphospholanes ligate to a variety of transition metals, yielding chiral, catalytically active, metal complexes. Previous work has established that amino acid derivatization of the carboxyl groups of (R,R)-N,N'-phthaloyl-2,3-(2-carboxyphenyl)-phenyl-3,4-diazaphospholane (1) yields phosphines that are excellent ligands for palladium-catalyzed asymmetric allylic alkylation reactions. Alanine functionalization is particularly effective for allylic alkylation of 1,3-dimethylallyl acetate. Standard Merrifield resins and amino acid

  11. SuperQuat N-acyl-5,5-dimethyloxazolidin-2-ones for the asymmetric synthesis of alpha-alkyl and beta-alkyl aldehydes.

    PubMed

    Bull, Steven D; Davies, Stephen G; Nicholson, Rebecca L; Sanganee, Hitesh J; Smith, Andrew D

    2003-08-21

    The proclivity of alpha-branched N-2'-benzyl-3'-phenylpropionyl derivatives of (S)-4-benzyl-5,5-dimethyl-, (S)-4-phenyl-5,5-dimethyl-, (S)-4-isopropyl-5,5-dimethyl-, (S)-4-benzyl- and (S)-4-benzyl-5,5-diphenyl-oxazolidin-2-ones to generate directly 2-benzyl-3-phenylpropionaldehyde upon hydride reduction with DIBAL is investigated. The (S)-4-benzyl-5,5-dimethyl-derivative proved optimal for inhibition of endocyclic nucleophilic attack, giving 2-benzyl-3-phenylpropionaldehyde in good yield upon reduction. Application of this methodology for the asymmetric synthesis of chiral aldehydes via diastereoselective enolate alkylation of a range of (S)-N-acyl-4-benzyl-5,5-dimethyloxazolidin-2-ones to afford and array of alpha-substituted-N-acyl-5,5-dimethyloxazolidin- 2-ones (85-94% de) and subsequent reduction with DIBAL afforded directly non-racemic alpha-substituted aldehydes without loss of stereochemical integrity (87-94% ee). The extension of this protocol for the asymmetric synthesis of beta-substituted aldehydes is demonstrated, via the diastereoselective conjugate addition of a range of organocuprates to (S)-N-acyl-4-phenyl-5,5-dimethyloxazolidin-2-ones which proceeds with high diastereoselectivity (generally > 95% de). Reduction of the conjugate addition products with DIBAL gives non-racemic beta-substituted aldehydes in high yields and in high ee (generally > 95% ee). This methodology is exemplified by the asymmetric synthesis of (R)-3-isopropenylhept-6-enal, which has previously been used in the synthesis of (3Z,6R)-3-methyl-6-isopropenyl-3,9-decadien-1-yl acetate, a component of the sex pheromones of the California red scale. PMID:12968339

  12. Catalytic Asymmetric Synthesis Using Feedstocks. An Enantioselective Route to 2-Arylpropionic Acids and 1-Arylethyl Amines via Hydrovinylation of Vinyl Arenes

    PubMed Central

    Smith, Craig R.; RajanBabu, T. V.

    2009-01-01

    A three-step procedure for the synthesis of 2-arylpropionic acids (profens) from vinyl arenes in nearly enantiomerically pure form has been developed. Excellent yields (>97%), regioselectivities (>99%), and enantioselectivities (>97% ee) for the desired branched products were obtained in the asymmetric hydrovinylation reactions of vinyl arenes, and the products from these reactions were transformed into 2-arylpropionic acids via oxidative degradation. Subsequent Curtius or Schmidt rearrangements of these acids provided highly valued 1-arylethyl amines, including a prototypical primary amine with an ?-chiral tertiary N-alkyl group, in very good yields. PMID:19317393

  13. Cloning, overexpression, and characterization of a high enantioselective nitrilase from Sphingomonas wittichii RW1 for asymmetric synthesis of (R)-phenylglycine.

    PubMed

    Qiu, Jian; Su, Er-Zheng; Wang, Hua-Lei; Cai, Wen-Wen; Wang, Wei; Wei, Dong-Zhi

    2014-05-01

    In this study, a high (R)-enantioselective nitrilase gene from Sphingomonas wittichii RW1 was cloned and overexpressed in Escherichia coli BL21 (DE3). The recombinant nitrilase was purified to homogeneity with a molecular weight of 40 kDa. The pH and temperature optima were shown to be pH 8.0 and 40 °C, respectively. The purified nitrilase was most active toward succinonitrile, approximately 30-fold higher than that for phenylglycinonitrile. Using the E. coli BL21/ReSWRW1 whole cells as biocatalysts, the kinetic resolution for asymmetric synthesis of (R)-phenylglycine was investigated at pH 6.0. A yield of 46 % was obtained with 95 % enantiomeric excess (ee), which made it a promising biocatalyst for synthesis of (R)-phenylglycine. PMID:24664232

  14. A gram-scale route to phlegmarine alkaloids: rapid total synthesis of (-)-cermizine B.

    PubMed

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

    2014-07-11

    The synthesis of the Lycopodium alkaloid (-)-cermizine B (1), which establishes its absolute configuration, is achieved by combining asymmetric organocatalysis and an uninterrupted eight-step reaction sequence, followed by a final reduction step. This "pot-economy" strategy provides access to the cis-phlegmarine stereoparent embedded in 1 for the first time, rapidly and on a gram-scale. PMID:24727855

  15. Acid-base catalysis of chiral Pd complexes: development of novel catalytic asymmetric reactions and their application to synthesis of drug candidates.

    PubMed

    Hamashima, Yoshitaka

    2006-10-01

    Using the unique character of the chiral Pd complexes 1 and 2, highly efficient catalytic asymmetric reactions have been developed. In contrast to conventional Pd(0)-catalyzed reactions, these complexes function as an acid-base catalyst. Thus active methine and methylene compounds were activated to form chiral palladium enolates, which underwent enantioselective carbon-carbon bond-forming reactions such as Michael reaction and Mannich-type reaction with up to 99% ee. Interestingly, these palladium enolates acted cooperatively with a strong protic acid, formed concomitantly during the formation of the enolates to activate electrophiles, thereby promoting the C-C bond-forming reaction. This palladium enolate chemistry was also applicable to electrophilic enantioselective fluorination reactions, and various carbonyl compounds including beta-ketoesters, beta-ketophosphonates, tert-butoxycarbonyl lactone/lactams, cyanoesters, and oxindole derivatives could be fluorinated in a highly enantioselective manner (up to 99% ee). Using this method, the catalytic enantioselective synthesis of BMS-204352, a promising anti-stroke agent, was achieved. In addition, the direct enantioselective conjugate addition of aromatic and aliphatic amines to alpha,beta-unsaturated carbonyl compound was successfully demonstrated. In this reaction, combined use of the Pd complex 2 having basic character and the amine salt was the key to success, allowing controlled generation of the nucleophilic free amine. This aza-Michael reaction was successfully applied to asymmetric synthesis of the CETP inhibitor torcetrapib. PMID:17015970

  16. Absolut Vodka

    Microsoft Academic Search

    Paul Farris; Elizabeth Collins

    This case depicts the history of an unusual brand in the "super premium" segment of the vodka market. The top-of-line positioning is supported with creative advertising, narrow distribution, point-of-purchase advertising, and expensive advertising production. Absolut has used very expensive inserts as advertisements in print vehicles during the Christmas season. The last inserts described in the case cost approximately $1 each

  17. 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.

  18. All-catalytic, efficient, and asymmetric synthesis of alpha,omega-diheterofunctional reduced polypropionates via "one-pot" Zr-catalyzed asymmetric carboalumination-Pd-catalyzed cross-coupling tandem process.

    PubMed

    Novak, Tibor; Tan, Ze; Liang, Bo; Negishi, Ei-Ichi

    2005-03-01

    A highly efficient method for the synthesis of stereochemically pure (>/=99% ee and >50/1 dr) alpha,omega-diheterofunctional reduced polypropionates has been developed. The essential features of the method are represented by the conversion of inexpensive styrene into 2-methyl-4-phenyl-1-pentanol (1) in 50% yield over two steps from styrene via Zr-catalyzed asymmetric carboalumination (ZACA) reaction in the presence of (NMI)2ZrCl2 and Pd-catalyzed vinylation of the in situ generated isoalkylalanes in the presence of Zn(OTf)2 and a catalytic amount of Pd(DPEphos)Cl2. This ZACA-Pd-catalyzed vinylation may be repeated as needed without purification. After the final ZACA reaction, oxidation with O2 provides alpha-hydroxy-omega-phenyl reduced polypropionates, which can be fully or partially purified by chromatography. After acetylation, Ru-catalyzed oxidative cleavage of the Ph ring, and reduction with BH3.THF, the second chromatographic purification provides stereoisomerically pure alpha,omega-diheterofunctional reduced polypropionates (e.g., 9 and 11) that can be further converted to key intermediates 6 and 7 for the synthesis of ionomycin (4) and borrelidin (5), respectively, by known reactions. PMID:15740104

  19. 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

    ?ukasik, Beata; Miko?ajczyk, Marian; Bujacz, Grzegorz; ?urawi?ski, 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. PMID:25407777

  20. A catalytic asymmetric total synthesis of (–)-perophoramidine† †Electronic supplementary information (ESI) available: Details of experimental procedures, spectroscopic data, and copies of 1H and 13C spectra. See DOI: 10.1039/c4sc01826e

    PubMed Central

    Osipov, M.; Krüger, S.; Zhang, Y.

    2015-01-01

    We report a catalytic asymmetric total synthesis of the ascidian natural product perophoramidine. The synthesis employs a molybdenum-catalyzed asymmetric allylic alkylation of an oxindole nucleophile and a monosubstituted allylic electrophile as a key asymmetric step. The enantioenriched oxindole product from this transformation contains vicinal quaternary and tertiary stereocenters, and is obtained in high yield along with high levels of regio-, diastereo-, and enantioselectivity. To install the second quaternary stereocenter in the target, the route utilizes a novel regio- and diastereoselective allylation of a cyclic imino ether to deliver an allylated imino ether product in near quantitative yield and with complete regio- and diastereocontrol. Oxidative cleavage and reductive amination are used as final steps to access the natural product. PMID:25485074

  1. Enantioselective synthesis of 2,3-disubstituted indanones via Pd-catalyzed intramolecular asymmetric allylic alkylation of ketones.

    PubMed

    Li, Xiao-Hui; Zheng, Bao-Hui; Ding, Chang-Hua; Hou, Xue-Long

    2013-12-01

    A Pd-catalyzed intramolecular asymmetric allylic alkylation (AAA) reaction with "hard" carbanions has been developed for the first time, affording 2,3-disubstituted indanones with high diastereo- and enantioselectivities. The transformation of these products into other core structures of natural products has been demonstrated. PMID:24206052

  2. Nucleophilic Chiral Amines as Catalysts in Asymmetric Synthesis Stefan France, David J. Guerin, Scott J. Miller,*, and Thomas Lectka*,

    E-print Network

    Lectka, Thomas

    . Historically, the cinchona alkaloids were the first chiral amines to be used in asymmetric catalysis, most alkaloids also possess a rich and colorful history that is rooted in natural products and phar- maceutical to tropical regions. Outside of organic chem- istry, the cinchona alkaloids have found wide use as food

  3. Asymmetric synthesis of ?-amino-1,3-dithianes via chiral N-phosphonyl imine-based Umpolung reaction without using chromatography and recrystallization.

    PubMed

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

    2011-04-15

    A series of ?-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 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 ?-amino-1,3-dithianes attached with the chiral N-phosphonyl group were readily obtained by washing the solid crude products with hexane or a mixture of hexane-ethyl acetate. PMID:21405041

  4. Asymmetric synthesis of densely functionalized medium-ring carbocycles and lactones through modular assembly and ring-closing metathesis of sulfoximine-substituted trienes and dienynes.

    PubMed

    Lejkowski, Michal; Banerjee, Prabal; Schüller, Sabine; Münch, Alexander; Runsink, Jan; Vermeeren, Cornelia; Gais, Hans-Joachim

    2012-03-19

    An asymmetric synthesis of densely functionalized 7-11-membered carbocycles and 9-11-membered lactones has been developed. Its key steps are a modular assembly of sulfoximine-substituted C- and O-tethered trienes and C-tethered dienynes and their Ru-catalyzed ring-closing diene and enyne metathesis (RCDEM and RCEYM). The synthesis of the C-tethered trienes and dienynes includes the following steps: 1) hydroxyalkylation of enantiomerically pure titanated allylic sulfoximines with unsaturated aldehydes, 2) ?-lithiation of alkenylsulfoximines, 3) alkylation, hydroxy-alkylation, formylation, and acylation of ?-lithioalkenylsulfoximines, and 4) addition of Grignard reagents to ?-formyl(acyl)alkenylsulfoximines. The sulfoximine group provided for high asymmetric induction in steps 1) and 4). RCDEM of the sulfoximine-substituted trienes with the second-generation Ru catalyst stereoselectively afforded the corresponding functionalized 7-11-membered carbocyles. RCDEM of diastereomeric silyloxy-substituted 1,6,12-trienes revealed an interesting difference in reactivity. While the (R)-diastereomer gave the 11-membered carbocyle, the (S)-diastereomer delivered in a cascade of cross metathesis and RCDEM 22-membered macrocycles. RCDEM of cyclic trienes furnished bicyclic carbocycles with a bicyclo[7.4.0]tridecane and bicyclo[9.4.0]pentadecane skeleton. Selective transformations of the sulfoximine- and bissilyloxy-substituted carbocycles were performed including deprotection, cross-coupling reaction and reduction of the sulfoximine moiety. Esterification of a sulfoximine-substituted homoallylic alcohol with unsaturated carboxylic acids gave the O-tethered trienes, RCDEM of which yielded the sulfoximine-substituted 9-11-membered lactones. RCEYM of a sulfoximine-substituted 1,7-dien-10-yne showed an unprecedented dichotomy in ring formation depending on the Ru catalyst. While the second-generation Ru catalyst gave the 9-membered exo 1,3-dienyl carbocycle, the first-generation Ru catalyst furnished a truncated 9-membered 1,3-dieny carbocycle having one CH(2) unit less than the dienyne. PMID:22345000

  5. 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. PMID:25369521

  6. A Casein Kinase 1 and PAR Proteins Regulate Asymmetry of a PIP 2 Synthesis Enzyme for Asymmetric Spindle Positioning

    Microsoft Academic Search

    Costanza Panbianco; David Weinkove; Esther Zanin; David Jones; Nullin Divecha; Monica Gotta; Julie Ahringer

    2008-01-01

    SUMMARY Spindle positioning is an essential feature of asym- metric cell division. The conserved PAR proteins to- gether with heterotrimeric G proteins control spindle positioning inanimalcells,buthowthesearelinked is not known. In C. elegans, PAR protein activity leads to asymmetric spindle placement through cortical asymmetry of Ga regulators GPR-1\\/2. Here, we es- tablish that the casein kinase 1 gamma CSNK-1 and a

  7. Synthesis of novel Schiff base ligands from gluco- and galactochloraloses for the Cu(II) catalyzed asymmetric Henry reaction.

    PubMed

    Alkan, Sevda; Telli, Fatma Ç; Salman, Ye?im; Astley, Stephen T

    2015-04-30

    A series of chiral Schiff base ligands has been prepared using aminochloralose derivatives of glucose and galactose. These ligands were used as catalysts in the asymmetric Henry reaction in the presence of Cu(II) ions giving yields of up to 95%. An interesting solvent dependency on enantiomeric control was observed with the best enantiomeric excesses (up to 91%) being obtained in the presence of water. PMID:25742867

  8. A simplified catalytic system for direct catalytic asymmetric aldol reaction of thioamides; application to an enantioselective synthesis of atorvastatin

    Microsoft Academic Search

    Yuji Kawato; Mitsutaka Iwata; Ryo Yazaki; Naoya Kumagai; Masakatsu Shibasaki

    2011-01-01

    A new catalytic system was developed for the direct catalytic asymmetric aldol reaction of thioamides. The new lithium-free Cu catalyst (second-generation catalyst) exhibited enhanced catalytic efficiency over the previously developed catalyst comprising [Cu(CH3CN)4]PF6\\/Ph-BPE\\/LiOAr (first-generation catalyst), which required a tedious catalyst preparation process. In the reaction with the second-generation catalyst, the intermediate Cu-aldolate functioned as a Brønsted base to generate thioamide

  9. A Multistage, One-Pot Procedure Mediated by a Single Catalyst: A New Approach to the Catalytic Asymmetric Synthesis of

    E-print Network

    Lectka, Thomas

    of the catalyst. This approach was also amenable to the synthesis of small polypeptides containing -substituted aspartic acid units, including a non-natural fragment of the antibiotic lysobactin. The addition of Lewis

  10. Synthesis of an azido precursor to (2S,5R)-5-hydroxylysine using an asymmetric organocatalytic chlorination/reduction sequence.

    PubMed

    Johannes, Manuel; Brimble, Margaret A

    2013-12-20

    An efficient, robust, and scalable synthesis of an azido precursor to the modified amino acid (2S,5R)-5-hydroxylysine was developed on the basis of the use of a highly stereoselective organocatalytic ?-chlorination-reduction protocol. The final Fmoc-protected (2S,5R)-6-azido-5-hydroxylysine derivative can be used in solid-phase peptide synthesis, providing access to proteins that contain large quantities of post-translationally modified lysine (e.g., collagens). PMID:24175670

  11. A Systematic Investigation of Quaternary Ammonium Ions as Asymmetric Phase Transfer Catalysts. Synthesis of Catalyst Libraries and Evaluation of Catalyst Activity

    PubMed Central

    Denmark, Scott E.; Gould, Nathan D.; Wolf, Larry M.

    2011-01-01

    Despite over three decades of research into asymmetric phase transfer catalysis (APTC), a fundamental understanding of the factors that affect the rate and stereoselectivity of this important process are still obscure. This paper describes the initial stages of a long-term program aimed at elucidating the physical organic foundations of APTC employing a chemoinformatic analysis of the alkylation of a protected glycine imine with a libraries of enantiomerically enriched quaternary ammonium ions. The synthesis of the quaternary ammonium ions follows a diversity oriented approach wherein the tandem inter[4+2]/intra[3+2] cycloaddition of nitroalkenes serves as the key transformation. A two part synthetic strategy comprised of: (1) preparation of enantioenriched scaffolds and (2) development of parallel synthesis procedures is described. The strategy allows for the facile introduction of four variable groups in the vicinity of a stereogenic quaternary ammonium ion. The quaternary ammonium ions exhibited a wide range of activity and to a lesser degree enantioselectivity. Catalyst activity and selectivity are rationalized in a qualitative way based on the effective positive potential of the ammonium ion. PMID:21446721

  12. Synthesis and Asymmetric Diels-Alder Reactions of Enantiopure 3-(Alkylsulfinyl)-1-methoxy-1,3-butadienes.

    PubMed

    Aversa, Maria C.; Barattucci, Anna; Bonaccorsi, Paola; Giannetto, Placido; Jones, David Neville

    1997-06-27

    Simple syntheses of enantiopure (E)- and (Z)-3-(alkylsulfinyl)-1-methoxy-1,3-butadienes 2and 3 were provided by the addition of (1S)-isoborneol-10-sulfenic and (S)-phenyl-2-hydroxyethanesulfenic acids 8 to (E)- and (Z)-1-methoxybut-1-en-3-ynes (9) and (10). These additions proceeded with asymmetric induction, the extent of which depended upon the nature of the chiral hydroxyalkyl group. Cycloadditions of methyl acrylate to the enantiopure dienes proceeded with complete regioselectivity and very high stereoselectivity when catalyzed by lithium perchlorate or zinc chloride in dichloromethane. The chirality at sulfur controlled the diastereofacial selectivity in these Diels-Alder cycloadditions. PMID:11671762

  13. Asymmetric synthesis of the main core of kaurane family members triggered by an oxidative polycyclization-pinacol tandem process.

    PubMed

    Desjardins, Samuel; Maertens, Gaëtan; Canesi, Sylvain

    2014-09-19

    Polycyclization processes represent expeditious routes used in both nature and the laboratory to produce complex polycyclic molecules. A new stereoselective oxidative variant of such a polycyclization has been developed in which the cascade is triggered by a phenol dearomatization and is concluded by a pinacol transposition. This unprecedented avenue combines the synthetic power of a polycyclization and a transposition in tandem and enables the rapid formation of the tetracyclic main core of kaurane diterpenes containing several asymmetric and quaternary carbon centers in a single step from a simple phenol derivative. PMID:25191786

  14. Diastereomeric aziridine carbinol catalyzed enantioselective arylation reaction: toward the asymmetric synthesis of both enantiomers of chiral 3-aryl phthalide.

    PubMed

    Song, Xixi; Hua, Yuan-Zhao; Shi, Jing-Guo; Sun, Ping-Ping; Wang, Min-Can; Chang, Junbiao

    2014-07-01

    The diastereomeric aziridine carbinols are applied, respectively, as efficient chiral ligand in the catalysis of asymmetric arylation and sequential arylation-lactonization cascade. The two diastereomers, which are facilely synthesized from the same chiral source, function as pseudo enantiomers in arylation of aromatic aldehydes providing the different enantiomers of the diarylmethanols with almost the same excellent enantioselectivities. The arylation method is also carried out in tandem with lactonization process to afford a concise synthetic approach to both enantiomers of optically active 3-aryl phthalide. PMID:24912109

  15. 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. [Oregon Graduate Institute of Science & Technology, Beaverton, OR (United States)

    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.

  16. A photoisomerization-coupled asymmetric Stetter reaction: application to the total synthesis of three diastereomers of (?)-cephalimysin A

    PubMed Central

    Lathrop, Stephen P.

    2013-01-01

    The total synthesis of 8-epi, 8,9-epi, and 9-epi-(?)-cephalimysin A is described. Our catalytic enantioselective synthesis takes advantage of a novel tandem photoisomerization/Stetter reaction. The approach provides rapid access to the desired spirofuranone lactam core in good yield and excellent enantioselectivity. A late stage oxidation strategy allows for flexible access to three of the four diastereomers of cephalimysin A. Access to the epimers provides further support for the correction of the initially proposed relative stereochemistry of cephalimysin A. PMID:24224080

  17. Heck cyclization strategy for preparation of erythrinan alkaloids: asymmetric synthesis of unnatural (-)-erysotramidine from L-tartaric acid.

    PubMed

    Mostowicz, Danuta; Dygas, Miros?aw; Ka?u?a, Zbigniew

    2015-02-01

    With an imide derived from L-tartaric acid as the starting material, ent-erysotramidine was synthesized for the first time. The synthesis features the use of the enantiopure synthon, prepared in a set of highly stereoselective reactions, including N-acyliminium cyclization, dihydrofuranyl ring formation via silver-catalyzed intramolecular alcohol addition to acetylene, and vinyl ether catalytic hydrogen reduction. The crucial step of the synthesis, assembly of ring A, was achieved by using Heck cyclization of (Z)-iodoolefin. PMID:25569446

  18. 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. PMID:25367779

  19. Asymmetric domino synthesis of indanes bearing four contiguous stereocentres catalyzed by sub-mol% loadings of a squaramide in minutes.

    PubMed

    Loh, Charles C J; Hack, Daniel; Enders, Dieter

    2013-11-11

    An efficient diastereo- and enantioselective synthesis of polyfunctionalized indanes bearing four contiguous stereogenic centres in generally very short reaction times and sub-mol% squaramide catalyst loadings has been developed. The novel methodology creates a maximum of two stereocentres per bond formation via an organocatalytic Michael-Henry domino reaction. PMID:24064746

  20. 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

  1. 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…

  2. 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

  3. Bioreduction of ( R)-carvone and regioselective Baeyer-Villiger oxidations: Application to the asymmetric synthesis of cryptophycin fragment A

    Microsoft Academic Search

    David L. Varie; John Brennan; Barbara Briggs; Jason S. Cronin; David A. Hay; John A. Rieck; Milton J. Zmijewski

    1998-01-01

    Cryptophycin fragment A (1) was prepared in high enantiomeric purity in 10 steps from (R)-carvone. A stereoselective bioreduction of (R)-carvone to neodihydrocarveol and a regioselective Baeyer-Villiger oxidation of cyclohexanone 8 with pertrifluoroacetic acid were employed in this synthesis.

  4. Brucine Diol-Copper-Catalyzed Asymmetric Synthesis of endo-Pyrrolidines: The Mechanistic Dichotomy of Imino Esters.

    PubMed

    Li, Jian-Yuan; Kim, Hun Young; Oh, Kyungsoo

    2015-03-01

    Enantio- and diastereodivergent approaches to pyrrolidines are described by using catalyst- and substrate-controlled reaction pathways. A concerted endo-selective [3 + 2]-cycloaddition pathway is developed for the reaction of methyl imino ester, whereas endo-pyrrolidines with an opposite absolute stereochemical outcome are prepared by using the stepwise reaction pathway of tert-butyl imino ester. The development of catalyst- and substrate-controlled stereodivergent approaches highlights the inherent substrate-catalyst interactions in the [3 + 2]-cycloaddition reactions of metalated azomethine ylides. PMID:25695534

  5. Ring-opening hydrofluorination of 2,3- and 3,4-epoxy amines by HBF4·OEt2: application to the asymmetric synthesis of (S,S)-3-deoxy-3-fluorosafingol.

    PubMed

    Cresswell, Alexander J; Davies, Stephen G; Lee, James A; Morris, Melloney J; Roberts, Paul M; Thomson, James E

    2011-06-01

    Treatment of a range of 2,3- and 3,4-epoxy amines with HBF(4)·OEt(2) at room temperature results in fast and efficient S(N)2-type ring-opening hydrofluorination to give stereodefined amino fluorohydrins. Operational simplicity, scalability, and short reaction time at ambient temperature are notable features of this method. The utility of this methodology is exemplified in a concise asymmetric synthesis of (S,S)-3-deoxy-3-fluorosafingol. PMID:21495698

  6. Using the same organocatalyst for asymmetric synthesis of both enantiomers of glutamic acid-derived Ni(II) complexes via 1,4-additions of achiral glycine and dehydroalanine Schiff base Ni(II) complexes.

    PubMed

    Belokon, Yuri N; Gugkaeva, Zalina T; Hakobyan, Karine V; Maleev, Victor I; Moskalenko, Margarita A; Khrustalev, Victor N; Saghyan, Ashot S; Tsaloev, Alan T; Babievsky, Kiryl K

    2012-07-01

    (S)- and (R)-BIMBOL were efficient PT catalysts of asymmetric Michael addition of prochiral Ni-PBP-Gly (1) to acrylic esters and malonic esters to Ni-PBP-?-Ala (2) correspondingly. The salient feature of the catalysis is opposite configurations of Glu prepared via the two paths with BIMBOL of the same configuration and a perspective novel catalytic procedure for the synthesis of Gla derivatives. PMID:21935708

  7. Asymmetric synthesis of 3,4-anti- and 3,4-syn-substituted aminopyrrolidines via lithium amide conjugate addition.

    PubMed

    Davies, Stephen G; Garner, A Christopher; Goddard, Euan C; Kruchinin, Dennis; Roberts, Paul M; Smith, Andrew D; Rodriguez-Solla, Humberto; Thomson, James E; Toms, Steven M

    2007-06-21

    The diastereoselective conjugate addition of homochiral lithium amides to methyl 4-(N-allyl-N-benzylamino)but-2-enoate has been used as the key step in a simple and efficient protocol for the preparation of 3,4-substituted aminopyrrolidines. This protocol provides a complementary and stereoselective route to both anti- and syn-3-amino-4-alkylpyrrolidines as well as anti- and syn-3-hydroxy-4-aminopyrrolidines, in high de and ee viabeta-amino enolate functionalisation. This methodology has been applied to the synthesis of anti-(3S,4S)- and syn-(3R,4S)-3-methoxy-4-(N-methylamino)pyrrolidine. PMID:17551646

  8. Synthesis of Silyloxy Dienes by Silylene Tranfer to Divinyl Ketones: Application to the Asymmetric Sythesis of Substituted Cyclohexanes

    PubMed Central

    Ventocilla, Christian C.; Woerpel, K. A.

    2012-01-01

    Silver-catalyzed silylene transfer to divinyl ketones provided 2-silyloxy-1,3-dienes with control of stereochemistry and regioselectivity. The products participated in Diels–Alder reactions with electron-deficient alkenes and imines to form six-membered ring products diastereoselectively. Cycloaddition reactions with alkenes bearing chiral auxiliaries provided access to chiral, non-racemic cyclohexenes. The methodology therefore represents a synthesis of diastereomerically and enantiomerically pure products in a single flask. The highly substituted cyclohexene products could be functionalized stereoselectively to provide cyclohexanols after oxidation of the carbon–silicon bond. PMID:22372733

  9. Asymmetric Synthesis and Evaluation of Danshensu-Cysteine Conjugates as Novel Potential Anti-Apoptotic Drug Candidates

    PubMed Central

    Pan, Li-Long; Wang, Jie; Jia, Yao-Ling; Zheng, Hong-Ming; Wang, Yang; Zhu, Yi-Zhun

    2014-01-01

    We have previously reported that the danshensu-cysteine conjugate N-((R)-3-benzylthio-1-methoxy-1-oxo-2-propanyl)-2-acetoxy-3-(3,4-diacetoxyphenyl) propanamide (DSC) is a potent anti-oxidative and anti-apoptotic agent. Herein, we further design and asymmetrically synthesize two diastereoisomers of DSC and explore their potential bioactivities. Our results show that DSC and its two diastereoisomers exert similar protective effects in hydrogen peroxide (H2O2)-induced cellular injury in SH-SY5Y cells, as evidenced by the increase of cell viability, superoxide dismutase (SOD), and reduced glutathione (GSH) activity, and glutathione peroxidase (GPx) expression, and the decrease of cellular morphological changes and nuclear condensation, lactate dehydrogenase (LDH) release, and malondialdehyde (MDA) production. In H2O2-stimulated human umbilical vein endothelial cells (HUVEC), DSC concentration-dependently attenuates H2O2-induced cell death, LDH release, mitochondrial membrane potential collapse, and modulates the expression of apoptosis-related proteins (Bcl-2, Bax, caspase-3, and caspase-9). Our results provide strong evidence that DSC and its two diastereoisomers have similar anti-oxidative activity and that DSC exerts significant vascular-protective effects, at least in part, through inhibition of apoptosis and modulation of endogenous antioxidant enzymes. PMID:25551606

  10. Cyclic beta-amino acid derivatives: synthesis via lithium amide promoted tandem asymmetric conjugate addition-cyclisation reactions.

    PubMed

    Davies, Stephen G; Díez, David; Dominguez, Sara H; Garrido, Narciso M; Kruchinin, Dennis; Price, Paul D; Smith, Andrew D

    2005-04-01

    The product distribution upon conjugate addition of homochiral lithium N-benzyl-N-alpha-methylbenzylamide to dimethyl-(E,E)-nona-2,7-dienedioate can be controlled to give either the cyclic 1,2-anti-1,6-anti-beta-amino ester (derived from conjugate addition and intramolecular enolate cyclisation) or the acyclic bis-beta-amino ester derivative (derived from double conjugate addition) in high de. The introduction of a protected nitrogen functionality into the diester skeleton facilitates, after conjugate addition and intramolecular enolate cyclisation, the asymmetric construction of piperidines in high de; variation in the N-protecting group indicates that the highest stereoselectivity is observed with alpha-branched N-substituents. Tandem conjugate addition-aldol reactions can also be achieved stereoselectively, with lithium amide conjugate addition to epsilon- and zeta-oxo-alpha,beta-unsaturated esters giving the corresponding five and six membered cyclic beta-amino esters in high de. N-deprotection by hydrogenolysis of the products arising from these reactions furnishes a range of polyfunctionalised transpentacin and transhexacin derivatives in high de and ee. PMID:15785819

  11. 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

    2015-04-01

    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. PMID:25803004

  12. 1: Mass asymmetric fission barriers for {sup 98}Mo; 2: Synthesis and characterization of actinide-specific chelating agents

    SciTech Connect

    Veeck, A.C. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; [Lawrence Livermore National Lab., CA (United States). Glenn T. Seaborg Inst. for Transactinium Science; [Lawrence Berkeley National Lab., CA (United States). Nuclear Science Div.

    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.

  13. 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. PMID:25130070

  14. 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…

  15. Synthesis and determination of the absolute configuration of Armatol A through a polyepoxide cyclization cascade : revision of the proposed structures of Armatols A-F

    E-print Network

    Underwood, Brian Saxton

    2011-01-01

    Cyclization Cascades Leading to the Tricyclic Fragment of Armatol A The synthesis of the fused 6,7,7-tricycle of armatol A was investigated. Fragments containing both a ketone and an aldehyde for subsequent fragment coupling ...

  16. Asymmetric synthesis of (4R,5R)-cytoxazone and (4R,5S)-epi-cytoxazone.

    PubMed

    Davies, Stephen G; Hughes, Deri G; Nicholson, Rebecca L; Smith, Andrew D; Wright, Angela J

    2004-05-21

    (4R,5R)-Cytoxazone has been prepared in four steps and in 61% overall yield and >98% ee. Conjugate addition of lithium (R)-N-benzyl-N-[small alpha]-methylbenzylamide to tert-butyl (E)-3-(p-methoxyphenyl)prop-2-enoate and subsequent in situ diastereoselective enolate oxidation with (+)-(camphorsulfonyl)oxaziridine gave tert-butyl (2R,3R,[small alpha]R)-2-hydroxy-3-(p-methoxyphenyl)-3-(N-benzyl-N-[small alpha]-methylbenzylamino)propanoate in >98% de. Subsequent N-benzyl deprotection to the primary [small beta]-amino ester via hydrogenolysis, oxazolidinone formation with C(2)-retention by treatment with diphosgene and chemoselective ester reduction furnishes (4R,5R)-cytoxazone. The synthesis of the C(5)-epimer, (4R,5S)-epi-cytoxazone in 44% overall yield, has also been completed via a protocol involving N-Boc protection of the primary [small beta]-amino ester, utilization of the N-Boc group to facilitate simultaneous C(2)-inversion and oxazolidinone formation, and subsequent reduction. PMID:15136813

  17. Asymmetric conjugate reductions with samarium diiodide: asymmetric synthesis of (2S,3R)- and (2S,3S)-[2-2H,3-2H]-leucine-(S)-phenylalanine dipeptides and (2S,3R)-[2-(2)H,3-2H]-phenylalanine methyl ester.

    PubMed

    Davies, Stephen G; Rodriguez-Solla, Humberto; Tamayo, Juan A; Cowley, Andrew R; Concellon, Carmen; Garner, A Christopher; Parkes, Alastair L; Smith, Andrew D

    2005-04-21

    The highly diastereoselective samarium diiodide and D(2)O-promoted conjugate reduction of homochiral (E)- and (Z)-benzylidene and isobutylidene diketopiperazines (E)-5,7 and (Z)-6,8 has been demonstrated. This methodology allows the asymmetric synthesis of methyl (2S,3R)-dideuteriophenylalanine 27 in > or = 95% de and >98% ee, and (2S,3R)- or (2S,3S)-dideuterioleucine-(S)-phenylalanine dipeptides 37 and 38 in moderate de, 66% and 74% respectively. A mechanism is proposed to account for this process. PMID:15827639

  18. 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

    2008-05-01

    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). PMID:18421401

  19. Pd-Catalyzed Asymmetric Intramolecular Aryl C-O Bond Formation with SDP(O) Ligand: Enantioselective Synthesis of (2,3-Dihydrobenzo[b][1,4]dioxin-2-yl)methanols.

    PubMed

    Shi, Jialing; Wang, Ting; Huang, Yusha; Zhang, Xinhao; Wu, Yun-Dong; Cai, Qian

    2015-02-20

    Employing a chiral spirodiphosphine monoxide ligand with 1,1'-spirobiindane backbone (SDP(O)), a desymmetrization strategy of Pd-catalyzed intramolecular asymmetric aryl C-O coupling of 2-(2-halophenoxy)propane-1,3-diols, was developed. The SDP(O) ligand shows much better results than its SDP counterpart. The protocol provides an efficient and highly enantioselective method for the synthesis of 2-hydroxymethyl-1,4-benzodioxanes. Density functional theory studies provide a model that accounts for the origin of the enantioselectivity. PMID:25656954

  20. Synthesis and absolute configuration of 2-(12?-aminotridecyl)-pyrrolidine, a defensive alkaloid from the Mexican bean beetle, Epilachna varivestis

    Microsoft Academic Search

    Xiongwei Shi; Athula B. Attygalle; Shang-Cheng Xu; Viqar U. Ahmad; Jerrold Meinwald

    1996-01-01

    The synthesis of 2-(12?-aminotridecyl)-pyrrolidine (1), a defensive alkaloid recently isolated from the Mexican bean beetle, Epilachna varivestis, is described. The (2S,12?R) configuration is assigned to this alkaloid by comparing the 1H NMR spectrum of its (S)-MTPA derivative with that of (R)- and (S)-MTPA [?-methoxy-?-(trifluoromethyl)phenylacetyl] derivatives of the synthetic sample. These results suggest that the seventeen carbon skeleton of 1 is

  1. I. A1,3-Strain Enabled Retention of Chirality During Bis-Cyclization of ?-Ketoamides: Asymmetric Synthesis and Bioactivity of Salinosporamide A and Derivatives II. Optimization of an Organic Syntheses: Asymmetric Nucleophile-Catalyzed Aldol- Lactonization of Aldehyde Acids

    E-print Network

    Nguyen, Henry

    2010-11-17

    Trifluoromethane Sulfonate????????????? 91 6.2.4. Preparation of O-trimethylsilylquinidine (O-TMS QND)?.. 91 ix CHAPTER Page 6.2.5. Asymmetric... ether to to afford oxazoline 1.4 . Reduction of 1.4 with NaBH3CN/AcOH afforded threonine derivative 1.5 . Transient TMS silylation of 3 1.5 was followed by acylation with acrolyl chloride and acidic work-up to give ?- hydroxy amide 1...

  2. 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.

  3. One-pot synthesis of symmetric and asymmetric p-quinone ligands and unprecedented substituent induced reactivity in their dinuclear ruthenium complexes.

    PubMed

    Schweinfurth, David; Das, Hari Sankar; Weisser, Fritz; Bubrin, Denis; Sarkar, Biprajit

    2011-02-01

    The compounds 2-[2-(trifluoromethyl)-anilino]-5-hydroxy-1,4-benzoquinone (L(1)), 2,5-di-[2-(trifluoromethyl)-anilino]-1,4-benzoquinone (L(2)), 2-[2-(methylthio)-anilino]-5-hydroxy-1,4-benzoquinone (L(3)), and 2,5-di-[2-(methylthio)-anilino]-1,4-benzoquinone (L(4)) were prepared in high yields by reacting 2,5-dihydroxy-1,4-benzoquinone with the corresponding amines in a one-pot synthesis in refluxing acetic acid. This straightforward and "green" synthesis delivers biologically relevant asymmetric p-quinones such as L(1) and L(3) in a rare, simple, one-step process. The proposed synthetic route is general and can be applied to generate a variety of such molecules with different substituents on the nitrogen atoms. Structural characterization of L(2) and L(4) shows electron delocalization across the "upper" and "lower" parts of the molecule, thus showing the importance of charge separated species in the proper description of such molecules. Reactions of these ligands with [Cl(?(6)-Cym)Ru(?-Cl)(2)Ru(?(6)-Cym)Cl] (Cym = p-Cymene = 1-isopropyl-4-methyl-benzene) in the presence of a base result in the formation of complexes [{Cl(?(6)-Cym)Ru}(2)(?-L(-2H)(1))] (1), [{Cl(?(6)-Cym)Ru}(2)(?-L(-2H)(2))] (2), [{Cl(?(6)-Cym)Ru}(2)(?-L(-2H)(3))] (3), and [{Cl(?(6)-Cym)Ru}(2)(?-L(-2H)(4))] (4). Structural characterization of 2 and 4 shows a rare syn-coordination of the chloride atoms. The SMe groups in 3 and 4 are not coordinated to the ruthenium center, and the bridging ligands thus function in a bis-bidentate form. Abstraction of the chloride atoms in these complexes with AgClO(4) in CH(3)CN results in the expected formation of solvent substituted complexes [{(CH(3)CN)(?(6)-Cym)Ru}(2)(?-L(-2H)(1))][ClO(4)](2) (5[ClO(4)](2)) and [{(CH(3)CN)(?(6)-Cym)Ru}(2)(?-L(-2H)(2))][ClO(4)](2) (6[ClO(4)](2)) with the ligands where there are no additional donor atoms on the nitrogen substituents. The same chloride abstraction reaction in the cases of 3 and 4 leads to an unprecedented substituent induced release of the Cym ligand, resulting in complexes of the form [(CH(3)CN)(?(6)-Cym)Ru(?-L(-2H)(3))Ru(CH(3)CN)(3)][ClO(4)](2) (7[ClO(4)](2)) and [{(CH(3)CN)(3)Ru}(2)(?-L(-2H)(4))][ClO(4)](2) (8[ClO(4)](2)), where the SMe groups are now coordinated to the metal center. In the case of complex 3, which contains an asymmetric bridging ligand, Cym release is observed only at the side that contains an additional SMe donor, thus proving the necessity of such donor substituents for the observed reactivity. The increase in Lewis acidity at the ruthenium center on chloride abstraction is made responsible for SMe coordination and the rigidity of the ligand systems, and their concomitant failure to coordinate in a "fac" manner as is required for a piano stool configuration results in the eventual Cym release. The bridging ligand which then coordinates in a bis-meridional fashion in 8[ClO(4)](2) results in a bis-pincer type of coordination. These observations were validated by a structural analysis of 8[ClO(4)](2). The results show the potential hemilabile character of ligands such as L(3) and L(4). Electrochemical and spectroscopic investigations are reported on 8[ClO(4)](2), and substitution reactions of the CH(3)CN molecules are presented to show the use of 8[ClO(4)](2) as a versatile precursor for other reactions. PMID:21214266

  4. Isolation and complete structural assignment of Lycopodium alkaloid cernupalhine A: theoretical prediction and total synthesis validation.

    PubMed

    Dong, Liao-Bin; Wu, Ya-Nan; Jiang, Shi-Zhi; Wu, Xing-De; He, Juan; Yang, Yu-Rong; Zhao, Qin-Shi

    2014-05-16

    Cernupalhine A (1) is a trace Lycopodium alkaloid (0.7 mg) possessing a new C17N skeleton with an unusual hydroxydihydrofuranone motif newly isolated from Palhinhaea cernua L. Its complete structural assignment, including absolute stereochemistry, was established through a combination of high-field NMR techniques and computational methods and further unequivocal confirmation by the first asymmetric total synthesis. Following the first total synthesis of lobscurinine (3), 1 was achieved via regio- and stereoselective cyanide ion addition and subsequent acid treatment. PMID:24779557

  5. Simultaneous axial screw dislocation-mediated growth and radial layer-by-layer deposition for controlled synthesis of asymmetric axial ZnO nanospindles.

    PubMed

    Yang, Hong-Jie; He, Sheng-Yan; Tuan, Hsing-Yu

    2014-08-01

    Single-component nanostructures with axial asymmetry were successfully synthesized in organic solvents via a new type of growth model. Asymmetric axial ZnO nanospindles with a hexagonal cross-section were produced by a growth model consisting of simultaneous axial screw dislocation-mediated growth and radial layer-by-layer deposition. The growth process of ZnO nanospindles is explained by comprehensively characterizing and monitoring the products at different reaction time intervals. Hexagonal discs containing dislocations were first generated at a reaction time of 2.5 min. When the reaction time continued to increase, the nanodiscs grew along the ?0002? direction. Half-nanospindles were formed at mid-reaction stage when the growth rate of [0001] was greater than [000-1]. Finally, the asymmetric nanospindles were obtained at 40 min. Further, the length of the asymmetric axial ZnO spindles can be precisely tuned by the adjustment of reaction temperature. Thus, the growth model presented here can synthesize a new category of one-dimensional asymmetric nanostructures. PMID:24970315

  6. Eosinophil count - absolute

    MedlinePLUS

    An absolute eosinophil count is a blood test that measures the number of white blood cells called eosinophils. Eosinophils become active when you have certain allergic diseases, infections, and other medical conditions.

  7. Application of Catalytic Dynamic Resolution of N-Boc-2-lithiopiperidine to the Asymmetric Synthesis of 2-Aryl and 2-Vinyl Piperidines

    PubMed Central

    Beng, Timothy K.; Gawley, Robert E.

    2011-01-01

    The highly enantioselective synthesis of 2-aryl- and 2-vinyl-piperidines has been accomplished through a catalytic dynamic resolution (CDR) of N-Boc-2-lithiopiperidine. The method has been applied to the synthesis of both enantiomers of the tobacco alkaloid anabasine. PMID:21174392

  8. An absolute Johnson noise thermometer

    E-print Network

    Luca Callegaro; Vincenzo D'Elia; Marco Pisani; Alessio Pollarolo

    2009-01-30

    We developed an absolute Johnson noise thermometer (JNT), an instrument to measure the thermodynamic temperature of a sensing resistor, with traceability to voltage, resistance and frequency quantities. The temperature is measured in energy units, and can be converted to SI units (kelvin) with the accepted value of the Boltzmann constant kb; or, conversely, it can be employed to perform measurements at the triple point of water, and obtain a determination of kb. The thermometer is composed of a correlation spectrum analyzer an a calibrated noise source, both constructed around commercial mixed-signal boards. The calibrator generates a pseudorandom noise, by digital synthesis and amplitude scaling with inductive voltage dividers; the signal spectrum is a frequency comb covering the measurement bandwidth. JNT measurements at room temperature are compatible with those of a standard platinum resistance thermometer within the combined uncertainty of 60 ppm. A path towards future improvements of JNT accuracy is also sketched.

  9. Asymmetric fluorocyclizations of alkenes.

    PubMed

    Wolstenhulme, Jamie R; Gouverneur, Véronique

    2014-12-16

    CONSPECTUS: The vicinal fluorofunctionalization of alkenes is an attractive transformation that converts feedstock olefins into valuable cyclic fluorinated molecules for application in the pharmaceutical, agrochemical, medical, and material sectors. The challenges associated with asymmetric fluorocyclizations induced by F(+) reagents are distinct from other types of halocyclizations. Processes initiated by the addition of an F(+) reagent onto an alkene do not involve the reversible formation of bridged fluoronium ions but generate acyclic ?-fluorocationic intermediates. This mechanistic feature implies that fluorocyclizations are not stereospecific. A discontinuity exists between the importance of this class of fluorocyclization and the activation modes currently available to implement successful catalysis. Progress toward fluorocyclization has been achieved by investing in neutral and cationic [NF] reagent development. The body of work on asymmetric fluorination using chiral cationic [NF](+) reagents prepared by fluorine transfer from the dicationic [NF](2+) reagent Selectfluor to quinuclidines, inspired the development of asymmetric F(+)-induced fluorocyclizations catalyzed by cinchona alkaloids; for catalysis, the use of N-fluorobenzenesulfonimide, which is less reactive than Selectfluor, ensures that the achiral F(+) source remains unreactive toward the alkene. These organocatalyzed enantioselective fluorocyclizations can be applied to indoles to install the fluorine on a quaternary benzylic stereogenic carbon center and to afford fluorinated analogues of natural products featuring the hexahydropyrrolo[2,3-b]indole or the tetrahydro-2H-furo[2,3-b]indole skeleton. In an alternative approach, the poor solubility of dicationic Selectfluor bis(tetrafluoroborate) in nonpolar solvent was exploited with anionic phase transfer catalysis as the operating activation mode. Exchange of the tetrafluoroborate ions of Selectfluor with bulky lipophilic chiral anions (e.g., TRIP and derivatives) brings into solution the resulting chiral Selectfluor reagent, now capable of asymmetric fluorocyclization. This strategy is best applied to a subset of substrates bearing a nucleophilic pendent group (benzamide is best) capable of hydrogen bonding for association with the chiral phosphate catalyst. These contributions focused on fluoroheterocyclization involving either O- or N-nucleophiles. As for other halocyclizations, alkenes armed with ? C-nucleophiles represent the most demanding class of substrates for asymmetric F(+)-induced electrophilic fluorination-cyclization. Successful implementation required the design of new chiral Selectfluor reagents featuring stereogenicity on the DABCO core. These reagents, accessible from chiral vicinal diamines, allowed the synthesis of unusual chiral fluorine-containing tetracyclic compounds, some composed of carbon, hydrogen, and fluorine exclusively. The challenges associated with F(+)-induced fluorocarbocyclizations prompted methodologists to consider chemistry where the Csp(3)-F bond formation event follows a catalyst-controlled cyclization. An exciting development built on in the area of transition metal ?-cyclization of polyenes leading to cationic metal-alkyl intermediates. When intercepted by oxidative fluorodemetalation with a F(+) source, the resulting products are complex polycyclic structures emerging from an overall catalytic cascade fluorocarbocyclization. Complementing F(+)-based reactions, examples of fluorocyclizations with fluoride in the presence of an oxidant were reported. Despite some exciting developments, the field of asymmetric fluorocyclizations is in its infancy and undoubtedly requires new activation modes, catalysts, as well as F(+) and F(-) reagents to progress into general retrosynthetic approach toward enantioenriched fluorocycles. Numerous opportunities emerge, not least the use of a latent fluorine source as a means to minimize background fluorination. PMID:25379791

  10. Absolute Biodiesel Potential Country Name

    E-print Network

    Wisconsin at Madison, University of

    Absolute Biodiesel Potential Country Name Production Cost ($/liter) Potential Biodiesel Volume,234 0% 0% #12;Absolute Biodiesel Potential Country Name Production Cost ($/liter) Potential Biodiesel;Absolute Biodiesel Potential Country Name Production Cost ($/liter) Potential Biodiesel Volume (liters

  11. 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

    2009-02-01

    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. PMID:19105680

  12. Enantioselective Synthesis of All-Carbon Quaternary Stereogenic Centers via Copper-Catalyzed Asymmetric Allylic Alkylation of (Z)-Allyl Bromides with Organolithium Reagents.

    PubMed

    Fañanás-Mastral, Martín; Vitale, Romina; Pérez, Manuel; Feringa, Ben L

    2015-03-01

    A copper/phosphoramidite catalyzed asymmetric allylic alkylation of Z?trisubstituted allyl bromides with organolithium reagents is reported. The reaction affords all-carbon quaternary stereogenic centers in high yields and very good regio- and enantioselectivity. This systematic study illustrates the crucial role of the olefin geometry of the allyl substrate on the outcome of the reaction and provides a viable alternative to access these important structural motifs. PMID:25631942

  13. Improved synthesis and application of planar-chiral nucleophilic catalysts in asymmetric reactions and copper-catalyzed enantioselective N-H insertion reactions

    E-print Network

    Lee, Elaine C

    2007-01-01

    The development of an improved synthesis of nucleophilic planar-chiral catalysts is described in Chapter 1. This route is amenable to scale-up and preparative chiral HPLC is unnecessary to resolve the racemic catalysts. ...

  14. Asymmetric Ashes

    NASA Astrophysics Data System (ADS)

    2006-11-01

    Astronomers are reporting remarkable new findings that shed light on a decade-long debate about one kind of supernovae, the explosions that mark a star's final demise: does the star die in a slow burn or with a fast bang? From their observations, the scientists find that the matter ejected by the explosion shows significant peripheral asymmetry but a nearly spherical interior, most likely implying that the explosion finally propagates at supersonic speed. These results are reported today in Science Express, the online version of the research journal Science, by Lifan Wang, Texas A&M University (USA), and colleagues Dietrich Baade and Ferdinando Patat from ESO. "Our results strongly suggest a two-stage explosion process in this type of supernova," comments Wang. "This is an important finding with potential implications in cosmology." ESO PR Photo 44/06 ESO PR Photo 44/06 Clumpy Explosion (Artist's Impression) Using observations of 17 supernovae made over more than 10 years with ESO's Very Large Telescope and the McDonald Observatory's Otto Struve Telescope, astronomers inferred the shape and structure of the debris cloud thrown out from Type Ia supernovae. Such supernovae are thought to be the result of the explosion of a small and dense star - a white dwarf - inside a binary system. As its companion continuously spills matter onto the white dwarf, the white dwarf reaches a critical mass, leading to a fatal instability and the supernova. But what sparks the initial explosion, and how the blast travels through the star have long been thorny issues. The supernovae Wang and his colleagues observed occurred in distant galaxies, and because of the vast cosmic distances could not be studied in detail using conventional imaging techniques, including interferometry. Instead, the team determined the shape of the exploding cocoons by recording the polarisation of the light from the dying stars. Polarimetry relies on the fact that light is composed of electromagnetic waves 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, it is. "This has some impact on the us

  15. Vo(IV), Fe(III), Co(II) and Cd(II) Complexes of Asymmetric Schiff Base Ligands (N2O3). Synthesis and Spectroscopic Studies

    Microsoft Academic Search

    Saied M. E. Khalil; Hoda F. O. El-Shafiy

    2000-01-01

    New series of mononuclear VO(IV), Co(II) and Cd(II) complexes of the formula [HLVO(OH2)]·nH2O, [HLCo]·xH2O and [HLCd]·xH2O and binuclear Fc(III) complexes of the formula [LFe2Cl2(H2O)3]Cl·H2O have been synthesized. L stands for one of the five asymmetrical pentadentate (N2O3) Schiff base ligands H3L-H3L prepared by the condensation of acetoacetylphenol and ethylenediamine in the molar ratio 1:1 to prepare a half-unit Schiff base

  16. Asymmetric dark matter

    SciTech Connect

    Kumar, Jason [Department of Physics and Astronomy, University of Hawaii, Honolulu, HI 96822 (United States)

    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.

  17. Divergent total synthesis of the Lycopodium alkaloids huperzine A, huperzine B, and huperzine U.

    PubMed

    Ding, Rui; Fu, Jian-Guo; Xu, Guang-Qiang; Sun, Bing-Feng; Lin, Guo-Qiang

    2014-01-01

    Huperzine A, huperzine B, and huperzine U are congeners isolated from the Chinese herb Huperzia serrata (= Lycopodium serratum ) in minuscule amounts. The most efficient total synthesis of huperzine A, the first asymmetric total syntheses of huperzine B, and the first total synthesis of huperzine U have been achieved efficiently in overall yields of 17%, 10%, and 9%, respectively, each spanning 10-13 steps from (R)-pulegone. The featured steps include palladium-catalyzed Buchwald-Hartwig coupling and Heck cyclization reactions and an Ir-catalyzed olefin isomerization reaction. This work has established the absolute configurations of huperzine B and huperzine U and revealed that natural huperzine A, huperzine B, and huperzine U possess the same set of absolute stereochemistries, thus providing support for the potential role of huperzine B and huperzine U in the biosynthesis of huperzine A. PMID:24299147

  18. Controlled synthesis, asymmetrical transport behavior and luminescence properties of lanthanide doped ZnO mushroom-like 3D hierarchical structures.

    PubMed

    Yue, Dan; Lu, Wei; Jin, Lin; Li, Chunyang; Luo, Wen; Wang, Mengnan; Wang, Zhenling; Hao, Jianhua

    2014-11-21

    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:Ln(3+) (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 ?m, and the diameters of pileus and stipe are about 0.8 ?m and 0.4 ?m, 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:Ln(3+) nanorods, whereas the stipe is composed of over layered ZnO:Ln(3+) nanosheets. Moreover, asymmetrical I-V characteristic curves of ZnO:Ln(3+) 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. PMID:25293373

  19. Heterobinuclear Zn-Ln (Ln?=?La, Nd, Eu, Gd, Tb, Er and Yb) complexes based on asymmetric Schiff-base ligand: synthesis, characterization and photophysical properties.

    PubMed

    Zhao, Shunsheng; Liu, Xiangrong; Lü, Xingqiang; Wong, Wai-Kwok

    2013-01-01

    With a novel asymmetric Schiff-base zinc complex ZnL (H2 L?=?N-(3-methoxysalicylidene)-N'-(5-bromo-3-methoxysalicylidene)phenylene-1,2-diamine), obtained from phenylene-1,2-diamine, 3-methoxysalicylaldehyde and 5-bromo-3-methoxysalicylaldehyde, as the precursor, a series of heterobinuclear Zn-Ln complexes [ZnLnL(NO3 )3 (CH3 CN)] (Ln?=?La, 1; Ln?=?Nd, 2; Ln?=?Eu, 3; Ln?=?Gd, 4; Ln?=?Tb, 5; Ln?=?Er, 6; Ln?=?Yb, 7) were synthesized by the further reaction with Ln(NO3 )3 ·6H2 O, and characterized by Fourier transform-infrared, fast atom bombardment mass spectroscopy and elemental analysis. Photophysical studies of these complexes show that the strong and characteristic near-infrared luminescence of Nd(3+) , Yb(3+) and Er(3+) with emissive lifetimes in the microsecond range has been sensitized from the excited state of the asymmetric Schiff-base ligand due to effective intramolecular energy transfer; the other complexes do not show characteristic emission due to the energy gap between the chromophore and lanthanide ions. PMID:23001932

  20. Synthesis and characterization of FePd magnetic nanoparticles modified with chiral BINAP ligand as a recoverable catalyst vehicle for the asymmetric coupling reaction.

    PubMed

    Mori, Kohsuke; Kondo, Yuichi; Yamashita, Hiromi

    2009-10-21

    The initial thermal decomposition of iron carbonyl (Fe(CO)(5)), followed by reduction of palladium acetylacetonate (Pd(acac)(2)) produced FePd nanoparticles (NPs) with an Fe(x)O(y)-rich core and a Pd-rich shell. The as-synthesized NPs were subsequently treated with (S)-2,2'-bis(diphenylphosphino)-1,1'-binaphthene ((S)-BINAP) as a chiral modifier, which provides them with the optical activity to show a negative Cotton effect in the circular dichroism (CD) spectrum. Characterization by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), superconducting quantum interface device (SQUID) and X-ray absorption fine structure (XAFS) measurements was performed. The FePd NPs modified with (S)-BINAP had a mean diameter of ca. 5.6 nm, and exhibited superparamagnetic behavior at 300 K with zero remanence and coercivity. The FePd-(S)-BINAP was shown to catalyze the asymmetric Suzuki-Miyaura coupling reaction with easy recovery from the reaction mixture by applying an external magnet. The designed architecture enabled the powerful combination of two functionalities, magnetism that responds to a magnetic field for easy recycling, as well as an optically active catalytic center that promotes the asymmetric coupling reaction. PMID:20449041

  1. Evolution of the Total Synthesis of (-)-Okilactomycin Exploiting a Tandem Oxy-Cope Rearrangement/Oxidation, the Petasis-Ferrier Union/Rearrangement and Ring Closing Metathesis

    PubMed Central

    Smith, Amos B.; Bosanac, Todd; Basu, Kallol

    2009-01-01

    An effective, asymmetric total synthesis of the antitumor antibiotic (-)-okilactomycin (1) and assignment of the absolute configuration, has been achieved exploiting a convergent strategy. Highlights of the synthesis include: a diastereoselective oxy-Cope rearrangement/oxidation sequence to install the C(1) and C(13) stereogenic centers; a Petasis-Ferrier union/rearrangement to construct the highly functionalized tetrahydropyranone inscribed within the thirteen membered macrocycle ring, employing for the first time a sterically demanding acetal; an intramolecular chemoselective acylation to access an embedded bicyclic lactone; and an efficient ring closing metathesis (RCM) reaction to generate the macrocyclic ring. PMID:19170499

  2. Total synthesis of Class II and Class III Galbulimima Alkaloids

    E-print Network

    Tjandra, Meiliana

    2010-01-01

    I. Total Synthesis of All Class III Galbulimima Alkaloids We describe the total synthesis of (+)- and (-)-galbulimima alkaloid 13, (-)-himgaline anad (-)-himbadine. The absolute stereochemistry of natural (-)-galbulimima ...

  3. Absolute configuration of neostenine

    NASA Astrophysics Data System (ADS)

    Jiang, Ren-Wang; Ye, Wencai; Shaw, Pang-Chui; But, Paul Pui-Hay; Mak, Thomas C. W.

    2010-03-01

    Heavy atoms bromine and iodine were incorporated into the neostenine ( 1) skeleton through reductive cleavage of the lactone ring, followed by acylation with 4-bromobenzoyl chloride, and salt formation with methyl iodide, respectively. The absolute configuration of the seven chiral centers C1, C9, C9a, C10, C11, C1 and C13 in 1 were assigned as S, S, R, R, R, R, and S, respectively, based on the Flack parameters in X-ray structure refinement, and results from the two heavy atom derivatives are consistent with each other. As many Stemona alkaloids share the same lactone and pyrrolo[1,2-?]azepine nucleus as those in 1, the facile method reported in this paper can be applied for the determination of absolute configurations of similar alkaloids.

  4. Estimating Absolute Site Effects

    Microsoft Academic Search

    L. Malagnini; K M Mayeda; A Akinci; P L Bragato

    2004-01-01

    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

  5. Asymmetric Ultrasonic Pulse Radiation Using Electromagnetic-Induction Transducer and PZT(Pb(Zr-Ti)O3) Transducer with Wave Synthesis Method

    NASA Astrophysics Data System (ADS)

    Endoh, Nobuyuki; Yamamoto, Koji

    1993-05-01

    In medical applications, especially in urology, we use a fragmentation calculus technique with shock waves. This technique is very profitable because of no abdominal surgery for a human being. Large negative sound amplitude pulses, however, can cause problems such as internal hemorrhage or pain in the human body. The final goal of this study is to develop a means to project an intense positive unipolar pulse without negative sound pressure. We improved a composite transducer consisting of an electromagnetic-induction-type (EMI) transducer and PZT (Pb(Zr-Ti)O3) transducers. An EMI transducer consisting of a metal coil and vibration membrane can project intense sound pulses into water. In order to suppress its negative sound pressure, we project a compensation pulse with PZT transducers using an inverse filtering method. An asymmetric pulse whose P+ to P- amplitude ratio was very high was projected in water.

  6. 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 ?m, and the diameters of pileus and stipe are about 0.8 ?m and 0.4 ?m, 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 ?m, and the diameters of pileus and stipe are about 0.8 ?m and 0.4 ?m, 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. Electronic supplementary information (ESI) available: STEM-SEI image and EDS elemental mapping of an individual ZnO: Eu3+ mushroom. See DOI: 10.1039/c4nr04359f

  7. 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)

    ?ahin, Mustafa; Koçak, Nuriye; Erdenay, Damla; Arslan, U?ur

    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.

  8. Design, synthesis and biological activity of novel asymmetric C66 analogs as anti-inflammatory agents for the treatment of acute lung injury.

    PubMed

    Yu, Pengtian; Dong, Lili; Zhang, Yali; Chen, Wenbo; Xu, Shanmei; Wang, Zhe; Shan, Xiaoou; Zhou, Jianmin; Liu, Zhiguo; Liang, Guang

    2015-04-13

    Acute lung injury (ALI) is a leading cause of morbidity and mortality in critically-ill patients. Previously, we reported that a symmetric mono-carbonyl analog of curcumin, (C66), exhibits enhanced stability and was found to have efficacy and be involved in potential cytokines inhibition. In the present study, a series of novel asymmetric C66 analogs were designed and synthesized. A majority of them effectively inhibited the LPS-induced expression of TNF-? and IL-6. Significantly, compound 4b2 was found to effectively reduce LPS-induced pulmonary inflammation, as reflected by reductions in concentration of total protein, inflammatory cell count as well as the lung W/D ratio in bronchoalveolar lavage (BAL) fluid. Furthermore, in vivo administration of 4b2 resulted in remarkable improvement in histopathological changes of lung in rats. PMID:25828826

  9. The Direct Catalytic Asymmetric Aldol Reaction

    PubMed Central

    Brindle, Cheyenne S.

    2013-01-01

    Asymmetric aldol reactions are a powerful method for the construction of carbon-carbon bonds in an enantioselective fashion. Historically this reaction has been performed in a stoichiometric fashion to control the various aspects of chemo-, diastereo-, regio- and enantioselectivity, however, a more atom economical approach would unite high selectivity with the use of only a catalytic amount of a chiral promoter. This critical review documents the development of direct catalytic asymmetric aldol methodologies, including organocatalytic and metal-based strategies. New methods have improved the reactivity, selectivity and substrate scope of the direct aldol reaction and enabled the synthesis of complex molecular targets PMID:20419212

  10. Theoretical study of the asymmetric phase-transfer mediated epoxidation of chalcone catalyzed by chiral crown ethers derived from monosaccharides

    NASA Astrophysics Data System (ADS)

    Makó, Attila; Menyhárd, Dóra K.; Bakó, Péter; Keglevich, György; T?ke, László

    2008-12-01

    The synthesis of a novel, optically active crown ether derived from ?- D-altropyranoside is described. A significantly different asymmetric induction was generated by the ?- D-glucopyranoside-, ?- D-mannopyranoside- and ?- D-altropyranoside-based chiral crown catalysts in the epoxidation of trans-chalcone with tert-butyl hydroperoxide under phase-transfer catalytic conditions. It was shown that absolute configuration of the crown-ring fused carbon atoms of the monosaccharides has a great impact on the enantioselectivity. The asymmetric induction could be well explained by considering the possible mechanistic pathway. Molecular modeling (MCMM) and subsequent DFT calculations - in accordance with the experimental results - indicate that the use of glucopyranoside-based catalyst 1 and that of mannopyranoside-based crown ether 2 results in the preferred formation of the opposite antipodes (2 R,3 S and 2 S,3 R, respectively) of the corresponding epoxyketone. At the same time, practically no asymmetric induction was proved if altropyranoside-based crown 3 is applied as the catalyst. The computational results are in qualitative agreement with the experimental data.

  11. New phosphine-diamine and phosphine-amino-alcohol tridentate ligands for ruthenium catalysed enantioselective hydrogenation of ketones and a concise lactone synthesis enabled by asymmetric reduction of cyano-ketones

    PubMed Central

    2012-01-01

    Enantioselective hydrogenation of ketones is a key reaction in organic chemistry. In the past, we have attempted to deal with some unsolved challenges in this arena by introducing chiral tridentate phosphine-diamine/Ru catalysts. New catalysts and new applications are presented here, including the synthesis of phosphine-amino-alcohol P,N,OH ligands derived from (R,S)-1-amino-2-indanol, (S,S)-1-amino-2-indanol and a new chiral P,N,N ligand derived from (R,R)-1,2-diphenylethylenediamine. Ruthenium pre-catalysts of type [RuCl2(L)(DMSO)] were isolated and then examined in the hydrogenation of ketones. While the new P,N,OH ligand based catalysts are poor, the new P,N,N system gives up to 98% e.e. on substrates that do not react at all with most catalysts. A preliminary attempt at realising a new delta lactone synthesis by organocatalytic Michael addition between acetophenone and acrylonitrile, followed by asymmetric hydrogenation of the nitrile functionalised ketone is challenging in part due to the Michael addition chemistry, but also since Noyori pressure hydrogenation catalysts gave massively reduced reactivity relative to their performance for other acetophenone derivatives. The Ru phosphine-diamine system allowed quantitative conversion and around 50% e.e. The product can be converted into a delta lactone by treatment with KOH with complete retention of enantiomeric excess. This approach potentially offers access to this class of chiral molecules in three steps from the extremely cheap building blocks acrylonitrile and methyl-ketones; we encourage researchers to improve on our efforts in this potentially useful but currently flawed process. PMID:23216944

  12. 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. PMID:23670801

  13. Stereocontrolled synthesis of bicyclic sulfamides via Pd-catalyzed alkene carboamination reactions. Control of 1,3-asymmetric induction by manipulating mechanistic pathways.

    PubMed

    Babij, Nicholas R; McKenna, Grace M; Fornwald, Ryan M; Wolfe, John P

    2014-06-20

    A new annulation strategy for the synthesis of trans-bicyclic sulfamides is described. The Pd-catalyzed alkene carboamination reactions of 2-allyl and cis-2,5-diallyl pyrrolidinyl sulfamides with aryl and alkenyl triflates afford the fused bicyclic compounds in good yields and with good diastereoselectivity (up to 13:1 dr). Importantly, by employing reaction conditions that favor an anti-aminopalladation mechanism, the relative stereochemistry between the C3 and C4a stereocenters of the products is reversed relative to related Pd-catalyzed carboamination reactions that proceed via syn-aminopalladation. PMID:24916343

  14. Facile synthesis of hierarchical Co3O4@MnO2 core-shell arrays on Ni foam for asymmetric supercapacitors

    NASA Astrophysics Data System (ADS)

    Huang, Ming; Zhang, Yuxin; Li, Fei; Zhang, Lili; Wen, Zhiyu; Liu, Qing

    2014-04-01

    Hierarchical Co3O4@MnO2 core-shell arrays on Ni foam have been fabricated by a facile hydrothermal approach and further investigated as the electrode for high-performance supercapacitors. Owing to the high conductivity of the well-defined mesoporous Co3O4 nanowire arrays in combination with the large surface area provided by the ultrathin MnO2 nanosheets, the unique designed Co3O4@MnO2 core-shell arrays on Ni foam have exhibited a high specific capacitance (560 F g-1 at a current density of 0.2 A g-1), good rate capability, and excellent cycling stability (95% capacitance retention after 5000 cycles). An asymmetric supercapacitor with Co3O4@MnO2 core-shell nanostructure as the positive electrode and activated microwave exfoliated graphite oxide activated graphene (MEGO) as the negative electrode yielded an energy density of 17.7 Wh kg-1 and a maximum power density of 158 kW kg-1. The rational design of the unique core-shell array architectures demonstrated in this work provides a new and facile approach to fabricate high-performance electrode for supercapacitors.

  15. 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-?-donor-?-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. PMID:24973792

  16. Synthesis, crystal structures, and properties of two novel cadmium(II)-organic frameworks based on asymmetric dicarboxylate and N-donor ligands

    NASA Astrophysics Data System (ADS)

    Chen, Xiaoli; Gao, Loujun; Zhang, Xiaoge; Han, Xuhua; Wang, Yao; Sun, Rong

    2014-08-01

    Two novel cadmium(II)-organic frameworks with asymmetric dicarboxylate and N-donor ligands, namely [Cd(cpa)(phen)]n (1) and {[Cd2(cpa)2(bpy)1.5]·0.5H2O}n (2) (H2cpa = 3-(4-benzoic)propionic acid, phen = 1,10-phenanthroline, bpy = 4,4";-bipyridine) have been hydrothermally synthesized and characterized by elemental analyses, FT-IR spectra, single-crystal X-ray diffraction analyses, TGA, powder XRD and fluorescent measurements. 1 displays a double zigzag chain structure containing 8-number and 22-number circles. 2 Shows a 6-connected 3D polymer network based on tetranuclear cadmium cluster units. The most striking feature of 2 is that a pair of identical 3D networks are interlocked with each other to the form a 2-fold interpenetrated 3D ?-Po structural topology. The diverse structures of two complexes indicate that the skeleton of N-donor ligands plays a great role in the assembly of such different frameworks. In addition, the thermal stabilities, XRD and photoluminescence properties of 1-2 were also studied.

  17. NOVA: Absolute Zero

    NSDL National Science Digital Library

    On a hot day, some might wish they could get the temperature down a bit. They might not wish it to be as cold as, say absolute zero, but there are many scientists who are interested in doing just that. For those who are curious, absolute zero clocks in at around minus 460 degrees Fahrenheit. This engaging website is meant to serve as a complementary resource to the two-part series that recently aired on NOVA on this engaging topic. Visitors can start by watching a short preview of the program, and then continuing on to look over some of the special interactive features on the site. All told, there are ten different features, including "A Sense of Scale", "How Low Can You Go?", and "Milestones in Cold Research". The "Milestones in Cold Research" is a great place to start, as it's an interactive timeline that chronicles the "netherworld of extraordinarily low temperatures" as investigated by everyone from Galileo to current researchers. Of course, there are also more playful features here, such as "The Ice Trade", which asks users to dispatch ships loaded with natural ice to Florida, Brazil, and India.

  18. 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.

  19. January 2004 Asymmetric Cell

    E-print Network

    Extavour, Cassandra

    ]. In the sensory organ precursor cell of Drosophila, asymmetric localization of Frizzled, Strabismus and Prickle proteins define two opposite domains before mitosis of the precursor cell. During mitosis, Strabismus planar cell polarity protein Strabismus promotes Pins anterior localization during asymmetric division

  20. Synthesis, spectroscopic characterization and antimicrobial activity of binuclear metal complexes of a new asymmetrical Schiff base ligand: DNA binding affinity of copper(II) complexes

    NASA Astrophysics Data System (ADS)

    Shebl, Magdy

    2014-01-01

    The 1:1 condensation of o-acetoacetylphenol and 1,2-diaminopropane under condition of high dilution gives the mono-condensed Schiff base, (E)-3-(1-aminopropan-2-ylimino)-1-(2-hydroxyphenyl)butan-1-one. The mono-condensed Schiff base has been used for further condensation with isatin to obtain the new asymmetrical dicompartmental Schiff base ligand, (E)-3-(2-((E)-4-(2-hydroxyphenyl)-4-oxobutan-2-ylideneamino) propylimino)indolin-2-one (H3L) with a N2O3 donor set. Reactions of the ligand with metal salts give a series of new binuclear complexes. The ligand and its metal complexes were characterized by elemental analyses, IR, 1H and 13C NMR, electronic, ESR and mass spectra, conductivity and magnetic susceptibility measurements as well as thermal analyses. The analytical and spectroscopic tools showed that the complexes can be formulated as: [(HL)(VO)2(SO4)(H2O)]·4H2O, [(HL)Fe2Cl4(H2O)3]·EtOH, [(HL)Fe2(ox)Cl2(H2O)3]·2H2O, [(L)M2(OAc)(H2O)m]·nH2O; M = Co, Ni or Cu, m = 4, 0 and n = 2, 3, [(HL)Cu2Cl]Cl·6H2O and [(L)(UO2)2(OAc)(H2O)3]·6H2O. The metal complexes exhibited octahedral geometrical arrangements except copper complexes that exhibited tetrahedral geometries and uranyl complex in which the metal ion is octa-coordinated. The Schiff base and its metal complexes were evaluated for antimicrobial activity against Gram positive bacteria (Staphylococcus aureus), Gram negative bacteria (Escherichia coli) and fungi (Candida albicans and Aspergillus flavus). The ligand and some of its complexes were found to be biologically active. The DNA-binding properties of the copper complexes (6 and 7) have been investigated by electronic absorption, fluorescence and viscosity measurements. The results obtained indicate that these complexes bind to DNA via an intercalation binding mode with an intrinsic binding constant, Kb of 1.34 × 104 and 2.5 × 104 M-1, respectively.

  1. Attempted asymmetric electrochemical reductions in magnetic fields

    NASA Astrophysics Data System (ADS)

    Bonner, William A.

    1990-01-01

    Because of negative, ambiguous or controversial results claimed by previous investigators studying the potential efficacy of magnetic fields in directing asymmetric syntheses and because of its potential importance as regards the origin of optical activity, we have attempted to confirm a recent report by Takahashiet al. (1986), who claimed that phenylglyoxylic acid (XIX) may be reduced electrochemically at a mercury cathode placed in a magnetic field of 0.168 T to optically active mandelic acid (XX), with optical yields favoring the S(+)-XX enantiomer as high as 25%. We have found that the complete reduction of XIX in pH 3.8 acetate buffer at a mercury cathode in magnetic fields of either 0.14 or 7.05 T leads only to racemic XX products. The earlier literature describing attempted absolute asymmetric syntheses in magnetic, electric and gravitational fields is briefly and critically reviewed.

  2. 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)

  3. 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

    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 (L(ij)) represent the interactions between the drug (d(i)) and the target (t(j)), characterized by different experimental measures (K(i), K(m), IC50, etc.) obtained in pharmacological assays under diverse boundary conditions (c(j)). 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

  4. 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

  5. Total synthesis of (-)-dolastatrienol.

    PubMed

    Leung, Lai To; Chiu, Pauline

    2015-04-01

    The first asymmetric total synthesis of the tricyclic diterpenoid natural product (-)-dolastatrienol has been accomplished using a rhodium(II)-catalyzed carbene cyclization cycloaddition cascade reaction as the key step to construct the [5.4.0]carbobicyclic core. An intramolecular Heck reaction furnished the tricyclic skeleton and a challenging methylenation completed the synthesis of the target. PMID:25556852

  6. Absolute Configurational Assignment in Chiral Compounds through Vibrational Circular Dichroism (VCD) Spectroscopy

    Microsoft Academic Search

    CORNELIA UNCUÞA; SIMONA ION; EMERIC BARTHA; FLORINA TEODORESCU; PETRU FILIP

    2009-01-01

    The determination of the absolute configuration is a major goal in stereochemical analysis. The main traditional methods for establishing absolute configuration include X-ray crystallography, synthesis of the target-molecule through a series of stereochemically controlled steps, optical rotation (OR) and electronic circular dichroism (CD). Among these methods, only X-ray crystallography is an absolute method. Although straightforward and highly reliable, this method

  7. Absolute stability of a class of trilateral haptic systems.

    PubMed

    Li, Jian; Tavakoli, Mahdi; Huang, Qi

    2014-01-01

    Trilateral haptic systems can be modeled as three-port networks. We present a criterion for absolute stability of a general class of three-port networks. Traditionally, existing (i.e., Llewellyn's) criteria have facilitated the stability analysis of bilateral haptic systems modeled as two-port networks. If the same criteria were to be used for stability analysis of a three-port network, its third port termination would need to be assumed known for it to reduce to a two-port network. This is restrictive because, for absolute stability, all three terminations of the three-port network must be allowed to be arbitrary (while passive). Extending Llewellyn's criterion, we present closed-form necessary and sufficient conditions for absolute stability of a general class of three-port networks. We first find a symmetrization condition under which a general asymmetric impedance (or admittance) matrix Z3 × 3 has a symmetric equivalent Zeq from a network stability perspective. Then, via the equivalence of passivity and absolute stability for reciprocal networks, an absolute stability condition for the original nonreciprocal network is derived. To demonstrate the convenience and utility of using this criterion for both analysis and design, it is applied to the problem of designing stabilizing controllers for dual-user haptic teleoperation systems, with simulations and experiments validating the criterion. PMID:25248167

  8. Fast Parallel Absolute Irreducibility Testing

    Microsoft Academic Search

    Erich Kaltofen

    1985-01-01

    e present a fast parallel deterministic algorithm for testing multivariate integral polyno- - c mials for absolute irreducibility, that is irreducibility over the complex numbers. More pre isely, we establish that the set of absolutely irreducible integral polynomials belongs to the e i complexity class NC of Boolean circuits of polynomial size and logarithmic depth. Therefor t also belongs to

  9. 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 the distance-corrected S-wave spectra. Typically, removing the S-wave source spectrum is difficult because of inadequate corrections for the source radiation pattern, directivity and random interference. In addition to complexities near the source, 2-D and 3-D structure beneath the recording site will result in an azimuth-dependent site effect. Since the direct wave only samples a narrow range in take-off and back-azimuth angles, multi-station averaging is needed to minimize the inherent scatter. To minimize these complicating effects, they apply the coda methodology outlined by Mayeda et al., (2003) to obtain stable moment-rate spectra. This methodology provides source amplitude and derived source spectra that are a factor of 3-to-4 times more stable than those derived from direct waves. Since the coda is commonly thought of as scattered energy that samples all ray parameters and back-azimuths, it is not very sensitive to the source radiation pattern and 3-D structure. This property makes it an excellent choice for use in obtaining average properties of the source, site and path effects in a region. Due to the characteristics of the techniques used in this study, all the inverted quantities are azimuthally averaged, since the aximuthal information is lost in the processing.

  10. A highly enantioselective benzothiepine synthesis

    PubMed

    Wang; Li; Huang; Lee; Reitz

    2000-05-01

    A highly enantioselective synthesis of benzothiepine 1a has been accomplished via an enantioenriched sulfoxide intermediate obtained by asymmetric oxidation with a chiral oxaziridine in 89:11 er. The key step is a thermodynamically controlled asymmetric cyclization reaction that produces two new stereogenic centers. The (4R,5R) isomer 1a was obtained in 98:2 er. PMID:10808444

  11. Absolute judgments of odor intensity

    Microsoft Academic Search

    Trygg Engen; Carl Pfaffmann

    1959-01-01

    Results obtained with the method of absolute judgment suggest that a relatively unpracticed S can identify correctly three levels of intensity of an odorant and that a well-practiced S can identify about four levels.

  12. 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.

  13. Development of chiral conducting polymers for asymmetric electrosynthesis

    Microsoft Academic Search

    Yingpit Pornputtkul

    2005-01-01

    This thesis describes novel synthetic routes and characterization of chiral conducting polymers based on aniline and substituted anilines that have potential applications in the areas of asymmetric electrosynthesis and chiral separations. Ionic liquids and novel chiral ionic liquids are used as novel electrolytes for the polymer synthesis and for improvement of the electrochemical stability of chiral polyaniline doped with (+)-10-

  14. Catalytic asymmetric oxidation of sulfide with titanium–mandelic acid complex: practical synthesis of ( S)-3-[1-(2-methylphenyl)imidazol-2-ylsulfinyl]propan-1-ol, the key intermediate of OPC29030

    Microsoft Academic Search

    Masato Matsugi; Norio Fukuda; Yasuaki Muguruma; Taizo Yamaguchi; Jun-ichi Minamikawa; Sei Otsuka

    2001-01-01

    An effective catalytic asymmetric oxidation of prochiral sulfide 1a to (S)-2a has been achieved by the use of chiral titanium–mandelic acid complex. The enantioselectivity was found to be not influenced by moisture, and moderate to high selectivity (76% ee) was obtained at room temperature (25°C). Thus a practical synthetic method for the platelet adhesion inhibitor, OPC-29030, was established utilising asymmetric

  15. Asymmetric passive dynamic walker.

    PubMed

    Honeycutt, Craig; Sushko, John; Reed, Kyle B

    2011-01-01

    The objective of this research is to better understand the dynamics of gait asymmetry in humans with central nervous system damage, such as stroke, by using a model of a passive dynamic walker (PDW). By changing the mass, mass location, knee location, and leg length of one leg while leaving the parameters of the other leg unchanged, we show that stable asymmetric walking patterns exist for PDW models. The asymmetric PDW model shows several stable walking patterns that have a single, double, and quadruple repeat pattern where the step lengths between the two legs differ by over 15%. This model will allow an analysis of the passive dynamics of walking separate from the cognitive control in asymmetric human walking to test different gait rehabilitation hypotheses. PMID:22275663

  16. Inductive asymmetric cell division

    PubMed Central

    Ishidate, Takao; Kim, Soyoung; Mello, Craig C; Shirayama, Masaki

    2013-01-01

    C. elegans, with its invariant cell lineage, provides a powerful model system in which to study signaling-dependent asymmetric cell division. The C. elegans ?-catenin-related protein, WRM-1, specifies endoderm at the 4-cell stage during the first cell signaling-induced asymmetric cell division of embryogenesis. During this interaction, Wnt signaling and the cell cycle regulator CDK-1 act together to induce the asymmetric cortical release of WRM-1 at prophase of the EMS cell cycle. Genetic studies suggest that release of WRM-1 unmasks a cortical site that drives EMS spindle rotation onto the polarized axis of the cell, simultaneously making WRM-1 available for nuclear translocation, and downstream signaling to specify endoderm. These studies suggest a general paradigm for how cortical factors like WRM-1 can function at the cell cortex to mask potentially confounding polarity cues, and when released with appropriate cell cycle timing, can also function downstream to define cell fate. PMID:24524013

  17. Asymmetrical field emitter

    DOEpatents

    Fleming, James G. (Albuquerque, NM); Smith, Bradley K. (Albuquerque, NM)

    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. Asymmetric spindle positioning.

    PubMed

    McCarthy, Erin K; Goldstein, Bob

    2006-02-01

    When a spindle is positioned asymmetrically in a dividing cell, the resulting daughter cells are unequal in size. Asymmetric spindle positioning is driven by regulated forces that can pull or push a spindle. The physical and molecular mechanisms that can position spindles asymmetrically have been studied in several systems, and some themes have begun to emerge from recent research. Recent work in budding yeast has presented a model for how cytoskeletal motors and cortical capture molecules can function in orienting and positioning a spindle. The temporal regulation of microtubule-based pulling forces that move a spindle has been examined in one animal system. Although the spindle positioning force generators have not been identified in most animal systems, the forces have been found to be regulated by both PAR polarity proteins and G-protein signaling pathways in more than one animal system. PMID:16361093

  19. Absolute configuration of naturally occurring glabridin

    PubMed Central

    Simmler, Charlotte; Fronczek, Frank R.; Pauli, Guido F.; Santarsiero, Bernard D.

    2013-01-01

    The title compound {systematic name: 4-[(3R)-8,8-dimethyl-3,4-di­hydro-2H-pyrano[2,3-f]chromen-3-yl]benzene-1,3-diol, commonly named glabridin}, C20H20O4, is a species-specific biomarker from the roots Glycyrrhiza glabra L. (European licorice, Fabaceae). In the present study, this prenylated isoflavan has been purified from an enriched CHCl3 fraction of the extract of the root, using three steps of medium-pressure liquid chromatography (MPLC) by employing HW-40F, Sephadex LH-20 and LiChroCN as adsorbents. Pure glabridin was crystallized from an MeOH–H2O mixture (95:5?v/v) to yield colorless crystals containing one mol­ecule per asymmetric unit (Z? = 1) in the space group P212121. Although the crystal structure has been reported before, the determination of the absolute configuration remained uncertain. Stereochemical analysis, including circular dichroism, NMR data and an X-ray diffraction data set with Bijvoet differences, confirms that glabridin, purified from its natural source, is found only in a C3 R configuration. These results can therefore be used as a reference for the assignment of the configuration and enantio­purity of any isolated or synthetic glabridin sample. PMID:24192160

  20. Asymmetric ion trap

    DOEpatents

    Barlow, Stephan E. (Richland, WA); Alexander, Michael L. (Richland, WA); Follansbee, James C. (Pasco, WA)

    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.

  1. 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.

  2. Advances in the Catalytic, Asymmetric Synthesis of

    E-print Network

    Lectka, Thomas

    Fleming's landmark 1929 discov- ery of penicillin.2 The resulting recognition of the -lactam moiety years after its initial discovery, penicillin and its derivatives are still the most commonly used rates are often so high using this process that it was necessary for us to first break the reaction

  3. Errordifference Asymmetrical face perception

    E-print Network

    -6 -4 -2 0 2 4 6 8 right VF Asymmetrical face perception with in-depth rotated faces A Normal Faces RESULTS3 Burt &Perrett (1997) showed that subject's judgment of gender, age and expression were more influenced by the left than by the right side of the face (viewer's perspective). Also

  4. Against "Absolutely Everything"! Georey Hellman

    E-print Network

    Hellman, Geoffrey

    - ence and cannot be made sense of. This avoids the trap of sayi, even make sense? How could one possibly doubt it? According to Lewis [1991, 68], the skeptical position-constructively a¢ rm) existence, and can one ultimately avoid falling back on absolutely unrestricted quanti

  5. 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.-

  6. Feinberg on Absolute Legal Rights

    ERIC Educational Resources Information Center

    James, Gene G.

    1976-01-01

    Although the author wished that there were absolute rights, as Joel Feinberg has argued there are, he presented an argument to the contrary. Among the points he attempted to establish was that there is no hard and fast distinction between legal rights and legal privileges as Feinberg has maintained. (Author/RK)

  7. Enantioselective Total Synthesis of (?)-Jiadifenolide**

    PubMed Central

    Xu, Jing; Trzoss, Lynnie; Chang, Weng K.; Theodorakis, Emmanuel. A.

    2011-01-01

    The first total synthesis of jiadifenolide (1), a potent neurotrophic modulator, has been reported. Highlights of the synthesis include: construction of the B ring via an asymmetric Robinson annulation; assembly of the E ring lactone via a novel acid-induced cascade reaction; and Pd(0)-mediated carbomethoxylation and methylation reactions for the construction of the C and A rings respectively. PMID:21400650

  8. Asymmetric dipolar ring

    DOEpatents

    Prosandeev, Sergey A. (Fayetteville, AR); Ponomareva, Inna V. (Tampa, FL); Kornev, Igor A. (Ill-de-France, FR); Bellaiche, Laurent M. (Fayetteville, AR)

    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.

  9. 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.

  10. Oscillating asymmetric dark matter

    SciTech Connect

    Tulin, Sean; Yu, Hai-Bo; Zurek, Kathryn M., E-mail: tulin@umich.edu, E-mail: haiboyu@umich.edu, E-mail: kzurek@umich.edu [Michigan Center for Theoretical Physics, Department of Physics, University of Michigan, Ann Arbor, MI, 48109 (United States)

    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.

  11. Asymmetric Catalysis on Sequentially-Linked Columns Ahmed M. Hafez, Andrew E. Taggi, Travis Dudding, and Thomas Lectka*

    E-print Network

    Lectka, Thomas

    stoichiometric reagents that convert precursors into substrates for the catalytic, asym- metric reaction. Column Charles Street, Baltimore, Maryland 21218 ReceiVed July 6, 2001 Abstract: We report a catalytic asymmetric of a series of "reaction columns". This process was applied to the catalytic asymmetric synthesis of -lactams

  12. 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.

  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. Total Synthesis of (?)-Mucocin

    PubMed Central

    Crimmins, Michael T.; Zhang, Yan; Diaz, Frank A.

    2008-01-01

    An enantioselective total synthesis of (?)-mucocin has been completed. A combination of asymmetric glycolate aldol additions and ring closing metathesis reactions were exploited to construct the C18-C34 and C7-C17 fragments. A selective cross metathesis reaction was employed as the key step to couple two complex fragments. PMID:16706528

  15. Total synthesis of (-)-mucocin.

    PubMed

    Crimmins, Michael T; Zhang, Yan; Diaz, Frank A

    2006-05-25

    [reaction: see text] An enantioselective total synthesis of (-)-mucocin has been completed. A combination of asymmetric glycolate aldol additions and ring closing metathesis reactions were exploited to construct the C18-C34 and C7-C17 fragments. A selective cross-metathesis reaction was employed as the key step to couple two complex fragments. PMID:16706528

  16. Enantioselective synthesis of ( S)-dapoxetine

    Microsoft Academic Search

    Shafi A. Siddiqui; Kumar V. Srinivasan

    2007-01-01

    An efficient enantioselective synthesis leading directly to (+)-(S)-dapoxetine has been described for the first time using a Sharpless asymmetric dihydroxylation, Barton–McCombie deoxygention, and Mitsunobu reaction as the key steps.

  17. A Formal Total Synthesis of (?)-Brevisamide

    PubMed Central

    Smith, Amos B.; Kutsumura, Noriki; Potuzak, Justin

    2011-01-01

    A formal total synthesis of (?)-brevisamide has been achieved. The synthetic approach highlights a chemoselective asymmetric dihydroxylation and a one-pot Fraser-Reid epoxidation/PMB protection reaction sequence. PMID:21572531

  18. Electronic effects in asymmetric hydroboration

    Microsoft Academic Search

    Charles M. Garner; Shirley Chiang; Matthew Nething; Robert Monestel

    2002-01-01

    To determine whether electronic effects are operative in asymmetric hydroboration, a series of para-substituted 2-aryl-1-propenes were prepared and reacted with four asymmetric borane reagents. A significant correlation between the electronic nature of the para-substituent and the degree of asymmetric induction was observed only for a chloroborane–ether complex, not for any of several simple alkylboranes. A quantitative analysis of the relative

  19. Asymmetric substitution masking Jiang & Chun1 Running title: Asymmetric substitution masking

    E-print Network

    Chun, Marvin M.

    Asymmetric substitution masking Jiang & Chun1 Running title: Asymmetric substitution masking Asymmetric object substitution masking Yuhong Jiang Marvin M. Chun Yale University Vanderbilt University. 232 Fax: (203)-624-4950 #12;Asymmetric substitution masking Jiang & Chun2 Abstract Object substitution

  20. Bias in Absolute Magnitude Determination from Parallaxes

    E-print Network

    Michael Feast

    2002-08-29

    Relations are given for the correction of bias when mean absolute magnitudes are derived by the method of reduced parallaxes. The bias in the case of the derivation of the absolute magnitudes of individual objects is also considered.

  1. SpinPhox/iridium(I)-catalyzed asymmetric hydrogenation of cyclic ?-alkylidene carbonyl compounds.

    PubMed

    Liu, Xu; Han, Zhaobin; Wang, Zheng; Ding, Kuiling

    2014-02-10

    Optically active medium-sized cyclic carbonyl compounds bearing an ?-chiral carbon center are of interest in pharmaceutical sciences and asymmetric synthesis. Herein, SpinPhox/Ir(I) catalysts have been demonstrated to be highly enantioselective in the asymmetric hydrogenation of the C?C bonds in the exocyclic ?,?-unsaturated cyclic carbonyls, including a broad range of ?-alkylidene lactams, unsaturated cyclic ketones, and lactones. It is noteworthy that the procedure can be successfully used in the asymmetric hydrogenation of the challenging ?-alkylidenelactam substrates with six- or seven-membered rings, thus affording the corresponding optically active carbonyl compounds with an ?-chiral carbon center in generally excellent enantiomeric excesses (up to 98?%?ee). Synthetic utility of the protocol has also been demonstrated in the asymmetric synthesis of the anti-inflammatory drug loxoprofen and its analogue, as well as biologically important ?-aminocaproic acid derivatives. PMID:24446418

  2. Astronomy Ranking Task: Apparent and Absolute Magnitude

    E-print Network

    Farritor, Shane

    Astronomy Ranking Task: Apparent and Absolute Magnitude Exercise #3 Description: The figure below shows five stars (A - E) as they appear in the night sky from Earth. The absolute magnitude number: ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ D. Ranking Instructions: Rank the absolute magnitude number (from greatest to least) of each star (A

  3. What is wrong with absolute individual fitness?

    E-print Network

    Wilson, David. S.

    What is wrong with absolute individual fitness? David Sloan Wilson Departments of Biology is that fit- ness is a relative concept. It does not matter how well an organism survives and reproduces, only arguments are framed in terms of absolute individual fitness. The absolute fitness criterion (AFC) can

  4. Compressor performance, absolutely! M. R. Titchener

    E-print Network

    Titchener, Mark R.

    Compressor performance, absolutely! M. R. Titchener Dept of CS, U. of Auck., N.Z. (Email: mark the absolute performance of existing string compressors may be measured. Kolmogorov (1958) recognised://tcode.auckland.ac.nz/~corpus has been used to evaluate the `absolute' performance of a series of popular compressors. The results

  5. Colon Cryptogenesis: Asymmetric Budding

    PubMed Central

    Tan, Chin Wee; Hirokawa, Yumiko; Gardiner, Bruce S.; Smith, David W.; Burgess, Antony W.

    2013-01-01

    The process of crypt formation and the roles of Wnt and cell-cell adhesion signaling in cryptogenesis are not well described; but are important to the understanding of both normal and cancer colon crypt biology. A quantitative 3D-microscopy and image analysis technique is used to study the frequency, morphology and molecular topography associated with crypt formation. Measurements along the colon reveal the details of crypt formation and some key underlying biochemical signals regulating normal colon biology. Our measurements revealed an asymmetrical crypt budding process, contrary to the previously reported symmetrical fission of crypts. 3D immunofluorescence analyses reveals heterogeneity in the subcellular distribution of E-cadherin and ?-catenin in distinct crypt populations. This heterogeneity was also found in asymmetrical budding crypts. Singular crypt formation (i.e. no multiple new crypts forming from one parent crypt) were observed in crypts isolated from the normal colon mucosa, suggestive of a singular constraint mechanism to prevent aberrant crypt production. The technique presented improves our understanding of cryptogenesis and suggests that excess colon crypt formation occurs when Wnt signaling is perturbed (e.g. by truncation of adenomatous polyposis coli, APC protein) in most colon cancers. PMID:24205248

  6. Asymmetric inclusion process

    NASA Astrophysics Data System (ADS)

    Reuveni, Shlomi; Eliazar, Iddo; Yechiali, Uri

    2011-10-01

    We introduce and explore the asymmetric inclusion process (ASIP), an exactly solvable bosonic counterpart of the fermionic asymmetric exclusion process (ASEP). In both processes, random events cause particles to propagate unidirectionally along a one-dimensional lattice of n sites. In the ASEP, particles are subject to exclusion interactions, whereas in the ASIP, particles are subject to inclusion interactions that coalesce them into inseparable clusters. We study the dynamics of the ASIP, derive evolution equations for the mean and probability generating function (PGF) of the sites’ occupancy vector, obtain explicit results for the above mean at steady state, and describe an iterative scheme for the computation of the PGF at steady state. We further obtain explicit results for the load distribution in steady state, with the load being the total number of particles present in all lattice sites. Finally, we address the problem of load optimization, and solve it under various criteria. The ASIP model establishes bridges between statistical physics and queueing theory as it represents a tandem array of queueing systems with (unlimited) batch service, and a tandem array of growth-collapse processes.

  7. Colon cryptogenesis: asymmetric budding.

    PubMed

    Tan, Chin Wee; Hirokawa, Yumiko; Gardiner, Bruce S; Smith, David W; Burgess, Antony W

    2013-01-01

    The process of crypt formation and the roles of Wnt and cell-cell adhesion signaling in cryptogenesis are not well described; but are important to the understanding of both normal and cancer colon crypt biology. A quantitative 3D-microscopy and image analysis technique is used to study the frequency, morphology and molecular topography associated with crypt formation. Measurements along the colon reveal the details of crypt formation and some key underlying biochemical signals regulating normal colon biology. Our measurements revealed an asymmetrical crypt budding process, contrary to the previously reported symmetrical fission of crypts. 3D immunofluorescence analyses reveals heterogeneity in the subcellular distribution of E-cadherin and ?-catenin in distinct crypt populations. This heterogeneity was also found in asymmetrical budding crypts. Singular crypt formation (i.e. no multiple new crypts forming from one parent crypt) were observed in crypts isolated from the normal colon mucosa, suggestive of a singular constraint mechanism to prevent aberrant crypt production. The technique presented improves our understanding of cryptogenesis and suggests that excess colon crypt formation occurs when Wnt signaling is perturbed (e.g. by truncation of adenomatous polyposis coli, APC protein) in most colon cancers. PMID:24205248

  8. 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. [LPO-COPEA and Instituto de Fisica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, 21941-590 (Brazil); Departamento de Fisica, Instituto de Ciencias ExatasUniversidade Federal de Minas Gerais, Belo Horizonte, MG, 30123-970 (Brazil)

    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.

  9. [Asymmetric syntheses of azacycloalkanes by one-pot [1+2+n] cyclization].

    PubMed

    Harada, Shingo

    2013-01-01

    Enantio- and diastereoselective one-pot synthesis of three- to seven-membered cis-azaheterocycles was achieved using a triggered asymmetric conjugate addition reaction of lithium amide with an enoate, followed by C- and N-alkylation of the resulting lithium 3-aminoenolate with ?, ?-dihaloalkane, which can be regarded as a [1+2+n] cyclization. The usefulness of the developed methodology was clearly demonstrated by the short-step asymmetric syntheses of azirinomycin ester, nemonapride, and kopsinine. PMID:23995805

  10. 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.

  11. Asymmetric photoredox transition-metal catalysis activated by visible light.

    PubMed

    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. PMID:25373679

  12. 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.

  13. Absolute MR thermometry using nanocarriers.

    PubMed

    Deckers, Roel; Sprinkhuizen, Sara M; Crielaard, Bart J; Ippel, Johannes H; Boelens, Rolf; Bakker, Chris J G; Storm, Gert; Lammers, Twan; Bartels, Lambertus W

    2014-01-01

    Accurate time-resolved temperature mapping is crucial for the safe use of hyperthermia-mediated drug delivery. We here propose a magnetic resonance imaging temperature mapping method in which drug delivery systems serve not only to improve tumor targeting, but also as an accurate and absolute nano-thermometer. This method is based on the temperature-dependent chemical shift difference between water protons and the protons in different groups of drug delivery systems. We show that the chemical shift of the protons in the ethylene oxide group in polyethylene glycol (PEG) is temperature-independent, whereas the proton resonance of water decreases with increasing temperature. The frequency difference between both resonances is linear and does not depend on pH and physiological salt conditions. In addition, we show that the proton resonance of the methyl group in N-(2-hydroxypropyl)-methacrylamide (HPMA) is temperature-independent. Therefore, PEGylated liposomes, polymeric mPEG-b-pHPMAm-Lac2 micelles and HPMA copolymers can provide a temperature-independent reference frequency for absolute magnetic resonance (MR) thermometry. Subsequently, we show that multigradient echo MR imaging with PEGylated liposomes in situ allows accurate, time-resolved temperature mapping. In conclusion, nanocarrier materials may serve as highly versatile tools for tumor-targeted drug delivery, acting not only as hyperthermia-responsive drug delivery systems, but also as accurate and precise nano-thermometers. PMID:24706612

  14. Synthesis of 3,8-Dichloro-6-ethyl-1,2,5,7-tetramethyl-BODIPY from an Asymmetric Dipyrroketone and Reactivity Studies at the 3,5,8-Positions.

    PubMed

    Zhao, Ning; Vicente, M Graça H; Fronczek, Frank R; Smith, Kevin M

    2015-04-13

    The asymmetric BODIPY 1?a (BODIPY=4,4-difluoro-4-bora-3a,4a-diaza-s-indacene), containing two chloro substituents at the 3,8-positions and a reactive 5-methyl group, was synthesized from the asymmetric dipyrroketone 3, which was readily obtained from available pyrrole 2?a. The reactivity of 3,8-dichloro-6-ethyl-1,2,5,7-tetramethyl-BODIPY 1?a was investigated by using four types of reactions. This versatile BODIPY undergoes regioselective Pd(0) -catalyzed Stille coupling reactions and/or regioselective nucleophilic addition/elimination reactions, first at the 8-chloro and then at the 3-chloro group, using a variety of organostannanes and N-, O-, and S-centered nucleophiles. On the other hand, the more reactive 5-methyl group undergoes regioselective Knoevenagel condensation with an aryl aldehyde to produce a monostyryl-BODIPY, and oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) gives the corresponding 5-formyl-BODIPY. Investigation of the reactivity of asymmetric BODIPY 1?a led to the preparation of a variety of functionalized BODIPYs with ?max of absorption and emission in the ranges 487-587 and 521-617?nm, respectively. The longest absorbing/emitting compound was the monostyryl-BODIPY 16, and the largest Stokes shift (49?nm) and fluorescence quantum yield (0.94) were measured for 5-thienyl-8-phenoxy-BODIPY 15. The structural properties (including 16 X-ray structures) of the new series of BODIPYs were investigated. PMID:25761150

  15. Minimal Asymmetric Dark Matter

    E-print Network

    Sofiane M. Boucenna; Martin B. Krauss; Enrico Nardi

    2015-03-23

    In the early Universe, any particle carrying a conserved quantum number and in chemical equilibrium with the thermal bath will unavoidably inherit a particle-antiparticle asymmetry. A new particle of this type, if stable, would represent a candidate for asymmetric dark matter (DM) with an asymmetry directly related to the baryon asymmetry. We study this possibility for a minimal DM sector constituted by just one (generic) $SU(2)_L$ multiplet $\\chi$ carrying hypercharge, assuming that at temperatures above the electroweak phase transition an effective operator enforces chemical equilibrium between $\\chi$ and the Higgs boson. We argue that limits from DM direct detection searches severely constrain this scenario, leaving as the only possibilities scalar or fermion multiplets with hypercharge $y = 1/2$ and $y = 1$, preferentially in large $SU(2)$ representations, and with a mass in the few TeV range.

  16. Minimal Asymmetric Dark Matter

    E-print Network

    Boucenna, Sofiane M; Nardi, Enrico

    2015-01-01

    In the early Universe, any particle carrying a conserved quantum number and in chemical equilibrium with the thermal bath will unavoidably inherit a particle-antiparticle asymmetry. A new particle of this type, if stable, would represent a candidate for asymmetric dark matter (DM) with an asymmetry directly related to the baryon asymmetry. We study this possibility for a minimal DM sector constituted by just one (generic) $SU(2)_L$ multiplet $\\chi$ carrying hypercharge, assuming that at temperatures above the electroweak phase transition an effective operator enforces chemical equilibrium between $\\chi$ and the Higgs boson. We argue that limits from DM direct detection searches severely constrain this scenario, ruling out the possibility of scalar multiplets, and leaving as the only possibilities fermion DM with hypercharge $y = 1/2$ and $y = 1$ with a mass in the few TeV range.

  17. Annihilating asymmetric dark matter

    NASA Astrophysics Data System (ADS)

    Bell, Nicole F.; Horiuchi, Shunsaku; Shoemaker, Ian M.

    2015-01-01

    The relic abundance of particle and antiparticle dark matter (DM) need not be vastly different in thermal asymmetric dark matter (ADM) models. By considering the effect of a primordial asymmetry on the thermal Boltzmann evolution of coupled DM and anti-DM, we derive the requisite annihilation cross section. This is used in conjunction with cosmic microwave background and Fermi-LAT gamma-ray data to impose a limit on the number density of anti-DM particles surviving thermal freeze-out. When the extended gamma-ray emission from the Galactic Center is reanalyzed in a thermal ADM framework, we find that annihilation into ? leptons prefer anti-DM number densities 1%-4% that of DM while the b -quark channel prefers 50%-100%.

  18. Highly enantioselective synthesis of 2,3-dihydro-1H-imidazo[2,1-a]isoindol-5(9bH)-ones via catalytic asymmetric intramolecular cascade imidization-nucleophilic addition-lactamization.

    PubMed

    He, Yuwei; Cheng, Chuyu; Chen, Bin; Duan, Kun; Zhuang, Yue; Yuan, Bo; Zhang, Meisan; Zhou, Yougui; Zhou, Zihong; Su, Yu-Jun; Cao, Rihui; Qiu, Liqin

    2014-12-19

    Highly enantioselective catalytic asymmetric intramolecular cascade imidization-nucleophilic addition-lactamization of N(1)-alkylethane-1,2-diamine with methyl 2-formylbenzoate catalyzed by a chiral phosphoric acid represents the first efficient method for the preparation of medicinally interesting chiral 2,3-dihydro-1H-imidazo[2,1-a]isoindol-5(9bH)-ones with high yields and excellent enantioselectivities. This strategy has been shown to be quite general toward various methyl 2-formylbenzoates. PMID:25468078

  19. Frequency spectra of absolute optical instruments

    NASA Astrophysics Data System (ADS)

    Tyc, Tomáš; Danner, Aaron

    2012-08-01

    We analyse frequency spectra of absolute optical instruments and show that they have very specific properties: the eigenfrequencies form tight groups that are almost equidistantly spaced. We prove this by theoretical analysis and demonstrate by numerically calculated spectra of various examples of absolute instruments. We also show that in rotationally and spherically symmetric absolute instruments a source, its image and the centre of the device must lie on a straight line.

  20. A vector asymmetrical NNV equation

    NASA Astrophysics Data System (ADS)

    Yu, Guo-Fu; Tam, Hon-Wah

    2008-08-01

    A vector asymmetrical Nizhnik-Novikov-Veselov (NNV) equation is proposed based on its bilinear form. Soliton solutions expressed by Pfaffians are obtained. Bilinear Bäcklund transformation and the corresponding Lax pair for the vector ANNV equation are derived.

  1. Asymmetric bifurcated halogen bonds.

    PubMed

    Novák, Martin; Foroutan-Nejad, Cina; Marek, Radek

    2015-03-01

    Halogen bonding (XB) is being extensively explored for its potential use in advanced materials and drug design. Despite significant progress in describing this interaction by theoretical and experimental methods, the chemical nature remains somewhat elusive, and it seems to vary with the selected system. In this work we present a detailed DFT analysis of three-center asymmetric halogen bond (XB) formed between dihalogen molecules and variously 4-substituted 1,2-dimethoxybenzene. The energy decomposition, orbital, and electron density analyses suggest that the contribution of electrostatic stabilization is comparable with that of non-electrostatic factors. Both terms increase parallel with increasing negative charge of the electron donor molecule in our model systems. Depending on the orientation of the dihalogen molecules, this bifurcated interaction may be classified as '?-hole - lone pair' or '?-hole - ?' halogen bonds. Arrangement of the XB investigated here deviates significantly from a recent IUPAC definition of XB and, in analogy to the hydrogen bonding, the term bifurcated halogen bond (BXB) seems to be appropriate for this type of interaction. PMID:25656525

  2. Oscillating Asymmetric Dark Matter

    E-print Network

    Sean Tulin; Hai-Bo Yu; Kathryn M. Zurek

    2012-02-13

    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. 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, or annihilation to pairs of bosons. 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.

  3. Asymmetric Bessel modes.

    PubMed

    Kotlyar, V V; Kovalev, A A; Soifer, V A

    2014-04-15

    We propose a new, three-parameter family of diffraction-free asymmetric elegant Bessel modes (aB-modes) with an integer and fractional orbital angular momentum (OAM). The aB-modes are described by the nth-order Bessel function of the first kind with complex argument. The asymmetry degree of the nonparaxial aB-mode is shown to depend on a real parameter c?0: when c=0, the aB-mode is identical to a conventional radially symmetric Bessel mode; with increasing c, the aB-mode starts to acquire a crescent form, getting stretched along the vertical axis and shifted along the horizontal axis for c?1. On the horizontal axis, the aB-modes have a denumerable number of isolated intensity zeros that generate optical vortices with a unit topological charge of opposite sign on opposite sides of 0. At different values of the parameter c, the intensity zeros change their location on the horizontal axis, thus changing the beam's OAM. An isolated intensity zero on the optical axis generates an optical vortex with topological charge n. The OAM per photon of an aB-mode depends near-linearly on c, being equal to ?(n+cI1(2c)/I0(2c)), where ? is the Planck constant and In(x) is a modified Bessel function. PMID:24979002

  4. Synthesis and Suzuki-Miyaura Cross-Coupling of Enantioenriched Secondary Potassium ?-Trifluoroboratoamides: Catalytic, Asymmetric Conjugate Addition of Bisboronic Acid and Tetrakis(dimethylamino)diboron to ?,?-Unsaturated Carbonyl Compounds

    PubMed Central

    Wisniewski, Steven R.; Hosseini-Sarvari, Mona

    2014-01-01

    Enantioenriched potassium ?-trifluoroboratoamides have been synthesized via an asymmetric, copper-catalyzed 1,4-addition of tetrahydroxydiboron (BBA) and tetrakis(dimethylamino)diboron to ?,?-unsaturated amides. These dibora reagents provide access to the desired organotrifluoroborates using effective and atom economical sources of boron. The copper-catalyzed ?-boration is extended to ?,?-unsaturated ketones and esters. Desired potassium organotrifluoroborates are synthesized with yields up to 92% and enantiomeric ratios up to 98:2. The enantioenriched potassium ?-trifluoroboratoamides are successfully cross-coupled with an array of aryl and heteroaryl chlorides in high yield with complete stereochemical fidelity as the transmetalation proceeds through an SE2 mechanism via an open transition state. PMID:24741373

  5. Absolute instabilities of standing pulses

    NASA Astrophysics Data System (ADS)

    Sandstede, Björn; Scheel, Arnd

    2005-01-01

    We analyse instabilities of standing pulses in reaction-diffusion systems that are caused by an absolute instability of the homogeneous background state. Specifically, we investigate the impact of pitchfork, Turing and oscillatory bifurcations of the rest state on the standing pulse. At a pitchfork bifurcation, the standing pulse continues through the bifurcation point, where it selects precisely one of the two bifurcating equilibria. At a Turing instability, symmetric pulses emerge that are spatially asymptotic to the bifurcating spatially periodic Turing patterns. These pulses exist for any wavenumber inside the Eckhaus stability band. Oscillatory instabilities of the background state lead to genuinely time-periodic pulses that emit small wave trains with a unique selected wavenumber. We analyse these three bifurcations by studying the standing-wave and modulated-wave equations: in this setup, pulses correspond to homoclinic orbits to equilibria that undergo reversible bifurcations. We use blow-up techniques to show that the relevant stable and unstable manifolds can be continued across the bifurcation point and to investigate both the existence and stability of the bifurcating waves.

  6. Improving HST Pointing & Absolute Astrometry

    NASA Astrophysics Data System (ADS)

    Lallo, Matthew; Nelan, E.; Kimmer, E.; Cox, C.; Casertano, S.

    2007-05-01

    Accurate absolute astrometry is becoming increasingly important in an era of multi-mission archives and virtual observatories. Hubble Space Telescope's (HST's) Guidestar Catalog II (GSC2) has reduced coordinate error to around 0.25 arcsecond, a factor 2 or more compared with GSC1. With this reduced catalog error, special attention must be given to calibrate and maintain the Fine Guidance Sensors (FGSs) and Science Instruments (SIs) alignments in HST to a level well below this in order to ensure that the accuracy of science product's astrometry keywords and target positioning are limited only by the catalog errors. After HST Servicing Mission 4, such calibrations' improvement in "blind" pointing accuracy will allow for more efficient COS acquisitions. Multiple SIs and FGSs each have their own footprints in the spatially shared HST focal plane. It is the small changes over time in primarily the whole-body positions & orientations of these instruments & guiders relative to one another that is addressed by this work. We describe the HST Cycle 15 program CAL/OTA 11021 which, along with future variants of it, determines and maintains positions and orientations of the SIs and FGSs to better than 50 milli- arcseconds and 0.04 to 0.004 degrees of roll, putting errors associated with the alignment sufficiently below GSC2 errors. We present recent alignment results and assess their errors, illustrate trends, and describe where and how the observer sees benefit from these calibrations when using HST.

  7. 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…

  8. Astronomy Ranking Task: Apparent and Absolute Magnitude

    E-print Network

    Farritor, Shane

    Astronomy Ranking Task: Apparent and Absolute Magnitude Exercise #4 Description: The table below provides partial magnitude and distance information for five stars (A - E). Star Name Apparent Magnitude Absolute Magnitude Distance from Earth (parsecs) A -1 3 B 5 1 C 0 10 D 1 10,000 E 3 3 A. Ranking

  9. COMMUNICATIONS Determination of absolute photoionization cross sections

    E-print Network

    Neumark, Daniel M.

    product branching ratios in scattering experiments, absolute photo- ionization cross sections are requiredCOMMUNICATIONS Determination of absolute photoionization cross sections for vinyl and propargyl cross sections for vinyl and propargyl radicals at 10 eV of 11.1 2.2 and 8.3 1.6 Mb, respectively. From

  10. Frequency spectra of absolute optical instruments

    NASA Astrophysics Data System (ADS)

    Tyc, Tomáš; Danner, Aaron

    2012-09-01

    We analyze frequency spectra of optical devices called absolute optical instruments. We show that they have very specific properties: the eigenfrequencies form tight, almost equidistantly spaced groups. We prove this by theoretical analysis and demonstrate by numerically calculated spectra of various examples of absolute instruments.

  11. 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.

  12. 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. PMID:25801825

  13. Y2MoSe3O12 and Y2MoTe3O12: Solid-state synthesis, structure determination, and characterization of two new quaternary mixed metal oxides containing asymmetric coordination environment

    NASA Astrophysics Data System (ADS)

    Bang, Seong-eun; Pan, Zhi; Kim, Yeong Hun; Lee, Dong Woo; Ok, Kang Min

    2013-12-01

    Two new quaternary yttrium molybdenum selenium/tellurium oxides, Y2MoSe3O12 and Y2MoTe3O12 have been prepared by standard solid-state reactions using Y2O3, MoO3, and SeO2 (or TeO2) as reagents. Single-crystal X-ray diffraction was used to determine the crystal structures of the reported materials. Although both of the materials contain second-order Jahn-Teller (SOJT) distortive cations and are stoichiometrically similar, they reveal different structural features: while Y2MoSe3O12 shows a three-dimensional framework consisting of YO8, MoO6, and SeO3 groups, Y2MoTe3O12 exhibits a layered structure composed of YO8, MoO4, TeO3, and TeO4 polyhedra. With the Mo6+ cations in Y2MoSe3O12, a C3-type intraoctahedral distortion toward a face is observed, in which the direction of the out-of-center distortion for Mo6+ is away from the oxide ligand linked to a Se4+ cation. The Se4+ and Te4+ cations in both materials are in asymmetric coordination environment attributed to the lone pairs. Elemental analyses, infrared spectroscopy, thermal analyses, intraoctahedral distortions, and dipole moment calculations for the compounds are also presented.

  14. A Facile Stereoselective Total Synthesis of (R)-Rugulactone

    PubMed Central

    Reddy, B. Narasimha; Singh, R. P.

    2014-01-01

    An efficient and novel synthesis of (R)-rugulactone has been achieved employing Sharpless asymmetric epoxidation of allyl alcohols followed by selective hydride reduction of epoxy alcohols and olefin cross metathesis reactions. PMID:24971179

  15. Formal total synthesis of borrelidin: synthesis of C1–C11 fragment via desymmetrization strategy

    Microsoft Academic Search

    J. S. Yadav; Padmavani Bezawada; Venugopal Chenna

    2009-01-01

    A stereoselective formal total synthesis of borrelidin is described. The synthetic strategy for synthesis of C1–C11 fragment features desymmetrization of Diels–Alder adduct, Sharpless asymmetric epoxidation, regioselective opening of chiral epoxide, and alkylation using Evans chiral auxiliary.

  16. Synthesis of (-)-Hamigeran B Douglass F. Taber* and Weiwei Tian

    E-print Network

    Taber, Douglass

    and polio viruses at low concentration and with only slight cytotoxicity. A central concern in the total reported an asymmetric synthesis utilizing a [4 + 2] photocy- cloaddition. This route started from installed the quaternary stereogenic center by Pd-catalyzed asymmetric allylic alkylation of a preformed

  17. Secondary standard stars for absolute spectrophotometry

    NASA Technical Reports Server (NTRS)

    Oke, J. B.; Gunn, J. E.

    1983-01-01

    Based on an adopted absolute spectral energy distribution for the primary standard star Alpha Lyrae, absolute fluxes are given for the four very metal-deficient F type subdwarfs HD 19445, HD 84937, BD + 26.2606 deg, and BD + 17.4703 deg. Somewhat inferior data are also given for HD 140283. The data are given for 40-A bands and cover the wavelength range from 3080 A to 12,000 A. The four stars, all near magnitude 9 and distributed around the sky, are intended as secondary standards for absolute spectrophotometry.

  18. Experimental and computational study of the catalytic asymmetric 4?-electrocyclization of N-heterocycles.

    PubMed

    Raja, Sadiya; Nakajima, Masaki; Rueping, Magnus

    2015-02-23

    The first asymmetric metal-catalyzed Nazarov cyclization of N-heterocycles has been developed. The use of a chiral catalyst allows the enantioselective electrocyclization of N-heterocycles under mild conditions and the corresponding products are obtained in good yields with excellent enantio- and diastereoselectivity. The reaction mechanism and the absolute configuration of the obtained products are explained by means of computational studies. PMID:25533025

  19. Total synthesis of (-)-ophiodilactone A and (-)-ophiodilactone B.

    PubMed

    Matsubara, Takaaki; Takahashi, Keisuke; Ishihara, Jun; Hatakeyama, Susumi

    2014-01-13

    The first asymmetric total synthesis of (-)-ophiodilactone A and (-)-ophiodilactone B, isolated from the ophiuroid (Ophiocoma scolopendrina), is reported. The key features of the synthesis include the highly stereocontrolled construction of the structurally congested ?-lactone/?-lactone skeleton through an asymmetric epoxidation, diastereoselective iodolactonization, and intramolecular epoxide-opening with a carboxylic acid, and biomimetic radical cyclization of ophiodilactone A to ophiodilactone B. PMID:24339128

  20. Synthesis, characterization and X-ray crystal structures of Vanadium(IV), Cobalt(III), Copper(II) and Zinc(II) complexes derived from an asymmetric bidentate Schiff-base ligand at ambient temperature

    NASA Astrophysics Data System (ADS)

    Khorshidifard, Mahsa; Amiri Rudbari, Hadi; Kazemi-Delikani, Zahra; Mirkhani, Valiollah; Azadbakht, Reza

    2015-02-01

    An asymmetric bidentate Schiff-base ligand (HL: 2-((allylimino)methyl)phenol) was prepared from reaction of salicylaldehyde and Allylamine. Vanadium(IV), Cobalt(III), Copper(II) and Zinc(II) complexes, VOL2, CoL3, CuL2 and ZnL2 were synthesized from the reaction of VO(acac)2, CoCl2·6H2O, CuCl2·2H2O and Zn(NO3)2·6H2O with the bidentate Schiff base ligand (HL: 2-allyliminomethyl-phenol) in methanol at ambient temperature. The ligand and its metal complexes were characterized by elemental analysis (CHN), FT-IR spectroscopy. In addition, 1H and 13C NMR techniques were employed for characterization of the ligand (HL) and diamagnetic complex ZnL2. The molecular structures of all complexes were determined by single crystal X-ray diffraction technique. In the ZnL2 and CuL2 complexes, the metal ion is coordinated by two nitrogen and two oxygen atoms from two Schiff base ligands in an approximately square planar trans-[MN2O2] coordination geometry. In the Vanadium(IV) complex, VOL2, the vanadium center in this structure has a distorted tetragonal pyramidal N2O3 coordination sphere and for Cobalt(III) complex, CoL3, the CoIII ion is six coordinated by three bidentate Schiff base ligands in a distorted octahedral environment.

  1. 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 ?-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 (?1-blocker) and (S)-Propranolol (?-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. PMID:23899243

  2. Recent progress in asymmetric fluorination and trifluoromethylation reactions.

    PubMed

    Bizet, Vincent; Besset, Tatiana; Ma, Jun-An; Cahard, Dominique

    2014-01-01

    All domains of society are impacted by fluorine chemistry. In particular, fluorine plays a key role in medicinal, pharmaceutical and agrochemical sciences in which the synthesis and evaluation of molecules featuring one or more fluorine atoms is nowadays routine in every new discovery and development program. Since the beginning of this century, enantiopure fluorinated molecules are at the forefront of innovation of the tremendous achievements in fluorine chemistry. This review introduces the reader to the recent progress in asymmetric installation of one fluorine and a trifluoromethyl group via nucleophilic, electrophilic and radical diastereo- and enantioselective reactions. PMID:24484424

  3. 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

  4. 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)

  5. New absolute magnitude calibrations for detached binaries

    E-print Network

    S. Bilir; T. Ak; E. Soydugan; F. Soydugan; E. Yaz; N. Filiz Ak; Z. Eker; O. Demircan; M. Helvaci

    2008-06-07

    Lutz-Kelker bias corrected absolute magnitude calibrations for the detached binary systems with main-sequence components are presented. The absolute magnitudes of the calibrator stars were derived at intrinsic colours of Johnson-Cousins and 2MASS (Two Micron All Sky Survey) photometric systems. As for the calibrator stars, 44 detached binaries were selected from the Hipparcos catalogue, which have relative observed parallax errors smaller than 15% ($\\sigma_{\\pi}/\\pi\\leq0.15$). The calibration equations which provide the corrected absolute magnitude for optical and near-infrared pass bands are valid for wide ranges of colours and absolute magnitudes: $-0.18magnitude calibrations of this study can be used as a convenient statistical tool to estimate the true distances of detached binaries out of Hipparcos' distance limit.

  6. Absolute colorimetric characterization of a DSLR camera

    NASA Astrophysics Data System (ADS)

    Guarnera, Giuseppe Claudio; Bianco, Simone; Schettini, Raimondo

    2014-03-01

    A simple but effective technique for absolute colorimetric camera characterization is proposed. It offers a large dynamic range requiring just a single, off-the-shelf target and a commonly available controllable light source for the characterization. The characterization task is broken down in two modules, respectively devoted to absolute luminance estimation and to colorimetric characterization matrix estimation. The characterized camera can be effectively used as a tele-colorimeter, giving an absolute estimation of the XYZ data in cd=m2. The user is only required to vary the f - number of the camera lens or the exposure time t, to better exploit the sensor dynamic range. The estimated absolute tristimulus values closely match the values measured by a professional spectro-radiometer.

  7. The absolute magnitudes of Type IA supernovae

    Microsoft Academic Search

    M. M. Phillips

    1993-01-01

    Absolute magnitudes in the B, V, and I bands are derived for nine well-observed Type Ia supernovae, using host galaxy distances estimated via the surface brightness fluctuations or Tully-Fisher methods. These data indicate that there is a significant intrinsic dispersion in the absolute magnitudes at maximum light of Type Ia supernovae, amounting to +\\/- 0.8 mag in B, +\\/- 0.6

  8. Absolute calibration of imaging atmospheric Cherenkov telescopes

    E-print Network

    N. Shepherd; J. H. Buckley; O. Celik; J. Holder; S. LeBohec; H. Manseri; F. Pizlo; M. Roberts

    2005-07-04

    A calibrated laser pulse propagating through the atmosphere produces a flash of Rayleigh scattered light with an intensity that can be calculated very accurately when atmospheric conditions are good. This is used in a technique developed for the absolute calibration of ultra high energy cosmic ray fluorescence telescopes, and it can also be applied to imaging atmospheric Cherenkov telescopes (IACTs). In this paper we present the absolute calibration system being constructed and tested for the VERITAS project.

  9. Absolute and relative quantification of RNA modifications via biosynthetic isotopomers

    PubMed Central

    Kellner, Stefanie; Ochel, Antonia; Thüring, Kathrin; Spenkuch, Felix; Neumann, Jennifer; Sharma, Sunny; Entian, Karl-Dieter; Schneider, Dirk; Helm, Mark

    2014-01-01

    In the resurging field of RNA modifications, quantification is a bottleneck blocking many exciting avenues. With currently over 150 known nucleoside alterations, detection and quantification methods must encompass multiple modifications for a comprehensive profile. LC–MS/MS approaches offer a perspective for comprehensive parallel quantification of all the various modifications found in total RNA of a given organism. By feeding 13C-glucose as sole carbon source, we have generated a stable isotope-labeled internal standard (SIL-IS) for bacterial RNA, which facilitates relative comparison of all modifications. While conventional SIL-IS approaches require the chemical synthesis of single modifications in weighable quantities, this SIL-IS consists of a nucleoside mixture covering all detectable RNA modifications of Escherichia coli, yet in small and initially unknown quantities. For absolute in addition to relative quantification, those quantities were determined by a combination of external calibration and sample spiking of the biosynthetic SIL-IS. For each nucleoside, we thus obtained a very robust relative response factor, which permits direct conversion of the MS signal to absolute amounts of substance. The application of the validated SIL-IS allowed highly precise quantification with standard deviations <2% during a 12-week period, and a linear dynamic range that was extended by two orders of magnitude. PMID:25129236

  10. Asymmetric perturbations of signalling oligomers.

    PubMed

    Maksay, Gábor; T?ke, Orsolya

    2014-05-01

    This review focuses on rapid and reversible noncovalent interactions for symmetric oligomers of signalling proteins. Symmetry mismatch, transient symmetry breaking and asymmetric perturbations via chemical (ligand binding) and physical (electric or mechanic) effects can initiate the signalling events. Advanced biophysical methods can reveal not only structural symmetries of stable membrane-bound signalling proteins but also asymmetric functional transition states. Relevant techniques amenable to distinguish between symmetric and asymmetric architectures are discussed including those with the capability of capturing low-populated transient conformational states. Typical examples of signalling proteins are overviewed for symmetry breaking in dimers (GPCRs, growth factor receptors, transcription factors); trimers (acid-sensing ion channels); tetramers (voltage-gated cation channels, ionotropic glutamate receptor, CNG and CHN channels); pentameric ligand-gated and mechanosensitive channels; higher order oligomers (gap junction channel, chaperonins, proteasome, virus capsid); as well as primary and secondary transporters. In conclusion, asymmetric perturbations seem to play important functional roles in a broad range of communicating networks. PMID:24650570

  11. Control of asymmetric cell division.

    PubMed

    Roubinet, Chantal; Cabernard, Clemens

    2014-12-01

    Asymmetric cell division (ACD) is a mechanism to generate cellular diversity and used by prokaryotes and eukaryotes alike. Stem cells in particular rely on ACD to self-renew the stem cell while simultaneously generating a differentiating sibling. It is well established that the differential partitioning of cell fate determinants in the form of RNA and proteins between sibling cells induces changes in cell behavior and fate. Recently, insight into molecular mechanisms has been gained that could explain how centrosomes and centrosome-associated structures such as histones, chromosomes or the primary cilium, segregate asymmetrically. Similarly, many cell types also generate physical asymmetry in the form of sibling cell size differences. Emerging data suggests that spindle-induced cleavage furrow positioning through regulated spindle placement and spindle geometry is insufficient to explain all occurrence of cell-size asymmetry. Instead, asymmetric membrane extension based on asymmetric Myosin localization and cortical remodeling could be a driving force for the generation of physical asymmetry. PMID:25264944

  12. Ideal 3D asymmetric concentrator

    Microsoft Academic Search

    Angel Garcia-Botella; Antonio Alvarez Fernandez-Balbuena; Daniel Vázquez; Eusebio Bernabeu

    2009-01-01

    Nonimaging optics is a field devoted to the design of optical components for applications such as solar concentration or illumination. In this field, many different techniques have been used for producing reflective and refractive optical devices, including reverse engineering techniques. In this paper we apply photometric field theory and elliptic ray bundles method to study 3D asymmetric – without rotational

  13. Asymmetric second-stage concentrators

    Microsoft Academic Search

    E. M. Kritchman

    1982-01-01

    It is demonstrated that asymmetric ideal second-stage concentrators may be designed for any given concentrator and absorber (within certain limits) and hence may be used in the field of solar energy to eliminate the shading of the primary by the secondary stage. An application involving an off-acceptance angle concentrator in which the primary is not shaded by the secondary from

  14. Fibring as biporting subsumes asymmetric combinations

    E-print Network

    Lisboa, Universidade Técnica de

    . We concentrate in this paper on importing (and, so, indirectly, in all the asymmetric mechanismsFibring as biporting subsumes asymmetric combinations J. Rasga A. Sernadas C. Sernadas Dep. Matem between importing (a logic combination mechanism that subsumes several asymmetrical mechanisms

  15. Electroporation of asymmetric phospholipid membranes.

    PubMed

    Gurtovenko, Andrey A; Lyulina, Anastasia S

    2014-08-21

    As plasma membranes of animal cells are known to be asymmetric, the transmembrane lipid asymmetry, being essential for many membranes' properties and functions, should be properly accounted for in model membrane systems. In this paper, we employ atomic-scale molecular dynamics simulations to explore electroporation phenomena in asymmetric model membranes comprised of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) lipid monolayers that mimic the outer and inner leaflets of plasma membranes, respectively. Our findings clearly demonstrate that the molecular mechanism of electroporation in asymmetric phospholipid membranes differs considerably from the picture observed for their single-component symmetric counterparts: The initial stages of electric-field-induced formation of a water-filled pore turn out to be asymmetric and occur mainly on the PC side of the PC/PE membrane. In particular, water molecules penetrate in the membrane interior mostly from the PC side, and the reorientation of lipid head groups, being crucial for stabilizing the hydrophilic pore, also takes place in the PC leaflet. In contrast, the PE lipid head groups do not enter the central region of the membrane until the water pore becomes rather large and partly stabilized by PC head groups. Such behavior implies that the PE leaflet is considerably more robust against an electric field most likely due to interlipid hydrogen bonding. We also show that an electric field induces asymmetric changes in the lateral pressure profile of PC/PE membranes, decreasing the cohesion between lipid molecules predominantly in the PC membrane leaflet. Overall, our simulations provide compelling evidence that the transmembrane lipid asymmetry can be essential for understanding electroporation phenomena in living cells. PMID:24986456

  16. Total synthesis of (+)-vibsanin A.

    PubMed

    Takao, Ken-ichi; Tsunoda, Kohei; Kurisu, Takuya; Sakama, Akihiro; Nishimura, Yoshiyasu; Yoshida, Keisuke; Tadano, Kin-ichi

    2015-02-01

    The first total synthesis of (+)-vibsanin A, an 11-membered vibsane diterpenoid, was achieved, unambiguously establishing its relative and absolute stereochemistry. Highlights of the synthesis include the stereoselective formation of an all-carbon quaternary stereocenter by a zinc-mediated Barbier-type allylation in an aqueous medium, and the efficient construction of an 11-membered ring skeleton by a combination of an intramolecular Nozaki-Hiyama-Kishi (NHK) reaction and a Mitsunobu reaction. PMID:25622000

  17. 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. PMID:19831037

  18. 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.

  19. Molecular iodine absolute frequencies. Final report

    SciTech Connect

    Sansonetti, C.J. [National Inst. of Standards and Technology, Gaithersburg, MD (United States)

    1990-06-25

    Fifty specified lines of {sup 127}I{sub 2} were studied by Doppler-free frequency modulation spectroscopy. For each line the classification of the molecular transition was determined, hyperfine components were identified, and one well-resolved component was selected for precise determination of its absolute frequency. In 3 cases, a nearby alternate line was selected for measurement because no well-resolved component was found for the specified line. Absolute frequency determinations were made with an estimated uncertainty of 1.1 MHz by locking a dye laser to the selected hyperfine component and measuring its wave number with a high-precision Fabry-Perot wavemeter. For each line results of the absolute measurement, the line classification, and a Doppler-free spectrum are given.

  20. Absolute calibration in vivo measurement systems

    SciTech Connect

    Kruchten, D.A.; Hickman, D.P.

    1991-02-01

    Lawrence Livermore National Laboratory (LLNL) is currently investigating a new method for obtaining absolute calibration factors for radiation measurement systems used to measure internally deposited radionuclides in vivo. Absolute calibration of in vivo measurement systems will eliminate the need to generate a series of human surrogate structures (i.e., phantoms) for calibrating in vivo measurement systems. The absolute calibration of in vivo measurement systems utilizes magnetic resonance imaging (MRI) to define physiological structure, size, and composition. The MRI image provides a digitized representation of the physiological structure, which allows for any mathematical distribution of radionuclides within the body. Using Monte Carlo transport codes, the emission spectrum from the body is predicted. The in vivo measurement equipment is calibrated using the Monte Carlo code and adjusting for the intrinsic properties of the detection system. The calibration factors are verified using measurements of existing phantoms and previously obtained measurements of human volunteers. 8 refs.

  1. 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. PMID:24117660

  2. Terahertz metamaterial with asymmetric transmission

    E-print Network

    Singh, R; Menzel, C; Rockstuhl, C; Azad, A K; Cheville, R A; Lederer, F; Zhang, W; Zheludev, N I

    2009-01-01

    We show for the first time that a planar metamaterial, an array of coupled metal split-ring resonators with a unit cell lacking mirror symmetry, exhibits asymmetric transmission of terahertz radiation propagating through it in opposite directions. This intriguing effect, that is compatible with Lorentz reciprocity and time-reversal, depends on a directional difference in conversion efficiency of the incident circularly polarized wave into one of opposite handedness, that is only possible in lossy low-symmetry planar chiral metamaterials. We show that asymmetric transmission is linked to excitation of enantiomerically sensitive plasmons, these are induced charge-field excitations that depend on the mutual handedness of incident wave and metamaterial pattern. Various bands of positive, negative and zero phase and group velocities have been identified indicating the opportunity to develop polarization sensitive negative index and slow light media based on such metamaterials.

  3. Glycals in enantiospecific synthesis

    NASA Astrophysics Data System (ADS)

    Tolstikov, Alexander G.; Tolstikov, Genrikh A.

    1993-06-01

    The reactions of 1,2-unsaturated sugars (glycals) are considered in this review in relation to problems of the enantiospecific synthesis of natural products, their fragments, and their analogues. The reactions occurring both with retention of the heterocycle and those carried out with the aim of obtaining open chain chiral units are discussed. It is shown that the use of glycals as a stock of chiral substances which determine the configuration of the asymmetric centres in the target products of multistage synthesis is promising. Schemes for the synthesis of natural products of different types are considered: O- and C-glycosides, nucleosides, oligosaccharides, pheromones, antibiotics, toxins, glycosphingolipids, etc. The bibliography includes 161 references.

  4. Asymmetric fingerprinting for larger collusions

    Microsoft Academic Search

    Birgit Pfitzmann; Michael Waidner

    1997-01-01

    . Fingerprinting schemes deter people from illegallyredistributing digital data by enabling the original merchant ofthe data to identify the original buyer of a redistributed copy.So-called traitor-tracing schemes have the same goal for keysused to decrypt information that is broadcast in encryptedform. Recently, asymmetric fingerprinting and traitor-tracingschemes were introduced. Here, only the buyer knows thefingerprinted copy after a sale, and if

  5. Catalytic asymmetric hydrogenation of pyrimidines.

    PubMed

    Kuwano, Ryoichi; Hashiguchi, Yuta; Ikeda, Ryuhei; Ishizuka, Kentaro

    2015-02-16

    The asymmetric hydrogenation of pyrimidines proceeded with high enantioselectivity (up to 99?%?ee) using an iridium catalyst composed of [IrCl(cod)]2 , a ferrocene-containing chiral diphosphine ligand (Josiphos), iodine, and Yb(OTf)3 (cod=1,5-cyclooctadiene). The chiral catalyst converted various 4-substituted pyrimidines into chiral 1,4,5,6-tetrahydropyrimidines in high yield. The lanthanide triflate is crucial for achieving the high enantioselectivity as well as for activating the heteroarene substrate. PMID:25565291

  6. Dividend Policy under Asymmetric Information

    Microsoft Academic Search

    Merton H. Miller; Kevin Rock

    1985-01-01

    ABSTRACT We extend the standard finance model of the firm's dividend\\/investment\\/financing decisions by allowing the firm's managers,to know,more than outside investors about the true state of the firm's current earnings. The extension endogenizes the dividend (and financing) announcement,effects amply documented,in recent research. But once trading of shares is admitted to the model along with asymmetric information, the familiar Fisherian criterion

  7. Development of Asymmetric Deacylative Allylation

    PubMed Central

    Grenning, Alexander J.; Van Allen, Christie K.; Maji, Tapan; Lang, Simon B.

    2013-01-01

    Herein we present the development of asymmetric deacylative allylation of ketone enolates. The reaction directly couples readily available ketone pronucleophiles with allylic alcohols using facile retro-Claisen cleavage to form reactive intermediates in situ. The simplicity and robustness of the reaction conditions is demonstrated by the preparation of > 6 grams of an allylated tetralone from commercially available materials. Furthermore, use of non-racemic PHOX ligands allows intermolecular formation of quaternary stereocenters directly from allylic alcohols. PMID:23734611

  8. Asymmetric second-stage concentrators

    Microsoft Academic Search

    E. M. Kritchman

    1982-01-01

    Given a linear (2-D) primary optical concentrator and a convex concentrator and a convex close surface of any shape and location (within known limits) underneath, an ideal second-stage reflective element that redirects the primary radiation onto a section of that surface may be designed. A useful application is to asymmetric two-stage concentrators for solar energy, the primary of which is

  9. Asymmetric second-stage concentrators

    SciTech Connect

    Kritchman, E.M.

    1982-03-01

    Given a linear (2-D) primary optical concentrator and a convex concentrator and a convex close surface of any shape and location (within known limits) underneath, an ideal second-stage reflective element that redirects the primary radiation onto a section of that surface may be designed. A useful application is to asymmetric two-stage concentrators for solar energy, the primary of which is not shaded from the illuminating source by the secondary.

  10. Asymmetric second-stage concentrators.

    PubMed

    Kritchman, E M

    1982-03-01

    Given a linear (2-D) primary optical concentrator and a convex close surface of any shape and location (within known limits) underneath, an ideal second-stage reflective element that redirects the primary radiation onto a section of that surface may be designed. A useful application is to asymmetric two-stage concentrators for solar energy, the primary of which is not shaded from the illuminating source by the secondary. PMID:20372553

  11. Asymmetric dark matter from leptogenesis

    Microsoft Academic Search

    Adam Falkowski; Joshua T. Ruderman; Tomer Volansky

    2011-01-01

    We present a new realization of asymmetric dark matter in which the dark matter and lepton asymmetries are generated simultaneously\\u000a through two-sector leptogenesis. The right-handed neutrinos couple both to the Standard Model and to a hidden sector where\\u000a the dark matter resides. This framework explains the lepton asymmetry, dark matter abundance and neutrino masses all at once.\\u000a In contrast to

  12. Enantioselective Total Syntheses of (?)-Taiwaniaquinone H and (?)-Taiwaniaquinol B by Iridium-Catalyzed Borylation and Palladium-Catalyzed Asymmetric ?-Arylation

    PubMed Central

    Liao, Xuebin; Stanley, Levi M.; Hartwig, John F.

    2011-01-01

    We report a concise, enantioselective total synthesis of (?)-taiwaniaquinone H and the first enantioselective total synthesis of (?)-taiwaniaquinol B by a route that includes enantioselective, palladium-catalyzed ?-arylation of a ketone with an aryl bromide that was generated by sterically controlled halogenation via iridium-catalyzed C–H borylation. This asymmetric ?-arylation creates the benzylic, quaternary stereogenic center present in the taiwaniaquinoids. The synthesis was completed efficiently by developing a Lewis acid-promoted cascade to construct the [6,5,6] tricyclic core of an intermediate common to the synthesis of a number of taiwaniaquinoids. Through the preparation of these compounds, we demonstrate the utility of constructing benzylic, quaternary, stereogenic centers, even those lacking a carbonyl group in the ?-position, by asymmetric ?-arylation. PMID:21268578

  13. Asymmetric Wettability Directs Leidenfrost Droplets

    SciTech Connect

    Agapov, Rebecca L [ORNL] [ORNL; Boreyko, Jonathan B [ORNL] [ORNL; Briggs, Dayrl P [ORNL] [ORNL; Srijanto, Bernadeta R [ORNL] [ORNL; Retterer, Scott T [ORNL] [ORNL; Collier, Pat [ORNL] [ORNL; Lavrik, Nickolay V [ORNL] [ORNL

    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.

  14. Asymmetric Total Syntheses of (+)- and (?)-Versicolamide B and Biosynthetic Implications

    PubMed Central

    Miller, Kenneth A.; Tsukamoto, Sachiko; Williams, Robert M.

    2010-01-01

    The Diels-Alder reaction is one of the most well-studied, synthetically useful organic transformations. While a significant number of naturally occurring substances are postulated to arise by biosynthetic Diels-Alder reactions, rigorous confirmation of a mechanistically distinct natural Diels-Alderase enzyme remains elusive. Within this context, several related fungi within the Aspergillus genus produce a number of metabolites of opposite absolute configuration including (+)- or (?)-versicolamide B. These alkaloids are hypothesized to arise via biosynthetic Diels-Alder reactions implying that each Aspergillus species possesses enantiomerically distinct Diels-Alderases. Herein, experimental validation of these biosynthetic proposals via deployment of the IMDA reaction as a key step in the asymmetric total syntheses of (+)- and (?)-versicolamide B is described. Laboratory validation of the proposed biosynthetic Diels-Alder construction, coupled with the secondary metabolite profile of the producing fungi, reveals that each Aspergillus species has evolved enantiomerically distinct indole oxidases, as well as enantiomerically distinct Diels-Alderases. PMID:20300443

  15. Asymmetric acetylcholinesterase is assembled in the Golgi apparatus.

    PubMed Central

    Rotundo, R L

    1984-01-01

    The synthesis, assembly, and processing of the multiple molecular forms of acetylcholinesterase (AcChoEase; acetylcholine acetylhydrolase, EC 3.1.1.7) in quail muscle cultures was studied by using lectins to distinguish enzyme molecules residing in different subcellular compartments. Special emphasis was given to the assembly of asymmetric AcChoEase molecules because these appear to be the predominant, if not unique, forms of AcChoEase at the vertebrate neuromuscular junction. All cell surface and secreted AcChoEase forms bind to immobilized wheat germ agglutinin, ricin, and concanavalin A, indicating that they have complex oligosaccharides. After treatment of muscle cells with a membrane-permeable irreversible AcChoEase inhibitor, there is a rapid reappearance of the globular monomeric, dimeric, and tetrameric AcChoEase forms. However, the collagen-tailed asymmetric form does not appear until about 90 min after treatment. Analysis of the AcChoEase oligosaccharides with lectins indicates maturation to complex forms over a 90-min period. A large fraction of the intracellular globular AcChoEase molecules bind only to concanavalin A, indicating that they are assembled in the rough endoplasmic reticulum. In contrast, all intracellular asymmetric AcChoEase binds to wheat germ agglutinin, and a significant fraction binds to ricin, indicating that this unique AcChoEase form is assembled from subunits that have previously acquired complex sugars. I conclude that assembly of asymmetric AcChoEase, hence acquisition of information specifying basal lamina localization, occurs in the Golgi apparatus. PMID:6582503

  16. Astronomy Ranking Task: Apparent and Absolute Magnitude

    E-print Network

    Farritor, Shane

    Astronomy Ranking Task: Apparent and Absolute Magnitude Exercise #1 Description: The figure below is equipped with identical headlights. A. Ranking Instructions: Rank the distance (from greatest to least) that each car is from you. Ranking Order: Greatest 1 _______ 2 _______ 3 _______ 4 _______ Least Or

  17. Absolute configuration of remisporines A & B.

    PubMed

    Sherer, Edward C; Cheeseman, James R; Williamson, R Thomas

    2015-04-14

    The absolute configuration of remisporine B was determined based on a comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Density functional theory (DFT) was used to calculate the ECD spectra varying the parameter controlling the number of calculated electronic transitions. Mapping the reaction surface provided support for the proposed Diels-Alder dimerization of remisporine A to form remisporine B. PMID:25735997

  18. Absolute head media spacing measurement in situ

    Microsoft Academic Search

    Zhi-Min Yuan; Bo Liu

    2006-01-01

    For the nanometer-spaced head disk interface, the demand for precision flying height (FH) measurement increases. The conventional optical FH testing technology is facing physical challenges, and the industry is seeking the alternative technology for nanometer FH test. This work proposes to use logarithmic harmonic ratio of reproduced waveform versus testing frequency to derive absolute head media spacing (HMS) in situ.

  19. Astronomy Ranking Task: Apparent and Absolute Magnitude

    E-print Network

    Farritor, Shane

    Astronomy Ranking Task: Apparent and Absolute Magnitude Exercise #2 Description: The figure below magnitude. Ranking Order: Greatest 1 _______ 2 _______ 3 _______ 4 _______ 5 _______ Least Or, the apparent magnitude number would be the same for each star. ______ (indicate with check mark). Carefully explain your

  20. The amount of information in absolute judgments

    Microsoft Academic Search

    W. R. Garner; Harold W. Hake

    1951-01-01

    The distribution of an O's absolute judgments, in which he identifies a stimulus as having a particular value, may indicate how much information he obtained about which of several alternative stimuli occurred at a particular time. The amount of information conveyed to O can be measured in bits This measure may give an estimate of the minimum number of stimulus

  1. Absolute partial photoionization cross sections of ozone.

    SciTech Connect

    Berkowitz, J.; Chemistry

    2008-04-01

    Despite the current concerns about ozone, absolute partial photoionization cross sections for this molecule in the vacuum ultraviolet (valence) region have been unavailable. By eclectic re-evaluation of old/new data and plausible assumptions, such cross sections have been assembled to fill this void.

  2. Absolute instability of a viscous hollow jet

    Microsoft Academic Search

    Alfonso M. Gañán-Calvo

    2007-01-01

    An investigation of the spatiotemporal stability of hollow jets in unbounded coflowing liquids, using a general dispersion relation previously derived, shows them to be absolutely unstable for all physical values of the Reynolds and Weber numbers. The roots of the symmetry breakdown with respect to the liquid jet case, and the validity of asymptotic models are here studied in detail.

  3. 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.)

  4. Teaching Absolute Value Inequalities to Mature Students

    ERIC Educational Resources Information Center

    Sierpinska, Anna; Bobos, Georgeana; Pruncut, Andreea

    2011-01-01

    This paper gives an account of a teaching experiment on absolute value inequalities, whose aim was to identify characteristics of an approach that would realize the potential of the topic to develop theoretical thinking in students enrolled in prerequisite mathematics courses at a large, urban North American university. The potential is…

  5. Absolute pitch: perception, coding, and controversies

    E-print Network

    Levitin, Daniel

    Absolute pitch: perception, coding, and controversies Daniel J. Levitin and Susan E. Rogers are converging to shed light on the nature of processing, categorization and memory for pitch in humans and animals. Although most people are unable to name or place pitch values in consistent, well

  6. Highly asymmetric quantum cloning in arbitrary dimension

    E-print Network

    Jaromir Fiurasek; Radim Filip; Nicolas J. Cerf

    2005-05-27

    We investigate the universal asymmetric cloning of states in a Hilbert space of arbitrary dimension. We derive the class of optimal and fully asymmetric 1->3 cloners, which produce three copies, each having a different fidelity. A simple parametric expression for the maximum achievable cloning fidelity triplets is then provided. As a side-product, we also prove the optimality of the 1->2 asymmetric cloning machines that have been proposed in the literature.

  7. 1262 J.CHEM. SOC., CHEM. COMMUN., 1993 Asymmetric Hydrogenationin Water by a RhodiumComplex of Sulfonated

    E-print Network

    Winfree, Erik

    -soluble organometallic catalysts.1 The water solubil- ization of known organometallic catalysts is typically per- formed effective catalyst immobilization. Here we report the synthesis of a new water soluble ligand, sulfonated 21262 J.CHEM. SOC., CHEM. COMMUN., 1993 Asymmetric Hydrogenationin Water by a Rhodium

  8. 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 the conflict with their specific individual style.

  9. Symmetric mortality and asymmetric suicide cycles.

    PubMed

    Wu, Wen-Chieh; Cheng, Hui-Pei

    2010-06-01

    In this investigation, tests were performed to determine whether mortality cycles are asymmetric. Results from an asymmetry test of U.S. time-series data from 1951 to 2005 provide no evidence that all-cause mortality or mortality caused by disease causes asymmetric cycles. However, the rate of fatalities from suicide exhibits the pattern of an asymmetric cycle. The evidence for asymmetric suicide cycles is statistically significant for men and working-age groups but not for women and non-working-age groups. PMID:20378221

  10. Asymmetric Activity Waves in Synaptic Cortical Systems

    NASA Astrophysics Data System (ADS)

    Pinto, David J.; Troy, William; Kneezel, Timothy

    2009-01-01

    This study explores asymmetric activity wave propagation in cortical systems, both experimentally and mathematically. Experimentally, we find that activity waves passing through the same neural tissue but in different directions exhibit different speeds and spatial profiles and evoke different firing patterns in individual neurons. Mathematically, we extend our previously published results on the existence of traveling pulse solutions to account for our experimental observations. Specifically, our analysis suggests that asymmetric connectivity is sufficient to account for asymmetric propagation. Moreover, it predicts that unidirectional propagation can occur in cases of extreme asymmetry. Finally, we experimentally validate our analytic findings by examining wave propagation in a cortical region where asymmetric coupling is known to exist.

  11. Modal analysis of continuous asymmetrical rotor-bearing systems

    Microsoft Academic Search

    Y.-G. Jei; C.-W. Lee

    1992-01-01

    Modal analysis of an asymmetrical rotor-bearing system which consists of asymmetrical Rayleigh shafts, asymmetrical rigid disks and isotropic bearings is performed. The rotor includes the effects of rotary inertia and gyroscopic moment. A solution method for the vibration analysis of a rotating uniform asymmetrical shaft is developed. The whirl speeds and mode shapes of the uniform asymmetrical shaft are investigated,

  12. Synthesis of novel adamantyl and homoadamantyl-substituted ?-hydroxybutyric acids.

    PubMed

    Matkovi?, Marija; Vukeli?, Stella; Cirimoti?, Ružica; Kragol, Goran; Mol?anov, Krešimir; Mlinari?-Majerski, Kata

    2013-11-01

    Several new adamantyl and homoadamantyl-substituted [Formula: see text]-hydroxybutyric acids, 2-[2-(1-adamantyl)ethyl]-3-hydroxybutyric acid (2), 2-(3-homoadamantyl)-3-hydroxybutyric acid (3), and 2-(1-homoadamantyl)-3-hydroxybutyric acid (4), analogues of the 2-(1-adamantyl)-3-hydroxybutyric acid (1), have been prepared as mixtures of diastereoisomers using selective reduction of corresponding [Formula: see text]-keto esters or aldol condensation of the corresponding carboxylic acid and acetaldehyde. The rearrangement of adamantylmethyl and 3-homoadamantyl groups provided entry to both 3-homoadamantyl and 1-homoadamantyl-substituted hydroxy acids 3 and 4, respectively. The relative configurations of diastereoisomers 3 and 4 have been determined by NMR spectroscopy comparing the values of coupling constants. Adamantyl-substituted [Formula: see text]-hydroxybutyric acid 2 has also been prepared in enantiomerically pure form by Evan's asymmetric synthesis and the absolute configuration has been determined by X-ray crystallography. Contrary to the long-chain acid 2, the attempt to prepare short-chain hydroxy acids 1 and 4 by the same method failed indicating pronounced sensitivity of the used method to the vicinity of the bulky cage group. PMID:24043584

  13. Direct Asymmetric Amination of ?-Branched Cyclic Ketones Catalyzed by a Chiral Phosphoric Acid.

    PubMed

    Yang, Xiaoyu; Toste, F Dean

    2015-03-11

    Here we report the direct asymmetric amination of ?-substituted cyclic ketones catalyzed by a chiral phosphoric acid, yielding products with a N-containing quaternary stereocenter in high yields and excellent enantioselectivities. Kinetic resolution of the starting ketone was also found to occur on some of the substrates under milder conditions, providing enantioenriched ?-branched ketones, another important building block in organic synthesis. The utility of this methodology was demonstrated in the short synthesis of (S)-ketamine, the more active enantiomer of this versatile pharmaceutical. PMID:25719604

  14. Preparation of asymmetrical polyynes by a solid-supported Glaser-Hay reaction.

    PubMed

    Lampkowski, Jessica S; Durham, Corinn E; Padilla, Marshall S; Young, Douglas D

    2015-01-14

    Polyynes exhibit both unique photophysical properties and biological activities, necessitating efficient syntheses towards these core structures. A novel methodology for the construction of highly conjugated asymmetrical polyynes has been developed in a chemoselective fashion utilizing a solid-support. The synthesis has been applied to prepare a small library of polyynes in good to moderate yield. Moreover, their interesting fluorescence properties have been investigated, demonstrating the ability to tune fluorescence through selection of appropriate synthetic building blocks. PMID:25371282

  15. A porphyrin-inspired iron catalyst for asymmetric epoxidation of electron-deficient olefins.

    PubMed

    Dai, Wen; Li, Guosong; Chen, Bo; Wang, Lianyue; Gao, Shuang

    2015-02-20

    An in situ formed porphyrin-inspired iron complex that catalyzes asymmetric epoxidation of di- and trisubstituted enones is described. The reaction provides highly enantioenriched ?,?-epoxyketones (up to 99% ee). The practical utility of the new catalyst system is demonstrated by the gram-scale synthesis of optically pure epoxide. Hammett analysis suggests that the transition state of the reaction is electron-demanding and the active oxidant is electrophilic. PMID:25643130

  16. Absolute absorption spectroscopy based on molecule interferometry

    E-print Network

    Stefan Nimmrichter; Klaus Hornberger; Hendrik Ulbricht; Markus Arndt

    2008-11-07

    We propose a new method to measure the absolute photon absorption cross section of neutral molecules in a molecular beam. It is independent of our knowledge of the particle beam density, nor does it rely on photo-induced fragmentation or ionization. The method is based on resolving the recoil resulting from photon absorption by means of near-field matter-wave interference, and it thus applies even to very dilute beams with low optical densities. Our discussion includes the possibility of internal state conversion as well as fluorescence. We assess the influence of various experimental uncertainties and show that the measurement of absolute absorption cross sections is conceivable with high precision and using existing technologies.

  17. Absolute quantification method for protein concentration.

    PubMed

    Li, Mingdong; Tan, Jiaojie; Tarlov, Michael J; Zachariah, Michael R

    2014-12-16

    A fast and accurate assay to determine the absolute concentration of proteins is described based on direct measurement of droplet entrapped oligomer formation in electrospray. Here we demonstrate the approach using electrospray differential mobility analysis (ES-DMA), which can distinguish monomers and dimers from higher order oligomers. A key feature of the method is that it allows determination of the absolute number concentration of proteins eliminating the need for protein-specific calibration. The method was demonstrated by measuring the concentration of a NIST Standard Reference Material 927e (bovine serum albumin), a high-purity immunoglobulin G 1?, and a formulated Rituximab. The method may be applied to any electrospray source, regardless of diagnostic tool (e.g., MS or ion-mobility, etc.), provided the electrospray is operated in a droplet-fission mode. PMID:25412350

  18. 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.

  19. Absolute absorption spectroscopy based on molecule interferometry

    E-print Network

    Nimmrichter, Stefan; Ulbricht, Hendrik; Arndt, Markus

    2008-01-01

    We propose a new method to measure the absolute photon absorption cross section of neutral molecules in a molecular beam. It is independent of our knowledge of the particle beam density, nor does it rely on photo-induced fragmentation or ionization. The method is based on resolving the recoil resulting from photon absorption by means of near-field matter-wave interference, and it thus applies even to very dilute beams with low optical densities. Our discussion includes the possibility of internal state conversion as well as fluorescence. We assess the influence of various experimental uncertainties and show that the measurement of absolute absorption cross sections is conceivable with high precision and using existing technologies.

  20. Absolute and relative dosimetry for ELIMED

    SciTech Connect

    Cirrone, G. A. P.; Schillaci, F.; Scuderi, V. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Institute of Physics Czech Academy of Science, ELI-Beamlines project, Na Slovance 2, Prague (Czech Republic)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Institute of Physics Czech Academy of Science, ELI-Beamlines project, Na Slovance 2, Prague (Czech Republic); Cuttone, G.; Candiano, G.; Musumarra, A.; Pisciotta, P.; Romano, F. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania (Italy)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania (Italy); Carpinelli, M. [INFN Sezione di Cagliari, c/o Dipartimento di Fisica, Università di Cagliari, Cagliari (Italy)] [INFN Sezione di Cagliari, c/o Dipartimento di Fisica, Università di Cagliari, Cagliari (Italy); Leonora, E.; Randazzo, N. [INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy)] [INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy); Presti, D. Lo [INFN-Sezione di Catania, Via Santa Sofia 64, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy)] [INFN-Sezione di Catania, Via Santa Sofia 64, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy); Raffaele, L. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy); Tramontana, A. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy); Cirio, R.; Sacchi, R.; Monaco, V. [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino, Italy and Università di Torino, Dipartimento di Fisica, Via P.Giuria, 1 10125 Torino (Italy)] [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino, Italy and Università di Torino, Dipartimento di Fisica, Via P.Giuria, 1 10125 Torino (Italy); Marchetto, F.; Giordanengo, S. [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino (Italy)] [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino (Italy)

    2013-07-26

    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.

  1. 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.

  2. 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.

  3. 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.

  4. 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. PMID:25423049

  5. The Asymmetric Current Mirror Probe

    NASA Astrophysics Data System (ADS)

    Maggs, J. E.; Carter, T. A.

    2008-11-01

    The difference in floating potential, between two closely spaced probe tips, is often used as a measure of the electric field in plasmas. This technique assumes a thermal Maxwellian distribution for plasma electrons and is unreliable in the presence of a fast non-Maxwellian electron tail. The influence of fast-tail electrons on floating potential measurements can be mitigated by using emissive probes or probes of unbalanced collection area. These probes have floating potentials that are closer to plasma potential than the floating potential of a standard Langmuir probe. An example of an unbalanced area probe is the ball-pen probe [Schrittwieser, et al., Rom. Journ. Phys., Vol. 50, 2005], in which the ion collection area is substantially larger than the electron collection area. The asymmetric current mirror probe achieves the effect of unbalanced collection area electronically, by amplification of the current drawn to the ion tip. Comparisons of radial profiles of floating potential in the LAPD at UCLA, measured using a Langmuir probe, ball-pen probe and asymmetric mirror probe are presented. The effects of using differences in floating potential, measured by these various probes, to determine the electric field is discussed.

  6. Asymmetrical membranes and surface tension.

    PubMed Central

    Traïkia, Mounir; Warschawski, Dror E; Lambert, Olivier; Rigaud, Jean-Louis; Devaux, Philippe F

    2002-01-01

    The (31)P-nuclear magnetic resonance chemical shift of phosphatidic acid in a membrane is sensitive to the lipid head group packing and can report qualitatively on membrane lateral compression near the aqueous interface. We have used high-resolution (31)P-nuclear magnetic resonance to evaluate the lateral compression on each side of asymmetrical lipid vesicles. When monooleoylphosphatidylcholine was added to the external monolayer of sonicated vesicles containing dioleoylphosphatidylcholine and dioleoylphosphatidic acid, the variation of (31)P chemical shift of phosphatidic acid indicated a lateral compression in the external monolayer. Simultaneously, a slight dilation was observed in the inner monolayer. In large unilamellar vesicles on the other hand the lateral pressure increased in both monolayers after asymmetrical insertion of monooleoylphosphatidylcholine. This can be explained by assuming that when monooleoylphosphatidylcholine is added to large unilamellar vesicles, the membrane bends until the strain is the same in both monolayers. In the case of sonicated vesicles, a change of curvature is not possible, and therefore differential packing in the two layers remains. We infer that a variation of lipid asymmetry by generating a lateral strain in the membrane can be a physiological way of modulating the conformation of membrane proteins. PMID:12202370

  7. Scatterometry measurement of asymmetric gratings

    NASA Astrophysics Data System (ADS)

    Li, Jie; Hwu, Justin J.; Liu, Yongdong; Rabello, Silvio; Liu, Zhuan; Hu, Jiangtao

    2009-12-01

    Scatterometry has been used extensively for the characterization of critical dimensions (CD) and detailed sidewall profiles of periodic structures in microelectronics fabrication processes. So far the majority of applications are for symmetric gratings. In most cases devices are designed to be symmetric although errors could occur during fabrication process and result in undesired asymmetry. The problem with conventional optical scatterometry techniques lies in the lack of capability to distinguish between left and right asymmetries. In this work we investigate the possibility of measuring grating asymmetry using Mueller matrix spectroscopic ellipsometry (MM-SE). A patterned hard disk prepared by nano-imprint technique is used for the study. The relief image on the disk sometimes has asymmetrical sidewall profile, presumably due to the uneven separation of the template from the disk. The undesired tilting resist profile causes difficulties to the downstream processes or even makes them fail. Cross-section SEM reveals that the asymmetrical resist lines are typically tilted towards the outer diameter direction. The simulation and experimental data show that certain Mueller matrix elements are proportional to the direction and amplitude of profile asymmetry, providing a direct indication to the sidewall tilting. The tilting parameter can be extracted using rigorous optical critical dimension (OCD) modeling or calibration method. We demonstrate that this technique has good sensitivity for measuring and distinguishing left and right asymmetry caused by sidewall tilting, and can therefore be used for monitoring processes, such as lithography and etch processing, for which symmetric structures are desired.

  8. Geometry-induced asymmetric diffusion

    E-print Network

    Robert S. Shaw; Norman Packard; Matthias Schröter; Harry L. Swinney

    2007-05-24

    Past work has shown that ions can pass through a membrane more readily in one direction than the other. We demonstrate here in a model and an experiment that for a mixture of small and large particles such asymmetric diffusion can arise solely from an asymmetry in the geometry of the pores of the membrane. Our deterministic simulation considers a two-dimensional gas of elastic disks of two sizes diffusing through a membrane, and our laboratory experiment examines the diffusion of glass beads of two sizes through a metal membrane. In both experiment and simulation, the membrane is permeable only to the smaller particles, and the asymmetric pores lead to an asymmetry in the diffusion rates of these particles. The presence of even a small percentage of large particles can clog a membrane, preventing passage of the small particles in one direction while permitting free flow of the small particles in the other direction. The purely geometric kinetic constraints may play a role in common biological contexts such as membrane ion channels.

  9. The absolute bioavailability of caffeine in man

    Microsoft Academic Search

    J. Blanchard; S. J. A. Sawers

    1983-01-01

    The absolute bioavailability of orally administered caffeine was investigated in 10 healthy adult male volunteers, aged 18.8 to 30.0 years. The subjects were administered a 5 mg\\/kg dose of caffeine as either an aqueous oral solution or an intravenous infusion, on separate occasions about 1 week apart, in a randomized crossover fashion. Plasma samples were collected over the 24-h period

  10. The Risks of Absolute Medical Confidentiality

    Microsoft Academic Search

    M. A. Crook

    Some ethicists argue that patient confidentiality is absolute and thus should never be broken. I examine these arguments that\\u000a when critically scrutinised, become porous. I will explore the concept of patient confidentiality and argue that although,\\u000a this is a very important medical and bioethical issue, this needs to be wisely delivered to reduce third party harm or even\\u000a detriment to

  11. Teaching absolute value inequalities to mature students

    Microsoft Academic Search

    Anna Sierpinska; Georgeana Bobos; Andreea Pruncut

    This paper gives an account of a teaching experiment on absolute value inequalities, whose aim was to identify characteristics\\u000a of an approach that would realize the potential of the topic to develop theoretical thinking in students enrolled in prerequisite\\u000a mathematics courses at a large, urban North American university. The potential is demonstrated in an epistemological analysis\\u000a of the topic. It

  12. The absolute spectrophotometric catalog by Anita Cochran

    NASA Astrophysics Data System (ADS)

    Burnashev, V. I.; Burnasheva, B. A.; Ruban, E. V.; Hagen-Torn, E. I.

    2014-06-01

    The absolute spectrophotometric catalog by Anita Cochran is presented in a machine-readable form. The catalog systematizes observations acquired at the McDonald Observatory in 1977-1978. The data are compared with other sources, in particular, the calculated broadband stellar magnitudes are compared with photometric observations by other authors, to show that the observational data given in the catalog are reliable and suitable for a variety of applications. Observations of variable stars of different types make Cochran's catalog especially valuable.

  13. Absolute detector calibration using twin beams

    E-print Network

    Jan Perina Jr; Ondrej Haderka; Vaclav Michalek; Martin Hamar

    2012-05-09

    A method for the determination of absolute quantum detection efficiency is suggested based on the measurement of photocount statistics of twin beams. The measured histograms of joint signal-idler photocount statistics allow to eliminate an additional noise superimposed on an ideal calibration field composed of only photon pairs. This makes the method superior above other approaches presently used. Twin beams are described using a paired variant of quantum superposition of signal and noise.

  14. Absolute Calibration Using the MSX Reference Spheres

    NASA Astrophysics Data System (ADS)

    Price, S. D.; Paxson, C.; Murdock, T. L.

    2004-12-01

    MSX conducted five absolute calibration experiments against emissive reference spheres between 25 August 1996 and 20 February 1997. The 2 cm diameter, T6061 Al spheres are coated with Martin Black. The thermal properties of the spheres are well known and their emissivities and reflectivities were accurately measured in the laboratory. The spheres were ejected at an elevation angle of 15 degrees above the MSX velocity vector in the orbital plane; the velocities were measured at the time of ejection. The geometric parameters of the spheres at the time of measurement were determined from orbital dynamics. The energy balance equation between the thermal input from the direct Sunlight, Sunlight reflected by the Earth and upwelling Earthshine and the total flux emitted by the sphere is solved to derive the instantaneous temperature of the sphere. The MSX in-band fluxes are then calculated from the blackbody at the temperature of the sphere predicted by the model modified by the wavelength dependent infrared emissivity at the distance of the sphere plus infrared Earthshine and Sunlight reflected by the sphere. The weighted results for the five spheres agree to within the uncertainties with the SPIRIT III responsivities determined from the absolute fluxes for infrared standard stars derived by Cohen et al. The MSX calibration against the reference spheres thus validate the absolute fluxes for the standard stars to <2%.

  15. The upside of downsizing: asymmetric trifunctional organocatalysts as small enzyme mimics for cooperative enhancement of both rate and enantioselectivity with regulation.

    PubMed

    Liu, Fei

    2013-11-01

    Small molecule organic catalysts (organocatalysts) are widely used in asymmetric catalysis and synthesis. Compared to their enzymatic and transition-metal counterparts, organocatalysts have advantages in catalytic scope and efficiency but are more limited in proficiency. Chiral trifunctional organocatalysts, in which multiple catalytic motifs act cooperatively on a chiral scaffold, are an emerging class of organocatalysts with improved proficiency. Cooperativity design that enables both enantioselectivity and rate enhancement is essential to developing future generations of organocatalysts in biomimetic asymmetric catalysis. PMID:23966336

  16. The mechanism by which an asymmetric distribution of plant growth hormone is attained

    NASA Astrophysics Data System (ADS)

    Bandurski, Robert S.; Schulze, Aga; Jensen, Philip; Desrosiers, Mark; Epel, Bernard; Kowalczyk, Stanley

    Zea mays (sweet corn) seedlings attain an asymmetric distribution of the growth hormone indole-3-acetic acid (IAA) within 3 minutes following a gravity stimulus. Both free and esterified IAA (that is total IAA) accumulate to a greater extent in the lower half of the mesocotyl cortex of a horizontally placed seedling than in the upper half. Thus, changes in the ratio of free IAA to ester IAA cannot account for the asymmetric distribution. Our studies demonstrate there is no de novo synthesis of IAA in young seedlings. We conclude that asymmetric IAA distribution is attained by a gravity-induced, potential-regulated gating of the movement of IAA from kernel to shoot and from stele to cortex. As a working theory, which we call the Potential Gating Theory, we propose that perturbation of the plant's bioelectric field, induced by gravity, causes opening and closing of transport channels in the plasmodesmata connecting the vascular stele to the surrounding cortical tissues. This results in asymmetric growth hormone distribution which results in the asymmetric growth characteristic of the gravitropic response.

  17. Asymmetric Total Synthesis of Callystatin A: Asymmetric Aldol Additions with Titanium Enolates

    E-print Network

    with chlorotitanium enolates of acyl oxazolidi- nethiones.9 Strategically, E-selective olefination10 of aldehyde 2 convergent assembly of callystatin A. Aldehyde 2 representing C1 to C12 would be constructed from a similar olefination between the masked pyranone aldehyde 4 (Scheme 2) and phosphonium salt 5 (Scheme 3). The C13 to C

  18. Synthesis of (+)-discodermolide by catalytic stereoselective borylation reactions.

    PubMed

    Yu, Zhiyong; Ely, Robert J; Morken, James P

    2014-09-01

    The marine natural product (+)-discodermolide was first isolated in 1990 and, to this day, remains a compelling synthesis target. Not only does the compound possess fascinating biological activity, but it also presents an opportunity to test current methods for chemical synthesis and provides an inspiration for new reaction development. A new synthesis of discodermolide employs a previously undisclosed stereoselective catalytic diene hydroboration and also establishes a strategy for the alkylation of chiral enolates. Furthermore, this synthesis of discodermolide provides the first examples of the asymmetric 1,4-diboration of dienes and borylative diene-aldehyde couplings in complex-molecule synthesis. PMID:25045037

  19. Total Synthesis of Theopederin D

    PubMed Central

    Green, Michael E.; Rech, Jason C.

    2012-01-01

    The total synthesis of the potent cytotoxin theopederin D has been achieved through the use of an oxidative carbon–carbon bond cleavage reaction to form an acyliminium ion in the presence of acid labile acetal groups Other key transformations include an acid mediated functionalization of a tetrahydrofuranyl alcohol in the presence of a tetrahydropyranyl alcohol, a syn-selective glycal epoxide opening, and a catalytic asymmetric aldehyde-acid chloride condensation. PMID:18683833

  20. Synthesis of proposed aglycone of mandelalide A.

    PubMed

    Reddy, Karla Mahender; Yamini, Vanipenta; Singarapu, Kiran K; Ghosh, Subhash

    2014-05-16

    A highly convergent synthesis of the proposed mandelalide A aglycone is reported. The cornerstones of the synthetic strategy include the following: E-selective intramolecular Heck cyclization, Masamune-Roush olefination, Stork-Zhao-Wittig olefination, modified Prins cyclization; Sharpless asymmetric dihydroxylation followed by Williamson-type etherification, Julia-Kocienski olefination, Brown crotylation, and Brown allylation reactions. PMID:24738830

  1. Stereoselective Synthesis of Quaternary Proline Analogues

    PubMed Central

    Calaza, M. Isabel

    2009-01-01

    This review describes available methods for the diastereoselective and asymmetric synthesis of quaternary prolines. The focus is on the preparation of ?-functionalized prolines with the pyrrolidine moiety not embedded in a polycyclic frame. The diverse synthetic approaches are classified according to the bond which is formed to complete the quaternary skeleton. PMID:19655047

  2. Enantioselective total synthesis of the lignan (+)-linoxepin.

    PubMed

    Tietze, Lutz F; Clerc, Jérôme; Biller, Simon; Duefert, Svenia-C; Bischoff, Matthias

    2014-12-15

    An enantioselective total synthesis of the natural (+)-linoxepin (1) was accomplished in eleven steps from bromovanin (24). Key steps are a domino carbopalladation/ Mizoroki-Heck reaction with the formation of a pentacyclic system, an asymmetric hydroboration as well as an oxidative lactonization. PMID:25345835

  3. A convenient synthesis of cis and trans 4-tert-butoxycarbonyl-substituted cyclohexylglycine.

    PubMed

    Venkatraman, Srikanth; Njoroge, F George; Girijavallabhan, Viyyoor; McPhail, Andrew T

    2002-04-19

    A novel synthesis of cis and trans substituted 4-tert-butoxycarbonyl cyclohexylglycines via asymmetric aminohydroxylation of vinyl styrene followed by reduction of the aromatic ring and subsequent oxidation is reported. PMID:11950318

  4. Enantioselective Synthesis of Tetrahydroprotoberberines and Bisbenzylisoquinoline Alkaloids from a Deprotonated -Aminonitrile

    E-print Network

    Lawson, Catherine L.

    Enantioselective Synthesis of Tetrahydroprotoberberines and Bisbenzylisoquinoline Alkaloids from for the preparation of various alkaloids. Here, the preparation of the benzylisoquinolines (+)-laudanidine and (-)-tetrahydropseudoepiberberine using Noyori's asymmetric transfer hydrogenation are described. The dimeric alkaloids (+)-O

  5. The Catalytic Asymmetric Intramolecular Stetter Reaction

    PubMed Central

    de Alaniz, Javier Read; Rovis, Tomislav

    2010-01-01

    This account chronicles our efforts at the development of a catalytic asymmetric Stetter reaction using chiral triazolium salts as small molecule organic catalysts. Advances in the mechanistically related azolium-catalyzed asymmetric benzoin reaction are discussed, particularly as they apply to catalyst design. A chronological treatise of reaction discovery, catalyst optimization and reactivity extension follows. PMID:20585467

  6. Branching Cells for Asymmetric Event Structures

    E-print Network

    Boyer, Edmond

    Branching Cells for Asymmetric Event Structures Samy Abbes December 2012 Abstract We introduce branching cells for Asymmetric Event Structures. They provide a way to decompose maximal configuration-prefixes. . . . . . . . . . . . . . . . . . . . 9 4 Defining Branching Cells for AES 11 Informal Description of Branching Cells on an Example. . 11

  7. Tolerating Asymmetric Data Races with Unintrusive Hardware

    E-print Network

    Torrellas, Josep

    Pacman: Tolerating Asymmetric Data Races with Unintrusive Hardware Shanxiang Qi, Norimasa Otsuki 9, 12 #12;Pacman: Tolerating Asymmetric Races University of Illinois http://iacoma.cs.uiuc.edu/Shanxiang Qi Data Race Two threads access same variable without intervening sync At least one is write Data

  8. cybersecurity.pnnl.gov Asymmetric Resilient Cybersecurity

    E-print Network

    cybersecurity.pnnl.gov Asymmetric Resilient Cybersecurity Cyber attacks are persistent Cyber attack have disastrous consequences on the rest of the system. The Asymmetric Resilient Cybersecurity altering how cybersecurity is implemented today. These capabilities will be driven by and measured by real

  9. Dielectric receivers for asymmetrical ideal concentrators

    Microsoft Academic Search

    Francesco Bloisi; Paolo Cavaliere; Sergio Martellucci; Joseph Quartieri; Luciano Vicari

    1988-01-01

    Cylindrical asymmetrical nonimaging concentrators with receivers based on fin absorbers immersed in dielectric rhombuses are introduced and shown to be ideal. They have the same concentration factor as dielectric filled devices but require only a small amount of dielectric around the absorber. The asymmetric shape and nontracking property of the collectors allow their arrangement in flat panels that, integrated with

  10. Turbo Codes for Asymmetric Binary Channels

    E-print Network

    Linder, Tamás

    Turbo Codes for Asymmetric Binary Channels by Ka Sin Tong A dissertation submitted the past 10 years, most of the work concentrated on standard channel models, such as binary symmetric: the Z­channel (ZC) and the binary asymmetric channel (BAC). The performance of Turbo codes are evaluated

  11. Asymmetric explosion of core collapse supernovae

    Microsoft Academic Search

    T. Foglizzo; J. Guilet; J. Sato

    2009-01-01

    The explosion of most massive stars depends on the revival of a stalled shock, a few hundred milliseconds after the birth of the central neutron star. Recent numerical simulations suggest that this revival is possible through an asymmetric explosion helped by a hydrodynamical instability named SASI. Its asymmetric character is also able to influence the kick and the spin of

  12. Concise Total Synthesis and Stereochemical Revision of all (?)-Trigonoliimines

    PubMed Central

    Han, Sunkyu

    2012-01-01

    The concise and enantioselective total syntheses of (?)-trigonoliimines A, B, and C are described. Our unified strategy to all three natural products is based on asymmetric oxidation and reorganization of a single bistryptamine, a sequence of transformations with possible biogenetic relevance. We revise the absolute stereochemistry of (?)-trigonoliimines A, B, and C. PMID:21667943

  13. Kinetic simulation of capacitively coupled plasmas driven by trapezoidal asymmetric voltage pulses

    SciTech Connect

    Diomede, Paola, E-mail: padiomede@gmail.com; Economou, Demetre J., E-mail: economou@uh.edu [Plasma Processing Laboratory, Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204-4004 (United States)

    2014-06-21

    A kinetic Particle-In-Cell simulation with Monte Carlo Collisions was performed of a geometrically symmetric capacitively coupled, parallel-plate discharge in argon, driven by trapezoidal asymmetric voltage pulses with a period of 200?ns. The discharge was electrically asymmetric, making the ion energy distributions at the two electrodes different from one another. The fraction of the period (?), during which the voltage was kept at a constant (top-flat) positive value, was a critical control parameter. For the parameter range investigated, as ? increased, the mean ion energy on the grounded electrode increased and the ions became more directional, whereas the opposite was found for the ions striking the powered electrode. The absolute value of the DC self-bias voltage decreased as ? increased. Plasma instabilities, promoted by local double layers and electric field reversals during the time of the positive voltage excursion, were characterized by electron plasma waves launched from the sheath edge.

  14. Kinetic simulation of capacitively coupled plasmas driven by trapezoidal asymmetric voltage pulses

    NASA Astrophysics Data System (ADS)

    Diomede, Paola; Economou, Demetre J.

    2014-06-01

    A kinetic Particle-In-Cell simulation with Monte Carlo Collisions was performed of a geometrically symmetric capacitively coupled, parallel-plate discharge in argon, driven by trapezoidal asymmetric voltage pulses with a period of 200 ns. The discharge was electrically asymmetric, making the ion energy distributions at the two electrodes different from one another. The fraction of the period (?), during which the voltage was kept at a constant (top-flat) positive value, was a critical control parameter. For the parameter range investigated, as ? increased, the mean ion energy on the grounded electrode increased and the ions became more directional, whereas the opposite was found for the ions striking the powered electrode. The absolute value of the DC self-bias voltage decreased as ? increased. Plasma instabilities, promoted by local double layers and electric field reversals during the time of the positive voltage excursion, were characterized by electron plasma waves launched from the sheath edge.

  15. Total synthesis of marinomycin A based on a direct dimerization strategy.

    PubMed

    Nishimaru, Tatsuya; Kondo, Masashi; Takeshita, Kimito; Takahashi, Keisuke; Ishihara, Jun; Hatakeyama, Susumi

    2014-08-01

    The asymmetric total synthesis of (+)-marinomycin?A, a 44-membered macrodiolide antitumor agent and antibiotic isolated from a marine actinomycete, Marinispora strain CNQ-140, is reported. The key features of the synthesis include the highly convergent stereocontrolled construction of the monomeric hydroxy salicylate starting from asymmetric epoxidation of the ?-symmetrical dialkenyl carbinol, and an unprecedented direct dimerization through NaHMDS-promoted double transesterification. PMID:24962551

  16. Absolute configuration assignment of a chiral molecule in the gas phase using foil-induced Coulomb explosion imaging

    NASA Astrophysics Data System (ADS)

    Herwig, Philipp; Zawatzky, Kerstin; Schwalm, Dirk; Grieser, Manfred; Heber, Oded; Jordon-Thaden, Brandon; Krantz, Claude; Novotný, Old?ich; Repnow, Roland; Schurig, Volker; Vager, Zeev; Wolf, Andreas; Trapp, Oliver; Kreckel, Holger

    2014-11-01

    Chiral molecules exist in two configurations that are nonsuperposable mirror images of one another. The underlying molecular structure is referred to as the absolute configuration. In chiral environments, the handedness of molecules influences their chemical characteristics dramatically, and therefore the determination of absolute configurations is of fundamental interest in organic chemistry and biology. Commonly applied techniques to assign absolute configuration are anomalous single-crystal x-ray diffraction and vibrational circular dichroism. However, these techniques become increasingly more challenging when applied to molecules that are made out of light atoms exclusively. Furthermore, there is no established method to determine the absolute handedness of gas-phase molecules that are not optically active. In this work, we apply the foil-induced Coulomb explosion imaging technique to determine directly the absolute configuration of the chiral molecule trans-2,3-dideuterooxirane (C2OD2H2) in the gas phase. The experiment leads to the definitive assignment of the (R ,R ) configuration to an enantio-selected dideuterooxirane sample with a statistical confidence of 5 ? . As the handedness of trans-2,3-dideuterooxirane is unambiguously linked by chemical synthesis to the stereochemical key reference glyceraldehyde, our results provide an independent verification of the absolute configuration of the stereochemical reference standard.

  17. Condensation on Slippery Asymmetric Bumps

    E-print Network

    Park, Kyoo-Chul; He, Neil; Aizenberg, Joanna

    2015-01-01

    Bumps are omnipresent from human skin to the geological structures on planets, which offer distinct advantages in numerous phenomena including structural color, drag reduction, and extreme wettability. Although the topographical parameters of bumps such as radius of curvature of convex regions significantly influence various phenomena including anti-reflective structures and contact time of impacting droplets, the effect of the detailed bump topography on growth and transport of condensates have not been clearly understood. Inspired by the millimetric bumps of the Namib Desert beetle, here we report the identified role of radius of curvature and width of bumps with homogeneous surface wettability in growth rate, coalescence and transport of water droplets. Further rational design of asymmetric convex topography and synergetic combination with slippery coating simultaneously enable self-transport, leading to unseen five-fold higher growth rate and an order of magnitude faster shedding time of droplets compared...

  18. Recent Developments in Asymmetric Catalysis

    NASA Astrophysics Data System (ADS)

    Toullec, Patrick Y.; Pradal, Alexandre; Michelet, Véronique

    2014-04-01

    The field of gold catalysis has experienced exponential expansion within the last 15 years [1]. The majority of gold-catalyzed reactions rely on the activation of carbon-carbon ?-bonds enhancing the electrophilicity of the unsaturated moiety and therefore favoring nucleophilic additions to the carbon-carbon bond. Rare examples employing the activation of a nucleophilic derivative have been reported. The enantioselective transformations employing gold catalysts have appeared only recently and rely mainly on gold(I) linear chiral complexes, which make the control of stereogenic centers much more difficult [2]. This situation therefore slowed the expansion of the field and made it difficult to generalize chiral systems. This chapter intends to present the seminal examples related to asymmetric catalysis focusing exclusively on the use of a chiral catalyst [3]…

  19. Asymmetric diffusion of cosmic rays

    E-print Network

    Medvedev, Mikhail V

    2015-01-01

    Cosmic ray propagation is diffusive because of pitch angle scattering by waves. We demonstrate that if the high-amplitude magnetohydrodynamic turbulence with $\\tilde B/\\langle B\\rangle \\sim 1$ is present on top of the mean field gradient, the diffusion becomes asymmetric. As an example, we consider the vertical transport of cosmic rays in our Galaxy propagating away from a point-like source. We solve this diffusion problem analytically using a one-dimensional Markov chain analysis. We obtained that the cosmic ray density markedly differs from the standard diffusion prediction and has a sizable effect on their distribution throughout the galaxy. The equation for the continuous limit is also derived, which shows limitations of the convection-diffusion equation.

  20. Total Synthesis of (+)-Laurencin: An Asymmetric Alkylation-Ring-Closing

    E-print Network

    . H.; Overman, L. E.; Takemoto, T. J. Am. Chem. Soc. 1995, 117, 5958-5966. Mujica, M. T.; Afonso, M. M, 119, 7499-7504. Mujica, M. T.; Afonso, M. M.; Galindo, A.; Palenzuela, J. A. J. Org. Chem. 1998, 63 1. Medium ring natural products. ORGANIC LETTERS 1999 Vol. 1, No. 12 2029-2032 10.1021/ol991201e CCC

  1. Asymmetric Synthesis DOI: 10.1002/anie.200503852

    E-print Network

    Toste, Dean

    , catalysts based on vanadium(v) have proven to be the most useful in this transformation. Indeed, the reagent alcohols by catalytic epoxidation[4] resulted in very low stereoselectivity factors.[5] In sharp contrast, we recently described an efficient kinetic resolution of a- hydroxyesters catalyzed by a chiral

  2. Studies on the Synthesis of Reidispongiolide A: Stereoselective Synthesis of the C(22)-C(36) Fragment

    PubMed Central

    Ying, Maben; Roush, William R.

    2011-01-01

    A highly stereoselective synthesis of the C(22)-C(36) fragment 2 of reidispongiolide A is described. This synthesis features the highly stereoselective mismatched double asymmetric crotylboration reaction of the aldehyde derived from 5 and the new chiral reagent (S)-(E)-7 that provides 12 with >15:1 d.r. Subsequent coupling of the derived vinyl iodide 3 with aldehyde 16 provided allylic alcohol 17, that was elaborated by three steps into the targeted reidispongiolide fragment 2. PMID:22711935

  3. Using, Seeing, Feeling, and Doing Absolute Value for Deeper Understanding

    ERIC Educational Resources Information Center

    Ponce, Gregorio A.

    2008-01-01

    Using sticky notes and number lines, a hands-on activity is shared that anchors initial student thinking about absolute value. The initial point of reference should help students successfully evaluate numeric problems involving absolute value. They should also be able to solve absolute value equations and inequalities that are typically found in…

  4. Mixed Integer Linear Programming Method for Absolute Value Equations

    Microsoft Academic Search

    Longquan Yong

    2009-01-01

    We formulate the NP-hard absolute value equation as linear complementary problem when the singular values of A exceed one, and we proposed a mixed integer linear programming method to absolute value equation problem. The effectiveness of the method is demonstrated by its ability to solve random problems. Index Terms—absolute value equation; linear complementary problem; mixed integer linear programming. The basic

  5. Absolute instruments and perfect imaging in geometrical optics

    E-print Network

    Tyc, Tomas

    Absolute instruments and perfect imaging in geometrical optics Tom´as Tyc, Lenka Herz symmetric absolute instruments that provide perfect imaging in the sense of geometrical optics. We derive to propose several new absolute instruments, in particular a lens providing a stigmatic image of an optically

  6. Measurement of the rate of cholesterol synthesis in various organs of the rat in vivo.

    E-print Network

    Paris-Sud XI, Université de

    Measurement of the rate of cholesterol synthesis in various organs of the rat in vivo. T. MAGOT F. Summary. A method to measure the absolute values of the rate of cholesterol synthesis in vivo in each organ being corrected for cholesterol transfer. The rate of cholesterol synthesis in the intact

  7. Absolute neutron measurements in neutron decay

    NASA Astrophysics Data System (ADS)

    Chowdhuri, Zema

    Neutrons undergo ?-decay to produce a proton, an electron and an anti-neutrino. The decay rate plays an important role in particle physics and in cosmology, and since the late 1940s, numerous attempts have been made at the most precise measurement of this rate. The difficulty in detecting neutrons has kept this a challenging experimental problem. This work, based at the NIST reactor, is concerned with a decay rate measurement method in which simultaneous measurements are made of the decay protons and the neutrons in a well-defined volume of neutron beam. From the two, the lifetime can be determined by employing the differential form of the radioactive decay law, dN/dt = -N/? n. The precision goal of the NIST measurement is a part in a thousand; at this time, the largest source of uncertainty is in the determination of the neutron density in the beam. In order to improve on this, we compare the device at the 0.1% level against an absolute detector with unit efficiency for neutron detection. This absolute neutron detector operates by measuring the thermal power produced by neutron capture reactions in a neutron absorber. The primary challenges to this technique are: (1)the accurate detection of very small amounts of power (less than a ?Watt) produced in the particular beam used for this measurement, and (2)the demonstration that all of the kinetic energy of the reaction products appear as heat in the target. Such small energy deposits are detectable with a cryogenic radiometer operating at liquid helium temperatures and we have achieved the required precision goal for the instrument: the measurement uncertainty in the neutron rate over a period of a day is below 0.1% for a neutron rate of 3 × 10 5 s-1. The verification of the absolute accuracy of the radiometer is in progress.

  8. Absolute Radiometric Calibration of EUNIS-06

    NASA Technical Reports Server (NTRS)

    Thomas, R. J.; Rabin, D. M.; Kent, B. J.; Paustian, W.

    2007-01-01

    The Extreme-Ultraviolet Normal-Incidence Spectrometer (EUNIS) is a soundingrocket payload that obtains imaged high-resolution spectra of individual solar features, providing information about the Sun's corona and upper transition region. Shortly after its successful initial flight last year, a complete end-to-end calibration was carried out to determine the instrument's absolute radiometric response over its Longwave bandpass of 300 - 370A. The measurements were done at the Rutherford-Appleton Laboratory (RAL) in England, using the same vacuum facility and EUV radiation source used in the pre-flight calibrations of both SOHO/CDS and Hinode/EIS, as well as in three post-flight calibrations of our SERTS sounding rocket payload, the precursor to EUNIS. The unique radiation source provided by the Physikalisch-Technische Bundesanstalt (PTB) had been calibrated to an absolute accuracy of 7% (l-sigma) at 12 wavelengths covering our bandpass directly against the Berlin electron storage ring BESSY, which is itself a primary radiometric source standard. Scans of the EUNIS aperture were made to determine the instrument's absolute spectral sensitivity to +- 25%, considering all sources of error, and demonstrate that EUNIS-06 was the most sensitive solar E W spectrometer yet flown. The results will be matched against prior calibrations which relied on combining measurements of individual optical components, and on comparisons with theoretically predicted 'insensitive' line ratios. Coordinated observations were made during the EUNIS-06 flight by SOHO/CDS and EIT that will allow re-calibrations of those instruments as well. In addition, future EUNIS flights will provide similar calibration updates for TRACE, Hinode/EIS, and STEREO/SECCHI/EUVI.

  9. Absolute Physical Calibration in the Infrared

    E-print Network

    G. H. Rieke; M. Blaylock; L. Decin; C. Engelbracht; P. Ogle; E. Avrett; J. Carpenter; R. M. Cutri; L. Armus; K. Gordon; R. O. Gray; J. Hinz; K. Su; Christopher N. A. Willmer

    2008-06-11

    We determine an absolute calibration for the MIPS 24 microns band and recommend adjustments to the published calibrations for 2MASS, IRAC, and IRAS photometry to put them on the same scale. We show that consistent results are obtained by basing the calibration on either an average A0V star spectral energy distribution (SED), or by using the absolutely calibrated SED of the sun in comparison with solar-type stellar photometry (the solar analog method). After the rejection of a small number of stars with anomalous SEDs (or bad measurements), upper limits of ~ 1.5% (rms) are placed on the intrinsic infrared SED variations in both A dwarf and solar-type stars. These types of stars are therefore suitable as general-purpose standard stars in the infrared. We provide absolutely calibrated SEDs for a standard zero magnitude A star and for the sun to allow extending this work to any other infrared photometric system. They allow the recommended calibration to be applied from 1 to 25 microns with an accuracy of ~2 %, and with even higher accuracy at specific wavelengths such as 2.2, 10.6, and 24 microns, near which there are direct measurements. However, we confirm earlier indications that Vega does not behave as a typical A0V star between the visible and the infrared, making it problematic as the defining star for photometric systems. The integration of measurements of the sun with those of solar-type stars also provides an accurate estimate of the solar SED from 1 through 30 microns, which we show agrees with theoretical models.

  10. Achieving Climate Change Absolute Accuracy in Orbit

    NASA Technical Reports Server (NTRS)

    Wielicki, Bruce A.; Young, D. F.; Mlynczak, M. G.; Thome, K. J; Leroy, S.; Corliss, J.; Anderson, J. G.; Ao, C. O.; Bantges, R.; Best, F.; Bowman, K.; Brindley, H.; Butler, J. J.; Collins, W.; Dykema, J. A.; Doelling, D. R.; Feldman, D. R.; Fox, N.; Huang, X.; Holz, R.; Huang, Y.; Jennings, D.; Jin, Z.; Johnson, D. G.; Jucks, K.; Kato, S.; Kratz, D. P.; Liu, X.; Lukashin, C.; Mannucci, A. J.; Phojanamongkolkij, N.; Roithmayr, C. M.; Sandford, S.; Taylor, P. C.; Xiong, X.

    2013-01-01

    The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission will provide a calibration laboratory in orbit for the purpose of accurately measuring and attributing climate change. CLARREO measurements establish new climate change benchmarks with high absolute radiometric accuracy and high statistical confidence across a wide range of essential climate variables. CLARREO's inherently high absolute accuracy will be verified and traceable on orbit to Système Internationale (SI) units. The benchmarks established by CLARREO will be critical for assessing changes in the Earth system and climate model predictive capabilities for decades into the future as society works to meet the challenge of optimizing strategies for mitigating and adapting to climate change. The CLARREO benchmarks are derived from measurements of the Earth's thermal infrared spectrum (5-50 micron), the spectrum of solar radiation reflected by the Earth and its atmosphere (320-2300 nm), and radio occultation refractivity from which accurate temperature profiles are derived. The mission has the ability to provide new spectral fingerprints of climate change, as well as to provide the first orbiting radiometer with accuracy sufficient to serve as the reference transfer standard for other space sensors, in essence serving as a "NIST [National Institute of Standards and Technology] in orbit." CLARREO will greatly improve the accuracy and relevance of a wide range of space-borne instruments for decadal climate change. Finally, CLARREO has developed new metrics and methods for determining the accuracy requirements of climate observations for a wide range of climate variables and uncertainty sources. These methods should be useful for improving our understanding of observing requirements for most climate change observations.

  11. Correlated effects of noise on symmetry of an asymmetric bistable system

    NASA Astrophysics Data System (ADS)

    Li, Chun; Long, Fei; Mei, Dong-Cheng

    2015-04-01

    The effects of correlation between additive and multiplicative noises on the symmetry of an asymmetric bistable system are investigated. The steady-state probability distribution function of the system was calculated by using analytical and numerical methods. Results indicate that i) for the case of positive correlation between noises, as the correlation strength between additive and multiplicative noises, ?, increases, the symmetry of the system is restored; ii) for the case of negative correlation between noises, as the absolute value of ? increases, the symmetry of the system is destroyed; and iii) the analytic prediction agrees well with the stochastic simulation result.

  12. Least absolute deviation (LAD) image matching

    NASA Astrophysics Data System (ADS)

    Calitz, M. F.; Rüther, H.

    The robust estimator properties of the L,-norm or least absolute deviation (LAD) is shown to provide better subpixel matching accuracy in the presence of outlier points than the least squares method widely employed for image matching applications. Two LAD algorithms are compared with each other and with the least squares (LS) method and the iteratively reweighted least squares (IRLS) method. Results indicate that the Barrodale-Roberts LAD algorithm can be used advantageously in conjunction with or in place of the IRLS and LS algorithms.

  13. Absolute Priority for a Vehicle in VANET

    NASA Astrophysics Data System (ADS)

    Shirani, Rostam; Hendessi, Faramarz; Montazeri, Mohammad Ali; Sheikh Zefreh, Mohammad

    In today's world, traffic jams waste hundreds of hours of our life. This causes many researchers try to resolve the problem with the idea of Intelligent Transportation System. For some applications like a travelling ambulance, it is important to reduce delay even for a second. In this paper, we propose a completely infrastructure-less approach for finding shortest path and controlling traffic light to provide absolute priority for an emergency vehicle. We use the idea of vehicular ad-hoc networking to reduce the imposed travelling time. Then, we simulate our proposed protocol and compare it with a centrally controlled traffic light system.

  14. Absolute Calibration of the Auger Fluorescence Detectors

    E-print Network

    P. Bauleo; J. Brack; L. Garrard; J. Harton; R. Knapik; R. Meyhandan; A. C. Rovero; A. Tamashiro; D. Warner; for the Auger Collaboration

    2005-07-14

    Absolute calibration of the Pierre Auger Observatory fluorescence detectors uses a light source at the telescope aperture. The technique accounts for the ombined effects of all detector components in a single measurement. The calibrated 2.5 m diameter light source fills the aperture, providing uniform illumination to each pixel. The known flux from the light source and the response of the acquisition system give the required calibration for each pixel. In the lab, light source uniformity is studied using CCD images and the intensity is measured relative to NIST-calibrated photodiodes. Overall uncertainties are presently 12%, and are dominated by systematics.

  15. Asymmetric Ruthenium-Catalyzed Hydrogenation of 2,6-Disubstituted 1,5-Naphthyridines: Access to Chiral 1,5-Diaza-cis-Decalins.

    PubMed

    Zhang, Jianwei; Chen, Fei; He, Yan-Mei; Fan, Qing-Hua

    2015-04-01

    The first asymmetric hydrogenation (AH) of 2,6-disubstituted and 2,3,6-trisubstituted 1,5-naphthyridines, catalyzed by chiral cationic ruthenium diamine complexes, has been developed. A wide range of 1,5-naphthyridine derivatives were efficiently hydrogenated to give 1,2,3,4-tetrahydro-1,5-naphthyridines with up to 99?%?ee and full conversions. This facile and green protocol is applicable to the scaled-up synthesis of optically pure 1,5-diaza-cis-decalins, which have been used as rigid chelating diamine ligands for asymmetric synthesis. PMID:25694113

  16. Stereoselective synthesis of (+)-loline alkaloid skeleton.

    PubMed

    Miller, Kelsey E; Wright, Anthony J; Olesen, Margaret K; Hovey, M Todd; Scheerer, Jonathan R

    2015-02-01

    The loline alkaloids present a compact polycyclic pyrrolizidine skeleton and contain a strained five-membered ethereal bridge, structural features that have proven challenging for synthetic chemists to incorporate since the discovery of this natural product family more than 100 years ago. These alkaloids are produced by mutualistic fungal symbionts (endophytes) living on certain species of pasture grasses and protect the host plant from insect herbivory. The asymmetric total synthesis of loline alkaloids is reported and extends our first-generation (racemic) synthesis of this alkaloid family. Key to the synthesis is a diastereoselective tethered aminohydroxylation of a homoallylic carbamate function and a Petasis Borono-Mannich addition. PMID:25611615

  17. Forced structural response using component mode synthesis

    SciTech Connect

    Allen, J.J.; Martinez, D.R.

    1985-03-01

    This report discusses the effects of omitting constraint modes corresponding to applied loads in systems modeled with component mode synthesis. A method of correcting for the omitted constraint modes is also developed. A free component mode synthesis method is applied to a continuous model of an axial rod-spring system, and the effect of omitted constraint modes on the static, steady-state harmonic, and transient response is studied. The effect of omitted constraint modes on the transient response of an asymmetric beam is presented using the free and fixed component mode synthesis methods implemented in MSC/NASTRAN. A simple pinned truss finite element model is also studied.

  18. Measurement of the Absolute Branching Fraction of D0 to K- pi+

    SciTech Connect

    Aubert, B.; Bona, M.; Boutigny, D.; Karyotakis, Y.; Lees, J.P.; Poireau, V.; Prudent, X.; Tisserand, V.; Zghiche, A.; /Annecy, LAPP; Garra Tico, J.; Grauges, E.; /Barcelona U., ECM; Lopez, L.; Palano, A.; /Bari U.; Eigen, G.; Ofte, I.; Stugu, B.; Sun, L.; /Bergen U.; Abrams, G.S.; Battaglia, M.; Brown, D.N.; Button-Shafer, J.; /LBL, Berkeley

    2007-04-25

    The authors measure the absolute branching fraction for D{sup 0} {yields} K{sup -} {pi}{sup +} using partial reconstruction of {bar B}{sup 0} {yields} D*{sup +}X{ell}{sup -}{bar {nu}}{sub {ell}} decays, in which only the charged lepton and the pion from the decay D*{sup +} {yields} D{sup 0}{pi}{sup +} are used. Based on a data sample of 230 million B{bar B} pairs collected at the {Upsilon}(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC, they obtain {Beta}(D{sup 0} {yields} K{sup -}{pi}{sup +}) = (4.007 {+-} 0.037 {+-} 0.070)%, where the first error is statistical and the second error is systematic.

  19. Organocatalytic cascade reactions as a new tool in total synthesis

    NASA Astrophysics Data System (ADS)

    Grondal, Christoph; Jeanty, Matthieu; Enders, Dieter

    2010-03-01

    The total synthesis of natural products and biologically active compounds, such as pharmaceuticals and agrochemicals, has reached an extraordinary level of sophistication. We are, however, still far away from the 'ideal synthesis' and the state of the art is still frequently hampered by lengthy protecting-group strategies and costly purification procedures derived from the step-by-step protocols. In recent years several new criteria have been brought forward to solve these problems and to improve total synthesis: atom, step and redox economy or protecting-group-free synthesis. Over the past decade the research area of organocatalysis has rapidly grown to become a third pillar of asymmetric catalysis standing next to metal and biocatalysis, thus paving the way for a new and powerful strategy that can help to address these issues - organocatalytic cascade reactions. In this Review we present the first applications of such asymmetric organocascade reactions to the total synthesis of natural products.

  20. New coumarins from Harbouria trachypleura: isolation and synthesis

    Microsoft Academic Search

    Nathan R Guz; Peter Lorenz; Frank R Stermitz

    2001-01-01

    Two known furanocoumarins, (+)-oxypeucedanin and (+)-saxalin, two known coumarins, umbelliferone and (+)-epoxysuberosin, and two new coumarins (+)-trachypleuranin-A and (±)-trachypleuranin-B, were isolated from the methanol extract of Harbouria trachypleura. An efficient five-step asymmetric synthesis of (+)-trachypleuranin-A was performed using a sequential [3,3] Claisen–Cope rearrangement and a Shi asymmetric epoxidation. (±)-Trachypleuranin-B, a chlorinated coumarin, was synthesized from (±)-epoxysuberosin.

  1. A method for absolute calibration of compasses

    NASA Astrophysics Data System (ADS)

    LeMenn, Marc; LeGoff, Michel

    2007-05-01

    In order to reference the speed and direction of ocean currents, currentmeters are fitted with a magnetic compass. The manufacturers of currentmeters provide users so-called autocalibration procedures and software to allow for the verification of the good working order and rectification of the bias of compass magnetic field sensors. Nevertheless, these tests do not make it possible to correct all the errors that can alter field measurements and particularly the nonlinear effects. In order to calculate corrections and estimate the accuracy of the 'autocalibration' procedure, an absolute calibration method has been devised, based on the GPS positioning of two geodetic reference points and on the measurement of angles and distances between one of these points and the instrument being tested. The standard uncertainty of this method has been assessed as 0.64°. It is below the compass accuracy and makes it possible to underscore the bias resulting from the 'autocalibration' operations and to evaluate corrections. This method, which can be extended to other equipment, is a solution for absolute compass calibrations.

  2. Absolute configuration of 7-epi-sesquithujene.

    PubMed

    Khrimian, Ashot; Cossé, Allard A; Crook, Damon J

    2011-06-24

    7-epi-sesquithujene (1) is a bicyclic sesquiterpene isolated from phoebe oil, an essential oil of the Brazilian walnut tree, Phoebe porosa. It is also produced by stressed ash trees and has been shown to elicit strong electrophysiological responses on emerald ash borer, Agrilus planipennis, antennae. In the course of the development of a synthetic 7-epi-sesquithujene lure for field testing against the emerald ash borer, we found that the absolute configuration of this compound had not been determined. We isolated >95% pure 7-epi-sesquithujene from phoebe oil via successive fractionation and conventional and argentation (HPLC) chromatographies. The specific optical rotation of this compound matched that of a synthetic product of known configuration. We also synthesized two other stereoisomers of sesquithujene and developed a chiral GC method to separate all four. Based on the specific rotation, stereoselective syntheses, and chiral GC analyses, 7-epi-sesquithujene present in phoebe oil and white ash was found to have the 2S,6S,7R absolute configuration. PMID:21574561

  3. Standardization of the cumulative absolute velocity

    SciTech Connect

    O'Hara, T.F.; Jacobson, J.P. (Yankee Atomic Electric Co., Bolton, MA (United States))

    1991-12-01

    EPRI NP-5930, A Criterion for Determining Exceedance of the Operating Basis Earthquake,'' was published in July 1988. As defined in that report, the Operating Basis Earthquake (OBE) is exceeded when both a response spectrum parameter and a second damage parameter, referred to as the Cumulative Absolute Velocity (CAV), are exceeded. In the review process of the above report, it was noted that the calculation of CAV could be confounded by time history records of long duration containing low (nondamaging) acceleration. Therefore, it is necessary to standardize the method of calculating CAV to account for record length. This standardized methodology allows consistent comparisons between future CAV calculations and the adjusted CAV threshold value based upon applying the standardized methodology to the data set presented in EPRI NP-5930. The recommended method to standardize the CAV calculation is to window its calculation on a second-by-second basis for a given time history. If the absolute acceleration exceeds 0.025g at any time during each one second interval, the earthquake records used in EPRI NP-5930 have been reanalyzed and the adjusted threshold of damage for CAV was found to be 0.16g-set.

  4. Enantioselective total syntheses of several bioactive natural products based on the development of practical asymmetric catalysis.

    PubMed

    Ohshima, Takashi

    2004-09-01

    I present herewith enantioselective total syntheses of several bioactive natural products, such as (-)-strychnine, (+)-decursin, (-)-cryptocaryolone diacetate, (-)-fluoxetine, and aeruginosin 298-A, based on practical asymmetric catalyses (Michael reaction, epoxidation, and phase-transfer reaction) that I developed with co-workers in Prof. Shibasaki's group over the past 5 years. In the first part of this review, I discuss the great improvement of catalyst efficiency in an ALB-catalyzed asymmetric Michael reaction of malonate and application to the pre-manufacturing scale (greater than kilogram scale) and enantioselective total synthesis of (-)-strychnine with the development of novel domino cyclization. To broaden the substrate generality of the Michael reaction, we developed a highly stable, storable, and reusable La-O-linked-BINOL complex. Further extension of the reaction using beta-keto ester as a Michael donor was achieved with the development of a La-NR-linked-BINOL complex, thereby improving indole alkaloid syntheses. In the second section, I discuss enantioselective total synthesis of (+)-decursin using catalytic asymmetric epoxidation. To achieve the synthesis, we developed a new La-BINOL-Ph(3)As = O (1:1:1) complex catalyst system, which has much higher reactivity and broader substrate generality than the previously developed catalyst systems. This allowed us to achieve catalytic asymmetric epoxidation of alpha,beta-unsaturated carboxylic acid derivatives with high enantioselectivity and broad substrate generality for the first time by changing the lanthanide metal and reaction conditions. Among them, catalytic asymmetric epoxidation of alpha,beta-unsaturated morpholinyl amides is quite useful in terms of synthetic utility of the corresponding alpha,beta-epoxy morpholinyl amides. Highly catalyst-controlled enantio- or diastereoselective epoxidation of the alpha,beta-unsaturated morpholinyl amides, coupled with diastereoselective reduction of beta-hydroxy ketones, enabled the synthesis of all possible stereoisomers of 1,3-polyol arrays with successful enantioselective total synthesis of several 1,3-polyol natural products, such as (-)-cryptocaryolone diacetate. In addition, the development of a new regioselective epoxide-opening reaction of alpha,beta-epoxy amides to the corresponding alpha- and beta-hydroxy amides enhanced the usefulness of the present epoxidation and was applied to the enantioselective total synthesis of (-)-fluoxetine. In the final section, I report the development of a new asymmetric two-center organocatalyst (TaDiAS) and its application to the enantioselective synthesis of aeruginosin 298-A and its analogues. Because of the remarkable structural diversity of TaDiAS, a practical asymmetric phase-transfer reaction with broad substrate generality was achieved. As a result, we succeeded in developing a highly versatile synthetic method for aeruginosin 298-A and its analogues. Inhibitory activity studies of the compounds against the serine protease trypsin provided preliminary information about their structure-activity relations. PMID:15340187

  5. 0 PROLOGUE --ABSOLUTE VALUE INEQUALITIES 1 0.1 Absolute Value Inequalities . . . . . . . . . . . . . . . . . . . . 1

    E-print Network

    Sarkar, Amites

    the relevant material about the manipulation of absolute value inequalities. The main point will be this: to solve an inequality like |2x - 5| picture rather than just trying to do algebra. Some algebraic manipulation is unavoidable, but to avoid manipulative errors, geometric insight

  6. Investigation of asymmetric plasma blob dynamics

    E-print Network

    Soane, Alexander (Alexander Visotsky)

    2009-01-01

    The dynamics of asymmetric blobs is investigated in the Versatile Toroidal Facility (VTF) at MIT. Blobs are local regions of enhanced plasma density. Blobs are relevant to several areas of physics research, including fusion ...

  7. Quantum key distribution with asymmetric channel noise

    SciTech Connect

    Wang Xiangbin [Imai Quantum Computation and Information Project, ERATO, JST, Hongo White Building 201, 5-28-3, Hongo, Bunkyo, Tokyo 113-0033 (Japan)

    2005-05-15

    We show that, one may take advantage of the asymmetry of channel noise. With appropriate modifications to the standard protocols, both the key rate and the tolerable total channel noise can be increased if the channel noise is asymmetric.

  8. [Asymmetric septal hypertrophy associated with "subclinical hypothyroidism"].

    PubMed

    Felices Nieto, Andrés; Quero Cuevas, José; González Barrero, Antonio; Cabello González, Alicia; López Chozas, José M; Alvarez Aragón, Luis M

    2004-08-01

    We report a case of hypothyroid cardiomyopathy manifested as reversible asymmetric septal hypertrophy in a 61-year-old white woman diagnosed 20 years previously with primary hypothyroidism. PMID:15282071

  9. Asymmetric Abelian Avalanches and Sandpiles Andrei Gabrielov

    E-print Network

    Gabrielov, Andrei

    Asymmetric Abelian Avalanches and Sandpiles Andrei Gabrielov Mathematical Sciences Institute consider two classes of threshold failure models, Abel- ian avalanches and sandpiles, with the redistribution matrices satisfying nat- ural conditions guaranteeing absence of infinite avalanches. We

  10. Asymmetric wave propagation in planar chiral fibers

    E-print Network

    Shemuly, Dana

    We demonstrate the realization of a two-dimensional chiral optical waveguide with an infinite translational symmetry that exhibits asymmetric wave propagation. The low-symmetry geometry of the cross-section that lacks any ...

  11. Reflection asymmetric shapes in nuclei

    SciTech Connect

    Ahmad, I.; Carpenter, M.P.; Emling, H.; Holzmann, R.; Janssens, R.V.F.; Khoo, T.L.; Moore, E.F.; Morss, L.R.; Durell, J.L.; Fitzgerald, J.B.; Mowbary, A.S.; Hotchkiss, M.A.; Phillips, W.R.; Drigert, M.W.; Ye, D.; Benet, P. (Argonne National Lab., IL (USA); Manchester Univ. (UK). Dept. of Physics; EG and G Idaho, Inc., Idaho Falls, ID (USA); Notre Dame Univ., IN (USA); Purdue Univ., Lafayette, IN (USA))

    1989-01-01

    Experimental data show that there is no even-even nucleus with a reflection asymmetric shape in its ground state. Maximum octupole- octupole correlations occur in nuclei in the mass 224 (N{approximately}134, Z{approximately}88) region. Parity doublets, which are the characteristic signature of octupole deformation, have been observed in several odd mass Ra, Ac and Pa nuclei. Intertwined negative and positive parity levels have been observed in several even-even Ra and Th nuclei above spin {approximately}8{Dirac h}. In both cases, the opposite parity states are connected by fast El transitions. In some medium-mass nuclei intertwined negative and positive parity levels have also been observed above spin {approximately}7{Dirac h}. The nuclei which exhibit octupole deformation in this mass region are {sup 144}Ba, {sup 146}Ba and {sub 146}Ce; {sup 142}Ba, {sup 148}Ce, {sup 150}Ce and {sup 142}Xe do not show these characteristics. No case of parity doublet has been observed in the mass 144 region. 32 refs., 16 figs., 1 tab.

  12. Condensation on Slippery Asymmetric Bumps

    E-print Network

    Kyoo-Chul Park; Philseok Kim; Neil He; Joanna Aizenberg

    2015-01-14

    Bumps are omnipresent from human skin to the geological structures on planets, which offer distinct advantages in numerous phenomena including structural color, drag reduction, and extreme wettability. Although the topographical parameters of bumps such as radius of curvature of convex regions significantly influence various phenomena including anti-reflective structures and contact time of impacting droplets, the effect of the detailed bump topography on growth and transport of condensates have not been clearly understood. Inspired by the millimetric bumps of the Namib Desert beetle, here we report the identified role of radius of curvature and width of bumps with homogeneous surface wettability in growth rate, coalescence and transport of water droplets. Further rational design of asymmetric convex topography and synergetic combination with slippery coating simultaneously enable self-transport, leading to unseen five-fold higher growth rate and an order of magnitude faster shedding time of droplets compared to superhydrophobic surfaces. We envision that our fundamental understanding and innovative design of bumps can be applied to lead enhanced performance in various phase change applications including water harvesting.

  13. Asymmetric parasitic dicephalus conjoined twins.

    PubMed

    Esenkaya, Semra; Gürbüz, Birgül; Yalti, Serap

    2004-02-01

    In this report, we describe the case of a 19-year-old primigravida pregnant woman who had been hospitalized for 2 days with bleeding and a diagnosis of imminent abortion. Sonographic examination revealed a single fetus of approximately 17 weeks' gestation that initially appeared normal except for a mass on its neck. Further evaluation of the mass identified it as an anencephalic fetal head that was joined to the body with deformed cervical vertebrae. We diagnosed asymmetric parasitic dicephalus conjoined twins. The parents elected to terminate the pregnancy. Labor was induced, and the patient delivered a 20-cm, 208-g male fetus. The fetus had 4 normal limbs and a normal abdomen. Both its heads had a cleft lip, and its spine was U shaped with closed spina bifida at the spinal union in the thoracolumbar area. The patterns of conjoined twins are infinitely varied, but they can be generally classified according to standardized terms based on the anatomic site of their union. Cases of conjoined twins occur so rarely that it is important to learn as much as possible from each case. PMID:14750144

  14. Asymmetric reduction of racemic 2-isoxazolines

    Microsoft Academic Search

    Masashi Tokizane; Kaori Sato; Tetsuo Ohta; Yoshihiko Ito

    2008-01-01

    The kinetic resolution of racemic 2-isoxazolines was carried out by asymmetric reduction using borane with 1,2-amino alcohols as a chiral source. Using excess BH3–THF in the presence of (?)-norephedrine, optically active 1,3-amino alcohol derivatives were obtained with good ee but in lower yield, while the optically active substrates 2-isoxazolines were recovered with modest ee. The asymmetric reduction using 2.0equiv of

  15. On the Construction of Asymmetric Quantum Codes

    NASA Astrophysics Data System (ADS)

    La Guardia, Giuliano G.

    2014-07-01

    Several families of good nonbinary asymmetric quantum codes are constructed in this paper. These new quantum codes are derived from the Calderbank-Shor-Steane (CSS) construction as well as the Hermitian construction applied respectively to two classical nested Bose-Chaudhuri-Hocquenghem (BCH) codes where one of them are additionally Euclidean (Hermitian) dual-containing. The asymmetric codes constructed here have parameters better than the ones available in the literature.

  16. Asymmetrical non-imaging cylindrical solar concentrators

    Microsoft Academic Search

    D. R. Mills; J. E. Giutronich

    1978-01-01

    Two types of asymmetrical concentrators, parabolic and nonparabolic, are compared to those with symmetrical designs. Asymmetrical configurations are found to provide many advantages, including: (1) a concentration versus time-of-day relationship which can compensate for projected solar-area fall-off, allowing more uniform energy output when this is desirable, (2) greater operational flexibility, (3) easier adaptation to vacuum-insulated receivers, and (4) possible increased

  17. Asymmetric Magnetic Reconnection in the Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Murphy, N. A.; Miralles, M.; Ranquist, D. A.; Pope, C. L.; Raymond, J. C.; Lukin, V. S.; McKillop, S.; Shen, C.; Winter, H. D.; Reeves, K. K.; Lin, J.

    2013-12-01

    Models of solar flares and coronal mass ejections typically predict the development of an elongated current sheet in the wake behind the rising flux rope. In reality, reconnection in these current sheets will be asymmetric along the inflow, outflow, and out-of-plane directions. We perform resistive MHD simulations to investigate the consequences of asymmetry during solar reconnection. We predict several observational signatures of asymmetric reconnection, including flare loops with a skewed candle flame shape, slow drifting of the current sheet into the strong field upstream region, asymmetric footpoint speeds and hard X-ray emission, and rolling motions within the erupting flux rope. There is net plasma flow across the magnetic field null along both the inflow and outflow directions. We compare simulations to SDO/AIA, Hinode/XRT, and STEREO observations of flare loop shapes, current sheet drifting, and rolling motions during prominence eruptions. Simulations of the plasmoid instability with different upstream magnetic fields show that the reconnection rate remains enhanced even during the asymmetric case. The islands preferentially grow into the weak field upstream region. The islands develop net vorticity because the outflow jets impact them obliquely rather than directly. Asymmetric reconnection in the chromosphere occurs when emerging flux interacts with pre-existing overlying flux. We present initial results on asymmetric reconnection in partially ionized chromospheric plasmas. Finally, we discuss how comparisons to observations are necessary to understand the role of three-dimensional effects.

  18. Asymmetric Magnetic Reconnection in the Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Murphy, N. A.; Miralles, M. P.; Ranquist, D. A.; Pope, C. L.; Raymond, J. C.; Lukin, V. S.; McKillop, S. C.; Shen, C.; Winter, H. D.; Reeves, K. K.; Lin, J.

    2013-12-01

    Models of solar flares and coronal mass ejections typically predict the development of an elongated current sheet in the wake behind the rising flux rope. In reality, reconnection in these current sheets will be asymmetric along the inflow, outflow, and out-of-plane directions. We perform resistive MHD simulations to investigate the consequences of asymmetry during solar reconnection. We predict several observational signatures of asymmetric reconnection, including flare loops with a skewed candle flame shape, slow drifting of the current sheet into the strong field upstream region, asymmetric footpoint speeds and hard X-ray emission, and rolling motions within the erupting flux rope. There is net plasma flow across the magnetic field null along both the inflow and outflow directions. We compare simulations to SDO/AIA, Hinode/XRT, and STEREO observations of flare loop shapes, current sheet drifting, and rolling motions during prominence eruptions. Simulations of the plasm! oid instability with different upstream magnetic fields show that the reconnection rate remains enhanced even during the asymmetric case. The islands preferentially grow into the weak field upstream region. The islands develop net vorticity because the outflow jets impact them obliquely rather than directly. Asymmetric reconnection in the chromosphere occurs when emerging flux interacts with pre-existing overlying flux. We present initial results on asymmetric reconnection in partially ionized chromospheric plasmas. Finally, we discuss how comparisons to observations are necessary to understand the role of three-dimensional effects.

  19. Absolute measurements of fast neutrons using yttrium.

    PubMed

    Roshan, M V; Springham, S V; Rawat, R S; Lee, P; Krishnan, M

    2010-08-01

    Yttrium is presented as an absolute neutron detector for pulsed neutron sources. It has high sensitivity for detecting fast neutrons. Yttrium has the property of generating a monoenergetic secondary radiation in the form of a 909 keV gamma-ray caused by inelastic neutron interaction. It was calibrated numerically using MCNPX and does not need periodic recalibration. The total yttrium efficiency for detecting 2.45 MeV neutrons was determined to be f(n) approximately 4.1x10(-4) with an uncertainty of about 0.27%. The yttrium detector was employed in the NX2 plasma focus experiments and showed the neutron yield of the order of 10(8) neutrons per discharge. PMID:20815606

  20. Absolute instability of a viscous hollow jet

    NASA Astrophysics Data System (ADS)

    Gañán-Calvo, Alfonso M.

    2007-02-01

    An investigation of the spatiotemporal stability of hollow jets in unbounded coflowing liquids, using a general dispersion relation previously derived, shows them to be absolutely unstable for all physical values of the Reynolds and Weber numbers. The roots of the symmetry breakdown with respect to the liquid jet case, and the validity of asymptotic models are here studied in detail. Asymptotic analyses for low and high Reynolds numbers are provided, showing that old and well-established limiting dispersion relations [J. W. S. Rayleigh, The Theory of Sound (Dover, New York, 1945); S. Chandrasekhar, Hydrodynamic and Hydromagnetic Stability (Dover, New York, 1961)] should be used with caution. In the creeping flow limit, the analysis shows that, if the hollow jet is filled with any finite density and viscosity fluid, a steady jet could be made arbitrarily small (compatible with the continuum hypothesis) if the coflowing liquid moves faster than a critical velocity.

  1. Absolute instability of a viscous hollow jet.

    PubMed

    Gañán-Calvo, Alfonso M

    2007-02-01

    An investigation of the spatiotemporal stability of hollow jets in unbounded coflowing liquids, using a general dispersion relation previously derived, shows them to be absolutely unstable for all physical values of the Reynolds and Weber numbers. The roots of the symmetry breakdown with respect to the liquid jet case, and the validity of asymptotic models are here studied in detail. Asymptotic analyses for low and high Reynolds numbers are provided, showing that old and well-established limiting dispersion relations [J. W. S. Rayleigh, The Theory of Sound (Dover, New York, 1945); S. Chandrasekhar, Hydrodynamic and Hydromagnetic Stability (Dover, New York, 1961)] should be used with caution. In the creeping flow limit, the analysis shows that, if the hollow jet is filled with any finite density and viscosity fluid, a steady jet could be made arbitrarily small (compatible with the continuum hypothesis) if the coflowing liquid moves faster than a critical velocity. PMID:17358457

  2. Absolute radiometric calibration of the Thematic Mapper

    NASA Technical Reports Server (NTRS)

    Slater, P. N.; Biggar, S. F.; Holm, R. G.; Jackson, R. D.; Mao, Y.

    1986-01-01

    Calibration data for the solar reflective bands of the Landsat-5 TM obtained from five in-flight absolute radiometric calibrations from July 1984-November 1985 at White Sands, New Mexico are presented and analyzed. Ground reflectance and atmospheric data were utilized to predict the spectral radiance at the entrance pupil of the TM and the average number of digital counts in each TM band. The calibration of each of the TM solar reflective bands was calculated in terms of average digital counts/unit spectral radiance for each band. It is observed that for the 12 reflectance-based measurements the rms variation from the means as a percentage of the mean is + or - 1.9 percent; for the 11 measurements in the IR bands, it is + or - 3.4 percent; and the rms variation for all 23 measurements is + or - 2.8 percent.

  3. MAGSAT: Vector magnetometer absolute sensor alignment determination

    NASA Technical Reports Server (NTRS)

    Acuna, M. H.

    1981-01-01

    A procedure is described for accurately determining the absolute alignment of the magnetic axes of a triaxial magnetometer sensor with respect to an external, fixed, reference coordinate system. The method does not require that the magnetic field vector orientation, as generated by a triaxial calibration coil system, be known to better than a few degrees from its true position, and minimizes the number of positions through which a sensor assembly must be rotated to obtain a solution. Computer simulations show that accuracies of better than 0.4 seconds of arc can be achieved under typical test conditions associated with existing magnetic test facilities. The basic approach is similar in nature to that presented by McPherron and Snare (1978) except that only three sensor positions are required and the system of equations to be solved is considerably simplified. Applications of the method to the case of the MAGSAT Vector Magnetometer are presented and the problems encountered discussed.

  4. Absolute measurements of fast neutrons using yttrium

    SciTech Connect

    Roshan, M. V.; Springham, S. V.; Rawat, R. S.; Lee, P.; Krishnan, M. [National Institute of Education, Nanyang Technological University, Singapore, 637616 (Singapore)

    2010-08-15

    Yttrium is presented as an absolute neutron detector for pulsed neutron sources. It has high sensitivity for detecting fast neutrons. Yttrium has the property of generating a monoenergetic secondary radiation in the form of a 909 keV gamma-ray caused by inelastic neutron interaction. It was calibrated numerically using MCNPX and does not need periodic recalibration. The total yttrium efficiency for detecting 2.45 MeV neutrons was determined to be f{sub n}{approx}4.1x10{sup -4} with an uncertainty of about 0.27%. The yttrium detector was employed in the NX2 plasma focus experiments and showed the neutron yield of the order of 10{sup 8} neutrons per discharge.

  5. Measured and modelled absolute gravity in Greenland

    NASA Astrophysics Data System (ADS)

    Nielsen, E.; Forsberg, R.; Strykowski, G.

    2012-12-01

    Present day changes in the ice volume in glaciated areas like Greenland will change the load on the Earth and to this change the lithosphere will respond elastically. The Earth also responds to changes in the ice volume over a millennial time scale. This response is due to the viscous properties of the mantle and is known as Glaical Isostatic Adjustment (GIA). Both signals are present in GPS and absolute gravity (AG) measurements and they will give an uncertainty in mass balance estimates calculated from these data types. It is possible to separate the two signals if both gravity and Global Positioning System (GPS) time series are available. DTU Space acquired an A10 absolute gravimeter in 2008. One purpose of this instrument is to establish AG time series in Greenland and the first measurements were conducted in 2009. Since then are 18 different Greenland GPS Network (GNET) stations visited and six of these are visited more then once. The gravity signal consists of three signals; the elastic signal, the viscous signal and the direct attraction from the ice masses. All of these signals can be modelled using various techniques. The viscous signal is modelled by solving the Sea Level Equation with an appropriate ice history and Earth model. The free code SELEN is used for this. The elastic signal is modelled as a convolution of the elastic Greens function for gravity and a model of present day ice mass changes. The direct attraction is the same as the Newtonian attraction and is calculated as this. Here we will present the preliminary results of the AG measurements in Greenland. We will also present modelled estimates of the direct attraction, the elastic and the viscous signals.

  6. Asymmetric autocatalysis induced by meteoritic amino acids with hydrogen isotope chirality† †This article is part of a ChemComm ‘Catalysis in Organic Synthesis’ web-theme issue showcasing high quality research in organic chemistry. Please see our website (http://www.rsc.org/chemcomm/organicwebtheme2009) to access the other papers in this issue. ‡ ‡Electronic supplementary information (ESI) available: Procedures for the asymmetric autocatalysis in the presence of 1 and 2, the preparation of enantiomers of 1 and 2, and the determination of the enantiomeric purity of 1 and 2. See DOI: 10.1039/b908754k Click here for additional data file.

    PubMed Central

    Kawasaki, Tsuneomi; Shimizu, Masako; Nishiyama, Daisuke; Ito, Masateru; Ozawa, Hitomi

    2009-01-01

    Achiral meteoritic amino acids, glycine and ?-methylalanine, with hydrogen isotope (D/H) chirality, acted as the source of chirality in asymmetric autocatalysis with amplification of ee to afford highly enantioenriched 5-pyrimidyl alkanols. PMID:19597604

  7. A new route to methyl (R,E)-(-)-tetradeca-2,4,5-trienoate (pheromone of Acanthoscelides obtectus) utilizing a palladium-catalyzed asymmetric allene formation reaction.

    PubMed

    Ogasawara, Masamichi; Nagano, Takashi; Hayashi, Tamio

    2005-07-01

    [reaction: see text] A formal total synthesis of the sex attractant of male dried bean beetle, methyl (R,E)-(-)-tetradeca-2,4,5-trienoate, was achieved by a new efficient route utilizing the Pd-catalyzed asymmetric allene synthesis reaction. It was found that the atropisomeric biaryl bisphosphine (R)-segphos showed better enantioselectivity than (R)-binap in the Pd-catalyzed reaction for preparing alkyl-substituted axially chiral allenes. PMID:15989370

  8. Asymmetric Bessel-Gauss beams.

    PubMed

    Kotlyar, V V; Kovalev, A A; Skidanov, R V; Soifer, V A

    2014-09-01

    We propose a three-parameter family of asymmetric Bessel-Gauss (aBG) beams with integer and fractional orbital angular momentum (OAM). The aBG beams are described by the product of a Gaussian function by the nth-order Bessel function of the first kind of complex argument, having finite energy. The aBG beam's asymmetry degree depends on a real parameter c?0: at c=0, the aBG beam is coincident with a conventional radially symmetric Bessel-Gauss (BG) beam; with increasing c, the aBG beam acquires a semicrescent shape, then becoming elongated along the y axis and shifting along the x axis for c?1. In the initial plane, the intensity distribution of the aBG beams has a countable number of isolated optical nulls on the x axis, which result in optical vortices with unit topological charge and opposite signs on the different sides of the origin. As the aBG beam propagates, the vortex centers undergo a nonuniform rotation with the entire beam about the optical axis (c?1), making a ?/4 turn at the Rayleigh range and another ?/4 turn after traveling the remaining distance. At different values of the c parameter, the optical nulls of the transverse intensity distribution change their position, thus changing the OAM that the beam carries. An isolated optical null on the optical axis generates an optical vortex with topological charge n. A vortex laser beam shaped as a rotating semicrescent has been generated using a spatial light modulator. PMID:25401437

  9. Issues in Absolute Spectral Radiometric Calibration: Intercomparison of Eight Sources

    NASA Technical Reports Server (NTRS)

    Goetz, Alexander F. H.; Kindel, Bruce; Pilewskie, Peter

    1998-01-01

    The application of atmospheric models to AVIRIS and other spectral imaging data to derive surface reflectance requires that the sensor output be calibrated to absolute radiance. Uncertainties in absolute calibration are to be expected, and claims of 92% accuracy have been published. Measurements of accurate surface albedos and cloud absorption to be used in radiative balance calculations depend critically on knowing the absolute spectral-radiometric response of the sensor. The Earth Observing System project is implementing a rigorous program of absolute radiometric calibration for all optical sensors. Since a number of imaging instruments that provide output in terms of absolute radiance are calibrated at different sites, it is important to determine the errors that can be expected among calibration sites. Another question exists about the errors in the absolute knowledge of the exoatmospheric spectral solar irradiance.

  10. Absolute nuclear material assay using count distribution (LAMBDA) space

    DOEpatents

    Prasad, Manoj K. (Pleasanton, CA); Snyderman, Neal J. (Berkeley, CA); Rowland, Mark S. (Alamo, CA)

    2012-06-05

    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.

  11. Absolute luminosity measurements with the LHCb detector at the LHC

    Microsoft Academic Search

    R. Aaij; B. Adeva; M. Adinolfi; C. Adrover; A. Affolder; Z. Ajaltouni; J. Albrecht; F. Alessio; M. Alexander; G. Alkhazov; P. Alvarez Cartelle; A. A. Alves Jr; S. Amato; Y. Amhis; J. Anderson; R. B. Appleby; O. Aquines Gutierrez; F. Archilli; L. Arrabito; A. Artamonov; M. Artuso; E. Aslanides; G. Auriemma; S. Bachmann; J. J. Back; D. S. Bailey; V. Balagura; W. Baldini; R. J. Barlow; C. Barschel; S. Barsuk; W. Barter; A. Bates; C. Bauer; Th. Bauer; A. Bay; I. Bediaga; K. Belous; I. Belyaev; E. Ben-Haim; M. Benayoun; G. Bencivenni; S. Benson; J. Benton; R. Bernet; M van Beuzekom; A. Bien; S. Bifani; A. Bizzeti; P. M. Bjørnstad; T. Blake; F. Blanc; C. Blanks; J. Blouw; S. Blusk; A. Bobrov; V. Bocci; A. Bondar; N. Bondar; W. Bonivento; S. Borghi; A. Borgia; T. J. V. Bowcock; C. Bozzi; T. Brambach; J. van den Brand; J. Bressieux; D. Brett; S. Brisbane; M. Britsch; T. Britton; N. H. Brook; H. Brown; A. Büchler-Germann; I. Burducea; A. Bursche; J. Buytaert; S. Cadeddu; J. M. Caicedo Carvajal; O. Callot; M. Calvi; M. Calvo Gomez; A. Camboni; P. Campana; A. Carbone; G. Carboni; R. Cardinale; A. Cardini; L. Carson; K. Carvalho Akiba; G. Casse; M. Cattaneo; M. Charles; Ph. Charpentier; N. Chiapolini; K. Ciba; X. Cid Vidal; G. Ciezarek; P. E. L. Clarke; M. Clemencic; H. V. Cliff; J. Closier; C. Coca; V. Coco; J. Cogan; P. Collins; F. Constantin; G. Conti; A. Contu; A. Cook; M. Coombes; G A Cowan; R. Currie; B. D'Almagne; C. D'Ambrosio; P. David; I. De Bonis; S. De Capua; M. De Cian; F. De Lorenzi; J. M. De Miranda; L. De Paula; P. De Simone; D. Decamp; M. Deckenhoff; H. Degaudenzi; M. Deissenroth; L. Del Buono; C. Deplano; O. Deschamps; F. Dettori; J. Dickens; H. Dijkstra; P. Diniz Batista; S. Donleavy; F. Dordei; A. Dosil Suárez; D. Dossett; A. Dovbnya; F. Dupertuis; R. Dzhelyadin; C. Eames; S. Easo; U. Egede; V. Egorychev; S. Eidelman; D. van Eijk; F. Eisele; S. Eisenhardt; R. Ekelhof; L. Eklund; Ch. Elsasser; D. G. d'Enterria; D. Esperante Pereira; L. Estève; A. Falabella; E. Fanchini; C. Färber; G. Fardell; C. Farinelli; S. Farry; V. Fave; V. Fernandez Albor; M. Ferro-Luzzi; S. Filippov; C. Fitzpatrick; M. Fontana; F. Fontanelli; R. Forty; M. Frank; C. Frei; M. Frosini; S. Furcas; A. Gallas Torreira; D. Galli; M. Gandelman; P. Gandini; Y. Gao; J. C. Garnier; J. Garofoli; J. Garra Tico; L. Garrido; C. Gaspar; N. Gauvin; M. Gersabeck; T. Gershon; Ph. Ghez; V V Gligorov; C. Göbel; D. Golubkov; A. Golutvin; A. Gomes; H. Gordon; M. Grabalosa Gándara; R. Graciani Diaz; L. A. Granado Cardoso; E. Graugés; G. Graziani; A. Grecu; S. Gregson; B. Gui; E. Gushchin; Yu. Guz; T. Gys; G. Haefeli; C. Haen; S. C. Haines; T. Hampson; S. Hansmann-Menzemer; R. Harji; N. Harnew; J. Harrison; P. F. Harrison; J. He; V. Heijne; K. Hennessy; P. Henrard; J. A. Hernando Morata; E. van Herwijnen; E. Hicks; W. Hofmann; K. Holubyev; P. Hopchev; W. Hulsbergen; P. Hunt; T. Huse; R. S. Huston; D. Hutchcroft; D. Hynds; V. Iakovenko; P. Ilten; J. Imong; R. Jacobsson; A. Jaeger; M. Jahjah Hussein; E. Jans; F. Jansen; P. Jaton; B. Jean-Marie; F. Jing; M. John; D. Johnson; C. R. Jones; B. Jost; S. Kandybei; M. Karacson; T. M. Karbach; J. Keaveney; U. Kerzel; T. Ketel; A. Keune; B. Khanji; Y. M. Kim; M. Knecht; S. Koblitz; P. Koppenburg; A. Kozlinskiy; L. Kravchuk; K. Kreplin; M. Kreps; G. Krocker; P. Krokovny; F. Kruse; K. Kruzelecki; M. Kucharczyk; S. Kukulak; R. Kumar; T. Kvaratskheliya; V. N. La Thi; D. Lacarrere; G. Lafferty; A. Lai; D. Lambert; R. W. Lambert; E. Lanciotti; G. Lanfranchi; C. Langenbruch; T. Latham; R. Le Gac; J. van Leerdam; J.-P. Lees; R. Lefèvre; A. Leflat; J. Lefrançois; O. Leroy; T. Lesiak; L. Li; L. Li Gioi; M. Lieng; M. Liles; R. Lindner; C. Linn; B. Liu; G. Liu; J. H. Lopes; E. Lopez Asamar; N. Lopez-March; J. Luisier; F. Machefert; I. V. Machikhiliyan; F. Maciuc; O. Maev; J. Magnin; S. Malde; R. M. D. Mamunur; G Mancinelli; N. Mangiafave; U. Marconi; R. Märki; J. Marks; G. Martellotti; A. Martens; L. Martin; A. Martín Sánchez; D. Martinez Santos; A. Massafferri; R. Matev; Z. Mathe; C. Matteuzzi; M. Matveev; E. Maurice; B. Maynard; A. Mazurov; G. McGregor; R. McNulty; C. Mclean; M. Meissner; M. Merk; J. Merkel; R. Messi; S. Miglioranzi; D. A. Milanes; M.-N. Minard; S. Monteil; D. Moran; P. Morawski; I. Mous; F. Muheim; K. Müller; R. Muresan; B. Muryn; M. Musy; J. Mylroie-Smith; P. Naik; T. Nakada; R. Nandakumar; J. Nardulli; I. Nasteva; M Needham; N. Neufeld; C. Nguyen-Mau; M. Nicol; S. Nies; V. Niess; N. Nikitin; A. Oblakowska-Mucha; V. Obraztsov; S. Oggero; S. Ogilvy; O. Okhrimenko; R. Oldeman; M. Orlandea; J. M. Otalora Goicochea; P. Owen; B. Pal; J. Palacios; M. Palutan; J. Panman; A. Papanestis; M. Pappagallo; C J Parkinson; G. Passaleva; G. D. Patel; M. Patel; S. K. Paterson; G. N. Patrick; C Pavel-Nicorescu; A. Pazos Alvarez; A. Pellegrino; G. Penso

    2011-01-01

    Absolute luminosity measurements are of general interest for colliding-beam experiments at storage rings. These measurements are necessary to determine the absolute cross-sections of reaction processes and are valuable to quantify the performance of the accelerator. LHCb has applied two methods to determine the absolute scale of its luminosity measurements for proton-proton collisions at the LHC with a centre-of-mass energy of

  12. Application of cyclic phosphonamide reagents in the total synthesis of natural products and biologically active molecules

    PubMed Central

    Focken, Thilo

    2014-01-01

    Summary A review of the synthesis of natural products and bioactive compounds adopting phosphonamide anion technology is presented highlighting the utility of phosphonamide reagents in stereocontrolled bond-forming reactions. Methodologies utilizing phosphonamide anions in asymmetric alkylations, Michael additions, olefinations, and cyclopropanations will be summarized, as well as an overview of the synthesis of the employed phosphonamide reagents. PMID:25246946

  13. Absolute and Convective Instability of a Liquid Jet

    NASA Technical Reports Server (NTRS)

    Lin, S. P.; Hudman, M.; Chen, J. N.

    1999-01-01

    The existence of absolute instability in a liquid jet has been predicted for some time. The disturbance grows in time and propagates both upstream and downstream in an absolutely unstable liquid jet. The image of absolute instability is captured in the NASA 2.2 sec drop tower and reported here. The transition from convective to absolute instability is observed experimentally. The experimental results are compared with the theoretical predictions on the transition Weber number as functions of the Reynolds number. The role of interfacial shear relative to all other relevant forces which cause the onset of jet breakup is explained.

  14. Total Synthesis of the Opioid Agonistic Indole Alkaloid, Mitragynine, as well as the First Total Synthesis of 9-Methoxygeissoschizol and 9-Methoxy-Nb-methylgeissoschizol

    PubMed Central

    Ma, Jun; Yin, Wenyuan; Zhou, Hao; Cook, James M.

    2008-01-01

    An enantiospecific method for the synthesis of 4-methoxytryptophan has been developed via a regiospecific Larock heteroannulation and employed for the first total synthesis of 9-methoxygeissoschizol, and 9-methoxy-Nb–methylgeissoschizol as well as the total synthesis of the opioid agonistic alkaloid, mitragynine. The asymmetric Pictet-Spengler reaction and a Ni(COD)2 mediated cyclization served as key steps. PMID:17685530

  15. Temperature-controlled bidirectional enantioselectivity in a dynamic catalyst for asymmetric hydrogenation.

    PubMed

    Storch, Golo; Trapp, Oliver

    2015-03-16

    Asymmetric catalysis using enantiomerically pure catalysts is one of the most widely used methods for the preparation of enantiomerically pure compounds. The separate synthesis of both enantiomerically pure compounds requires tedious and time-consuming preparation of both enantiomerically pure catalysts or chiral separation of the racemic products. Here, we report a stereochemically flexible diastereomeric rhodium(I) catalyst for asymmetric hydrogenations of prochiral (Z)-?-acetamidocinnamates and ?-substituted acrylates, which changes its enantioselectivity depending on the temperature to produce each enantiomerically pure compound in high yield with constant high enantioselectivity over time. The same axially chiral rhodium(I) catalyst produces (R)-phenylalanine derivatives in enantiomeric ratios of up to 87:13 (R/S) at low temperature and up to 3:97 (R/S) of the corresponding S?enantiomers after re-equilibration of the same catalyst at elevated temperature. PMID:25708097

  16. Organelle-based aggregation and retention of damaged proteins in asymmetrically dividing cells.

    PubMed

    Zhou, Chuankai; Slaughter, Brian D; Unruh, Jay R; Guo, Fengli; Yu, Zulin; Mickey, Kristen; Narkar, Akshay; Ross, Rhonda Trimble; McClain, Melainia; Li, Rong

    2014-10-23

    Aggregation of damaged or misfolded proteins is a protective mechanism against proteotoxic stress, abnormalities of which underlie many aging-related diseases. Here, we show that in asymmetrically dividing yeast cells, aggregation of cytosolic misfolded proteins does not occur spontaneously but requires new polypeptide synthesis and is restricted to the surface of ER, which harbors the majority of active translation sites. Protein aggregates formed on ER are frequently also associated with or are later captured by mitochondria, greatly constraining aggregate mobility. During mitosis, aggregates are tethered to well-anchored maternal mitochondria, whereas mitochondria acquired by the bud are largely free of aggregates. Disruption of aggregate-mitochondria association resulted in increased mobility and leakage of mother-accumulated aggregates into the bud. Cells with advanced replicative age exhibit gradual decline of aggregates-mitochondria association, likely contributing to their diminished ability to rejuvenate through asymmetric cell division. PMID:25417105

  17. Pd-catalyzed asymmetric allylic alkylation of pyrazol-5-ones with allylic alcohols: the role of the chiral phosphoric acid in C-O bond cleavage and stereocontrol.

    PubMed

    Tao, Zhong-Lin; Zhang, Wen-Quan; Chen, Dian-Feng; Adele, Arafate; Gong, Liu-Zhu

    2013-06-26

    The combination of a palladium complex with a chiral phosphoramidite ligand and a chiral phosphoric acid enables the first highly efficient asymmetric allylic alkylation of pyrazol-5-ones with allylic alcohols, affording multiply functionalized heterocyclic products in high yields with excellent enantioselectivities that would be of great potential in the synthesis of pharmaceutically interesting molecules. PMID:23734612

  18. Diphenylprolinol silyl ether catalyzed asymmetric Michael reaction of nitroalkanes and ?,?-disubstituted ?,?-unsaturated aldehydes for the construction of all-carbon quaternary stereogenic centers.

    PubMed

    Hayashi, Yujiro; Kawamoto, Yuya; Honda, Masaki; Okamura, Daichi; Umemiya, Shigenobu; Noguchi, Yuka; Mukaiyama, Takasuke; Sato, Itaru

    2014-09-15

    The asymmetric Michael reaction of nitroalkanes and ?,?-disubstituted ?,?-unsaturated aldehydes was catalyzed by diphenylprolinol silyl ether to afford 1,4-addition products with an all-carbon quaternary stereogenic center with excellent enantioselectivity. The reaction is general for ?-substituents such as ?-aryl and ?-alkyl groups, and both nitromethane and nitroethane can be employed. The addition of nitroethane is considered a synthetic equivalent of the asymmetric Michael reaction of ethyl and acetyl substituents by means of radical denitration and Nef reaction, respectively. The short asymmetric synthesis of (S)-ethosuximide with a quaternary carbon center was accomplished by using the present asymmetric Michael reaction as the key step. The reaction mechanism that involves the E/Z isomerization of ?,?-unsaturated aldehydes, the retro-Michael reaction, and the different reactivity between nitromethane and nitroethane is discussed. PMID:25164711

  19. Asymmetric tandem organic solar cells

    NASA Astrophysics Data System (ADS)

    Howells, Thomas J.

    Organic photovoltaics (OPVs) is an area that has attracted much attention recently as a potential low cost, sustainable source of energy with a good potential for full-scale commercialisation. Understanding the factors that determine the efficiency of such cells is therefore a high priority, as well as developing ways to boost efficiency to commercially-useful levels. In addition to an intensive search for new materials, significant effort has been spent on ways to squeeze more performance out of existing materials, such as multijunction cells. This thesis investigates double junction tandem cells in the context of small molecule organic materials. . Two different organic electron donor materials, boron subphthalocyanine chloride (SubPc) and aluminium phthalocyanine chloride (ClAlPc) were used as donors in heterojunctions with C60 to create tandem cells for this thesis. These materials have been previously used for solar cells and the absorption spectra of the donor materials complement each other, making them good candidates for tandem cell architectures. The design of the recombination layer between the cells is considered first, with silver nanoparticles demonstrated to work well as recombination centres for charges from the front and back sub-cells, necessary to avoid a charge build-up at the interface. The growth conditions for the nanoparticles are optimised, with the tandem cells outperforming the single heterojunction architecture. Optical modelling is considered as a method to improve the understanding of thin film solar cells, where interference effects from the reflective aluminium electrode are important in determining the magnitude of absorption a cell can achieve. The use of such modelling is first demonstrated in hybrid solar cells based on a SubPc donor with a titanium oxide (TiOx) acceptor; this system is ideal for observing the effects of interference as only the SubPc layer has significant absorption. The modelling is then applied to tandem cells where it is used to predict the short-circuit current (Jsc) generation of the sub-cells, which is not accessible experimentally. Current-matching is then used to predict the Jsc of the complete tandem device. . As a support to the optical modelling, ellipsometry measurements of thin films of ClAlPc are presented. These films of known thickness are analysed to extract the complex refractive index for use in optical modelling calculations. A dependence of the complex refractive index on film thickness and substrate is also noted. Finally, the external quantum efficiency (EQE) technique is considered as applied to solar cells, and an additional method is proposed to characterise current balancing in asymmetric tandem cells under illumination. This technique is verified experimentally by two separate sets of data..

  20. Control of apoptosis by asymmetric cell division.

    PubMed

    Hatzold, Julia; Conradt, Barbara

    2008-04-01

    Asymmetric cell division and apoptosis (programmed cell death) are two fundamental processes that are important for the development and function of multicellular organisms. We have found that the processes of asymmetric cell division and apoptosis can be functionally linked. Specifically, we show that asymmetric cell division in the nematode Caenorhabditis elegans is mediated by a pathway involving three genes, dnj-11 MIDA1, ces-2 HLF, and ces-1 Snail, that directly control the enzymatic machinery responsible for apoptosis. Interestingly, the MIDA1-like protein GlsA of the alga Volvox carteri, as well as the Snail-related proteins Snail, Escargot, and Worniu of Drosophila melanogaster, have previously been implicated in asymmetric cell division. Therefore, C. elegans dnj-11 MIDA1, ces-2 HLF, and ces-1 Snail may be components of a pathway involved in asymmetric cell division that is conserved throughout the plant and animal kingdoms. Furthermore, based on our results, we propose that this pathway directly controls the apoptotic fate in C. elegans, and possibly other animals as well. PMID:18399720