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Sample records for absolute asymmetric synthesis

  1. Competitive exclusion principle in ecology and absolute asymmetric synthesis in chemistry.

    PubMed

    Rib, Josep M; Hochberg, David

    2015-10-01

    The key concepts underlying the Frank model (1953) for spontaneous asymmetric synthesis in chemistry are traced back to the pioneering works of Volterra (1926) and Lotka (1932) on biological species competition. The Lotka-Volterra (L-V) two-species exclusive competition model reduces to the Frank model for the special case of distinguishable but degenerate species (i.e., the enantiomers). The important ecological principle of competitive exclusion, originally derived from the L-V two-competitors model, is a consequence of sufficiently antagonistic interactions between the species competing for limited common resources, or mutual inhibition, as the term is known in the chemical literature on absolute asymmetric synthesis. The L-V and Frank models are described by the same general differential equations, nevertheless a crucial thermodynamic distinction between these models is necessary to correlate ecological selection and chemical selectivity arising from 1) the absence of reversibility in biological transformations, in marked contrast to chemical reactions, and 2) the constraints in chemical scenarios on the reaction rate constants required to fulfill the principle of micro-reversibility. PMID:26301597

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

    PubMed

    Barabs, Bla; Zucchi, Claudia; Maioli, Marco; Micskei, Kroly; Plyi, 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 Plya-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

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

    PubMed

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

    2015-01-01

    Bedaquiline is the first FDA-approved new chemical entity to fight multidrug-resistant tuberculosis in the last forty years. Our group replaced the quinoline ring with a naphthalene ring, leading to a new type of triarylbutanol skeleton. An asymmetric synthetic route was established for our bedaquiline analogues, and the goal of assigning their absolute configurations was achieved by comparison of experimental and calculated electronic circular dichroism spectra, and was confirmed by the combined use of circular dichroism and NMR spectroscopy. PMID:26690407

  4. Asymmetric total synthesis of neoxaline.

    PubMed

    Ideguchi, Tetsuya; Yamada, Takeshi; Shirahata, Tatsuya; Hirose, Tomoyasu; Sugawara, Akihiro; Kobayashi, Yoshinori; ?mura, Satoshi; Sunazuka, Toshiaki

    2013-08-28

    A first asymmetric total synthesis and determination of the absolute configuration of neoxaline has been accomplished through the highly stereoselective introduction of a reverse prenyl group to create a quaternary carbon stereocenter using (-)-3a-hydroxyfuroindoline as a building block, construction of the indoline spiroaminal via cautious stepwise oxidations with cyclizations from the indoline, assembly of (Z)-dehydrohistidine, and photoisomerization of unnatural (Z)-neoxaline to the natural (E)-neoxaline as the key steps. PMID:23957424

  5. 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

  6. Asymmetric total synthesis of rollicosin.

    PubMed

    Quinn, Kevin J; Isaacs, Andr 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

  7. Asymmetric Formal Synthesis of Azadirachtin.

    PubMed

    Mori, Naoki; Kitahara, Takeshi; Mori, Kenji; Watanabe, Hidenori

    2015-12-01

    An asymmetric formal synthesis of azadirachtin, a potent insect antifeedant, was accomplished in 30 steps to Ley's synthetic intermediate (longest linear sequence). The synthesis features: 1)?rapid access to the optically active right-hand segment starting from the known 5-hydroxymethyl-2-cyclopentenone scaffold; 2)?construction of the B and E rings by a key intramolecular tandem radical cyclization; 3)?formation of the hemiacetal moiety in the C ring through the ?-oxidation of the six-membered lactone followed by methanolysis. PMID:26474211

  8. Catalytic Asymmetric Total Synthesis of Hedyosumins A, B, and C.

    PubMed

    Sun, Wang-Bin; Wang, Xuan; Sun, Bing-Feng; Zou, Jian-Ping; Lin, Guo-Qiang

    2016-03-18

    The first and asymmetric total synthesis of hedyosumins A, B, and C was accomplished in 13-14 steps from simple starting materials. The essential tools that allow us to access the tetracyclic skeleton include an organocatalytic [4 + 3] cycloaddition reaction, an intramolecular aldol condensation, and an intramolecular carboxymercuration/demercuration enabled lactonization. A CBS-catalyzed asymmetric reduction was employed to boost the ee of the synthetic natural products to an excellent level. This synthesis established the absolute configurations of hedyosumins A, B, and C. PMID:26925758

  9. Establishment of relative and absolute configurations of phaeosphaeride A: total synthesis of ent-phaeosphaeride A.

    PubMed

    Kobayashi, Kenichi; Kobayashi, Yukiko; Nakamura, Misato; Tamura, Osamu; Kogen, Hiroshi

    2015-01-16

    The relative and absolute configurations of phaeosphaeride A have been established via the first total synthesis of ent-phaeosphaeride A. The three contiguous stereogenic centers were installed by Sharpless asymmetric dihydroxylation and a stereoselective intramolecular vinyl anion aldol reaction. This synthesis has altered the originally proposed structure of natural phaeosphaeride A. PMID:25517514

  10. Asymmetric Total Synthesis of (-)-Kravanhin?B.

    PubMed

    Zhong, Zhuliang; Ma, Donghui; Zhao, Gaoyuan; Li, Huilin; Xu, Dengyu; Xie, Xingang; She, Xuegong

    2015-12-01

    The first asymmetric total synthesis of kravanhin?B has been accomplished with a linear reaction sequence of 13?steps starting from (R)-(-)-carvone. The synthesis features an intramolecular aldol cyclization to construct the desired cis-fused decalin skeleton and an acid-catalyzed dehydration and olefin isomerization to install the ?-butenolide ring. PMID:26398294

  11. Asymmetric synthesis: Cascades of catalytic selectivity

    NASA Astrophysics Data System (ADS)

    Dewhurst, Rian D.; Marder, Todd B.

    2014-04-01

    A combination of catalytic asymmetric diboration of terminal alkenes and Suzuki-Miyaura cross-coupling has been exploited in the synthesis of a variety of important medicinal agents. The process overcomes a number of problems in the application of these important catalytic processes.

  12. Nitrogen cation-? interactions in asymmetric organocatalytic synthesis.

    PubMed

    Yamada, Shinji; Fossey, John S

    2011-11-01

    Cation-? interactions have been widely exploited and utilised in the structural biology arena, their fundamental importance in supramolecular chemistry and the pivotal role they play in host guest chemistry has rapidly expanded. In terms of organic synthesis ?-?, CH-? and cation-? interactions are often invoked providing hypotheses for observed selectivities and reaction outcomes although fundamental studies of these interactions are less well reported, especially in the organic synthesis arena. This article considers cation-? interactions in the field of asymmetric organocatalysis and provides a summary of cases where such interactions may play an important role. Importantly this article sets out to highlight where such interactions could be operating in order to highlight the potential wealth of investigations to be had in this area rather than categorically claiming such interactions are in operation. For asymmetric catalysis this is particularly important as the geometry of a transition state dictates the stereochemical outcome of the reaction, this article provides a perspective on such phenomena. PMID:21670810

  13. Catalytic Asymmetric Total Synthesis of (-)-Actinophyllic Acid.

    PubMed

    Cai, Lingchao; Zhang, Kui; Kwon, Ohyun

    2016-03-16

    Described herein is a catalytic asymmetric total synthesis of (-)-actinophyllic acid, with the key step being a chiral phosphine-catalyzed [3 + 2] annulation between an imine and an allenoate to form a pyrroline intermediate in 99% yield and 94% ee. The synthesis also features CuI-catalyzed coupling between a ketoester and a 2-iodoindole to shape the tetrahydroazocine ring; intramolecular alkylative lactonization; SmI2-mediated intramolecular pinacol coupling between ketone and lactone subunits to assemble the complex skeleton of (-)-actinophyllic acid; and an unprecedented regioselective dehydroxylation. PMID:26910382

  14. 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.

  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. Catalytic asymmetric formal synthesis of beraprost

    PubMed Central

    Kobayashi, Yusuke; Kuramoto, Ryuta

    2015-01-01

    Summary The first catalytic asymmetric synthesis of the key intermediate for beraprost has been achieved through an enantioselective intramolecular oxa-Michael reaction of an α,β-unsaturated amide mediated by a newly developed benzothiadiazine catalyst. The Weinreb amide moiety and bromo substituent of the Michael adduct were utilized for the C–C bond formations to construct the scaffold. All four contiguous stereocenters of the tricyclic core were controlled via Rh-catalyzed stereoselective C–H insertion and the subsequent reduction from the convex face. PMID:26734111

  17. Catalytic Asymmetric Synthesis of Chiral Allylic Esters

    PubMed Central

    Cannon, Jeffrey S.; Kirsch, Stefan F.; Overman, Larry E.

    2010-01-01

    A broadly useful catalytic enantioselective synthesis of branched allylic esters from prochiral (Z)-2-alkene-1-ols has been developed. The starting allylic alcohol is converted to its trichloroacetimidate intermediate by reaction with trichloroacetonitrile, either in situ or in a separate step, and this intermediate undergoes clean enantioselective SN2? substitution with a variety of carboxylic acids in the presence of the palladium(II) catalyst (Rp,S)-di-? -acetatobis[(?5-2-(2'-(4'-methylethyl)oxazolinyl)cyclopentadienyl,1-C,3'-N)(?4-tetraphenylcyclobutadiene)cobalt]dipalladium, (Rp,S)-[COP-OAc]2 or its enantiomer. The scope and limitations of this useful catalytic asymmetric allylic esterification are defined. PMID:15740118

  18. A novel and practical asymmetric synthesis of dapoxetine hydrochloride.

    PubMed

    Zhu, Yijun; Liu, Zhenren; Li, Hongyan; Ye, Deyong; Zhou, Weicheng

    2015-01-01

    A novel and practical asymmetric synthesis of dapoxetine hydrochloride by using the chiral auxiliary (S)-tert-butanesulfinamide was explored. The synthesis was concise, mild, and easy to perform. The overall yield and stereoselectivity were excellent. PMID:26734109

  19. A novel and practical asymmetric synthesis of dapoxetine hydrochloride

    PubMed Central

    Zhu, Yijun; Liu, Zhenren; Li, Hongyan

    2015-01-01

    Summary A novel and practical asymmetric synthesis of dapoxetine hydrochloride by using the chiral auxiliary (S)-tert-butanesulfinamide was explored. The synthesis was concise, mild, and easy to perform. The overall yield and stereoselectivity were excellent. PMID:26734109

  20. 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…

  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. Asymmetric Synthesis of Spiroketals with Aminothiourea Catalysts.

    PubMed

    Yoneda, Naoki; Fukata, Yukihiro; Asano, Keisuke; Matsubara, Seijiro

    2015-12-14

    Chiral spiroketal skeletons are found as core structures in a range of bioactive compounds. These natural compounds and their analogues have attracted much attention in the field of drug discovery. However, methods for their enantioselective construction are limited, and easily available optically active spiroketals are rare. We demonstrate a novel catalytic asymmetric synthesis of spiroketal compounds that proceeds through an intramolecular hemiacetalization/oxy-Michael addition cascade mediated by a bifunctional aminothiourea catalyst. This results in spiroketal structures through the relay formation of contiguous oxacycles, in which multipoint recognition by the catalyst through hydrogen bonding imparts high enantioselectivity. This method offers facile access to spiroketal frameworks bearing an alkyl group at the 2-position, which are prevalent in insect pheromones. Optically active (2S,5S)-chalcogran, a pheromone of the six-spined spruce bark beetle, and an azide derivative could be readily synthesized from the bicyclic reaction product. PMID:26510921

  3. Asymmetric Synthesis of Diastereometric Diaminohepatanetetraols. A Proposal for the Configuration of (+)-Zwittermicin A

    PubMed Central

    Rogers, Evan W.; Molinski, Tadeusz F.

    2008-01-01

    A proposed absolute configuration for the 7 stereocenters in (+)-zwittermicin A is described based on asymmetric synthesis of six diastereomeric 2,6-diamino-1,3,5,7-heptanetetraols corresponding to the C9-C15 segment, pair-wise 13C NMR chemical shift difference analysis of the models with the natural product, interpretation of enantiospecificity of serine loading domain of the zwittermicin A biosynthetic gene cluster, and degradation of the natural product. PMID:17249781

  4. Synthesis and Determination of Absolute Configuration of Lentztrehalose A.

    PubMed

    Zhang, Ming; Wada, Shun-ichi; Amemiya, Fuyuki; Watanabe, Takumi; Shibasaki, Masakatsu

    2015-01-01

    The synthesis of lentztrehalose A, a naturally occurring trehalose derivative exhibiting various biological activities including autophagy-inducing activity, was achieved. The synthesis commenced with the selective protection of hydroxyl groups of commercially available trehalose, followed by the introduction of the side chain moiety by two methods: 1) prenylation and successive diastereoselective dihydroxylation; or 2) etherification by opening of the chiral epoxide. The present synthetic study clarified the unreported absolute configuration of the secondary alcohol part in the side chain portion. PMID:26521862

  5. Enantioselective total synthesis and absolute configuration of apiosporic acid.

    PubMed

    Grtner, Martin; Kossler, David; Pflsterer, Daniel; Helmchen, Gnter

    2012-05-01

    The first total synthesis of the polyketide apiosporic acid is presented. Key steps are a Julia-Kocienski olefination, a Suzuki-Miyaura cross-coupling, and an intramolecular Diels-Alder reaction. The absolute configuration of the natural product was determined. PMID:22510063

  6. Botcinolide/botcinin: asymmetric synthesis of the key fragments.

    PubMed

    Ramírez-Fernández, Jacinto; Botubol, José Manuel; Bustillo, Antonio J; Aleu, Josefina; Collado, Isidro G; Hernández-Galán, Rosario

    2011-04-01

    The asymmetric synthesis of key fragments of the phytotoxic toxins botcinolide/botcinin is reported. The synthesis of 1 and 1a are based on a convergent route via esterification and alkene metathesis of fragments A, B or C, B, which were obtained by Evans aldol condensation and stereoselective crotylation, respectively. PMID:21560756

  7. Organocatalytic, Asymmetric Total Synthesis of (-)-Haliclonin A.

    PubMed

    Guo, Lian-Dong; Huang, Xiong-Zhi; Luo, Shi-Peng; Cao, Wen-Sen; Ruan, Yuan-Ping; Ye, Jian-Liang; Huang, Pei-Qiang

    2016-03-14

    The first total synthesis of the alkaloid (-)-haliclonin A is reported. The asymmetric synthesis relied on a novel organocatalytic asymmetric conjugate addition of nitromethane with 3-alkenyl cyclohex-2-enone to set the stereochemistry of the all-carbon quaternary stereogenic center. The synthesis also features a Pd-promoted cyclization to form the 3-azabicyclo[3,3,1]nonane core, a SmI2 -mediated intermolecular reductive coupling of enone with aldehyde to form the requisite secondary chiral alcohol, ring-closing alkene and alkyne metathesis reactions to build the two aza-macrocyclic ring systems, and an unprecedented direct transformation of enol into enone. PMID:26890255

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

    PubMed

    Shirakawa, Seiji; Liu, Shiyao; Kaneko, Shiho

    2016-02-01

    Axially, planar, and helical chiral compounds are indispensable building blocks in modern organic synthesis. A wide variety of chiral ligands and catalysts were designed based on these chiral scaffolds, and these chiral ligands and catalysts were used for various catalytic asymmetric transformations to produce important chiral compounds in an optically enriched form. Furthermore, these chiral skeletons are found in the structure of biologically active natural products. Thus, the development of efficient enantioselective methods for the synthesis of these chiral compounds is an important task in the field of organic chemistry. In the last few years, organocatalyzed approaches, which are one of the most reliable catalytic asymmetric methods, became a hot topic. This Focus Review summarizes asymmetric organocatalytic methods for the synthesis of axially, planar, and helical chiral compounds as useful chiral building blocks. PMID:26395547

  9. 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...

  10. Asymmetric Total Synthesis of Bioactive Natural Lipid Mycalol.

    PubMed

    Das, Subhendu; Kuilya, Tapan Kumar; Goswami, Rajib Kumar

    2015-06-19

    A concise and convergent route for stereoselective total synthesis of promising anticancer natural lipid mycalol has been achieved using cheap and readily available l-arabinose as a chiral pool. The notable features of our synthesis comprised regioselective Wacker oxidation, Sharpless asymmetric dihydroxylation, Julia-Kocienski olefination, Wittig olefination, Zipper reaction, and Sonogashira reaction. Comparison of the spectroscopic data on a series of isomers supports the revised structure (Org. Lett. 2015, 17, 1652) instead of the one originally proposed. PMID:25992780

  11. The asymmetric total synthesis of (+)-N-acetyl norloline.

    PubMed

    Ye, Jian-Liang; Liu, Yang; Yang, Zhi-Ping; Huang, Pei-Qiang

    2016-01-11

    The asymmetric total synthesis of (+)-N-acetyl norloline, the putative biogenic precursor of all known loline alkaloids, has been achieved in 12 steps from commercially available (R)-glyceraldehyde acetonide. The synthesis relies on the Rassu/Casiraghi's vinylogous aldol reaction, an intramolecular oxa-heteroconjugate addition and a reductive amination to establish the four contiguous stereogenic centers and construct the strained oxygen-bridge under mild conditions. PMID:26538080

  12. Asymmetric total synthesis of ent-cyclooroidin

    PubMed Central

    Mukherjee, Sabuj; Sivappa, Rasapalli; Yousufuddin, Muhammed; Lovely, Carl J.

    2010-01-01

    An enantiospecific total synthesis of the pyrrole-imidazole natural product cyclooroidin from histidine is described. The key N1-C9 bond is constructed through an intramolecular SN2-type of reaction of a chloro ester. Subsequent imidazole C2-azidation at the 2-position, pyrrole bromination, azide reduction and deprotection leads to the completion of the synthesis. PMID:20929213

  13. The first asymmetric total synthesis of lycoposerramine-R.

    PubMed

    Ishida, Hiroaki; Kimura, Shinya; Kogure, Noriyuki; Kitajima, Mariko; Takayama, Hiromitsu

    2015-07-28

    The first asymmetric total synthesis of lycoposerramine-R, a Lycopodium alkaloid possessing a novel skeleton, was accomplished by a strategy featuring the stereoselective intramolecular aldol cyclization giving a cis-fused 5/6 bicyclic skeleton and a new method for the construction of the pyridone ring via the aza-Wittig reaction. PMID:26091485

  14. Pseudoephenamine: A Practical Chiral Auxiliary for Asymmetric Synthesis

    PubMed Central

    Morales, Marvin R.; Mellem, Kevin T.; Myers, Andrew G.

    2013-01-01

    Pseudoephenamine is shown to be a versatile chiral auxiliary for asymmetric synthesis. It is free from regulatory restrictions and exhibits remarkable stereocontrol in alkylation reactions, especially those that form quaternary carbon centers. Amides derived from pseudoephenamine exhibit a high propensity to be crystalline substances and provide sharp, well-defined peaks in NMR spectra. PMID:22461381

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

    PubMed Central

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

    2016-01-01

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

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

    PubMed

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

    2016-01-01

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

  17. First asymmetric synthesis of planar chiral [2.2]metacyclophanes.

    PubMed

    Blangetti, Marco; Mller-Bunz, Helge; O'Shea, Donal F

    2013-07-14

    A general three step asymmetric synthesis of planar chiral [2.2]metacyclophanes utilizing selective benzylic and aryl metalations is described. The final enantioselective step is achieved using a (-)-sparteine mediated aryl metalation, following which electrophile reaction gives planar chiral cyclophanes with enantiomeric ratios (er) above 90?:?10. PMID:23615867

  18. Studies towards the synthesis of halomon: asymmetric hexafunctionalisation of myrcene.

    PubMed

    Braddock, D Christopher; Gao, Alison X; White, Andrew J P; Whyte, Mariko

    2014-11-18

    A novel dihydroxylation-dibromination-dihydroxylation sequence employing in situ protection of diols as boronate esters during the dihydroxylation reactions provides the first enantiomerically pure hexafunctionalised myrcene derivative. This concise four-step asymmetric sequence provides an advanced intermediate for the targeted synthesis of halomon via stereospecific transformations, where both stereogenic centres of the natural product have been set. PMID:25249474

  19. Asymmetric, stereodivergent synthesis of (-)-clusianone utilizing a biomimetic cationic cyclization.

    PubMed

    Boyce, Jonathan H; Porco, John A

    2014-07-21

    We report a stereodivergent, asymmetric total synthesis of (-)-clusianone in six steps from commercial materials. We implement a challenging cationic cyclization forging a bond between two sterically encumbered quaternary carbon atoms. Mechanistic studies point to the unique ability of formic acid to mediate the cyclization forming the clusianone framework. PMID:24916169

  20. Synthesis of conducting asymmetric hydrogel particles showing autonomous motion.

    PubMed

    Srinivasan, A; Roche, J; Ravaine, V; Kuhn, A

    2015-05-28

    In the present work, we introduce a new approach for the synthesis of asymmetric particles made from electrically conducting polyaniline-alginate hydrogels by using bipolar electrochemistry. Such an intrinsic break of symmetry allows the soft beads to exhibit tunable motion at the air/water interface when loaded with ethanol due to controllable directed release of the solvent. PMID:25907320

  1. Direct Catalytic Asymmetric Synthesis of ?-Hydroxy Acids from Malonic Acid.

    PubMed

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

    2015-12-18

    A nickel(II) catalyzed asymmetric synthesis of ?-hydroxy acids from malonic acid and ketones was developed, revealing for the first time the synthetic utility of malonic acid in the construction of chiral carboxyl acids; importantly, the synthetic potential of this strategy was further demonstrated by the rapid construction of cephalanthrin A, phaitanthrin B, cruciferane, and rice metabolites. PMID:26587748

  2. Asymmetric Synthesis of the Aminocyclitol Pactamycin, a Universal Translocation Inhibitor

    PubMed Central

    Sharpe, Robert J.; Malinowski, Justin T.; Johnson, Jeffrey S.

    2014-01-01

    An asymmetric total synthesis of the aminocyclopentitol pactamycin is described, which delivers the title compound in 15 steps from 2,4-pentanedione. Critical to this approach was the exploitation of a complex symmetry-breaking reduction strategy to assemble the C1, C2, and C7 relative stereochemistry within the first four steps of the synthesis. Multiple iterations of this reduction strategy are described, and a thorough analysis of stereochemical outcomes is detailed. In the final case, an asymmetric Mannich reaction was developed to install a protected amine directly at the C2 position. Symmetry-breaking reduction of this material gave way to a remarkable series of stereochemical outcomes leading to the title compound without recourse to non-strategic downstream manipulations. This synthesis is immediately accommodating to the facile preparation of structural analogs. PMID:24245656

  3. Phase-transfer-catalysed asymmetric synthesis of tetrasubstituted allenes

    NASA Astrophysics Data System (ADS)

    Hashimoto, Takuya; Sakata, Kazuki; Tamakuni, Fumiko; Dutton, Mark J.; Maruoka, Keiji

    2013-03-01

    Allenes are molecules based on three carbons connected by two cumulated carbon-carbon double bonds. Given their axially chiral nature and unique reactivity, substituted allenes have a variety of applications in organic chemistry as key synthetic intermediates and directly as part of biologically active compounds. Although the demands for these motivated many endeavours to make axially chiral, substituted allenes by exercising asymmetric catalysis, the catalytic asymmetric synthesis of fully substituted ones (tetrasubstituted allenes) remained largely an unsolved issue. The fundamental obstacle to solving this conundrum is the lack of a simple synthetic transformation that provides tetrasubstituted allenes in the action of catalysis. We report herein a strategy to overcome this issue by the use of a phase-transfer-catalysed asymmetric functionalization of 1-alkylallene-1,3-dicarboxylates with N-arylsulfonyl imines and benzylic and allylic bromides.

  4. Catalytic asymmetric synthesis of ?-substituted vinyl sulfones.

    PubMed

    Lpez, Rosa; Zalacain, Maitane; Palomo, Claudio

    2011-02-18

    A fast new entry for the stereoselective construction of ?-substituted vinyl sulfones is presented. The key for success is the use of a readily available chiral secondary amine catalyst that allows the use of base-sensitive ?-nitroethyl sulfones as masked ?-sulfonyl vinyl anions in conjugate additions. The method performed in a three-step one-pot operation gives access to a great variety of vinyl sulfones in good yields and with excellent enantioselectivities. The method has also been extended to other relatively base-sensitive ?-electron-withdrawing-substituted nitroalkanes to afford products with manifold functionality, providing a quick entry to very attractive synthetic intermediates for organic synthesis. PMID:21254268

  5. A Facile Synthesis of Asymmetric Hybrid Colloidal Particles

    PubMed Central

    Ohnuma, Akira; Cho, Eun Chul; Camargo, Pedro H. C.; Au, Leslie; Ohtani, Bunsho; Xia, Younan

    2009-01-01

    This paper describes a simple approach to the synthesis of asymmetric, hybrid colloidal particles by precipitation polymerization. The key is to introduce Au or Ag colloids 2 min after (rather than before) starting the polymerization. The hybrid particles were uniform in size, and each one of them only contained one Au (or Ag) nanoparticle in its surface. Due to the simplicity of this procedure, it should be possible to use it for large-scale production. This method can be extended to metal nanoparticles other than Au and Ag and with a range of sizes, as long as they have appropriate charges on the surface. PMID:19140763

  6. 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

  7. Mo-catalyzed asymmetric olefin metathesis in target-oriented synthesis: Enantioselective synthesis of (+)-africanol

    PubMed Central

    Weatherhead, Gabriel S.; Cortez, G. A.; Schrock, Richard R.; Hoveyda, Amir H.

    2004-01-01

    Catalytic asymmetric ring-opening metathesis (AROM) provides an efficient method for the synthesis of a variety of optically enriched small organic molecules that cannot be easily prepared by alternative methods. The development of Mo-catalyzed AROM transformations that occur in tandem with ring-closing metathesis are described. The utility of the Mo-catalyzed AROM/ring-closing metathesis is demonstrated through an enantioselective approach to the synthesis of (+)-africanol. PMID:15056762

  8. Synthesis of asymmetric biphenyl derivatives for optoelectronic applications

    NASA Astrophysics Data System (ADS)

    Zhu, Cai-Cai; Guo, Kun-Ping; Liu, Wang-Bo; He, Yan-Bo; Li, Zhi-Mei; Gao, Xi-Cun; Deng, Feng-Jie; Wei, Bin

    2013-10-01

    We report the synthesis and optical properties of a series of ten organic compounds with biphenyl as the backbone and asymmetrically modified by triphenylamines, carbazoles and tetraphenylsilanes (BP 1-10). BP 1-10 were synthesized mainly by Ullmann coupling reaction and Suzuki cross-coupling reaction and characterized by EA, NMR, MS, UV-Vis, DSC, TGA, fluorescence spectra and cyclic voltammetry. They exhibit reversible electrochemical behavior with low oxidation potentials and emit intense pure-blue light with high fluorescence quantum yields (up to 80%). BP 1 was fabricated into multi-layered light-emitting diodes as blue-emitting, host and hole transport materials. Based on the performance of BP 1 and the similarity in chemical structure to those compounds reported in literature, these compounds are expected to be good and versatile hole transport, host and blue emitting materials.

  9. Asymmetric Synthesis of Inhibitors of Glycinamide Ribonucleotide Transformylase

    PubMed Central

    DeMartino, Jessica K.; Hwang, Inkyu; Connelly, Stephen; Wilson, Ian A.; Boger, Dale L.

    2008-01-01

    Glycinamide ribonucleotide transformylase (GAR Tfase) catalyzes the first of two formyl transfer steps in the de novo purine biosynthetic pathway that require folate cofactors and has emerged as a productive target for antineoplastic therapeutic intervention. The asymmetric synthesis and evaluation of the two diastereomers of 10-methylthio-DDACTHF (10R-3 and 10S-3) and related analogues as potential inhibitors of GAR Tfase are reported. This work, which defines the importance of the C10 stereochemistry for this class of inhibitors of GAR Tfase, revealed that both diastereomers are potent inhibitors of rhGAR Tfase (10R-3 Ki = 210 nM, 10S-3 Ki = 180 nM) that exhibit effective cell growth inhibition (CCRF-CEM IC50 = 80 and 50 nM, respectively) which is dependent on intracellular polyglutamation by folylpolyglutamate synthetase (FPGS), but not intracellular transport by the reduced folate carrier. PMID:18686942

  10. Absolute Configuration Determination of Azulenyl Diols Isolated From Asymmetric Pinacol Coupling.

    PubMed

    Dragu, Eugenia Andreea; Naubron, Jean-Valere; Hanganu, Anamaria; Razus, Alexandru C; Nica, Simona

    2015-11-01

    A convenient enantioselective approach for the pinacol coupling of 1-acetylazulene involving easily accessible (R)- or (S)-BINOLs as chiral additive is reported. This supposes the preformation of the chiral titanium-BINOL complex in 1:2 ratio and subsequent reduction with zinc when, 2,3-di(azulen-1-yl)butane-2,3-diol can be isolated in around 60% enantiomeric excess. The absolute configuration of the isolated enantiomers was assigned by comparison of the experimental and Boltzmann-weighted calculated VCD and ECD spectra and assigned as (+)-(2S;3S)-di(azulen-1-yl)butane-2,3-diol. Chirality 27:826-834, 2015. 2015 Wiley Periodicals, Inc. PMID:26364568

  11. Stereoselective synthesis and absolute configuration of the C1'-C25' fragment of symbiodinolide.

    PubMed

    Takamura, Hiroyoshi; Murata, Takeshi; Asai, Takahiro; Kadota, Isao; Uemura, Daisuke

    2009-09-01

    Stereoselective synthesis of the C1'-C25' fragment of symbiodinolide, which was obtained as a degraded product from symbiodinolide by alkaline hydrolysis, has been accomplished. The synthetic route features Kotsuki coupling and Julia-Kocienski olefination in the introduction of the side chains. This enantio- and stereoselective synthesis has established the absolute configuration of the C1'-C25' fragment. PMID:19655754

  12. 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.

  13. Asymmetric Synthesis of trans-2,5-Disubstituted Pyrrolidines from Enantiopure Homoallylic Amines. Synthesis of Pyrrolidine (?)-197B

    PubMed Central

    Davis, Franklin A.; Song, Minsoo; Augustine, Alexander

    2008-01-01

    Iodocyclization of sulfinimine-derived enantiopure homoallylic sulfonamides affords trans-2,5-disubstituted 3-iodopyrrolidines and represents valuable methodology for the asymmetric synthesis of this important heterocyclic ring system. PMID:16555832

  14. Total Synthesis and Absolute Stereochemical Assignment of Kibdelone C

    PubMed Central

    Sloman, David L.; Bacon, Jeffrey W.; Porco, John A.

    2011-01-01

    The kibdelones are hexacyclic tetrahydroxanthones and potent anticancer agents isolated from an Australian microbe. Herein, we describe the synthesis of a chiral, non-racemic iodocyclohexene carboxylate EF ring fragment of the kibdelones employing an intramolecular iodo halo-Michael aldol reaction and its merger with an ABCD ring fragment to afford the congener kibdelone C. PMID:21648477

  15. 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.

  16. 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

  17. Formal synthesis of the bisbenzylisoquinoline alkaloid berbamunine by asymmetric substitution of chiral organolithium compounds

    PubMed Central

    Gawley, Robert E.; Smith, Gregory A.

    2011-01-01

    Asymmetric alkylation of enantiomeric tetrahydroisoquinolyl oxazolines was achieved with 96–97% diastereoselectivity. Removal of the oxazoline chiral auxiliary and further transformations provide a straightforward synthesis of the two synthetic intermediates that were previously synthesized by resolution, and which comprise a formal synthesis of berbamunine by Ullman coupling. PMID:22003473

  18. NHC-Catalyzed Asymmetric Synthesis of Functionalized Succinimides from Enals and α-Ketoamides

    PubMed Central

    Wang, Lei; Ni, Qijian; Blümel, Marcus; Shu, Tao; Raabe, Gerhard; Enders, Dieter

    2015-01-01

    The efficient asymmetric synthesis of highly substituted succinimides from α,β-unsaturated aldehydes and α-ketoamides via NHC-catalyzed [3+2] cycloaddition has been developed. The new scalable protocol significantly expands the utility of NHC catalysis for the synthesis of heterocycles and provides easy access to assemble a wide range of succinimides from simple starting materials. PMID:25877658

  19. Total synthesis of 10-isocyano-4-cadinene and determination of its absolute configuration.

    PubMed

    Nishikawa, Keisuke; Nakahara, Hiroshi; Shirokura, Yousuke; Nogata, Yasuyuki; Yoshimura, Erina; Umezawa, Taiki; Okino, Tatsufumi; Matsuda, Fuyuhiko

    2010-03-01

    The first enantioselective total synthesis of 10-isocyano-4-cadinene, a marine sesquiterpene isolated from nudibranchs of the family Phyllidiidae, was achieved. The cadinene is expected to be a novel nontoxic antifouling agent. In the synthesis, an intermolecular Diels-Alder reaction and a SmI(2)-induced Barbier-type reaction were employed as key steps. The absolute configuration of 10-isocyano-4-cadinene was determined to be (1S, 6S, 7R, 10S) on the basis of the total synthesis. Antifouling activities against Balanus amphitrite with both enantiomers of 10-isocyano-4-cadinene were also evaluated. PMID:20131890

  20. Asymmetric oxidation of sulfides catalyzed by titanium and vanadium complexes in the synthesis of biologically active sulfoxides

    NASA Astrophysics Data System (ADS)

    Volcho, Konstantin P.; Salakhutdinov, Nariman F.

    2009-05-01

    Published data on the asymmetric synthesis of chiral biologically active sulfoxides by oxidation of appropriate sulfides catalyzed by titanium and vanadium complexes are generalized. Bibliography — 87 references.

  1. Total synthesis of (+)-lithospermic acid by asymmetric intramolecular alkylation via catalytic C-H bond activation.

    PubMed

    O'Malley, Steven J; Tan, Kian L; Watzke, Anja; Bergman, Robert G; Ellman, Jonathan A

    2005-10-01

    The total synthesis of (+)-lithospermic acid is described. The efficient synthesis features an asymmetric alkylation via C-H bond activation to assemble the dihydrobenzofuran core of the natural product. This was accomplished via a chiral imine-directed C-H bond functionalization and represents the first application of this C-H activation method to natural product synthesis. Furthermore, a challenging deprotection of a late-stage permethylated lithospermic acid was achieved. PMID:16190703

  2. Quantifying absolute protein synthesis rates reveals principles underlying allocation of cellular resources

    PubMed Central

    Li, Gene-Wei; Burkhardt, David; Gross, Carol; Weissman, Jonathan S.

    2014-01-01

    Quantitative views of cellular functions requires precise measures of rates of biomolecule production, especially proteins—the direct effectors of biological processes. Here we present a genome-wide approach, based on ribosome profiling, for measuring absolute protein synthesis rates. The resultant E. coli dataset transforms our understanding of the extent to which protein synthesis is precisely controlled to optimize function and efficiency. Members of multi-protein complexes are made in precise proportion to their stoichiometry, whereas components of functional modules are produced differentially according to their hierarchical role. Estimates of absolute protein abundance also reveal principles used to optimize design. These include how the level of different types of transcription factors is optimized for rapid response, and how a metabolic pathway (methionine biosynthesis) balances production cost with activity requirements. Our studies reveal how general principles, important both for understanding natural systems and for synthesizing new ones, emerge from quantitative analyses of protein synthesis. PMID:24766808

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

    PubMed

    Rastelli, Ettore J; Coltart, Don M

    2015-11-16

    A concise asymmetric (>99:1 e.r.) total synthesis of (+)-anti- and (-)-syn-mefloquine hydrochloride from a common intermediate is described. The key asymmetric transformation is a Sharpless dihydroxylation of an olefin that is accessed in three steps from commercially available materials. The Sharpless-derived diol is converted into either a trans or cis epoxide, and these are subsequently converted into (+)-anti- and (-)-syn-mefloquine, respectively. The synthetic (+)-anti- and (-)-syn-mefloquine samples were derivatized with (S)-(+)-mandelic acid tert-butyldimethylsilyl ether, and a crystal structure of each derivative was obtained. These are the first X-ray structures for mefloquine derivatives that were obtained by coupling to a known chiral, nonracemic compound, and provide definitive confirmation of the absolute stereochemistry of (+)-anti- as well as (-)-syn-mefloquine. PMID:26422780

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

    PubMed Central

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

    2010-01-01

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

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

    SciTech Connect

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

    2011-12-20

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

  6. Enantiopure 2,3-dihydro-4-pyridones as synthetic intermediates: a concise asymmetric synthesis of (+)-allopumiliotoxin 267A.

    PubMed

    Comins, D L; Huang, S; McArdle, C L; Ingalls, C L

    2001-02-01

    [figure: see text] A concise asymmetric synthesis of (+)-allopumillotoxin 267A has been accomplished using an enantiopure dihydropyridone building block. The synthesis is highly stereoselective and requires 10 steps from readily available material. PMID:11428041

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

    PubMed

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

    2015-12-01

    The first asymmetric synthesis of (R,R)-clemastine (1) has been accomplished by the coupling of (R)-tertiary alcohol 2 and (R)-chloroethylpyrrolidine 3 via O-alkylation. (R)-Tertiary alcohol 2 was synthesized by stereoselective alkylation of chiral ?-benzyloxy ketone with Grignard reagent via chelation-controlled 1,4-asymmetric induction. In the reaction, chiral benzyl group acts as a chiral auxiliary as well as a protecting group. (R)-Chloroethylpyrrolidine 3 was prepared by asymmetric transformation starting with L-homoserine lactone, in which racemization-minimized N-allylation and ring-closing metathesis were involved as key steps. PMID:26219510

  8. Enantioselective Total Synthesis of (+)-Steenkrotin?A and Determination of Its Absolute Configuration.

    PubMed

    Pan, Saiyong; Gao, Beiling; Hu, Jialei; Xuan, Jun; Xie, Hujun; Ding, Hanfeng

    2016-01-01

    The first enantioselective total synthesis of (+)-steenkrotin?A has been achieved in 18?steps and 4.2?% overall yield. The key features of the strategy entail a Rh-catalyzed O-H bond insertion followed by an intramolecular carbonyl-ene reaction, two sequential SmI2 -mediated Ueno-Stork and ketyl-olefin cyclizations, and a cascade intramolecular aldol condensation/vinylogous retro-aldol/aldol process with inversion of the relative configuration at the C7 position. The absolute configuration of (+)-steenkrotin A was determined based on the stepwise construction of the stereocenters during the total synthesis. PMID:26660855

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

    PubMed Central

    Xu, Kun; Gilles, Thomas; Breit, Bernhard

    2015-01-01

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

  10. Asymmetric total synthesis of onoseriolide, bolivianine, and isobolivianine.

    PubMed

    Du, Biao; Yuan, Changchun; Yu, Tianzi; Yang, Li; Yang, Yang; Liu, Bo; Qin, Song

    2014-02-24

    In this article, we describe our efforts on the total synthesis of bolivianine (1) and isobolivianine (2), involving the synthesis of onoseriolide (3). The first generation synthesis of bolivianine was completed in 21 steps by following a chiral resolution strategy. Based on the potential biogenetic relationship between bolivianine (1), onoseriolide (3), and β-(E)-ocimene (8), the second generation synthesis of bolivianine was biomimetically achieved from commercially available (+)-verbenone in 14 steps. The improved total synthesis features an unprecedented palladium-catalyzed intramolecular cyclopropanation through an allylic metal carbene, for the construction of the ABC tricyclic system, and a Diels-Alder/intramolecular hetero-Diels-Alder (DA/IMHDA) cascade for installation of the EFG tricyclic skeleton with the correct stereochemistry. Transformation from bolivianine to isobolivianine was facilitated in the presence of acid. The biosynthetic mechanism and the excellent regio- and endo selectivities in the cascade are well supported by theoretical chemistry based on the DFT calculations. PMID:24488706

  11. Asymmetric synthesis of trifluoromethylated amines via catalytic enantioselective isomerization of imines.

    PubMed

    Wu, Yongwei; Deng, Li

    2012-09-01

    A new approach toward the asymmetric synthesis of optically active trifluoromethylated amines was enabled by an unprecedented, highly enantioselective catalytic isomerization of trifluoromethyl imines with a new chiral organic catalyst. Not only aryl but also alkyl trifluoromethylated amines could be obtained in high enantioselectivities. PMID:22906148

  12. Asymmetric, Stereodivergent Synthesis of (−)-Clusianone Utilizing a Biomimetic Cationic Cyclization **

    PubMed Central

    Boyce, Jonathan H.

    2014-01-01

    We report a stereodivergent, asymmetric total synthesis of (−)-clusianone in six steps from commercial materials. We implement a challenging cationic cyclization forging a bond between two sterically encumbered quaternary carbons. Mechanistic studies point to the unique ability of formic acid to bring about successful cyclization to the clusianone framework. PMID:24916169

  13. Synthesis of Chiral ?-Amino Nitroalkanes via Rhodium-Catalyzed Asymmetric Hydrogenation.

    PubMed

    Li, Pan; Zhou, Ming; Zhao, Qingyang; Wu, Weilong; Hu, Xinquan; Dong, Xiu-Qin; Zhang, Xumu

    2016-01-01

    The asymmetric hydrogenation of ?-amino nitroolefins has been successfully achieved by rhodium/bis(phosphine)-thiourea L1 with excellent enantioselectivities and yields (up to 96% ee, 96% yield, >99% conversion, TON up to 1000) under mild conditions. Chiral ?-amino nitroalkane products and their derivatives are versatile intermediates in organic synthesis. PMID:26652759

  14. New ureas containing glycosyl and diphenylphosphinyl scaffolds: synthesis and the first attempts to use them in asymmetric synthesis.

    PubMed

    Porwa?ski, Stanis?aw

    2014-07-23

    Chiral ureas containing glycosyl and diphenylphosphinyl scaffolds were found to be an effective organocatalyst. They were synthesised in high yields by a one-pot tandem Staudinger/aza-Wittig coupling reaction. The first attempts of using them in asymmetric synthesis are presented. Yields of the Morita-Baylis-Hillman reaction were moderate with an enantiomeric excess of up to 80%. PMID:24905550

  15. Efficient Asymmetric Synthesis of Tryptophan Analogues Having Useful Photophysical Properties

    PubMed Central

    Talukder, Poulami; Chen, Shengxi; Arce, Pablo M.

    2014-01-01

    Two new fluorescent probes of protein structure and dynamics have been prepared by concise asymmetric syntheses using the Schllkopf chiral auxiliary. The site-specific incorporation of one probe into dihydrofolate reductase is reported. The utility of these tryptophan derivatives lies in their absorption and emission maxima which differ from those of tryptophan, as well as in their large Stokes shifts and high molar absorptivities. PMID:24392870

  16. 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

  17. Concise total synthesis of albaflavenone utilizing sequential intramolecular aldol condensation: determination of absolute configuration.

    PubMed

    Kobayashi, Toyoharu; Kon, Yutaro; Abe, Hideki; Ito, Hisanaka

    2014-12-19

    The first total synthesis of albaflavenone, a novel antibiotic sesquiterpene, has been accomplished via the concise construction of its zizaene skeleton utilizing sequential intramolecular aldol condensation followed by chemo- and diastereoselective reduction of the conjugated carbon-carbon double bond. This synthetic work was completed in nine steps from 2-cyclopenten-1-one as a starting material without the use of protecting groups and with high stereocontrol. In addition, the absolute configuration of naturally occurring albaflavenone was determined to be 1R,2S and 8S. PMID:25469861

  18. Asymmetric total synthesis and structural elucidation of NFAT-68.

    PubMed

    Wang, Lin; Xi, Yumeng; Yang, Shouliang; Zhu, Rong; Liang, Yufan; Chen, Jiahua; Yang, Zhen

    2011-01-01

    Total synthesis of NFAT-68 (7) has been achieved and its relative stereochemistry has been determined. A key step thereof is the utilization of the chelation-controlled vinylogous Mukaiyama aldol reaction (VMAR) to stereoselectively synthesize the syn-aldol product 8. This developed chemistry is anticipated to have wider application in total syntheses of many other natural products. PMID:21121639

  19. Asymmetric synthesis of the carbapenam core from serine.

    PubMed

    Hart, Barry P; Verma, Sharad K; Rapoport, Henry

    2003-01-10

    The stereospecific synthesis of the functionalized carbapenam core 16 from the serine-derived trisubstituted pyrrolidine 9 is reported. The synthetic strategy relies on synthesizing an appropriately functionalized pyrrolidine, followed by an intramolecular azetidone formation utilizing a modified Mukiyama reagent. The efficient one-pot conversion of the benzenesulfonamide-protected pyrrolidine 9 to the Cbz-protected pyrrolidine 10 is also reported. PMID:12515481

  20. Catalytic enantioselective synthesis of planar-chiral cyclic amides based on a Pd-catalyzed asymmetric allylic substitution reaction.

    PubMed

    Igawa, Kazunobu; Ichikawa, Nobumasa; Ano, Yusuke; Katanoda, Keisuke; Ito, Masato; Akiyama, Toshiyuki; Tomooka, Katsuhiko

    2015-06-17

    The highly enantioselective synthesis of planar-chiral nine-membered cyclic amides was achieved by the Pd-catalyzed asymmetric allylic cyclization of achiral linear precursors in the presence of a catalytic amount of chiral ligand. PMID:26053786

  1. An Enantioselective Synthesis of the ABD Tricycle for (-)-Phomactin A Featuring Rawal's Asymmetric Diels-Alder Cycloaddition.

    PubMed

    You, Ling-Feng; Hsung, Richard P; Bedermann, Aaron A; Kurdyumov, Aleksey V; Tang, Yu; Buchanan, Grant S; Cole, Kevin P

    2008-12-18

    An enantioselective synthesis of the ABD-ring of (-)-phomactin A is described here. The sequence features Rawal's asymmetric Diels-Alder cycloaddition. The overall length is significantly reduced from our previous attempt. PMID:20351791

  2. Synthesis of Chiral Tertiary Boronic Esters by Oxime-Directed Catalytic Asymmetric Hydroboration.

    PubMed

    Shoba, Veronika M; Thacker, Nathan C; Bochat, Andrew J; Takacs, James M

    2016-01-01

    Chiral boronic esters are useful intermediates in asymmetric synthesis. We have previously shown that carbonyl-directed catalytic asymmetric hydroboration (CAHB) is an efficient approach to the synthesis of functionalized primary and secondary chiral boronic esters. We now report that the oxime-directed CAHB of alkyl-substituted methylidene and trisubstituted alkene substrates by pinacolborane (pinBH) affords oxime-containing chiral tertiary boronic esters with yields up to 87?% and enantiomeric ratios up to 96:4 e.r. The utility of the method is demonstrated by the formation of chiral diols and O-substituted hydroxylamines, the generation of quaternary carbon stereocenters through carbon-carbon coupling reactions, and the preparation of chiral 3,4,4-trisubstituted isoxazolines. PMID:26662460

  3. Synthesis and spectroscopic properties of novel asymmetric Schiff bases

    NASA Astrophysics Data System (ADS)

    Gngr, zlem; Grkan, Perihan

    2010-09-01

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

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

    PubMed

    Gngr, Ozlem; Grkan, Perihan

    2010-09-15

    Three novel diimine Schiff bases including two asymmetric imines (2-OH)R-CHN-C(6)H(4)-CHN-R'(2-OH) type [where R=R'=phenyl for H(2)L(1); R=naphthyl, R'=phenyl for H(2)L(2) and R=R'=naphthyl for H(2)L(3)] have been synthesized with a new two step method. For this purpose, the starting Schiff bases 4-nitrobenzylidene-2-hydroxyaniline (SB(1)-NO(2)) and 4-nitrobenzylidene-2-hydroxy-3-naphthylamine (SB(2)-NO(2)) have been synthesized, previously. Nitro groups of them have been reduced into their amino derivatives (SB(1)-NH(2) and SB(2)-NH(2)) with sodium dithionite as selective reductant and the other imino groups have been formed by adding salicylaldehyde or 2-hydroxy-1-naphthaldehyde to the same solutions. The structures of the diimine Schiff bases were confirmed by elemental analyses, ESI-MS, FT-IR, (1)H NMR and (13)C NMR spectroscopy. The phenol-imine and keto-amine tautomerism of the Schiff bases were investigated by FT-IR, (1)H NMR, (13)C NMR techniques and UV-vis spectra in different solvents (DMSO, methanol, chloroform, toluene and cyclohexane). The effects of acidic and basic media on the tautomeric equilibria were discussed. PMID:20541456

  5. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  7. Catalytic, Enantioselective Synthesis of 1,2-anti Diols via Asymmetric Ring Opening/Cross Metathesis

    PubMed Central

    Hartung, John

    2014-01-01

    An enantioselective method for the synthesis of 1,2-anti diols has been developed. A cyclometallated chiral-at-Ru complex catalyzes the asymmetric ring opening/cross metathesis of dioxygenated cyclobutenes, resulting in functionally rich synthetic building blocks. Syntheses of the insect pheromone (+)-endo brevicomin and monosaccharide ribose demonstrate the synthetic utility of the 1,2-anti diol fragments generated in the title reaction. PMID:24554613

  8. Asymmetric Synthesis of Fluorinated Isoindolinones through Palladium-Catalyzed Carbonylative Amination of Enantioenriched Benzylic Carbamates.

    PubMed

    Barrio, Pablo; Ibez, Ignacio; Herrera, Lidia; Romn, Raquel; Cataln, Silvia; Fustero, Santos

    2015-08-01

    The asymmetric synthesis of fluorinated isoindolinones has been achieved by a palladium-catalyzed aminocarbonylation reaction of the corresponding ?-fluoroalkyl o-iodobenzylamines. A base-mediated anti ?-hydride elimination process was suggested to explain the partial erosion of the optical purity observed in some cases. This mechanistic rationale enabled the minimization of this partial racemization by fine-tuning the pKa of the base. PMID:26121312

  9. Asymmetric Synthesis of Heterocyclic Analogues of a CGRP Receptor Antagonist for Treating Migraine.

    PubMed

    Luo, Guanglin; Chen, Ling; Conway, Charles M; Kostich, Walter; Macor, John E; Dubowchik, Gene M

    2015-12-18

    An asymmetric synthesis of novel heterocyclic analogue of the CGRP receptor antagonist rimegepant (BMS-927711, 3) is reported. The cycloheptane ring was constructed by an intramolecular Heck reaction. The application of Hayashi-Miyaura and Ellman reactions furnished the aryl and the amine chiral centers, while the separable diastereomeric third chiral center alcohols led to both carbamate and urea analogues. This synthetic approach was applicable to both 6- and 5-membered heterocycles as exemplified by pyrazine and thiazole derivatives. PMID:26650258

  10. Ru-catalyzed asymmetric hydrogenation of δ-keto Weinreb amides: enantioselective synthesis of (+)-Centrolobine.

    PubMed

    Zhao, Mengmeng; Lu, Bin; Ding, Guangni; Ren, Kai; Xie, Xiaomin; Zhang, Zhaoguo

    2016-02-24

    An efficient asymmetric hydrogenation of δ-keto Weinreb amides catalyzed by a Ru-Xyl-SunPhos-Daipen bifunctional catalyst has been achieved. This method afforded a series of enantio-enriched δ-hydroxy Weinreb amides in good yields (up to 93%) and enantioselectivities (up to 99%). This protocol was successfully applied to the synthesis of the key intermediate of (+)-Centrolobine. PMID:26837278

  11. Asymmetric catalytic alkynylation of acetaldehyde and its application to the synthesis of (+)-tetrahydropyrenophorol

    PubMed Central

    Trost, Barry. M.; Quintard, Adrien

    2012-01-01

    By controlling the kinetics of alkynylation over aldolisation (by slowing adding the acceptor), the challenging asymmetric catalytic alkynylation of acetaldehyde has been realized. This protocol yields the corresponding attractive synthons in good to excellent enantiocontrol and shows broad tolerance and applicability. This was highlighted by its application to the synthesis of several natural products such as the rapid construction of the macrocyclic diolide (+)-tetrahydropyrenophorol. PMID:22674869

  12. Asymmetric Synthesis of Fully Substituted Cyclopentane-Oxindoles through an Organocatalytic Triple Michael Domino Reaction

    PubMed Central

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

    2015-01-01

    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

  13. Synthesis of ?-Chiral Butyrolactones by Highly Stereoselective Radical Transfer or Sequential Asymmetric Alkylations: Concise Preparation of Leupyrrin Moieties.

    PubMed

    Schrempp, Michael; Thiede, Sebastian; Herkommer, Daniel; Gansuer, Andreas; Menche, Dirk

    2015-11-01

    Inspired by the bioactive natural metabolites leupyrrin?A1 and B1 , two novel stereoselective methods for the highly concise synthesis of densely substituted ?-chiral butyrolactones are reported. The first approach relies on an innovative three-step Ti(III) -catalyzed radical reaction that proceeds with excellent chemo-, regio-, and stereoselectivity. The alternative route utilizes sequential asymmetric alkylations and enables asymmetric synthesis of the authentic ?-tetrasubstituted butyrolactone motif of the leupyrrins in only four steps from commercially available substrates. PMID:26354047

  14. Studies Toward the Asymmetric Synthesis of the Right Part of the Mycalamides

    PubMed Central

    Zhong, H. Marlon; Sohn, Jeong-Hun; Rawal, Viresh H.

    2008-01-01

    Described herein is the asymmetric synthesis of a functionalized, trioxadecalin unit that comprises the right-hand part of the mycalamides and related natural products. The synthetic route involves a 16-step sequence that accomplishes the formation of two heterocyclic rings and the generation of five stereocenters. The synthesis commenced with a C2 symmetric starting material, diethyl D-tartrate, and took advantage of a relay of diastereoselective reactions to extend this four-carbon chain and introduce new chiral centers. Subsequent electrophile mediated cyclization afforded the desired pyran ring, which was then transformed into the desired, functionalized trioxadecalin skeleton. PMID:17221953

  15. New and Accurate Synthesis Formulas for Asymmetric Coplanar Stripline with an Infinitely Wide Strip

    NASA Astrophysics Data System (ADS)

    Guney, K.; Yildiz, C.; Kaya, S.; Turkmen, M.

    2009-02-01

    New and accurate synthesis formulas for the asymmetric coplanar stripline with an infinitely wide strip (ACPS-IWS) are presented. They are obtained by using a differential evolution algorithm (DEA) and particle swarm optimization (PSO) algorithm, and are useful to microwave engineers for accurately computing the physical dimensions of ACPS-IWS. The average percentage errors of the synthesis formulas found by using DEA and PSO are calculated to be 0.85% and 1.62%, respectively, for 4913 ACPS-IWS samples having different electrical parameters and physical dimensions, as compared with the results of quasi-static analysis.

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

    PubMed Central

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

    2015-01-01

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

  17. 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; Grger, 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

  18. Asymmetric synthesis of trisubstituted oxazolidinones by the thiourea-catalyzed aldol reaction of 2-isocyanatomalonate diester.

    PubMed

    Sakamoto, Shota; Kazumi, Naoya; Kobayashi, Yusuke; Tsukano, Chihiro; Takemoto, Yoshiji

    2014-09-19

    A new method has been developed for the synthesis of chiral 4-carboxyl oxazolidinones by the catalytic asymmetric aldol reaction of an isocyanatomalonate diester with an aldehyde in the presence of a thiourea catalyst. The resulting chiral 4-carboxyl oxazolidinones are the equivalent of ?-hydroxy-?-amino acids bearing a tri- or tetrasubstituted carbon center at their ? position. With this in mind, this procedure was successfully applied to the first total synthesis of mycestericin C, which was completed in 12 steps and represents one of the shortest reported sequences for the construction of natural products of this type. PMID:25203516

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

    PubMed Central

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

    2009-01-01

    Enantioenriched diaryl-, aryl heteroaryl- and diheteroarylmethanols exhibit important biological and medicinal properties. One-pot catalytic asymmetric syntheses of these compounds beginning from readily available aryl bromides are introduced. Thus, lithium-bromide exchange with commercially available aryl bromides and n-BuLi was followed by salt metathesis with ZnCl2 to generate ArZnCl. A second equivalent of n-BuLi was added to form the mixed organozinc, ArZnBu. In the presence of enantioenriched amino alcohol-based catalysts, ArZnBu adds to aldehydes to afford essentially racemic diarylmethanols. The low enantioselectivities were attributed to a LiCl-promoted background reaction. To inhibit this background reaction, the chelating diamine TEEDA (tetraethylethylene diamine) was introduced prior to aldehyde addition. Under these conditions, enantioenriched diarylmethanols were obtained with >90% ee. Arylations of enals generated allylic alcohols with 8190% ee. This procedure was unsuccessful, however, when applied to heteraryl bromides, which was attributed to decomposition of the heteroaryl lithium under the salt metathesis conditions. To avoid this problem, the metathesis was conducted with EtZnCl, which enabled the salt metathesis to proceed at low temperatures. The resulting EtZn(ArHetero) intermediates (ArHetero=2- and 3-thiophenyl, 2-benzothiophenyl, 3-furyl, and 5-indolyl) were successfully added to aldehydes and heteroaryl aldehydes with enantioselectivities between 8199%. These are the first examples of catalytic and highly enantioselective syntheses of diheteroarylmethanols. In a similar fashion, ferrocenyl bromide was used to generate FcZnEt and the ferrocenyl group added to benzaldehyde and heteroaromatic aldehydes to form ferrocene-based ligand precursors in 8695% yield with 9698% ee. It was also found that the arylation and heteroarylation of enals could be followed by diastereoselective epoxidations to provide epoxy alcohols with high enantio- and diastereoselectivities in a one-pot procedure. PMID:19653691

  20. Enantioselective Synthesis of 3,4-Chromanediones via Asymmetric Rearrangement of 3-Allyloxyflavones

    PubMed Central

    Mari, Jean-Charles; Xiong, Yuan; Min, Geanna K.; Yeager, Adam R.; Taniguchi, Tohru; Berova, Nina; Schaus, Scott E.; Porco, John A.

    2010-01-01

    Asymmetric scandium (III)-catalyzed rearrangement of 3-allyloxyflavones was utilized to prepare chiral, non-racemic 3,4-chromanediones in high yields and enantioselectivities. These synthetic intermediates have been further elaborated to novel heterocyclic frameworks including angular pyrazines and dihydropyrazines. The absolute configuration of rearrangement products was initially determined by a nonempirical analysis of circular dichroism (CD) using time-dependent density functional theory (TDDFT) calculations and verified by x-ray crystallography of a hydrazone derivative. Initial studies of the mechanism support an intramolecular rearrangement pathway that may proceed through a benzopyrylium intermediate. PMID:20527786

  1. Solid-phase synthesis of asymmetrically branched sequence-defined poly/oligo(amidoamines).

    PubMed

    Wojcik, Felix; Mosca, Simone; Hartmann, Laura

    2012-05-01

    We present for the first time the synthesis of asymmetrically branched sequence-defined poly/oligo(amidoamines) (PAAs) using solid-phase synthesis with the capability of introducing diversity at the side chains. We introduce two new versatile (diethylenetriamine) building blocks for solid-phase synthesis bearing Fmoc/Boc and Fmoc/Alloc protecting groups expanding recently used Fmoc/Boc protecting group strategy for linear PAAs to an Fmoc/Alloc/Boc strategy. This allows for orthogonal on-resin cleavage of Fmoc and Alloc protecting groups during solid-phase synthesis of PAAs with backbones differing in chain length and sequence. With these structures we then demonstrate the potential for generating asymmetrical branching by automated multiple on-resin cleavage of Alloc protecting groups as well as the introduction of side chains varying in length and number. Such systems have high potential as nonviral vectors for gene delivery and will allow for more detailed studies on the correlation between the degree of branching of PAAs and their resulting biological properties. PMID:22486248

  2. 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; Ltzen, 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

  3. Asymmetric Total Synthesis of Indole Alkaloids Containing an Indoline Spiroaminal Framework.

    PubMed

    Yamada, Takeshi; Ideguchi-Matsushita, Tetsuya; Hirose, Tomoyasu; Shirahata, Tatsuya; Hokari, Rei; Ishiyama, Aki; Iwatsuki, Masato; Sugawara, Akihiro; Kobayashi, Yoshinori; Otoguro, Kazuhiko; ?mura, Satoshi; Sunazuka, Toshiaki

    2015-08-10

    The total synthesis of the indole alkaloids, neoxaline, oxaline and meleagrin?A, all containing a unique indoline spiroaminal framework, was accomplished through the stereoselective introduction of a reverse prenyl group to the congested benzylic carbon of furoindoline, a two-pot transformation of indoline (containing three nitrogen atoms at appropriate positions) to the featured indoline spiroaminal framework, and elimination of carbonate assisted by the adjacent imidazole moiety to construct the (E)-dehydrohistidine. The absolute stereochemistry of neoxaline was elucidated through our total synthesis. In addition, we evaluated the bioactivity, especially the anti-infectious properties, of neoxaline and oxaline, and of some synthetic intermediates. PMID:26147398

  4. One-Pot Catalysis Using a Chiral Iridium Complex/Brnsted Base: Catalytic Asymmetric Synthesis of Catalponol.

    PubMed

    Suzuki, Takeyuki; Ismiyarto; Ishizaka, Yuka; Zhou, Da-Yang; Asano, Kaori; Sasai, Hiroaki

    2015-11-01

    Tandem asymmetric hydrogen transfer oxidation/aldol condensation under relay catalysis of a chiral iridium complex/achiral Brnsted base binary system is described for the synthesis of ?-benzylidene-?-hydroxytetralones with high ee's. A two-step synthesis of catalponol was achieved using this sequential methodology together with regio- and stereoselective hydroboration. PMID:26496409

  5. 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

  6. Synthesis and absolute configuration assignment of albucidin: a late-stage reductive deiodination by visible light photocatalysis.

    PubMed

    Zhang, Hu; Liu, Peng-Fei; Chen, Qiong; Wu, Qiong-You; Seville, Anne; Gu, Yu-Cheng; Clough, John; Zhou, Shao-Lin; Yang, Guang-Fu

    2016-04-01

    The synthesis of albucidin and its enantiomer are described. It involves a visible-light photocatalysis deiodination at the late stage. The absolute configuration of natural albucidin is determined as (1R,3S). This work provides a basis for structural modification to develop a new type of herbicidal from an old structure. PMID:26972382

  7. The origins of homochirality examined by using asymmetric autocatalysis.

    PubMed

    Soai, Kenso; Kawasaki, Tsuneomi; Matsumoto, Arimasa

    2014-02-01

    Pyrimidyl alkanol was found to act as an asymmetric autocatalyst in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde. Asymmetric autocatalysis of 2-alkynylpyrimidyl alkanol with an extremely low enantiomeric excess (ca. 0.00005% ee) exhibits enormous asymmetric amplification to afford the same compound with >99.5% ee. This asymmetric autocatalysis with amplification of ee has been employed to examine the validity of proposed theories of the origins of homochirality. Circularly polarized light, quartz, sodium chlorate, cinnabar, chiral organic crystals and spontaneous absolute asymmetric synthesis were considered as possible candidates for the origin of chirality; each could act as a chiral source in asymmetric autocatalysis. Asymmetric autocatalysis can discriminate the isotope chirality arising from the small difference between carbon (carbon-13/carbon-12) and hydrogen (D/H) isotopes. Cryptochiral compounds were also discriminated by asymmetric autocatalysis. PMID:24449510

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

    PubMed

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

    2015-11-17

    Methods for the absolute quantification of glycans are needed in glycoproteomics, during development and production of biopharmaceuticals and for the clinical analysis of glycan disease markers. Here we present a strategy for the chemo-enzymatic synthesis of (13)C labeled N-glycan libraries and provide an example for their use as internal standards in the profiling and absolute quantification of mAb glycans by matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry. A synthetic biantennary glycan precursor was (13)C-labeled on all four amino sugar residues and enzymatically derivatized to produce a library of 15 glycan isotopologues with a mass increment of 8 Da over the natural products. Asymmetrically elongated glycans were accessible by performing enzymatic reactions on partially protected UV-absorbing intermediates, subsequent fractionation by preparative HPLC, and final hydrogenation. Using a preformulated mixture of eight internal standards, we quantified the glycans in a monoclonal therapeutic antibody with excellent precision and speed. PMID:26482441

  9. Total synthesis of the hydroxyketone kurasoin A using asymmetric phase-transfer alkylation.

    PubMed

    Andrus, Merritt B; Hicken, Erik J; Stephens, Jeffrey C; Bedke, D Karl

    2006-10-27

    The total synthesis of the farnesyltransferase inhibitor kurasoin A has been achieved using a novel asymmetric phase-transfer-catalyzed glycolate alkylation reaction. 2,5-Dimethoxyacetophenone 7 with cinchonidinium catalyst 9(10 mol %) and hydroxide base with pivaloyl benzyl bromide 8 provided S-alkylation product 10 in high yield (80-99%) and excellent enantioselectivity. Baeyer-Villiger oxidation, Weinreb amide formation, and benzyl Grignard addition to the TES-ether 17 gave the protected target. Lithium hydroxide and peroxide generated kurasoin A ([alpha](D) +8.4 degrees ) without isomerization. PMID:17064051

  10. One-Pot, Four-Step Organocatalytic Asymmetric Synthesis of Functionalized Nitrocyclopropanes.

    PubMed

    Zaghi, Anna; Bernardi, Tatiana; Bertolasi, Valerio; Bortolini, Olga; Massi, Alessandro; De Risi, Carmela

    2015-09-18

    The asymmetric synthesis of functionalized nitrocyclopropanes has been achieved by a one-pot, four-step method catalyzed by (S)-diphenylprolinol TMS ether, which joins two sequential domino reactions, namely a domino sulfa-Michael/aldol condensation of ?,?-unsaturated aldehydes with 1,4-dithiane-2,5-diol, and a domino Michael/?-alkylation reaction of the derived chiral dihydrothiophenes with bromonitromethane. The title compounds were obtained in 27-45% yields, with high levels of diastereoselectivity (93:7 to 100:0 dr) and generally good enantioselectivities (up to 95:5 er). PMID:26317611

  11. Stereocontrolled asymmetric synthesis of alpha-hydroxy-beta-amino acids. A stereodivergent approach.

    PubMed

    Aoyagi, Y; Jain, R P; Williams, R M

    2001-04-18

    The stereocontrolled asymmetric synthesis of alpha-hydroxy-beta-amino acids has been investigated via the Lewis acid-promoted cyanation of (5R,6S)-2-acetoxy-4-(benzyloxycarbonyl)-5,6-diphenyl-2,3,5,6-tetrahydro-4H-1,4-oxazines with trimethylsilyl cyanide. Base-catalyzed hydrolysis of the resulting cyano compounds proceeds with excellent stereoselectivity, providing access to diastereomerically pure oxazine-2-carboxylic acids which were readily converted to each enantiomer of the alpha-hydroxy-beta-amino acids isothreonine and nor-C-statine. PMID:11472118

  12. Synthesis of novel monodentate phosphoramidites and their application in iridium-catalyzed asymmetric hydrogenations.

    PubMed

    Erre, Giulia; Junge, Kathrin; Enthaler, Stephan; Addis, Daniele; Michalik, Dirk; Spannenberg, Anke; Beller, Matthias

    2008-05-01

    New monodentate H(8)-binaphthol based phosphoramidites 6 b-i have been prepared. Starting from (S)-3,3'-dibromo-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl-2,2'-diol 3, a general protocol for the synthesis of ligands 6 is presented. A small ligand library bearing aryl substituents in the 3,3'-position of the binaphthol core was synthesized and successfully tested in the iridium-catalyzed asymmetric hydrogenation of 2-amidocinnamates to obtain different alpha-amino acid derivatives in up to 99 % ee. PMID:18444240

  13. Total synthesis and determination of the absolute configuration of 5,6-dihydro-α-pyrone natural product synargentolide B.

    PubMed

    Prasad, Kavirayani R; Gutala, Phaneendra

    2013-04-01

    Enantiospecific total synthesis and determination of the absolute stereochemistry of the α-pyrone-containing natural product synargentolide B were accomplished. The absolute stereochemistry of the natural product was established by synthesizing the possible diastereomers and comparison of the data with those reported for the natural product. During the process, total synthesis of the putative structure of related natural product 6R-[1S,2R,5R,6S-(tetraacetyloxy)-3E-heptenyl]-5,6-dihydro-2H-pyran-2-one was also accomplished and confirmed by X-ray crystal structure analysis. Wittig-Horner reaction of a chiral phosphonate derived from (S)-lactic acid and ring-closing metathesis were the key reactions during the course of the total synthesis. PMID:23477705

  14. Asymmetric Total Synthesis of (-)-Englerin A through Catalytic Diastereo- and Enantioselective Carbonyl Ylide Cycloaddition.

    PubMed

    Hanari, Taiki; Shimada, Naoyuki; Kurosaki, Yasunobu; Thrimurtulu, Neetipalli; Nambu, Hisanori; Anada, Masahiro; Hashimoto, Shunichi

    2015-08-10

    An asymmetric total synthesis of the guaiane sesquiterpene (-)-englerin A, a potent and selective inhibitor of the growth of renal cancer cell lines, was accomplished. The basis of the approach is a highly diastereo- and enantioselective carbonyl ylide cycloaddition with an ethyl vinyl ether dipolarophile under catalysis by dirhodium(II) tetrakis[N-tetrachlorophthaloyl-(S)-tert-leucinate], [Rh2 (S-TCPTTL)4 ], to construct the oxabicyclo[3.2.1]octane framework with concomitant introduction of the oxygen substituent at C9 on the exo-face. Another notable feature of the synthesis is ruthenium tetraoxide-catalyzed chemoselective oxidative conversion of C9 ethyl ether to C9 acetate. PMID:26179743

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

    NASA Astrophysics Data System (ADS)

    Raj, Hans; Szyma?ski, Wiktor; de Villiers, Jandr; Rozeboom, Henritte 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).

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

    PubMed Central

    Perreault, Stéphane; Rovis, Tomislav

    2010-01-01

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

  17. Divergent Synthesis of ?,?-Disubstituted ?-Butyrolactones through Diastereoselective Bromolactonization with Alkali Metal Bromide: Asymmetric Total Synthesis of (+)-Dubiusamine C.

    PubMed

    Moriyama, Katsuhiko; Sugiue, Toru; Nishinohara, Chihiro; Togo, Hideo

    2015-09-18

    A divergent synthesis of ?-substituted bromomethyl ?-lactones was developed, which involves the diastereoselective bromolactonization of ?-substituted 4-pentenoic acids and 4-pentenamides via umpolung of bromide by use of alkali metal bromide and Oxone (potassium peroxymonosulfate mixture, 2KHSO5KHSO4K2SO4) to obtain mainly cis-products from ?-substituted 4-pentenoic acids and trans-products from ?-substituted 4-pentenamides, and it was found that the bromonium species generated from KBr and Oxone had higher activity than N-bromosuccinimide. Furthermore, the asymmetric total synthesis of (+)-dubiusamine C, which was isolated as a minor diastereomer from Pandanus dubius, was accomplished for the first time through the cis-selective bromolactonization of (S)-?-methyl-4-pentenoic acid in nine linear steps and 36% overall yield. PMID:26313874

  18. [Asymmetric synthesis of aromatic L-amino acids catalyzed by transaminase].

    PubMed

    Xia, Wenna; Sun, Yu; Min, Cong; Han, Wei; Wu, Sheng

    2012-11-01

    Aromatic L-Amino acids are important chiral building blocks for the synthesis of many drugs, pesticides, fine chemicals and food additives. Due to the high activity and steroselectivity, enzymatic synthesis of chiral building blocks has become the main research direction in asymmetric synthesis field. Guided by the phylogenetic analysis of transaminases from different sources, two representative aromatic transaminases TyrB and Aro8 in type I subfamily, from the prokaryote Escherichia coli and eukaryote Saccharomyces cerevisia, respectively, were applied for the comparative study of asymmetric transamination reaction process and catalytic efficiency of reversely converting keto acids to the corresponding aromatic L-amino acid. Both TyrB and Aro8 could efficiently synthesize the natural aromatic amino acids phenylalanine and tyrosine as well as non-natural amino acid phenylglycine. The chiral HPLC analysis showed the produced amino acids were L-configuration and the e.e value was 100%. L-alanine was the optimal amino donor, and the transaminase TyrB and Aro8 could not use D-amino acids as amino donor. The optimal molar ratio of amino donor (L-alanine) and amino acceptor (aromatic alpha-keto acids) was 4:1. Both of the substituted group on the aromatic ring and the length of fatty acid carbon chain part in the molecular structure of aromatic substrate alpha-keto acid have the significant impact on the enzyme-catalyzed transamination efficiency. In the experiments of preparative-scale transamination synthesis of L-phenylglycine, L-phenylalanine and L-tyrosine, the specific production rate catalyzed by TryB were 0.28 g/(g x h), 0.31 g/(g x h) and 0.60 g/(g x h) and the specific production rate catalyzed by Aro8 were 0.61 g/(g x h), 0.48 g/(g x h) and 0.59 g/(g x h). The results obtained here were useful for applying the transaminases to asymmetric synthesis of L-amino acids by reversing the reaction balance in industry. PMID:23457787

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    PubMed Central

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

    2015-01-01

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

  1. Asymmetric synthesis and biological activities of natural product (+)-balasubramide and its derivatives.

    PubMed

    Li, Jun; Li, Jianzu; Xu, Yuan; Wang, Yunjie; Zhang, Luyong; Ding, Li; Xuan, Yining; Pang, Tao; Lin, Hansen

    2016-04-01

    The natural product (+)-balasubramide (3j) and its derivatives (3a-3i) were synthesized using a two-step asymmetric synthesis, and the biological activities of 3a-3j were determined in vitro. Methyl (2S,3R)-(+)-3-phenyloxirane-2-carboxylate (1h), the asymmetric synthesis of which was described in a previous paper, was selected as the starting material. Compounds 3a-3j were evaluated for their neuroprotective, antioxidative, and anti-neuroinflammatory effects. (+)-Balasubramide and its derivatives with different electronegative groups in the 6-phenyl ring produced little neuroprotection and antioxidation, but induced potent anti-neuroinflammatory effects in BV-2 microglial cells (with the exception of 3g). Compound 3c, with a trifluoromethyl group in its 6-phenyl ring, was a particularly potent anti-neuroinflammatory agent. These results demonstrated that the electronegativity of the 6-phenyl ring of (+)-balasubramide is an important determinant of its inhibitory effect on neuroinflammation. More electronegative substituents result in more potent anti-neuroinflammatory effects. Moreover, cytotoxicity assays indicated no significant effects of the tested compounds. PMID:26247374

  2. Total synthesis and determination of the absolute configuration of rakicidin A.

    PubMed

    Sang, Feng; Li, Dongmei; Sun, Xiaolong; Cao, Xianqiang; Wang, Liang; Sun, Jianlei; Sun, Bingxia; Wu, Lingling; Yang, Guang; Chu, Xiaoqian; Wang, Jinghan; Dong, Changming; Geng, Yan; Jiang, Hong; Long, Haibo; Chen, Sijia; Wang, Guiyan; Zhang, Shuzhong; Zhang, Quan; Chen, Yue

    2014-11-01

    Rakicidin A is a cyclic depsipeptide that has exhibited unique growth inhibitory activity against chronic myelogenous leukemia stem cells. Furthermore, rakicidin A has five chiral centers with unknown stereochemical assignment, and thus, can be represented by one of 32 possible stereoisomers. To predict the most probable stereochemistry of rakicidin A, calculations and structural comparison with natural cyclic depsipeptides were applied. A total synthesis of the proposed structure was subsequently completed and highlighted by the creation of a sterically hindered ester bond (C1-C15) through trans-acylation from an easily established isomer (C1-C13). The analytic data of the synthetic target were consistent with that of natural rakicidin A, and then the absolute configuration of rakicidin A was assigned as 2S, 3S, 14S, 15S, 16R. This work suggests strategies for the determination of unknown chiral centers in other cyclic depsipeptides, such as rakicidin B, C, D, BE-43547, and vinylamycin, and facilitates the investigations of rakicidin A as an anticancer stem cell agent. PMID:25286338

  3. The use of tritiated water to measure absolute rates of hepatic glycogen synthesis.

    PubMed

    Postle, A D; Bloxham, D P

    1980-10-15

    Glucogen synthesis in rat liver in vivo was measured by the incorporation of 3H from 3H2O into glycogen. In meal-fed rats incorporation and the incorporation of 3H into glycogen was linear up to 100 min. Before feeding glycogen concentration and the incorporation of 3H were both low; and both rose on feeding to give maximal values after 2-3h. The glycogen concentration was maintained for a further 5h but the incorporation of 3H rapidly declined to pre-feeding values. This shows that glycogen turnover was low in the post-prandial rat. Streptozotocin diabetes decreased the rise in glycogen concentration on feeding and had a similar effect on 3H2O incorporation. Both effects were reversed by insulin administration. The number of 3H atoms incorporated per glycogen glucose moiety formed in biosynthetic experiments (2.84 +/- 0.47) was relatively constant and allowed absolute biosynthetic rates to be calculated. Degradation of glucose from glycogen labelled by 3H2O showed that most of the 3H was located at C-2 and C-5. The incorporation would arise by rapid equilibration of hexose phosphates through phosphoglucose isomerase, transaldolase and triose phosphate isomerase. PMID:7305913

  4. Asymmetric Total Synthesis of (+)- and ent-(−)-Yatakemycin and Duocarmycin SA: Evaluation of Yatakemycin Key Partial Structures and its Unnatural Enantiomer

    PubMed Central

    Tichenor, Mark S.; Trzupek, John D.; Kastrinsky, David B.; Shiga, Futoshi; Hwang, Inkyu; Boger, Dale L.

    2008-01-01

    Complementary to studies that provided the first yatakemycin total synthesis resulting in its structure revision and absolute stereochemistry assignment, a second generation asymmetric total synthesis is disclosed herein. Since the individual yatakemycin subunits are identical to those of duocarmycin SA (alkylation subunit) or CC-1065 (central and right-hand subunits), the studies also provide an improvement in our earlier total synthesis of CC-1065 and, as detailed herein, have been extended to an asymmetric total synthesis of (+)-duocarmycin SA. Further extensions of the studies provided key yatakemycin partial structures and analogues for comparative assessments. This included the definition of the DNA selectivity (adenine central to a five base-pair AT sequence, eg. 5′-AAAAA), efficiency, relative rate, and reversibility of ent-(−)-yatakemycin and its comparison with the natural enantiomer (identical selectivity and efficiency), structural characterization of the adenine N3 adduct confirming the nature of the DNA reaction, and comparisons of the cytotoxic activity of the natural product (L1210 IC50 = 5 pM) with its unnatural enantiomer (IC50 = 5 pM) and a series of key partial structures including those that probe the role of the C-terminus thiomethyl ester. The only distinguishing features between the enantiomers is that ent-(−)-yatakemycin alkylates DNA at a slower rate (krel = 0.13) and is reversible, whereas (+)-yatakemycin is not. Nonetheless, even ent-(−)-yatakemycin alkylates DNA at a faster rate and with a greater thermodynamic stability than (+)-duocarmycin SA illustrating the unique characteristics of such “sandwiched” agents. PMID:17147378

  5. Enantioselective Synthesis of α-Secondary and α-Tertiary Piperazin-2-ones and Piperazines by Catalytic Asymmetric Allylic Alkylation

    PubMed Central

    Korch, Katerina M.; Eidamshaus, Christian; Behenna, Douglas C.; Nam, Sangkil; Horne, David

    2014-01-01

    The asymmetric Pd-catalyzed decarboxylative allylic alkylation of differentially N-protected piperazin-2-ones allows for the synthesis of a variety of highly enantioenriched tertiary piperazine-2-ones. Deprotection and reduction affords the corresponding tertiary piperazines, which can be employed for the synthesis of medicinally important analogs. The introduction of these chiral tertiary piperazines resulted in imatinib analogs that exhibited comparable antiproliferative activity to that of their corresponding imatinib counterparts. PMID:25382664

  6. Absolute configuration and total synthesis of a novel antimalarial lipopeptide by the de novo preparation of chiral nonproteinogenic amino acids.

    PubMed

    Ghosh, Shibaji K; Somanadhan, Brinda; Tan, Kevin S-W; Butler, Mark S; Lear, Martin J

    2012-03-16

    The absolute configuration (via degradation and Marfey's derivatization studies) and the total synthesis of a novel antimalarial lipid-peptide isolated from Streptomyces sp. (IC(50) = 0.8 ?M, Plasmodium falciparum 3D7) is disclosed. To this end, versatile stereocontrolled routes to nonproteinogenic amino acids (via catalytic Mannich, Sharpless methods) and enantiomeric trans fatty acids (via Evans alkylation, Kocienski-Julia olefination) have been developed. PMID:22390733

  7. 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.

  8. Asymmetric synthesis of cyclopentanes bearing four contiguous stereocenters via an NHC-catalyzed Michael/Michael/esterification domino reaction.

    PubMed

    Shu, Tao; Ni, Qijian; Song, Xiaoxiao; Zhao, Kun; Wu, Tianyu; Puttreddy, Rakesh; Rissanen, Kari; Enders, Dieter

    2016-02-11

    An NHC-catalyzed Michael/Michael/esterification domino reaction via homoenolate/enolate intermediates for the asymmetric synthesis of tetrasubstituted cyclopentanes bearing four contiguous stereocenters is described. A variety of ?,?-unsaturated aldehydes and 2-nitroallylic acetates react well with good domino yields and high stereoselectivities. PMID:26750327

  9. Multicomponent Synthesis of Cyclic Depsipeptide Mimics by Ugi Reaction Including Cyclic Hemiacetals Derived from Asymmetric Organocatalysis.

    PubMed

    de la Torre, Alexander F; Rivera, Daniel G; Concepción, Odette; Echemendia, Radell; Correa, Arlene G; Paixão, Márcio W

    2016-02-01

    The synthesis of novel cyclic depsipeptide mimics by means of an organocatalytic conjugate addition, leading to chiral cyclic hemiacetals, followed by a multicomponent reaction with α-amino acids and isocyanides, is described. The initial organocatalytic step is employed for the asymmetric derivatization of α,β-unsaturated aldehydes to 4,5-disubstituted 2-hydroxytetrahydropyrans, which are next used as chiral bifunctional substrates on the Ugi five-center three-component reaction, giving rise to nine-membered-ring lactones. This sequential approach proved to be suitable for the rapid generation of molecular complexity through the combination of aliphatic, dipeptidic, glucosidic, and lipidic isocyanides with several amino acids, thus giving access to amido-, glyco-, and lipo-depsipeptide scaffolds featuring natural product-like structures. PMID:26720907

  10. Total synthesis of (+)-geldanamycin and (-)-o-quinogeldanamycin: asymmetric glycolate aldol reactions and biological evaluation.

    PubMed

    Andrus, Merritt B; Meredith, Erik L; Hicken, Erik J; Simmons, Bryon L; Glancey, Russell R; Ma, Wei

    2003-10-17

    The total synthesis of (+)-geldanamycin (GA), following a linear route, has been completed using a demethylative quinone-forming reaction as the last step. Key steps include the use of two new asymmetric boron glycolate aldol reactions. To set the anti-C11,12 hydroxymethoxy functionality, (S,S)-5,6-bis-4-methoxyphenyldioxanone 8 was used. Methylglycolate derived from norephedrine 5 set the C6,7 methoxyurethane stereochemistry. The quinone formation step using nitric acid gave the non-natural o-quino-GA product 55 10:1 over geldanamycin. Other known oxidants gave an unusual azaquinone product 49. o-Quino-GA 55 binds Hsp90 with good affinity but is less cytotoxic compared to GA. PMID:14535799

  11. [Stereocontrolled synthesis of phosphinyl dipeptide isosteres using an asymmetric center at the phosphorus atom].

    PubMed

    Yamagishi, Takehiro

    2014-01-01

    Phosphinyl dipeptide isosteres (PDIs) are important compounds for the development of potent and selective inhibitors of various aspartic proteases and Zn metalloproteases. The stereochemistry of PDIs affects their biological activity. PDIs were prepared successfully using the concept of asymmetric induction from the chiral phosphorus atom of the phosphinate moiety to the neighboring carbon atom. This methodology involves diastereoselective ?-alkylation and ?'-alkylation of P-chiral phosphinate derivatives, prepared through lipase-catalyzed kinetic resolution, which produces Phe-Ala type and Pro-Phe type PDIs. The synthesis of Leu-Pro type PDIs in a protected form was achieved through a cross-coupling reaction of stereodefined ?-amino-H-phosphinate with alkenyl triflate, followed by diastereoselective hydrogenation of the alkene moiety. PMID:25174361

  12. Asymmetric synthesis of anti-aldol segments via a nonaldol route: synthetic applications to statines and (-)-tetrahydrolipstatin.

    PubMed

    Ghosh, Arun K; Shurrush, Khriesto; Kulkarni, Sarang

    2009-06-19

    An asymmetric synthesis of anti-aldol segments via a nonaldol route is described. The strategy involves a highly diastereoselective synthesis of functionalized tetrahydrofuran derivatives from optically active 4-phenylbutyrolactone. Treatment of the tetrahydrofuran derivatives with a Lewis acid and acetic anhydride provided the corresponding ring-opened styrene derivatives. Oxidative cleavage of the styrene derivatives provided access to the anti-aldol segments. The utility of this methodology was demonstrated by the synthesis of statine derivatives and pancreatic lipase inhibitor, (-)-tetrahydrolipstatin. PMID:19438217

  13. Asymmetric allylation/ring closing metathesis: one-pot synthesis of benzo-fused cyclic homoallylic amines. Application to the formal synthesis of Sertraline derivatives.

    PubMed

    Fustero, Santos; Lzaro, Rubn; Herrera, Lidia; Rodrguez, Elsa; Mateu, Natalia; Barrio, Pablo

    2013-07-19

    A one-pot asymmetric allylation/ring closing metathesis (RCM) sequence for the synthesis of cyclic homoallylic amines has been developed. A library of six- and seven-membered benzo-fused products has been synthesized in good yields and complete diastereoselectivity. The new methodology has been applied to the formal syntheses of the antidepressant Sertraline and the epimeric Norsertraline. The methodology is amenable for the synthesis of analogs. PMID:23834527

  14. Enzymatic- and iridium-catalyzed asymmetric synthesis of a benzothiazepinylphosphonate bile acid transporter inhibitor.

    PubMed

    Cowan, David J; Collins, Jon L; Mitchell, Mark B; Ray, John A; Sutton, Peter W; Sarjeant, Amy A; Boros, Eric E

    2013-12-20

    A synthesis of the benzothiazepine phosphonic acid 3, employing both enzymatic and transition metal catalysis, is described. The quaternary chiral center of 3 was obtained by resolution of ethyl (2-ethyl)norleucinate (4) with porcine liver esterase (PLE) immobilized on Sepabeads. The resulting (R)-amino acid (5) was converted in two steps to aminosulfate 7, which was used for construction of the benzothiazepine ring. Benzophenone 15, prepared in four steps from trimethylhydroquinone 11, enabled sequential incorporation of phosphorus (Arbuzov chemistry) and sulfur (Pd(0)-catalyzed thiol coupling) leading to mercaptan intermediate 18. S-Alkylation of 18 with aminosulfate 7 followed by cyclodehydration afforded dihydrobenzothiazepine 20. Iridium-catalyzed asymmetric hydrogenation of 20 with the complex of [Ir(COD)2BArF] (26) and Taniaphos ligand P afforded the (3R,5R)-tetrahydrobenzothiazepine 30 following flash chromatography. Oxidation of 30 to sulfone 31 and phosphonate hydrolysis completed the synthesis of 3 in 12 steps and 13% overall yield. PMID:24256447

  15. An advance on exploring N-tert-butanesulfinyl imines in asymmetric synthesis of chiral amines.

    PubMed

    Lin, Guo-Qiang; Xu, Ming-Hua; Zhong, Yu-Wu; Sun, Xing-Wen

    2008-07-01

    Although catalytic asymmetric synthesis has undergone tremendous growth in the last 30 years, chiral auxiliary-aided asymmetric synthesis continues to attract considerable attention. Chiral N- tert-butanesulfinamide, as pioneered by Ellman and co-workers, is undoubtedly one of the most efficient auxiliaries developed to date; it allows the preparation, through simple conversion, of a diverse range of enantiopure amines, which are ubiquitous in natural products and biologically active molecules. Following on from our studies of the SmI(2)-mediated asymmetric syntheses of alpha,gamma-substituted gamma-butyrolactones, we found that simple homocoupling of chiral N- tert-butanesulfinyl imines in the presence of SmI(2) produced enantiopure vicinal C2-symmetric diamines in high yield. In addition, C2-unsymmetric chiral diamines are readily prepared through SmI(2)-mediated cross-couplings of N- tert-butanesulfinyl imines and nitrones; these transformations represented the first successful examples of asymmetric cross-coupling between two different imine species. Subsequently, we discovered another useful reaction induced by SmI(2), the efficient cross-coupling of N- tert-butanesulfinyl imines and aldehydes, which provides ready access to enantiopure anti-1,2-amino alcohols. The synthetic applicability of this reaction was demonstrated through its use in the facile total syntheses of (3R,4S)-statine, d- erythro-sphinganine, (+)-CP-99,994, and (+)-L-733,060. The Zn/In-mediated allylation of chiral N- tert-butanesulfinyl imines yields homoallylic amines. After pondering the reaction mechanism, we developed optimal reaction conditions for reversing the stereogenic outcome, thereby allowing the preparation of enantiopure homoallylic amines of either handedness from single enantiomers of the (R)- or (S)-sulfinyl imine. When a benzoyl-substituted allyl bromide is used for allylation, the reaction proceeds smoothly to give 2-vinyl-substituted anti-1,2-amino alcohols in high yields and diastereoselectivities, another simple method for preparing enantiopure amino alcohols. We employed these reactions in the syntheses of enantiopure allylglycine, 3-allyl-isoindolinones, and (-)-cytoxazone. Further studies led to the discovery that the allylations of N- tert-butanesulfinyl aldimines can be performed in water. The reactions described in this Account are among the simplest and most efficient synthetic methods available for preparing enantio-enriched diamines, amino alcohols, homoallylic amines, and other amine derivatives. These reactions are additionally attractive because of the ready availability of the starting materials, the simplicity of the reaction conditions, and the high degree of stereochemical control. Their applications in the total syntheses of several biologically interesting molecules illustrate the versatility of these transformations; we hope that they will stimulate the development of new synthetic methods. PMID:18533688

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

    PubMed

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

    2015-12-23

    A simple method for the isolation of the bioactive compound alliin from garlic, as well as a method for the synthesis of diastereomerically pure alliin and allo-alliin on a preparative laboratory scale, was developed. The absolute configuration of the sulfur atom in alliin and allo-alliin was assigned on the basis of enzyme reactivity, optical rotatory dispersion, and circular dichroism analyses. A comparison of the results from these analyses, in combination with an X-ray diffraction study on a protected allo-alliin derivative, revealed S and R configurations of the sulfur atoms in alliin and allo-alliin, respectively. In addition, the same (1)H NMR spectrum was observed for synthetic and natural alliin. The absolute configuration of natural alliin was assigned for the first time on the basis of the NMR spectrum and X-ray coordinates. PMID:26638713

  17. One-Pot Synthesis of (S)-Baclofen via Aldol Condensation of Acetaldehyde with Diphenylprolinol Silyl Ether Mediated Asymmetric Michael Reaction as a Key Step.

    PubMed

    Hayashi, Yujiro; Sakamoto, Daisuke; Okamura, Daichi

    2016-01-01

    An efficient asymmetric total synthesis of (S)-baclofen was accomplished via a one-pot operation from commercially available materials using sequential reactions, such as aldol condensation of acetaldehyde, diphenylprolinol silyl ether mediated asymmetric Michael reaction of nitromethane, Kraus-Pinnick oxidation, and Raney Ni reduction. Highly enantioenriched baclofen was obtained in one pot with a good yield over four reactions. PMID:26636719

  18. Stereoselective Synthesis of Isochromanones by an Asymmetric Ortho-Lithiation Strategy: Synthetic Access to the Isochromanone Core of the Ajudazols.

    PubMed

    Essig, Sebastian; Menche, Dirk

    2016-03-01

    Full details on the design, development, and application of a highly stereoselective strategy for the synthesis of isochromanones are reported. The method is based on an asymmetric ortho lithiation with aldehyde electrophiles and utilizes the chiral memory of a preoriented atropisomeric amide axis for stereocontrol. For direct transformation of sterically hindered amides to isochromanones, efficient and mild one-pot protocols involving either O-alkylation or acidic microwave activation were developed. The procedures may be applied also to highly functionalized as well as stereochemically complex and sensitive substrates and demonstrate a high protective group tolerance. Furthermore, asymmetric crotylborations of axially chiral amides were studied in detail. These methodologies enable a general access to all possible stereoisomers of hydroxyl-isochromanones with up to three contiguous stereocenters. The true applicability of our approach was finally demonstrated by synthesis of the authentic anti,anti-configured isochromanone core of the ajudazols, highly potent inhibitors of the mitochondrial respiratory chain from myxobacteria. PMID:26824669

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

    PubMed

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

    2016-01-01

    Synthesized aromatic ?-amino acids have recently attracted considerable attention for their application as precursors in many pharmacologically relevant compounds. Previous studies on asymmetric synthesis of aromatic ?-amino acids using ?-transaminases could not be done efficiently due to the instability of ?-keto acids. In this study, a strategy to circumvent the instability problem of ?-keto acids was utilized to generate ?-amino acids efficiently via asymmetric synthesis. In this work, thermodynamically stable ?-ketoesters were initially converted to ?-keto acids using lipase, and the ?-keto acids were subsequently aminated using ?-transaminase. By optimizing the lipase concentration, we successfully overcame the instability problem of ?-keto acids and enhanced the production of ?-amino acids. This strategy can be used as a general approach to efficiently generate ?-amino acids from ?-ketoesters. PMID:26494487

  20. Synthesis of iriomoteolide-1a C13-C23 fragment via asymmetric conjugate addition and Julia-Kocienski coupling reaction.

    PubMed

    Chin, Yen-Jin; Wang, Shun-Yi; Loh, Teck-Peng

    2009-08-20

    The key C13-C23 fragment toward the total synthesis of iriomoteolide-1a (1) has been constructed from an 1,2-acetonide containing aldehyde 5 via a Julia-Kocienski olefination with the C16-C23 segment 6. The key step involves stereoselective introduction of the C29 methyl group by a highly efficient CuI-Tol-BINAP-catalyzed asymmetric conjugate addition of methylmagnesium bromide to an alpha,beta-unsaturated ester. PMID:19627100

  1. Synthesis of 2,5-asymmetrically substituted 3,4-diaminothieno[2,3-b]thiophenes by domino reaction.

    PubMed

    Zubarev, Andrey A; Larionova, Natalia A; Rodinovskaya, Lyudmila A; Mortikov, Valery Yu; Shestopalov, Anatoliy M

    2013-10-14

    A convenient one pot synthesis of 2,5-asymmetrically substituted thieno[2,3-b]thiophenes is developed. The method is based on consecutive domino reactions (SN2 reaction ? Thorpe-Ziegler reaction) using malononitrile and carbon disulfide as starting materials with the generation of potassium 2,2-dicyanoethene-1,1-bis(thiolate) in a solution. The high yield of the target thienothiophenes was achieved using the Ziegler dilution effect. PMID:24028177

  2. Highly efficient asymmetric hydrogenation of cyano-substituted acrylate esters for synthesis of chiral ?-lactams and amino acids.

    PubMed

    Kong, Duanyang; Li, Meina; Wang, Rui; Zi, Guofu; Hou, Guohua

    2016-01-28

    A highly efficient and enantioselective synthesis of ?-lactams and ?-amino acids by Rh-catalyzed asymmetric hydrogenation has been developed. Using the Rh-(S,S)-f-spiroPhos complex, under mild conditions a wide range of 3-cyano acrylate esters including both E and Z-isomers and ?-cyano-?-aryl-?,?-unsaturated ketones were first hydrogenated with excellent enantioselectivities (up to 98% ee) and high turnover numbers (TON up to 10?000). PMID:26661067

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

    PubMed

    Iseki, K

    1999-11-01

    The synthesis of chiral fluorinated molecules is important in the biological and medicinal chemistry fields in view of the influence of fluorine's unique properties on biological activity. In recent years, we have studied asymmetric synthesis focussing on such optically active compounds. This review describes 1) diastereoselective trifluoromethylation of chiral N-acyloxazolidinones, 2) catalytic enantioselective aldol reactions of fluorine-substituted ketene silyl acetals, and 3) catalytic enantioselective allylation of aldehydes mediated by chiral Lewis bases. The trifluoromethylation of lithium enolates of N-acyloxazolidinones with iodotrifluoromethane is mediated by triethylborane to give the corresponding trifluoromethylated products with up to 86% diastereomeric excess. The stereoselective reaction is considered to proceed through the attack of the trifluoromethyl radical on the less hindered face of the lithium imide. Difluoroketene and bromofluoroketene trimethylsilyl ethyl acetals react with various aldehydes in the presence of chiral Lewis acids to afford the corresponding desired aldols with up to 99% enantiomeric excess (ee). It is noteworthy that the aldol reactions of the fluorine-substituted acetals at -78 degrees C and at higher temperatures (-45 or -20 degrees C) provide the (+)- and (-)-aldols, respectively, with excellent-to-good enantioselectivity. Chiral phosphoramides newly prepared from (S)-proline were found to catalyze the allylation and crotylation of aromatic aldehydes with allylic trichlorosilanes in good enantioselective yields (up to 90% ee). (S,S)-Bis(alpha-methylbenzyl)formamide developed as an efficient catalyst for the allylation and crotylation of aliphatic aldehydes mediates the enantioselective addition with the assistance of hexamethylphosphoramide (HMPA) to afford the corresponding homoallylic alcohols in up to 98% ee. PMID:10590709

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

    PubMed

    Benfodda, Z; Bnimlis, 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

  5. Mechanism of the Cobalt Oxazoline Palladacycle (COP)-Catalyzed Asymmetric Synthesis of Allylic Esters

    PubMed Central

    Cannon, Jeffrey S.; Kirsch, Stefan F.; Overman, Larry E.; Sneddon, Helen F.

    2010-01-01

    The catalytic enantioselective SN2? displacement of (Z)-allylic trichloroacetimidates catalyzed by the palladium(II) complex [COP-OAc]2 is a broadly useful method for the asymmetric synthesis of chiral branched allylic esters. A variety of experiments aimed at elucidating the nature of the catalytic mechanism and its rate- and enantiodetermining steps are reported. Key findings include: (a) the demonstration that a variety of bridged-dipalladium complexes are present and constitute resting states of the COP catalyst, however, monomeric palladium (II) complexes are likely involved in the catalytic cycle; (b) labeling experiments establishing that the reaction proceeds in an overall antarafacial fashion; (c) secondary deuterium kinetic isotope effects that suggest substantial rehybridization at both C1 and C3 in the rate-limiting step; and (d) DFT computational studies (B3-LYP/def2-TZVP) that provide evidence for bidentate substrate-bound intermediates and an anti-oxypalladation/syn-deoxypalladation pathway. These results are consistent with a novel mechanism in which chelation of the imidate nitrogen to form a cationic palladium (II) intermediate activates the alkene for attack by external carboxylate in the enantiodetermining step. Computational modeling of the transition-state structure for the acyloxy palladation step provides a model for enantioinduction. PMID:20942424

  6. Synthesis of Phosphorescent Asymmetrically π-Extended Porphyrins for Two-Photon Applications

    PubMed Central

    2015-01-01

    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 π-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 π-extended porphyrins for applications requiring high two-photon triplet action cross sections. PMID:25157580

  7. Synthesis of phosphorescent asymmetrically π-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 π-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 π-extended porphyrins for applications requiring high two-photon triplet action cross sections. PMID:25157580

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

    PubMed Central

    Omedes-Pujol, Marta

    2010-01-01

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

  9. Enantioselective total synthesis of (-)-limaspermidine and formal synthesis of (-)-1-acetylaspidoalbidine.

    PubMed

    Zhang, Shao-Xiong; Shen, Xiao-Lei; Li, Ze-Qian; Zou, Li-Wei; Wang, Feng-Qun; Zhang, Hong-Bin; Shao, Zhi-Hui

    2013-11-15

    Evolution of the synthetic strategy that culminated in the first asymmetric total synthesis of the Aspidosperma alkaloid limaspermidine is described. The successful enantioselective route to (-)-limaspermidine proceeds in 10 steps and with the isolation of only six intermediates using a Pd-catalyzed enantioselective decarboxylative allylation we have recently developed. This first enantioselective synthesis of (-)-limaspermidine establishes unambiguously its absolute configuration and allows the first asymmetric formal total synthesis of the Aspidoalbine alkaloid (-)-1-acetylaspidoalbidine. PMID:24131444

  10. Asymmetric Synthesis of Spirocyclic 2-Benzopyrans for Positron Emission Tomography of ?1 Receptors in the Brain.

    PubMed

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

  11. Catalytic asymmetric assembly of C3-monosubstituted chiral carbazolones and concise formal synthesis of (-)-aspidofractinine: application of enantioselective Pd-catalyzed decarboxylative protonation of carbazolones.

    PubMed

    Zhao, Ruirui; Sun, Zhongwen; Mo, Mingjie; Peng, Fangzhi; Shao, Zhihui

    2014-08-15

    The first method for the asymmetric synthesis of C3-monosubstituted chiral carbazolones, structural motifs common in medicinal chemistry, has been achieved using Pd-catalyzed decarboxylative protonation of carbazolones. This methodology has been applied to the first catalytic enantioselective formal synthesis of (-)-aspidofractinine with step economy and simplicity. PMID:25060656

  12. Easy Absolute Values? Absolutely

    ERIC Educational Resources Information Center

    Taylor, Sharon E.; Mittag, Kathleen Cage

    2015-01-01

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

  13. Chiral Boron Complex-Promoted Asymmetric Diels-Alder Cycloaddition and Its Application in Natural Product Synthesis.

    PubMed

    Li, Xia; Han, Jianguang; Jones, Alexander X; Lei, Xiaoguang

    2016-01-15

    An efficient method for the asymmetric Diels-Alder cycloaddition of 2'-hydroxychalcones with acyclic or cyclic dienes has been successfully developed. The Diels-Alder cycloaddition is mediated by a chiral boron complex with VANOL, affording the corresponding products in high yields and with excellent diastereo- and enantioselectivities. This reaction enabled the enantioselective construction of cyclohexene skeletons crucial for the total synthesis of a number of Diels-Alder-type natural products (-)-nicolaioidesin C, (-)-panduratine A, (-)-kuwanon I, (+)-kuwanon J, and (-)-brosimones A and B. PMID:26693852

  14. 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; DAmore, 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

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

    PubMed

    Li, Shen; Ma, Jun-An

    2015-11-01

    Dihydrobenzoxazinones and dihydroquinazolinones are the core units present in many anti-HIV agents, such as Efavirenz, DPC 961, DPC 963, and DPC 083. All these molecules contain a trifluoromethyl moiety at the quaternary stereogenic carbon center with S configuration. The enantioselective addition of carbon nucleophiles to ketones or cyclic ketimines could serve as a key step to access these molecules. This tutorial review provides an overview of significant advances in the synthesis of dihydrobenzoxazinone- and dihydroquinazolinone-based anti-HIV agents and relative analogues, with an emphasis on asymmetric addition reactions for the establishment of the CF3-containing quaternary carbon centers. PMID:26177889

  16. Synthesis of (-)-?9-trans-Tetrahydrocannabinol - Stereocontrol via Mo-catalyzed Asymmetric Allylic Alkylation Reaction

    PubMed Central

    Trost, Barry M.; Dogra, Kalindi

    2008-01-01

    ?9-THC is synthesized in enantiomericaly pure form, where all of the stereochemistry is derived from the molybdenum catalyzed asymmetric alkylation reaction of the extremely sterically congested bis-ortho substituted cinnamyl carbonate in high regio- and enantioselectivity. PMID:17266321

  17. Synergistic Kinetic Resolution and Asymmetric Propargyl Claisen Rearrangement for the Synthesis of Chiral Allenes.

    PubMed

    Liu, Yangbin; Liu, Xiaohua; Hu, Haipeng; Guo, Jing; Xia, Yong; Lin, Lili; Feng, Xiaoming

    2016-03-14

    The asymmetric propargyl Claisen rearrangement provides a convenient entry to chiral allene motifs. Herein, we describe the development of a kinetic resolution and asymmetric rearrangement of racemic propargyl vinyl ethers. This transformation afforded chiral allene products along with the enantiomerically enriched substrate in good yields with excellent diastereo- and enantioselectivity. The complete chirality transfer and facially selective rearrangement enabled the simultaneous construction of an axially chiral allenic unit and a quaternary carbon stereocenter. PMID:26889758

  18. One-pot, highly efficient, asymmetric synthesis of ring-fused piperidine derivatives bearing N,O- or N,N-acetal moieties.

    PubMed

    Li, Ji-Yao; Li, Zhi-Long; Zhao, Wei-Wei; Liu, Yan-Kai; Tong, Zhi-Ping; Tan, Rui

    2016-02-16

    We successfully expand the application of lactols or cyclic hemiaminals as nucleophiles for the asymmetric synthesis of both N,O- and N,N-acetal moieties contained in the structure of ring-fused piperidine derivatives. This efficient one-pot protocol involves an organocatalyzed asymmetric aza-Diels-Alder reaction and iminium ion induced cyclization sequence to ultimately deliver heterocyclic compounds with excellent stereoselectivity in high yield, containing three continuous stereogenic centers. PMID:26810888

  19. ORGANIC SYNTHESIS. Comment on "Asymmetric syntheses of sceptrin and massadine and evidence for biosynthetic enantiodivergence".

    PubMed

    Sherman, David H; Tsukamoto, Sachiko; Williams, Robert M

    2015-07-10

    Ma et al. (Reports, 10 October 2014, p. 219) report asymmetric syntheses of sceptrin and massadine and, through a stereochemical reassignment, claim to "uncover enantiodivergence as a new biosynthetic paradigm for natural products." We challenge and clarify this claim with relevant examples from the literature of this well-known phenomenon of enantiodivergent congener biosynthesis within the same producing organism. PMID:26160938

  20. Spiroborate esters in the borane-mediated asymmetric synthesis of pyridyl and related heterocyclic alcohols

    PubMed Central

    Stepanenko, Viatcheslav; De Jess, Melvin; Correa, Wildeliz; Guzmn, Irisbel; Vzquez, Cindybeth; Ortiz, Lymaris; Ortiz-Marciales, Margarita

    2009-01-01

    The effectiveness of several spiroborate ester catalysts was investigated in the asymmetric borane reduction of 2-, 3-, 4-acetylpyridines under different reaction conditions. Highly enantiomerically enriched 1-(2-, 3- and 4-pyridyl)ethanols and 1-(heterocyclic)ethanols were obtained using 1 to 10% catalytic loads of the spiroborate 5 derived from diphenylprolinol and ethylene glycol. PMID:20890455

  1. Asymmetric total syntheses of megacerotonic acid and shimobashiric acid A.

    PubMed

    Krabbe, Scott W; Johnson, Jeffrey S

    2015-03-01

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

  2. Catalytic Asymmetric Iterative/Domino Aldehyde Cross-Aldol Reactions for the Rapid and Flexible Synthesis of 1,3-Polyols.

    PubMed

    Lin, Luqing; Yamamoto, Kumiko; Mitsunuma, Harunobu; Kanzaki, Yamato; Matsunaga, Shigeki; Kanai, Motomu

    2015-12-16

    We report here catalytic asymmetric iterative and domino cross-aldol reactions between aldehydes, endowed with a high level of robustness, flexibility, and generality. A Cu(I)-DTBM-SEGPHOS complex catalyzes an asymmetric cross-aldol reaction between acceptor aldehydes and boron enolates derived from donor aldehydes, which are generated through Ir-catalyzed isomerization of allyloxyboronates. The unit process can be repeated using the aldol products in turn as acceptor substrates for the subsequent asymmetric aldol reaction. The donor aldehydes and stereoselectivity can be flexibly switched in a stepwise manner for the double-aldol reaction. Furthermore, asymmetric triple- and quadruple-aldol reactions are possible in one-pot using the appropriate amounts of donors and amine additives, rapidly elongating the carbon skeleton with controlling up to eight stereocenters. The method should be useful for straightforward synthesis of enantiomerically and diastereomerically enriched 1,3-polyols. PMID:26632863

  3. A stereoselective synthesis of (-)-viridiofungin A utilizing a TiCl(4)-promoted asymmetric multicomponent reaction.

    PubMed

    Ghosh, Arun K; Kass, Jorden

    2012-01-20

    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 acyloxycarbonium ion-mediated tetrahydrofuran ring-opening reaction and a Julia-Kocienski olefination. PMID:22195730

  4. 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

  5. Towards an asymmetric synthesis of the bacterial peptide deformylase (PDF) inhibitor fumimycin.

    PubMed

    Hartmann, Caroline E; Gross, Patrick J; Nieger, Martin; Brse, Stefan

    2009-12-21

    Studies towards the synthesis of the bacterial peptide deformylase (PDF) inhibitor fumimycin are reported. The synthetic approach features an organocatalytic access to the alpha,alpha-disubstituted amino acid unit and results in the synthesis of an advanced intermediate which already contains all functionalities of fumimycin. PMID:20024097

  6. One-pot asymmetric synthesis of ?-nitroaldehydes from aldehydes and nitroalkanes through a catalytic tandem reaction using an amino acid lithium salt.

    PubMed

    Yoshida, Masanori; Kitamikado, Naoki; Ikehara, Hiroto; Hara, Shoji

    2011-04-01

    One-pot asymmetric synthesis of ?-nitroaldehydes from aldehydes and nitroalkanes was achieved by a catalytic tandem reaction using a primary amino acid lithium salt, O-tert-butyldiphenylsilyl l-tyrosine lithium salt, as a catalyst. Various aryl, alkenyl, and alkyl aldehydes were converted into ?-nitroaldehydes via in situ generation of nitroalkenes. PMID:21388203

  7. Correction: Studies towards asymmetric synthesis of 4(S)-11-dihydroxydocosahexaenoic acid (diHDHA) featuring cross-coupling of chiral stannane under mild conditions.

    PubMed

    Wang, Rui; He, Anyu; Ramu, Errabelli; Falck, John R

    2015-02-21

    Correction for 'Studies towards asymmetric synthesis of 4(S)-11-dihydroxydocosahexaenoic acid (diHDHA) featuring cross-coupling of chiral stannane under mild conditions' by Rui Wang et al., Org. Biomol. Chem., 2015, DOI: 10.1039/c4ob02324b. PMID:25609001

  8. Utilizing an o-Quinone Methide in Asymmetric Transfer Hydrogenation: Enantioselective Synthesis of Brosimine?A, Brosimine?B, and Brosimacutin?L.

    PubMed

    Keberg, Anton; Metz, Peter

    2016-01-01

    A concise and highly enantioselective synthesis of the flavonoids brosimine?A, brosimine?B, and brosimacutin?L is reported for the first time. The key transformation is a single-step conversion of a flavanone into a flavan by means of an asymmetric transfer hydrogenation/deoxygenation cascade. PMID:26634801

  9. 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 43.7g/L, respectively. The optimal bioconversion conditions of 4H2B catalyzed by HBY61 were pH 7.4, 30C, and 250rpm with 6% (v/v) glucose as the co-substrate. Accordingly, when 45g/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 38.3g/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

  10. Remarkably diastereoselective synthesis of a chiral biphenyl diphosphine ligand and its application in asymmetric hydrogenation

    PubMed Central

    Qiu, Liqin; Wu, Jing; Chan, Shusun; Au-Yeung, Terry T.-L.; Ji, Jian-Xin; Guo, Rongwei; Pai, Cheng-Chao; Zhou, Zhongyuan; Li, Xingshu; Fan, Qing-Hua; Chan, Albert S. C.

    2004-01-01

    Essentially complete atropdiastereoselectivity was realized in the preparation of biaryl diphosphine dioxide by asymmetric intramolecular Ullmann coupling and oxidative coupling with central-to-axial chirality transfer. A bridged C2-symmetric biphenyl phosphine ligand possessing additional chiral centers on the linking unit of the biphenyl groups was synthesized. No resolution step was required for the preparation of the enantiomerically pure chiral ligand. These findings offer a general and practical tool for the development of previously uninvestigated atropdiastereomeric biaryl phosphine ligands. The diphosphine ligand was found to be highly effective in the asymmetric hydrogenation of ?- and ?-ketoesters, 2-(6?-methoxy-2?-naphthyl)propenoic acid, ?-(acylamino)acrylates, and enol acetates. PMID:15067137

  11. A general strategy for the chemoenzymatic synthesis of asymmetrically branched N-glycans.

    PubMed

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

    2013-07-26

    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 specific saccharide moieties by chemical glycosylation. The appendages were selected so 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

  12. 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 FriedelCrafts 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 BINOLSnCl4 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

  13. Coordinating Chiral Ionic Liquids: Design, Synthesis, and Application in Asymmetric Transfer Hydrogenation under Aqueous Conditions

    PubMed Central

    Vasiloiu, Maria; Gaertner, Peter; Zirbs, Ronald; Bica, Katharina

    2015-01-01

    Hydrophilic coordinating chiral ionic liquids with an amino alcohol substructure were developed and efficiently applied to the asymmetric reduction of ketones. Their careful design and adaptability to the desired reaction conditions allow for these chiral ionic liquids to be used as the sole source of chirality in a ruthenium-catalyzed transfer hydrogenation reaction of aromatic ketones. When used in this reaction system, these chiral ionic liquids afforded excellent yields and high enantioselectivities. PMID:26279638

  14. Asymmetric Synthesis of Diverse Glycolic Acid Scaffolds via Dynamic Kinetic Resolution of ?-Keto Esters

    PubMed Central

    Steward, Kimberly M.; Corbett, Michael T.; Goodman, C. Guy; Johnson, Jeffrey S.

    2012-01-01

    The dynamic kinetic resolution of ?-keto esters via asymmetric transfer hydrogenation has been developed as a technique for the highly stereoselective construction of structurally diverse ?-substituted-?-hydroxy carboxylic acid derivatives. Through the development of a privileged m-terphenylsulfonamide for (arene)RuCl(monosulfonamide) complexes with a high affinity for selective ?-keto ester reduction, excellent levels of chemo-, diastereo-, and enantiocontrol can be realized in the reduction of ?-aryl- and ?-chloro-?-keto esters. PMID:23186551

  15. Metal-Free Asymmetric Synthesis of Indanes through Chiral Hypervalent Iodine(III)-Mediated Ring Contraction.

    PubMed

    Ahmad, Anees; Silva, Luiz F

    2016-03-01

    The iodine(III)-mediated asymmetric oxidative rearrangement of 1,2-dihydronaphthalenes was investigated to prepare optically active 1-substituted indanes. The chiral hypervalent iodine species is generated in situ from a chiral aryl iodide, prepared in 94% yield in one step. This metal-free protocol was applied to different cyclic alkenes, substituted with oxygen, with nitrogen, or at position 1 with aryl or methyl. Indanes can be isolated as an acetal or alcohol in up to 78% ee. PMID:26866897

  16. Synthesis of Several Cleistrioside and Cleistetroside Natural Products via a Divergent De Novo Asymmetric Approach

    PubMed Central

    Wu, Bulan; Li, Miaosheng; ODoherty, George A.

    2010-01-01

    The de novo asymmetric syntheses of several partially acylated dodecanyl tri- and tetra-rhamnoside natural products (cleistriosides-5 & 6 and cleistetrosides-2 to 7) have been achieved (19 to 24 steps). The divergent route requires the use of three or less protecting groups. The asymmetry was derived via Noyori reduction of an acylfuran. The rhamno-stereochemistry was installed by a diastereoselective palladium-catalyzed glycosylation, ketone reduction and dihydroxylation. PMID:21038879

  17. 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

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

    PubMed Central

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

    2015-01-01

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

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

    PubMed

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

    2015-10-14

    An enantioselective intramolecular allylic C-H oxidation to generate optically active chromans has been accomplished under the cooperative catalysis of a palladium complex of chiral phosphoramidite ligand and 2-fluorobenzoic acid. Mechanistic studies suggest that this reaction commences with a Pd-catalyzed allylic C-H activation event and then undergoes asymmetric allylic alkoxylation. The synthetic significance of the method has been embodied by concisely building up a key chiral intermediate to access (+)-diversonol. PMID:26400002

  20. 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

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

    PubMed Central

    Kraft, Jochen; Golkowski, Martin

    2016-01-01

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

  2. Preparation of Enantiomerically Pure Perfluorobutanesulfinamide and Its Application to the Asymmetric Synthesis of α-Amino Acids.

    PubMed

    Wangweerawong, Apiwat; Hummel, Joshua R; Bergman, Robert G; Ellman, Jonathan A

    2016-02-19

    A high yielding and practical two-step synthesis of enantiomerically pure perfluorobutanesulfinamide from Senanayake's 2-aminoindanol-derived sulfinyl transfer reagent was developed and carried out on a multigram scale. Straightforward condensation of this sulfinamide with ethyl glyoxylate provided the N-perfluorobutanesulfinyl imino ester. The utility of this activated N-sulfinyl imino ester was demonstrated for reactions that gave either no product or very low yields with the corresponding less electrophilic N-tert-butanesulfinyl derivative. Specifically, the Rh(III)-catalyzed C-H bond addition of aromatic compounds to the N-perfluorobutanesulfinyl imino ester provided arylglycines with very high diastereoselectivities for a range of directing groups including pyrrolidine amide, azo, sulfoximine, 1-pyrazole, and 1,2,3-triazole functionalities. Thermal asymmetric aza-Diels-Alder reactions also proceeded in good yields and with high selectivity, including for the substituted dienes (E)-1,3-pentadiene and (2E,4E)-2,4-hexadiene. PMID:26844947

  3. Asymmetric Synthesis of 1,3-Butadienyl-2-carbinols by the Homoallenylboration of Aldehydes with a Chiral Phosphoric Acid Catalyst.

    PubMed

    Huang, Yiyong; Yang, Xing; Lv, Zongchao; Cai, Chen; Kai, Cheng; Pei, Yong; Feng, Yu

    2015-06-15

    Asymmetric C(sp)-C(sp(2)) bond formation to give enantiomerically enriched 1,3-butadienyl-2-carbinols occurred through a homoallenylboration reaction between a 2,3-dienylboronic ester and aldehydes under the catalysis of a chiral phosphoric acid (CPA). A diverse range of enantiomerically enriched butadiene-substituted secondary alcohols with aryl, heterocyclic, and aliphatic substituents were synthesized in very high yield with high enantioselectivity. Preliminary density functional theory (DFT) calculations suggest that the reaction proceeds via a cyclic six-membered chairlike transition state with essential hydrogen-bond activation in the allene reagent. The catalytic reaction was amenable to the gram-scale synthesis of a chiral alkyl butadienyl adduct, which was converted into an interesting optically pure compound bearing a benzo-fused spirocyclic cyclopentenone framework. PMID:25939725

  4. Palladium-Catalyzed Asymmetric Alkylation in the Synthesis of Cyclopentanoid and Cycloheptanoid Core Structures Bearing All-Carbon Quaternary Stereocenters

    PubMed Central

    Hong, Allen Y.; Bennett, Nathan B.; Krout, Michael R.; Jensen, Thomas; Harned, Andrew. M.

    2011-01-01

    General catalytic asymmetric routes toward cyclopentanoid and cycloheptanoid core structures embedded in numerous natural products have been developed. The central stereoselective transformation in our divergent strategies is the enantioselective decarboxylative alkylation of seven-membered ?-ketoesters to form ?-quaternary vinylogous esters. Recognition of the unusual reactivity of ?-hydroxyketones resulting from the addition of hydride or organometallic reagents enabled divergent access to ?-quaternary acylcyclopentenes through a ring contraction pathway or ?-quaternary cycloheptenones through a carbonyl transposition pathway. Synthetic applications of these compounds were explored through the preparation of mono-, bi-, and tricyclic derivatives that can serve as valuable intermediates for the total synthesis of complex natural products. This work complements our previous work with cyclohexanoid systems. PMID:22347731

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

    PubMed Central

    2015-01-01

    A short, asymmetric synthesis of a cyclic N-acyl O-amino phenol duocarmycin prodrug subject to reductive activation based on the simplified 1,2,9,9a-tetrahydrocyclopropa[c]benz[e]indol-4-one (CBI) DNA alkylation subunit is described. A key element of the approach entailed treatment of iodo-epoxide 7, prepared by N-alkylation of 6 with (S)-glycidal 3-nosylate, with EtMgBr at room temperature to directly provide the optically pure alcohol 8 in 78% yield (99% ee) derived from an effective metalhalogen exchange and subsequent regioselective intramolecular 6-endo-tet cyclization. Following O-debenzylation, introduction of a protected N-methylhydroxamic acid, direct trannannular spirocyclization, and subsequent stereoelectronically controlled acid-catalyzed cleavage of the resulting cyclopropane (HCl), further improvements in a unique intramolecular cyclization with NO bond formation originally introduced for formation of the reductively labile prodrug functionality are detailed. PMID:25247380

  6. Total Synthesis of Gobiusxanthin Stereoisomers and Their Application to Determination of Absolute Configurations of Natural Products: Revision of Reported Absolute Configuration of Epigobiusxanthin

    PubMed Central

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

    2014-01-01

    (3R)-Gobiusxanthin stereoisomers (1ad) 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

  7. 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

  8. Hydroxyproline-Derived Pseudoenantiomeric [2.2.1] Bicyclic Phosphines: Asymmetric Synthesis of (+)- and (?)-Pyrrolines

    PubMed Central

    2015-01-01

    We have prepared two new diastereoisomeric 2-aza-5-phosphabicyclo[2.2.1]heptanes from naturally occurring trans-4-hydroxy-l-proline in six chemical operations. These syntheses are concise and highly efficient, with straightforward purification. When we used these chiral phosphines as catalysts for reactions of ?-substituted allenoates with imines, we obtained enantiomerically enriched pyrrolines in good yields with excellent enantioselectivities. These two diastereoisomeric phosphines functioned as pseudoenantiomers, providing their chiral pyrrolines with opposite absolute configurations. PMID:25099350

  9. Phosphine-Catalyzed Formation of CarbonSulfur Bonds: Catalytic Asymmetric Synthesis of ?-Thioesters

    PubMed Central

    Sun, Jianwei; Fu, Gregory C.

    2010-01-01

    A method for the 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 add to the ? position in the absence of a catalyst, but do so with very good enantioselectivity. Sulfur nucleophiles are now added to the three families of nucleophiles (carbon, nitrogen, and oxygen) that had earlier been shown to participate in catalyzed ? additions. The phosphine catalyst of choice, TangPhos, had previously only been employed as a chiral ligand for transition metals, not as an efficient enantioselective nucleophilic catalyst. PMID:20222657

  10. Concise methods for the synthesis of chiral polyoxazolines and their application in asymmetric hydrosilylation.

    PubMed

    Li, Wei Jie; Xu, Zun Le; Qiu, Sheng Xiang

    2010-01-01

    Seven polyoxazoline ligands were synthesized in high yield in a one-pot reaction by heating polycarboxylic acids or their esters and chiral ?-amino alcohols under reflux with concomitant removal of water or the alcohol produced in the reaction. The method is much simpler and more efficient in comparison to those methods reported in the literature.The compounds were used as chiral ligands in the rhodium-catalyzed asymmetric hydrosilylation of aromatic ketones, and the effects of the linkers and the substituents present on the oxazoline rings on the yield and enantioselectivity investigated. Compound 2 was identified as the best ligand of this family for the hydrosilylation of aromatic ketones. PMID:20502654

  11. Direct catalytic asymmetric aldol reactions of thioamides: toward a stereocontrolled synthesis of 1,3-polyols.

    PubMed

    Iwata, Mitsutaka; Yazaki, Ryo; Suzuki, Yuta; Kumagai, Naoya; Shibasaki, Masakatsu

    2009-12-30

    A direct catalytic asymmetric aldol reaction of thioamides with a soft Lewis acid/hard Brnsted base cooperative catalytic system comprising (R,R)-Ph-BPE/[Cu(CH(3)CN)(4)]PF(6)/LiOAr is described. Highly chemoselective deprotonative activation of thioamides allows for a direct aldol reaction of alpha-nonbranched aliphatic aldehydes, which are susceptible to self-condensation. Facile reduction of the thioamide functionality and a catalyst-controlled second aldol reaction provides 1,3-diols in a highly stereoselective manner. PMID:19994862

  12. Catalytic Asymmetric Synthesis of Branched Chiral Allylic Phenyl Ethers from (E)-Allylic Alcohols

    PubMed Central

    Olson, Angela C.; Overman, Larry E.; Sneddon, Helen F.; Ziller, Joseph W.

    2013-01-01

    The first di-?-amidate dipalladium complexes and a new di-?-carboxylate dipalladium complex of the COP (cobalt oxazoline palladacycle) palladium(II) catalyst family are reported and characterized crystallographically. The di-?-amidate complex 3 or its enantiomer (ent-3) are the first asymmetric catalysts that allow commercially available, or readily accessible, (E)-2-alkene-1-ols to be transformed to enantioenriched branched allylic aryl ethers upon reaction of their trichloroacetimidate derivatives with phenols. The 3-aryloxy-1-alkene products are formed in high enantiomeric purity (typically 9098% ee) and useful yields (6188%). PMID:23795152

  13. Synthesis, photo- and electroluminescence properties of asymmetrical alternating copoly( p-phenylenevinylene) derivatives

    NASA Astrophysics Data System (ADS)

    Tan, Songting; Zou, Yingping; Zhu, Weiguo; Jiang, Changyun

    2006-06-01

    A series of asymmetrical alternating copoly( p-phenylenevinylene) derivatives (PPVs), poly(2-methoxy-5-alkoxy)-1,4-(phenylene vinylene)-alt-1,4-(phenylene vinylene), have been successfully synthesized via the Wittig polycondensation reaction as potential electroluminescent (EL) materials. These copolymers contain two components, one is phenylene vinylene with asymmetrical flexible side chain to improve the solubility of the copolymer in common solvents and to suppress its crystallization; the other is a rigid phenylene vinylene moiety to improve the luminescent quantum efficiency and the thermal stability. The photoluminescent (PL) properties and thermal behavior of these copolymers have been investigated in detail. The results showed that the PL intensity increased but the thermal stability decreased with increasing side chain length. A double-layer device of ITO/PEDOT-PSS/Polymer 3/Ba/Al showed a greenish yellow emission peaking at 548 nm with a turn-on voltage as low as 6.2 V. A maximum brightness of 534 cd/m 2 was obtained at a driving voltage of 10 V.

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

    PubMed

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

    2015-09-16

    Three-dimensional (3D) hierarchical nanostructures have been demonstrated as one of the most ideal electrode materials in energy storage systems due to the synergistic combination of the advantages of both nanostructures and microstructures. In this study, the honeycomb-like mesoporous NiO microspheres as promising cathode materials for supercapacitors have been achieved using a hydrothermal reaction, followed by an annealing process. The electrochemical tests demonstrate the highest specific capacitance of 1250 F g(-1) at 1 A g(-1). Even at 5 A g(-1), a specific capacitance of 945 F g(-1) with 88.4% retention after 3500 cycles was obtained. In addition, the 3D porous graphene (reduced graphene oxide, rGO) has been prepared as an anode material for supercapacitors, which displays a good capacitance performance of 302 F g(-1) at 1 A g(-1). An asymmetric supercapacitor has been successfully fabricated based on the honeycomb-like NiO and rGO. The asymmetric supercapacitor achieves a remarkable performance with a specific capacitance of 74.4 F g(-1), an energy density of 23.25 Wh kg(-1), and a power density of 9.3 kW kg(-1), which is able to light up a light-emitting diode. PMID:26301430

  15. Studies towards asymmetric synthesis of 4(S)-11-dihydroxydocosahexaenoic acid (diHDHA) featuring cross-coupling of chiral stannane under mild conditions.

    PubMed

    Wang, Rui; He, Anyu; Ramu, Errabelli; Falck, John R

    2015-02-14

    An efficient and asymmetric synthetic approach towards one of the biologically interesting 4(S)-11-diHDHA derivatives was developed. This process mainly relied on two reactions, one is the copper-catalyzed mild cross-coupling that allows for the efficient construction of a chiral ?-alkynyl ?-hydroxy motif and another is the synthesis of chiral ?-hydroxy ?-stannanes that has previously been developed by our group featuring the asymmetric stannylation using the well-established tributyltin hydride/diethyl zinc system from an aldehyde. PMID:25425336

  16. A highly enantioselective Biginelli reaction using self-assembled methanoproline-thiourea organocatalysts: asymmetric synthesis of 6-isopropyl-3,4-dihydropyrimidines.

    PubMed

    Hang, Zhijun; Zhu, Jun; Lian, Xiang; Xu, Peng; Yu, Han; Han, Sheng

    2015-12-15

    An efficient self-assembled methanoproline-thiourea organocatalyst for the synthesis of optically active 6-isopropyl-3,4-dihydro-pyrimidines via an asymmetric Biginelli reaction was developed, which is superior to the individual precatalyst. A wide range of optically active 6-isopropyl-3,4-dihydropyrimidines with remarkable pharmacological interest was obtained in high yields with excellent enantioselectivities (up to 99% ee). A plausible transition state has been proposed to explain the origin of the activation and the asymmetric induction. PMID:26498376

  17. Asymmetric synthesis of 2-arylpyrrolidines starting from gamma-chloro N-(tert-butanesulfinyl)ketimines.

    PubMed

    Leemans, Erika; Mangelinckx, Sven; De Kimpe, Norbert

    2010-05-14

    The enantioselective reductive cyclization of gamma-chloro N-(tert-butanesulfinyl)ketimines towards the short and efficient synthesis of (S)- and (R)-2-arylpyrrolidines (ee >99%) is described for the first time by treatment with LiBEt(3)H and subsequent acid deprotection. PMID:20358047

  18. Asymmetric epoxidation of cis-alkenes mediated by iminium salts: highly enantioselective synthesis of levcromakalim.

    PubMed

    Page, Philip C Bulman; Buckley, Benjamin R; Heaney, Harry; Blacker, A John

    2005-02-01

    [reaction: see text] A range of cis-substituted olefins has been epoxidized with a new dihydroisoquinolinium salt catalyst, using tetraphenylphosphonium monoperoxysulfate as the stoichiometric oxidant, giving ee's of up to 97%. The reaction has been used as the key step in an enantioselective synthesis of the antihypertensive agent levcromakalim. PMID:15673243

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

    PubMed Central

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  1. The synthesis and characterization of new iron coordination complexes utilizing an asymmetric coordinating chelate ligand

    SciTech Connect

    Watkins, B.E.; Satcher, J.H.

    1995-07-01

    A binuclear, unsymmetric coordinating ligand that is an effective metal chelator has been designed and synthesized. The new ligand has been shown to react readily with iron(II)/(III) forming a variety of coordination complexes. The binuclear complexes are of significant interest since they represent proof-of-principle for the development of coordinatively asymmetric, binuclear metal chelate compounds. Although this structural type of chelator now appears to be common in biological systems, it has not been previously described for inorganic coordination chemistry. The isolation of oxidation products will be helpful in establishing reaction mechanism(s) of these complexes with molecular oxygen. It is expected that this ligand and derivatives of it will play an important role in the development of bioinorganic complexes that aim to mimic enzyme active sites that function by substrate interaction at only one metal site of a multimetal active site.

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

    PubMed

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

    2015-07-27

    Novel aza-diisoindolylmethene and their BF2 -chelating complexes (benzo-fused aza-BODIPYs) were synthesized on a large scale and in a facile manner from phthalonitrile in tBuOK-DMF solution. The unique asymmetric donor-?-acceptor structure facilitates B-N bond detachment in the presence of trifluoroacetic acid (TFA) in dichloromethane, resulting in sharp color change from red to colorless, with over 250?nm hypsochromic shift in the absorption maximum. This colorimetric process can be reversed by adding a very small amount of proton-accepting solvents or compounds. A (1) H and (11) B?NMR spectroscopy study and also density functional theory (DFT) calculations suggest that TFA-induced B-N bond cleavage may disrupt the whole ?-conjugation of the BODIPY molecule, resulting in significant colorimetric behavior. PMID:26110590

  3. 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

  4. Catalytic, asymmetric, and stereodivergent synthesis of non-symmetric ?,?-diaryl-?-amino acids.

    PubMed

    Molinaro, Carmela; Scott, Jeremy P; Shevlin, Michael; Wise, Christopher; Mnard, Alain; Gibb, Andrew; Junker, Ellyn M; Lieberman, David

    2015-01-21

    We report a concise, enantio- and diastereoselective route to novel nonsymmetrically substituted N-protected ?,?-diaryl-?-amino acids and esters, through the asymmetric hydrogenation of tetrasubstituted olefins, some of the most challenging examples in the field. Stereoselective generation of an E- or Z-enol tosylate, when combined with stereoretentive Suzuki-Miyaura cross-coupling and enantioselective hydrogenation catalyzed by (NBD)2RhBF4 and a Josiphos ligand, allows for full control over the two vicinal stereogenic centers. High yields and excellent enantioselectivities (up to 99% ee) were obtained for a variety of N-acetyl, N-methoxycarbonyl, and N-Boc ?,?-diaryldehydroamino acids, containing a diverse and previously unreported series of heterocyclic and aryl substituted groups (24 examples) and allowing access to all four stereoisomers of these valuable building blocks. PMID:25523503

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

    PubMed

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

    2016-01-01

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

  6. Asymmetric Synthesis of Dihydroindanes by Convergent Alkoxide-Directed Metallacycle-Mediated Bond Formation

    PubMed Central

    Greszler, Stephen N.; Reichard, Holly A.; Micalizio, Glenn C.

    2012-01-01

    A convergent synthesis of highly substituted and stereodefined dihydroindanes is described from alkoxide-directed Ti-mediated cross-coupling of internal alkynes with substituted 4-hydroxy-1,6-enynes (substrates that derive from 2-directional functionalization of readily available epoxy alcohol derivatives). In addition to describing a new and highly stereoselective approach to bimolecular [2+2+2] annulation that delivers products not available with other methods in this area of chemical reactivity, evidence is provided to support annulation by way of regioselective alkynealkyne coupling, followed by metal-centered [4+2] rather than stepwise alkene insertion and reductive elimination. Overall, the reaction proceeds with exquisite stereochemical control and defines a convenient, convergent, and enantiospecific entry to fused carbocycles of great potential value in target-oriented synthesis and medicinal chemistry. PMID:22235773

  7. Lewis Acid Catalyzed Asymmetric Three-Component Coupling Reaction: Facile Synthesis of ?-Fluoromethylated Tertiary Alcohols.

    PubMed

    Aikawa, Kohsuke; Kondo, Daisuke; Honda, Kazuya; Mikami, Koichi

    2015-12-01

    A chiral dicationic palladium complex is found to be an efficient Lewis acid catalyst for the synthesis of ?-fluoromethyl-substituted tertiary alcohols using a three-component coupling reaction. The reaction transforms three simple and readily available components (terminal alkyne, arene, and fluoromethylpyruvate) to valuable chiral organofluorine compounds. This strategy is completely atom-economical and results in perfect regioselectivities and high enantioselectivities of the corresponding tertiary allylic alcohols in good to excellent yields. PMID:26486488

  8. Bis-(2,5-diphenylphospholanes) with sp2 carbon linkers: synthesis and application in asymmetric hydrogenation.

    PubMed

    Fox, Martin E; Jackson, Mark; Lennon, Ian C; Klosin, Jerzy; Abboud, Khalil A

    2008-02-01

    Four chiral diphosphine ligands consisting of bis(2,5-diphenylphospholan-1-yl) groups connected by the sp(2) carbon linkers 2,3-quinoxaline ((S,S)-Ph-Quinox), 2,3-pyrazine ((S,S)-Ph-Pyrazine), maleic anhydride ((S,S)-Ph-MalPhos), and 1,1'-ferrocene ((S,S)-Ph-5-Fc) were synthesized, and their cationic [rhodium(I)(COD)] complexes were prepared. These complexes were tested in asymmetric hydrogenation of functionalized olefins. [((S,S)-Ph-Quinox)Rh(COD)]BF4 showed high activity and selectivity against itaconate and dehydroamino acid substrates. The corresponding (S,S)-Ph-Pyrazine and (S,S)-Ph-MalPhos complexes exhibited lower activities and selectivities. [((S,S)-Ph-5-Fc)Rh(COD)]BF4 showed high activity with low selectivity for these substrates, but high activity and selectivity against 2-C-substituted cinnamate salts, whereas rhodium complexes of (S,S)-Ph-Quinox and (R,R)-Ph-BPE showed low activity and selectivity against 2-C-substituted cinnamate salts. PMID:17949042

  9. Synthesis, Single Crystal, and Physical Properties of Asymmetrical Thiophene/Selenophene-Fused Twistacenes.

    PubMed

    Lv, Bo; Shen, Xingxing; Xiao, Jinchong; Duan, Jingdan; Wang, Xuefei; Yi, Yuanping

    2015-12-01

    Two asymmetrical twistacenes, PyPT and PyPS, have been synthesized and characterized. Single crystal X-ray analyses show that both of them have twisted structures with a torsion angle of 26.65 for PyPT and 26.59 for PyPS measured between plane C5-C23-C25 and plane C13-C15-C26. The thiophene/selenophene-fused acenes emit blue fluorescence with quantum yields of 0.39 for PyPT and 0.04 for PyPS in organic solvents, whereas the all-carbon molecule HBP emits green fluorescence. Meanwhile, PyPT and PyPS show a similar reversible oxide procedure with the onset potentials of 0.73 and 0.72?V, respectively. In addition, PyPT and PyPS can self-assemble to form nanoparticles in a mixture of THF/H2 O through re-precipitation method. PMID:26282451

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

    SciTech Connect

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

    2013-01-01

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

  11. Anisotropic encapsulation-induced synthesis of asymmetric single-hole mesoporous nanocages.

    PubMed

    Li, Xiaomin; Zhou, Lei; Wei, Yong; El-Toni, Ahmed Mohamed; Zhang, Fan; Zhao, Dongyuan

    2015-05-13

    Asymmetric single-hole mesoporous silica nanocages, which are eccentric hollow structured spheres and consist of mesoporous shell with an open hole on their surface, with uniform particle size (100-240 nm), have successfully been synthesized via a novel anisotropic encapsulation of the mesoporous silica. In this unique nanocarrier, the eccentric hollow cavity and big hole (∼25 nm) can serve as a storage space and passage for large guest molecules. Meanwhile, the uniform mesopores (2-10 nm) with a high surface area (∼500 m(2)/g) in the silica shells of the nanocages can provide storage space for small guest molecules. The obtained single-hole mesoporous nanocages can be endowed upconversion luminescence. The obtained upconversion nanoparticles functionalized eccentric single-hole nanorattles were used to codeliver bovine serum albumin and doxorubicin dual-sized guests. The release of the dual-sized guests can be well controlled independently by heat and near-infrared (NIR) light with the assistance of NIR to ultraviolet/visible (UV/vis) optical properties of upconversion nanoparticles and heat-sensitive phase change materials. PMID:25909815

  12. 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 (12 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

  13. Trienamine catalyzed asymmetric synthesis and biological investigation of a cytochalasin B-inspired compound collection.

    PubMed

    Sellstedt, Magnus; Schwalfenberg, Melanie; Ziegler, Slava; Antonchick, Andrey P; Waldmann, Herbert

    2016-01-01

    Due to their enhanced metabolic needs many cancers need a sufficient supply of glucose, and novel inhibitors of glucose import are in high demand. Cytochalasin B (CB) is a potent natural glucose import inhibitor which also impairs the actin cytoskeleton leading to undesired toxicity. With a view to identifying selective glucose import inhibitors we have developed an enantioselective trienamine catalyzed synthesis of a CB-inspired compound collection. Biological analysis revealed that indeed actin impairment can be distinguished from glucose import inhibition and led to the identification of the first selective glucose import inhibitor based on the basic structural architecture of cytochalasin B. PMID:26606903

  14. α-Allyl-α-aryl α-Amino Esters in the Asymmetric Synthesis of Acyclic and Cyclic Amino Acid Derivatives by Alkene Metathesis

    PubMed Central

    2015-01-01

    Allylating agents were explored for the asymmetric synthesis of α-allyl-α-aryl α-amino acids by tandem N-alkylation/π-allylation. Cross-metathesis of the tandem product was developed to provide allylic diversity not afforded in the parent reaction; the synthesis of homotyrosine and homoglutamate analogues was completed. Cyclic α-amino acid derivatives could be accessed by ring-closing metathesis presenting a viable strategy to higher ring homologue of enantioenriched α-substituted proline. The eight-membered proline analogue was successfully converted to the pyrrolizidine natural product backbone. PMID:24828423

  15. Asymmetric phase-transfer catalyzed glycolate alkylation, investigation of the scope, and application to the synthesis of (-)-ragaglitazar.

    PubMed

    Andrus, Merritt B; Hicken, Erik J; Stephens, Jeffrey C; Bedke, D Karl

    2005-11-11

    [Reaction: see text]. Asymmetric glycolate alkylation using a protected acetophenone surrogate under solid-liquid phase-transfer conditions is a new approach to the synthesis of 2-hydroxy esters and acids. Diphenylmethyloxy-2,5-dimethoxyacetophenone 1 with a trifluorobenzyl cinchonidinium bromide catalyst 9 (10 mol %) and cesium hydroxide provided S-alkylation products 2 at -35 degrees C in high yield (80-99%) and with excellent enantioselectivities using a wide range of electrophiles (80-90% ee). Alkylated products were elaborated to useful alpha-hydroxy intermediates 3 using bis-TMS peroxide Baeyer-Villiger conditions and selective transesterification reactions. The ester products have been enantioenriched by simple recrystallization from ether to give a single isomer (99% ee). A tight ion-pair model is proposed for the observed S-stereoinduction that includes van der Waals contacts between the extended enolate and the isoquinoline of the catalyst. To demonstrate the utility of the new methodology, the anti-diabetes drug (-)-ragaglitazar 24 was synthesized in six steps from a key 2-alkoxy-3-p-phenoxypropionic acid 26 that was made using PTC glycolate alkylation. PMID:16268622

  16. Asymmetric Synthesis of 1,2,9,9a-Tetrahydrocyclopropa[c]benzo[e]indol-4-one (CBI)

    PubMed Central

    Lajiness, James P.; Boger, Dale L.

    2011-01-01

    A short, asymmetric synthesis of the 1,2,9,9a-tetrahydrocyclopropa[c]benzo[e]indol-4-one (CBI) analogue of the CC-1065 and duocarmycin DNA alkylation subunits is described. Treatment of iodo-epoxide 5, prepared by late-stage alkylation of 4 with (S)-glycidal-3-nosylate, with EtMgBr at room temperature directly provides the optically pure alcohol 6 in 87% yield (99% ee) derived from selective metalhalogen exchange and subsequent regioselective intramolecular 6-endo-tet cyclization. The use of MeMgBr or i-PrMgBr also provides the product in high yields (8287%), but requires larger amounts of the Grignard reagent to effect metalhalogen exchange and cyclization. Direct transannular spirocyclization of 7 following O-debenzylation of 6 provides N-Boc-CBI. This approach represents the most efficient (9-steps, 31% overall) and effective (99% ee) route to the optically pure CBI alkylation subunit yet described. PMID:21192653

  17. Development of a large scale asymmetric synthesis of the glucocorticoid agonist BI 653048 BS H3PO4.

    PubMed

    Reeves, Jonathan T; Fandrick, Daniel R; Tan, Zhulin; Song, Jinhua J; Rodriguez, Sonia; Qu, Bo; Kim, Soojin; Niemeier, Oliver; Li, Zhibin; Byrne, Denis; Campbell, Scot; Chitroda, Ashish; DeCroos, Phil; Fachinger, Thomas; Fuchs, Victor; Gonnella, Nina C; Grinberg, Nelu; Haddad, Nizar; Jäger, Burkhard; Lee, Heewon; Lorenz, Jon C; Ma, Shengli; Narayanan, Bikshandarkoil A; Nummy, Larry J; Premasiri, Ajith; Roschangar, Frank; Sarvestani, Max; Shen, Sherry; Spinelli, Earl; Sun, Xiufeng; Varsolona, Richard J; Yee, Nathan; Brenner, Michael; Senanayake, Chris H

    2013-04-19

    The development of a large scale synthesis of the glucocorticoid agonist BI 653048 BS H3PO4 (1·H3PO4) is presented. A key trifluoromethyl ketone intermediate 22 containing an N-(4-methoxyphenyl)ethyl amide was prepared by an enolization/bromine-magnesium exchange/electrophile trapping reaction. A nonselective propargylation of trifluoromethyl ketone 22 gave the desired diastereomer in 32% yield and with dr = 98:2 from a 1:1 diastereomeric mixture after crystallization. Subsequently, an asymmetric propargylation was developed which provided the desired diastereomer in 4:1 diastereoselectivity and 75% yield with dr = 99:1 after crystallization. The azaindole moiety was efficiently installed by a one-pot cross coupling/indolization reaction. An efficient deprotection of the 4-methoxyphenethyl group was developed using H3PO4/anisole to produce the anisole solvate of the API in high yield and purity. The final form, a phosphoric acid cocrystal, was produced in high yield and purity and with consistent control of particle size. PMID:23544738

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

    PubMed

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

    2006-03-29

    The application of metalated, enantiomerically pure acyclic and cyclic 2-alkenyl sulfoximines for the synthesis of highly substituted aza(poly)cyclic ring systems is described. The method relies on a one-pot combination of a reagent-controlled allyl transfer reaction to alpha- or beta-amino aldehydes, followed by a Michael-type cyclization of the intermediate vinyl sulfoximines generated in the first step. The sulfur-free target compounds are preferentially obtained by samarium iodide treatment of the sulfonimidoyl substituted heterocycles. In addition to this methodological work, initial results on the biological activity of selected examples are reported. Furthermore, a concept for the transformation of peptidic lead structures into non-peptide mimetics is described, and the relevance of the new approach to highly substituted azaheterocycles in this context is discussed. PMID:16551111

  19. Systematic Asymmetric Synthesis of All Diastereomers of (-)-Talaumidin and Their Neurotrophic Activity.

    PubMed

    Harada, Kenichi; Kubo, Miwa; Horiuchi, Hiroki; Ishii, Akiko; Esumi, Tomoyuki; Hioki, Hideaki; Fukuyama, Yoshiyasu

    2015-07-17

    (-)-Talaumidin (1), a 2,5-biaryl-3,4-dimethyltetrahydrofuran lignan isolated from Aristolochia arcuata Masters, shows significant neurite-outgrowth promotion and neuroprotection in primary cultured rat cortical neurons and in NGF-differentiated PC12 cells. The four stereogenic centers on the tetrahydrofuran moiety in 1 result in the presence of seven diastereomers except for their enantiomers. In order to investigate the stereochemistry-activity relationships of the stereoisomers, the systematic synthesis of all stereoisomers of 1 was accomplished by employing Evans aldol, diastereoselective hydroboration, reductive deoxygenation, and Mitsunobu reactions as key steps. The ability of all of the synthesized stereoisomers to promote neurite-outgrowth in PC12 and neuronal cells was evaluated. All stereoisomers exhibited moderate to potent neurotrophic activities in NGF-differentiated PC12 cells at 30 μM and in primary cultured rat cortical neuronal cells at 0.01 μM. In particular, 1e bearing all cis substituents resulted in the most potent neurite-outgrowth promotion. PMID:26108800

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

    PubMed Central

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  2. Copper-catalyzed asymmetric synthesis and comparative aldose reductase inhibition activity of (+)/(-)-1,2-benzothiazine-1,1-dioxide acetic acid derivatives.

    PubMed

    Parveen, Shagufta; Hussain, Saghir; Qin, Xiangyu; Hao, Xin; Zhu, Shaojuan; Rui, Miao; Zhang, Shuzhen; Fu, Fengyan; Ma, Bing; Yu, Qun; Zhu, Changjin

    2014-06-01

    A copper catalyst system for the asymmetric 1,4-hydrosilylation of the ?,?-unsaturated carboxylate class was developed by which synthesis of (+)- and (-)-enantiomers of 1,2-benzothiazine-1,1-dioxide acetates has been achieved with a good yield and an excellent level of enantioselectivity. A comparative structure-activity relationship study yielded the following order of aldose reductase inhibition activity: (-)-enantiomers > racemic > (+)-enantiomers. Further, a molecular docking study suggested that the (-)-enantiomer had significant binding affinity and thus increased inhibition activity. PMID:24785266

  3. New highly asymmetric Henry reaction catalyzed by Cu(II) and a C(1)-symmetric aminopyridine ligand, and its application to the synthesis of miconazole.

    PubMed

    Blay, Gonzalo; Domingo, Luis R; Hernndez-Olmos, Victor; Pedro, Jos R

    2008-01-01

    A new catalytic asymmetric Henry reaction has been developed that uses a C(1)-symmetric chiral aminopyridine ligand derived from camphor and picolylamine. A variety of aromatic, heteroaromatic, aliphatic, and unsaturated aldehydes react with nitromethane and other nitroalkanes in the presence of DIPEA (1.0 equiv), Cu(OAc)(2)*H(2)O (5 mol %), and an aminopyridine ligand (5 mol %) to give the expected products in high yields (up to 99 %), moderate-to-good diastereoselectivites (up to 82:18), and excellent enantioselectivities (up to 98 %). The reaction is air-tolerant and has been used in the synthesis of the antifungal agent miconazole. PMID:18384026

  4. The concise synthesis of chiral tfb ligands and their application to the rhodium-catalyzed asymmetric arylation of aldehydes.

    PubMed

    Nishimura, Takahiro; Kumamoto, Hana; Nagaosa, Makoto; Hayashi, Tamio

    2009-10-14

    New C2-symmetric tetrafluorobenzobarrelene ligands were prepared and applied successfully to the rhodium-catalyzed asymmetric addition of arylboronic acids to aromatic aldehydes giving chiral diarylmethanols in high yield with high enantioselectivity. PMID:19774245

  5. Absolute Zero

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

  6. Asymmetric dearomatization of phenols.

    PubMed

    Sun, Wangsheng; Li, Guofeng; Hong, Liang; Wang, Rui

    2016-02-21

    This review summarizes the recent advances in the field of asymmetric dearomatization of phenols and their applications in the total synthesis of some complex natural products. The dearomatization discussed here includes metal catalysed direct dearomatization, organocatalytic dearomatization and hypervalent iodine mediated dearomatization. PMID:26740241

  7. Total synthesis of (+)-crotogoudin.

    PubMed

    Breitler, Simon; Carreira, Erick M

    2013-10-11

    Fellowship of the ring: The first total synthesis of (+)-crotogoudin, a 3,4-seco-atisane diterpenoid natural product, is reported. Asymmetric access to the bicyclo[2.2.2]octane core is achieved through a desymmetrization of a meso-diketone with baker's yeast (LG=leaving group, PG=protecting group). A SmI2 -induced radical cyclopropane-opening/annulation/elimination cascade affords the suitably decorated tetracyclic structure of (+)-crotogoudin. The synthesis led to revision of the reported optical rotation of the natural product and to assignment of its absolute configuration as an ent-atisane (5R,10R). PMID:24039092

  8. Asymmetric synthesis of the four diastereoisomers of a novel non-steroidal farnesoid X receptor (FXR) agonist: role of the chirality on the biological activity.

    PubMed

    Marinozzi, Maura; Carotti, Andrea; Sardella, Roccaldo; Buonerba, Federica; Ianni, Federica; Natalini, Benedetto; Passeri, Daniela; Rizzo, Giovanni; Pellicciari, Roberto

    2013-07-01

    An asymmetric synthetic strategy was designed for the preparation of the four possible diastereoisomers of 3,6-dimethyl-1-(2-methylphenyl)-4-(4-phenoxyphenyl)-4,8-dihydro-1H-pyrazolo[3,4-e][1,4]thiazepin-7-one, a non-steroidal FXR agonist, we recently discovered following a virtual screening approach. The results obtained from an AlphaScreen assay clearly demonstrated that only the isomer endowed with 4R,6S absolute configuration is responsible for the biological activity. A deep investigation of the different putative binding modes adopted by these enantiomerically pure ligands using computational modeling studies confirmed the enantioselectivity of FXR towards this class of molecules. PMID:23684233

  9. Application of 3-Methyl-2-vinylindoles in Catalytic Asymmetric Povarov Reaction: Diastereo- and Enantioselective Synthesis of Indole-Derived Tetrahydroquinolines.

    PubMed

    Dai, Wei; Jiang, Xiao-Li; Tao, Ji-Yu; Shi, Feng

    2016-01-01

    The first application of 3-methyl-2-vinylindoles in catalytic asymmetric Povarov reactions has been established via the three-component reactions of 3-methyl-2-vinylindoles, aldehydes, and anilines in the presence of chiral phosphoric acid, providing easy access to chiral indole-derived tetrahydroquinolines with three contiguous stereogenic centers at high yields (up to 99%) and with excellent diastereo- and enantioselectivities (all >95:5 dr, up to 96% ee). This mode of catalytic asymmetric three-component reaction offers a step-economic and atom-economic strategy for accessing enantioenriched indole-derived tetrahydroquinolines with structural diversity and complexity. PMID:26652222

  10. Organocatalytic enantioselective Michael-Michael-Michael-aldol condensation reactions: control of five stereocenters in a quadruple-cascade asymmetric synthesis of highly functionalized hexahydrophenanthrenes.

    PubMed

    Raja, Arun; Hong, Bor-Cherng; Lee, Gene-Hsiang

    2014-11-01

    A cascade organocatalysis has been developed for the enantioselective synthesis of a highly functionalized hexahydrophenanthrene-2-carbaldehyde containing five contiguous stereogenic centers with high diastereoselectivity and high enantioselectivity (>99% ee). The one-pot method comprises a cascade of organocatalytic Michael-Michael-Michael-aldol reactions of 2-methyl-1,5-dinitro-3-((E)-2-nitrovinyl)benzene and ?,?-unsaturated aldehydes (e.g., cinnamaldehyde). The structure and absolute configuration of a product were confirmed by X-ray analysis of an appropriate derivative. PMID:25337635

  11. Non-cross-linked polystyrene-supported 2-imidazolidinone chiral auxiliary: synthesis and application in asymmetric alkylation reactions.

    PubMed

    Nguyen, Quynh Pham Bao; Kim, Taek Hyeon

    2013-01-01

    Asymmetric alkylation reactions using non-cross-linked polystyrene (NCPS)-supported 2-imidazolidinone chiral auxiliaries were successfully investigated with excellent diastereocontrol (>99% de). The recovery and the recycling of this soluble polymer-supported chiral auxiliary were achieved in order to produce highly optical pure carboxylic acids. PMID:24204423

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

    ERIC Educational Resources Information Center

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

    2015-01-01

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

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

    ERIC Educational Resources Information Center

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

    2015-01-01

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

  14. Direct asymmetric aldol addition-isomerization of ?,?-unsaturated ?-butyrolactam with aryl ?-ketoesters: synthesis of MBH-type products.

    PubMed

    Zhang, Jinlong; Liu, Xihong; Ma, Xiaojuan; Wang, Rui

    2013-04-25

    A highly efficient direct asymmetric aldol addition-isomerization reaction at the ?-position of ?,?-unsaturated ?-butyrolactam and aryl ?-ketoesters by using a bifunctional thiourea catalyst was achieved. Morita-Baylis-Hillman type adducts containing a quaternary stereocenter can be obtained in high yields and with excellent enantioselectivities (up to 99% ee). PMID:23503364

  15. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

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

  18. Efficient Synthesis of Differentiated syn-1,2-Diol Derivatives by Asymmetric Transfer Hydrogenation-Dynamic Kinetic Resolution of ?-Alkoxy-Substituted ?-Ketoesters.

    PubMed

    Monnereau, Laure; Cartigny, Damien; Scalone, Michelangelo; Ayad, Tahar; Ratovelomanana-Vidal, Virginie

    2015-08-10

    Asymmetric transfer hydrogenation was applied to a wide range of racemic aryl ?-alkoxy-?-ketoesters in the presence of well-defined, commercially available, chiral catalyst Ru(II) -(N-p-toluenesulfonyl-1,2-diphenylethylenediamine) and a 5:2 mixture of formic acid and triethylamine as the hydrogen source. Under these conditions, dynamic kinetic resolution was efficiently promoted to provide the corresponding syn ?-alkoxy-?-hydroxyesters derived from substituted aromatic and heteroaromatic aldehydes with a high level of diastereoselectivity (diastereomeric ratio (d.r.)>99:1) and an almost perfect enantioselectivity (enantiomeric excess (ee)>99?%). Additionally, after extensive screening of the reaction conditions, the use of Ru(II) - and Rh(III) -tethered precatalysts extended this process to more-challenging substrates that bore alkenyl-, alkynyl-, and alkyl substituents to provide the corresponding syn ?-alkoxy-?-hydroxyesters with excellent enantiocontrol (up to 99?%?ee) and good to perfect diastereocontrol (d.r.>99:1). Lastly, the synthetic utility of the present protocol was demonstrated by application to the asymmetric synthesis of chiral ester ethyl (2S)-2-ethoxy-3-(4-hydroxyphenyl)-propanoate, which is an important pharmacophore in a number of peroxisome proliferator-activated receptor ?/? dual agonist advanced drug candidates used for the treatment of type-II diabetes. PMID:26139327

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

    PubMed

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

    2015-04-01

    We report a catalytic asymmetric synthesis of piperidines through [4 + 2] cycloaddition of 1-azadienes and nitro-alkenes. The reaction uses earth abundant Zn as catalyst and is highly diastereo- and regioselective. A novel BOPA ligand (F-BOPA) confers high reactivity and enantioselectivity in the process. The presence of ortho substitution on the arenes adjacent to the bis(oxazolines) was found to be particularly impactful, due to limiting the undesired coordination of 1-azadiene to the Lewis acid and thus allowing the reaction to be carried out at lower temperature. A series of secondary kinetic isotope effect studies using a range of ligands implicates a stepwise mechanism for the transformation, involving an initial Michael-type addition of the imine to the nitro-alkene followed by a cyclization event. The stepwise mechanism obviates the electronic requirement inherent to a concerted mechanism, explaining the successful cycloaddition between two electron-deficient partners. PMID:25821893

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

    PubMed Central

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

    2013-01-01

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

  1. Enantioselective synthesis of nitroalkanes bearing all-carbon quaternary stereogenic centers through Cu-catalyzed asymmetric conjugate additions.

    PubMed

    Wu, Jing; Mampreian, Dawn M; Hoveyda, Amir H

    2005-04-01

    The first examples of catalytic asymmetric conjugate addition (ACA) of alkylzinc reagents to trisubstituted nitroalkenes, leading to the formation of nitroalkanes bearing a quaternary carbon stereogenic center, are reported. Reactions are promoted in the presence of 4 mol % of a readily available amino acid-based phosphine and 2 mol % (CuOTf).C6H6. Cu-catalyzed reactions proceed efficiently in up to 98% ee and can be carried out with a variety of dialkylzinc reagents and trisubstituted nitroolefins. We highlight the synthetic utility of the products obtained by efficient conversion of optically enriched nitroalkanes to the corresponding carboxylic acids. PMID:15796518

  2. Asymmetric Synthesis of Functionalized Cyclopentanones via a Multicatalytic Secondary Amine/N-Heterocyclic Carbene Catalyzed Cascade Sequence

    PubMed Central

    Lathrop, Stephen P.; Rovis, Tomislav

    2009-01-01

    A one-pot, asymmetric multicatalytic formal [3+2] reaction between 1,3-dicarbonyls and α,β-unsaturated aldehydes is described. The multicatalytic process involves a secondary amine catalyzed Michael addition followed by a N-heterocyclic carbene catalyzed intramolecular crossed benzoin reaction to afford densely functionalized cyclopentanones with high enantioselectivities. The reaction proceeds with a variety of alkyl and aryl enals as well as a range of 1,3-dicarbonyls (diketones and β-ketoesters). The functionalized products are obtained from cheap, readily available starting materials in a rapid and efficient manner in a one-pot, one-step operation. PMID:19731910

  3. 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

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

    SciTech Connect

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

    1994-06-03

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

  5. Synthesis of Azacyclic Nucleoside Analogues via Asymmetric [3 + 2] Cycloaddition of 9-(2-Tosylvinyl)-9H-purines.

    PubMed

    Zhang, Dan-Jie; Xie, Ming-Sheng; Qu, Gui-Rong; Gao, Yao-Wei; Guo, Hai-Ming

    2016-02-19

    With 9-(2-tosylvinyl)-9H-purines as the dipolarophiles, a series of chiral azacyclic nucleosides with four continuous stereocenters were obtained in 86-99% yields, >20:1 dr, and 94 ? 99% ee via the Cu(I)-catalyzed asymmetric [3 + 2] cycloaddition. Both (E)- and (Z)-9-(2-tosylvinyl)-9H-purines were suitable dipolarophiles, enriching the structure diversity of azacyclic nucleosides. Furthermore, when ?-methyl imino ester was explored, the corresponding azacyclic nucleoside with a chiral quaternary stereocenter could also be afforded with excellent results. PMID:26844591

  6. Asymmetric Ion-Pairing Catalysis

    PubMed Central

    Brak, Katrien

    2014-01-01

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

  7. Synthesis, absolute configuration, and bacterial mutagenicity of the 8 stereoisomeric vicinal diol epoxides at the terminal benzo ring of carcinogenic dibenz[a,h]anthracene.

    PubMed

    Frank, Heinz; Funk, Mario; Oesch, Franz; Platt, Karl L

    2011-12-19

    The synthesis of the 8 possible stereoisomeric diol epoxides (DEs) at the terminal benzo ring of carcinogenic dibenz[a,h]anthracene (DBA) is reported. trans-3,4-Dihydroxy-3,4-dihydro-DBA (1) afforded the 4 bay region DEs: the enantiomeric pairs of the anti diastereomers (+)-3/(-)-3 and of the syn diastereomers (-)-4/(+)-4, respectively. trans-1,2-Dihydroxy-1,2-dihydro-DBA (2) served as precursor of the 4 reverse DEs: the enantiomeric pairs of the anti diastereomers (+)-5/(-)-5 and of the syn diastereomers (-)-6/(+)-6, respectively. The transformation of the olefinic double bond in the enantiomeric trans-dihydrodiols to epoxides was achieved by either (i) oxidation with m-chloroperoxybenzoic acid or (ii) formation of a bromohydrin with N-bromoacetamide/H(2)O followed by dehydrobromination with an anion exchange resin. Because of the pseudodiequatorial conformation of the hydroxyl groups in 1, both reactions proceeded highly stereoselectively, while the stereoselectivity was impaired by the pseudodiaxial conformation of the hydroxyl groups in 2. Diastereomers and racemic compounds were efficiently separated without derivatization by HPLC on achiral or chiral stationary phases, respectively. The absolute configurations of the DEs were deduced from the absolute configuration of 1 and 2 considering the regio- and stereoselectivity of the subsequent reactions and resulted in (+)-(1R,2S,3S,4R)-3/(-)-(1S,2R,3R,4S)-3, (-)-(1S,2R,3S,4R)-4/(+)-(1R,2S,3R,4S)-4, (+)-(1R,2S,3S,4R)-5/(-)-(1S,2R,3R,4S)-5, and (-)-(1R,2S,3R,4S)-6/(+)-(1S,2R,3S,4R)-6. The bacterial mutagenicity of the 8 stereoisomeric DEs was determined in histidine-dependent strains TA98 and TA100 of Salmonella typhimurium in the absence of a metabolizing system. In general, the bay region DEs of DBA were stronger mutagens than the reverse DEs. In strain TA98, the syn diastereomers of bay region DEs were stronger mutagens than their anti isomers, while in the case of reverse DEs the anti diastereomers were more potent than their syn isomers. In strain TA100, all syn diastereomers surpassed the bacterial mutagenicity of their anti isomers. Concerning the bay region DEs of DBA, this corresponds to the situation described for benzo[a]pyrene: of the 4 enantiomeric bay region DEs of DBA and benzo[a]pyrene, the syn diastereomer with [(R,S)-diol (R,S)-epoxide] absolute configuration is the most potent mutagen in both bacterial strains, while the anti isomer with [(S,R)-diol (R,S)-epoxide] configuration is the weakest mutagen. PMID:22087540

  8. Chiral fullerenes from asymmetric catalysis.

    PubMed

    Maroto, Enrique E; Izquierdo, Marta; Reboredo, Silvia; Marco-Martnez, Juan; Filippone, Salvatore; Martn, Nazario

    2014-08-19

    Fullerenes are among the most studied molecules during the last three decades, and therefore, a huge number of chemical reactions have been tested on these new carbon allotropes. However, the aim of most of the reactions carried out on fullerenes has been to afford chemically modified fullerenes that are soluble in organic solvents or even water in the search for different mechanical, optical, or electronic properties. Therefore, although a lot of effort has been devoted to the chemical functionalization of these molecular allotropes of carbon, important aspects in the chemistry of fullerenes have not been properly addressed. In particular, the synthesis of chiral fullerenes at will in an efficient manner using asymmetric catalysis has not been previously addressed in fullerene science. Thus, despite the fact that the chirality of fullerenes has always been considered a fundamental issue, the lack of a general stereoselective synthetic methodology has restricted the use of enantiopure fullerene derivatives, which have usually been obtained only after highly expensive HPLC isolation on specific chiral columns or prepared from a pool of chiral starting materials. In this Account, we describe the first stereodivergent catalytic enantioselective syntheses in fullerene science, which have allowed the highly efficient synthesis of enantiomerically pure derivatives with total control of the stereochemical result using metallic catalysts and/or organocatalysts under very mild conditions. Density functional theory calculations strongly support the experimental findings for the assignment of the absolute configuration of the new stereocenters, which has also been ascertained by application of the sector rule and single-crystal X-ray diffraction. The use of the curved double bond of fullerene cages as a two-?-electron component in a variety of stereoselective cycloaddition reactions represents a challenging goal considering that, in contrast to most of the substituted olefins used in these reactions, pristine fullerene is a noncoordinating dipolarophile. The aforementioned features make the study of stereoselective 1,3-dipolar cycloadditions onto fullerenes a unique scenario to shed light onto important mechanistic aspects. On the other hand, the availability of achiral starting materials as well as the use of nonexpensive asymmetric catalysts should provide access to chiral fullerenes and their further application in a variety of different fields. In this regard, in addition to biomedical applications, chiral fullerenes are of interest in less-studied areas such as materials science, organic electronics, and nanoscience, where control of the order and morphology at the nanometer scale are critical issues for achieving better device efficiencies. PMID:25080165

  9. 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

  10. A Double Asymmetric Hydrogenation Strategy for the Reduction of 1,1-Diaryl Olefins Applied to an Improved Synthesis of CuIPhEt, a C2-Symmetric N-Heterocyclic Carbenoid

    PubMed Central

    Spahn, Elizabeth; Albright, Abigail; Shevlin, Michael; Pauli, Larissa; Pfaltz, Andreas; Gawley, Robert E.

    2013-01-01

    A library of iridium and rhodium phosphine catalysts have been screened for the double asymmetric hydrogenation of 2,6-di-(1-phenylethenyl)-4-methyl aniline to produce the C2-symmetric aniline precursor of the N-heterocyclic carbenoid CuIPhEt. The best catalyst produced the desired enantiomer in 98.6% selectivity. This rare example of a highly selective hydrogenation of a 1,1-diaryl olefin enables a 4 step asymmetric synthesis of the C2-symmetric phenylethyl imidazolium ion (IPhEt) from p-toluidine and phenylacetylene, and its conversion to the hydrosilylation catalyst CuIPhEt. PMID:23383707

  11. Concise diastereoselective synthesis of calcaripeptide C via asymmetric transfer hydrogenation/Pd-induced chiral allenylzinc as a key reaction.

    PubMed

    Kumaraswamy, Gullapalli; Narayanarao, Vykunthapu; Raju, Ragam

    2015-08-21

    Synthesis of the natural product calcaripeptide C derived from the fungal metabolite mycelium KF525 of Calcarisporium sp. has been achieved. This complementary approach avoids the use of a stoichiometric amount of chiral auxiliary reagents as commonly used to generate enantioenriched advanced precursors. The enantioselective synthesis of calcaripeptide C is remarkable in that using catalytic reactions sets the two stereogenic centers efficiently with good levels of enantioselectivity. Further diversification of the calcaripeptide C structures is possible by employing a complementary catalytic enantioenriched Ru-catalyst. PMID:26156428

  12. Absolute optical instruments without spherical symmetry

    NASA Astrophysics Data System (ADS)

    Tyc, Tomáš; Dao, H. L.; Danner, Aaron J.

    2015-11-01

    Until now, the known set of absolute optical instruments has been limited to those containing high levels of symmetry. Here, we demonstrate a method of mathematically constructing refractive index profiles that result in asymmetric absolute optical instruments. The method is based on the analogy between geometrical optics and classical mechanics and employs Lagrangians that separate in Cartesian coordinates. In addition, our method can be used to construct the index profiles of most previously known absolute optical instruments, as well as infinitely many different ones.

  13. Effect of high pressure on the organocatalytic asymmetric Michael reaction: highly enantioselective synthesis of ?-nitroketones with quaternary stereogenic centers.

    PubMed

    Kwiatkowski, Piotr; Dudzi?ski, Krzysztof; ?y?wa, Dawid

    2011-07-15

    The significant effect of hydrostatic pressure on the difficult organocatalytic 1,4-conjugate addition of nitroalkanes to prochiral sterically congested ?,?-disubstituted enones is demonstrated. This approach allows for the synthesis of ?-nitroketones containing quaternary stereogenic centers with good yields, excellent enantioselectivity, and low loading (1-5 mol %) of simple chiral primary amine catalysts. PMID:21671564

  14. 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

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

    ERIC Educational Resources Information Center

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

    2008-01-01

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

  16. Stereoselective synthesis of (R)-3-quinuclidinol through asymmetric reduction of 3-quinuclidinone with 3-quinuclidinone reductase of Rhodotorula rubra.

    PubMed

    Uzura, Atsuko; Nomoto, Fumiki; Sakoda, Akiko; Nishimoto, Yukifumi; Kataoka, Michihiko; Shimizu, Sakayu

    2009-06-01

    A novel nicotinamide adenine dinucleotide phosphate-dependent carbonyl reductase, 3-quinuclidinone reductase, was isolated from Rhodotorula rubra JCM3782. The enzyme catalyzes the asymmetric reduction of 3-quinuclidinone to (R)-3-quinuclidinol. The gene encoding the enzyme was also cloned and sequenced. A 819-bp nucleotide fragment was confirmed to be the gene encoding the 3-quinuclidinone reductase by agreement of the internal amino acid sequences of the purified enzyme. The gene encodes a total of 272 amino acid residues, and the deduced amino acid sequence shows similarity to those of several short-chain dehydrogenase/reductase family proteins. An expression vector, pWKLQ, which contains the full length 3-quinuclidinone reductase gene was constructed. Using Escherichia coli cells coexpressing the 3-quinuclidinone reductase and glucose dehydrogenase (cofactor regeneration enzyme) genes, 618 mM 3-quinuclidinone was almost stiochiometrically converted to (R)-3-quinuclidinol with an >99.9% enantiomeric excess within 21 h of reaction. PMID:19234697

  17. Asymmetric total synthesis of paecilomycin E, 10'-epi-paecilomycin E and 6'-epi-cochliomycin C.

    PubMed

    Pal, Pratik; Jana, Nandan; Nanda, Samik

    2014-11-01

    The asymmetric total syntheses of naturally occurring resorcylic acid lactone paecilomycin E and two of its structural congeners have been reported in this article. The major highlight of the synthetic venture is the application of the late stage Mitsunobu macrolactonization method (as it is difficult to achieve the desired products through the standard carboxyl activation method) of a properly functionalized seco-acid. The macrolactonization precursor was synthesized by applying an "E"-selective Julia-Kocienski olefination of a highly functionalized aromatic aldehyde and a sulphone, which constitutes all the stereocenters (C4', C5', C6' and C10'; 3S,7R,8R,9S) in the target molecule. PMID:25204742

  18. Base-dependent stereodivergent intramolecular aza-Michael reaction: asymmetric synthesis of 1,3-disubstituted isoindolines.

    PubMed

    Fustero, Santos; Herrera, Lidia; Lzaro, Ruben; Rodrguez, Elsa; Maestro, Miguel A; Mateu, Natalia; Barrio, Pablo

    2013-08-26

    The nucleophilic addition (A(N)) / intramolecular aza-Michael reaction (IMAMR) process on Ellman's tert-butylsulfinyl imines, bearing a Michael acceptor in the ortho position, is studied. This reaction affords 1,3-disubstituted isoindolines with a wide range of substituents in good yields and diastereoselectivities. Interestingly, careful choice of the base for the aza-Michael step allows either the cis or the trans diastereoisomers to be exclusively obtained. This stereodivergent cyclization has enabled the synthesis of C2-symmetric bisacetate-substituted isoindolines. In addition, bisacetate isoindolines bearing two well-differentiated ester moieties are also noteworthy because they may allow for the orthogonal synthesis of ?,?'-dipeptides using a single nitrogen atom as a linchpin. PMID:23852920

  19. Total Synthesis of (?)-18-epi-peloruside A: An Alkyne Linchpin Strategy

    PubMed Central

    Michaelis, David J.; Malhotra, Sushant

    2013-01-01

    A convergent synthetic route towards cytotoxic agent peloruside A that hinges on the use of an alkyne linchpin to assemble the natural product is described. Other highlights of this synthesis include an asymmetric desymmetrization reaction of a 1,3-diol, a one pot conversion of a dibromoolefin to a stereodefined enone, and a diastereoselective aldol condensation. Misassignment of the absolute stereochemistry of the C18 stereocenter in our synthesis provided the natural product epimeric at the C18 ethyl stereocenter. PMID:24490808

  20. 1: Mass asymmetric fission barriers for {sup 98}Mo; 2: Synthesis and characterization of actinide-specific chelating agents

    SciTech Connect

    Veeck, A.C.

    1996-08-01

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

  1. 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

  2. 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

  3. Stereoselective Synthesis of β-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 β-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 β-amino alkenyl boranes. In situ boron to zinc transmetalation generates β-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 β-hydroxy enamines in good isolated yields (68–86%) with 54–98% enantioselectivity. The intermediate zinc β-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 β-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

  4. Synthesis, structural characterization and luminescence studies of three novel complexes of asymmetric 5-(1-imidazolyl)pyrimidine ligand

    NASA Astrophysics Data System (ADS)

    Hou, Gui-Ge; Sun, Ju-Feng; Wang, Chun-Hua; Zhao, Feng; Dai, Xian-Ping; Li, Hong-Juan; Han, Jing-Tian

    2013-09-01

    Three novel complexes (L)2CdI2 (1), (L)4Zn(NO3)2 (2) and (L)2Cd(NO3)2(CH3CN)2 (3) were prepared based on asymmetric ligand 5-(1-imidazolyl)pyrimidine (L) with metal salts, respectively. The single-crystal structure reveals that L acts as a monodentate ligand to coordinate a M(II) center to generate a discrete {(L)2CdI2} in 1 and a tetrahedral [Zn(L)4]2+ moiety in 2, respectively. For 3, ligands L as bridging bidentate ligands link two Cd(II) centres to generate a (4, 4) net architecture, further arrange in an -AA- stacking fashion to generate inerratic channels encapsulated guest acetonitrile molecules. In addition, the luminescent properties of L and 1-3 were investigated primarily in the solid state. The structure-property relationship indicates the luminescent property is basically related to its incorporation into the metal-containing complexes, as well as the molecular coplanarity and the intermolecular ?-? interactions.

  5. Synthesis and thermotropic properties of novel double-chained quaternary ammonium chlorides with symmetric and asymmetric hydrocarbon chain length

    NASA Astrophysics Data System (ADS)

    Ding, Zhaoyun; Hao, Aiyou

    2009-04-01

    A series of novel double-chained quaternary ammonium chlorides with symmetrical and asymmetrical hydrocarbon chain length R 1-O-CH 2-CH(OH)-CH 2-N +(CH 3) 2-R 2·Cl - (R 1, R 2: C 12H 25, C 14H 29, C 16H 33) have been synthesized by the reaction of 1- O-alkyl glycidyl ether with N, N-dimethylalkylamine and N, N-dimethylalkylamine hydrochloride. Their chemical structures have been characterized through FT-IR, 1H NMR, MS and elementary analysis. Their thermotropic properties have been examined by differential scanning calorimetry (DSC), polarizing light microscopy (PLM) and X-ray diffraction (XRD). It has been found that the compounds with longer hydrocarbon chain length and being higher asymmetry in hydrocarbon chain length exhibit lower melting point ( Tm) , isotropization temperature ( Ti) and narrower mesophase temperature range. However, the hydrocarbon chain length and the symmetry in the hydrocarbon chain length have little influence on the type of liquid crystals. All compounds form cholesteric liquid crystal.

  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. 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 DielsAlder 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 carbonsilicon bond. PMID:22372733

  8. The mimic of type II aldolases chemistry: asymmetric synthesis of beta-hydroxy ketones by direct aldol reaction.

    PubMed

    Lu, Zhijin; Mei, Haibo; Han, Jianlin; Pan, Yi

    2010-08-01

    An efficient direct aldol reaction has been developed for the synthesis of chiral beta-hydroxy ketone using a combination of C(1)-symmetric chiral prolinamides based on o-phenylenediamine and zinc triflate as catalyst. The reaction was convenient to carry out in aqueous media with up to 98% chemical yields and up to 94% ee values. The current strategy can be regarded as the analogue of aldolase type II, which suggests a new pathway for the designing of new organocatalysts. PMID:20572810

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

    PubMed

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

    2016-04-01

    Asymmetric synthesis of (1R,2S)-1-amino-2-vinylcyclopropanecarboxylic acid (vinyl-ACCA) is in extremely high demand due to the pharmaceutical importance of this tailor-made, sterically constrained α-amino acid. Here we report the development of an advanced procedure for preparation of the target amino acid via two-step SN2 and SN2' alkylation of novel axially chiral nucleophilic glycine equivalent. Excellent yields and diastereoselectivity coupled with reliable and easy scalability render this method of immediate use for practical synthesis of (1R,2S)-vinyl-ACCA. PMID:26661034

  10. Nitrogen-functionalized Isohexides in Asymmetric Induction.

    PubMed

    Janvier, Marine; Moebs-Sanchez, Sylvie; Popowycz, Florence

    2016-01-01

    Biosourced isohexides have attracted the considerable attention of both the academic and industrial chemistry communities over the last 50 years. This highlight focuses on the synthesis of nitrogen-containing isohexides and their applications in asymmetric catalysis. PMID:26931221

  11. Synthesis of C1-symmetric chiral secondary diamines and their applications in the asymmetric copper(II)-catalyzed Henry (nitroaldol) reactions.

    PubMed

    Zhou, Yirong; Dong, Junfang; Zhang, Fanglin; Gong, Yuefa

    2011-01-21

    A small library of C(1)-symmetric chiral diamines (L1-L9) was constructed via condensing exo-(-)-bornylamine or (+)-(1S,2S,5R)-menthylamine with various Cbz-protected amino acids. Among them, ligand L1/CuCl(2)2H(2)O complex (2.5 mol %) shows outstanding catalytic efficiency for Henry reaction between a variety of aldehydes and nitroalkanes to afford the expected products in high yields (up to 98%) with excellent enantioselectivities (up to 99%) and moderate to good diastereoselectivities (up to 90:10). This process is air- and moisture tolerant and has been applied to the synthesis of (S)-2-amino-1-(3,4-dimethoxyphenyl)ethanol (9), a key intermediate for (S)-epinephrine and (S)-norepinephrine. On the basis of HRMS and X-ray diffraction analysis of the L1/CuCl(2) complex, a transition-state model was proposed to explain the origin of asymmetric induction. The low catalyst loading, excellent yields and enantioselectivities, inexpensive copper salt, and mild reaction conditions make our catalytic system to be practically useful. PMID:21190323

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

    PubMed

    Sorochinsky, Alexander E; Acea, Jos Luis; Moriwaki, Hiroki; Sato, Tatsunori; Soloshonok, Vadim A

    2013-10-01

    Alkylations of chiral or achiral Ni(II) complexes of glycine Schiff bases constitute a landmark in the development of practical methodology for asymmetric synthesis of ?-amino acids. Straightforward, easy preparation as well as high reactivity of these Ni(II) complexes render them ready available and inexpensive glycine equivalents for preparing a wide variety of ?-amino acids, in particular on a relatively large scale. In the case of Ni(II) complexes containing benzylproline moiety as a chiral auxiliary, their alkylation proceeds with high thermodynamically controlled diastereoselectivity. Similar type of Ni(II) complexes derived from alanine can also be used for alkylation providing convenient access to quaternary, ?,?-disubstituted ?-amino acids. Achiral type of Ni(II) complexes can be prepared from picolinic acid or via recently developed modular approach using simple secondary or primary amines. These Ni(II) complexes can be easily mono/bis-alkylated under homogeneous or phase-transfer catalysis conditions. Origin of diastereo-/enantioselectivity in the alkylations reactions, aspects of practicality, generality and limitations of this methodology is critically discussed. PMID:23832533

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

    PubMed Central

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

    2015-01-01

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

  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 of ribo-hexopyranoside- and altrose-based azacrown ethers and their application in an asymmetric Michael addition.

    PubMed

    Rapi, Zsolt; Bak, Pter; Keglevich, Gyrgy; Szll?sy, ron; Drahos, Lszl; Heged?s, Lszl

    2013-01-10

    The synthesis of four new ribo-hexopyranoside-based chiral lariat ethers of monoaza-15-crown-5 type and two altropyranoside-based crown ethers were elaborated. Our syntheses utilized the regioselective ring opening of the oxiran moiety of the 2,3-anhydro sugars by nucleophilic reagents to afford the key intermediates. The reaction of methyl-2,3-anhydro-4,6-O-benzylidene-?-D-mannopyranoside with ethanolamine is especially of interest to afford a 3-substituted altropyranoside. One of the ribo-hexopyranoside-based lariat ethers with a 4-methoxyphenyl substituent induced an enantioselectivity of 80% when used as catalyst in the Michael addition of diethyl acetamidomalonate to trans-?-nitrostyrene under phase transfer catalytic conditions. PMID:23220061

  16. Asymmetric Mannich reaction of dicarbonyl compounds with alpha-amido sulfones catalyzed by cinchona alkaloids and synthesis of chiral dihydropyrimidones.

    PubMed

    Lou, Sha; Dai, Peng; Schaus, Scott E

    2007-12-21

    The highly enantioselective cinchona alkaloid-catalyzed Mannich reaction of dicarbonyl compounds with alpha-amido sulfones as acyl imine precursors is described. The reaction requires 10 mol % of the cinchona alkaloid catalyst, which serves as a general base to generate acyl imines in situ, and aqueous Na2CO3 to maintain the concentration of free alkaloid catalyst. The reaction products are obtained in good yields and high enantioselectivities, and in diastereoselectivities that range from 1:1 to >95:5. The cinchonine-catalyzed reactions provide practical access to highly functionalized building blocks which have been employed in the synthesis of chiral dihydropyrimidones, a class of compounds rich in diverse biological activity. Dihydropyrimidone modifications include a highly diastereoselective hydrogenation of the enamide moiety, using an H-Cube flow hydrogenator and a Rh(II)-mediated 1,3-dipolar cycloaddition to afford highly functionalized complex heterocycles. PMID:18047372

  17. Asymmetric Synthesis of Nonracemic Primary Amines via Spiroborate Catalyzed Reduction of pure (E)- and (Z)-O-Benzyloximes: Applications toward the Synthesis of Calcimimetic Agents

    PubMed Central

    Ou, Wenhua; Espinosa, Sandraliz; Melndez, Hctor J.; Farr, Silvia M.; Alvarez, Jaime L.; Torres, Valerie; Martnez, Ileanne; Santiago, Kiara M.; Ortiz-Marciales, Margarita

    2013-01-01

    Highly enantiopure (1-aryl)- and (1-naphthyl)-1-ethylamines were synthesized by the borane-mediated reduction of single-isomeric (E)- and (Z)-O-benzyloxime ethers using the stable spiroborate ester derived from (S)-diphenyl valinol and ethylene glycol as the chiral catalyst. Primary (R)-arylethylamines were prepared by the reduction of pure (Z)-ethanone oxime ethers in up to 99% ee using 15% of catalyst. Two convenient and facile approaches to the synthesis of new and known calcimimetic analogs employing enantiopure (1-naphthalen-1-yl)ethylamine as chiral precursor are described. PMID:23638707

  18. Organocatalytic Asymmetric Biginelli-like Reaction Involving Isatin.

    PubMed

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

    2016-03-01

    The first asymmetric, Brønsted acid catalyzed Biginelli-like reaction of a ketone has been developed, employing N-substituted isatins as carbonyl substrates, and urea and alkyl acetoacetates as further components. BINOL-derived phosphoric acid catalysts have been used to achieve the synthesis of a small library of chiral, enantioenriched spiro(indoline-pyrimidine)-diones derivatives. The absolute configuration of the new spiro stereocenter was assessed on diastereoisomeric derivatives through computer-assisted NMR spectroscopy. X-ray diffractometry allowed the disclosure of the overall molecular conformation in the solid state and the characterization of the crystal packing of a Br-substituted Biginelli-like derivative, while computational studies on the reaction transition state allowed us to rationalize the stereochemical outcome. PMID:26836474

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

    NASA Astrophysics Data System (ADS)

    Horgen, Dana Ann

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

  20. Enantioselective synthesis of (–)-chloramphenicol via silver-catalysed asymmetric isocyanoacetate aldol reaction† †Electronic supplementary information (ESI) available: Experimental procedures, characterisation data, copies of 1H and 13C NMR spectra, and HPLC traces. See DOI: 10.1039/c5ob02141c Click here for additional data file.

    PubMed Central

    Franchino, Allegra; Jakubec, Pavol

    2015-01-01

    The highly enantio- and diastereoselective aldol reaction of isocyanoacetates catalysed by Ag2O and cinchona-derived amino phosphines applied to the synthesis of (–)- and (+)-chloramphenicol is described. The concise synthesis showcases the utility of this catalytic asymmetric methodology for the preparation of bioactive compounds possessing α-amino-β-hydroxy motifs. PMID:26510469

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

    PubMed

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

    2011-03-01

    The scope of MacMillan's organocatalytic asymmetric conjugate addition reaction of indoles and electron-rich aromatics to α,β-unsaturated aldehydes has been extended to the use of 3-amino crotonaldehydes as substrates. The aromatics used include indoles as well as an aniline and a furan. The scope and effect of the groups on nitrogen (R, R') has also been studied. The method has been applied to the concise synthesis of an advanced precursor to S-(+)-1, a drug prototype for the treatment of migraine headaches. PMID:21271688

  2. Synthesis and determination of the absolute configuration of (−)-(5R,6Z)-dendrolasin-5-acetate from the nudibranch Hypselodoris jacksoni

    PubMed Central

    Mudianta, I Wayan; Challinor, Victoria L; Winters, Anne E; Cheney, Karen L; De Voss, James J

    2013-01-01

    Summary A small sample of (−)-(5R,6Z)-dendrolasin-5-acetate, which was fully characterized by 2D NMR studies, was isolated from the nudibranch Hypselodoris jacksoni, along with the sesquiterpenes (+)-agassizin, (−)-furodysinin, (−)-euryfuran, (−)-dehydroherbadysidolide and (+)-pallescensone. A synthetic sample ([α]D −8.7) of the new metabolite was prepared by [1,2]-Wittig rearrangement of a geranylfuryl ether followed by acetylation of purified alcohol isomers. The absolute configuration at C-5 was established as R by the analysis of MPA ester derivatives of (Z)-5-hydroxydendrolasin obtained by preparative enantioselective HPLC. PMID:24454572

  3. Total synthesis and structural revision of (+)-uprolide G acetate.

    PubMed

    Zhu, Liangyu; Liu, Yuan; Ma, Renze; Tong, Rongbiao

    2015-01-01

    The first, asymmetric total synthesis of the proposed structure of (+)-uprolide?G acetate (UGA) is reported, and the spectral properties of the synthetic compound clearly differed from those reported for natural UGA. On the basis of comprehensive analysis of the NMR data, two possible structures for the natural UGA were proposed and their total synthesis achieved, thus leading to the identification and confirmation of the correct structure and absolute configuration of the natural UGA. This synthesis was enabled by development of a novel synthetic strategy, which revolved around three key cyclization reactions: an Achmatowicz rearrangement, Sharpless asymmetric dihydroxylation/lactonization, and ring-closing metathesis. These synthetic studies pave the way for further studies on this class of structurally unusual cytotoxic cembranolides. PMID:25385395

  4. Absolute nuclear material assay

    DOEpatents

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

    2010-07-13

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

  5. Absolute nuclear material assay

    DOEpatents

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

    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.

  6. Synthesis of (3S,3'S)- and meso-stereoisomers of alloxanthin and determination of absolute configuration of alloxanthin isolated from aquatic animals.

    PubMed

    Yamano, Yumiko; Maoka, Takashi; Wada, Akimori

    2014-05-01

    In order to determine the absolute configuration of naturally occurring alloxanthin, a HPLC analytical method for three stereoisomers 1a-c was established by using a chiral column. Two authentic samples, (3S,3'S)- and meso-stereoisomers 1b and 1c, were chemically synthesized according to the method previously developed for (3R,3'R)-alloxanthin (1a). Application of this method to various alloxanthin specimens of aquatic animals demonstrated that those isolated from shellfishes, tunicates, and crucian carp are identical with (3R,3'R)-stereoisomer 1a, and unexpectedly those from lake shrimp, catfish, biwa goby, and biwa trout are mixtures of three stereoisomers of 1a-c. PMID:24862182

  7. Ligand-enabled multiple absolute stereocontrol in metal-catalysed cycloaddition for construction of contiguous all-carbon quaternary stereocentres

    NASA Astrophysics Data System (ADS)

    Ohmatsu, Kohsuke; Imagawa, Naomichi; Ooi, Takashi

    2014-01-01

    The development of a general catalytic method for the direct and stereoselective construction of contiguous all-carbon quaternary stereocentres remains a formidable challenge in chemical synthesis. Here, we report a highly enantio- and diastereoselective [3+2] annulation reaction of 5-vinyloxazolidinones and activated trisubstituted alkenes catalysed by a palladium complex bearing a newly devised phosphine ligand with a chiral ammonium salt component, which enables the single-step construction of three contiguous stereocentres, including vicinal all-carbon quaternary stereocentres, in a five-membered heterocyclic framework. This stereoselective cycloaddition protocol relies on the remarkable ability of the chiral ligand to rigorously control the absolute stereochemistry of each chiral centre associated with the multiple bond-forming events, and provides a reliable catalytic process for the asymmetric synthesis of densely functionalized pyrrolidines.

  8. Enantioselective synthesis of cis-1,2-disubstituted cyclopentanes and cyclohexanes by Suzuki-Miyaura cross-coupling and iridium-catalyzed asymmetric hydrogenation.

    PubMed

    Schumacher, Andreas; Schrems, Marcus G; Pfaltz, Andreas

    2011-11-25

    A series of 1,2-disubstituted cyclohexene derivatives was prepared through Suzuki-Miyaura cross-coupling of 2-bromo-1-cyclohexenecarbaldehyde or 2-carbomethoxy-1-cyclohexen-1-yl triflate with arylboronates. These tetra-substituted cyclic alkenes were subjected to Ir-catalyzed asymmetric hydrogenation. In this way cis-1-methoxymethyl-2-arylcyclohexanes were obtained in high yield with excellent enantio- and diastereoselectivities (up to >99% ee, >99% cis) by using phosphinomethyloxazolines as ligands. Asymmetric hydrogenation of analogous cyclopentene derivatives, prepared by Suzuki-Miyaura cross-coupling, proved to be more difficult and proceeded with lower enantioselectivities of up to 88% ee. The synthetic potential of this cross-coupling/asymmetric-hydrogenation strategy was demonstrated by an enantioselective route to chiral hexahydrofluorenones. PMID:22052572

  9. Stereoselective and Regiodivergent Allylic Suzuki-Miyaura Cross-Coupling of 2-Ethoxydihydropyranyl Boronates: Synthesis and Confirmation of Absolute Stereochemistry of Diospongin B.

    PubMed

    Rybak, Taras; Hall, Dennis G

    2015-09-01

    Oxygen-containing heterocycles such as pyrans are a common substructure present in a variety of natural products and pharmaceutical drugs. Highly functionalized 4- and 6-aryl/heteroaryl dihydropyran derivatives are assembled by a highly stereoselective, ligand-controlled regiodivergent sp(3)-sp(2) Suzuki-Miyaura cross-coupling of a 2-ethoxy dihydropyranyl boronate derived from a catalytic enantioselective inverse-electron-demand oxa[4 + 2] cycloaddition. The scope and selectivity of this method were assessed along with an application to a concise total synthesis of the diarylheptanoid natural product diospongin B. PMID:26291472

  10. Synthesis and structure revision of the C43-C67 part of amphidinol 3.

    PubMed

    Ebine, Makoto; Kanemoto, Mitsunori; Manabe, Yoshiyuki; Konno, Yosuke; Sakai, Ken; Matsumori, Nobuaki; Murata, Michio; Oishi, Tohru

    2013-06-01

    Stereoselective synthesis of the C43-C67 part of amphidinol 3 (AM3) and its C51-epimer was achieved starting from a common intermediate corresponding to the tetrahydropyran moiety of AM3, via asymmetric oxidations and Julia-Kocienski olefination. By comparing NMR data of the synthetic specimens with those of AM3, the absolute configuration at C51 of AM3 was revised from R to S. PMID:23692417

  11. Synthesis, Crystal Structure, Absolute Configuration and Antitumor Activity of the Enantiomers of 5-Bromo-2-chloro-N-(1-phenylethyl)pyridine-3-sulfonamide.

    PubMed

    Zhou, Zhixu; Li, Linwei; Yan, Ning; Du, Lei; Sun, Changshan; Sun, Tiemin

    2015-01-01

    Pyridinesulfonamide is an important fragment which has a wide range of applications in novel drugs. R- and S-isomers of 5-bromo-2-chloro-N-(1-phenylethyl)pyridine-3-sulfonamide have been synthesized, and the stereostructures have been researched. Single crystals of both compounds were obtained for X-ray analysis, and the absolute configurations (ACs) have been further confirmed by electronic circular dichroism (ECD), optical rotation (OR) and quantum chemical calculations. The crystal structures and calculated geometries were extremely similar, which permitted a comparison of the relative reliabilities of ACs obtained by ECD analyses and theoretical simulation. In addition, the effect of stereochemistry on the PI3Kα kinase and anticancer activity were investigated. Compounds 10a and 10b inhibit the activity of PI3Kα kinase with IC50 values of 1.08 and 2.69 μM, respectively. Furthermore, molecular docking was performed to analyze the binding modes of R- and S-isomers. PMID:26610458

  12. Absolute biological needs.

    PubMed

    McLeod, Stephen

    2014-07-01

    Absolute needs (as against instrumental needs) are independent of the ends, goals and purposes of personal agents. Against the view that the only needs are instrumental needs, David Wiggins and Garrett Thomson have defended absolute needs on the grounds that the verb 'need' has instrumental and absolute senses. While remaining neutral about it, this article does not adopt that approach. Instead, it suggests that there are absolute biological needs. The absolute nature of these needs is defended by appeal to: their objectivity (as against mind-dependence); the universality of the phenomenon of needing across the plant and animal kingdoms; the impossibility that biological needs depend wholly upon the exercise of the abilities characteristic of personal agency; the contention that the possession of biological needs is prior to the possession of the abilities characteristic of personal agency. Finally, three philosophical usages of 'normative' are distinguished. On two of these, to describe a phenomenon or claim as 'normative' is to describe it as value-dependent. A description of a phenomenon or claim as 'normative' in the third sense does not entail such value-dependency, though it leaves open the possibility that value depends upon the phenomenon or upon the truth of the claim. It is argued that while survival needs (or claims about them) may well be normative in this third sense, they are normative in neither of the first two. Thus, the idea of absolute need is not inherently normative in either of the first two senses. PMID:23586876

  13. 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 use of Type Ia supernovae as standard candles," says Ferdinando Patat. "This kind of supernovae is used to measure the rate of acceleration of the expansion of the Universe, assuming these objects behave in a uniform way. But asymmetries can introduce dispersions in the quantities observed." "Our discovery puts strong constraints on any successful models of thermonuclear supernova explosions," adds Wang. Models have suggested that the clumpiness is caused by a slow-burn process, called 'deflagration', and leaves an irregular trail of ashes. The smoothness of the inner regions of the exploding star implies that at a given stage, the deflagration gives way to a more violent process, a 'detonation', which travels at supersonic speeds - so fast that it erases all the asymmetries in the ashes left behind by the slower burning of the first stage, resulting in a smoother, more homogeneous residue.

  14. 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

  15. Asymmetric dark matter

    SciTech Connect

    Kumar, Jason

    2014-06-24

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

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

    PubMed

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

    2015-12-01

    A simple and versatile methodology, which employs a combination of ring-opening polymerization and alkyne-azide click chemistry to synthesize amphiphilic AB3 miktoarm stars, is reported. Their aqueous self-assembly behavior was studied using dynamic light scattering, fluorescence, and asymmetrical flow field-flow fractionation (AF4 ). AB3 miktoarm stars form micelles which incorporate curcumin with high efficiency, and significantly reduce the viability of glioblastoma cells in spheroids. We demonstrate that AF4 is an effective technique to determine the size distribution of self-assembled structures exposed to a biological medium. The ease, with which asymmetric AB3 miktoarm polymers are constructed, provides a platform that can be widely employed to deliver a variety of lipophilic drugs. PMID:26259625

  17. Asymmetric Redox-Annulation of Cyclic Amines

    PubMed Central

    2015-01-01

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

  18. Microwave Assisted Synthesis of Porous NiCo2O4 Microspheres: Application as High Performance Asymmetric and Symmetric Supercapacitors with Large Areal Capacitance

    PubMed Central

    Khalid, Syed; Cao, Chuanbao; Wang, Lin; Zhu, Youqi

    2016-01-01

    Large areal capacitance is essentially required to integrate the energy storage devices at the microscale electronic appliances. Energy storage devices based on metal oxides are mostly fabricated with low mass loading per unit area which demonstrated low areal capacitance. It is still a challenge to fabricate supercapacitor devices of porous metal oxides with large areal capacitance. Herein we report microwave method followed by a pyrolysis of the as-prepared precursor is used to synthesize porous nickel cobaltite microspheres. Porous NiCo2O4 microspheres are capable to deliver large areal capacitance due to their high specific surface area and small crystallite size. The facile strategy is successfully demonstrated to fabricate aqueous-based asymmetric & symmetric supercapacitor devices of porous NiCo2O4 microspheres with high mass loading of electroactive materials. The asymmetric & symmetric devices exhibit maximum areal capacitance and energy density of 380 mF cm−2 & 19.1 Wh Kg−1 and 194 mF cm−2 & 4.5 Wh Kg−1 (based on total mass loading of 6.25 & 6.0 mg) respectively at current density of 1 mA cm−2. The successful fabrication of symmetric device also indicates that NiCo2O4 can also be used as the negative electrode material for futuristic asymmetric devices. PMID:26936283

  19. Microwave Assisted Synthesis of Porous NiCo2O4 Microspheres: Application as High Performance Asymmetric and Symmetric Supercapacitors with Large Areal Capacitance

    NASA Astrophysics Data System (ADS)

    Khalid, Syed; Cao, Chuanbao; Wang, Lin; Zhu, Youqi

    2016-03-01

    Large areal capacitance is essentially required to integrate the energy storage devices at the microscale electronic appliances. Energy storage devices based on metal oxides are mostly fabricated with low mass loading per unit area which demonstrated low areal capacitance. It is still a challenge to fabricate supercapacitor devices of porous metal oxides with large areal capacitance. Herein we report microwave method followed by a pyrolysis of the as-prepared precursor is used to synthesize porous nickel cobaltite microspheres. Porous NiCo2O4 microspheres are capable to deliver large areal capacitance due to their high specific surface area and small crystallite size. The facile strategy is successfully demonstrated to fabricate aqueous-based asymmetric & symmetric supercapacitor devices of porous NiCo2O4 microspheres with high mass loading of electroactive materials. The asymmetric & symmetric devices exhibit maximum areal capacitance and energy density of 380 mF cm‑2 & 19.1 Wh Kg‑1 and 194 mF cm‑2 & 4.5 Wh Kg‑1 (based on total mass loading of 6.25 & 6.0 mg) respectively at current density of 1 mA cm‑2. The successful fabrication of symmetric device also indicates that NiCo2O4 can also be used as the negative electrode material for futuristic asymmetric devices.

  20. The absolute path command

    Energy Science and Technology Software Center (ESTSC)

    2012-05-11

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

  1. Asymmetric synthesis of (2S,3R)-(-)-epi-CP-99,994 using sulfinimine-derived anti-2,3-diamino esters

    PubMed Central

    Davis, Franklin A.; Zhang, Yanfeng

    2009-01-01

    A differentially protected C-3 N-sulfinyl, C-2 N,N-(diphenylmethylene) 2,3-diamino ester was employed in the synthesis of the amino piperidine (2S,3R)-(-)-epi-CP-99,994. Key steps in the synthesis included the chemoselective hydrolysis of the C-2 N,N-(diphenylmethylene) group and its reprotection as a dibenzylamino group PMID:20161386

  2. Catalytic asymmetric [3+2] cycloaddition of aromatic aldehydes with oxiranes by C-C bond cleavage of epoxides: highly efficient synthesis of chiral 1,3-dioxolanes.

    PubMed

    Chen, Weiliang; Lin, Lili; Cai, Yunfei; Xia, Yong; Cao, Weidi; Liu, Xiaohua; Feng, Xiaoming

    2014-02-28

    A novel and efficient N,N'-dioxide-Gd(III) complex was developed for the highly diastereo- and enantioselective [3+2] cycloaddition of aryl oxiranyl diketones and aldehydes via C-C bond cleavage of oxiranes. The corresponding chiral 1,3-dioxolanes were obtained in excellent yields (up to 99%) with high diastereoselectivities (>95 : 5 dr) and enantioselectivities (up to 91% ee). Moreover, a possible transition model was proposed to explain the origin of the asymmetric induction. PMID:24430105

  3. 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 μm, and the diameters of pileus and stipe are about 0.8 μm and 0.4 μm, respectively. It is found that the flow of N2 is the key parameter for the formation of the novel ZnO structure and the addition of (NH4)2HPO4 has a prominent effect on the phase structure and the growth of mushroom-like morphology. The potential mechanism of forming this morphology is proposed. The pileus of the formed mushroom is assembled by several radial ZnO: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

  4. Synthesis, crystal structure, in vitro acetohydroxyacid synthase inhibition, in vivo herbicidal activity, and 3D-QSAR of new asymmetric aryl disulfides.

    PubMed

    Shang, Jun; Wang, Wei-Min; Li, Yong-Hong; Song, Hai-Bin; Li, Zheng-Ming; Wang, Jian-Guo

    2012-08-29

    Acetohydroxyacid synthase (AHAS; EC 2.2.1.6) is an important bioactive target for the design of environmentally benign herbicides. On the basis of previous virtual screening, 50 asymmetric aryl disulfides containing [1,2,4]triazole groups were synthesized and characterized by (1)H NMR, HRMS, and crystal structure. Compounds I-a, I-b, and I-p show Ki values of 1.70, 4.69, and 5.57 μM, respectively, for wild type Arabidopsis thaliana AHAS (AtAHAS) and low resistance against mutant type AtAHAS W574L. At 100 mg L(-1) concentration, compounds I-a, II-a, and II-b exhibit 86.6, 81.7, and 87.5% in vivo rape root growth inhibition. CoMFA steric and electrostatic contour maps were established, and a possible binding mode was suggested from molecular docking, which provide valuable information to understand the key structural features of these disulfide compounds. To the authors' knowledge, this is the first comprehensive case suggesting that asymmetric aryl disulfides are novel AHAS inhibitors. PMID:22905906

  5. 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

  6. 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

  7. 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-α]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.

  8. Bicyclic Guanidine Catalyzed Asymmetric Tandem Isomerization Intramolecular-Diels-Alder Reaction: The First Catalytic Enantioselective Total Synthesis of (+)-alpha-Yohimbine.

    PubMed

    Feng, Wei; Jiang, Danfeng; Kee, Choon-Wee; Liu, Hongjun; Tan, Choon-Hong

    2016-02-01

    Hydroisoquinoline derivatives were prepared in moderate to good enantioselectivities via a bicyclic guanidine-catalyzed tandem isomerization intramolecular-Diels-Alder (IMDA) reaction of alkynes. With this synthetic method, the first enantioselective synthesis of (+)-alpha-yohimbine was completed in 9 steps from the IMDA products. PMID:25932622

  9. Zn(II), Ni(II), Cu(II) and Pb(II) complexes of tridentate asymmetrical Schiff base ligands: Synthesis, characterization, properties and biological activity

    NASA Astrophysics Data System (ADS)

    Şahin, Mustafa; Koçak, Nuriye; Erdenay, Damla; Arslan, Uğur

    2013-02-01

    New asymmetrical tridentate Schiff base ligands were synthesized using 1,2-phenylenediamine, 4-methyl-1,2-phenylenediamine, 2-hydroxy-1-napthaldehyde, 9-anthracenecarboxaldehyde. Schiff base ligands and their metal complexes were synthesised and characterized by using FT-IR, 1H NMR, 13C NMR, UV-Vis, XRD, ESR, elemental analysis and fluorescence studies. The antimicrobial activity of the ligands and their metal complexes were studied against Staphylococcus aureus ATCC 29213, S. aureus ATCC 25923, Streptococcus mutans RSHM 676, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853. The determination of the antibacterial activity was done using the broth microdilution methods. In general, it has been determined that the studied compounds have MIC values similar to Gram-positive and Gram-negative bacteria. It has been found that Ni, Pb, Zn derivatives of HL1A and ZnL2A has lower MIC values than ampicillin for P. aeruginosa ATCC 27853 strain.

  10. A new method for the synthesis of α-aminoalkylidenebisphosphonates and their asymmetric phosphonyl-phosphinyl and phosphonyl-phosphinoyl analogues

    PubMed Central

    Mazurkiewicz, Roman; Grymel, Mirosława; Zielińska, Katarzyna; Adamek, Jakub; Chmielewska, Ewa; Bochno, Marta; Kubica, Sonia

    2015-01-01

    Summary A convenient approach has been developed to α-aminoalkylidenebisphosphonates and their asymmetric phosphonyl-phosphinyl and phosphonyl-phosphinoyl analogues by α-phosphonylation, α-phosphinylation or α-phosphinoylation of 1-(N-acylamino)alkylphosphonates, that, in turn, are easily accessible from N-acyl-α-amino acids. Effective electrophilic activation of the α-position of 1-(N-acetylamino)alkylphosphonates was achieved by electrochemical α-methoxylation of these compounds in methanol, mediated with NaCl, followed by displacement of the methoxy group with triphenylphosphonium tetrafluoroborate to give hitherto unknown 1-(N-acetylamino)-1-triphenylphosphoniumalkylphosphonate tetrafluoroborates. The latter compounds react smoothly with trialkyl phosphites, dialkyl phosphonites or alkyl phosphinites in the presence of Hünig’s base and methyltriphenylphosphonium iodide in a Michaelis–Arbuzov-like reaction to give the expected alkylidenebisphosphonates, 1-phosphinylalkylphosphonates or 1-phosphinoylalkylphosphonates, respectively, in good yields. PMID:26425197

  11. 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

  12. Palladium-N-heterocyclic carbene (NHC)-catalyzed asymmetric synthesis of indolines through regiodivergent C(sp3)-H activation: scope and DFT study.

    PubMed

    Katayev, Dmitry; Larionov, Evgeny; Nakanishi, Masafumi; Besnard, Cline; Kndig, E Peter

    2014-11-10

    Two bulky, chiral, monodentate N-heterocyclic carbene ligands were applied to palladium-catalyzed asymmetric C-H arylation to incorporate C(sp(3))-H bond activation. Racemic mixtures of the carbamate starting materials underwent regiodivergent reactions to afford different trans-2,3-substituted indolines. Although this CAr-Calkyl coupling requires high temperatures (140-160?C), chiral induction is high. This regiodivergent reaction, when carried out with enantiopure starting materials, can lead to single structurally different enantiopure products, depending on the catalyst chirality. The C-H activation at a tertiary center was realized only in the case of a cyclopropyl group. No C-H activation takes place alpha to a tertiary center. A detailed DFT study is included and analyses of methyl versus methylene versus methine C-H activation is used to rationalize experimentally observed regio- and enantioselectivities. PMID:25262613

  13. Catalytic asymmetric synthesis of 3-(alpha-hydroxy-beta-carbonyl) oxindoles by a Sc(III)-catalyzed direct aldol-type reaction.

    PubMed

    Shen, Ke; Liu, Xiaohua; Zheng, Ke; Li, Wei; Hu, Xiaolei; Lin, Lili; Feng, Xiaoming

    2010-03-22

    A direct catalytic asymmetric aldol-type reaction of 3-substituted-2-oxindoles with glyoxal derivatives and ethyl trifluoropyruvate, catalyzed by a chiral N,N'-dioxide-Sc(OTf)(3) (Tf = trifluoromethanesulfonyl) complex, has been developed that tolerates a wide range of substrates. The reaction proceeds in good yields and excellent enantioselectivities (up to 93% yield, 99:1 diastereomeric ratio (dr), and >99% enantiomeric excess (ee)) under mild conditions, to deliver 3-(alpha-hydroxy-beta-carbonyl) oxindoles with vicinal quaternary-tertiary or quaternary-quaternary stereocenters. Even with 1 mol % catalyst loading or on scaleup (10 mmol of starting material), maintenance of ee was observed, which showed the potential value of the catalyst system. In studies probing the reaction mechanism, a positive nonlinear effect was observed and Sc(III)-based enolate intermediates were detected by using ESIMS. On the basis of the experimental results and previous reports, a possible catalytic cycle was assumed. PMID:20175165

  14. Solvothermal Synthesis of Three-Dimensional Hierarchical CuS Microspheres from a Cu-Based Ionic Liquid Precursor for High-Performance Asymmetric Supercapacitors.

    PubMed

    Zhang, Jing; Feng, Huijie; Yang, Jiaqin; Qin, Qing; Fan, Hongmin; Wei, Caiying; Zheng, Wenjun

    2015-10-01

    It is meaningful to exploit copper sulfide materials with desired structure as well as potential application due to their cheapness and low toxicity. A low-temperature and facile solvothermal method for preparing three-dimensional (3D) hierarchical covellite (CuS) microspheres from an ionic liquid precursor [Bmim]2Cu2Cl6 (Bmim = 1-butyl-3-methylimidazolium) is reported. The formation of CuS nanostructures was achieved by decomposition of intermediate complex Cu(Tu)3Cl (thiourea = Tu), which produced CuS microspheres with diameters of 2.5-4 μm assembled by nanosheets with thicknesses of 10-15 nm. The ionic liquid, as an "all-in-one" medium, played a key role for the fabrication and self-assembly of CuS nanosheets. The alkylimidazolium rings ([Bmim](+)) were found to adsorb onto the (001) facets of CuS crystals, which inhibited the crystal growth along the [001] direction, while the alkyl chain had influence on the assembly of CuS nanosheets. The CuS microspheres showed enhanced electrochemical performance and high stability for the application in supercapacitors due to intriguing structural design and large specific surface area. When this well-defined CuS electrode was assembled into an asymmetric supercapacitor (ASC) with an activated carbon (AC) electrode, the CuS//AC-ASC demonstrated good cycle performance (∼88% capacitance after 4000 cycles) and high energy density (15.06 W h kg(-1) at a power density of 392.9 W kg(-1)). This work provides new insights into the use of copper sulfide electrode materials for asymmetric supercapacitors and other electrochemical devices. PMID:26371955

  15. Absolute configuration of odorine

    PubMed Central

    Fun, Hoong-Kun; Chantrapromma, Suchada; Yodsaoue, Orapun; Karalai, Chatchanok

    2010-01-01

    The title compound, known as odorine or roxburghiline {systematic name: (S)-N-[(R)-1-cinnamoylpyrrolidin-2-yl]-2-methylbutanamide}, C18H24N2O2, is a nitrogenous compound isolated from the leaves of Aglaia odorata. The absolute configuration was determined by refinement of the Flack parameter with data collected using Cu K? radiation showing positions 2 and 2? to be S and R, respectively. The pyrrolidine ring adopts an envelope conformation. In the crystal, molecules are linked into chains along [010] by intermolecular NH?O hydrogen bonds. PMID:21588760

  16. Electronic Absolute Cartesian Autocollimator

    NASA Technical Reports Server (NTRS)

    Leviton, Douglas B.

    2006-01-01

    An electronic absolute Cartesian autocollimator performs the same basic optical function as does a conventional all-optical or a conventional electronic autocollimator but differs in the nature of its optical target and the manner in which the position of the image of the target is measured. The term absolute in the name of this apparatus reflects the nature of the position measurement, which, unlike in a conventional electronic autocollimator, is based absolutely on the position of the image rather than on an assumed proportionality between the position and the levels of processed analog electronic signals. The term Cartesian in the name of this apparatus reflects the nature of its optical target. Figure 1 depicts the electronic functional blocks of an electronic absolute Cartesian autocollimator along with its basic optical layout, which is the same as that of a conventional autocollimator. Referring first to the optical layout and functions only, this or any autocollimator is used to measure the compound angular deviation of a flat datum mirror with respect to the optical axis of the autocollimator itself. The optical components include an illuminated target, a beam splitter, an objective or collimating lens, and a viewer or detector (described in more detail below) at a viewing plane. The target and the viewing planes are focal planes of the lens. Target light reflected by the datum mirror is imaged on the viewing plane at unit magnification by the collimating lens. If the normal to the datum mirror is parallel to the optical axis of the autocollimator, then the target image is centered on the viewing plane. Any angular deviation of the normal from the optical axis manifests itself as a lateral displacement of the target image from the center. The magnitude of the displacement is proportional to the focal length and to the magnitude (assumed to be small) of the angular deviation. The direction of the displacement is perpendicular to the axis about which the mirror is slightly tilted. Hence, one can determine the amount and direction of tilt from the coordinates of the target image on the viewing plane.

  17. Asymmetric Black Diholes

    SciTech Connect

    Manko, V. S.; Sanchez-Mondragon, J.; Ruiz, E.

    2009-05-01

    In the present paper we enlarge the list of black dihole spacetimes by introducing the notion of asymmetric black diholes which describe configurations composed of two static charged black holes endowed with unequal masses and equal but opposite charges. The asymmetric dihole solutions are considered both in the Einstein-Maxwell and Einstein-Maxwell-dilaton theories.

  18. Absolute configuration of micromelin

    PubMed Central

    Fun, Hoong-Kun; Siridechakorn, Ittipon; Laphookhieo, Surat; Chantrapromma, Suchada

    2011-01-01

    The title compound {systematic name: 7-methoxy-6-[(1R,2R,5R)-5-methyl-4-oxo-3,6-dioxabicyclo[3.1.0]hexan-2-yl]-2H-chromen-2-one}, C15H12O6, is a coumarin, which was isolated from the roots of Micromelum glanduliferum. There are two molecules in the asymmetric unit with slight differences in bond angles. In both molecules, the furan ring adopts a flattened envelope conformation. In the crystal, molecules are linked by weak CH?O interactions into chains along the a axis. Aromatic ?? stacking interactions with centroidcentroid distances in the range 3.6995?(11)3.8069?(11)? and C?O short contacts [3.030?(2)3.171?(3)?] also occur. PMID:21837101

  19. ABSOLUTE POLARIMETRY AT RHIC.

    SciTech Connect

    OKADA; BRAVAR, A.; BUNCE, G.; GILL, R.; HUANG, H.; MAKDISI, Y.; NASS, A.; WOOD, J.; ZELENSKI, Z.; ET AL.

    2007-09-10

    Precise and absolute beam polarization measurements are critical for the RHIC spin physics program. Because all experimental spin-dependent results are normalized by beam polarization, the normalization uncertainty contributes directly to final physics uncertainties. We aimed to perform the beam polarization measurement to an accuracy Of {Delta}P{sub beam}/P{sub beam} < 5%. The absolute polarimeter consists of Polarized Atomic Hydrogen Gas Jet Target and left-right pairs of silicon strip detectors and was installed in the RHIC-ring in 2004. This system features proton-proton elastic scattering in the Coulomb nuclear interference (CNI) region. Precise measurements of the analyzing power A{sub N} of this process has allowed us to achieve {Delta}P{sub beam}/P{sub beam} = 4.2% in 2005 for the first long spin-physics run. In this report, we describe the entire set up and performance of the system. The procedure of beam polarization measurement and analysis results from 2004-2005 are described. Physics topics of AN in the CNI region (four-momentum transfer squared 0.001 < -t < 0.032 (GeV/c){sup 2}) are also discussed. We point out the current issues and expected optimum accuracy in 2006 and the future.

  20. Absolute polarimetry at RHIC

    SciTech Connect

    Okada, H.; Saito, N.; Alekseev, I.; Sviridia, D.; Bravar, A.; Gill, R.; Huang, H.; Makdisi, Y.; Nass, A.; Wood, J.; Zelenski, A.; Bunce, G.; Dhawan, S.; Eyser, K. O.; Haeberli, W.; Wise, T.; Jinnouchi, O.; Nakagawa, I.; Stephenson, E.

    2008-02-06

    Precise and absolute beam polarization measurements are critical for the RHIC spin physics program. Because all experimental spin-dependent results are normalized by beam polarization, the normalization uncertainty contributes directly to final physics uncertainties. We aimed to perform the beam polarization measurement to an accuracy of {delta}P{sub beam}/P{sub beam}<5%. The absolute polarimeter consists of Polarized Atomic Hydrogen Gas Jet Target and left-right pairs of silicon strip detectors and was installed in the RHIC-ring in 2004. This system features proton-proton elastic scattering in the Coulomb nuclear interference (CNI) region. Precise measurements of the analyzing power A{sub N} of this process has allowed us to achieve {delta}P{sub beam}/P{sub beam} = 4.2% in 2005 for the first long spin-physics run. In this report, we describe the entire set up and performance of the system. The procedure of beam polarization measurement and analysis results from 2004-2005 are described. Physics topics of A{sub N} in the CNI region (four-momentum transfer squared 0.001<-t<0.032(GeV/c){sup 2}) are also discussed. We point out the current issues and expected optimum accuracy in 2006 and the future.

  1. A new copper(II) Schiff base complex containing asymmetrical tetradentate N2O2 Schiff base ligand: Synthesis, characterization, crystal structure and DFT study

    NASA Astrophysics Data System (ADS)

    Grivani, Gholamhossein; Baghan, Sara Husseinzadeh; Vakili, Mohammad; Khalaji, Aliakbar Dehno; Tahmasebi, Vida; Eigner, Vclav; Duek, Michal

    2015-02-01

    A new copper (II) Schiff base complex, CuL1, was prepared from the reaction of asymmetrical Schiff base ligand of L1 and Cu(OAC)2 (L1 = salicylidene imino-ethylimino-pentan-2-one). The Schiff base ligand, L1, and its copper (II) complex, CuL1, have been characterized by elemental analysis (CHN) and FT-IR and UV-vis spectroscopy. In addition, 1H NMR was employed for characterization of the ligand. Thermogrametric analysis of the CuL1 reveals its thermal stability and its decomposition pattern shows that it is finally decomposed to the copper oxide (CuO). The crystal structure of CuL1 was determined by the single crystal X-ray analysis. The CuL1 complex crystallizes in the monoclinic system, with space group P21/n and distorted square planar coordination around the metal ion. The Schiff base ligand of L1 acts as a chelating ligand and coordinates via two nitrogen and two oxygen atoms to the copper (II) ion with C1 symmetry. The structure of the CuL1 complex was also studied theoretically at different levels of DFT and basis sets. According to calculated results the Csbnd O bond length of the salicylate fragment is slightly higher than that in the acetylacetonate fragment of ligand, which could be interpreted by resonance increasing between phenyl and chelated rings in ligand in relative to the acetylacetonate fragment.

  2. Copper-catalyzed asymmetric synthesis of tertiary α-hydroxy phosphonic acid derivatives with in situ generated nitrosocarbonyl compounds as the oxygen source.

    PubMed

    Maji, Biplab; Yamamoto, Hisashi

    2014-12-22

    α-Hydroxy phosphonic acids and their derivatives are highly bioactive structural motifs. It is now reported that these compounds can be accessed through the copper-catalyzed direct α-oxidation of β-ketophosphonates using in situ generated nitrosocarbonyl compounds as an electrophilic oxygen source. These reactions proceeded in high yields (up to 95 %) and enantioselectivities (up to >99 % ee) for both cyclic as well as acyclic substrates. This method was also applied for the synthesis of α,β-dihydroxy phosphonates and β-amino-α-hydroxy phosphonates. PMID:25348199

  3. Synthesis of alpha-amino acids via asymmetric phase transfer-catalyzed alkylation of achiral nickel(II) complexes of glycine-derived Schiff bases.

    PubMed

    Belokon, Yuri N; Bespalova, Natalia B; Churkina, Tatiana D; Csarov, Ivana; Ezernitskaya, Marina G; Harutyunyan, Syuzanna R; Hrdina, Radim; Kagan, Henri B; Kocovsk, Pavel; Kochetkov, Konstantin A; Larionov, Oleg V; Lyssenko, Konstantin A; North, Michael; Polsek, Miroslav; Peregudov, Alexander S; Prisyazhnyuk, Vladimir V; Vyskocil, Stepn

    2003-10-22

    Achiral, diamagnetic Ni(II) complexes 1 and 3 have been synthesized from Ni(II) salts and the Schiff bases, generated from glycine and PBP (7) and PBA (11), respectively, in MeONa/MeOH solutions. The requisite carbonyl-derivatizing agents pyridine-2-carboxylic acid(2-benzoyl-phenyl)-amide 7 (PBP) and pyridine-2-carboxylic acid(2-formyl-phenyl)-amide 11 (PBA) were readily prepared from picolinic acid and o-aminobenzophenone or picolinic acid and methyl o-anthranilate, respectively. The structure of 1 was established by X-ray crystallography. Complexes 1 and 3 were found to undergo C-alkylation with alkyl halides under PTC conditions in the presence of beta-naphthol or benzyltriethylammonium bromide as catalysts to give mono- and bis-alkylated products, respectively. Decomposition of the complexes with aqueous HCl under mild conditions gave the required amino acids, and PBP and PBA were recovered. Alkylation of 1 with highly reactive alkyl halides, carried out under the PTC conditions in the presence of 10% mol of (S)- or (R)-2-hydroxy-2'-amino-1,1'-binaphthyl 31a (NOBIN) and/or its N-acyl derivatives and by (S)- or (R)-2-hydroxy-8'-amino-1,1'-binaphthyl 32a (iso-NOBIN) and its N-acyl derivatives, respectively, gave rise to alpha-amino acids with high enantioselectivities (90-98.5% ee) in good-to-excellent chemical yields at room temperature within several minutes. An unusually large positive nonlinear effect was observed in these reactions. The Michael addition of acrylic derivatives 37 to 1 was conducted under similar conditions with up to 96% ee. The (1)H NMR and IR spectra of a mixture of the sodium salt of NOBIN and 1 indicated formation of a complex between the two components. Implications of the association and self-association of NOBIN for the observed sense of asymmetric induction and nonlinear effects are discussed. PMID:14558835

  4. Implants as absolute anchorage.

    PubMed

    Rungcharassaeng, Kitichai; Kan, Joseph Y K; Caruso, Joseph M

    2005-11-01

    Anchorage control is essential for successful orthodontic treatment. Each tooth has its own anchorage potential as well as propensity to move when force is applied. When teeth are used as anchorage, the untoward movements of the anchoring units may result in the prolonged treatment time, and unpredictable or less-than-ideal outcome. To maximize tooth-related anchorage, techniques such as differential torque, placing roots into the cortex of the bone, the use of various intraoral devices and/or extraoral appliances have been implemented. Implants, as they are in direct contact with bone, do not possess a periodontal ligament. As a result, they do not move when orthodontic/orthopedic force is applied, and therefore can be used as "absolute anchorage." This article describes different types of implants that have been used as orthodontic anchorage. Their clinical applications and limitations are also discussed. PMID:16463910

  5. 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.

  6. Measurement of the absolute \

    SciTech Connect

    Aunion, Jose Luis Alcaraz; /Barcelona, IFAE

    2010-07-01

    This thesis presents the measurement of the charged current quasi-elastic (CCQE) neutrino-nucleon cross section at neutrino energies around 1 GeV. This measurement has two main physical motivations. On one hand, the neutrino-nucleon interactions at few GeV is a region where existing old data are sparse and with low statistics. The current measurement populates low energy regions with higher statistics and precision than previous experiments. On the other hand, the CCQE interaction is the most useful interaction in neutrino oscillation experiments. The CCQE channel is used to measure the initial and final neutrino fluxes in order to determine the neutrino fraction that disappeared. The neutrino oscillation experiments work at low neutrino energies, so precise measurement of CCQE interactions are essential for flux measurements. The main goal of this thesis is to measure the CCQE absolute neutrino cross section from the SciBooNE data. The SciBar Booster Neutrino Experiment (SciBooNE) is a neutrino and anti-neutrino scattering off experiment. The neutrino energy spectrum works at energies around 1 GeV. SciBooNE was running from June 8th 2007 to August 18th 2008. In that period, the experiment collected a total of 2.65 x 10{sup 20} protons on target (POT). This thesis has used full data collection in neutrino mode 0.99 x 10{sup 20} POT. A CCQE selection cut has been performed, achieving around 70% pure CCQE sample. A fit method has been exclusively developed to determine the absolute CCQE cross section, presenting results in a neutrino energy range from 0.2 to 2 GeV. The results are compatible with the NEUT predictions. The SciBooNE measurement has been compared with both Carbon (MiniBoonE) and deuterium (ANL and BNL) target experiments, showing a good agreement in both cases.

  7. Cold asymmetrical fermion superfluids

    SciTech Connect

    Caldas, Heron

    2004-06-01

    In this work we investigate the general properties and the ground state of an asymmetrical dilute gas of cold fermionic atoms, formed by two particle species having different densities. We have shown in a recent paper, that a mixed phase composed of normal and superfluid components is the energetically favored ground state of such a cold fermionic system. Here we extend the analysis and verify that in fact, the mixed phase is the preferred ground state of an asymmetrical superfluid in various situations. We predict that the mixed phase can serve as a way of detecting superfluidity and estimating the magnitude of the gap parameter in asymmetrical fermionic systems.

  8. Exploiting the Multidentate Nature of Chiral Disulfonimides in a Multicomponent Reaction for the Asymmetric Synthesis of Pyrrolo[1,2-a]indoles: A Remarkable Case of Enantioinversion.

    PubMed

    Galván, Alicia; González-Pérez, Adán B; Álvarez, Rosana; de Lera, Angel R; Fañanás, Francisco J; Rodríguez, Félix

    2016-03-01

    A new multicomponent coupling reaction for the enantioselective synthesis of pyrrolo[1,2-a]indoles under the catalysis of a chiral disulfonimide is described. The high specificity of the reaction is a consequence of the multidentate character of the Brønsted acid catalyst. Insights from DFT calculations helped explain the unexpected high enantioselectivity observed with the simplest 3,3'-unsubstituted binaphthyl catalyst as a result of transition-state stabilization by a network of cooperative noncovalent interactions. The remarkable enantioinversion resulting from the simple introduction of substituents at 3- and 3'-positions, the first reported example of this phenomenon in the context of binaphthalene-derived Brønsted acid catalysis, was instead attributed to destabilizing steric interactions. PMID:26833640

  9. Spontaneous resolution, asymmetric catalysis, and fluorescence properties of ?- and ?-[cu(tzmp)]N enantiomers from in situ [2 + 3] cycloaddition synthesis.

    PubMed

    Tang, Yun-Zhi; Xiong, Jian-Bo; Gao, Ji-Xing; Tan, Yu-Hui; Xu, Qing; Wen, He-Rui

    2015-06-01

    Although a number of acentric or chiral tetrazole complexes were synthesized from Sharpless reaction, there are no spontaneous resolution Cu(I)-tetrazole compounds from in situ [2 + 3] cycloaddition synthesis that have been reported before. The first enantiomers ?- and ?- of metal tetrazole compound [Cu(Tzmp)]n (1) (HTzmp = 3-tetrazolemethylpyridine) were obtained and isolated from in situ [2 + 3] cycloaddition reactions of a flexible organic nitrile (3-cyanomethylpyridine) with sodium azide in the presence of CuCl2 as the Lewis acid. ?-1 and ?-1 feature a homochiral helical coordination polymeric system and {4(4).6(2)} two-dimensional framework. The photoluminescence study suggests 1 exhibits strong green fluorescence in solid state with maximal emission peaks around 535 nm. Remarkably, the ?- and ?- of [Cu(Tzmp)]n (1) catalyzes the enantioselective Henry reaction with high yield (more than 96%) and certain enantioselectivity (up to 69%). PMID:25970815

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

    PubMed

    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, (1)H and (13)C 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]Cl6H2O 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 1.3410(4) and 2.510(4) M(-1), respectively. PMID:23988527

  11. 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.

  12. 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 Durn, Francisco J.; Alonso, Nerea; Caamao, Olga; Garca-Mera, Xerardo; Yaez, Matilde; Prado-Prado, Francisco J.; Gonzlez-Daz, 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

  13. Generic approach for synthesizing asymmetric nanoparticles and nanoassemblies

    DOEpatents

    Sun, Yugang; Hu, Yongxing

    2015-05-26

    A generic route for synthesis of asymmetric nanostructures. This approach utilizes submicron magnetic particles (Fe.sub.3O.sub.4--SiO.sub.2) as recyclable solid substrates for the assembly of asymmetric nanostructures and purification of the final product. Importantly, an additional SiO.sub.2 layer is employed as a mediation layer to allow for selective modification of target nanoparticles. The partially patched nanoparticles are used as building blocks for different kinds of complex asymmetric nanostructures that cannot be fabricated by conventional approaches. The potential applications such as ultra-sensitive substrates for surface enhanced Raman scattering (SERS) have been included.

  14. Synthesis, structures, and magnetic properties of novel mononuclear, tetranuclear, and 1D chain Mn(III) complexes involving three related asymmetrical trianionic ligands.

    PubMed

    Costes, Jean-Pierre; Dahan, Franoise; Donnadieu, Bruno; Rodriguez Douton, Maria-Jesus; Fernandez Garcia, Maria-Isabel; Bousseksou, Azzedine; Tuchagues, Jean-Pierre

    2004-04-19

    The manganese(III) complexes studied in this report derive from asymmetrical trianionic ligands abbreviated H(3)L(i) (i = 4-6). These ligands are obtained through reaction of salicylaldehyde with "half-units", the latter resulting from monocondensation of different diamines with phenylsalicylate,. Upon deprotonation, L(i) (i = 4-6) possess an inner N(2)O(2) coordination site with one amido, one imine, and two phenoxo functions, and an outer amido oxygen donor. The trianionic character of such ligands yields original neutral complexes with the L/Mn stoichiometry. The crystal and molecular structures of three complexes have been determined at 190 K (1) or 180 K (2 and 3). Complex 1 crystallizes in the triclinic space group P (No. 2): a = 7.8582(14) A, b = 10.9225(16) A, c = 12.4882(18) A, alpha = 67.231(14) degrees, beta = 72.134(14) degrees, gamma = 82.589(13) degrees, V = 940.6(3) A(3), Z = 2. Complex 2 crystallizes in the orthorhombic space group Pbcn (Nuomicron. 60): a = 23.8283(15) A, b = 11.1605(7) A, c = 26.152(2) A, V = 6954.8(8) A(3), Z = 8, while complex 3 crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 11.7443(14) A, b = 7.5996(10) A, c = 18.029(2) A, beta = 100.604(10) degrees, V = 1581.6(3) A(3), Z = 4. Owing to hydrogen bonds and pi-pi stackings, the mononuclear neutral molecules of 1 are arranged in a 2D network while complexes 2 and 3 are tetranuclear and polymeric (1D chain) species, respectively, owing to the bridging ability of the oxygen atom of the amido function. The experimental magnetic susceptibilities of complexes 2 and 3 indicate the occurrence of similarly weak Mn(III)-Mn(III) antiferromagnetic interactions (J = -1.1 cm(-1)). Single ion zero-field splitting of manganese(III) must be taken into account for satisfactorily fitting the data by exact calculation of the energy levels associated to the spin Hamiltonian through diagonalization of the full matrix for axial symmetry in 2 (J = - 1.1 cm(-1), D(1) = 2.2 cm(-1), D(2) = -2.8 cm(-1)), D(1) and D(2) being associated to the six- and five-coordinate Mn ions, respectively. A weaker antiferromagnetic interaction (J = - 0.2 cm(-1)) operates through pi-pi stacking in complex 1. Complex 3 is a weak ferromagnet (ordering temperature approximately 7 K) as a result of the spin canting originating from the crystal packing. PMID:15074994

  15. Asymmetric transformations of achiral 2,5-cyclohexadienones

    PubMed Central

    Kalstabakken, Kyle A.; Harned, Andrew M.

    2014-01-01

    Cyclohexadienones are versatile platforms for performing asymmetric synthesis as evidenced by the numerous natural product syntheses that exploit their diverse reactivity profile. However, there are few general methods available for the direct asymmetric synthesis of chiral cyclohexadienones. To circumvent this problem, several researchers have developed catalytic asymmetric methods that employ readily available achiral 2,5-cyclohexadienones as substrates. Many of these reactions are desymmetrizations in which one of the enantiotopic alkenes of an achiral dienone is transformed. Others involve selective reaction at one alkene of an unsymmetrically substituted, achiral dienone. This review will cover advances in this area over the last 20 years and the application of these strategies in complex molecule synthesis. PMID:26688596

  16. 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

  17. An Enantioselective Synthesis of a MEM-Protected Aetheramide A Derivative

    PubMed Central

    Ghosh, Arun K.; Rao, Kalapala Venkateswara; Akasapu, Siddhartha

    2014-01-01

    Aetheramides A and B are very potent anti-HIV agents. An enantioselective synthesis of a MEM-protected aetheramide A derivative is described. The synthesis was accomplished in a convergent and stereoselective manner. The key reactions involved asymmetric dihydroxylation, asymmetric allylation, asymmetric syn-aldol reactions and asymmetric hydrogenation. PMID:25197148

  18. An Enantioselective Synthesis of a MEM-Protected Aetheramide A Derivative.

    PubMed

    Ghosh, Arun K; Rao, Kalapala Venkateswara; Akasapu, Siddhartha

    2014-09-10

    Aetheramides A and B are very potent anti-HIV agents. An enantioselective synthesis of a MEM-protected aetheramide A derivative is described. The synthesis was accomplished in a convergent and stereoselective manner. The key reactions involved asymmetric dihydroxylation, asymmetric allylation, asymmetric syn-aldol reactions and asymmetric hydrogenation. PMID:25197148

  19. Absolute Identification by Relative Judgment

    ERIC Educational Resources Information Center

    Stewart, Neil; Brown, Gordon D. A.; Chater, Nick

    2005-01-01

    In unidimensional absolute identification tasks, participants identify stimuli that vary along a single dimension. Performance is surprisingly poor compared with discrimination of the same stimuli. Existing models assume that identification is achieved using long-term representations of absolute magnitudes. The authors propose an alternative

  20. 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

  1. Asymmetrical field emitter

    SciTech Connect

    Fleming, James G.; Smith, Bradley K.

    1995-01-01

    Providing a field emitter with an asymmetrical emitter structure having a very sharp tip in close proximity to its gate. One preferred embodiment of the present invention includes an asymmetrical emitter and a gate. The emitter having a tip and a side is coupled to a substrate. The gate is connected to a step in the substrate. The step has a top surface and a side wall that is substantially parallel to the side of the emitter. The tip of the emitter is in close proximity to the gate. The emitter is at an emitter potential, and the gate is at a gate potential such that with the two potentials at appropriate values, electrons are emitted from the emitter. In one embodiment, the gate is separated from the emitter by an oxide layer, and the emitter is etched anisotropically to form its tip and its asymmetrical structure.

  2. Cold asymmetrical fermion superfluids

    SciTech Connect

    Caldas, Heron

    2003-12-19

    The recent experimental advances in cold atomic traps have induced a great amount of interest in fields from condensed matter to particle physics, including approaches and prospects from the theoretical point of view. In this work we investigate the general properties and the ground state of an asymmetrical dilute gas of cold fermionic atoms, formed by two particle species having different densities. We have show in a recent paper, that a mixed phase composed of normal and superfluid components is the energetically favored ground state of such a cold fermionic system. Here we extend the analysis and verify that in fact, the mixed phase is the preferred ground state of an asymmetrical superfluid in various situations. We predict that the mixed phase can serve as a way of detecting superfluidity and estimating the magnitude of the gap parameter in asymmetrical fermionic systems.

  3. Asymmetrical field emitter

    DOEpatents

    Fleming, J.G.; Smith, B.K.

    1995-10-10

    A method is disclosed for providing a field emitter with an asymmetrical emitter structure having a very sharp tip in close proximity to its gate. One preferred embodiment of the present invention includes an asymmetrical emitter and a gate. The emitter having a tip and a side is coupled to a substrate. The gate is connected to a step in the substrate. The step has a top surface and a side wall that is substantially parallel to the side of the emitter. The tip of the emitter is in close proximity to the gate. The emitter is at an emitter potential, and the gate is at a gate potential such that with the two potentials at appropriate values, electrons are emitted from the emitter. In one embodiment, the gate is separated from the emitter by an oxide layer, and the emitter is etched anisotropically to form its tip and its asymmetrical structure. 17 figs.

  4. 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.

  5. 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)

  6. Asymmetric Amino Acid Catalysis

    NASA Astrophysics Data System (ADS)

    Crdova, Armando

    2008-03-01

    The origins of biological homochirality have intrigued researchers since Pasteur's discovery of the optical activity of biomolecules. Herein, I discuss our observations of asymmetric amplification in amino acid catalyzed carbon-carbon bond-forming reactions under homogenous reaction conditions. Our model shows a synergistic mechanism between the amino acid catalyst and the optically active products such as sugars and amino acid derivatives.

  7. Asymmetric Epoxidation Using Hydrogen Peroxide as Oxidant.

    PubMed

    Wang, Chuan; Yamamoto, Hisashi

    2015-10-01

    Asymmetric epoxidation is one of the most important transformations in organic synthesis. Although tremendous progress was achieved in this field in the 1980s and 1990s, it is still desirable from both economical and ecological views to develop environmentally friendly catalytic epoxidation with a broad substrate scope. Hydrogen peroxide is a safe and cheap oxidant, which is easy to handle and generates water as the sole byproduct. Therefore, asymmetric epoxidation of olefins using hydrogen peroxide as oxidant has been a very active research field and has been investigated by many research groups in recent years. In this review, the exciting very recent developments of this rapidly growing area are surveyed and organized according to the catalyst systems. PMID:26061144

  8. Improved synthesis of structural analogues of (-)-epicatechin gallate for modulation of staphylococcal ?-lactam resistance.

    PubMed

    Anderson, James C; Grounds, Helen; Reeves, Suzanna; Taylor, Peter W

    2014-05-27

    The high-yielding synthesis of enantiomerically pure epicatechin gallate analogues where the A and/or B-ring hydroxylation is reduced or altered has been achieved by optimising routes to the catechin stereochemistry. The B-ring analogues were synthesised by using an electrophilic ring closure onto an enantiomerically enriched epoxide as a key step. The A and B-ring hydroxyl-deleted analogues were synthesised through a Mitsunobu cyclisation. For the B-ring analogues, the anti- (catechin) stereochemistry was converted to the syn- (epicatechin) stereochemistry by a known oxidation/reduction protocol. Absolute stereochemistry was derived from either a Sharpless epoxidation or asymmetric dihydroxylation. PMID:24876661

  9. Cu(I)-NHC catalyzed asymmetric silyl transfer to unsaturated lactams and amides.

    PubMed

    Pace, Vittorio; Rae, James P; Procter, David J

    2014-01-17

    The first asymmetric silylation of unsaturated lactams and amides using Cu(I)-NHC catalysts and PhMe2SiBpin has been accomplished. The method has been exploited in an expedient asymmetric synthesis of the (R)-enantiomer of the nootropic drug oxiracetam. PMID:24350760

  10. Cryogenic, Absolute, High Pressure Sensor

    NASA Technical Reports Server (NTRS)

    Chapman, John J. (Inventor); Shams. Qamar A. (Inventor); Powers, William T. (Inventor)

    2001-01-01

    A pressure sensor is provided for cryogenic, high pressure applications. A highly doped silicon piezoresistive pressure sensor is bonded to a silicon substrate in an absolute pressure sensing configuration. The absolute pressure sensor is bonded to an aluminum nitride substrate. Aluminum nitride has appropriate coefficient of thermal expansion for use with highly doped silicon at cryogenic temperatures. A group of sensors, either two sensors on two substrates or four sensors on a single substrate are packaged in a pressure vessel.

  11. Asymmetric pyrene derivatives for organic field-effect transistors.

    PubMed

    Zöphel, Lukas; Beckmann, Dirk; Enkelmann, Volker; Chercka, Dennis; Rieger, Ralph; Müllen, Klaus

    2011-06-28

    For the synthesis of an ortho-dithienylpyrene, a K-region bromination of pyrene was developed which enabled the first reported, non-statistical asymmetric functionalization of pyrene at the 4, 5, 9 and 10 positions. Crystal structures, optical and electronic properties and FET characteristics have been investigated. PMID:21594241

  12. Dynamic kinetic asymmetric transformations of ?-stereogenic ?-ketoesters by direct aldolization.

    PubMed

    Corbett, Michael T; Johnson, Jeffrey S

    2014-01-01

    Dynamic kinetic asymmetric transformations (DyKAT) of racemic ?-bromo-?-keto esters by direct aldolization of nitromethane and acetone provide access to fully substituted ?-glycolic acid derivatives bearing a ?-stereocenter. The aldol adducts are obtained in excellent yield with high relative and absolute stereocontrol under mild reaction conditions. Mechanistic studies determined that the reactions proceed through a facile catalyst-mediated racemization of the ?-bromo-?-keto esters under a DyKAT Type I manifold. PMID:24222195

  13. Multipartite asymmetric quantum cloning

    SciTech Connect

    Iblisdir, S.; Gisin, N.; Acin, A.; Cerf, N.J.; Filip, R.; Fiurasek, J.

    2005-10-15

    We investigate the optimal distribution of quantum information over multipartite systems in asymmetric settings. We introduce cloning transformations that take N identical replicas of a pure state in any dimension as input and yield a collection of clones with nonidentical fidelities. As an example, if the clones are partitioned into a set of M{sub A} clones with fidelity F{sup A} and another set of M{sub B} clones with fidelity F{sup B}, the trade-off between these fidelities is analyzed, and particular cases of optimal N{yields}M{sub A}+M{sub B} cloning machines are exhibited. We also present an optimal 1{yields}1+1+1 cloning machine, which is an example of a tripartite fully asymmetric cloner. Finally, it is shown how these cloning machines can be optically realized.

  14. Absolute configuration of naturally occurring glabridin.

    PubMed

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

    2013-11-01

    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

  15. Asymmetric information and economics

    NASA Astrophysics Data System (ADS)

    Frieden, B. Roy; Hawkins, Raymond J.

    2010-01-01

    We present an expression of the economic concept of asymmetric information with which it is possible to derive the dynamical laws of an economy. To illustrate the utility of this approach we show how the assumption of optimal information flow leads to a general class of investment strategies including the well-known Q theory of Tobin. Novel consequences of this formalism include a natural definition of market efficiency and an uncertainty principle relating capital stock and investment flow.

  16. Asymmetric dipolar ring

    DOEpatents

    Prosandeev, Sergey A.; Ponomareva, Inna V.; Kornev, Igor A.; Bellaiche, Laurent M.

    2010-11-16

    A device having a dipolar ring surrounding an interior region that is disposed asymmetrically on the ring. The dipolar ring generates a toroidal moment switchable between at least two stable states by a homogeneous field applied to the dipolar ring in the plane of the ring. The ring may be made of ferroelectric or magnetic material. In the former case, the homogeneous field is an electric field and in the latter case, the homogeneous field is a magnetic field.

  17. Sentinel-2/MSI absolute calibration: first results

    NASA Astrophysics Data System (ADS)

    Lonjou, V.; Lachrade, S.; Fougnie, B.; Gamet, P.; Marcq, S.; Raynaud, J.-L.; Tremas, T.

    2015-10-01

    Sentinel-2 is an optical imaging mission devoted to the operational monitoring of land and coastal areas. It is developed in partnership between the European Commission and the European Space Agency. The Sentinel-2 mission is based on a satellites constellation deployed in polar sun-synchronous orbit. It will offer a unique combination of global coverage with a wide field of view (290km), a high revisit (5 days with two satellites), a high resolution (10m, 20m and 60m) and multi-spectral imagery (13 spectral bands in visible and shortwave infra-red domains). CNES is involved in the instrument commissioning in collaboration with ESA. This paper reviews all the techniques that will be used to insure an absolute calibration of the 13 spectral bands better than 5% (target 3%), and will present the first results if available. First, the nominal calibration technique, based on an on-board sun diffuser, is detailed. Then, we show how vicarious calibration methods based on acquisitions over natural targets (oceans, deserts, and Antarctica during winter) will be used to check and improve the accuracy of the absolute calibration coefficients. Finally, the verification scheme, exploiting photometer in-situ measurements over Lacrau plain, is described. A synthesis, including spectral coherence, inter-methods agreement and temporal evolution, will conclude the paper.

  18. Asymmetric Evolutionary Games

    PubMed Central

    McAvoy, Alex; Hauert, Christoph

    2015-01-01

    Evolutionary game theory is a powerful framework for studying evolution in populations of interacting individuals. A common assumption in evolutionary game theory is that interactions are symmetric, which means that the players are distinguished by only their strategies. In nature, however, the microscopic interactions between players are nearly always asymmetric due to environmental effects, differing baseline characteristics, and other possible sources of heterogeneity. To model these phenomena, we introduce into evolutionary game theory two broad classes of asymmetric interactions: ecological and genotypic. Ecological asymmetry results from variation in the environments of the players, while genotypic asymmetry is a consequence of the players having differing baseline genotypes. We develop a theory of these forms of asymmetry for games in structured populations and use the classical social dilemmas, the Prisoners Dilemma and the Snowdrift Game, for illustrations. Interestingly, asymmetric games reveal essential differences between models of genetic evolution based on reproduction and models of cultural evolution based on imitation that are not apparent in symmetric games. PMID:26308326

  19. Oscillating asymmetric dark matter

    SciTech Connect

    Tulin, Sean; Yu, Hai-Bo; Zurek, Kathryn M. E-mail: haiboyu@umich.edu

    2012-05-01

    We study the dynamics of dark matter (DM) particle-antiparticle oscillations within the context of asymmetric DM. Oscillations arise due to small DM number-violating Majorana-type mass terms, and can lead to recoupling of annihilation after freeze-out and washout of the DM density. Asymmetric DM oscillations 'interpolate' between symmetric and asymmetric DM freeze-out scenarios, and allow for a larger DM model-building parameter space. We derive the density matrix equations for DM oscillations and freeze-out from first principles using nonequilibrium field theory, and our results are qualitatively different than in previous studies. DM dynamics exhibits particle-vs-antiparticle 'flavor' effects, depending on the interaction type, analogous to neutrino oscillations in a medium. 'Flavor-sensitive' DM interactions include scattering or annihilation through a new vector boson, while 'flavor-blind' interactions include scattering or s-channel annihilation through a new scalar boson. In particular, we find that flavor-sensitive annihilation does not recouple when coherent oscillations begin, and that flavor-blind scattering does not lead to decoherence.

  20. 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.

  1. Oscillating asymmetric dark matter

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

    We study the dynamics of dark matter (DM) particle-antiparticle oscillations within the context of asymmetric DM. Oscillations arise due to small DM number-violating Majorana-type mass terms, and can lead to recoupling of annihilation after freeze-out and washout of the DM density. Asymmetric DM oscillations "interpolate" between symmetric and asymmetric DM freeze-out scenarios, and allow for a larger DM model-building parameter space. We derive the density matrix equations for DM oscillations and freeze-out from first principles using nonequilibrium field theory, and our results are qualitatively different than in previous studies. DM dynamics exhibits particle-vs-antiparticle "flavor" effects, depending on the interaction type, analogous to neutrino oscillations in a medium. "Flavor-sensitive" DM interactions include scattering or annihilation through a new vector boson, while "flavor-blind" interactions include scattering or s-channel annihilation through a new scalar boson. In particular, we find that flavor-sensitive annihilation does not recouple when coherent oscillations begin, and that flavor-blind scattering does not lead to decoherence.

  2. Absolute flux scale for radioastronomy

    SciTech Connect

    Ivanov, V.P.; Stankevich, K.S.

    1986-07-01

    The authors propose and provide support for a new absolute flux scale for radio astronomy, which is not encumbered with the inadequacies of the previous scales. In constructing it the method of relative spectra was used (a powerful tool for choosing reference spectra). A review is given of previous flux scales. The authors compare the AIS scale with the scale they propose. Both scales are based on absolute measurements by the ''artificial moon'' method, and they are practically coincident in the range from 0.96 to 6 GHz. At frequencies above 6 GHz, 0.96 GHz, the AIS scale is overestimated because of incorrect extrapolation of the spectra of the primary and secondary standards. The major results which have emerged from this review of absolute scales in radio astronomy are summarized.

  3. Database applicaton for absolute spectrophotometry

    NASA Astrophysics Data System (ADS)

    Bochkov, Valery V.; Shumko, Sergiy

    2002-12-01

    32-bit database application with multidocument interface for Windows has been developed to calculate absolute energy distributions of observed spectra. The original database contains wavelength calibrated observed spectra which had been already passed through apparatus reductions such as flatfielding, background and apparatus noise subtracting. Absolute energy distributions of observed spectra are defined in unique scale by means of registering them simultaneously with artificial intensity standard. Observations of sequence of spectrophotometric standards are used to define absolute energy of the artificial standard. Observations of spectrophotometric standards are used to define optical extinction in selected moments. FFT algorithm implemented in the application allows performing convolution (deconvolution) spectra with user-defined PSF. The object-oriented interface has been created using facilities of C++ libraries. Client/server model with Windows Socket functionality based on TCP/IP protocol is used to develop the application. It supports Dynamic Data Exchange conversation in server mode and uses Microsoft Exchange communication facilities.

  4. Potential Skin Regeneration Activity and Chemical Composition of Absolute from Pueraria thunbergiana Flower.

    PubMed

    Kim, Do-Yoon; Won, Kyung-Jong; Hwang, Dae-Il; Yoon, Seok Won; Lee, Su Jin; Park, Joo-Hoon; Yoon, Myeong Sik; Kim, Bokyung; Lee, Hwan Myung

    2015-11-01

    The flower of Pueraria thunbergiana BENTH (PTBF) contains isoflavonoids and essential oil components. It has many biological and pharmacological activities, including anti-diabetes, anti-oxidant, and weight loss. However, its effect on skin regeneration remains unknown. In the present study, we isolated the absolute from PTBF through solvent extraction and determined the role of the absolute on skin regeneration-associated responses in human epidermal-keratinocytes (HaCats). The PTBF absolute, which contained 10 compounds, stimulated migration and proliferation and increased the phosphorylation of serine/threonine-specific protein kinase and extracellular signal-regulated kinasel/2 in HaCats. It induced type I and IV collagen synthesis in HaCats. In addition, treatment with PTBF absolute resulted in increased sprout outgrowth in HaCats. These findings suggest that PTBF absolute may participate in skin regeneration, probably through promotion of migration, proliferation, and collagen synthesis. PMID:26749850

  5. 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)

  6. Relativistic Absolutism in Moral Education.

    ERIC Educational Resources Information Center

    Vogt, W. Paul

    1982-01-01

    Discusses Emile Durkheim's "Moral Education: A Study in the Theory and Application of the Sociology of Education," which holds that morally healthy societies may vary in culture and organization but must possess absolute rules of moral behavior. Compares this moral theory with current theory and practice of American educators. (MJL)

  7. 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.-

  8. Asymmetric quantum convolutional codes

    NASA Astrophysics Data System (ADS)

    La Guardia, Giuliano G.

    2016-01-01

    In this paper, we construct the first families of asymmetric quantum convolutional codes (AQCCs). These new AQCCs are constructed by means of the CSS-type construction applied to suitable families of classical convolutional codes, which are also constructed here. The new codes have non-catastrophic generator matrices, and they have great asymmetry. Since our constructions are performed algebraically, i.e. we develop general algebraic methods and properties to perform the constructions, it is possible to derive several families of such codes and not only codes with specific parameters. Additionally, several different types of such codes are obtained.

  9. Asymmetric hydrogenation using monodentate phosphoramidite ligands.

    PubMed

    Minnaard, Adriaan J; Feringa, Ben L; Lefort, Laurent; de Vries, Johannes G

    2007-12-01

    Monodentate phosphoramidites are excellent ligands for Rh-catalyzed asymmetric hydrogenations of substituted olefins. Enantioselectivities between 95 and 99% were obtained in the asymmetric hydrogenation of protected alpha- and beta-dehydroamino acids and esters, itaconic acid and esters, aromatic enamides, aromatic enol esters, aromatic and aliphatic enol carbamates, and alpha-substituted cinnamic acids. An iridium catalyst Ir(L*)(COD)Cl was developed that contains only a single bulky phosphoramidite based on 3,3'-disubstituted BINOL or bisphenol as a chiral ligand. With this catalyst, acetylated dehydroamino acid esters could be hydrogenated with very good enantioselectivity. Most reactions have turnover frequencies of 250-1600 h (-1), depending upon the hydrogen pressure. The enantioselectivity is unaffected by the pressure over a wide range. Because of their modularity and easy synthesis, parallel ligand synthesis is possible. Results obtained with these library ligands deviate only slightly from those obtained with purified ligands. Using this instant ligand library protocol, DSM has developed catalysts for industrial processes. These MonoPhos ligands are currently used in production for pharmaceutical intermediates by DSM. It is possible to use catalysts based on a mixture of two different monodentate ligands, such as two different monodentate phosphoramidites or one phosphoramidite and one achiral phosphine ligand. Dependent upon the substrate, the "mixed" catalyst may lead to higher enantioselectivity and rate than the "homocatalysts". PMID:17705446

  10. (E)-2-boryl 1,3-dienes from the 10-TMS-9-BBDs: highly selective reagents for the asymmetric synthesis of anti-α,β-disubstituted β-allenylamines from the allylboration of aldimines.

    PubMed

    González, Javier R; Soderquist, John A

    2014-07-18

    The asymmetric allylboration of N-H aldimines with optically pure trans-4-substituted-2-boryl-1,3-dienes 6 is described. These organoboranes 6 serve as near-perfect asymmetric allylborating agents for N-H aldimines for the preparation of anti-1,2-disubstituted-3,4-pentadien-1-amines 11 as essentially single diastereomers in enantiomerically pure form (>98% de, ≥98% ee). Enantiomerically pure cis-2,3-disubstitued piperidines 12 and α,β-disubstituted-β-amino acids 17 are readily prepared through the standard protocols. A novel Ru-catalyzed hydroamination provides trans-4,5-disubstituted-1-pyrrolines 21 from 11. PMID:25003976

  11. Asymmetric multiscale detrended fluctuation analysis of California electricity spot price

    NASA Astrophysics Data System (ADS)

    Fan, Qingju

    2016-01-01

    In this paper, we develop a new method called asymmetric multiscale detrended fluctuation analysis, which is an extension of asymmetric detrended fluctuation analysis (A-DFA) and can assess the asymmetry correlation properties of series with a variable scale range. We investigate the asymmetric correlations in California 1999-2000 power market after filtering some periodic trends by empirical mode decomposition (EMD). Our findings show the coexistence of symmetric and asymmetric correlations in the price series of 1999 and strong asymmetric correlations in 2000. What is more, we detect subtle correlation properties of the upward and downward price series for most larger scale intervals in 2000. Meanwhile, the fluctuations of Δα(s) (asymmetry) and | Δα(s) | (absolute asymmetry) are more significant in 2000 than that in 1999 for larger scale intervals, and they have similar characteristics for smaller scale intervals. We conclude that the strong asymmetry property and different correlation properties of upward and downward price series for larger scale intervals in 2000 have important implications on the collapse of California power market, and our findings shed a new light on the underlying mechanisms of power price.

  12. Asymmetric organocatalytic epoxidations: reactions, scope, mechanisms, and applications.

    PubMed

    Davis, Rebecca L; Stiller, Julian; Naicker, Tricia; Jiang, Hao; Jrgensen, Karl Anker

    2014-07-14

    Chiral epoxides serve as versatile building blocks in the synthesis of complex organic frameworks. The high strain imposed by the three-membered ring system makes epoxides prone to a variety of nucleophilic ring-opening reactions. Since the development of the Sharpless epoxidation, there have been many important contributions and advances in this area. With the rapid development of the field of asymmetric organocatalysis, a wide range of organocatalysts is now able to catalyze the epoxidation of broad class of unsaturated carbonyl compounds. In this Minireview, recent progress in the development of organocatalytic asymmetric epoxidation methods, the proposed mechanisms of these reactions and their applications as intermediates is reported. PMID:24919420

  13. 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.

  14. Asymmetric coevolutionary voter dynamics

    NASA Astrophysics Data System (ADS)

    Wieland, Stefan; Nunes, Ana

    2013-12-01

    We consider a modification of the adaptive contact process that, interpreted in the context of opinion dynamics, breaks the symmetry of the coevolutionary voter model by assigning to each node type a different strategy to promote consensus: Orthodox opinion holders spread their opinion via social pressure and rewire their connections following a segregationist strategy; heterodox opinion holders adopt a proselytic strategy, converting their neighbors through personal interactions, and relax to the orthodox opinion according to its representation in the population. We give a full description of the phase diagram of this asymmetric model, using the standard pair approximation equations and assessing their performance by comparison with stochastic simulations. We find that although global consensus is favored with regard to the symmetric case, the asymmetric model also features an active phase. We study the stochastic properties of the corresponding metastable state in finite-size networks, discussing the applicability of the analytic approximations developed for the coevolutionary voter model. We find that, in contrast to the symmetric case, the final consensus state is predetermined by the system's parameters and independent of initial conditions for sufficiently large system sizes. We also find that rewiring always favors consensus, both by significantly reducing convergence times and by changing their scaling with system size.

  15. Absolute calibration of optical flats

    SciTech Connect

    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.

  16. Moral absolutism and ectopic pregnancy.

    PubMed

    Kaczor, C

    2001-02-01

    If one accepts a version of absolutism that excludes the intentional killing of any innocent human person from conception to natural death, ectopic pregnancy poses vexing difficulties. Given that the embryonic life almost certainly will die anyway, how can one retain one's moral principle and yet adequately respond to a situation that gravely threatens the life of the mother and her future fertility? The four options of treatment most often discussed in the literature are non-intervention, salpingectomy (removal of tube with embryo), salpingostomy (removal of embryo alone), and use of methotrexate (MXT). In this essay, I review these four options and introduce a fifth (the milking technique). In order to assess these options in terms of the absolutism mentioned, it will also be necessary to discuss various accounts of the intention/foresight distinction. I conclude that salpingectomy, salpingostomy, and the milking technique are compatible with absolutist presuppositions, but not the use of methotrexate. PMID:11262641

  17. Absolute Radiometric Calibration of SERTS

    NASA Astrophysics Data System (ADS)

    Thomas, R. J.; Condor, C. E.; Haas, J. P.; Linard, D. L., II; Swartz, M.; Kent, B. J.; Hollandt, J.

    1997-12-01

    The Solar EUV Rocket Telescope and Spectrograph (SERTS) obtains imaged high-resolution spectra of individual solar features, providing information about the Sun's corona and upper transition region. We have recently carried out a complete end-to-end calibration of the instrument to determine its absolute radiometric response over the full bandpass of 300 -- 365 Angstroms. 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 calibration of the Coronal Diagnostic Spectrometer (CDS) experiment now flying aboard the SOHO spacecraft. For our SERTS project, the unique radiation source provided by the Physikalisch-Technische Bundesanstalt (PTB) in Germany was re-calibrated to an absolute accuracy of 7% (1sigma ) at 12 wavelengths covering our bandpass directly against the Berlin electron storage ring BESSY, which is a primary radiometric source standard. Scans of the SERTS aperture over a range of pitch and yaw angles were made to determine the instrument's absolute spectral sensitivity to <= 25%, considering all sources of error. These 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. The recent measurements at RAL also give information about the uniformity of illumination across the collimated source beam, as well as about polarization characteristics of both the instrument and radiation source, which may prove helpful in correctly interpreting the original CDS calibration data. We hope to repeat such calibration measurements and to provide future SERTS flights annually, at least throughout the duration of the SOHO mission. Coordinated observing programs would then allow these updated absolute calibrations to be transferred on a regular basis to several of the instruments onboard SOHO, including CDS, EIT, and CELIAS.

  18. 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.

  19. Models for asymmetric hybrid brane

    NASA Astrophysics Data System (ADS)

    Bazeia, D.; Marques, M. A.; Menezes, R.

    2015-10-01

    We deal with relativistic models described by a single real scalar field, searching for topological structures that behave asymmetrically, connecting minima with a distinct profile. We use such features to build a new braneworld scenario, in which the source scalar field contributes to generate asymmetric hybrid brane.

  20. Asymmetric twin Dark Matter

    SciTech Connect

    Farina, Marco

    2015-11-09

    We study a natural implementation of Asymmetric Dark Matter in Twin Higgs models. The mirroring of the Standard Model strong sector suggests that a twin baryon with mass around 5 GeV is a natural Dark Matter candidate once a twin baryon number asymmetry comparable to the SM asymmetry is generated. We explore twin baryon Dark Matter in two different scenarios, one with minimal content in the twin sector and one with a complete copy of the SM, including a light twin photon. The essential requirements for successful thermal history are presented, and in doing so we address some of the cosmological issues common to many Twin Higgs models. The required interactions we introduce predict signatures at direct detection experiments and at the LHC.

  1. Asymmetric Higgsino dark matter.

    PubMed

    Blum, Kfir; Efrati, Aielet; Grossman, Yuval; Nir, Yosef; Riotto, Antonio

    2012-08-01

    In the supersymmetric framework, prior to the electroweak phase transition, the existence of a baryon asymmetry implies the existence of a Higgsino asymmetry. We investigate whether the Higgsino could be a viable asymmetric dark matter candidate. We find that this is indeed possible. Thus, supersymmetry can provide the observed dark matter abundance and, furthermore, relate it with the baryon asymmetry, in which case the puzzle of why the baryonic and dark matter mass densities are similar would be explained. To accomplish this task, two conditions are required. First, the gauginos, squarks, and sleptons must all be very heavy, such that the only electroweak-scale superpartners are the Higgsinos. With this spectrum, supersymmetry does not solve the fine-tuning problem. Second, the temperature of the electroweak phase transition must be low, in the (1-10) GeV range. This condition requires an extension of the minimal supersymmetric standard model. PMID:23006163

  2. Asymmetrically warped spacetimes

    SciTech Connect

    Csaki, C.

    2001-01-01

    We investigate spacetimes in which the speed of light along flat 4D sections varies over the extra dimensions due to different warp factors for the space and the time coordinates ('asymmetrically warped' spacetimes). The main property of such spaces is that while the induced metric is flat, implying Lorentz invariant particle physics on a brane, bulk gravitational effects will cause apparent violations of Lorentz invariance and of causality from the brane observer's point of view. An important experimentally verifiable consequence of this is that gravitational waves may travel with a speed different from the speed of light on the brane, and possibly even faster. We find the most general spacetimes of this sort, which are given by certain types of black hole spacetimes characterized by the m a s and the charge of the black hole. We show how to satisfy the junction conditions and analyze the properties of these space-times.

  3. Asymmetric twin Dark Matter

    NASA Astrophysics Data System (ADS)

    Farina, Marco

    2015-11-01

    We study a natural implementation of Asymmetric Dark Matter in Twin Higgs models. The mirroring of the Standard Model strong sector suggests that a twin baryon with mass around 5 GeV is a natural Dark Matter candidate once a twin baryon number asymmetry comparable to the SM asymmetry is generated. We explore twin baryon Dark Matter in two different scenarios, one with minimal content in the twin sector and one with a complete copy of the SM, including a light twin photon. The essential requirements for successful thermal history are presented, and in doing so we address some of the cosmological issues common to many Twin Higgs models. The required interactions we introduce predict signatures at direct detection experiments and at the LHC.

  4. Asymmetric Latent Carbocation Catalysis with Chiral Trityl Phosphate.

    PubMed

    Lv, Jian; Zhang, Qichao; Zhong, Xingren; Luo, Sanzhong

    2015-12-16

    Stable carbocations such as tritylium ions have been widely explored as organic Lewis acid catalysts and reagents in organic synthesis. However, achieving asymmetric carbocation catalysis remains elusive ever since they were first identified over one century ago. The challenges mainly come from their limited compatibility, scarcity of chiral carbocations, as well as the extremely low barrier to racemization of chiral carbenium ions. We reported here a latent concept for asymmetric carbocation catalysis. In this strategy, chiral trityl phosphate is employed as the carbocation precursor, which undergoes facile ionic dissociation upon mild external stimulation (e.g., acid, H-bonding, polar substrates) to form a catalytically active chiral ion pair for substrate activation and chiral induction. The latent strategy provides a solution for the long sought-after asymmetric carbocation catalysis as illustrated in three different enantioselective transformations. PMID:26594778

  5. Total synthesis of brazilin.

    PubMed

    Jung, Youngeun; Kim, Ikyon

    2015-02-01

    Described herein is a highly efficient total synthesis of brazilin from commercially available starting materials in 9 steps with 70% overall yield. Mitsunobu coupling followed by In(III)-catalyzed alkyne-aldehyde metathesis allowed for rapid construction of brazilin core skeleton in quantitative yield. Subsequent modulation of oxidation levels and acid-catalyzed cyclization led to the trimethyl ether of brazilin. Asymmetric dihydroxylation of the key intermediate was also demonstrated, which would permit asymmetric access to (+)-brazilin. PMID:25562504

  6. Familial aggregation of absolute pitch.

    PubMed

    Baharloo, S; Service, S K; Risch, N; Gitschier, J; Freimer, N B

    2000-09-01

    Absolute pitch (AP) is a behavioral trait that is defined as the ability to identify the pitch of tones in the absence of a reference pitch. AP is an ideal phenotype for investigation of gene and environment interactions in the development of complex human behaviors. Individuals who score exceptionally well on formalized auditory tests of pitch perception are designated as "AP-1." As described in this report, auditory testing of siblings of AP-1 probands and of a control sample indicates that AP-1 aggregates in families. The implications of this finding for the mapping of loci for AP-1 predisposition are discussed. PMID:10924408

  7. Synthesis and Stereochemical Assignment of Crypto-Optically Active (2) H6 -Neopentane.

    PubMed

    Masarwa, Ahmad; Gerbig, Dennis; Oskar, Liron; Loewenstein, Aharon; Reisenauer, Hans Peter; Lesot, Philippe; Schreiner, Peter R; Marek, Ilan

    2015-10-26

    The determination of the absolute configuration of chiral molecules is at the heart of asymmetric synthesis. Here we probe the spectroscopic limits for chiral discrimination with NMR spectroscopy in chiral aligned media and with vibrational circular dichroism spectroscopy of the sixfold-deuterated chiral neopentane. The study of this compound presents formidable challenges since its stereogenicity is only due to small mass differences. For this purpose, we selectively prepared both enantiomers of (2) H6 -1 through a concise synthesis utilizing multifunctional intermediates. While NMR spectroscopy in chiral aligned media could be used to characterize the precursors to (2) H6 -1, the final assignment could only be accomplished with VCD spectroscopy, despite the fleetingly small dichroic properties of 1. Both enantiomers were assigned by matching the VCD spectra with those computed with density functional theory. PMID:26480341

  8. Asymmetric MRI Magnet Design Using a Hybrid Numerical Method

    NASA Astrophysics Data System (ADS)

    Zhao, Huawei; Crozier, Stuart; Doddrell, David M.

    1999-12-01

    This paper describes a hybrid numerical method for the design of asymmetric magnetic resonance imaging magnet systems. The problem is formulated as a field synthesis and the desired current density on the surface of a cylinder is first calculated by solving a Fredholm equation of the first kind. Nonlinear optimization methods are then invoked to fit practical magnet coils to the desired current density. The field calculations are performed using a semi-analytical method. A new type of asymmetric magnet is proposed in this work. The asymmetric MRI magnet allows the diameter spherical imaging volume to be positioned close to one end of the magnet. The main advantages of making the magnet asymmetric include the potential to reduce the perception of claustrophobia for the patient, better access to the patient by attending physicians, and the potential for reduced peripheral nerve stimulation due to the gradient coil configuration. The results highlight that the method can be used to obtain an asymmetric MRI magnet structure and a very homogeneous magnetic field over the central imaging volume in clinical systems of approximately 1.2 m in length. Unshielded designs are the focus of this work. This method is flexible and may be applied to magnets of other geometries.

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

    NASA Astrophysics Data System (ADS)

    Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Rse, 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.

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

    PubMed

    Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Rse, 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

  11. Catalytic asymmetric nucleophilic openings of 3-substituted oxetanes.

    PubMed

    Wang, Zhaobin; Chen, Zhilong; Sun, Jianwei

    2014-08-28

    Asymmetric ring-opening of 3-substituted oxetanes provides rapid access to highly functionalized chiral building blocks. However, progress in this field is limited. Recently we developed a new catalytic system based on chiral Brnsted acids for this type of reaction and demonstrated the synthesis of a range of useful molecules under mild and operationally simple conditions. In this perspective, we describe the challenges, progress, and potential future efforts on this topic. PMID:24968137

  12. [Biomechanic of the asymmetrical headgear].

    PubMed

    Sander, F G

    1990-11-01

    The asymmetrical headgear is a very useful treatment device for the unilateral distalisation of molars or for the correction of an unilateral anchorage loss. 1. The dimension of the asymmetrical effect depends on the configuration of the outer bows. 2. The function of an asymmetrical face-bow can be increased or decreased by eccentric bendings. 3. According to the geometry at the outer-bows the force at the outer-bow is divided at a different percentage onto the molars. 4. While the forces increase the asymmetrical effect will decrease when the outer-bow is too flexible. 5. Attention has to be payed at each control-appointment to the distance of the longer outer-bow to the cheek. 6. The asymmetrical swivel face-bow did not produce a greater asymmetrical function than other asymmetrical headgears. The reason of this fact is, that only the geometry of the outer-bows is responsible for the unilateral distalisation. 7. The asymmetrical swivel face-bow as described above is advisable to use because eccentric bendings and less forces at the outer-bows will decrease, stop or even reverse the asymmetrical effect. 8. The side-effect of any asymmetrical face-bow is a lateral force-component. This force-component can cause a cross-bite at the molar which has to be more distalized. The molar which is not be moved by the asymmetrical face-bow will be moved buccally by this force-component. 9. The swivel face-bow according to Sander prevents the buccal movement of the molar which should not be moved. But the tendency to create a cross-bite for the molar which should be more distalized, increases. 10. The swivel face-bow according to Sander can be combined with all well-known extraoral tractions. 11. Equal forces at the outer-bows can be reached while using a cervical-pull neckstrap according to Sander. 12. The asymmetrical face-bow and the bite-jumping-appliance can be used simultaneously if the face-bow inserts directly into the attachments of the molar bands. PMID:2135592

  13. Metal rolling - Asymmetrical rolling process

    NASA Astrophysics Data System (ADS)

    Alexa, V.; Raţiu, S.; Kiss, I.

    2016-02-01

    The development of theory and practice related to the asymmetric longitudinal rolling process is based on the general theory of metalworking by pressure and symmetric rolling theory, to which a large number of scientists brought their contribution. The rolling of metal materials was a serious problem throughout history, either economically or technically, because the plating technologies enabled the consumption of raw materials (scarce and expensive) to be reduced, while improving the mechanical properties. Knowing the force parameters related to asymmetric rolling leads to the optimization of energy and raw material consumption. This paper presents data on symmetric rolling process, in order to comparatively highlight the particularities of the asymmetric process.

  14. Absolute Measurement of STIRAP Efficiency

    NASA Astrophysics Data System (ADS)

    Lu, Xiaoxu; Sun, Yuan; Allred, Claire; Metcalf, Harold

    2010-03-01

    Driving atoms from an initial to a final state of the same parity via an intermediate state of opposite parity is most efficiently done using STIRAPfootnotetextU. Gaubatz et al., J. Chem. Phys., 92, 5363 (1990)., because it doesn't populate the intermediate state. For optical transitions this requires appropriate pulses of light in the counter-intuitive order - first coupling the intermediate and final states. We populate Rydberg states of He (n = 26) in a beam of average velocity 1070 m/s by having them cross two laser beams in a tunable dc electric field of ˜100 V/cm. The ``red" light near λ= 796 nm connects the 3^3P states to the Rydberg states and the ``blue" beam connects the metastable 2^3S state atoms emitted by our source to their 3^3P states. By varying the relative position of these beams we can vary the order and overlap encountered by the atoms. We vary the dc field to sweep across several Stark states of the Rydberg manifold. We measure the absolute efficiency using a curved wavefront beam of λ= 1.083,m light to deflect residual 2^3S atoms out of the beam, and we measure their flux with and without the STIRAP beams. This uncontaminated measurement has high absolute accuracy. *Presently at Columbia Univ., 1027 Pupin Hall, New York, NY 10027

  15. Absolute Measurement of STIRAP Efficiency

    NASA Astrophysics Data System (ADS)

    Lu, Xiaoxu; Sun, Yuan; Allred, Claire; Metcalf, Harold

    2010-03-01

    Driving atoms from an initial to a final state of the same parity via an intermediate state of opposite parity is most efficiently done using STIRAPootnotetextU. Gaubatz et al., J. Chem. Phys., 92, 5363 (1990)., because it doesn't populate the intermediate state. For optical transitions this requires appropriate pulses of light in the counter-intuitive order - first coupling the intermediate and final states. We populate Rydberg states of He (n = 26) in a beam of average velocity 1070 m/s by having them cross two laser beams in a tunable dc electric field of ˜100 V/cm. The ``red" light near λ= 796 nm connects the 3^3P states to the Rydberg states and the ``blue" beam connects the metastable 2^3S state atoms emitted by our source to their 3^3P states. By varying the relative position of these beams we can vary the order and overlap encountered by the atoms. We vary the dc field to sweep across several Stark states of the Rydberg manifold. We measure the absolute efficiency using a curved wavefront beam of λ= 1.083,m light to deflect residual 2^3S atoms out of the beam, and we measure their flux with and without the STIRAP beams. This uncontaminated measurement has high absolute accuracy.

  16. Absolute pitch--electrophysiological evidence.

    PubMed

    Barnea, A; Granot, R; Pratt, H

    1994-02-01

    People who have the ability to label or to produce notes without any reference are considered to possess Absolute Pitch (AP). Others, who need a reference in order to identify the notes, possess Relative Pitch (RP). The AP ability is assumed to reflect a unique, language-like representation of non-lexical musical notes in memory. The purpose of this study was to examine this assumption by comparing Event Related Potentials (ERP) of musicians with and without AP, to lexical and non-lexical representation of musical material. Subjects were eighteen young adult musicians. Seven were AP and eleven RP. Auditory stimuli, presented through earphones, were piano notes (non-lexical) or a voice saying the note's name (lexical). Visual stimuli, presented on a computer display were note symbols (non-lexical) or letters (lexical). Subjects performed a number of tasks, combining the two modalities (visual and auditory) and stimulus types (lexical and non-lexical), and reaction times (RT), performance accuracy and evoked potentials were recorded. The tasks forced the subjects to transfer mental representations of musical material from one mode to another. Our most important findings were the differences, between groups, in the scalp distribution of P300 amplitudes. We conclude that absolute pitch possessors use the same internal language as relative pitch possessors, when possible, but the distribution of the underlying brain activity is different between AP and RP subjects. PMID:8206802

  17. Absolute pitch: a case study.

    PubMed

    Vernon, P E

    1977-11-01

    The auditory skill known as 'absolute pitch' is discussed, and it is shown that this differs greatly in accuracy of identification or reproduction of musical tones from ordinary discrimination of 'tonal height' which is to some extent trainable. The present writer possessed absolute pitch for almost any tone or chord over the normal musical range, from about the age of 17 to 52. He then started to hear all music one semitone too high, and now at the age of 71 it is heard a full tone above the true pitch. Tests were carried out under controlled conditions, in which 68 to 95 per cent of notes were identified as one semitone or one tone higher than they should be. Changes with ageing seem more likely to occur in the elasticity of the basilar membrane mechanisms than in the long-term memory which is used for aural analysis of complex sounds. Thus this experience supports the view that some resolution of complex sounds takes place at the peripheral sense organ, and this provides information which can be incorrect, for interpretation by the cortical centres. PMID:588883

  18. Asymmetric bifurcated halogen bonds.

    PubMed

    Novk, 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

  19. 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

  20. Asymmetric inheritance of cytoophidia in Schizosaccharomyces pombe

    PubMed Central

    Zhang, Jing; Hulme, Lydia; Liu, Ji-Long

    2014-01-01

    ABSTRACT A general view is that Schizosaccharomyces pombe undergoes symmetric cell division with two daughter cells inheriting equal shares of the content from the mother cell. Here we show that CTP synthase, a metabolic enzyme responsible for the de novo synthesis of the nucleotide CTP, can form filamentous cytoophidia in the cytoplasm and nucleus of S. pombe cells. Surprisingly, we observe that both cytoplasmic and nuclear cytoophidia are asymmetrically inherited during cell division. Our time-lapse studies suggest that cytoophidia are dynamic. Once the mother cell divides, the cytoplasmic and nuclear cytoophidia independently partition into one of the two daughter cells. Although the two daughter cells differ from one another morphologically, they possess similar chances of inheriting the cytoplasmic cytoophidium from the mother cell, suggesting that the partition of cytoophidium is a stochastic process. Our findings on asymmetric inheritance of cytoophidia in S. pombe offer an exciting opportunity to study the inheritance of metabolic enzymes in a well-studied model system. PMID:25361577

  1. Catalytic asymmetric umpolung reactions of imines

    NASA Astrophysics Data System (ADS)

    Wu, Yongwei; Hu, Lin; Li, Zhe; Deng, Li

    2015-07-01

    The carbon-nitrogen double bonds in imines are fundamentally important functional groups in organic chemistry. This is largely due to the fact that imines act as electrophiles towards carbon nucleophiles in reactions that form carbon-carbon bonds, thereby serving as one of the most widely used precursors for the formation of amines in both synthetic and biosynthetic settings. If the carbon atom of the imine could be rendered electron-rich, the imine could react as a nucleophile instead of as an electrophile. Such a reversal in the electronic characteristics of the imine functionality would facilitate the development of new chemical transformations that convert imines into amines via carbon-carbon bond-forming reactions with carbon electrophiles, thereby creating new opportunities for the efficient synthesis of amines. The development of asymmetric umpolung reactions of imines (in which the imines act as nucleophiles) remains uncharted territory, in spite of the far-reaching impact such reactions would have in organic synthesis. Here we report the discovery and development of new chiral phase-transfer catalysts that promote the highly efficient asymmetric umpolung reactions of imines with the carbon electrophile enals. These catalysts mediate the deprotonation of imines and direct the 2-azaallyl anions thus formed to react with enals in a highly chemoselective, regioselective, diastereoselective and enantioselective fashion. The reaction tolerates a broad range of imines and enals, and can be carried out in high yield with as little as 0.01 mole per cent catalyst with a moisture- and air-tolerant operational protocol. These umpolung reactions provide a conceptually new and practical approach to chiral amino compounds.

  2. Catalytic asymmetric umpolung reactions of imines.

    PubMed

    Wu, Yongwei; Hu, Lin; Li, Zhe; Deng, Li

    2015-07-23

    The carbon-nitrogen double bonds in imines are fundamentally important functional groups in organic chemistry. This is largely due to the fact that imines act as electrophiles towards carbon nucleophiles in reactions that form carbon-carbon bonds, thereby serving as one of the most widely used precursors for the formation of amines in both synthetic and biosynthetic settings. If the carbon atom of the imine could be rendered electron-rich, the imine could react as a nucleophile instead of as an electrophile. Such a reversal in the electronic characteristics of the imine functionality would facilitate the development of new chemical transformations that convert imines into amines via carbon-carbon bond-forming reactions with carbon electrophiles, thereby creating new opportunities for the efficient synthesis of amines. The development of asymmetric umpolung reactions of imines (in which the imines act as nucleophiles) remains uncharted territory, in spite of the far-reaching impact such reactions would have in organic synthesis. Here we report the discovery and development of new chiral phase-transfer catalysts that promote the highly efficient asymmetric umpolung reactions of imines with the carbon electrophile enals. These catalysts mediate the deprotonation of imines and direct the 2-azaallyl anions thus formed to react with enals in a highly chemoselective, regioselective, diastereoselective and enantioselective fashion. The reaction tolerates a broad range of imines and enals, and can be carried out in high yield with as little as 0.01 mole per cent catalyst with a moisture- and air-tolerant operational protocol. These umpolung reactions provide a conceptually new and practical approach to chiral amino compounds. PMID:26201597

  3. Catalytic Asymmetric Umpolung Reactions of Imines

    PubMed Central

    Wu, Yongwei; Hu, Lin; Li, Zhe; Deng, Li

    2015-01-01

    Imines, carbon-nitrogen double bonds, are fundamentally important functional groups in organic chemistry. This is largely due to the fact that imines act as electrophiles in CC bond forming reactions towards carbon nucleophiles, thereby serving one of the most widely used precursors for the formation of amines in both synthetic and biosynthetic settings.15 If the carbon atom of the imine could be rendered electron-rich, the imine could react as a nucleophile instead of as an electrophile. Such a reversal in the electronic characteristics of the imine functionality would facilitate the development of new chemical transformations that convert imines into amines via CC bond forming reactions with carbon electrophiles, thereby creating new opportunities for the efficient synthesis of amines. The development of asymmetric umpolung reactions of imines remains an uncharted ground, in spite of the far-reaching impact of such reactions in organic synthesis. Here we report the discovery and development of new chiral phase transfer catalysts that promote the highly efficient asymmetric umpolung reactions of imines and enals. These catalysts mediate the deprotonation of imines and direct the 2-azaallylanions thus formed to react in a highly chemoselective, regioselective, diastereoselective and enantioselective fashion with enals. The reaction tolerates a broad range of imines and enals, and can be carried out in high yield with as little as 0.01 mol % catalyst with a moisture and air-tolerant operational protocol. These umpolung reactions provide a conceptually new and practical approach towards chiral amino compounds. PMID:26201597

  4. Asymmetric Hybrid Nanoparticles

    SciTech Connect

    Chumanov, George

    2015-11-05

    Hybrid Nanoparticles (AHNs) are rationally-designed multifunctional nanostructures and novel building blocks for the next generation of advanced materials and devices. Nanoscale materials attract considerable interest because of their unusual properties and potential for practical applications. Most of the activity in this field is focused on the synthesis of homogeneous nanoparticles from metals, metal oxides, semiconductors, and polymers. It is well recognized that properties of nanoparticles can be further enhanced if they are made as hybrid structures. This program is concerned with the synthesis, characterization, and application of such hybrid structures termed AHNs. AHNs are composed of a homogeneous core and several caps of different materials deposited on its surface (Fig. 1). Combined properties of the core and the caps as well as new properties that arise from core-cap and cap-cap interactions render AHNs multifunctional. In addition, specific chemical reactivity of the caps enables directional self-assembly of AHNs into complex architectures that are not possible with only spherical nanoparticles.

  5. Development of asymmetric reactions catalyzed by chiral organotin-alkoxide reagents.

    PubMed

    Yanagisawa, Akira; Yoshida, Kazuhiro

    2013-02-01

    Asymmetric catalysis under almost-neutral reaction conditions is key for the efficient synthesis of optically active polar molecules. We have developed catalytic enantioselective reactions of acyclic or cyclic alkenyl esters by using an (S)-BINOL-derived chiral tin-dibromide reagent that possesses a bulky aryl group at the 3 or 3' position as the chiral pre-catalyst in the presence of a sodium alkoxide and an alcohol, in which a chiral tin alkoxide bromide is generated in situ and recycled with the assistance of an alcohol. In this Personal Account, we describe three types of asymmetric transformation that proceed through a chiral tin enolate: 1) The asymmetric aldol reaction of alkenyl esters or unsaturated lactones with aldehydes or isatins; 2) the asymmetric three-component Mannich-type reaction of alkenyl esters and related cycloaddition reactions; and 3) the asymmetric N-nitroso aldol reaction of unsaturated lactones with nitrosoarenes. PMID:23424074

  6. Asymmetric alkynylation of seven-membered cyclic imines by combining chiral phosphoric acids and Ag(I) catalysts: synthesis of 11-substituted-10,11-dihydrodibenzo[b,f][1,4]oxazepine derivatives.

    PubMed

    Ren, Yuan-Yuan; Wang, You-Qing; Liu, Shuang

    2014-12-01

    Asymmetric alkynylation of seven-membered cyclic imine dibenzo[b,f][1,4]oxazepines is successfully achieved by combining chiral phosphoric acid and Ag(I) catalysts. Various arylacetylenes, conjugated enynes, and terminal 1,3-diynes are good substrates for this reaction, and aliphatic hexyne is also a suitable donor at elevated temperature. Optimization of this approach has provided a facile method to synthesize optically active 11-substituted-10,11-dihydrodibenzo[b,f][1,4]oxazepine derivatives containing a carbon-carbon triple bond with 63-99% ee. Subsequent transformations of the carbon-carbon triple bond for the heterocyclic products have been disclosed. PMID:25375832

  7. Experiences with modern absolute instruments

    NASA Astrophysics Data System (ADS)

    Lauridsen, E. Kring

    1990-02-01

    The author has worked with geomagnetic instruments for more than 40 years and had arrived at the attitude that it was hardly worth while to devote one's time to fractions of a nT because there were so many sources of error which came into play when you approached this accuracy. Lately, the author has changed his mind. It seems that modern instruments are definitely better than the classical instruments, and it is now possible to measure, even absolutely, with an accuracy of less than 1 nT. A historical account is given of when and why a shift was made from classical to electronic instruments in our observatories in Denmark and Greenland.

  8. Absolute configuration of xerophenone A

    PubMed Central

    Fun, Hoong-Kun; Tantapakul, Cholpisut; Laphookhieo, Surat; Boonnak, Nawong; Chantrapromma, Suchada

    2012-01-01

    The title compound, C33H42O5, known as xerophenone A {systematic name: (1R,3R,4R,6S,8E,10R)-10-hydroxy-8-[hydroxy(phenyl)methylene]-4-methyl-1,6-bis(3-methylbut-2-en-1-yl)-3-(3-methylbut-3-en-1-yl)-11-oxatricyclo[4.3.1.14,10]undecane-7,9-dione} is a naturally occurring rearranged benzophenone compound which was isolated from the twigs of Garcinia propinqua. The absolute configuration was determined by refining the Flack parameter to 0.18?(16). The absolute configurations at positions 1, 3, 4, 6 and 10 of the xerophenone A are R, R, R, S and R. In the molecule, the cyclohexane-1,3-dione, tetrahydro-2H-pyran and tetrahydrofuran rings adopt twisted boat, standard chair and envelope conformations, respectively. The 3-methylbut-3-en-1-yl substituent is disordered over two sets of sites in a 0.771?(11):0.229?(11) ratio. An intramolecular OH?O hydrogen bond generates an S(6) ring motif. In the crystal, molecules are linked by OH?O and weak CH?O interactions into a chain along the a axis. A very weak CH?? interaction and C?O short contact [2.989?(2)?] are also present. PMID:22590330

  9. Uncertainty of absolute gravity measurements

    NASA Astrophysics Data System (ADS)

    van Camp, Michel; Williams, Simon D. P.; Francis, Olivier

    2005-05-01

    A total of 96 absolute gravity (AG) measurements at the Membach station and 221 at the Proudman Oceanographic Laboratory (POL) is analyzed for noise content. The lengths of the series were around 10 years (POL) and 8 years (Membach). First the noise at frequencies lower than 1 cpd is studied. This noise consists in setup-dependent offsets and geophysical colored sources. The setup white noise is estimated using continuous relative superconducting gravity (SG) measurements at Membach. The colored environmental noise affecting both AG and SG is estimated using the maximum likelihood estimation technique to fit two types of stochastic models to the SG time series, power law noise, and first-order Gauss Markov (FOGM) noise. We estimate the noise amplitudes of a white noise process plus power law model while simultaneously solving for the spectral index and the noise amplitudes of a white noise process plus FOGM noise model is also estimated. The gravity rate of change and the associated uncertainties as a function of the noise structure are then computed. At frequencies higher than 1 cpd, a time-varying white noise component usually dominates AG time series. Finally, the POL and Membach experiments are applied to estimate the uncertainties for AG campaigns repeated once or twice a year to monitor crustal deformation. Such repeated AG measurements should allow one to constrain gravity rate of change with an uncertainty of 1 nm s-2 yr-1 (or 0.5 mm yr-1) after 14 or 24 years, depending on the noise model. Therefore long-term measurements using absolute gravimeters are appropriate for monitoring slow vertical tectonic deformation.

  10. Asymmetric AgPd-AuNR heterostructure with enhanced photothermal performance and SERS activity

    NASA Astrophysics Data System (ADS)

    Zhang, Han; Liu, Zeke; Kang, Xiaolin; Guo, Jun; Ma, Wanli; Cheng, Si

    2016-01-01

    Most as-reported nanostructures through galvanic replacement reactions are still symmetric hollow structures, until now. Asymmetric structures fabricated through a galvanic replacement reaction have been rarely reported. However, asymmetric heterostructures can generally lead to new intriguing properties through asymmetric synergistic coupling. Here, we report a simple synthesis of an asymmetric one-ended AgPd bimetal on Au nanorods (AuNR) by combining a galvanic replacement reaction with an Ostwald ripening process. The morphological evolution from a nanodumbbell to a dandelion structure is thoroughly investigated. The unique asymmetric AgPd-AuNR heterostructures possess the required plasmonic performance and avoid strong damping caused by the poor plasmonic metal Pd, resulting in a superior photothermal heating performance and enhanced SERS sensitivity for in situ monitoring of a catalytic reaction compared with the symmetric counterparts.Most as-reported nanostructures through galvanic replacement reactions are still symmetric hollow structures, until now. Asymmetric structures fabricated through a galvanic replacement reaction have been rarely reported. However, asymmetric heterostructures can generally lead to new intriguing properties through asymmetric synergistic coupling. Here, we report a simple synthesis of an asymmetric one-ended AgPd bimetal on Au nanorods (AuNR) by combining a galvanic replacement reaction with an Ostwald ripening process. The morphological evolution from a nanodumbbell to a dandelion structure is thoroughly investigated. The unique asymmetric AgPd-AuNR heterostructures possess the required plasmonic performance and avoid strong damping caused by the poor plasmonic metal Pd, resulting in a superior photothermal heating performance and enhanced SERS sensitivity for in situ monitoring of a catalytic reaction compared with the symmetric counterparts. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07333b

  11. A Stereoselective Synthesis of (+)-Herboxidiene/GEX1A

    PubMed Central

    Ghosh, Arun K.; Li, Jianfeng

    2010-01-01

    A stereoselective synthesis of (+)-herboxidiene is described. The convergent synthesis utilized a Suzuki cross-coupling reaction to assemble the key segments. The synthesis of the functionalized tetrahydropyran ring utilized an Achmatowicz reaction as the key step. The synthesis of the C10-C19 segment was accomplished using Brown's crotylboration, asymmetric alkylation, and a stereoselective allylic chlorination reaction. PMID:21126066

  12. Robot arm with positional absolute encoded joints

    NASA Astrophysics Data System (ADS)

    Yeung, S. K.; Baribeau, C.; Pharand, A.; Petriu, E.

    An absolute position measurement method used for control of an experimental three-joint robot arm is based on pseudo random binary sequence properties. A scanning technique is used to solve the code reading ambiguity problems. An 8-bit absolute position encoder was implemented in each robot joint and tested. The absolute encoder is used in conjunction with a conventional incremental encoder mounted on the input motor shaft. This solution provides the advantages of both position measuring techniques, the absolute encoder's noise immunity, and the incremental encoder's very high resolution. The control algorithm and hardware implementation are discussed.

  13. Absolute negative mobility of interacting Brownian particles

    NASA Astrophysics Data System (ADS)

    Ou, Ya-li; Hu, Cai-tian; Wu, Jian-chun; Ai, Bao-quan

    2015-12-01

    Transport of interacting Brownian particles in a periodic potential is investigated in the presence of an ac force and a dc force. From Brownian dynamic simulations, we find that both the interaction between particles and the thermal fluctuations play key roles in the absolute negative mobility (the particle noisily moves backwards against a small constant bias). When no the interaction acts, there is only one region where the absolute negative mobility occurs. In the presence of the interaction, the absolute negative mobility may appear in multiple regions. The weak interaction can be helpful for the absolute negative mobility, while the strong interaction has a destructive impact on it.

  14. Asymmetric counterpropagating fronts without flow

    NASA Astrophysics Data System (ADS)

    Andrade-Silva, I.; Clerc, M. G.; Odent, V.

    2015-06-01

    Out-of-equilibrium systems exhibit domain walls between different states. These walls, depending on the type of connected states, can display rich spatiotemporal dynamics. In this Rapid Communication, we investigate the asymmetrical counterpropagation of fronts in an in-plane-switching cell filled with a nematic liquid crystal. Experimentally, we characterize the different front shapes and propagation speeds. These fronts present dissimilar elastic deformations that are responsible for their asymmetric speeds. Theoretically, using a phenomenological model, we describe the observed dynamics with fair agreement.

  15. Synthesis of (-)-epibatidine.

    PubMed

    Evans, D A; Scheidt, K A; Downey, C W

    2001-09-20

    The synthesis of (-)-epibatidine has been accomplished utilizing a highly exo-selective asymmetric hetero Diels-Alder reaction. The key steps employed to transform the resulting bicycle into the natural product include a fluoride-promoted fragmentation and a Hofmann rearrangement. Reaction: see text. PMID:11554830

  16. Absolute Income, Relative Income, and Happiness

    ERIC Educational Resources Information Center

    Ball, Richard; Chernova, Kateryna

    2008-01-01

    This paper uses data from the World Values Survey to investigate how an individual's self-reported happiness is related to (i) the level of her income in absolute terms, and (ii) the level of her income relative to other people in her country. The main findings are that (i) both absolute and relative income are positively and significantly

  17. Inequalities, Absolute Value, and Logical Connectives.

    ERIC Educational Resources Information Center

    Parish, Charles R.

    1992-01-01

    Presents an approach to the concept of absolute value that alleviates students' problems with the traditional definition and the use of logical connectives in solving related problems. Uses a model that maps numbers from a horizontal number line to a vertical ray originating from the origin. Provides examples solving absolute value equations and

  18. Investigating Absolute Value: A Real World Application

    ERIC Educational Resources Information Center

    Kidd, Margaret; Pagni, David

    2009-01-01

    Making connections between various representations is important in mathematics. In this article, the authors discuss the numeric, algebraic, and graphical representations of sums of absolute values of linear functions. The initial explanations are accessible to all students who have experience graphing and who understand that absolute value simply…

  19. Absolute optical metrology : nanometers to kilometers

    NASA Technical Reports Server (NTRS)

    Dubovitsky, Serge; Lay, O. P.; Peters, R. D.; Liebe, C. C.

    2005-01-01

    We provide and overview of the developments in the field of high-accuracy absolute optical metrology with emphasis on space-based applications. Specific work on the Modulation Sideband Technology for Absolute Ranging (MSTAR) sensor is described along with novel applications of the sensor.

  20. 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

  1. Estimating the absolute wealth of households

    PubMed Central

    Gerkey, Drew; Hadley, Craig

    2015-01-01

    Abstract Objective To estimate the absolute wealth of households using data from demographic and health surveys. Methods We developed a new metric, the absolute wealth estimate, based on the rank of each surveyed household according to its material assets and the assumed shape of the distribution of wealth among surveyed households. Using data from 156 demographic and health surveys in 66 countries, we calculated absolute wealth estimates for households. We validated the method by comparing the proportion of households defined as poor using our estimates with published World Bank poverty headcounts. We also compared the accuracy of absolute versus relative wealth estimates for the prediction of anthropometric measures. Findings The median absolute wealth estimates of 1?403?186 households were 2056 international dollars per capita (interquartile range: 7236103). The proportion of poor households based on absolute wealth estimates were strongly correlated with World Bank estimates of populations living on less than 2.00 United States dollars per capita per day (R2?=?0.84). Absolute wealth estimates were better predictors of anthropometric measures than relative wealth indexes. Conclusion Absolute wealth estimates provide new opportunities for comparative research to assess the effects of economic resources on health and human capital, as well as the long-term health consequences of economic change and inequality. PMID:26170506

  2. Quantum nonequilibrium equalities with absolute irreversibility

    NASA Astrophysics Data System (ADS)

    Funo, Ken; Murashita, Yto; Ueda, Masahito

    2015-07-01

    We derive quantum nonequilibrium equalities in absolutely irreversible processes. Here by absolute irreversibility we mean that in the backward process the density matrix does not return to the subspace spanned by those eigenvectors that have nonzero weight in the initial density matrix. Since the initial state of a memory and the postmeasurement state of the system are usually restricted to a subspace, absolute irreversibility occurs during the measurement and feedback processes. An additional entropy produced in absolutely irreversible processes needs to be taken into account to derive nonequilibrium equalities. We discuss a model of a feedback control on a qubit system to illustrate the obtained equalities. By introducing N heat baths each composed of a qubit and letting them interact with the system, we show how the entropy reduction via feedback control can be converted into work. An explicit form of extractable work in the presence of absolute irreversibility is given.

  3. Substrate-Controlled Asymmetric Total Syntheses of Microcladallenes?A, B, and C Based on the Proposed Structures.

    PubMed

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

    2015-11-01

    Substrate-controlled asymmetric total syntheses of (+)-microcladallenes?A, B, and C have been accomplished based on the proposed structures. The syntheses of microcladallenes?A and B confirmed the structures and absolute configurations of both natural products. However, the synthesis of microcladallene?C, which includes seven stereogenic centers and an (R)-bromoallene in its compact C15 framework, brought the realization that its proposed structure must be revised. The introduction of C12-bromine into these natural products with retention of configuration relied on TiBr4 -mediated nucleophile-assisting leaving group brominations, the stereochemical outcome of which could be attributed, at least in part, to an oxonium or halonium ion formation-fragmentation sequence through intricate neighboring group participation. In addition, the pivotal ?-oriented vicinal cis-dichloride function in microcladallene?C was elaborated through a novel tandem Cl2 -induced electrophilic cyclization/imidate chlorination process. The positive rotations of these natural products with an (R)-bromoallene constitute exceptions to Lowe's rule for reasons yet to be determined. PMID:26376617

  4. Asymmetrical Switch Costs in Children

    ERIC Educational Resources Information Center

    Ellefson, Michelle R.; Shapiron, Laura R.; Chater, Nick

    2006-01-01

    Switching between tasks produces decreases in performance as compared to repeating the same task. Asymmetrical switch costs occur when switching between two tasks of unequal difficulty. This asymmetry occurs because the cost is greater when switching to the less difficult task than when switching to the more difficult task. Various theories about

  5. 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.

  6. Absolute quantitation of protein posttranslational modification isoform.

    PubMed

    Yang, Zhu; Li, Ning

    2015-01-01

    Mass spectrometry has been widely applied in characterization and quantification of proteins from complex biological samples. Because the numbers of absolute amounts of proteins are needed in construction of mathematical models for molecular systems of various biological phenotypes and phenomena, a number of quantitative proteomic methods have been adopted to measure absolute quantities of proteins using mass spectrometry. The liquid chromatography-tandem mass spectrometry (LC-MS/MS) coupled with internal peptide standards, i.e., the stable isotope-coded peptide dilution series, which was originated from the field of analytical chemistry, becomes a widely applied method in absolute quantitative proteomics research. This approach provides more and more absolute protein quantitation results of high confidence. As quantitative study of posttranslational modification (PTM) that modulates the biological activity of proteins is crucial for biological science and each isoform may contribute a unique biological function, degradation, and/or subcellular location, the absolute quantitation of protein PTM isoforms has become more relevant to its biological significance. In order to obtain the absolute cellular amount of a PTM isoform of a protein accurately, impacts of protein fractionation, protein enrichment, and proteolytic digestion yield should be taken into consideration and those effects before differentially stable isotope-coded PTM peptide standards are spiked into sample peptides have to be corrected. Assisted with stable isotope-labeled peptide standards, the absolute quantitation of isoforms of posttranslationally modified protein (AQUIP) method takes all these factors into account and determines the absolute amount of a protein PTM isoform from the absolute amount of the protein of interest and the PTM occupancy at the site of the protein. The absolute amount of the protein of interest is inferred by quantifying both the absolute amounts of a few PTM-site-independent peptides in the total cellular protein and their peptide yields. The PTM occupancy determination is achieved by measuring the absolute amounts of both PTM and non-PTM peptides from the highly purified protein sample expressed in transgenic organisms or directly isolated from an organism using affinity purification. The absolute amount of each PTM isoform in the total cellular protein extract is finally calculated from these two variables. Following this approach, the ion intensities given by mass spectrometers are used to calculated the peptide amounts, from which the amounts of protein isoforms are then deduced. In this chapter, we describe the principles underlying the experimental design and procedures used in AQUIP method. This quantitation method basically employs stable isotope-labeled peptide standards and affinity purification from a tagged recombinant protein of interest. Other quantitation strategies and purification techniques related to this method are also discussed. PMID:25930697

  7. Asymmetric sequential Au(i)/chiral tertiary amine catalysis: an enone-formation/cyanosilylation sequence to synthesize optically active 3-alkenyloxindoles from diazooxindoles.

    PubMed

    Zhao, Yu-Lei; Cao, Zhong-Yan; Zeng, Xing-Ping; Shi, Jia-Meng; Yu, Yi-Hua; Zhou, Jian

    2016-03-11

    An unprecedented sequential gold-catalyzed enone-formation and bifunctional tertiary amine mediated asymmetric cyanosilylation reaction is developed, allowing the highly enantioselective synthesis of 3-alkenyloxindoles from diazooxindoles, furans and trimethylsilyl cyanide (TMSCN). PMID:26878106

  8. Trienamine catalyzed asymmetric synthesis and biological investigation of a cytochalasin B-inspired compound collection† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5ob02272j Click here for additional data file.

    PubMed Central

    Sellstedt, Magnus; Schwalfenberg, Melanie; Ziegler, Slava; Antonchick, Andrey P.

    2016-01-01

    Due to their enhanced metabolic needs many cancers need a sufficient supply of glucose, and novel inhibitors of glucose import are in high demand. Cytochalasin B (CB) is a potent natural glucose import inhibitor which also impairs the actin cytoskeleton leading to undesired toxicity. With a view to identifying selective glucose import inhibitors we have developed an enantioselective trienamine catalyzed synthesis of a CB-inspired compound collection. Biological analysis revealed that indeed actin impairment can be distinguished from glucose import inhibition and led to the identification of the first selective glucose import inhibitor based on the basic structural architecture of cytochalasin B. PMID:26606903

  9. 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.

  10. Absolute Configuration Assignment of a Paraconic Acid Derivative via Vibrational Circular Dichroism Spectroscopy and Density Functional Theory Calculation.

    PubMed

    Meninno, Sara; Rizzo, Paola; Abbate, Sergio; Longhi, Giovanna; Mazzeo, Giuseppe; Monaco, Guglielmo; Lattanzi, Alessandra; Zanasi, Riccardo

    2016-02-01

    Density functional theory calculation of the vibrational circular dichroism spectrum was used to assign the absolute configuration of an all-carbon quaternary ?-stereocenter of a ?-butyrolactone recently synthesized through an asymmetric organocatalytic tandem aldol/lactonization sequence. Comparison with the experimental spectrum is satisfactory, on account of the fact that spectroscopic features are weak due to the presence of multiple conformers. As a result, the (R) absolute configuration was assigned to the (+) optical isomer. Chirality 28:110-115, 2016. 2015 Wiley Periodicals, Inc. PMID:26634798

  11. Asymmetric 1,4-bis(ethynyl)bicyclo[2.2.2]octane rotators via monocarbinol functionalization. Ready access to polyrotors

    PubMed Central

    2015-01-01

    Summary Asymmetric rotators with a 1,4-bis(ethynyl)bicyclo[2.2.2]octane (BCO) core are needed for engineering crystalline arrays of functional molecular rotors. Their synthesis uses carbinol, 2-methyl-3-butyn-2-ol, as a protecting group because of its polar character and its ability to sustain orthogonal functionalization with the further advantage of being readily removed. The synthesis in good yields of unprecedented asymmetric rotors and polyrotors demonstrates the efficiency of this strategy. PMID:26664606

  12. 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.

  13. 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

  14. Miniature high-throughput chemosensing of yield, ee, and absolute configuration from crude reaction mixtures

    PubMed Central

    Bentley, Keith W.; Zhang, Peng; Wolf, Christian

    2016-01-01

    High-throughput experimentation (HTE) has emerged as a widely used technology that accelerates discovery and optimization processes with parallel small-scale reaction setups. A high-throughput screening (HTS) method capable of comprehensive analysis of crude asymmetric reaction mixtures (eliminating product derivatization or isolation) would provide transformative impact by matching the pace of HTE. We report how spontaneous in situ construction of stereodynamic metal probes from readily available, inexpensive starting materials can be applied to chiroptical chemosensing of the total amount, enantiomeric excess (ee), and absolute configuration of a wide variety of amines, diamines, amino alcohols, amino acids, carboxylic acids, α-hydroxy acids, and diols. This advance and HTS potential are highlighted with the analysis of 1 mg of crude reaction mixtures of a catalytic asymmetric reaction. This operationally simple assay uses a robust mix-and-measure protocol, is amenable to microscale platforms and automation, and provides critical time efficiency and sustainability advantages over traditional serial methods. PMID:26933684

  15. Nonequilibrium equalities in absolutely irreversible processes

    NASA Astrophysics Data System (ADS)

    Murashita, Yuto; Funo, Ken; Ueda, Masahito

    2015-03-01

    Nonequilibrium equalities have attracted considerable attention in the context of statistical mechanics and information thermodynamics. Integral nonequilibrium equalities reveal an ensemble property of the entropy production ? as = 1 . Although nonequilibrium equalities apply to rather general nonequilibrium situations, they break down in absolutely irreversible processes, where the forward-path probability vanishes and the entropy production diverges. We identify the mathematical origins of this inapplicability as the singularity of probability measure. As a result, we generalize conventional integral nonequilibrium equalities to absolutely irreversible processes as = 1 -?S , where ?S is the probability of the singular part defined based on Lebesgue's decomposition theorem. The acquired equality contains two physical quantities related to irreversibility: ? characterizing ordinary irreversibility and ?S describing absolute irreversibility. An inequality derived from the obtained equality demonstrates the absolute irreversibility leads to the fundamental lower bound on the entropy production. We demonstrate the validity of the obtained equality for a simple model.

  16. Absolute magnitudes of trans-neptunian objects

    NASA Astrophysics Data System (ADS)

    Duffard, R.; Alvarez-candal, A.; Pinilla-Alonso, N.; Ortiz, J. L.; Morales, N.; Santos-Sanz, P.; Thirouin, A.

    2015-10-01

    Accurate measurements of diameters of trans- Neptunian objects are extremely complicated to obtain. Radiomatric techniques applied to thermal measurements can provide good results, but precise absolute magnitudes are needed to constrain diameters and albedos. Our objective is to measure accurate absolute magnitudes for a sample of trans- Neptunian objects, many of which have been observed, and modelled, by the "TNOs are cool" team, one of Herschel Space Observatory key projects grantes with ~ 400 hours of observing time. We observed 56 objects in filters V and R, if possible. These data, along with data available in the literature, was used to obtain phase curves and to measure absolute magnitudes by assuming a linear trend of the phase curves and considering magnitude variability due to rotational light-curve. In total we obtained 234 new magnitudes for the 56 objects, 6 of them with no reported previous measurements. Including the data from the literature we report a total of 109 absolute magnitudes.

  17. 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)

  18. Asymmetric information and macroeconomic dynamics

    NASA Astrophysics Data System (ADS)

    Hawkins, Raymond J.; Aoki, Masanao; Roy Frieden, B.

    2010-09-01

    We show how macroeconomic dynamics can be derived from asymmetric information. As an illustration of the utility of this approach we derive the equilibrium density, non-equilibrium densities and the equation of motion for the response to a demand shock for productivity in a simple economy. Novel consequences of this approach include a natural incorporation of time dependence into macroeconomics and a common information-theoretic basis for economics and other fields seeking to link micro-dynamics and macro-observables.

  19. Organocatalytic and enantioselective Michael reaction between ?-nitroesters and nitroalkenes. Syn/anti-selectivity control using catalysts with the same absolute backbone chirality

    PubMed Central

    Martnez, Jose I; Uria, Uxue; Muiz, Maria; Reyes, Efram

    2015-01-01

    Summary The asymmetric and catalytic Michael reaction between ?-nitroesters and nitroalkenes has been studied in the presence of two bifunctional catalysts both containing the same absolute chirality at the carbon backbone. The reaction performed in similar conditions allows us to control the syn or anti selectivity of the Michael adduct obtaining good yields and high enantiocontrol in all cases. PMID:26734103

  20. Asymmetric Wettability Directs Leidenfrost Droplets

    SciTech Connect

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

    2014-01-01

    Leidenfrost phenomena on nano- and microstructured surfaces are of great importance for increasing control over heat transfer in high power density systems utilizing boiling phenomena. They also provide an elegant means to direct droplet motion in a variety of recently emerging fluidic systems. Here, we report the fabrication and characterization of tilted nanopillar arrays (TNPAs) that exhibit directional Leidenfrost water droplets under dynamic conditions, namely on impact with Weber numbers 40 at T 325 C. The batch fabrication of the TNPAs was achieved by glancing-angle anisotropic reactive ion etching of a thermally dewet platinum mask, with mean pillar diameters of 100 nm and heights of 200-500 nm. In contrast to previously implemented macro- and microscopic Leidenfrost ratchets, our TNPAs induce no preferential directional movement of Leidenfrost droplets under conditions approaching steady-state film boiling, suggesting that the observed droplet directionality is not a result of asymmetric vapor flow. Using high-speed imaging, phase diagrams were constructed for the boiling behavior upon impact for droplets falling onto TNPAs, straight nanopillar arrays, and smooth silicon surfaces. The asymmetric impact and directional trajectory of droplets was exclusive to the TNPAs for impacts corresponding to the transition boiling regime, revealing that asymmetric wettability upon impact is the mechanism for the droplet directionality.

  1. Deformation of an asymmetric film

    NASA Astrophysics Data System (ADS)

    Geng, Jun; Selinger, Jonathan

    2010-03-01

    Recent experiments have investigated shape changes of polymer films induced by asymmetric swelling by a chemical vapor. Inspired by recent work on the shaping of elastic sheets by non-Euclidean metrics [1,2], we represent the effect of chemical vapors by a change in the target metric tensor. In this problem, unlike Refs. [1,2], the target metric is asymmetric between the two sides of the film. Changing this metric induces a curvature of the film, which may be Gaussian curvature into a sphere or mean curvature into a cylinder. We calculate the elastic energy for each of these shapes, and show that the sphere is favored for films smaller than a critical size, which depends on the film thickness, while the cylinder is favored for larger films. We compare the formalism for asymmetric films with previous theoretical work on symmetric films, and compare the predictions with experimental results. [4pt] [1] Y. Klein, E. Efrati, and E. Sharon, Science 315, 1116 (2007).[0pt] [2] E. Efrati, E. Sharon, and R. Kupferman, J. Mech. Phys. Solids 57, 762 (2009).

  2. Asymmetric Dimethylarginine, Endothelial Dysfunction and Renal Disease

    PubMed Central

    Aldámiz-Echevarría, Luis; Andrade, Fernando

    2012-01-01

    l-Arginine (Arg) is oxidized to l-citrulline and nitric oxide (NO) by the action of endothelial nitric oxide synthase (NOS). In contrast, protein-incorporated Arg residues can be methylated with subsequent proteolysis giving rise to methylarginine compounds, such as asymmetric dimethylarginine (ADMA) that competes with Arg for binding to NOS. Most ADMA is degraded by dimethylarginine dimethyaminohydrolase (DDAH), distributed widely throughout the body and regulates ADMA levels and, therefore, NO synthesis. In recent years, several studies have suggested that increased ADMA levels are a marker of atherosclerotic change, and can be used to assess cardiovascular risk, consistent with ADMA being predominantly absorbed by endothelial cells. NO is an important messenger molecule involved in numerous biological processes, and its activity is essential to understand both pathogenic and therapeutic mechanisms in kidney disease and renal transplantation. NO production is reduced in renal patients because of their elevated ADMA levels with associated reduced DDAH activity. These factors contribute to endothelial dysfunction, oxidative stress and the progression of renal damage, but there are treatments that may effectively reduce ADMA levels in patients with kidney disease. Available data on ADMA levels in controls and renal patients, both in adults and children, also are summarized in this review. PMID:23109853

  3. Development of Non-C2-symmetric ProPhenol Ligands. The Asymmetric Vinylation of N-Boc Imines.

    PubMed

    Trost, Barry M; Hung, Chao-I Joey; Koester, Dennis C; Miller, Yan

    2015-08-01

    The development and application of a new generation of non-C2-symmetric ProPhenol ligands is reported herein. Rational design of the ProPhenol ligand paved the way to the first catalytic and asymmetric vinylation of N-Boc imines via hydrozirconation giving rise to valuable allylic amines in excellent yields and enantioselectivities. The utility of this method was demonstrated by developing the shortest reported asymmetric synthesis of the selective serotonine reuptake inhibitor (SSRI) (-)-dapoxetine. PMID:26200769

  4. Measurement of the absolute branching fraction of D0-->K-pi+.

    PubMed

    Aubert, B; Bona, M; Boutigny, D; Karyotakis, Y; Lees, J P; Poireau, V; Prudent, X; Tisserand, V; Zghiche, A; Garra Tico, J; Grauges, E; Lopez, L; Palano, A; Eigen, G; Ofte, I; Stugu, B; Sun, L; Abrams, G S; Battaglia, M; Brown, D N; Button-Shafer, J; Cahn, R N; Groysman, Y; Jacobsen, R G; Kadyk, J A; Kerth, L T; Kolomensky, Yu G; Kukartsev, G; Lopes Pegna, D; Lynch, G; Mir, L M; Orimoto, T J; Pripstein, M; Roe, N A; Ronan, M T; Tackmann, K; Wenzel, W A; Del Amo Sanchez, P; Hawkes, C M; Watson, A T; Held, T; Koch, H; Lewandowski, B; Pelizaeus, M; Schroeder, T; Steinke, M; Cottingham, W N; Walker, D; Asgeirsson, D J; Cuhadar-Donszelmann, T; Fulsom, B G; Hearty, C; Knecht, N S; Mattison, T S; McKenna, J A; Khan, A; Saleem, M; Teodorescu, L; Blinov, V E; Bukin, A D; Druzhinin, V P; Golubev, V B; Onuchin, A P; Serednyakov, S I; Skovpen, Yu I; Solodov, E P; Todyshev, K Yu; Bondioli, M; Curry, S; Eschrich, I; Kirkby, D; Lankford, A J; Lund, P; Mandelkern, M; Martin, E C; Stoker, D P; Abachi, S; Buchanan, C; Foulkes, S D; Gary, J W; Liu, F; Long, O; Shen, B C; Zhang, L; Paar, H P; Rahatlou, S; Sharma, V; Berryhill, J W; Campagnari, C; Cunha, A; Dahmes, B; Hong, T M; Kovalskyi, D; Richman, J D; Beck, T W; Eisner, A M; Flacco, C J; Heusch, C A; Kroseberg, J; Lockman, W S; Schalk, T; Schumm, B A; Seiden, A; Williams, D C; Wilson, M G; Winstrom, L O; Chen, E; Cheng, C H; Dvoretskii, A; Fang, F; Hitlin, D G; Narsky, I; Piatenko, T; Porter, F C; Mancinelli, G; Meadows, B T; Mishra, K; Sokoloff, M D; Blanc, F; Bloom, P C; Chen, S; Ford, W T; Hirschauer, J F; Kreisel, A; Nagel, M; Nauenberg, U; Olivas, A; Smith, J G; Ulmer, K A; Wagner, S R; Zhang, J; Gabareen, A M; Soffer, A; Toki, W H; Wilson, R J; Winklmeier, F; Zeng, Q; Altenburg, D D; Feltresi, E; Hauke, A; Jasper, H; Merkel, J; Petzold, A; Spaan, B; Wacker, K; Brandt, T; Klose, V; Lacker, H M; Mader, W F; Nogowski, R; Schubert, J; Schubert, K R; Schwierz, R; Sundermann, J E; Volk, A; Bernard, D; Bonneaud, G R; Latour, E; Lombardo, V; Thiebaux, Ch; Verderi, M; Clark, P J; Gradl, W; Muheim, F; Playfer, S; Robertson, A I; Xie, Y; Andreotti, M; Bettoni, D; Bozzi, C; Calabrese, R; Cecchi, A; Cibinetto, G; Franchini, P; Luppi, E; Negrini, M; Petrella, A; Piemontese, L; Prencipe, E; Santoro, V; Anulli, F; Baldini-Ferroli, R; Calcaterra, A; de Sangro, R; Finocchiaro, G; Pacetti, S; Patteri, P; Peruzzi, I M; Piccolo, M; Rama, M; Zallo, A; Buzzo, A; Contri, R; Lo Vetere, M; Macri, M M; Monge, M R; Passaggio, S; Patrignani, C; Robutti, E; Santroni, A; Tosi, S; Chaisanguanthum, K S; Morii, M; Wu, J; Dubitzky, R S; Marks, J; Schenk, S; Uwer, U; Bard, D J; Dauncey, P D; Flack, R L; Nash, J A; Nikolich, M B; Panduro Vazquez, W; Behera, P K; Chai, X; Charles, M J; Mallik, U; Meyer, N T; Ziegler, V; Cochran, J; Crawley, H B; Dong, L; Eyges, V; Meyer, W T; Prell, S; Rosenberg, E I; Rubin, A E; Gritsan, A V; Guo, Z J; Lae, C K; Denig, A G; Fritsch, M; Schott, G; Arnaud, N; Bquilleux, J; Davier, M; Grosdidier, G; Hcker, A; Lepeltier, V; Le Diberder, F; Lutz, A M; Pruvot, S; Rodier, S; Roudeau, P; Schune, M H; Serrano, J; Sordini, V; Stocchi, A; Wang, W F; Wormser, G; Lange, D J; Wright, D M; Chavez, C A; Forster, I J; Fry, J R; Gabathuler, E; Gamet, R; Hutchcroft, D E; Payne, D J; Schofield, K C; Touramanis, C; Bevan, A J; George, K A; Di Lodovico, F; Menges, W; Sacco, R; Cowan, G; Flaecher, H U; Hopkins, D A; Jackson, P S; McMahon, T R; Salvatore, F; Wren, A C; Brown, D N; Davis, C L; Allison, J; Barlow, N R; Barlow, R J; Chia, Y M; Edgar, C L; Lafferty, G D; West, T J; Yi, J I; Anderson, J; Chen, C; Jawahery, A; Roberts, D A; Simi, G; Tuggle, J M; Blaylock, G; Dallapiccola, C; Hertzbach, S S; Li, X; Moore, T B; Salvati, E; Saremi, S; Cowan, R; Fisher, P H; Sciolla, G; Sekula, S J; Spitznagel, M; Taylor, F; Yamamoto, R K; McLachlin, S E; Patel, P M; Robertson, S H; Lazzaro, A; Palombo, F; Bauer, J M; Cremaldi, L; Eschenburg, V; Godang, R; Kroeger, R; Sanders, D A; Summers, D J; Zhao, H W; Brunet, S; Ct, D; Simard, M; Taras, P; Viaud, F B; Nicholson, H; De Nardo, G; Fabozzi, F; Lista, L; Monorchio, D; Sciacca, C; Baak, M A; Raven, G; Snoek, H L; Jessop, C P; Losecco, J M; Benelli, G; Corwin, L A; Gan, K K; Honscheid, K; Hufnagel, D; Kagan, H; Kass, R; Morris, J P; Rahimi, A M; Regensburger, J J; Ter-Antonyan, R; Wong, Q K; Blount, N L; Brau, J; Frey, R; Igonkina, O; Kolb, J A; Lu, M; Rahmat, R; Sinev, N B; Strom, D; Strube, J; Torrence, E; Gagliardi, N; Gaz, A; Margoni, M; Morandin, M; Pompili, A; Posocco, M; Rotondo, M; Simonetto, F; Stroili, R; Voci, C; Ben-Haim, E; Briand, H; Chauveau, J; David, P; Del Buono, L; de la Vaissire, Ch; Hamon, O; Hartfiel, B L; Leruste, Ph; Malcls, J; Ocariz, J; Perez, A; Gladney, L; Biasini, M; Covarelli, R; Manoni, E; Angelini, C; Batignani, G; Bettarini, S; Calderini, G; Carpinelli, M; Cenci, R; Cervelli, A; Forti, F

    2008-02-01

    We measure the absolute branching fraction for D(0)-->K(-)pi(+) using partial reconstruction of B(0)-->D(*+)Xl(-)nu(l) decays, in which only the charged lepton and the pion from the decay D(*+)-->D(0)pi(+) are used. Based on a data sample of 230 x 10(6) BB pairs collected at the Upsilon(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC, we obtain B(D(0)-->K(-)pi(+)) = (4.007+/-0.037+/-0.072)%, where the first uncertainty is statistical and the second is systematic. PMID:18352359

  5. Absolute dimensions and masses of eclipsing binaries. V - IQ Persei

    NASA Astrophysics Data System (ADS)

    Lacy, C. H.; Frueh, M. L.

    1985-08-01

    New photometric and spectroscopic observations of the 1.7 day eclipsing binary IQ Persei (B8 + A6) have been analyzed to yield very accurate fundamental properties of the system. Reticon spectroscopic observations obtained at McDonald Observatory were used to determine accurate radial velocities of both stars in this slightly eccentric large light-ratio binary. A new set of VR light curves obtained at McDonald Observatory were analyzed by synthesis techniques, and previously published UBV light curves were reanalyzed to yield accurate photometric orbits. Orbital parameters derived from both sets of photometric observations are in excellent agreement. The absolute dimensions, masses, luminosities, and apsidal motion period (140 yr) derived from these observations agree well with the predictions of theoretical stellar evolution models. The A6 secondary is still very close to the zero-age main sequence. The B8 primary is about one-third of the way through its main-sequence evolution.

  6. Catalytic enantioselective synthesis of naturally occurring butenolides via hetero-allylic alkylation and ring closing metathesis.

    PubMed

    Mao, Bin; Geurts, Koen; Faans-Mastral, Martn; van Zijl, Anthoni W; Fletcher, Stephen P; Minnaard, Adriaan J; Feringa, Ben L

    2011-03-01

    An efficient catalytic asymmetric synthesis of chiral ?-butenolides was developed based on the hetero-allylic asymmetric alkylation (h-AAA) in combination with ring closing metathesis (RCM). The synthetic potential of the h-AAA-RCM protocol was illustrated with the facile synthesis of (-)-whiskey lactone, (-)-cognac lactone, (-)-nephrosteranic acid, and (-)-roccellaric acid. PMID:21268603

  7. Total synthesis of (-)-dihydrosporothriolide utilizing an indium-mediated Reformatsky-Claisen rearrangement.

    PubMed

    Ishihara, Jun; Tsuru, Hiroaki; Hatakeyama, Susumi

    2014-06-20

    The asymmetric synthesis of (-)-dihydrosporothriolide (1), a biologically active bis-?-butyrolactone, is described, that proceeds through a D-proline-catalyzed asymmetric aminooxylation, indium-mediated Reformatsky-Claisen rearrangement of an ?,?-dibromoacetate derivative, and diastereoselective dihydroxylation. The route requires no protective group manipulation and allows the concise seven-step synthesis of 1 from n-octanal. PMID:24877583

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

    PubMed Central

    Kellner, Stefanie; Ochel, Antonia; Thring, 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. LCMS/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

  9. Enantioselective Total Synthesis of Pladienolide B: A Potent Spliceosome Inhibitor

    PubMed Central

    Anderson, David D.

    2012-01-01

    An enantioselective and convergent total synthesis of pladienolide B (1) is described. Pladienolide B binds to the SF3b complex of a spliceosome and inhibits mRNA splicing activity. The synthesis features an epoxide opening reaction, an asymmetric reduction of a ?-keto ester, and a cross metathesis strategy for the side chain synthesis. PMID:22954141

  10. Universal Cosmic Absolute and Modern Science

    NASA Astrophysics Data System (ADS)

    Kostro, Ludwik

    The official Sciences, especially all natural sciences, respect in their researches the principle of methodic naturalism i.e. they consider all phenomena as entirely natural and therefore in their scientific explanations they do never adduce or cite supernatural entities and forces. The purpose of this paper is to show that Modern Science has its own self-existent, self-acting, and self-sufficient Natural All-in Being or Omni-Being i.e. the entire Nature as a Whole that justifies the scientific methodic naturalism. Since this Natural All-in Being is one and only It should be considered as the own scientifically justified Natural Absolute of Science and should be called, in my opinion, the Universal Cosmic Absolute of Modern Science. It will be also shown that the Universal Cosmic Absolute is ontologically enormously stratified and is in its ultimate i.e. in its most fundamental stratum trans-reistic and trans-personal. It means that in its basic stratum. It is neither a Thing or a Person although It contains in Itself all things and persons with all other sentient and conscious individuals as well, On the turn of the 20th century the Science has begun to look for a theory of everything, for a final theory, for a master theory. In my opinion the natural Universal Cosmic Absolute will constitute in such a theory the radical all penetrating Ultimate Basic Reality and will substitute step by step the traditional supernatural personal Absolute.

  11. 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.

  12. 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 3000C/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.

  13. Quantum theory allows for absolute maximal contextuality

    NASA Astrophysics Data System (ADS)

    Amaral, Barbara; Cunha, Marcelo Terra; Cabello, Adn

    2015-12-01

    Contextuality is a fundamental feature of quantum theory and a necessary resource for quantum computation and communication. It is therefore important to investigate how large contextuality can be in quantum theory. Linear contextuality witnesses can be expressed as a sum S of n probabilities, and the independence number ? and the Tsirelson-like number ? of the corresponding exclusivity graph are, respectively, the maximum of S for noncontextual theories and for the theory under consideration. A theory allows for absolute maximal contextuality if it has scenarios in which ? /? approaches n . Here we show that quantum theory allows for absolute maximal contextuality despite what is suggested by the examination of the quantum violations of Bell and noncontextuality inequalities considered in the past. Our proof is not constructive and does not single out explicit scenarios. Nevertheless, we identify scenarios in which quantum theory allows for almost-absolute-maximal contextuality.

  14. Molecular iodine absolute frequencies. Final report

    SciTech Connect

    Sansonetti, C.J.

    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.

  15. Theory of reflectivity of an asymmetric mirror

    NASA Astrophysics Data System (ADS)

    Murtaza, S. S.; Campbell, J. C.; Parent, M. A.; Bean, J. C.

    1996-04-01

    By using the concept of transfer matrices and Bloch waves, we have derived a set of equations that provide insight into the operation of asymmetric Bragg reflectors that have been demonstrated to be useful in achieving high reflectivities in strained-material systems. These equations will be useful in the design of asymmetric mirrors and can be used to compare the trade-offs between the conventional, symmetric (quarter-wavelength), and asymmetric mirrors.

  16. Unravelling Thiol's Role in Directing Asymmetric Growth of Au Nanorod-Au Nanoparticle Dimers.

    PubMed

    Huang, Jianfeng; Zhu, Yihan; Liu, Changxu; Shi, Zhan; Fratalocchi, Andrea; Han, Yu

    2016-01-13

    Asymmetric nanocrystals have practical significance in nanotechnologies but present fundamental synthetic challenges. Thiol ligands have proven effective in breaking the symmetric growth of metallic nanocrystals but their exact roles in the synthesis remain elusive. Here, we synthesized an unprecedented Au nanorod-Au nanoparticle (AuNR-AuNP) dimer structure with the assistance of a thiol ligand. On the basis of our experimental observations, we unraveled for the first time that the thiol could cause an inhomogeneous distribution of surface strains on the seed crystals as well as a modulated reduction rate of metal precursors, which jointly induced the asymmetric growth of monometallic dimers. PMID:26670659

  17. Absolutely relative or relatively absolute: violations of value invariance in human decision making.

    PubMed

    Teodorescu, Andrei R; Moran, Rani; Usher, Marius

    2016-02-01

    Making decisions based on relative rather than absolute information processing is tied to choice optimality via the accumulation of evidence differences and to canonical neural processing via accumulation of evidence ratios. These theoretical frameworks predict invariance of decision latencies to absolute intensities that maintain differences and ratios, respectively. While information about the absolute values of the choice alternatives is not necessary for choosing the best alternative, it may nevertheless hold valuable information about the context of the decision. To test the sensitivity of human decision making to absolute values, we manipulated the intensities of brightness stimuli pairs while preserving either their differences or their ratios. Although asked to choose the brighter alternative relative to the other, participants responded faster to higher absolute values. Thus, our results provide empirical evidence for human sensitivity to task irrelevant absolute values indicating a hard-wired mechanism that precedes executive control. Computational investigations of several modelling architectures reveal two alternative accounts for this phenomenon, which combine absolute and relative processing. One account involves accumulation of differences with activation dependent processing noise and the other emerges from accumulation of absolute values subject to the temporal dynamics of lateral inhibition. The potential adaptive role of such choice mechanisms is discussed. PMID:26022836

  18. Absolute Distance Measurement with the MSTAR Sensor

    NASA Technical Reports Server (NTRS)

    Lay, Oliver P.; Dubovitsky, Serge; Peters, Robert; Burger, Johan; Ahn, Seh-Won; Steier, William H.; Fetterman, Harrold R.; Chang, Yian

    2003-01-01

    The MSTAR sensor (Modulation Sideband Technology for Absolute Ranging) is a new system for measuring absolute distance, capable of resolving the integer cycle ambiguity of standard interferometers, and making it possible to measure distance with sub-nanometer accuracy. The sensor uses a single laser in conjunction with fast phase modulators and low frequency detectors. We describe the design of the system - the principle of operation, the metrology source, beamlaunching optics, and signal processing - and show results for target distances up to 1 meter. We then demonstrate how the system can be scaled to kilometer-scale distances.

  19. Geometry-induced asymmetric diffusion

    PubMed Central

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

    2007-01-01

    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. PMID:17522257

  20. Asymmetrical membranes and surface tension.

    PubMed Central

    Trakia, 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

  1. 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.

  2. Instability of asymmetric shaft system

    NASA Astrophysics Data System (ADS)

    Srinath, R.; Sarkar, Abhijit; Sekhar, A. S.

    2016-02-01

    In the present work, parametric instability of asymmetric shaft mounted on bearings is studied. Towards this end, four different models of increasing complexity are studied. The equations corresponding to these models are formulated in the inertial reference frame. These equations involve a periodically varying coefficient. This is similar to classical Mathieu equation but in a multi-degree of freedom context. As such, under suitable parameter combination these systems result in growing oscillation amplitudes or instability. For wider generalization, the equations and results are presented in a non-dimensional form. The unstable parameter regimes are found using the Floquet theory and perturbation methods. These results are also corroborated with existing results in the literature. The nature of the stability boundary and its dependence on various system parameters is discussed in elaborate detail. The stability boundary can be used to determine unstable operating speed ranges for different asymmetric shaft cross-sections. Further, material, geometry and bearing selection guidelines for ensuring stable operations can be inferred from these results.

  3. ASYMMETRIC SOLAR POLAR FIELD REVERSALS

    SciTech Connect

    Svalgaard, Leif; Kamide, Yohsuke

    2013-01-20

    The solar polar fields reverse because magnetic flux from decaying sunspots moves toward the poles, with a preponderance of flux from the trailing spots. If there is a strong asymmetry, in the sense that most activity is in the northern hemisphere, then that excess flux will move toward the north pole and reverse that pole first. If there is more activity in the south later on, then that flux will help to reverse the south pole. In this way, two humps in the solar activity and a corresponding difference in the time of reversals develop (in the ideal case). Such a difference was originally noted in the very first observation of polar field reversal just after the maximum of the strongly asymmetric solar cycle 19, when the southern hemisphere was most active before sunspot maximum and the south pole duly reversed first, followed by the northern hemisphere more than a year later, when that hemisphere became most active. Solar cycles since then have had the opposite asymmetry, with the northern hemisphere being most active before solar maximum. We show that polar field reversals for these cycles have all happened in the north first, as expected. This is especially noteworthy for the present solar cycle 24. We suggest that the association of two or more peaks of solar activity when separated by hemispheres with correspondingly different times of polar field reversals is a general feature of the cycle, and that asymmetric polar field reversals are simply a consequence of the asymmetry of solar activity.

  4. 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.

  5. Stereoselective Total Synthesis of (-)-Depudecin.

    PubMed

    García-Ruiz, Cristina; Cheng-Sánchez, Iván; Sarabia, Francisco

    2015-11-20

    The total synthesis of the natural product depudecin, an antiangiogenic microbial polyketide with inhibitory activity against histone deacetylases, is reported. Characterized by a highly oxidized 11-carbon chain containing two epoxides conjugated through a trans-disubstituted olefin, its total synthesis was efficiently accomplished by a novel asymmetric methodology of epoxide formation based on a new class of chiral sulfonium salts, allowing for the construction of the oxirane rings in an efficient and stereoselective fashion. PMID:26517569

  6. Tandem Reactions for Streamlining Synthesis

    PubMed Central

    HUSSAIN, MAHMUD M.; WALSH, PATRICK J.

    2009-01-01

    CONSPECTUS In 1980 Sharpless and Katsuki introduced the asymmetric epoxidation of prochiral allylic alcohols (the Sharpless-Katsuki Asymmetric Epoxidation), which enabled the rapid synthesis of highly enantioenriched epoxy alcohols. This reaction was a milestone in the development of asymmetric catalysis because it was the first highly enantioselective oxidation reaction. Furthermore, it provided access to enantioenriched allylic alcohols that are now standard starting materials in natural product synthesis. In 1981 Sharpless and coworkers made another seminal contribution by describing the kinetic resolution (KR) of racemic allylic alcohols. This work demonstrated that small-molecule catalysts could compete with enzymatic catalysts in KRs. For these pioneering works, Sharpless was awarded the 2001 Nobel Prize with Knowles and Noyori. Despite these achievements, the Sharpless KR is not an efficient method to prepare epoxy alcohols with high enantiomeric excess (ee). First, the racemic allylic alcohol must be prepared and purified. KR of the racemic allylic alcohol must be stopped at low conversion, because the ee of the product epoxy alcohol decreases as the KR progresses. Thus, better methods to prepare epoxy alcohols containing stereogenic carbinol carbons are needed. This Account summarizes our efforts to develop one-pot methods for the synthesis of various epoxy alcohols and allylic epoxy alcohols with high enantio-, diastereo-, and chemoselectivity. Our laboratory developed titanium-based catalysts for use in the synthesis of epoxy alcohols with tertiary carbinols. The catalysts are involved in the first step, which is an asymmetric alkyl or allyl addition to enones. The resulting intermediates are then subjected to a titanium-directed diastereoselective epoxidation to provide tertiary epoxy alcohols. Similarly, the synthesis of acyclic epoxy alcohols begins with asymmetric additions to enals and subsequent epoxidation. The methods described here enable the synthesis of skeletally diverse epoxy alcohols. PMID:18710197

  7. On Relative and Absolute Conviction in Mathematics

    ERIC Educational Resources Information Center

    Weber, Keith; Mejia-Ramos, Juan Pablo

    2015-01-01

    Conviction is a central construct in mathematics education research on justification and proof. In this paper, we claim that it is important to distinguish between absolute conviction and relative conviction. We argue that researchers in mathematics education frequently have not done so and this has lead to researchers making unwarranted claims

  8. 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.)

  9. Absolute Points for Multiple Assignment Problems

    ERIC Educational Resources Information Center

    Adlakha, V.; Kowalski, K.

    2006-01-01

    An algorithm is presented to solve multiple assignment problems in which a cost is incurred only when an assignment is made at a given cell. The proposed method recursively searches for single/group absolute points to identify cells that must be loaded in any optimal solution. Unlike other methods, the first solution is the optimal solution. The

  10. The Absolute Normal Scores Test for Symmetry

    ERIC Educational Resources Information Center

    Penfield, Douglas A.; Sachdeva, Darshan

    1976-01-01

    The absolute normal scores test is described as a test for the symmetry of a distribution of scores about a location parameter. The test is compared to the sign test and the Wilcoxon test as an alternative to the "t"-test. (Editor/RK)

  11. Absolute Differential Positronium-Formation Cross Sections

    NASA Astrophysics Data System (ADS)

    Shipman, M.; Armitage, S.; Beale, J.; Brawley, S. J.; Fayer, S. E.; Garner, A. J.; Leslie, D. E.; Van Reeth, P.; Laricchia, G.

    2015-07-01

    The first absolute experimental determinations of the differential cross sections for the formation of ground-state positronium are presented for He, Ar, H2 , and CO2 near 0. Results are compared with available theories. The ratio of the differential and integrated cross sections for the targets exposes the higher propensity for forward emission of positronium formed from He and H2 .

  12. On Relative and Absolute Conviction in Mathematics

    ERIC Educational Resources Information Center

    Weber, Keith; Mejia-Ramos, Juan Pablo

    2015-01-01

    Conviction is a central construct in mathematics education research on justification and proof. In this paper, we claim that it is important to distinguish between absolute conviction and relative conviction. We argue that researchers in mathematics education frequently have not done so and this has lead to researchers making unwarranted claims…

  13. 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.

  14. 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

  15. Absolute distance interferometry using diode lasers

    NASA Astrophysics Data System (ADS)

    Meiners-Hagen, K.; Abou-Zeid, A.; Hartmann, L.

    2008-10-01

    An approach to a homodyne absolute distance interferometer (ADI) was previously presented which makes use of two extended cavity diode lasers (ECDL). The length measurement is performed by combining variable synthetic wavelength interferometry and two wavelength interferometry in one setup. In this contribution the ADI was compared to a counting HeNe laser interferometer up to a length of 10 m.

  16. Total synthesis of (-)-bitungolide F.

    PubMed

    Su, Yingpeng; Xu, Yanfen; Han, Junjie; Zheng, Jiyue; Qi, Jing; Jiang, Tuo; Pan, Xinfu; She, Xuegong

    2009-04-01

    An efficient total synthesis of (-)-bitungolide F (6) in 17 steps and 20.1% yield is described herein. Key steps involve a Myers asymmetric alkylation to introduce the C6 methyl with proper stereochemistry, a Claisen-like cyclization to construct the alpha,beta-unsaturated delta-lactone and a Julia-Kocienski olefination to assemble the conjugated diene moiety. PMID:19323573

  17. Engineered Asymmetric Composite Membranes with Rectifying Properties.

    PubMed

    Wen, Liping; Xiao, Kai; Sainath, Annadanam V Sesha; Komura, Motonori; Kong, Xiang-Yu; Xie, Ganhua; Zhang, Zhen; Tian, Ye; Iyoda, Tomokazu; Jiang, Lei

    2016-01-01

    Asymmetric composite membranes with rectifying properties are developed by grafting pH-stimulus-responsive materials onto the top layer of the composite structure, which is prepared by two novel block copolymers using a phase-separation technique. This engineered asymmetric composite membrane shows potential applications in sensors, filtration, and nanofluidic devices. PMID:26630640

  18. Defect-free ultrahigh flux asymmetric membranes

    DOEpatents

    Pinnau, Ingo (Austin, TX); Koros, William J. (Austin, TX)

    1990-01-01

    Defect-free, ultrahigh flux integrally-skinned asymmetric membranes having extremely thin surface layers (<0.2 .mu.m) comprised of glassy polymers are disclosed. The membranes are formed by casting an appropriate drope followed by forced convective evaporation of solvent to obtain a dry phase separated asymmetrical structure. The structure is then washed in a precipitation liquid and dried.

  19. Mechanochemistry assisted asymmetric organocatalysis: A sustainable approach.

    PubMed

    Chauhan, Pankaj; Chimni, Swapandeep Singh

    2012-01-01

    Ball-milling and pestle and mortar grinding have emerged as powerful methods for the development of environmentally benign chemical transformations. Recently, the use of these mechanochemical techniques in asymmetric organocatalysis has increased. This review highlights the progress in asymmetric organocatalytic reactions assisted by mechanochemical techniques. PMID:23243475

  20. Superfluidity in asymmetric nuclear matter

    SciTech Connect

    Sedrakian, A.; Alm, T.; Lombardo, U.

    1997-02-01

    The onset of superfluidity in isospin-asymmetric nuclear matter is investigated within the BCS theory. A neutron-proton superfluid state in the channel {sup 3}S{sub 1}-{sup 3}D{sub 1} comes about from the interplay between thermal excitations and separation {delta}{mu} of the two Fermi surfaces. The superfluid state disappears above the threshold value of the density-asymmetry parameter {alpha}=(n{sub n}{minus}n{sub p})/n{approx_equal}0.35. For large enough shift between the two Fermi surfaces {delta}{mu}=(1)/(2)({mu}{sub n}{minus}{mu}{sub p}) the transition to the normal state becomes a first-order transition and a second gap solution develops. This solution, however, corresponds to a metastable superfluid state which is unstable with respect to the transition to the normal state. {copyright} {ital 1997} {ital The American Physical Society}

  1. Asymmetric diffusion of cosmic rays

    NASA Astrophysics Data System (ADS)

    Medvedev, Mikhail V.; Medvedev, Viktor V.

    2015-09-01

    Cosmic ray propagation is diffusive because of pitch angle scattering by waves. We demonstrate that if the high-amplitude magnetohydrodynamic turbulence with B ˜/˜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.

  2. 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 CH 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

  3. BASL Controls Asymmetric Cell Division in Arabidopsis

    PubMed Central

    Dong, Juan; MacAlister, Cora A.; Bergmann, Dominique C.

    2014-01-01

    SUMMARY Development in multicellular organisms requires the organized generation of differences. A universal mechanism for creating such differences is asymmetric cell division. In plants, as in animals, asymmetric divisions are correlated with the production of cellular diversity and pattern; however, structural constraints imposed by plant cell walls and the absence of homologs of known animal or fungal cell polarity regulators necessitates that plants utilize new molecules and mechanisms to create asymmetries. Here, we identify BASL, a novel regulator of asymmetric divisions in Arabidopsis. In asymmetrically dividing stomatal-lineage cells, BASL accumulates in a polarized crescent at the cell periphery before division, and then localizes differentially to the nucleus and a peripheral crescent in self-renewing cells and their sisters after division. BASL presence at the cell periphery is critical for its function, and we propose that BASL represents a plant-specific solution to the challenge of asymmetric cell division. PMID:19523675

  4. Asymmetric cancer cell division regulated by AKT

    PubMed Central

    Dey-Guha, Ipsita; Wolfer, Anita; Yeh, Albert C.; G. Albeck, John; Darp, Revati; Leon, Eduardo; Wulfkuhle, Julia; Petricoin, Emanuel F.; Wittner, Ben S.; Ramaswamy, Sridhar

    2011-01-01

    Human tumors often contain slowly proliferating cancer cells that resist treatment, but we do not know precisely how these cells arise. We show that rapidly proliferating cancer cells can divide asymmetrically to produce slowly proliferating G0-like progeny that are enriched following chemotherapy in breast cancer patients. Asymmetric cancer cell division results from asymmetric suppression of AKT/PKB kinase signaling in one daughter cell during telophase of mitosis. Moreover, inhibition of AKT signaling with small-molecule drugs can induce asymmetric cancer cell division and the production of slow proliferators. Cancer cells therefore appear to continuously flux between symmetric and asymmetric division depending on the precise state of their AKT signaling network. This model may have significant implications for understanding how tumors grow, evade treatment, and recur. PMID:21757645

  5. Reynolds number effects on supersonic asymmetrical flows over a cone at high angle of attack

    NASA Technical Reports Server (NTRS)

    Thomas, J. L.

    1991-01-01

    The supersonic viscous flow over a 5-degree half-angle cone at an angle of attack of four times the cone half-angle is studied computationally using both the conical and the three-dimensional Navier-Stokes equations. The numerical solutions were obtained with an implicit, upwind-biased algorithm. Asymmetrical flowfields of the absolute-instability type are found using the conical-flow equations which agree with published results. However, the absolute instabilities of the originally symmetric flow found with the conical equations do not occur in the three-dimensional simulations, although spurious asymmetric three-dimensional flows for symmetric bodies arise if the grid resolution is insufficient in the nose region. The asymmetric flows computed with the three-dimensional equations are convective instabilities and are possible if the local Reynolds number exceeds a critical value and a fixed geometric asymmetry is imposed. A continuous range of asymmetries can be developed, depending on the size of the disturbance and the Reynolds number. As the Reynolds number is increased, the asymmetries demonstrate a bistable behavior at levels of side force consistent with those predicted using the conical equations. Below a certain critical Reynolds number, any flow asymmetries arising from a geometrical asymmetry are damped with increasing distance downstream from the geometrical asymmetry.

  6. 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.

  7. Dynamo action by turbulence in absolute equilibrium

    NASA Astrophysics Data System (ADS)

    Gopalakrishnan Ganga Prasath, Srinivasa; Fauve, Stéphan; Brachet, Marc

    2014-04-01

    We consider the generation of a large-scale magnetic field by a turbulent flow driven by a small-scale helical forcing in a low magnetic Prandtl number fluid. We provide an estimate of the dynamo threshold that takes into account the presence of large-scale turbulent fluctuations by considering that the scales of the flow that mostly contribute to the dynamo process are roughly in absolute equilibrium. We show that turbulent flows in absolute equilibrium do generate dynamos and we compare their growth rates to their laminar counterparts. Finally, we show that the back reaction of the growing magnetic field modifies the statistical properties of turbulent flow by suppressing its kinetic helicity at large magnetic Reynolds number.

  8. Absolute and relative dosimetry for ELIMED

    SciTech Connect

    Cirrone, G. A. P.; Schillaci, F.; Scuderi, V.; Cuttone, G.; Candiano, G.; Musumarra, A.; Pisciotta, P.; Romano, F.; Carpinelli, M.; Presti, D. Lo; Raffaele, L.; Tramontana, A.; Cirio, R.; Sacchi, R.; Monaco, V.; Marchetto, F.; Giordanengo, S.

    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.

  9. Consistent thermostatistics forbids negative absolute temperatures

    NASA Astrophysics Data System (ADS)

    Dunkel, Jrn; 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.

  10. Relaxation towards negative absolute temperature states

    NASA Astrophysics Data System (ADS)

    Mandt, Stephan; Feiguin, Adrian; Manmana, Salvatore

    2014-03-01

    Motivated by the recent experimental observation of negative absolute temperature states with ultracold atoms in optical lattices, [Braun et al., Science 339 52 (2013)], we discuss the formation of these states. More specifically, we consider the relaxation after a sudden inversion of the external parabolic confining potential. First, previous numerical simulation results of a semiclassical Boltzmann equation for the case of fermions will be discussed, which show a surprisingly slow equilibration due to the diffusive rearrangement of the local kinetic energies in the inhomogeneous system. We then focus on the integrable system of one-dimensional hard-core bosons. Here, we provide convincing numerical evidence for the relaxation to a generalized Gibbs ensemble at negative absolute temperature, a notion we define in this context.

  11. FOC Absolute Sensitivity (F/48 Relay)

    NASA Astrophysics Data System (ADS)

    Paresce, Francesco

    1992-06-01

    The absolute DQE for the f/48 camera has not yet been directly measured in orbit. This has been in part due to the absence of faint enough standards. This proposal will attempt to correct this deficiency by observations of UV standard stars with combinations of filters and small formats to achieve count rates that are not seriously nonlinear. Because of the use of small formats, interactive acquisitions will be required as well as special commanding for nonstandard formats. Internal LED exposures will also be necessary to geometrically calibrate the nonstandard format and to tie its absolute response to those of other formats (there is a significant format- dependent response variation for f/48).

  12. An absolute measure for a key currency

    NASA Astrophysics Data System (ADS)

    Oya, Shunsuke; Aihara, Kazuyuki; Hirata, Yoshito

    It is generally considered that the US dollar and the euro are the key currencies in the world and in Europe, respectively. However, there is no absolute general measure for a key currency. Here, we investigate the 24-hour periodicity of foreign exchange markets using a recurrence plot, and define an absolute measure for a key currency based on the strength of the periodicity. Moreover, we analyze the time evolution of this measure. The results show that the credibility of the US dollar has not decreased significantly since the Lehman shock, when the Lehman Brothers bankrupted and influenced the economic markets, and has increased even relatively better than that of the euro and that of the Japanese yen.

  13. Redetermination and absolute configuration of (+)-7-epiclusianone

    PubMed Central

    Christian, Omar E.; Fronczek, Frank R.; Ky, Khoa; Pradhan, Shreedu; Manandhar, Anjela; Richmond, Cecilia

    2012-01-01

    The absolute configuration of 3-benzoyl-4-hy­droxy-6,6-dimethyl-1,5,7-tris­(3-methyl­but-2-en­yl)bicyclo­[3.3.1]non-3-ene-2,9-dione, C33H42O4, isolated from Hypericum hypericoides, has been determined. The previous study [Xiao et al. (2007 ▶). J. Nat. Prod. 70, 1779–1782] gave only the established relative configuration. The three stereogenic centers are now established as 1R, 5R and 7S on the basis of the refinement of the Flack absolute structure parameter against Cu Kα data and correspond to a specific rotation of [α]D 20 = +66°. The enol–hy­droxy group forms an intra­molecular O—H⋯O hydrogen bond to close an S(6) ring. PMID:23284527

  14. Absolute-magnitude distributions of supernovae

    SciTech Connect

    Richardson, Dean; Wright, John; Jenkins III, Robert L.; Maddox, Larry

    2014-05-01

    The absolute-magnitude distributions of seven supernova (SN) types are presented. The data used here were primarily taken from the Asiago Supernova Catalogue, but were supplemented with additional data. We accounted for both foreground and host-galaxy extinction. A bootstrap method is used to correct the samples for Malmquist bias. Separately, we generate volume-limited samples, restricted to events within 100 Mpc. We find that the superluminous events (M{sub B} < 21) make up only about 0.1% of all SNe in the bias-corrected sample. The subluminous events (M{sub B} > 15) make up about 3%. The normal Ia distribution was the brightest with a mean absolute blue magnitude of 19.25. The IIP distribution was the dimmest at 16.75.

  15. 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.

  16. Probing absolute spin polarization at the nanoscale.

    PubMed

    Eltschka, Matthias; Jck, 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 due to the different decay of the electron orbitals into vacuum. PMID:25423049

  17. Absolute photoionization cross sections of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.; Pareek, P. N.

    1985-01-01

    The absolute values of photoionization cross sections of atomic oxygen were measured from the ionization threshold to 120 A. An auto-ionizing resonance belonging to the 2S2P4(4P)3P(3Do, 3So) transition was observed at 479.43 A and another line at 389.97 A. The experimental data is in excellent agreement with rigorous close-coupling calculations that include electron correlations in both the initial and final states.

  18. Absolute photoionization cross sections of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.; Pareek, P. N.

    1982-01-01

    The absolute values of photoionization cross sections of atomic oxygen were measured from the ionization threshold to 120 A. An auto-ionizing resonance belonging to the 2S2P4(4P)3P(3Do, 3So) transition was observed at 479.43 A and another line at 389.97 A. The experimental data is in excellent agreement with rigorous close-coupling calculations that include electron correlations in both the initial and final states.

  19. Relative errors can cue absolute visuomotor mappings.

    PubMed

    van Dam, Loes C J; Ernst, Marc O

    2015-12-01

    When repeatedly switching between two visuomotor mappings, e.g. in a reaching or pointing task, adaptation tends to speed up over time. That is, when the error in the feedback corresponds to a mapping switch, fast adaptation occurs. Yet, what is learned, the relative error or the absolute mappings? When switching between mappings, errors with a size corresponding to the relative difference between the mappings will occur more often than other large errors. Thus, we could learn to correct more for errors with this familiar size (Error Learning). On the other hand, it has been shown that the human visuomotor system can store several absolute visuomotor mappings (Mapping Learning) and can use associated contextual cues to retrieve them. Thus, when contextual information is present, no error feedback is needed to switch between mappings. Using a rapid pointing task, we investigated how these two types of learning may each contribute when repeatedly switching between mappings in the absence of task-irrelevant contextual cues. After training, we examined how participants changed their behaviour when a single error probe indicated either the often-experienced error (Error Learning) or one of the previously experienced absolute mappings (Mapping Learning). Results were consistent with Mapping Learning despite the relative nature of the error information in the feedback. This shows that errors in the feedback can have a double role in visuomotor behaviour: they drive the general adaptation process by making corrections possible on subsequent movements, as well as serve as contextual cues that can signal a learned absolute mapping. PMID:26280315

  20. Absolute Differential Positronium-Formation Cross Sections.

    PubMed

    Shipman, M; Armitage, S; Beale, J; Brawley, S J; Fayer, S E; Garner, A J; Leslie, D E; Van Reeth, P; Laricchia, G

    2015-07-17

    The first absolute experimental determinations of the differential cross sections for the formation of ground-state positronium are presented for He, Ar, H2, and CO2 near 0. Results are compared with available theories. The ratio of the differential and integrated cross sections for the targets exposes the higher propensity for forward emission of positronium formed from He and H2. PMID:26230792