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Sample records for practical asymmetric synthesis

  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. Catalytic asymmetric synthesis of thiols.

    PubMed

    Monaco, Mattia Riccardo; Prévost, Sébastien; List, Benjamin

    2014-12-10

    The synthesis of enantiopure thiols is of significant interest for industrial and academic applications. However, direct asymmetric approaches to free thiols have previously been unknown. Here we describe a novel organocascade that is catalyzed by a confined chiral phosphoric acid and furnishes O-protected β-hydroxythiols with excellent enantioselectivities. The method relies on an asymmetric thiocarboxylysis of meso-epoxides, followed by an intramolecular trans-esterification reaction. By varying the reaction conditions, the intermediate thioesters can also be obtained chemoselectively and enantioselectively.

  3. 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 α-oxidation of the six-membered lactone followed by methanolysis. PMID:26474211

  4. Hydroxamic Acids in Asymmetric Synthesis

    PubMed Central

    Li, Zhi; Yamamoto, Hisashi

    2012-01-01

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

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

    PubMed

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

    2005-04-15

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

  6. Asymmetric total synthesis of halicholactone.

    PubMed

    Baba, Y; Saha, G; Nakao, S; Iwata, C; Tanaka, T; Ibuka, T; Ohishi, H; Takemoto, Y

    2001-01-12

    The asymmetric total synthesis of the marine metabolite, halicholactone 1, is described. The bisallylic triol 6 with three chiral centers at C8, C12, and C15 was constructed by [2,3]-sigmatropic rearrangement of the sulfoxide 18, which was prepared stereoselectively using the chirality of (diene)Fe(CO)3 complexes. Introduction of the trans-substituted cyclopropane subunit into 21 was successfully achieved using the modified regio- and stereoselective Simmons-Smith reaction. The use of RCM (ring-closing metathesis) methodology (4-->35) was pivotal for the formation of a nine-membered unsaturated lactone fragment of halicholactone 1. As this approach is flexible and stereoselective, other oxylipins could be synthesized by the protocol described herein.

  7. 1,6-asymmetric induction in boron-mediated aldol reactions: application to a practical total synthesis of (+)-discodermolide.

    PubMed

    Paterson, Ian; Delgado, Oscar; Florence, Gordon J; Lyothier, Isabelle; Scott, Jeremy P; Sereinig, Natascha

    2003-01-01

    By relying solely on substrate-based stereocontrol, a practical total synthesis of the microtubule-stabilizing anticancer agent (+)-discodermolide has been realized. This exploits a novel aldol bond construction with 1,6-stereoinduction from the boron enolate of (Z)-enone 3 in addition to aldehyde 2. The 1,3-diol 7 is employed as a common building block for the C(1)-C(5), C(9)-C(16), and C(17)-C(24) subunits. [reaction--see text

  8. Asymmetric total synthesis of vindoline.

    PubMed

    Kato, Daisuke; Sasaki, Yoshikazu; Boger, Dale L

    2010-03-24

    A concise asymmetric total synthesis of (-)-vindoline (1) is detailed based on a tandem intramolecular [4+2]/[3+2] cycloaddition cascade of a 1,3,4-oxadiazole inspired by the natural product structure, in which the tether linking the initiating dienophile and oxadiazole bears a chiral substituent that controls the facial selectivity of the initiating Diels-Alder reaction and sets absolute stereochemistry of the remaining six stereocenters in the cascade cycloadduct. This key reaction introduces three rings and four C-C bonds central to the pentacyclic ring system setting all six stereocenters and introducing essentially all the functionality found in the natural product in a single step. Implementation of the approach also required the development of a unique ring expansion reaction to provide a six-membered ring suitably functionalized for introduction of the Delta (6, 7)-double bond found in the core structure of vindoline and defined our use of a protected hydroxymethyl group as the substituent used to control the stereochemical course of the cycloaddition cascade.

  9. Catalytic Asymmetric Synthesis of Phosphine Boronates.

    PubMed

    Hornillos, Valentín; Vila, Carlos; Otten, Edwin; Feringa, Ben L

    2015-06-26

    The first catalytic enantioselective synthesis of ambiphilic phosphine boronate esters is presented. The asymmetric boration of α,β-unsaturated phosphine oxides catalyzed by a copper bisphosphine complex affords optically active organoboronate esters that bear a vicinal phosphine oxide group in good yields and high enantiomeric excess. The synthetic utility of the products is demonstrated through stereospecific transformations into multifunctional optically active compounds. PMID:25950871

  10. 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.

  11. Catalytic asymmetric formal synthesis of beraprost.

    PubMed

    Kobayashi, Yusuke; Kuramoto, Ryuta; Takemoto, Yoshiji

    2015-01-01

    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.

  12. 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

  13. A new approach for the asymmetric total synthesis of umbelactone.

    PubMed

    Liu, Huawei; Zhang, Tao; Li, Yulin

    2006-05-01

    The asymmetric total syntheses of (R)-(+)- and (S)-(-)-umbelactone were achieved by using the Sharpless asymmetric epoxidation reaction to generate the stereogenic center and a ring-closing metathesis (RCM) for the formation of the lactone structure. Starting from 3-methyl-2-buten-1-ol, the asymmetric total synthesis was achieved in an efficient 6-step protocol with an overall yield of 16%.

  14. Asymmetric Total Synthesis of (-)-Lycospidine A.

    PubMed

    Xu, Shiyan; Zhang, Jing; Ma, Donghui; Xu, Dengyu; Xie, Xingang; She, Xuegong

    2016-09-16

    The first asymmetric total synthesis of the structurally unique Lycopodium alkaloid (-)-lycospidine A, containing an unprecedented five-membered ring, has been accomplished in only 10 steps with 21.6% overall yield from the known conveniently available sulfoxide. This protecting-group-free short synthesis relied on the use of a key amidation/aza-Prins domino cyclization reaction to rapidly construct the tricyclic skeleton and two continuous stereocenters (one of which is a bridged quaternary stereocenter). An intramolecular aldol condensation was successfully utilized to establish the unique five-membered ring, and a late-stage oxidation inspired by biosynthesis pathway was adopted to synthesize the diosphenol ring of (-)-lycospidine A. PMID:27565006

  15. 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

  16. Asymmetric catalytic synthesis of the proposed structure of trocheliophorolide B.

    PubMed

    Trost, Barry M; Quintard, Adrien

    2012-09-01

    A concise catalytic asymmetric synthesis of the proposed structure of trocheliophorolide B is reported. The synthetic sequence notably features an asymmetric acetaldehyde alkynylation, a Ru-catalyzed alder-ene reaction, and a Zn-ProPhenol ynone aldol condensation. Comparison with the reported data suggests a misassignment of the natural product structure.

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

    PubMed

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

    2011-01-01

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

  18. 10 Step Asymmetric Total Synthesis and Stereochemistry of (+)-Dragmacidin D

    PubMed Central

    Jackson, Jeffrey J.; Kobayashi, Hiroyuki; Steffens, Sophia D.

    2015-01-01

    The asymmetric synthesis of dragmacidin D (1) has been completed in 10 steps. Its sole stereocenter was set using direct asymmetric alkylation enabled by a C2-symmetric tetramine and lithium N-(trimethylsilyl)-tert-butylamide as the enolization reagent. A central Larock indole synthesis was employed in a convergent assembly of heterocyclic subunits. The stereochemical evidence from this work strongly supports the predicted S configuration at 6′″ position consistent with other members of the dragmacidin family of natural products. PMID:26130270

  19. An Asymmetric Total Synthesis of Brevisamide

    PubMed Central

    Li, Jianfeng

    2009-01-01

    An enantioselective synthesis of marine alkaloid brevisamide was accomplished in a convergent manner. The synthesis utilized an enantioselective hetero-Diels-Alder reaction which sets three chiral centers in compound 11. The synthesis also features a modified Wolff-Kishner reduction, Rubottom oxidation and Suzuki-Miyaura coupling to furnish brevisamide. PMID:19694486

  20. 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

  1. 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...

  2. Catalytic asymmetric Torgov cyclization: a concise total synthesis of (+)-estrone.

    PubMed

    Prévost, Sébastien; Dupré, Nathalie; Leutzsch, Markus; Wang, Qinggang; Wakchaure, Vijay; List, Benjamin

    2014-08-11

    An asymmetric Torgov cyclization, catalyzed by a novel, highly Brønsted acidic dinitro-substituted disulfonimide, is described. The reaction delivers the Torgov diene and various analogues with excellent yields and enantioselectivity. This method was applied in a very short synthesis of (+)-estrone.

  3. 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

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

    PubMed

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

    2016-01-26

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

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

    PubMed

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

    2016-01-26

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

  6. Traceless Synthesis of Asymmetrically Modified Bivalent Nucleosomes.

    PubMed

    Lechner, Carolin C; Agashe, Ninad D; Fierz, Beat

    2016-02-18

    Nucleosomes carry extensive post-translational modifications (PTMs), which results in complex modification patterns that are involved in epigenetic signaling. Although two copies of each histone coexist in a nucleosome, they may not carry the same PTMs and are often differently modified (asymmetric). In bivalent domains, a chromatin signature prevalent in embryonic stem cells (ESCs), namely H3 methylated at lysine 4 (H3K4me3), coexists with H3K27me3 in asymmetric nucleosomes. We report a general, modular, and traceless method for producing asymmetrically modified nucleosomes. We further show that in bivalent nucleosomes, H3K4me3 inhibits the activity of the H3K27-specific lysine methyltransferase (KMT) polycomb repressive complex 2 (PRC2) solely on the same histone tail, whereas H3K27me3 stimulates PRC2 activity across tails, thereby partially overriding the H3K4me3-mediated repressive effect. To maintain bivalent domains in ESCs, PRC2 activity must thus be locally restricted or reversed.

  7. 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

  8. 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.

  9. Asymmetric synthesis using chiral-encoded metal.

    PubMed

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

    2016-08-26

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

  10. Asymmetric synthesis using chiral-encoded metal.

    PubMed

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

    2016-01-01

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

  11. Asymmetric synthesis using chiral-encoded metal

    PubMed Central

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

    2016-01-01

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

  12. Asymmetric synthesis using chiral-encoded metal

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

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

    PubMed

    Yu, Bin; Xing, Hui; Yu, De-Quan; Liu, Hong-Min

    2016-01-01

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

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

    PubMed Central

    2016-01-01

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

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

    PubMed

    Pramanik, Suman; Ghorai, Prasanta

    2013-08-01

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

  16. De Novo Synthesis of Furanose Sugars: Catalytic Asymmetric Synthesis of Apiose and Apiose-Containing Oligosaccharides.

    PubMed

    Kim, Mijin; Kang, Soyeong; Rhee, Young Ho

    2016-08-01

    A de novo synthetic method towards apiose, a structurally unusual furanose, is reported. The key feature is sequential metal catalysis consisting of the palladium-catalyzed asymmetric intermolecular hydroalkoxylation of an alkoxyallene and subsequent ring-closing metathesis (RCM). This strategy enabled the efficient synthesis of various apiose-containing disaccharides and a unique convergent synthesis of trisaccharides. PMID:27381592

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

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

    PubMed

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

    2013-06-21

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

  19. Catalytic asymmetric total synthesis of (-)-galanthamine and (-)-lycoramine.

    PubMed

    Li, Lei; Yang, Qiao; Wang, Yuan; Jia, Yanxing

    2015-05-18

    The catalytic asymmetric total syntheses of (-)-galanthamine (1) and (-)-lycoramine (2) have been achieved by using a conceptually new strategy featuring two metal-catalyzed reactions as the key steps. A new method for the construction of 3,4-fused benzofurans has been developed through a palladium-catalyzed intramolecular Larock annulation reaction, which was successfully applied to the construction of the ABD tricyclic skeleton of 1 and 2. To achieve the asymmetric synthesis of 1 and 2, a Sc(III)/N,N'-dioxide complex was used to catalyze the enantioselective conjugate addition of 3-alkyl-substituted benzofuranone to methyl vinyl ketone for the construction of a chiral quaternary carbon center. PMID:25847447

  20. Synthesis of novel metallocenes: Asymmetric hydrogenation catalysts to conductive polymers

    SciTech Connect

    Erickson, M.S.

    1992-01-01

    The goal of this research was to synthesize conductive polymers based on repeating ferrocene units. During the course of this study, the design of the conductive polymers evolved from the initial model based on [open quotes]stacked[open quotes] ferrocenes where ethano bridged cyclophentadienyl rings are linked by iron(II), to the latest ferrocene-diene model where ferrocene units were linked by double bonds. In the pursuit of these elusive monomers, attempts at their synthesis led down dead-end routes, even though new molecules were synthesized. Some of these dead-end routes, even though new molecules were synthesized. All the work reported in this dissertation had the eventual goal of synthesizing potential monomers for ferrocene conductive polymers. This dissertation is divided into three chapters. Chapter one describes the attempted synthesis of thiophene derivatives where a cyclopentadienyl ring is fused to the [c]-face. Although the target molecule was never synthesized, a convenient and safe new synthesis of 3,4-dibromo=2,5-dimethyl thiophene was developed along with the synthesis and full characterization of 3-bromo-4-trimethylsilyl-2,5-dimethylthiophene. Chapter two describes the design of asymmetric hydrogenation catalysts and the convenient synthesis of chiral titanocene derivatives. Chapter three summarizes the history of the attempts to prepare ferrocene containing conductive polymers and describes the synthesis of ferrocenophenes and diethano bridged bis(cyclophentadienyl) compounds for use as monomeric precursors to conductive polymers based on repeating ferrocene units.

  1. Asymmetric Total Synthesis of ent-Pyripyropene A.

    PubMed

    Fuse, Shinichiro; Ikebe, Ayako; Oosumi, Kazuya; Karasawa, Tomoya; Matsumura, Keisuke; Izumikawa, Miho; Johmoto, Kohei; Uekusa, Hidehiro; Shin-ya, Kazuo; Doi, Takayuki; Takahashi, Takashi

    2015-06-22

    An asymmetric total synthesis of ent-pyripyropene A was achieved by a convergent synthetic route. We used our originally developed Ti(III) -catalyzed radical cyclization to construct an AB-ring portion that consisted of a trans-decalin skeleton with five contiguous stereogenic centers. The coupling between the AB-ring and the DE-ring portions, and a subsequent C-ring cyclization, led to the total synthesis of ent-pyripyropene A. An evaluation of the insecticidal activity of ent-pyripyropene A against two aphid species revealed that ent-pyripyropene A was 35-175 times less active than naturally occurring pyripyropene A. This result indicated that the biological target of pyripyropene A recognizes the absolute configuration of pyripyropene A.

  2. 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

  3. Asymmetric Total Synthesis of ent-Pyripyropene A.

    PubMed

    Fuse, Shinichiro; Ikebe, Ayako; Oosumi, Kazuya; Karasawa, Tomoya; Matsumura, Keisuke; Izumikawa, Miho; Johmoto, Kohei; Uekusa, Hidehiro; Shin-ya, Kazuo; Doi, Takayuki; Takahashi, Takashi

    2015-06-22

    An asymmetric total synthesis of ent-pyripyropene A was achieved by a convergent synthetic route. We used our originally developed Ti(III) -catalyzed radical cyclization to construct an AB-ring portion that consisted of a trans-decalin skeleton with five contiguous stereogenic centers. The coupling between the AB-ring and the DE-ring portions, and a subsequent C-ring cyclization, led to the total synthesis of ent-pyripyropene A. An evaluation of the insecticidal activity of ent-pyripyropene A against two aphid species revealed that ent-pyripyropene A was 35-175 times less active than naturally occurring pyripyropene A. This result indicated that the biological target of pyripyropene A recognizes the absolute configuration of pyripyropene A. PMID:26014374

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

    PubMed

    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

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

    PubMed

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

    2015-10-01

    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.

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

    PubMed Central

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

    2015-01-01

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

  7. 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. Total Synthesis of Enantiopure (+)-γ -Lycorane Using Highly Efficient Pd-Catalyzed Asymmetric Allylic Alkylation

    PubMed Central

    Chapsal, Bruno D.; Ojima, Iwao

    2008-01-01

    Highly efficient short total synthesis of γ -lycorane (>99% ee, 41% overall yield) was achieved by using the asymmetric allylic alkylation in the key step catalyzed by palladium complexes with novel chiral biphenol-based monodentate phosphoramidite ligands. PMID:16562900

  9. Substrate-Controlled Asymmetric Total Synthesis and Structure Revision of (-)-Bisezakyne A.

    PubMed

    Shin, Iljin; Lee, Dongjoo; Kim, Hyoungsu

    2016-09-01

    The first asymmetric total synthesis and subsequent structure revision of (-)-bisezakyne A, a Laurencia C15 acetogenin from Alpysia oculifera, has been accomplished. Our substrate-controlled synthesis of this oxolane natural product features a highly stereoselective "protecting-group-dependent" intramolecular amide enolate alkylation strategy for the synthesis of the key 9,10-trans-9,12-cis-10-hydroxytetrahydrofuran intermediate through "nonchelate" control. In addition, our synthesis determined the absolute configuration of the halogenated marine natural product. PMID:27551943

  10. 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.

  11. 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

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

    SciTech Connect

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

    2011-12-20

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

  13. Asymmetric synthesis of cyclic indole aminals via 1,3-stereoinduction.

    PubMed

    Li, Hongmei; Chen, Cheng-yi; Nguyen, Hoa; Cohen, Ryan; Maligres, Peter E; Yasuda, Nobuyoshi; Mangion, Ian; Zavialov, Ilia; Reibarkh, Mikhail; Chung, John Y L

    2014-09-19

    A general and efficient asymmetric synthesis of cyclic indoline aminals was developed with a high level of 1,3-stereoinduction through a dynamic crystallization-driven condensation. Dehydrogenation of the indoline aminals with potassium permanganate produced the corresponding cyclic indole aminals in high yields and excellent enantioselectivities. This general methodology was successfully applied to the synthesis of a wide variety of chiral cyclic indoline aminals and indole aminals with aromatic and aliphatic functional groups. PMID:25162915

  14. Proline as chiral auxiliary for the economical asymmetric synthesis of ruthenium(II) polypyridyl complexes.

    PubMed

    Fu, Chen; Wenzel, Marianne; Treutlein, Elisabeth; Harms, Klaus; Meggers, Eric

    2012-09-17

    A straightforward method for the synthesis of virtually enantiomerically pure ruthenium(II) polypyridyl complexes [Ru(pp)(pp')(pp")](PF(6))(2), pp = bidentate polypyridyl has been developed. The synthesis draws from the readily available racemic starting material cis-[Ru(pp)(pp')Cl(2)] and the natural amino acids l- or d-proline and relies on a dynamic asymmetric transformation under thermodynamic control.

  15. Synthesis of Chiral β-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 β-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 β-amino nitroalkane products and their derivatives are versatile intermediates in organic synthesis. PMID:26652759

  16. Amitorines A and B, Nitrogenous Diterpene Metabolites of Theonella swinhoei: Isolation, Structure Elucidation, and Asymmetric Synthesis.

    PubMed

    Ota, Koichiro; Hamamoto, Yukiko; Eda, Wakiko; Tamura, Kenta; Sawada, Akiyoshi; Hoshino, Ayako; Mitome, Hidemichi; Kamaike, Kazuo; Miyaoka, Hiroaki

    2016-04-22

    Two new nitrogenous prenylbisabolanes never before found in Lithistid sponges have been isolated from Theonella swinhoei. These new diterpenes, named amitorine A (1) and amitorine B (2), containing a prenylbisabolane skeleton have been characterized by spectroscopic analyses, and the relative and absolute configurations of 1 and 2 were determined by asymmetric synthesis of both diastereomers via the common bicyclic lactone 6 intermediate.

  17. 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

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

    PubMed

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

    2015-12-18

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

  19. Asymmetric Synthesis of Trifluoromethylated Amines via Catalytic Enantioselective Isomerization of Imines

    PubMed Central

    Wu, Yongwei

    2012-01-01

    A new approach toward the asymmetric synthesis of optically active trifluromethylated 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 enantioselecitivities. PMID:22906148

  20. Amitorines A and B, Nitrogenous Diterpene Metabolites of Theonella swinhoei: Isolation, Structure Elucidation, and Asymmetric Synthesis.

    PubMed

    Ota, Koichiro; Hamamoto, Yukiko; Eda, Wakiko; Tamura, Kenta; Sawada, Akiyoshi; Hoshino, Ayako; Mitome, Hidemichi; Kamaike, Kazuo; Miyaoka, Hiroaki

    2016-04-22

    Two new nitrogenous prenylbisabolanes never before found in Lithistid sponges have been isolated from Theonella swinhoei. These new diterpenes, named amitorine A (1) and amitorine B (2), containing a prenylbisabolane skeleton have been characterized by spectroscopic analyses, and the relative and absolute configurations of 1 and 2 were determined by asymmetric synthesis of both diastereomers via the common bicyclic lactone 6 intermediate. PMID:27007992

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  2. Asymmetric Total Synthesis of the Indole Diterpene Alkaloid Paspaline.

    PubMed

    Sharpe, Robert J; Johnson, Jeffrey S

    2015-10-01

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

  3. Asymmetric Total Synthesis of the Indole Diterpene Alkaloid Paspaline

    PubMed Central

    Sharpe, Robert J.; Johnson, Jeffrey S.

    2015-01-01

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

  4. Large-scale asymmetric synthesis of a cathepsin S inhibitor.

    PubMed

    Lorenz, Jon C; Busacca, Carl A; Feng, XuWu; Grinberg, Nelu; Haddad, Nizar; Johnson, Joe; Kapadia, Suresh; Lee, Heewon; Saha, Anjan; Sarvestani, Max; Spinelli, Earl M; Varsolona, Rich; Wei, Xudong; Zeng, Xingzhong; Senanayake, Chris H

    2010-02-19

    A potent reversible inhibitor of the cysteine protease cathepsin-S was prepared on large scale using a convergent synthetic route, free of chromatography and cryogenics. Late-stage peptide coupling of a chiral urea acid fragment with a functionalized aminonitrile was employed to prepare the target, using 2-hydroxypyridine as a robust, nonexplosive replacement for HOBT. The two key intermediates were prepared using a modified Strecker reaction for the aminonitrile and a phosphonation-olefination-rhodium-catalyzed asymmetric hydrogenation sequence for the urea. A palladium-catalyzed vinyl transfer coupled with a Claisen reaction was used to produce the aldehyde required for the side chain. Key scale up issues, safety calorimetry, and optimization of all steps for multikilogram production are discussed. PMID:20102230

  5. Asymmetric Catalysis with Ethylene. Synthesis of Functionalized Chiral Enolates

    PubMed Central

    Biswas, Souvagya; Page, Jordan P.; Dewese, Kendra R.; RajanBabu, T. V.

    2016-01-01

    Trialkylsilyl enol ethers are versatile intermediates often used as enolate surrogates for the synthesis of carbonyl compounds. Yet there are no reports of broadly applicable, catalytic methods for the synthesis of chiral silyl enol ethers carrying latent functionalities useful for synthetic operations beyond the many possible reactions of the silyl enol ether moiety itself. Here we report a general procedure for highly catalytic (substrate:catalyst ratio up to 1000:1) and enantioselective (92% to 98% major enantiomer) synthesis of such compounds bearing a vinyl group at a chiral carbon at the β-position. The reactions, run under ambient conditions, use trialkylsiloxy-1,3-dienes and ethylene (1 atmosphere) as precursors, and readily available (bis-phosphine)-cobalt(II) complexes as catalysts. The silyl enolates can be readily converted into novel enantiopure vinyl triflates, a class of highly versatile cross-coupling reagents, enabling the syntheses of other enantiomerically pure, stereo-defined trisubstituted alkene intermediates not easily accessible by current methods. Examples of Kumada, Stille and Suzuki coupling reactions are illustrated. PMID:26529467

  6. Asymmetric synthesis of gem-difluoromethylenated linear triquinanes via cascade gem-difluoroalkyl radical cyclization.

    PubMed

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

    2015-01-16

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

  7. Vanadium in asymmetric synthesis: emerging concepts in catalyst design and applications.

    PubMed

    Takizawa, Shinobu; Gröger, Harald; Sasai, Hiroaki

    2015-06-15

    In recent years vanadium catalysis has been extended to a range of different and even complementary directions in asymmetric synthesis. Inspired by nature's way to activate both substrate and reagent in many cases, the design of efficient bifunctional and dinuclear vanadium catalysts has been achieved. Furthermore, vanadium catalysis has been an early field in which "hybrid catalysts" have been studied in detail by incorporation of oxovanadium complexes into proteins, thus giving artificial enzymes. In addition, a high compatibility of vanadium with proteins enabled the use of vanadium chemocatalysts for combinations with enzyme catalysis in one-pot, thus leading to dynamic kinetic resolutions. In this contribution, these three concepts of vanadium catalysis opening up new perspectives for asymmetric synthesis are reviewed.

  8. Asymmetric aerobic oxidative NHC-catalysed synthesis of dihydropyranones utilising a system of electron transfer mediators.

    PubMed

    Axelsson, A; Hammarvid, E; Ta, L; Sundén, H

    2016-10-01

    In the context of green chemistry, the replacement of high molecular weight stoichiometric oxidants with O2 is most desirable but difficult. Here, we report the asymmetric aerobic oxidative synthesis of dihydropyranones. The oxidation is aided by a system of electron transfer mediators and is selective toward the homoenolate. The dihydropyranones can be isolated in high to excellent yields, with high ee (up to 95%). PMID:27604573

  9. First asymmetric synthesis of the cyclohexanone subunit of baconipyrones A and B. Revision of its structure.

    PubMed

    Turks, Māris; Murcia, M Carmen; Scopelliti, Rosario; Vogel, Pierre

    2004-09-01

    [reaction: see text] An asymmetric synthesis of the 3,5-dihydroxycyclohexanone subunit of baconipyrones A and B, as well as that of the hydroxydiketone subunit of baconipyrones C and D ((-)-(4S,6S)-4,6-dimethyl-5-hydroxynonan-3,7-dione), is described. Key steps include sulfur dioxide-induced additions of enoxysilanes to 1,3-dioxy-1,3-dienes, followed by retro-ene desulfitations (retro-ene elimination of SO(2)).

  10. 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.

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

    PubMed

    Güngör, Ozlem; Gürkan, Perihan

    2010-09-15

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

  12. Asymmetric total synthesis of (-)-panacene and correction of its relative configuration.

    PubMed

    Boukouvalas, John; Pouliot, Martin; Robichaud, Joël; MacNeil, Stephen; Snieckus, Victor

    2006-08-01

    [reaction: see text] The first synthesis of (-)-panacene has been accomplished in concise, highly stereoselective fashion from commercially available 2-methoxy-6-methylbenzoic acid (15 steps, 8.3% overall yield). The synthesis unambiguously establishes the correct relative and absolute configuration of panacene, and demonstrates the serviceability of Pd(II)-mediated tandem intramolecular alkoxycarbonylation-lactonization for the expedient assembly of its tricyclic core, and the dual role of asymmetric alkynylation as an initial source of chirality and as a powerful tool for manipulating diastereoselectivity.

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

    PubMed

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

    2015-01-01

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

  14. 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

  15. 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

  16. Information synthesis: a practical guide.

    PubMed Central

    Goldschmidt, P G

    1986-01-01

    Information synthesis is one of the most valuable contributions a scientist can make. This paper offers guidance in preparing information synthesis and a means of assessing their adequacy. Preparing an information synthesis requires four steps: defining the topic and relevant information about that topic, the purpose of the synthesis, and the target audience; systematically gathering this relevant information; assessing the validity of such information; and presenting validated information in a way useful to the target audience. This paper presents guidelines and criteria for each step, and some helpful hints for authors in preparing an information synthesis. PMID:3733458

  17. Asymmetric synthesis of tetrahydroisoquinolines by enzymatic Pictet-Spengler reaction.

    PubMed

    Nishihachijo, Masakatsu; Hirai, Yoshinori; Kawano, Shigeru; Nishiyama, Akira; Minami, Hiromichi; Katayama, Takane; Yasohara, Yoshihiko; Sato, Fumihiko; Kumagai, Hidehiko

    2014-01-01

    Norcoclaurine synthase (NCS) catalyzes the stereoselective Pictet-Spengler reaction between dopamine and 4-hydroxyphenylacetaldehyde as the first step of benzylisoquinoline alkaloid synthesis in plants. Recent studies suggested that NCS shows relatively relaxed substrate specificity toward aldehydes, and thus, the enzyme can serve as a tool to synthesize unnatural, optically active tetrahydroisoquinolines. In this study, using an N-terminally truncated NCS from Coptis japonica expressed in Escherichia coli, we examined the aldehyde substrate specificity of the enzyme. Herein, we demonstrate the versatility of the enzyme by synthesizing 6,7-dihydroxy-1-phenethyl-1,2,3,4-tetrahydroisoquinoline and 6,7-dihydroxy-1-propyl-1,2,3,4-tetrahydroisoquinoline in molar yields of 86.0 and 99.6% and in enantiomer excess of 95.3 and 98.0%, respectively. The results revealed the enzyme is a promising catalyst that functions to stereoselectively produce various 1-substituted-1,2,3,4-tetrahydroisoquinolines. PMID:25036970

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

    PubMed

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

    2016-07-21

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

  19. Enantioselective Synthesis of Dialkylated α-Hydroxy Carboxylic Acids through Asymmetric Phase-Transfer Catalysis.

    PubMed

    Duan, Shaobo; Li, Sanliang; Ye, Xinyi; Du, Nuan-Nuan; Tan, Choon-Hong; Jiang, Zhiyong

    2015-08-01

    In the presence of an L-tert-leucine-derived urea-ammonium salt as phase-transfer catalyst, a highly enantioselective alkylation of 5H-oxazol-4-ones with various benzyl bromides and allylic bromides has been developed to furnish catalytic asymmetric synthesis of biologically important dialkylated α-hydroxy carboxylic acids with a broad scope. This is the first example of an L-amino acid-derived urea-ammonium salt being used as a phase-transfer catalyst with excellent catalytic efficiency.

  20. An efficient asymmetric synthesis of an estrogen receptor modulator by sulfoxide-directed borane reduction.

    PubMed

    Song, Zhiguo J; King, Anthony O; Waters, Marjorie S; Lang, Fengrui; Zewge, Daniel; Bio, Matthew; Leazer, Johnnie L; Javadi, Gary; Kassim, Amude; Tschaen, David M; Reamer, Robert A; Rosner, Thorsten; Chilenski, Jennifer R; Mathre, David J; Volante, R P; Tillyer, Richard

    2004-04-20

    An efficient asymmetric synthesis of a selective estrogen receptor modulator (SERM) that has a dihydrobenzoxathiin core structure bearing two stereogenic centers is reported. The stereogenic centers were established by an unprecedented chiral sulfoxide-directed stereospecific reduction of an alpha,beta-unsaturated sulfoxide to the saturated sulfide in one step. Studies to elucidate the mechanism for this reduction are reported. Highly efficient Cu(I)-mediated ether formation was used to install the ether side chain, and selective debenzylation conditions were developed to remove the benzyl protecting groups on the phenols.

  1. Characterization of Lassa Virus Cell Entry Inhibitors: Determination of the Active Enantiomer by Asymmetric Synthesis

    PubMed Central

    Whitby, Landon R.; Lee, Andrew M.; Kunz, Stefan; Oldstone, Michael B. A.; Boger, Dale L.

    2009-01-01

    The comparative characterization of a series of 4-acyl-1,6-dialkylpiperazin-2-ones as potent cell entry inhibitors of the hemorrhagic fever arenavirus Lassa (LASV) is disclosed. The resolution and examination of the individual enantiomers of the prototypical LASV cell entry inhibitor 3 (16G8) is reported and the more potent (–)-enantiomer was found to be 15-fold more active than the corresponding (+)-enantiomer. The absolute configuration of (–)-3 was established by asymmetric synthesis of the active inhibitor (–)-(S)-3 (lassamycin-1). A limited deletion scan of lassamycin-1 defined key structural features required of the prototypical inhibitors. PMID:19428249

  2. 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 α,β-unsaturated aldehydes with 1,4-dithiane-2,5-diol, and a domino Michael/α-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

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

    PubMed

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

    2015-03-20

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

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

    PubMed

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

    2015-08-31

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

  5. 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

  6. 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.

  7. [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.

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

    PubMed

    Ribó, 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

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

    PubMed

    Schrempp, Michael; Thiede, Sebastian; Herkommer, Daniel; Gansäuer, 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 α-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 α-tetrasubstituted butyrolactone motif of the leupyrrins in only four steps from commercially available substrates. PMID:26354047

  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 α- and β-ketoesters, 2-(6′-methoxy-2′-naphthyl)propenoic acid, β-(acylamino)acrylates, and enol acetates. PMID:15067137

  11. A practical synthesis of renin inhibitor MK-1597 (ACT-178882) via catalytic enantioselective hydrogenation and epimerization of piperidine intermediate.

    PubMed

    Molinaro, Carmela; Shultz, Scott; Roy, Amélie; Lau, Stephen; Trinh, Thao; Angelaud, Rémy; O'Shea, Paul D; Abele, Stefan; Cameron, Mark; Corley, Ed; Funel, Jacques-Alexis; Steinhuebel, Dietrich; Weisel, Mark; Krska, Shane

    2011-02-18

    A practical enantioselective synthesis of renin inhibitor MK-1597 (ACT-178882), a potential new treatment for hypertension, is described. The synthetic route provided MK-1597 in nine steps and 29% overall yield from commercially available p-cresol (7). The key features of this sequence include a catalytic asymmetric hydrogenation of a tetrasubstituted ene-ester, a highly efficient epimerization/saponification sequence of 4 which sets both stereocenters of the molecule, and a short synthesis of amine fragment 2.

  12. Short synthesis of the C1-C14 stretch of discodermolide from building blocks prepared by asymmetric catalysis.

    PubMed

    Cao, Huanyan; Parker, Kathlyn A

    2008-04-01

    A convergent and stereoselective synthesis of the C1-C14 stretch of (+)-discodermolide demonstrates the utility of the "asymmetric catalysis approach" to complex polypropionates. The preparation of this complex synthon requires 15 steps in the longest linear sequence and 19 steps total from inexpensive materials.

  13. 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.

  14. Enantioselective Synthesis of 3a-Amino-Pyrroloindolines by Copper-Catalyzed Direct Asymmetric Dearomative Amination of Tryptamines.

    PubMed

    Liu, Chuan; Yi, Ji-Cheng; Zheng, Zhong-Bo; Tang, Yong; Dai, Li-Xin; You, Shu-Li

    2016-01-11

    A direct asymmetric dearomative amination of tryptamines with O-(2,4-dinitrophenyl)hydroxylamine (DPH) was achieved using CuBr-bisoxazoline complex as a catalyst, affording 3a-amino-pyrroloindolines in good to excellent enantioselectivity under mild reaction conditions. Furthermore, the synthetic value of this method was demonstrated in the total synthesis of (-)-psychotriasine in a highly concise manner. PMID:26603145

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

    PubMed

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

    2014-10-01

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

  16. [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 α-alkylation and β'-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 α-amino-H-phosphinate with alkenyl triflate, followed by diastereoselective hydrogenation of the alkene moiety. PMID:25174361

  17. Asymmetric phosphorylation through catalytic P(III) phosphoramidite transfer: Enantioselective synthesis of d-myo-inositol-6-phosphate

    PubMed Central

    Jordan, Peter A.; Kayser-Bricker, Katherine J.; Miller, Scott J.

    2010-01-01

    Despite the ubiquitous use of phosphoramidite chemistry in the synthesis of biophosphates, catalytic asymmetric phosphoramidite transfer remains largely unexplored for phosphate ester synthesis. We have discovered that a tetrazole-functionalized peptide, in the presence of 10-Å molecular sieves, functions as an enantioselective catalyst for phosphite transfer. This chemistry in turn has been used as the key step in a streamlined synthesis of myo-inositol-6-phosphate. Mechanistic insights implicate phosphate as a directing group for a highly selective kinetic resolution of a protected inositol monophosphate. This work represents a distinct and efficient method for the selective catalytic phosphorylation of natural products. PMID:20439750

  18. Catalytic asymmetric synthesis of butane diacetal-protected (4S,5S)-dihydroxycyclohexen-1-one and use in natural product synthesis.

    PubMed

    Burns, David J; Hachisu, Shuji; O'Brien, Peter; Taylor, Richard J K

    2012-10-14

    Due to the lack of availability of unnatural (+)-quinic acid as a starting material, a 6-step synthesis of butane diacetal-protected (4S,5S)-dihydroxycyclohexen-1-one (formally derived from (+)-quinic acid) has been devised. The key catalytic asymmetric step involves a chiral Co-salen-catalysed epoxide ring-opening reaction. (4S,5S)-Dihydroxycyclohexen-1-one was utilised in the synthesis of two cyclohexenone natural products isolated from the mycelia of Lasiodiplodia theobromae. PMID:22930235

  19. 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.

  20. 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

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

    PubMed

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

    2015-02-01

    The first iridium-catalyzed intermolecular asymmetric allylic amination reaction with 2-hydroxypyridines has been developed, thus providing a highly efficient synthesis of enantioenriched N-substituted 2-pyridone derivatives from readily available starting materials. This protocol features a good tolerance of functional groups in both the allylic carbonates and 2-hydroxypyridines, thereby delivering multifunctionalized heterocyclic products with up to 98% yield and 99% ee. PMID:25504907

  2. Asymmetric total synthesis of (+)-aphanamol I based on the transition metal catalyzed [5 + 2] cycloaddition of allenes and vinylcyclopropanes.

    PubMed

    Wender, P A; Zhang, L

    2000-07-27

    A concise asymmetric total synthesis of (+)-aphanamol I is described, based on the transition metal catalyzed [5 + 2] allenyl-vinylcyclopropane cycloaddition. The key cycloaddition precursor is convergently assembled from (R)-(+)-limonene and cyclopropane diester through a novel decarboxylative dehydration reaction. The metal-catalyzed [5 + 2] cycloaddition of this precursor proceeds with complete chemo, endo/exo, and diastereoselectivity in 93% yield, representing an effective general route to bicyclo[5.3.0]decane derivatives.

  3. Design and synthesis of ternary Co3O4/carbon coated TiO2 hybrid nanocomposites for asymmetric supercapacitors.

    PubMed

    Kim, Myeongjin; Choi, Jaeho; Oh, Ilgeun; Kim, Jooheon

    2016-07-20

    Recently, attention has been focused on the synthesis and application of nanocomposites for supercapacitors, which can have superior electrochemical performance than single structured materials. Here, we report a carbon-coated TiO2/Co3O4 ternary hybrid nanocomposite (TiO2@C/Co) electrode for supercapacitors. A carbon layer was directly introduced onto the TiO2 surface via thermal vapor deposition. The carbon layer provides anchoring sites for the deposition of Co3O4, which was introduced onto the carbon-coated TiO2 surface by hydrazine and the thermal oxidation method. The TiO2@C/Co electrode exhibits much higher charge storage capacity relative to pristine TiO2, carbon-coated TiO2, and pristine Co3O4, showing a specific capacitance of 392.4 F g(-1) at a scan rate of 5 mV s(-1) with 76.2% rate performance from 5 to 500 mV s(-1) in 1 M KOH aqueous solution electrolyte. This outstanding electrochemical performance can be attributed to the high conductivity and high pseudo-capacitive contributions of the nanoscale particles. To evaluate the capacitive performance of a supercapacitor device employing the TiO2@C/Co electrode, we have successfully assembled TiO2@C/Co//activated carbon (AC) asymmetric supercapacitors. The optimized TiO2@C/Co//AC supercapacitor could be cycled reversibly in the voltage range from 0 to 1.5 V, and it exhibits a specific capacitance of 59.35 F g(-1) at a scan rate of 5 mV s(-1) with a specific capacitance loss of 15.4% after 5000 charge-discharge cycles. These encouraging results show great potential in terms of developing high-capacitive energy storage devices for practical applications. PMID:27381559

  4. Asymmetric Synthesis of Enantiomerically Pure Mono- and Binuclear Bis(cyclometalated) Iridium(III) Complexes.

    PubMed

    Yao, Su-Yang; Ou, Yan-Ling; Ye, Bao-Hui

    2016-06-20

    Chiral precursors Λ-[Ir(ppy)2(l-pro)] (Λ-L, where ppy is 2-phenylpyridine; pro is proline), Λ-[Ir(ppy)2(MeCN)2](PF6) (Λ-1), Δ-[Ir(ppy)2(d-pro)] (Δ-D), and Δ-[Ir(ppy)2(MeCN)2](PF6) (Δ-1) were synthesized from rac-[(Ir(ppy)2)2Cl2] and l-pro or d-pro by means of the auxiliary ligand strategy with 99% de values. The enantiopure mono complexes Λ/Δ-[Ir(ppy)2(L)](PF6) (L is 2,2'-bipyridine, Λ/Δ-2; L is 2,2'-dipyrimidine (dpm), Λ/Δ-3; L is 2,2'-bibenzimidazole (H2bbim), Λ/Δ-4) with 99% ee values and binuclear complexes ΛΛ/ΔΔ-[(Ir(ppy)2)2(dpm)](PF6)2 (ΛΛ-5 and ΔΔ-5) and ΛΛ/ΔΔ-[(Ir(ppy)2)2(bbim)] (ΛΛ-6 and ΔΔ-6) with 99% de values were synthesized in one step using the corresponding chiral precursors. The absolute configurations at Ir(III) centers of precursor Δ-1, mononuclear Λ-3, and binuclear ΔΔ-6 were confirmed by single-crystal structural analysis and characterized by circular dichroism (CD) spectroscopy. The correlation between the absolute configuration at Ir(III) center and CD spectra was established. The configurations at Ir(III) centers are stable during the reactions, and the chiral precursors can be used for the asymmetric synthesis of enantiomerically pure mono- and polynuclear Ir(III) complexes. Moreover, meso ΛΔ-[(Ir(ppy)2)2(dpm)](PF6)2 (meso-5) and ΛΔ-[(Ir(ppy)2)2(bbim)] (meso-6) were also synthesized using these precursors. PMID:27280959

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

    PubMed

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

    2014-09-01

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

  6. Proportion congruency and practice: A contingency learning account of asymmetric list shifting effects.

    PubMed

    Schmidt, James R

    2016-09-01

    Performance is impaired when a distracting stimulus is incongruent with the target stimulus (e.g., "green" printed in red). This congruency effect is decreased when the proportion of incongruent trials is increased, termed the proportion congruent effect. This effect is typically interpreted in terms of the adaptation of attention in response to conflict. In contrast, the contingency account argues that the effect is driven by the learning of predictive relationships between words and responses. In a recent report, Abrahamse, Duthoo, Notebaert, and Risko (2013) demonstrated larger changes in the magnitude of the proportion congruent effect when switching from a mostly congruent list to a mostly incongruent list, relative to the reverse order. They argued that this asymmetric list shifting effect fits only with the conflict adaptation perspective. However, the current paper presents reanalyses of this data and an adaptation of the Parallel Episodic Processing model that together demonstrate how the contingency account can explain these findings equally well when considering the generally accepted notion that performance improves with practice. The contingency account may still be the most parsimonious view. (PsycINFO Database Record

  7. Proportion congruency and practice: A contingency learning account of asymmetric list shifting effects.

    PubMed

    Schmidt, James R

    2016-09-01

    Performance is impaired when a distracting stimulus is incongruent with the target stimulus (e.g., "green" printed in red). This congruency effect is decreased when the proportion of incongruent trials is increased, termed the proportion congruent effect. This effect is typically interpreted in terms of the adaptation of attention in response to conflict. In contrast, the contingency account argues that the effect is driven by the learning of predictive relationships between words and responses. In a recent report, Abrahamse, Duthoo, Notebaert, and Risko (2013) demonstrated larger changes in the magnitude of the proportion congruent effect when switching from a mostly congruent list to a mostly incongruent list, relative to the reverse order. They argued that this asymmetric list shifting effect fits only with the conflict adaptation perspective. However, the current paper presents reanalyses of this data and an adaptation of the Parallel Episodic Processing model that together demonstrate how the contingency account can explain these findings equally well when considering the generally accepted notion that performance improves with practice. The contingency account may still be the most parsimonious view. (PsycINFO Database Record PMID:27585071

  8. Asymmetric Synthesis of 2,4,5-Trisubstituted Δ2-Thiazolines

    PubMed Central

    Bengtsson, Christoffer; Nelander, Hanna; Almqvist, Fredrik

    2013-01-01

    Δ2-Thiazolines are interesting heterocycles that display a wide variety of biological characteristics. They are also common in chiral ligands used for asymmetric syntheses and as synthetic intermediates. Herein, we present asymmetric routes to 2,4,5-trisubstituted Δ2-thiazolines. These Δ2-thiazolines were synthesized from readily accessible/commercially available α,β-unsaturated methyl esters through a Sharpless asymmetric dihydroxylation and an O→N acyl migration reaction as key steps. The final products were obtained in good yields with up to 97% enantiomeric excess. PMID:23776083

  9. Homogeneous asymmetric catalysis in fragrance chemistry.

    PubMed

    Ciappa, Alessandra; Bovo, Sara; Bertoldini, Matteo; Scrivanti, Alberto; Matteoli, Ugo

    2008-06-01

    Opposite enantiomers of a chiral fragrance may exhibit different olfactory activities making a synthesis in high enantiomeric purity commercially and scientifically interesting. Accordingly, the asymmetric synthesis of four chiral odorants, Fixolide, Phenoxanol, Citralis, and Citralis Nitrile, has been investigated with the aim to develop practically feasible processes. In the devised synthetic schemes, the key step that leads to the formation of the stereogenic center is the homogeneous asymmetric hydrogenation of a prochiral olefin. By an appropriate choice of the catalyst and the reaction conditions, Phenoxanol, Citralis, and Citralis Nitrile were obtained in high enantiomeric purity, and odor profiles of the single enantiomers were determined.

  10. Synthesis of Ferrocene Oxazoline N,O ligands and Their Application in Asymmetric Ethyl- and Phenylzinc Additions to Aldehydes.

    PubMed

    Nottingham, Chris; Benson, Robert; Müller-Bunz, Helge; Guiry, Patrick J

    2015-10-16

    The synthesis of a range of novel gem-disubstituted ferrocene-oxazoline ligands and their application in both the asymmetric ethyl- and phenylzinc additions to aldehydes is reported. These studies reveal that gem-disubstitution of i-Pr-containing ferrocene oxazoline ligands results in increased enantioselectivity compared to their unsubstituted counterparts. Utilizing zinc catalysis, these ligands provided a wide range of secondary alcohols in yields of up to 93% with ee's of up to >99%. An interesting crystal structure of a ferrocene oxide-lithium tetramer showing lithium-nitrogen coordination in the solid state is also presented.

  11. Asymmetric synthesis of 1,2,3-trisubstituted cyclopentanes and cyclohexanes as key components of substance p antagonists.

    PubMed

    Kuethe, Jeffrey T; Wong, Audrey; Wu, Jimmy; Davies, Ian W; Dormer, Peter G; Welch, Christopher J; Hillier, Michael C; Hughes, David L; Reider, Paul J

    2002-08-23

    An efficient asymmetric synthesis of 1,2,3-trisubstituted cyclopentanes and cyclohexanes is described. Three methods were developed for the preparation of the 2,3-disubstituted cyclopentenones and cyclohexenones, which are key achiral building blocks. These intermediates are reduced catalytically with (R)-2-methyloxazaborolidine in high yield (82-98%) and excellent ee (89-96%). Directed reduction of the chiral allylic alcohols using Red-Al gives exclusively the 1,2-anti stereochemistry (>99:1). Epimerization of the ester center followed by saponification/crystallization affords the desired hydroxyacids in good yield (65-70%) and in high enantiomeric excess (>99%).

  12. 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.

  13. Highly efficient asymmetric hydrogenation of cyano-substituted acrylate esters for synthesis of chiral γ-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 γ-lactams and γ-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 β-cyano-α-aryl-α,β-unsaturated ketones were first hydrogenated with excellent enantioselectivities (up to 98% ee) and high turnover numbers (TON up to 10,000). PMID:26661067

  14. Synthesis of l-muscone by asymmetric methylation via enol esters.

    PubMed

    Matsuda, Hiroyuki; Tanaka, Shigeru; Yamamoto, Kenichi; Ishida, Kenya

    2008-06-01

    An effective synthetic route of l-muscone (1) by asymmetric methylation, followed by enolate-trapping to generate enol esters as intermediates, was described. Interestingly, the enol esters can be used as substrates for enzymatic optical resolution to improve optical purity. Additionally, several excellent new chiral ligands were discovered for asymmetric methylation of (E)-cyclopentadec-2-enone to produce l-muscone with high optical purity.

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

    PubMed

    Zhou, Yi; Wu, Shuke; Li, Zhi

    2016-09-12

    Sustainable synthesis of useful and valuable chiral fine chemicals from renewable feedstocks is highly desirable but remains challenging. Reported herein is a designed and engineered set of unique non-natural biocatalytic cascades to achieve the asymmetric synthesis of chiral epoxide, diols, hydroxy acid, and amino acid in high yield and with excellent ee values from the easily available biobased l-phenylalanine. Each of the cascades was efficiently performed in one pot by using the cells of a single recombinant strain over-expressing 4-10 different enzymes. The cascade biocatalysis approach is promising for upgrading biobased bulk chemicals to high-value chiral chemicals. In addition, combining the non-natural enzyme cascades with the natural metabolic pathway of the host strain enabled the fermentative production of the chiral fine chemicals from glucose. PMID:27512928

  16. Catalytic asymmetric direct Mannich reaction: a powerful tool for the synthesis of alpha,beta-diamino acids.

    PubMed

    Arrayás, Ramón Gómez; Carretero, Juan C

    2009-07-01

    Optically active alpha,beta-diamino acids are very attractive targets in organic synthesis because of their wide-ranging biological significance and high versatility as synthetic building blocks. Efficient synthesis of such non-proteinogenic amino acid derivatives must face the challenge of generating two contiguous stereocenters with complete diastereo- and enantiocontrol in flexible, acyclic molecules. The catalytic asymmetric direct Mannich reaction has provided elegant and efficient solutions for the stereocontrolled assembly of both syn- and anti-alpha,beta-diamino acid derivatives, including those with a alpha-tetrasubstituted carbon stereocenter, with the aid of either organometallic or purely organic chiral catalysts (or the combination of both). This tutorial review highlights progress in this area, which has recently been boosted through two complementary strategies: the direct Mannich reaction of glycine ester Schiff bases with imines and the direct aza-Henry reaction between nitro compounds and imines. PMID:19551174

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

    PubMed

    Mori, Keiji; Itakura, Tsubasa; Akiyama, Takahiko

    2016-09-12

    Reported herein is an enantiodivergent synthesis of chiral biaryls by a chiral phosphoric acid catalyzed asymmetric transfer hydrogenation reaction. Upon treatment of biaryl lactols with aromatic amines and a Hantzsch ester in the presence of chiral phosphoric acid, dynamic kinetic resolution (DKR) involving a reductive amination reaction proceeded smoothly to furnish both R and S isomers of chiral biaryls with excellent enantioselectivities by proper choice of hydroxyaniline derivative. This trend was observed in wide variety of substrates, and various chiral biphenyl and phenyl naphthyl adducts were synthesized with satisfactory enantioselectivities in enantiodivergent fashion. The enantiodivergent synthesis of synthetically challenging, chiral o-tetrasubstituted biaryls were also accomplished, and suggests high synthetic potential of the present method. PMID:27491630

  18. PET imaging of nobiletin based on a practical total synthesis.

    PubMed

    Asakawa, Tomohiro; Hiza, Aiki; Nakayama, Miho; Inai, Makoto; Oyama, Dai; Koide, Hiroyuki; Shimizu, Kosuke; Wakimoto, Toshiyuki; Harada, Norihiro; Tsukada, Hideo; Oku, Naoto; Kan, Toshiyuki

    2011-03-14

    A practical synthesis of nobiletin, a polymethoxylated citrus flavone, was accomplished by utilizing our novel flavone synthesis. Synthetic nobiletin was labelled by selective demethylation and rapid incorporation of (11)C atom. Positron emission tomography images successfully visualized the brain distribution, which may provide therapeutic benefits in the treatment of Alzheimer's disease.

  19. Asymmetric reactions in continuous flow

    PubMed Central

    Mak, Xiao Yin; Laurino, Paola

    2009-01-01

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

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

    PubMed Central

    Hong, Allen Y.

    2014-01-01

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

  1. Asymmetric Synthesis of β-Substituted α-Methylenebutyro- lactones via TRIP-Catalyzed Allylation: Mechanistic Studies and Application to the Synthesis of (S)-(−)-Hydroxymatairesinol

    PubMed Central

    Fuchs, Michael; Schober, Markus; Orthaber, Andreas; Faber, Kurt

    2013-01-01

    Asymmetric allylation of (hetero)aromatic aldehydes by a zinc(II)-allylbutyrolactone species catalyzed by a chiral BINOL-type phosphoric acid gave β-substituted α-methylenebutyrolactones in 68 to >99% ee and 52–91% isolated yield. DFT studies on the intermediate Zn2+-complex – crucial for chiral induction – suggest a six-membered ring intermediate, which allows the phosphoric acid moiety to activate the aldehyde. The methodology was applied to the synthesis of the antitumour natural product (S)-(−)-hydroxymatairesinol. PMID:24415960

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

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

  3. Asymmetric Reduction of Lactam-Based β-Aminoacrylates. Synthesis of Heterocyclic β(2)-Amino Acids.

    PubMed

    Campello, Hugo Rego; Parker, Jeremy; Perry, Matthew; Ryberg, Per; Gallagher, Timothy

    2016-08-19

    The ability to affect asymmetric reduction of heterocyclic β-aminoacrylates 1 (n = 1-3) has been assessed with pyrrolidine and piperidone variants generating the corresponding N-heterocyclic β(2)-amino acids 3b and 5b with high enantioselectivity (≥97% ee) using a Rh/WALPHOS catalyst combination. The use of the carboxylic acid substrate was essential; the corresponding esters do undergo reduction but led to racemic products. The seven-ring azepanone variant (as the carboxylic acid 9b) underwent reduction, but only a minimal level of asymmetric induction was observed. PMID:27508307

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

    PubMed

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

    2013-08-16

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

  5. Synthesis of main-chain chiral quaternary ammonium polymers for asymmetric catalysis using quaternization polymerization.

    PubMed

    Haraguchi, Naoki; Ahamed, Parbhej; Parvez, Md Masud; Itsuno, Shinichi

    2012-01-01

    Main-chain chiral quaternary ammonium polymers were successfully synthesized by the quaternization polymerization of cinchonidine dimer with dihalides. The polymerization occurred smoothly under optimized conditions to give novel type of main-chain chiral quaternary ammonium polymers. The catalytic activity of the polymeric chiral organocatalysts was investigated on the asymmetric benzylation of N-(diphenylmethylidene)glycine tert-butyl ester.

  6. A Synthesis of Sloan-C Effective Practices, December 2011

    ERIC Educational Resources Information Center

    Moore, Janet C.

    2012-01-01

    Encouraging continuous improvement in the quality, scale and breadth of online education, the Sloan Consortium invites practitioners to share effective practices. This report synthesizes effective practices submitted by Sloan-C members to the online collection at http://www.sloanconsortium.org/effective as of December 2011. The synthesis includes…

  7. A Synthesis of Sloan-C Effective Practices, November 2010

    ERIC Educational Resources Information Center

    Moore, Janet C.

    2010-01-01

    Encouraging continuous improvement in the quality, scale and breadth of online education, the Sloan Consortium invites practitioners to share effective practices. This report synthesizes effective practices submitted by Sloan-C members to the online collection at http://www.sloanconsortium.org/effective as of November 2010. The synthesis includes…

  8. Enantioselective Synthesis of Spirobarbiturate-Cyclohexenes through Phosphine-Catalyzed Asymmetric [4 + 2] Annulation of Barbiturate-Derived Alkenes with Allenoates.

    PubMed

    Liu, Honglei; Liu, Yang; Yuan, Chunhao; Wang, Guo-Peng; Zhu, Shou-Fei; Wu, Yang; Wang, Bo; Sun, Zhanhu; Xiao, Yumei; Zhou, Qi-Lin; Guo, Hongchao

    2016-03-18

    An enantioselective synthesis of pharmaceutically important spirobarbiturates has been achieved via spirocyclic chiral phosphine-catalyzed asymmetric [4 + 2] annulation of barbiturate-derived alkenes with allenoates. With the use of this tool, various spirobarbiturate-cyclohexenes are obtained in good to excellent yields with excellent diastereo- and enantioselectivities. A wide range of α-substituted allenoates and barbiturate-derived alkenes were tolerated.

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

    PubMed

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

    2009-02-19

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

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

    PubMed

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

    2013-10-01

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

  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. 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

  13. 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

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

    PubMed Central

    Wu, Bulan; Li, Miaosheng; O’Doherty, 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

  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. Asymmetric domino multicatalysis for the synthesis of 3-substituted phthalides: cinchonine/NHC cooperative system.

    PubMed

    Youn, So Won; Song, Hyoung Sub; Park, Jong Hyub

    2014-02-01

    It is demonstrated that two organocatalysts, achiral NHC and chiral bifunctional cinchonine, are mutually compatible and operating concurrently and effectively to promote the asymmetric domino oxidation/oxa-Michael addition reaction. This protocol allowed access to both enantiomers of a product by using two natural, inexpensive pseudoenantiomeric cinchona alkaloids, cinchonine and cinchonidine, as well as to phthalides containing a chiral quaternary carbon center in good enantioselectivities.

  17. Stereodivergent Organocatalytic Intramolecular Michael Addition/Lactonization for the Asymmetric Synthesis of Substituted Dihydrobenzofurans and Tetrahydrofurans

    PubMed Central

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

    2014-01-01

    A stereodivergent asymmetric Lewis base catalyzed Michael addition/lactonization of enone acids into substituted dihydrobenzofuran and tetrahydrofuran derivatives is reported. Commercially available (S)-(−)-tetramisole hydrochloride gives products with high syn diastereoselectivity in excellent enantioselectivity (up to 99:1 d.r.syn/anti, 99 % eesyn), whereas using a cinchona alkaloid derived catalyst gives the corresponding anti-diastereoisomers as the major product (up to 10:90 d.r.syn/anti, 99 % eeanti). PMID:24989672

  18. Total Synthesis of Anti-Influenza Agents Zanamivir and Zanaphosphor via Asymmetric Aza-Henry Reaction.

    PubMed

    Lin, Long-Zhi; Fang, Jim-Min

    2016-09-01

    The potent anti-influenza agents, zanamivir and its phosphonate congener, are synthesized by using a nitro group as the latent amino group at C4 for asymmetric aza-Henry reaction with a chiral sulfinylimine, which is derived from inexpensive d-glucono-δ-lactone to establish the essential nitrogen-containing substituent at C5. This method provides an efficient way to construct the densely substituted dihydropyran core of zanamivir and zanaphosphor without using the hazardous azide reagent. PMID:27541804

  19. 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

  20. 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

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

    PubMed Central

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

    2011-01-01

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

  2. Asymmetric synthesis of crambescin A-C carboxylic acids and their inhibitory activity on voltage-gated sodium channels.

    PubMed

    Nakazaki, Atsuo; Nakane, Yoshiki; Ishikawa, Yuki; Yotsu-Yamashita, Mari; Nishikawa, Toshio

    2016-06-21

    Synthesis of both enantiomers of crambescin B carboxylic acid is described. A cis-enyne starting material was epoxidized under the conditions of Katsuki asymmetric epoxidation to give 95% ee of the epoxide, which was transformed to crambescin B carboxylic acid via bromocation-triggered cascade cyclization as the key step. Enantiomerically pure crambescin A and C carboxylic acids were also synthesized from the product of the cascade reaction. Structure-activity relationship (SAR) studies against voltage-gated sodium channel (VGSC) inhibition using those synthetic compounds revealed that the natural enantiomer of crambescin B carboxylic acid was most active and comparable to tetrodotoxin, and the unalkylated cyclic guanidinium structure is indispensible, while the carboxylate moiety is not important. The absolute stereochemistry of crambescin A was determined by a comparison of the methyl ester derived from natural crambescin A with that derived from the stereochemically defined crambescin A carboxylic acid synthesized in this study.

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

    PubMed Central

    2015-01-01

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

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

    PubMed

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

    2016-08-14

    A novel reverse microemulsion strategy was developed to asymmetrically encapsulate metal-oxide nanoparticles in silica by exploiting the self-catalytic growth of aminosilane-containing silica at a single surface site. This strategy produced various colloidal Janus nanoparticles, including Au/Fe3O4@asy-SiO2, which were converted to an Au-containing silica nanosphere, Au@con-SiO2, by reductive Fe3O4 dissolution. The use of Au@con-SiO2 as a metal-growing nanoreactor allowed the templated synthesis of various noble-metal nanocrystals, including a hollow dendritic Pt nanoshell which exhibits significantly better electrocatalytic activities for the oxygen reduction reaction than commercial Pt/C catalysts. PMID:27432650

  5. N,N-Diisopropyl-N-phosphonyl Imines Lead to Efficient Asymmetric Synthesis of Aziridine-2-Carboxylic Esters

    PubMed Central

    Kattamuri, Padmanabha V.; Xiong, Yiwen; Pan, Yi; Li, Guigen

    2013-01-01

    Highly diastereoselective asymmetric synthesis of chiral aziridine-2-carboxylic esters is reported for 20 examples with good yields (51–87%) and excellent diastereoselectivities (>99:1 dr for most cases). The modified N-phosphonyl imines are proven to be superior to previous imine auxiliaries for the aza Darzens reaction by using secondary isopropyl to replace primary benzyl group for N,N-diamino protection. In the meanwhile, a special operation by slowly adding the pre-cooled imine solution at −78 °C into the preformed β-bromo lithium enolate mixture at this temperature in the presence of 4 Å molecular sieves was found to be crucial in terms of yields and diastereoselectivity. The present method can provide an easy and general access to β-hydroxy α-amino acids and other important amino building blocks. PMID:23563304

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  7. Synthesis and biological evaluation of asymmetric gramicidin S analogues containing modified D-phenylalanine residues.

    PubMed

    van der Knaap, Matthijs; Engels, Eefje; Busscher, Henk J; Otero, José M; Llamas-Saiz, Antonio L; van Raaij, Mark J; Mars-Groenendijk, Roos H; Noort, Daan; van der Marel, Gijsbert A; Overkleeft, Herman S; Overhand, Mark

    2009-09-01

    The synthesis of new analogues of the cationic antimicrobial peptide gramicidin S, having a modified D-phenylalanine residue, their antibacterial properties against several gram positive and negative strains, as well as their hemolytic activity is reported.

  8. 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

  9. Asymmetric synthesis of anti-β-amino-α-hydroxy esters via dynamic kinetic resolution of β-amino-α-keto esters.

    PubMed

    Goodman, C Guy; Do, Dung T; Johnson, Jeffrey S

    2013-05-17

    A method for the asymmetric synthesis of enantioenriched anti-α-hydroxy-β-amino acid derivatives by enantioconvergent reduction of the corresponding racemic α-keto esters is presented. The requisite α-keto esters are prepared via Mannich addition of ethyl diazoacetate to imines followed by oxidation of the diazo group with Oxone. Implementation of a recently developed dynamic kinetic resolution of β-substituted-α-keto esters via Ru(II)-catalyzed asymmetric transfer hydrogenation provides the title motif in routinely high diastereo- and enantioselectivity.

  10. Synthesis of new asymmetric substituted boron amidines - reactions with CO and transfer hydrogenations of phenylacetylene.

    PubMed

    Cabrera, Alan R; Rojas, Rene S; Valderrama, Mauricio; Plüss, Pascal; Berke, Heinz; Daniliuc, Constantin G; Kehr, Gerald; Erker, Gerhard

    2015-12-01

    The syntheses of the new asymmetric substituted boron amidines [N'-(2,6-diisopropylphenyl)-N-(pentafluorophenyl)acetimidamide]bis(pentafluorophenyl)borate () and [N'-(2,6-diisopropylphenyl)-N-(4-cyanophenyl)acetimidamide]bis(pentafluorophenyl)borate () were achieved by reaction of one equivalent of HB(C6F5)2 and the respective amidines and . These adducts, bearing electron withdrawing groups, showed thermally induced H2 elimination forming the four-membered cyclic diazaborate derivatives and . These new species were characterized by spectroscopic methods. X-ray diffraction studies have been carried out on , and . To prevent undesired reactions at the nitrile group, one equivalent of B(C6F5)3 was added to yielding the -B(C6F5)3 nitrile adduct . Compound underwent thermally induced dehydrogenation to give the four-membered cyclic diazaborate derivative . CO was inserted into the ring systems of and forming the five-membered diazaborolone derivatives and . Phenylacetylene reacted stoichiometrically with the asymmetric substituted boron amidines , and to give styrene by double H transfer.

  11. Stereoselective synthesis of the C1-C13 fragment of (+)-discodermolide using asymmetric allyltitanations.

    PubMed

    BouzBouz, Samir; Cossy, Janine

    2003-08-21

    [reaction: see text] The synthesis of the C1-C13 fragment of (+)-discodermolide has been achieved. The configurations of the stereogenic centers have been controlled by enantioselective allyl- and crotyltitanations of aldehydes, and the Z configuration of the olefin at C8-C9 was controlled by a ring-closing metathesis.

  12. 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.

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

    PubMed Central

    Xu, Zun Le; Qiu, Sheng Xiang

    2010-01-01

    Summary Seven polyoxazoline ligands were synthesized in high yield in a one-pot reaction by heating polycarboxylic acids or their esters and chiral β-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

  14. 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

  15. A facile and practical synthesis of N-acetyl enamides.

    PubMed

    Tang, Wenjun; Capacci, Andrew; Sarvestani, Max; Wei, Xudong; Yee, Nathan K; Senanayake, Chris H

    2009-12-18

    A facile and practical method for the synthesis of N-acetyl alpha-arylenamides has been developed from corresponding ketoximes as the starting materials with ferrous acetate as the reducing reagent. This methodology offers mild reaction conditions, simple purification procedures, and high yields for a variety of N-acetyl enamides. PMID:19921804

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

    PubMed

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

    2016-08-01

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

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

    PubMed

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

    2014-06-14

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

  18. Asymmetric synthesis of anti-1,2-amino alcohols via the Borono-Mannich reaction: a formal synthesis of (-)-swainsonine.

    PubMed

    Au, Christopher W G; Pyne, Stephen G

    2006-09-01

    Chiral alpha-hydroxy aldehydes generated in situ by the ADH reaction of vinyl sulfones undergo a borono-Mannich reaction with beta-styrenyl boronic acid and primary amines to give anti-1,2-amino alcohols in high enantiomeric purities (83-95% ee). This new method allows much more rapid access to these valuable chiral building blocks that has been used in a short formal synthesis (10 synthetic steps from 4-penten-1-ol) of (-)-swainsonine.

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

    PubMed

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

    2016-01-01

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

  20. Enantioselective Synthesis of Spirobarbiturate-Cyclohexenes through Phosphine-Catalyzed Asymmetric [4 + 2] Annulation of Barbiturate-Derived Alkenes with Allenoates.

    PubMed

    Liu, Honglei; Liu, Yang; Yuan, Chunhao; Wang, Guo-Peng; Zhu, Shou-Fei; Wu, Yang; Wang, Bo; Sun, Zhanhu; Xiao, Yumei; Zhou, Qi-Lin; Guo, Hongchao

    2016-03-18

    An enantioselective synthesis of pharmaceutically important spirobarbiturates has been achieved via spirocyclic chiral phosphine-catalyzed asymmetric [4 + 2] annulation of barbiturate-derived alkenes with allenoates. With the use of this tool, various spirobarbiturate-cyclohexenes are obtained in good to excellent yields with excellent diastereo- and enantioselectivities. A wide range of α-substituted allenoates and barbiturate-derived alkenes were tolerated. PMID:26937706

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  2. Catalytic Asymmetric Synthesis of Ketene Heterodimer β-Lactones: Scope and Limitations.

    PubMed

    Chen, Shi; Ibrahim, Ahmad A; Peraino, Nicholas J; Nalla, Divya; Mondal, Mukulesh; Van Raaphorst, Maxwell; Kerrigan, Nessan J

    2016-09-01

    In this article we describe extensive studies of the catalytic asymmetric heterodimerization of ketenes to give ketene heterodimer β-lactones. The optimal catalytic system was determined to be a cinchona alkaloid derivative (TMS-quinine or Me-quinidine). The desired ketene heterodimer β-lactones were obtained in good to excellent yields (up to 90%), with excellent levels of enantioselectivity (≥90% ee for 33 Z and E isomer examples), good to excellent (Z)-olefin isomer selectivity (≥90:10 for 20 examples), and excellent regioselectivity (only one regioisomer formed). Full details of catalyst development studies, catalyst loading investigations, substrate scope exploration, protocol innovations (including double in situ ketene generation for 7 examples), and an application to a cinnabaramide A intermediate are described. The addition of lithium perchlorate (1-2 equiv) as an additive to the alkaloid catalyst system was found to favor formation of the E isomer of the ketene heterodimer. Ten examples were formed with moderate to excellent (E)-olefin isomer selectivity (74:25 to 97:3) and with excellent enantioselectivity (84-98% ee). PMID:27490092

  3. New pathways for organic synthesis. Practical applications of transition metals

    SciTech Connect

    Colquhoun, H.M.; Holton, J.; Thompson, D.J.; Twigg, M.V.

    1984-01-01

    This book contains a considerable number of transition-metal-based procedures that have genuine applications in synthesis, and which are arranged according to the nature of the organic product or synthetic transformation being carried out. The objective is to provide those engaged in the preparation of pharmaceuticals, natural products, herbicides, dyestuffs, and other organic chemicals with a practical guide to the application of transition metals in organic synthesis. Topics considered include the formation of carbon-carbon bonds, the formation of carbocyclic compounds, the formation of heterocyclic compounds, the isomerization of alkenes, the direct introduction and removal of carbonyl groups, reduction, oxidation, and preparing and handling transition metal catalysts.

  4. Ferroelectric liquid-crystalline compounds containing a sulfinyl group as unique source of chirality: Asymmetric synthesis and mesomorphic properties

    SciTech Connect

    Cherkaoui, M.Z.; Nicoud, J.F.; Guillon, D.

    1994-11-01

    The synthesis and mesomorphism of a series of new ferroelectric liquid crystals containing a sulfinyl group as the unique chiral center are described. This chiral center was introduced in the optically active form into the mesogenic molecules via the asymmetric synthesis of sulfinamide, sulfoxide, and sulfinate functional groups, directly connected to the aromatic rigid core. The role of the sulfinyl group nature, of the aromatic rigid core structure, of the chiral center position and of the alkyl chain length on the liquid-crystalline behavior have been investigated systematically. A central rigid core are not in favor of the occurrence of the mesomorphic character. On the contrary, sulfinates at the end of the core give a smectic C phase, stable within a reasonable temperature range. On the other hand, the only change of the sulfinyl group has large effects on the thermal stability of the mesophases, on the transition temperatures and more deeply on the polymorphic nature. This change leads to thermal instability with the sulfoxide compounds and with some sulfinamide ones, whereas the sulfinate mesogens are perfectly stable from both optical and thermal points of view. Thermal smectic C and A phases have been systematically studied as a function of aliphatic chain lengths. The alkyl chain of the sulfinate group plays a predominant role. Smectic A phases are favored when this chain is short, whereas smectic C phases are favored for long chains. The thermal stability of the smectic C mesophase is strongly correlated to the tilt angle of the molecules inside the smectic layers. 25 refs., 23 figs., 14 tabs.

  5. 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 α-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 α-olefins in >90% ee and, with the exception of site-controlled isotactic polymerization of α-olefins,1 none of these processes result in chain-extending C-C bond formation to the terminal carbon.2, 3, 4, 5, 6 Herein, we describe a strategy that directly addresses this gap in synthetic methodology and present a single-flask catalytic enantioselective conversion of terminal alkenes into a range of chiral products. These reactions are enabled by an unusual neighboring group participation effect that accelerates Pd-catalyzed cross-coupling of 1,2-bis(boronates) relative to nonfunctionalized alkyl boronate analogs. In tandem with enantioselective diboration, this reactivity feature connects abundant alkene starting materials to a diverse array of chiral products. Importantly with respect to synthesis utility, the tandem diboration/cross-coupling reaction (DCC reaction) generally provides products in high yield and high selectivity (>95:5 enantiomer ratio), employs low loadings (1–2 mol %) of commercially available catalysts and reagents, it offers an expansive substrate scope, and can address a broad range of alcohol and amine synthesis targets, many of which cannot be easily addressed with current technology. PMID:24352229

  6. The absolute configuration of (+)-oxopropaline D by theoretical calculation of specific rotation and asymmetric synthesis.

    PubMed

    Kuwada, Takeshi; Fukui, Miyako; Hata, Toshiyuki; Choshi, Tominari; Nobuhiro, Junko; Ono, Yukio; Hibino, Satoshi

    2003-01-01

    The specific optical rotations of (R)-oxopropaline D calculated by two ab initio MO methods were +52+/-31 degrees and +61+/-29 degrees, respectively, and (+)-oxopropaline D (3) was presumed to have an R-configuration. On the basis of this theoretical result, the reaction of 1-litio-beta-carboline with (R)-glyceraldehyde acetonide followed by oxidation with MnO(2) gave (R)-oxopropaline D acetonide (4a), which was consistent with the previously synthesized (+)-oxopropaline D acetonide (4) in all respects. From the results of theoretical calculations and the experimental synthesis, we determined that natural (+)-oxopropaline D (3) has an R-configuration.

  7. 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

  8. Air- and water-tolerant rare earth guanidinium BINOLate complexes as practical precatalysts in multifunctional asymmetric catalysis.

    PubMed

    Robinson, Jerome R; Fan, Xinyuan; Yadav, Jagjit; Carroll, Patrick J; Wooten, Alfred J; Pericàs, Miquel A; Schelter, Eric J; Walsh, Patrick J

    2014-06-01

    Shibasaki's REMB catalysts (REMB; RE = Sc, Y, La-Lu; M = Li, Na, K; B = 1,1'-bi-2-naphtholate; RE/M/B = 1/3/3) are among the most enantioselective asymmetric catalysts across a broad range of mechanistically diverse reactions. However, their widespread use has been hampered by the challenges associated with their synthesis and manipulation. We report here the self-assembly of novel hydrogen-bonded rare earth metal BINOLate complexes that serve as bench-stable precatalysts for Shibasaki's REMB catalysts. Incorporation of hydrogen-bonded guanidinium cations in the secondary coordination sphere leads to unique properties, most notably, improved stability toward moisture in solution and in the solid state. We have exploited these properties to develop straightforward, high-yielding, and scalable open-air syntheses that provide rapid access to crystalline, nonhygroscopic complexes from inexpensive hydrated RE starting materials. These compounds can be used as precatalysts for Shibasaki's REMB frameworks, where we have demonstrated that our system performs with comparable or improved levels of stereoselectivity in several mechanistically diverse reactions including Michael additions, aza-Michael additions, and direct Aldol reactions. PMID:24796452

  9. Asymmetric Mannich Synthesis of α-Amino Esters by Anion-Binding Catalysis

    PubMed Central

    2015-01-01

    We report a scalable, one-pot Mannich route to enantioenriched α-amino esters by direct reaction of α-chloroglycine ester as a practical imino ester surrogate. The reaction is promoted by a chiral aminothiourea, which is proposed to operate cooperatively by generating an iminium ion by chloride abstraction and an enolate by deprotonation, followed by highly stereoselective C–C bond formation between both reactive intermediates associated non-covalently within the catalyst framework. PMID:25178040

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

    PubMed

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

    2011-04-01

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

  11. A practical new chiral controller for asymmetric Diels-Alder and alkylation reactions.

    PubMed

    Sarakinos, G; Corey, E J

    1999-12-01

    [formula: see text] The enantiomerically pure hydroxy sulfones (+)- and (-)-2 have been prepared from 1,2-epoxycyclohexane by a simple and practical procedure. The acrylate esters of these alcohols undergo BCl3-catalyzed Diels-Alder reactions with a variety of dienes at -78 to -55 degrees C in CH2Cl2 or C7H8 with high dienophile face selectivity (Table 1). The chiral esters so formed are readily cleaved with recovery of the controllers (+)- or (-)-2. Esters of (+)- and (-)-2 can be converted to Z-potassium enolates and alkylated with high face selectivity. PMID:10836034

  12. Enantioselective synthesis of both enantiomers of methyl dihydrojasmonate using solid-liquid asymmetric phase-transfer catalysis.

    PubMed

    Perrard, T; Plaquevent, J C; Desmurs, J R; Hébrault, D

    2000-09-21

    Both enantiomers of methyl dihydrojasmonate (-)-1 and (+)-1 were obtained by a short route using asymmetric Michael addition of dimethyl malonate onto pentyl enone 3, followed by nonracemizing demethoxycarbonylation. The key enantioselective step involves a new system of asymmetric solid-liquid phase-transfer catalysis using solvent-free conditions. Enantiomeric excess as high as 90% (91% yield) was achieved.

  13. 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.

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

    PubMed

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

    2016-04-15

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

  15. Asymmetric synthesis of protected α-amino boronic acid derivatives with an air- and moisture-stable Cu(II) catalyst.

    PubMed

    Buesking, Andrew W; Bacauanu, Vlad; Cai, Irene; Ellman, Jonathan A

    2014-04-18

    The asymmetric borylation of N-tert-butanesulfinyl imines with bis(pinacolato)diboron is achieved using a Cu(II) catalyst and provides access to synthetically useful and pharmaceutically relevant α-amino boronic acid derivatives. The Cu(II)-catalyzed reaction is performed on the benchtop in air at room temperature using commercially available, inexpensive reagents at low catalyst loadings. A variety of N-tert-butanesulfinyl imines, including ketimines, react readily to provide α-sulfinamido boronate esters in good yields and with high stereoselectivity. In addition, this transformation is applied to the straightforward, telescoped synthesis of α-sulfinamido trifluoroborates. PMID:24684495

  16. Preparation of arylzinc reagents and their use in the rhodium-catalyzed asymmetric 1,4-addition for the synthesis of 2-aryl-4-piperidones.

    PubMed

    Shintani, Ryo; Hayashi, Tamio

    2007-01-01

    A protocol for the catalytic asymmetric synthesis of 2-aryl-4-piperidones with high enantiomeric excess (ee) (typically > or = 99% ee) has been described here. The preparation of arylzinc reagents, which are used as nucleophiles in catalysis, is also included. The whole protocol can be completed in 10-20 h, starting from the preparation of the arylzinc reagents, depending on the reaction time of the rhodium-catalyzed process. A detailed protocol is described using the preparation of 4-fluorophenylzinc chloride and its addition to benzyl 3,4-dihydro-4-oxo-1(2H)-pyridinecarboxylate in the presence of [RhCl((R)-binap)]2 as an example.

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

    PubMed

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

    2016-04-27

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

  18. 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…

  19. Chiral dirhodium(II) carboxylates and carboxamidates as effective chemzymes in asymmetric synthesis of three-membered carbocycles.

    PubMed

    Adly, Frady G; Ghanem, Ashraf

    2014-11-01

    In this review the recent advances in the utilization of two of the most important classes of dirhodium(II) paddlewheel complexes, dirhodium(II) carboxylates and carboxamidates, as chemzymes in inter- and intramolecular asymmetric cyclopropanation, as well as cyclopropenation reactions are discussed.

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

    PubMed Central

    Nguyen, Quynh Pham Bao

    2013-01-01

    Summary 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

  1. Direct and post-synthesis incorporation of chiral metallosalen catalysts into metal-organic frameworks for asymmetric organic transformations.

    PubMed

    Xi, Weiqin; Liu, Yan; Xia, Qingchun; Li, Zijian; Cui, Yong

    2015-09-01

    Two chiral porous metal-organic frameworks (MOFs) were constructed from [VO(salen)]-derived dicarboxylate and dipyridine bridging ligands. After oxidation of V(IV) to V(V) , they were found to be highly effective, recyclable, and reusable heterogeneous catalysts for the asymmetric cyanosilylation of aldehydes with up to 95 % ee. Solvent-assisted linker exchange (SALE) treatment of the pillared-layer MOF with [Cr(salen)Cl]- or [Al(salen)Cl]-derived dipyridine ligands led to the formation of mixed-linker metallosalen-based frameworks and incorporation of [Cr(salen)] enabled its use as a heterogeneous catalyst in the asymmetric epoxide ring-opening reaction.

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

    PubMed

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

    2015-07-11

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

  3. 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.

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

    PubMed

    Alkan, Sevda; Telli, Fatma Ç; Salman, Yeşim; Astley, Stephen T

    2015-04-30

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

  5. Facile synthesis of enantioenriched Cγ-tetrasubstituted α-amino acid derivatives via an asymmetric nucleophilic addition/protonation cascade.

    PubMed

    Duan, Shu-Wen; An, Jing; Chen, Jia-Rong; Xiao, Wen-Jing

    2011-05-01

    An asymmetric nucleophilic addition/protonation reaction of 3-substituted oxindoles and ethyl 2-phthalimidoacrylate has been described. This strategy can give direct access to C(γ)-tetrasubstituted α-amino acid derivatives bearing 1,3-nonadjacent stereocenters with up to 98% yield, 94:6 dr, and >99% ee. Dual activation is proposed in the transition state, and the opposite enantiomers can be obtained simply by changing cinchonidine-derived catalyst to the cinchonine analogue.

  6. Synthesis of IAN-type N,N-Ligands via Dynamic Kinetic Asymmetric Buchwald-Hartwig Amination.

    PubMed

    Ramírez-López, Pedro; Ros, Abel; Romero-Arenas, Antonio; Iglesias-Sigüenza, Javier; Fernández, Rosario; Lassaletta, José M

    2016-09-21

    The Pd(0)-catalyzed coupling of racemic heterobiaryl bromides, triflates, or nonaflates with aryl/alkyl primary amines using QUINAP as the ligand provides the corresponding axially chiral heterobiaryl amines with excellent yields and enantioselectivities. Reactivity and structural studies of neutral and cationic oxidative addition intermediates support a dynamic kinetic asymmetric amination mechanism based on the labilization of the stereogenic axis in the latter and suggest that coordination of the amine to the Pd center is the stereodetermining step. PMID:27595166

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

    PubMed

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

    2011-04-15

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

  8. 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

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

    PubMed

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

    2016-07-14

    The first synthesis of a labdane-type diterpenoid isolated from Isodon yuennanensis was achieved in fourteen steps from commercially available starting material, (+)-sclareolide. The synthesis features the Barton nitrite ester reaction to introduce an oxime at the angular methyl group and the Jones oxidation to construct the lactone segment. By comparison of the optical rotation of our synthetic sample and the natural sample, the absolute stereochemistry of the natural diterpenoid has been determined. PMID:27251032

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

    PubMed

    Mostowicz, Danuta; Dygas, Mirosław; Kałuża, Zbigniew

    2015-02-01

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

  11. 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

  12. 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.

  13. Asymmetric synthesis of 2,3-dihydropyrroles by ring-opening/cyclization of cyclopropyl ketones using primary amines.

    PubMed

    Xia, Yong; Liu, Xiaohua; Zheng, Haifeng; Lin, Lili; Feng, Xiaoming

    2015-01-01

    The asymmetric ring-opening/cyclization of cyclopropyl ketones with primary amine nucleophiles was catalyzed by a chiral N,N'-dioxide/scandium(III) complex through a kinetic resolution process. A broad range of cyclopropyl ketones and primary amines are suitable substrates of this reaction. The corresponding products were afforded in excellent enantioselectivities and yields (up to 97 % ee and 98 % yield) under mild reaction conditions. This method provides a promising access to chiral 2,3-dihydropyrroles as well as an effective procedure for the kinetic resolution of 2-substituted cyclopropyl ketones.

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

    PubMed

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

    2016-09-19

    An asymmetric organocatalytic domino oxa-Michael/1,6-addition reaction of ortho-hydroxyphenyl-substituted para-quinone methides and isatin-derived enoates has been developed. In the presence of 5 mol % of a bifunctional thiourea organocatalyst, this scalable domino reaction affords 4-phenyl-substituted chromans bearing spiro-connected oxindole scaffolds and three adjacent stereogenic centers in good to excellent yields (up to 98 %) and with very high stereoselectivities (up to >20:1 d.r., >99 % ee). PMID:27600477

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

    PubMed

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

    2016-09-19

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

  16. 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

  17. Design, synthesis, and applications of potential substitutes of t-Bu-phosphinooxazoline in Pd-catalyzed asymmetric transformations and their use for the improvement of the enantioselectivity in the Pd-catalyzed allylation reaction of fluorinated allyl enol carbonates.

    PubMed

    Bélanger, Étienne; Pouliot, Marie-France; Courtemanche, Marc-André; Paquin, Jean-François

    2012-01-01

    The design, synthesis, and applications of potential substitutes of t-Bu-PHOX in asymmetric catalysis is reported. The design relies on the incorporation of geminal substituents at C5 in combination with a substituent at C4 other than t-butyl (i-Pr, i-Bu, or s-Bu). Most of these new members of the PHOX ligand family behave similarly in terms of stereoinduction to t-Bu-PHOX in three palladium-catalyzed asymmetric transformations. Electronically modified ligands were also prepared and used to improve the enantioselectivity in the Pd-catalyzed allylation reaction of fluorinated allyl enol carbonates.

  18. Ring-closing metathesis of sulfoximine-substituted N-tethered trienes: modular asymmetric synthesis of medium-ring nitrogen heterocycles.

    PubMed

    Mahajan, Vishal; Gais, Hans-Joachim

    2011-05-23

    A synthesis of sulfoximine-substituted medium-ring nitrogen heterocycles (MRNHs) having a high degree of substitution has been developed. Its key steps are the modular asymmetric synthesis of sulfoximine-substituted N-tethered trienes and their Ru-catalyzed ring-closing metathesis (RCM) reaction. The highly substituted N-tethered trienes were obtained enantio- and diastereopure through 1) the diastereoselective aminoalkylation of sulfoximine-substituted allyltitanium complexes with N-tert-butylsulfonyliminoester, 2) N-allylation of homoallylic N-sulfonyl amines, 3) allylation, hydroxylalkylation, and formylation of α-lithioalkenylsulfoximines, and 4) allylation of α-formylalkenylsulfoximines. The Ru-catalyzed RCM reaction of the sulfoximine-substituted 1,7,10- and 1,7,12-trienes stereoselectively afforded the corresponding nine-, ten-, and eleven-membered MRNHs in good yields. An interesting difference in reactivity was noted in the case of a sulfoximine-substituted 1,7,10-triene and its corresponding 1,10-diene. While the triene readily underwent a RCM reaction, the diene reacted only in the presence of Ti(OiPr)(4) under formation of the corresponding MRNH. The feasibility of a removal of the sulfoximine auxiliary and the N-sulfonyl protecting group from the MRNHs were demonstrated through reduction and cleavage, respectively, of a nine-membered heterocycle, both of which proceeded readily and gave the corresponding cyclic alkene and amine, respectively.

  19. A Practical Synthesis and X-ray Crystallographic Analysis of Dithymoquinone, a Photodimer of Thymoquinone

    PubMed Central

    Myers, Alan L.; Zhang, Yan-Ping; Kramer, Mark A.; Bornmann, William G.; Kaseb, Ahmed; Yang, Peiying; Tran, Hai T.

    2014-01-01

    An updated and practical approach to the synthesis of dithymoquinone via one-step photoirradiation of thymoquinone (2-methyl-5-isopropyl-1,4-benzoquinone) is described. Synthesis resulted in a 55% yield of one structural isomer (trans-anti derivative), as confirmed by HPLC, NMR spectroscopy and first ever single-crystal X-ray diffraction analyses. PMID:24883052

  20. Asymmetric synthesis of (+)-17-epi-methoxy-kauran-3-one through tandem oxidative polycyclization-pinacol process.

    PubMed

    Maertens, Gaëtan; Desjardins, Samuel; Canesi, Sylvain

    2016-07-12

    A synthesis of (+)-17-epi-methoxy-kauran-3-one, an O-methylated isomer of the natural diterpene 17-hydroxy-kauran-3-one, has been achieved. The strategy is based on a diastereoselective oxidative polycyclization-pinacol tandem process consisting of transforming a functionalized phenol into a compact and complex tetracycle, which represents the main core of kaurane family members. The synthesis also includes an enantioselective Yamamoto's allylation, a diastereoselective Ru-catalyzed hydrocyanation, a ring-closing metathesis and a reductive isomerization process as key steps. The structure of our synthetic substrate was determined through comparison with an O-methylated derivative of the natural compound. PMID:27327903

  1. Concise Asymmetric Construction of C2 -symmetric 1,9-Diarylnonanoids Using a Hypervalent Silicon Complex: Total Synthesis of (-)-Ericanone.

    PubMed

    Kotani, Shunsuke; Kai, Kosuke; Shimoda, Yasushi; Hu, Hao; Gao, Shen; Sugiura, Masaharu; Ogasawara, Masamichi; Nakajima, Makoto

    2016-02-01

    By using a phosphine oxide-catalyzed enantioselective double aldol reaction, we achieved the concise construction of C2 -symmetric 1,9-diarylnonanoids, enabling the synthesis of (-)-ericanone from p-hydroxybenzaldehyde in 6 steps with 65 % overall yield. The enantioselective double aldol reaction is useful for establishing C2 -symmetric 1,9-diaryl-3,7-dihydroxy-5-nonanones with a single operation. Furthermore, the use of o-nosyl-protected p-hydroxybenzaldehyde and a 4,4'-disubstituted BINAP dioxide catalyst dramatically improved the reactivity and selectivity in the double aldol reaction, enabling the total synthesis of (-)-ericanone with high yield and with excellent enantiopurity.

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

    PubMed

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

    2013-11-11

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

  3. Catalytic asymmetric reductive coupling of alkynes and aldehydes: enantioselective synthesis of allylic alcohols and alpha-hydroxy ketones.

    PubMed

    Miller, Karen M; Huang, Wei-Sheng; Jamison, Timothy F

    2003-03-26

    A highly enantioselective method for catalytic reductive coupling of alkynes and aldehydes is described. Allylic alcohols are afforded with complete E/Z selectivity, generally >95:5 regioselectivity, and in up to 96% ee. In conjunction with ozonolysis, this process is complementary to existing methods of enantioselective alpha-hydroxy ketone synthesis. PMID:12643701

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

    PubMed Central

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

    2008-01-01

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

  5. 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.

  6. 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…

  7. 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

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

    PubMed

    Göksel, Meltem

    2016-09-15

    Zinc(II) phthalocyanine containing [2-(tert-butoxycarbonyl)amino]ethoxy and iodine groups (A and B), as well as their deprotected mono-amino and tri-iodine zinc(II) phthalocyanine (2) were obtained. This structure surrounds by substituents with functional groups. From this perspective it can be used a starting material for many reactions and applications, such as sonogashira coupling, carbodiimide coupling. An example of a first diversification reaction of this compound was obtained with conjugation of a biotin. Asymmetrically biotin conjugated and heavy atom bearing zinc(II) phthalocyanine (3) were synthesized characterized for the first time and photophysical, photochemical and photobiological properties of these phthalocyanines were compared in this study. PMID:27423301

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

    PubMed

    Göksel, Meltem

    2016-09-15

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

  10. Intramolecular Tsuji-Trost-type Allylation of Carboxylic Acids: Asymmetric Synthesis of Highly π-Allyl Donative Lactones.

    PubMed

    Suzuki, Yusuke; Seki, Tomoaki; Tanaka, Shinji; Kitamura, Masato

    2015-08-01

    Tsuji-Trost-type asymmetric allylation of carboxylic acids has been realized by using a cationic CpRu complex with an axially chiral picolinic acid-type ligand (Cl-Naph-PyCOOH: naph = naphthyl, py = pyridine). The carboxylic acid and allylic alcohol intramolecularly condense by the liberation of water without stoichiometric activation of either nucleophile or electrophile part, thereby attaining high atom- and step-economy, and low E factor. This success can be ascribed to the higher reactivity of allylic alcohols as compared with the allyl ester products in soft Ru/hard Brønstead acid combined catalysis, which can function under slightly acidic conditions unlike the traditional Pd-catalyzed system. Detailed analysis of the stereochemical outcome of the reaction using an enantiomerically enriched D-labeled substrate provides an intriguing view of enantioselection. PMID:26199057

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

    PubMed

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

    2015-07-27

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

  12. Synthesis of diverse β-quaternary ketones via palladium-catalyzed asymmetric conjugate addition of arylboronic acids to cyclic enones

    PubMed Central

    Holder, Jeffrey C.; Goodman, Emmett D.; Kikushima, Kotaro; Gatti, Michele; Marziale, Alexander N.; Stoltz, Brian M.

    2014-01-01

    The development and optimization of a palladium-catalyzed asymmetric conjugate addition of arylboronic acids to cyclic enone conjugate acceptors is described. These reactions employ air-stable and readily-available reagents in an operationally simple and robust transformation that yields β-quaternary ketones in high yields and enantioselectivities. Notably, the reaction itself is highly tolerant of atmospheric oxygen and moisture and therefore does not require the use of dry or deoxygenated solvents, specially purified reagents, or an inert atmosphere. The ring size and β-substituent of the enone are highly variable, and a wide variety of β-quaternary ketones can be synthesized. More recently, the use of NH4PF6 has further expanded the substrate scope to include heteroatom-containing arylboronic acids and β-acyl enone substrates. PMID:26461082

  13. Chiral ammonium-capped rhodium(0) nanocatalysts: synthesis, characterization, and advances in asymmetric hydrogenation in neat water.

    PubMed

    Bilé, Elodie Guyonnet; Cortelazzo-Polisini, Elodie; Denicourt-Nowicki, Audrey; Sassine, Rita; Launay, Franck; Roucoux, Alain

    2012-01-01

    Optically active amphiphilic compounds derived from N-methylephedrine, N-methylprolinol, or cinchona derivatives possessing bromide or chiral lactate counterions were efficiently used as protective agents for rhodium(0) nanoparticles. The full characterization of these surfactants and the obtained nanocatalysts was performed by means of different techniques. These spherical nanoparticles, with sizes between 0.8-2.5 nm depending on the stabilizer, were evaluated in the hydrogenation of model substrates in neat water as a green solvent. The rhodium catalysts showed relevant kinetic properties, but modest enantiomeric excess values of up to 13 % in the hydrogenation of ethyl pyruvate. They were also investigated in the hydrogenation of disubstituted arenes, such as m-methylanisole, providing interesting catalytic activities and a preferential cis selectivity of around 80 %; however, no asymmetric induction was observed.

  14. Enantioselective synthesis of primary 1-(aryl)alkylamines by nucleophilic 1,2-addition of organolithium reagents to hydroxyoxime ethers and application to asymmetric synthesis of G-protein-coupled receptor ligands.

    PubMed

    Atobe, Masakazu; Yamazaki, Naoki; Kibayashi, Chihiro

    2004-08-20

    (E)-Arylaldehyde oxime ethers bearing a (1S)-2-hydroxy-1-phenylethyl or (2R)-1-hydroxy-2-phenylethyl group as a chiral auxiliary, both derived from a single precursor, methyl (R)-mandelate, underwent nucleophilic addition with organolithium reagents via six-membered chelates to give the diastereomerically enriched (R)- and (S)-adducts, respectively, which, after chiral auxiliary removal by reductive N-O bond cleavage, led to the corresponding (R)- and (S)-1-(aryl)ethylamines. This organolithium addition protocol using methyllithium was applied in an enantiodivergent fashion to the preparation of both enantiomers of 1-(2-hydroxyphenyl)ethylamine, which has been previously used as an efficient chiral auxiliary for the synthesis of natural products in this laboratory. The synthetic utility of this methodology involving diastereoselective methyl addition was demonstrated by further application to the asymmetric synthesis of a new type of calcium receptor agonist (calcimimetics), (R)-(+)-NPS R-568 and its thio analogue. Furthermore, diastereoselective vinylation was accomplished by application of the hydroxy oxime ether-based protocol using vinyllithium, which allowed the development of the enantioselective synthesis of the NK-1 receptor antagonists, (+)-CP-99,994 and (+)-CP-122,721.

  15. One-pot multiple reactions: asymmetric synthesis of 2,6-cis-disubstituted piperidine alkaloids from chiral aziridine.

    PubMed

    Yadav, Nagendra Nath; Choi, Jihye; Ha, Hyun-Joon

    2016-07-01

    A divergent, new, and highly stereoselective synthesis of cis-2,6-disubstituted piperidine natural products including isosolenopsins, deoxocassine, and spectaline was achieved from chiral aziridine decorated with appropriate alkyl chains for isosolenopsins or alkynyl groups for deoxocassine and spectaline at C2. The characteristic feature of this synthesis is one-pot sequential reactions under atmospheric hydrogen including the reduction of alkyne (for deoxocassine and spectaline), reductive ring-opening of aziridine, debenzylation, and intramolecular reductive amination in high yields. The prerequisite aziridines were elaborated from commercially available (2S)-hydroxymethylaziridine through oxidation, Wittig olefination, and the Grignard reaction for isosolenopsins or substrate-controlled lithium alkynylate addition for deoxocassine and spectaline. PMID:27189444

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

    PubMed

    Fustero, Santos; Herrera, Lidia; Lázaro, Ruben; Rodríguez, 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 β,β'-dipeptides using a single nitrogen atom as a linchpin.

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

    PubMed

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

    2012-03-19

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

  18. Synthesis of chiral biphenol-based diphosphonite ligands and their application in palladium-catalyzed intermolecular asymmetric allylic amination reactions.

    PubMed

    Shi, Ce; Chien, Chih-Wei; Ojima, Iwao

    2011-02-01

    A library of new 2,2'-bis(diphenylphosphinoyloxy)-1,1'-binaphthyl (binapo)-type chiral diphosphonite ligands was designed and synthesized based on chiral 3,3',5,5',6,6'-hexasubstituted biphenols. These bop ligands have exhibited excellent efficiency in a palladium-catalyzed intermolecular allylic amination reaction, which provides a key intermediate for the total synthesis of Strychnos indole alkaloids with enantiopurities of up to 96% ee. PMID:21254441

  19. Lewis Acid Catalyzed Asymmetric Three-Component Coupling Reaction: Facile Synthesis of α-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 α-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.

  20. Improving carbene-copper-catalyzed asymmetric synthesis of α-aminoboronic esters using benzimidazole-based precursors.

    PubMed

    Wen, Kun; Wang, Han; Chen, Jinbo; Zhang, He; Cui, Xiaodan; Wei, Chao; Fan, Erkang; Sun, Zhihua

    2013-04-01

    By using a benzimidazole core and N-substitutions to tune the electronic properties of the corresponding N-heterocyclic carbenes, a one-pot protocol for efficient synthesis of α-aminoboronic esters without the need of a glovebox was developed in this work. The starting materials for the transformation can also be extended from aldehydes to ketones. An alternative protocol with short reaction time using preformed carbene-copper chloride is also described. PMID:23461780

  1. Beyond Synthesis: Augmenting Systematic Review Procedures with Practical Principles to Optimise Impact and Uptake in Educational Policy and Practice

    ERIC Educational Resources Information Center

    Green, Chris; Taylor, Celia; Buckley, Sharon; Hean, Sarah

    2016-01-01

    Whilst systematic reviews, meta-analyses and other forms of synthesis are considered amongst the most valuable forms of research evidence, their limited impact on educational policy and practice has been criticised. In this article, we analyse why systematic reviews do not benefit users of evidence more consistently and suggest how review teams…

  2. Asymmetric MRI magnet design using a hybrid numerical method.

    PubMed

    Zhao, H; Crozier, S; Doddrell, D 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.

  3. [Development of new methods in asymmetric reactions and their applications].

    PubMed

    Node, Manabu

    2002-01-01

    Several novel methods using chiral reagents and biocatalysts for asymmetric reactions are described. Among those reactions, asymmetric reduction via a novel tandem Michael addition/Meerwein-Ponndorf-Verley reduction of acyclic alpha,beta-unsaturated ketones using a chiral mercapto alcohol, asymmetric synthesis of allene-1,3-dicarboxylate via crystallization induced asymmetric transformation, and improved asymmetric nitroolefination of lactones and lactames at alpha-carbon using new chiral reagents were developed. In the reactions using biocatalysts, asymmetric dealkoxycarbonylation of bicyclic beta-keto diesters having sigma-symmetry with lipase or esterase to give optically active beta-keto esters, the asymmetric reduction of bicyclic 1,3-diketones having sigma-symmetry with Baker's yeast to give optically active keto alcohols, and the asymmetric aldol reaction of glycine with threonine aldolase were also developed. The above mentioned products were effectively utilized as chiral building blocks for the asymmetric synthesis of natural products and drugs.

  4. 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.

  5. 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

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

    NASA Astrophysics Data System (ADS)

    Hsu, Chun-Tsung; Hu, Chi-Chang

    2013-11-01

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

  7. Brønsted Acid Catalyzed Asymmetric Hydroamination of Alkenes: Synthesis of Pyrrolidines Bearing a Tetrasubstituted Carbon Stereocenter.

    PubMed

    Lin, Jin-Shun; Yu, Peng; Huang, Lin; Zhang, Pan; Tan, Bin; Liu, Xin-Yuan

    2015-06-26

    The first highly enantioselective Brønsted acid catalyzed intramolecular hydroamination of alkenes enables the efficient construction of a series of chiral (spirocyclic) pyrrolidines with an α-tetrasubstituted carbon stereocenter with excellent functional group tolerance. A unique feature of this strategy is the use of a thiourea group acting as both the activating and the directing group through cooperative multiple hydrogen bonding with a Brønsted acid and the double bond. The utility of this method is highlighted by the facile construction of chiral synthetic intermediates and important structural motifs that are widely found in organic synthesis.

  8. Inhibition of insect juvenile hormone epoxide hydrolase: asymmetric synthesis and assay of glycidol-ester and epoxy-ester inhibitors of trichoplusia ni epoxide hydrolase.

    PubMed

    Linderman, R J; Roe, R M; Harris, S V; Thompson, D M

    2000-01-01

    Juvenile hormone (JH) undergoes metabolic degradation by two major pathways involving JH esterase and JH epoxide hydrolase (EH). While considerable effort has been focussed on the study of JH esterase and the development of inhibitors for this enzyme, much less has been reported on the study of JH-EH. In this work, the asymmetric synthesis of two classes of inhibitors of recombinant JH-EH from Trichoplusia ni, a glycidol-ester series and an epoxy-ester series is reported. The most effective glycidol-ester inhibitor, compound 1, exhibited an I(50) of 1.2x10(-8) M, and the most effective epoxy-ester inhibitor, compound 11, exhibited an I(50) of 9.4x10(-8) M. The potency of the inhibitors was found to be dependent on the absolute configuration of the epoxide. In both series of inhibitors, the C-10 R-configuration was found to be significantly more potent that the corresponding C-10 S-configuration. A mechanism for epoxide hydration catalyzed by insect EH is also presented.

  9. Synthesis and spectroscopic studies of some cadmium(II) and mercury(II) complexes of an asymmetrical bidentate Schiff base ligand

    NASA Astrophysics Data System (ADS)

    Montazerozohori, Morteza; Joohari, Shiva; Musavi, Sayed Alireza

    2009-07-01

    Synthesis and spectroscopic studies on four-coordinate complexes of cadmium(II) and mercury(II) halides with a new asymmetrical bidentate Schiff base ligand of N,N'-bis[α-methylcinamaldehydene]propane-1,2-diamine(L) are described. The ligand and its complexes were characterized by elemental analysis, molar conductance, UV-visible spectra, FT-IR spectra, MS, 1H NMR and 13C NMR spectra. The complexes are non-electrolytes in DMF. The electronic spectra of the complexes were recorded in DMF solution. 1H and 13 C NMR spectra been studied in CDCl3. The molar conductance as well as spectral properties indicated the complexes do not dissociate in DMF and retain their coordination. FT-IR and NMR spectra of the complexes exhibit downfield as well as upfield shifts of the free ligand resonances that show change in geometry during the coordination. The suggested structure of the complexes is pseudo-tetrahedral. Molecular structures of the complexes have been optimized by MM+ calculations that supported pseudo-tetrahedral geometry around the metal (II) ions.

  10. Improved synthesis of cyclic tertiary allylic alcohols by asymmetric 1,2-addition of AlMe3 to enones.

    PubMed

    Kolb, Andreas; Zuo, Wei; Siewert, Jürgen; Harms, Klaus; von Zezschwitz, Paultheo

    2013-11-25

    The development of an improved protocol for the enantioselective Rh(I) /binap-catalysed 1,2-addition of AlMe3 to cyclic enones is reported. (31)P NMR analysis of the reaction revealed that the catalyst in its resting state is a chloride-bridged dimer. This insight led to the use of AgBF4 as an additive for in situ activation of the dimeric precatalyst. Thus, the catalyst loading can now be reduced to only 1 mol% with respect to rhodium. Various 5-7-membered cyclic enones can be transformed into tertiary allylic alcohols with excellent levels of enantioselectivity and high yields. The obtained products are versatile synthetic building blocks, shown by a highly enantioselective formal total synthesis of the pheromone (-)-frontalin as well as formation of a bicyclic lactone that has the core structure of the natural flavour component "wine lactone".

  11. Direct Catalytic Asymmetric Mannich Reaction with Dithiomalonates as Excellent Mannich Donors: Organocatalytic Synthesis of (R)-Sitagliptin.

    PubMed

    Bae, Han Yong; Kim, Mun Jong; Sim, Jae Hun; Song, Choong Eui

    2016-08-26

    In this study, dithiomalonates (DTMs) were demonstrated to be exceptionally efficient Mannich donors in terms of reactivity and stereoselectivity in cinchona-based-squaramide-catalyzed enantioselective Mannich reactions of diverse imines or α-amidosulfones as imine surrogates. Owing to the superior reactivity of DTMs as compared to conventional malonates, the catalyst loading could be reduced to 0.1 mol % without the erosion of enantioselectivity (up to 99 % ee). Furthermore, by the use of a DTM, even some highly challenging primary alkyl α-amidosulfones were smoothly converted into the desired adducts with excellent enantioselectivity (up to 97 % ee), whereas the use of a malonate or monothiomalonate resulted in no reaction under identical conditions. The synthetic utility of the chiral Mannich adducts obtained from primary alkyl substrates was highlighted by the organocatalytic, coupling-reagent-free synthesis of the antidiabetic drug (-)-(R)-sitagliptin. PMID:27486059

  12. 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.

  13. 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.

  14. A practical and general synthesis of unsymmetrical terphenyls.

    PubMed

    Miguez, Jose M Antelo; Adrio, Luis Angel; Sousa-Pedrares, Antonio; Vila, Jose M; Hii, King Kuok Mimi

    2007-09-28

    A synthetic procedure was developed that enables sequential chemoselective Suzuki-Miyaura cross-coupling of chlorobromobenzene with arylboronic acids. The first coupling is achieved at room temperature using a ligandless palladium catalyst. The chlorobiaryl product can then be subjected directly to the second coupling, facilitated by the SPhos ligand. Using this methodology, parallel synthesis of 32 unsymmetrical o-, m-, and p-terphenyl compounds was accomplished in good to excellent overall yields.

  15. Blended Course Design: A Synthesis of Best Practices

    ERIC Educational Resources Information Center

    McGee, Patricia; Reis, Abby

    2012-01-01

    Blended or hybrid course offerings in higher education are commonplace and much has been written about how to design a blended course effectively. This study examines publically available guides, documents, and books that espouse best or effective practices in blended course design to determine commonalities among such practices. A qualitative…

  16. Effective use of park-and-ride facilities. A synthesis of highway practice. Final report

    SciTech Connect

    Turnbull, K.F.

    1995-08-01

    This synthesis will be of interest to traffic planners and engineers, as well as to transit planners and operations personnel, design and construction contractors, and municipal, transit, and highway agencies. Security and management officials who are responsible for safe and efficient operation of park-and-ride facilities will also find the synthesis useful. The synthesis provides an assessment of the current status of park-and-ride facilities in the United States. The various aspects of park-and-ride facilities, including conceptual issues, location, design, administration, operation, maintenance, and other supporting elements are addressed in this synthesis. The report of the Transportation Research Board also provides information on the current usage of park-and-ride facilities throughout the nation, operating and maintenance practices at selected sites, descriptions of safety and security measures used at various facilities, and the relationship of ridesharing and travel demand management (TDM) programs to the success of park-and-ride facilities.

  17. Asymmetric Synthesis and Binding Study of New Long-Chain HPA-12 Analogues as Potent Ligands of the Ceramide Transfer Protein CERT.

    PubMed

    Ďuriš, Andrej; Daïch, Adam; Santos, Cécile; Fleury, Laurence; Ausseil, Frédéric; Rodriguez, Frédéric; Ballereau, Stéphanie; Génisson, Yves; Berkeš, Dušan

    2016-05-01

    A series of 12 analogues of the Cer transfer protein (CERT) antagonist HPA-12 with long aliphatic chains were prepared as their (1R,3S)-syn and (1R,3R)-anti stereoisomers from pivotal chiral oxoamino acids. The enantioselective access to these intermediates as well as their ensuing transformation relied on a practical crystallization-induced asymmetric transformation (CIAT) process. Sonogashira coupling followed by triple bond reduction and thiophene ring hydrodesulfurization (HDS) into the corresponding alkane moieties was then implemented to complete the synthetic routes delivering the targeted HPA-12 analogues in concise 4- to 6-step reaction sequences. Ten compounds were evaluated regarding their ability to bind to the CERT START domain by using the recently developed time-resolved FRET-based homogeneous (HTR-FRET) binding assay. The introduction of a lipophilic appendage on the phenyl moiety led to an overall 10- to 1000-fold enhancement of the protein binding, with the highest effect being observed for a n-hexyl residue in the meta position. The importance of the phenyl ring for the activity was indicated by the reduced potency of the 3-deoxyphytoceramide aliphatic analogues. The 1,3-syn stereoisomers were systematically more potent than their 1,3-anti analogues. In silico studies were used to rationalized these trends, leading to a model of protein recognition coherent with the stronger binding of (1R,3S)-syn HPAs.

  18. The CERT antagonist HPA-12: first practical synthesis and individual binding evaluation of the four stereoisomers.

    PubMed

    Santos, Cécile; Fleury, Laurence; Rodriguez, Frédéric; Markus, Jozef; Berkeš, Dušan; Daïch, Adam; Ausseil, Frédéric; Baudoin-Dehoux, Cécile; Ballereau, Stéphanie; Génisson, Yves

    2015-05-01

    The first unified synthetic route to the four enantiopure HPA-12 stereoisomers in multi-gram scale is reported based on Crystallization-Induced Asymmetric Transformation (CIAT) technology. This preparative stereoselective synthesis allowed the unprecedented comparative evaluation of HPA-12 stereoisomers regarding their interaction with the CERT START domain. In vitro binding assay coupled to in silico docking approach indicate a possible interaction for the four derivatives. The first TR-FRET homogeneous-phase assay was developed to quantify their binding to the START domain, allowing complete determination of HPA-12 EC₅₀. Results indicate that not only the (1R,3S) lead to the strongest binding, but that both 1R and 3S stereocenters similarly contribute to extent of recognition This automated homogenous assay further opens up promising prospect for the identification of novel potential CERT antagonist by means of high throughput screening.

  19. Classroom Literacy Practices in Low- and Middle-Income Countries: An Interpretative Synthesis of Ethnographic Studies

    ERIC Educational Resources Information Center

    Nag, Sonali; Snowling, Margaret J.; Asfaha, Yonas Mesfun

    2016-01-01

    Surveys in low- and middle-income (LMI countries) reveal persistently low levels of learning among children in disadvantaged communities. Against this background, our synthesis of ethnographies aims at a fresh interpretation of classroom practices to clarify instruction-related barriers to literacy attainments. The review focuses on the period…

  20. Teacher Performance Pay: Synthesis of Plans, Research, and Guidelines for Practice. Policy Brief RB-46

    ERIC Educational Resources Information Center

    Heneman III, Herbert G.; Milanowski, Anthony; Kimball, Steven

    2007-01-01

    This Policy Brief focuses on the nature and effectiveness of these plans. Generic descriptions of three types of plans are provided, followed by a synthesis of research results on their effectiveness. A set of guidelines for effective practice is then provided to help states and districts embarking on these forms of performance pay. The authors…

  1. Concise Asymmetric Synthesis and Pharmacological Characterization of All Stereoisomers of Glutamate Transporter Inhibitor TFB-TBOA and Synthesis of EAAT Photoaffinity Probes.

    PubMed

    Leuenberger, Michele; Ritler, Andreas; Simonin, Alexandre; Hediger, Matthias A; Lochner, Martin

    2016-05-18

    Glutamate is the major excitatory neurotransmitter in the mammalian brain. Its rapid clearance after the release into the synaptic cleft is vital in order to avoid toxic effects and is ensured by several transmembrane transport proteins, so-called excitatory amino acid transporters (EAATs). Impairment of glutamate removal has been linked to several neurodegenerative diseases and EAATs have therefore received increased attention as therapeutic targets. O-Benzylated l-threo-β-hydroxyaspartate derivatives have been developed previously as highly potent inhibitors of EAATs with TFB-TBOA ((2S,3S)-2-amino-3-((3-(4-(trifluoromethyl)benzamido)benzyl)oxy)succinic acid) standing out as low-nanomolar inhibitor. We report the stereoselective synthesis of all four stereoisomers of TFB-TBOA in less than a fifth of synthetic steps than the published route. For the first time, the inhibitory activity and isoform selectivity of these TFB-TBOA enantio- and diastereomers were assessed on human glutamate transporters EAAT1-3. Furthermore, we synthesized potent photoaffinity probes based on TFB-TBOA using our novel synthetic strategy. PMID:26918289

  2. 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.

  3. Synthesis of optically active dihydropyrans from asymmetric [4 + 2] cycloaddition of β,γ-unsaturated α-ketoesters with allenic esters.

    PubMed

    Pei, Cheng-Kui; Jiang, Yu; Shi, Min

    2012-06-14

    β-Isocupreidine (β-ICD) catalyzed asymmetric [4 + 2] cycloaddition of β,γ-unsaturated α-ketoesters with allenic esters afforded ester-substituted functionalized dihydropyran derivatives in high yields along with high enantioselectivities under mild conditions.

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

    PubMed

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

    2005-08-01

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

  5. Asymmetric synthesis of (-)-renieramycin T.

    PubMed

    Jia, Junhao; Chen, Ruijiao; Liu, Hao; Li, Xiong; Jia, Yuanliang; Chen, Xiaochuan

    2016-08-14

    (-)-Renieramycin T, an interesting tetrahydroisoquinolinequinone alkaloid with a novel renieramycin-ecteinascidin mixed framework, is synthesized from the known phenol 16 in 22 steps with 6.2% overall yield. In the convergent route, the key cyclocondensation between the isoquinoline moiety 27 and trisubstituted phenylalaninol 14 is achieved with good selectivity to furnish bistetrahydroisoquinoline 29, which permits a rapid construction of the pentacyclic framework having a fully substituted aromatic A ring. PMID:27405490

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

    PubMed

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

    2016-05-10

    A highly efficient asymmetric cascade reaction between keto esters and alkynyl alcohols and amides is reported. The success of the reaction was attributed to the combination of chiral Lewis acid N,N'-dioxide nickel(II) catalysis with achiral π-acid gold(I) catalysis working as an asymmetric relay catalytic system. The corresponding spiroketals and spiroaminals were synthesized in up to 99 % yield, 19:1 d.r., and more than 99 % ee under mild reaction conditions. Control experiments suggest that the N,N'-dioxide ligand was essential for the formation of the spiro products. PMID:27062196

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  8. Enantioselective synthesis of α-tri- and α-tetrasubstituted allylsilanes by copper-catalyzed asymmetric allylic substitution of allyl phosphates with silylboronates.

    PubMed

    Takeda, Momotaro; Shintani, Ryo; Hayashi, Tamio

    2013-05-17

    A copper/N-heterocyclic carbene-catalyzed asymmetric allylic substitution of allyl phosphates with a silylboronate has been developed to give highly enantioenriched allylsilanes. High regioselectivity has been achieved by employing NaOH as the base, and this catalyst system is effective for both γ-mono- and disubstituted allyl phosphates. PMID:23647080

  9. Ethylene in Organic Synthesis. A New Route to Anticholenergic Pyrrolidinoindolines, and Other Molecules with All Carbon-Quaternary Centers via Asymmetric Hydrovinylation

    PubMed Central

    Lim, Hwan Jung; RajanBabu, T. V.

    2011-01-01

    The asymmetric hydrovinylation (1 mol % Ni-cat., 1 atm, ethylene, >98% ee) products from 1-methylenetetralines are readily converted into 3,3-disubstituted oxindoles, and subsequently to pyrrolidinoindolines. These hydrovinylation products are also useful for the syntheses of enantiopure benzomorphans. PMID:22103775

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

    PubMed

    Takechi, Ryosuke; Nishimura, Takahiro

    2015-05-01

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

  11. Asymmetric Ashes

    NASA Astrophysics Data System (ADS)

    2006-11-01

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

  12. Uses of recycled rubber tires in highways: A synthesis of highway practice. Final report

    SciTech Connect

    Epps, J.A.; Mason, L.S.

    1994-01-01

    The synthesis on the use of recycled rubber tires in highways will be of interest to administrators and policymakers; pavement, materials, geotechnical, environmental, and traffic operations engineers; and research engineers involved with highway design and construction issues. Information is provided on the uses of rubber tires in asphalt paving materials as well as other uses, such as on fills and embankments, for erosion control and on railroad grade crossings. Specifically, information is included which identifies the highway agencies using or implementing applications for recycled rubber tires and defines the design parameters, technical and construction limitations, performance, costs, benefits, environmental limitations, specifications, and availability. This synthesis of information defines the use of recycled rubber tires in highways and is based on a review of nearly 500 references and on information recorded from state highway agency responses to a 1991 survey of practice.

  13. Advanced practice nursing in Canada: overview of a decision support synthesis.

    PubMed

    DiCenso, Alba; Martin-Misener, Ruth; Bryant-Lukosius, Denise; Bourgeault, Ivy; Kilpatrick, Kelley; Donald, Faith; Kaasalainen, Sharon; Harbman, Patricia; Carter, Nancy; Kioke, Sandra; Abelson, Julia; McKinlay, R James; Pasic, Dianna; Wasyluk, Brandi; Vohra, Julie; Charbonneau-Smith, Renee

    2010-12-01

    The objective of this decision support synthesis was to identify and review published and grey literature and to conduct stakeholder interviews to (1) describe the distinguishing characteristics of clinical nurse specialist (CNS) and nurse practitioner (NP) role definitions and competencies relevant to Canadian contexts, (2) identify the key barriers and facilitators for the effective development and utilization of CNS and NP roles and (3) inform the development of evidence-based recommendations for the individual, organizational and system supports required to better integrate CNS and NP roles into the Canadian healthcare system and advance the delivery of nursing and patient care services in Canada. Four types of advanced practice nurses (APNs) were the focus: CNSs, primary healthcare nurse practitioners (PHCNPs), acute care nurse practitioners (ACNPs) and a blended CNS/NP role. We worked with a multidisciplinary, multijurisdictional advisory board that helped identify documents and key informant interviewees, develop interview questions and formulate implications from our findings. We included 468 published and unpublished English- and French-language papers in a scoping review of the literature. We conducted interviews in English and French with 62 Canadian and international key informants (APNs, healthcare administrators, policy makers, nursing regulators, educators, physicians and other team members). We conducted four focus groups with a total of 19 APNs, educators, administrators and policy makers. A multidisciplinary roundtable convened by the Canadian Health Services Research Foundation formulated evidence-informed policy and practice recommendations based on the synthesis findings. This paper forms the foundation for this special issue, which contains 10 papers summarizing different dimensions of our synthesis. Here, we summarize the synthesis methods and the recommendations formulated at the roundtable.

  14. 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

  15. Asymmetric Ring Opening/Cyclization/Retro-Mannich Reaction of Cyclopropyl Ketones with Aryl 1,2-Diamines for the Synthesis of Benzimidazole Derivatives.

    PubMed

    Xia, Yong; Lin, Lili; Chang, Fenzhen; Liao, Yuting; Liu, Xiaohua; Feng, Xiaoming

    2016-09-26

    A highly efficient asymmetric ring-opening/cyclization/retro-Mannich reaction of cyclopropyl ketones with aryl 1,2-diamines has been realized using a chiral N,N'-dioxide/Sc(III) catalyst. Benzimidazoles containing chiral side chains were generated under mild reaction conditions in excellent outcomes (up to 99 % yield and 97 % ee). This method also provides efficient access to chiral benzimidazole-substituted amide and cycloheptene derivatives. PMID:27376785

  16. 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

  17. Engineered Asymmetric Synthetic Vesicles

    NASA Astrophysics Data System (ADS)

    Lu, Li; Chiarot, Paul

    2013-11-01

    Synthetic vesicles are small, fluid-filled spheres that are enclosed by a bilayer of lipid molecules. They can be used as models for investigating membrane biology and as delivery vehicles for pharmaceuticals. In practice, it is difficult to simultaneously control membrane asymmetry, unilamellarity, vesicle size, vesicle-to-vesicle uniformity, and luminal content. Membrane asymmetry, where each leaflet of the bilayer is composed of different lipids, is of particular importance as it is a feature of most natural membranes. In this study, we leverage microfluidic technology to build asymmetric vesicles at high-throughput. We use the precise flow control offered by microfluidic devices to make highly uniform emulsions, with controlled internal content, that serve as templates to build the synthetic vesicles. Flow focusing, dielectrophoretic steering, and interfacial lipid self-assembly are critical procedures performed on-chip to produce the vesicles. Fluorescent and confocal microscopy are used to evaluate the vesicle characteristics.

  18. Asymmetric synthesis of α-amino acids via homologation of Ni(II) complexes of glycine Schiff bases. Part 2: aldol, Mannich addition reactions, deracemization and (S) to (R) interconversion of α-amino acids.

    PubMed

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

    2013-11-01

    This review provides a comprehensive treatment of literature data dealing with asymmetric synthesis of α-amino-β-hydroxy and α,β-diamino acids via homologation of chiral Ni(II) complexes of glycine Schiff bases using aldol and Mannich-type reactions. These reactions proceed with synthetically useful chemical yields and thermodynamically controlled stereoselectivity and allow direct introduction of two stereogenic centers in a single operation with predictable stereochemical outcome. Furthermore, new application of Ni(II) complexes of α-amino acids Schiff bases for deracemization of racemic α-amino acids and (S) to (R) interconversion providing additional synthetic opportunities for preparation of enantiomerically pure α-amino acids, is also reviewed. Origin of observed diastereo-/enantioselectivity in the aldol, Mannich-type and deracemization reactions, generality and limitations of these methodologies are critically discussed.

  19. System-specific spare rail vehicle ratios: A synthesis of transit practice. Final report

    SciTech Connect

    Pierce, J.T.

    1995-12-31

    This synthesis addresses the system-specific variables that directly impact fleet size, and the spare ratios that are maintained by individual transit agencies. From the information obtained, it appears that most rail transit agencies closely monitor the spare vehicles they maintain to maximize efficiency and thereby reduce operating costs. This report of the Transportation Research Board describes operating environments at 21 selected rail transit agencies of various sizes in key geographical locations in North America. It contains survey information about operating practices, impediments, and strategies used to appropriately size fleets within each agency`s operating context.

  20. Synthesis of Chiral Cyclopentenones.

    PubMed

    Simeonov, Svilen P; Nunes, João P M; Guerra, Krassimira; Kurteva, Vanya B; Afonso, Carlos A M

    2016-05-25

    The cyclopentenone unit is a very powerful synthon for the synthesis of a variety of bioactive target molecules. This is due to the broad diversity of chemical modifications available for the enone structural motif. In particular, chiral cyclopentenones are important precursors in the asymmetric synthesis of target chiral molecules. This Review provides an overview of reported methods for enantioselective and asymmetric syntheses of cyclopentenones, including chemical and enzymatic resolution, asymmetric synthesis via Pauson-Khand reaction, Nazarov cyclization and organocatalyzed reactions, asymmetric functionalization of the existing cyclopentenone unit, and functionalization of chiral building blocks. PMID:27101336

  1. Bifunctional Asymmetric Catalysis

    PubMed Central

    PAULL, DANIEL H.; ABRAHAM, CIBY J.; SCERBA, MICHAEL T.; ALDEN-DANFORTH, ETHAN; LECTKA, THOMAS

    2008-01-01

    CONSPECTUS In the field of catalytic, asymmetric synthesis, there is a growing emphasis on multifunctional systems, in which multiple parts of a catalyst or multiple catalysts work together to promote a specific reaction. These efforts, in part, are result-driven, and they are also part of a movement toward emulating the efficiency and selectivity of nature’s catalysts, enzymes. In this Account, we illustrate the importance of bifunctional catalytic methods, focusing on the cooperative action of Lewis acidic and Lewis basic catalysts by the simultaneous activation of both electrophilic and nucleophilic reaction partners. For our part, we have contributed three separate bifunctional methods that combine achiral Lewis acids with chiral cinchona alkaloid nucleophiles, for example, benzoylquinine (BQ), to catalyze highly enantioselective cycloaddition reactions between ketene enolates and various electrophiles. Each method requires a distinct Lewis acid to coordinate and activate the electrophile, which in turn increases the reaction rates and yields, without any detectable influence on the outstanding enantioselectivities inherent to these reactions. To place our results in perspective, many important contributions to this emerging field are highlighted and our own reports are chronicled. PMID:18402470

  2. Facile template-free synthesis of vertically aligned polypyrrole nanosheets on nickel foams for flexible all-solid-state asymmetric supercapacitors

    NASA Astrophysics Data System (ADS)

    Yang, Xiangwen; Lin, Zhixing; Zheng, Jingxu; Huang, Yingjuan; Chen, Bin; Mai, Yiyong; Feng, Xinliang

    2016-04-01

    This paper reports a novel and remarkably facile approach towards vertically aligned nanosheets on three-dimensional (3D) Ni foams. Conducting polypyrrole (PPy) sheets were grown on Ni foam through the volatilization of the environmentally friendly solvent from an ethanol-water solution of pyrrole (Py), followed by the polymerization of the coated Py in ammonium persulfate (APS) solution. The PPy-decorated Ni foams and commercial activated carbon (AC) modified Ni foams were employed as the two electrodes for the assembly of flexible all-solid-state asymmetric supercapacitors. The sheet-like structure of PPy and the macroporous feature of the Ni foam, which render large electrode-electrolyte interfaces, resulted in good capacitive performance of the supercapacitors. Moreover, a high energy density of ca. 14 Wh kg-1 and a high power density of 6.2 kW kg-1 were achieved for the all-solid-state asymmetric supercapacitors due to the wide cell voltage window.This paper reports a novel and remarkably facile approach towards vertically aligned nanosheets on three-dimensional (3D) Ni foams. Conducting polypyrrole (PPy) sheets were grown on Ni foam through the volatilization of the environmentally friendly solvent from an ethanol-water solution of pyrrole (Py), followed by the polymerization of the coated Py in ammonium persulfate (APS) solution. The PPy-decorated Ni foams and commercial activated carbon (AC) modified Ni foams were employed as the two electrodes for the assembly of flexible all-solid-state asymmetric supercapacitors. The sheet-like structure of PPy and the macroporous feature of the Ni foam, which render large electrode-electrolyte interfaces, resulted in good capacitive performance of the supercapacitors. Moreover, a high energy density of ca. 14 Wh kg-1 and a high power density of 6.2 kW kg-1 were achieved for the all-solid-state asymmetric supercapacitors due to the wide cell voltage window. Electronic supplementary information (ESI) available: ESI

  3. Facile template-free synthesis of vertically aligned polypyrrole nanosheets on nickel foams for flexible all-solid-state asymmetric supercapacitors.

    PubMed

    Yang, Xiangwen; Lin, Zhixing; Zheng, Jingxu; Huang, Yingjuan; Chen, Bin; Mai, Yiyong; Feng, Xinliang

    2016-04-28

    This paper reports a novel and remarkably facile approach towards vertically aligned nanosheets on three-dimensional (3D) Ni foams. Conducting polypyrrole (PPy) sheets were grown on Ni foam through the volatilization of the environmentally friendly solvent from an ethanol-water solution of pyrrole (Py), followed by the polymerization of the coated Py in ammonium persulfate (APS) solution. The PPy-decorated Ni foams and commercial activated carbon (AC) modified Ni foams were employed as the two electrodes for the assembly of flexible all-solid-state asymmetric supercapacitors. The sheet-like structure of PPy and the macroporous feature of the Ni foam, which render large electrode-electrolyte interfaces, resulted in good capacitive performance of the supercapacitors. Moreover, a high energy density of ca. 14 Wh kg(-1) and a high power density of 6.2 kW kg(-1) were achieved for the all-solid-state asymmetric supercapacitors due to the wide cell voltage window. PMID:27050711

  4. Enantioselective organocatalytic formal [3 + 3]-cycloaddition of alpha,beta-unsaturated aldehydes and application to the asymmetric synthesis of (-)-isopulegol hydrate and (-)-cubebaol.

    PubMed

    Hong, Bor-Cherng; Wu, Ming-Fun; Tseng, Hsing-Chang; Liao, Ju-Hsiou

    2006-05-25

    [reaction: see text] The first highly enantioselective organocatalyzed carbo [3 + 3] cascade cycloaddition of alpha,beta-unsaturated aldehydes is reported. Using this methodology, crotonaldehyde is converted to 6-hydroxy-4-methylcyclohex-1-enecarbaldehyde, which is used in the synthesis of (-)-isopulegol hydrate, (-)-cubebaol, and p-tolualdehyde as well as (-)-6-hydroxy-4-methyl-1-cyclohexene-1-methanol acetate, an intermediate in the total synthesis of lycopodium alkaloid magellanine. Other alpha,beta-unsaturated aldehydes give rise to chiral cyclohexadienes via formal [4 + 2] reactions. PMID:16706490

  5. The Direct Catalytic Asymmetric Aldol Reaction

    PubMed Central

    Brindle, Cheyenne S.

    2013-01-01

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

  6. Asymmetric catalysis with short-chain peptides.

    PubMed

    Lewandowski, Bartosz; Wennemers, Helma

    2014-10-01

    Within this review article we describe recent developments in asymmetric catalysis with peptides. Numerous peptides have been established in the past two decades that catalyze a wide variety of transformations with high stereoselectivities and yields, as well as broad substrate scope. We highlight here catalytically active peptides, which have addressed challenges that had thus far remained elusive in asymmetric catalysis: enantioselective synthesis of atropoisomers and quaternary stereogenic centers, regioselective transformations of polyfunctional substrates, chemoselective transformations, catalysis in-flow and reactions in aqueous environments.

  7. Synthesis and Characterization of New Binuclear Co(0) Complexes with Diphosphinoamine Ligands. A Potential Approach for Asymmetric Pauson-Khand Reactions.

    PubMed

    Gimbert, Yves; Robert, Frédéric; Durif, André; Averbuch, Marie-Thérèse; Kann, Nina; Greene, Andrew E.

    1999-05-14

    The synthesis of P-N-P bidentate ligands and the evaluation, based on IR and X-ray data, of their pi-acceptor properties in the complexes derived from phenylacetylene-dicobalt hexacarbonyl have been carried out. In addition, the reactivity of these complexes in the Pauson-Khand reaction has been examined.

  8. 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.

  9. Asymmetric Synthesis of 2,3-Dihydro-2-arylquinazolin-4-ones: Methodology and Application to a Potent Fluorescent Tubulin Inhibitor with Anticancer Activity

    PubMed Central

    Chinigo, Gary M.; Paige, Mikell; Grindrod, Scott; Hamel, Ernest; Dakshanamurthy, Sivanesan; Chruszcz, Maksymilian; Minor, Wladek; Brown, Milton L.

    2008-01-01

    For several decades the 2,3-dihydroquinazolinone (DHQZ) heterocycle has been known to possess a variety of important biological and medicinal properties. Despite the many interesting facets of these molecules, synthetic access to nonracemic DHQZ analogues has remained elusive. Herein, we disclose a synthetic route that allows access to either enantiomer of a variety of DHQZ derivatives. We illustrate the utility of this chemistry with the asymmetric preparation and biological evaluation of a new chiral fluorescent tubulin binding agent with extremely potent antiproliferative properties against human cancer cells. A computational rationale for the increased potency of the (S)-enantiomer over the (R)-enantiomer is given, based on the crystal structure of α,β-tubulin complexed with colchicine. Taking advantage of the inherent fluorescence of these molecules, confocal images of GMC-5-193 (compound 7) in the cytoplasm of human melanoma cells (MDA-MB-435) cells are presented. PMID:18610995

  10. Diastereodivergent Asymmetric Michael Addition of Cyclic Azomethine Ylides to Nitroalkenes: Direct Approach for the Synthesis of 1,7-Diazaspiro[4.4]nonane Diastereoisomers.

    PubMed

    Li, Chun-Yan; Yang, Wu-Lin; Luo, Xiaoyan; Deng, Wei-Ping

    2015-12-21

    The first highly diastereoselective and enantioselective catalytic asymmetric Michael addition of cyclic azomethine ylides with nitroalkenes have been developed to diastereodivergently generate either the syn or anti adducts by employing N,O-ligand/Cu(OAc)2 and N,P-ligand/Cu(OAc)2 catalytic systems. Both catalytic systems exhibit broad substrate applicability to afford the corresponding Michael adducts in good to excellent yields, with excellent levels of diastereo- (up to 99:1 diastereomeric ratio) and enantioselectivities (up to >99% enantiomeric excess). Importantly, the chiral 1,7-diazaspiro[4.4]nonane diastereomer derivatives can be easily obtained in good yields through facile NaBH4 reduction of the Michael adducts.

  11. Asymmetric Synthesis of Conformationally Constrained Fingolimod Analogues—Discovery of an Orally Active Sphingosine 1-Phosphate Receptor Type-1 Agonist and Receptor Type-3 Antagonist

    PubMed Central

    Zhu, Ran; Snyder, Ashley H.; Kharel, Yugesh; Schaffter, Lisa; Sun, Qin; Kennedy, Perry C.; Lynch, Kevin R.; Macdonald, Timothy L.

    2010-01-01

    Compound 1 (FTY720, Fingolimod) represents a new generation of immunosuppressant that modulates lymphocyte trafficking by interacting with the S1P1 receptor. Compound 1 also provides a template molecule for studying the molecular biology of S1P receptors and related enzymes (kinases and phosphatases). In this study, two conformationally constrained analogues of 1 (3a and 3c) were asymmetrically synthesized in high optical purity. In vitro assessment documented that both analogues are Sphk2 substrates, their phosphorylated species are potent S1P1 receptor agonists, and 3a-P is a potent S1P3 antagonist. After oral administration in mice, both compounds evoked lymphopenia, but their duration of action differed markedly. PMID:17994678

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

    NASA Astrophysics Data System (ADS)

    Endoh, Nobuyuki; Yamamoto, Koji

    1993-05-01

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

  13. A practical synthesis of (+)-discodermolide and analogues: fragment union by complex aldol reactions.

    PubMed

    Paterson, I; Florence, G J; Gerlach, K; Scott, J P; Sereinig, N

    2001-10-01

    A practical stereocontrolled synthesis of (+)-discodermolide (1) has been completed in 10.3% overall yield (23 steps longest linear sequence). The absolute stereochemistry of the C(1)-C(6) (7), C(9)-C(16) (8), and C(17)-C(24) (9) subunits was established via substrate-controlled, boron-mediated, aldol reactions of the chiral ethyl ketones 10, 11, and 12. Key fragment coupling reactions were a lithium-mediated, anti-selective, aldol reaction of aryl ester 8 (under Felkin-Anh induction from the aldehyde component 9), followed by in situ reduction to produce the 1,3-diol 40, and a (+)-diisopinocampheylboron chloride-mediated aldol reaction of methyl ketone 7 (overturning the inherent substrate induction from the aldehyde component 52) to give the (7S)-adduct 58. The flexibility of our overall strategy is illustrated by the synthesis of a number of diastereomers and structural analogues of discodermolide, which should serve as valuable probes for structure-activity studies.

  14. Design and Implementation of a Laboratory-Based Drug Design and Synthesis Advanced Pharmacy Practice Experience

    PubMed Central

    Philip, Ashok; Stephens, Mark; Mitchell, Sheila L.

    2015-01-01

    Objective. To provide students with an opportunity to participate in medicinal chemistry research within the doctor of pharmacy (PharmD) curriculum. Design. We designed and implemented a 3-course sequence in drug design or drug synthesis for pharmacy students consisting of a 1-month advanced elective followed by two 1-month research advanced pharmacy practice experiences (APPEs). To maximize student involvement, this 3-course sequence was offered to third-year and fourth-year students twice per calendar year. Assessment. Students were evaluated based on their commitment to the project’s success, productivity, and professionalism. Students also evaluated the course sequence using a 14-item course evaluation rubric. Student feedback was overwhelmingly positive. Students found the experience to be a valuable component of their pharmacy curriculum. Conclusion. We successfully designed and implemented a 3-course research sequence that allows PharmD students in the traditional 4-year program to participate in drug design and synthesis research. Students report the sequence enhanced their critical-thinking and problem-solving skills and helped them develop as independent learners. Based on the success achieved with this sequence, efforts are underway to develop research APPEs in other areas of the pharmaceutical sciences. PMID:25995518

  15. A new practical strategy for the synthesis of long-chain phosphopeptide.

    PubMed

    Miyoshi, K; Otaka, A; Kaneko, M; Tamamura, H; Fujii, N

    2000-08-01

    A new practical strategy has been developed for the synthesis of long-chain phosphopeptide. Both the 2-chlorobenzyloxycarbonyl (CIZ) group for Lys and methyl (Me) for phosphoamino acids remained intact, while other commonly used side-chain protecting groups were cleaved quantitatively, during the reaction using a highly acidic trifluoromethanesulfonic acid (TFMSA)-based reagent system (High TFMSA: TFMSA-TFA-m-cresol=1:9:1, v/v). Selective deprotection of the CIZ and Me group-containing protected phosphopeptide resin with the High TFMSA gave a partially protected phosphopeptide fragment suitable for thioester-mediated fragment condensation. A deprotection protocol of the 9-fluorenylmethyloxycarbonyl (Fmoc) group, which evades significant side reaction toward the protected phosphoamino acid, was also developed. These two new findings enabled us to synthesize long-chain phosphopeptide via thioester-mediated fragment condensation.

  16. Cell-sized asymmetric lipid vesicles facilitate the investigation of asymmetric membranes

    NASA Astrophysics Data System (ADS)

    Kamiya, Koki; Kawano, Ryuji; Osaki, Toshihisa; Akiyoshi, Kazunari; Takeuchi, Shoji

    2016-09-01

    Asymmetric lipid giant vesicles have been used to model the biochemical reactions in cell membranes. However, methods for producing asymmetric giant vesicles lead to the inclusion of an organic solvent layer that affects the mechanical and physical characteristics of the membrane. Here we describe the formation of asymmetric giant vesicles that include little organic solvent, and use them to investigate the dynamic responses of lipid molecules in the vesicle membrane. We formed the giant vesicles via the inhomogeneous break-up of a lipid microtube generated by applying a jet flow to an asymmetric planar lipid bilayer. The asymmetric giant vesicles showed a lipid flip-flop behaviour in the membrane, superficially similar to the lipid flip-flop activity observed in apoptotic cells. In vitro synthesis of membrane proteins into the asymmetric giant vesicles revealed that the lipid asymmetry in bilayer membranes improves the reconstitution ratio of membrane proteins. Our asymmetric giant vesicles will be useful in elucidating lipid–lipid and lipid–membrane protein interactions involved in the regulation of cellular functions.

  17. Cell-sized asymmetric lipid vesicles facilitate the investigation of asymmetric membranes.

    PubMed

    Kamiya, Koki; Kawano, Ryuji; Osaki, Toshihisa; Akiyoshi, Kazunari; Takeuchi, Shoji

    2016-09-01

    Asymmetric lipid giant vesicles have been used to model the biochemical reactions in cell membranes. However, methods for producing asymmetric giant vesicles lead to the inclusion of an organic solvent layer that affects the mechanical and physical characteristics of the membrane. Here we describe the formation of asymmetric giant vesicles that include little organic solvent, and use them to investigate the dynamic responses of lipid molecules in the vesicle membrane. We formed the giant vesicles via the inhomogeneous break-up of a lipid microtube generated by applying a jet flow to an asymmetric planar lipid bilayer. The asymmetric giant vesicles showed a lipid flip-flop behaviour in the membrane, superficially similar to the lipid flip-flop activity observed in apoptotic cells. In vitro synthesis of membrane proteins into the asymmetric giant vesicles revealed that the lipid asymmetry in bilayer membranes improves the reconstitution ratio of membrane proteins. Our asymmetric giant vesicles will be useful in elucidating lipid-lipid and lipid-membrane protein interactions involved in the regulation of cellular functions. PMID:27554415

  18. Cell-sized asymmetric lipid vesicles facilitate the investigation of asymmetric membranes

    NASA Astrophysics Data System (ADS)

    Kamiya, Koki; Kawano, Ryuji; Osaki, Toshihisa; Akiyoshi, Kazunari; Takeuchi, Shoji

    2016-09-01

    Asymmetric lipid giant vesicles have been used to model the biochemical reactions in cell membranes. However, methods for producing asymmetric giant vesicles lead to the inclusion of an organic solvent layer that affects the mechanical and physical characteristics of the membrane. Here we describe the formation of asymmetric giant vesicles that include little organic solvent, and use them to investigate the dynamic responses of lipid molecules in the vesicle membrane. We formed the giant vesicles via the inhomogeneous break-up of a lipid microtube generated by applying a jet flow to an asymmetric planar lipid bilayer. The asymmetric giant vesicles showed a lipid flip-flop behaviour in the membrane, superficially similar to the lipid flip-flop activity observed in apoptotic cells. In vitro synthesis of membrane proteins into the asymmetric giant vesicles revealed that the lipid asymmetry in bilayer membranes improves the reconstitution ratio of membrane proteins. Our asymmetric giant vesicles will be useful in elucidating lipid-lipid and lipid-membrane protein interactions involved in the regulation of cellular functions.

  19. Metal-free transannulation reaction of indoles with nitrostyrenes: a simple practical synthesis of 3-substituted 2-quinolones†

    PubMed Central

    Aksenov, Alexander V.; Smirnov, Alexander N.; Aksenov, Nicolai A.; Aksenova, Inna V.; Frolova, Liliya V.; Kornienko, Alexander; Magedov, Igor V.; Rubin, Michael

    2016-01-01

    3-Substituted 2-quinolones are obtained via a novel, metal-free transannulation reaction of 2-substituted indoles with 2-nitroalkenes in polyphosphoric acid. The reaction can be used in conjunction with the Fisher indole synthesis offering a practical three-component heteroannulation methodology to produce 2-quinolones from arylhydrazines, 2-nitroalkenes and acetophenone. PMID:23999797

  20. Enantioselective synthesis of the novel chiral sulfoxide derivative as a glycogen synthase kinase 3beta inhibitor.

    PubMed

    Saitoh, Morihisa; Kunitomo, Jun; Kimura, Eiji; Yamano, Toru; Itoh, Fumio; Kori, Masakuni

    2010-09-01

    Glycogen synthase kinase 3beta (GSK-3beta) inhibitors are expected to be attractive therapeutic agents for the treatment of Alzheimer's disease (AD). Recently we discovered sulfoxides (S)-1 as a novel GSK-3beta inhibitor having in vivo efficacy. We investigated practical asymmetric preparation methods for the scale-up synthesis of (S)-1. The highly enantioselective synthesis of (S)-1 (94% ee) was achieved by titanium-mediated oxidation with D-(-)-diethyl tartrate on gram scale.

  1. Two 2D Cd(II) coordination polymers based on asymmetrical Schiff-base ligand: Synthesis, crystal structures and luminescent properties

    NASA Astrophysics Data System (ADS)

    Dang, Dong-Bin; Li, Meng-Meng; Bai, Yan; Zhou, Rui-Min

    2013-02-01

    Two new two-dimensional coordination polymers [Cd3L2(SCN)6]n (1) and [CdLI2]n (2) have been synthesized and characterized by IR spectroscopy, elemental analysis, TG technique, XRPD and complete single crystal structure analysis, where L is 4-(pyridine-2-yl)methyleneamino-1,2,4-trizaole. Asymmetrical Schiff-base ligand L with five- and six-membered N-containing heterocyclic rings acts as a tridentate bridging ligand to bind two Cd(II) centers through one terminal Ntriazolyl and one pyridylimine chelate unit in 1 and 2. For polymer 1, tridentate bridging ligands link Cd-(1,3-μ-SCN-) 1D inorganic chains to form a 2D layer network. The existence of Csbnd H⋯π and πsbnd π stacking interactions between 2D hybrid layers further gives rise to a 3D supramolecular network. In comparison with 1, polymer 2 shows a 2D layer network containing hexanuclear macrometallacyclic units. The 2D layers are staggered together through the combination of Csbnd H⋯π and πsbnd π stacking interactions and forming a 3D supramolecular structure. The luminescent properties of the polymers 1 and 2 were investigated in the solid state at room temperature.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  3. Synthesis, photophysical and charge-transporting properties of a novel asymmetric indolo [3,2-b]carbazole derivative containing benzothiazole and diphenylamino moieties

    NASA Astrophysics Data System (ADS)

    Shi, Heping; Yuan, Jiandong; Dong, Xiuqing; Cheng, Fangqin

    2014-12-01

    A novel asymmetric donor-π-donor-π-acceptor compound, 2-benzothiazolyl-8-diphenylamino-5,11-dihexylindolo[3,2-b]carbazole (BDDAICZ), has been successfully synthesized by introducing a benzothiazole moiety (as an electron-acceptor) and a diphenylamino moiety (as an electron-donor) to 2-position and 8-position of indolo[3,2-b]carbazole moiety (as a skeleton and an electron-donor), and characterized by elemental analysis, 1H NMR, 13C NMR and MS. The thermal, electrochemical properties of BDDAICZ were characterized by thermogravimetric analysis combined with electrochemistry. The absorption and emission spectra of BDDAICZ was experimentally determined in several solvents and computed using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The calculated absorption and emission wavelengths are coincident with the measured data. The ionization potential (IP), the electron affinity (EA) and reorganization energy of BDDAICZ were also investigated using density functional theory (DFT). Charge-transporting properties of BDDAICZ were characterized by OLEDs devices fabricated by using it as charge-transport layers. The results show that BDDAICZ has excellent thermal stability, electrochemical stability and hole-transporting properties, indicating its potential application as a hole-transporting material in OLEDs devices.

  4. Rational design and synthesis of Janus composites.

    PubMed

    Liang, Fuxin; Zhang, Chengliang; Yang, Zhenzhong

    2014-10-29

    Janus composites with two different components divided on the same object have gained growing interest in many fields, such as solid emulsion stabilizers, sensors, optical probes and self-propellers. Over the past twenty years, various synthesis methods have been developed including Pickering emulsion interfacial modification, block copolymer self-assembly, microfluidics, electro co-jetting, and swelling emulsion polymerization. Anisotropic shape and asymmetric spatial distribution of compositions and functionalities determine their unique performances. Rational design and large scale synthesis of functional Janus materials are crucial for the systematical characterization of performance and exploitation of practical applications.

  5. Scaleable catalytic asymmetric Strecker syntheses of unnatural α-amino acids

    PubMed Central

    Zuend, Stephan J.; Coughlin, Matthew P.; Lalonde, Mathieu P.; Jacobsen, Eric N.

    2009-01-01

    α-Amino acids are essential building blocks for protein synthesis, and are also widely useful as components of medicinally active molecules and chiral catalysts.1,2,3,4,5 Efficient chemo-enzymatic methods for the synthesis of enantioenriched α-amino acids have been devised, but the scope of these methods for the synthesis of unnatural amino acids is limited.6,7 Alkene hydrogenation is broadly useful for enantioselective catalytic synthesis of many classes of amino acids,8,9 but this approach is not applicable to the synthesis of α-amino acids bearing aryl or quaternary alkyl α-substituents. The Strecker synthesis—the reaction of an imine or imine equivalent with hydrogen cyanide, followed by nitrile hydrolysis—is an especially versatile chemical method for the synthesis of racemic α-amino acids (Fig. 1).10,11 Asymmetric Strecker syntheses using stoichiometric chiral reagents have been applied successfully on gram-to-multi-kilogram scales to the preparation of enantiomerically enriched α-amino acids.12,13,14 In principle, Strecker syntheses employing sub-stoichiometric quantities of a chiral reagent provide a practical alternative to these approaches, but the reported catalytic asymmetric methods have seen only limited use on preparative scales (e.g., > 1 gram).15,16 The limited use of existing catalytic methodologies may be ascribed to several important practical drawbacks, including the relatively complex and precious nature of the catalysts, and the requisite use of hazardous cyanide sources. Herein we report a new catalytic asymmetric method for the syntheses of highly enantiomerically enriched non-proteinogenic amino acids using a simple chiral amido-thiourea catalyst to control the key hydrocyanation step. Because this catalyst is robust and lacks sensitive functional groups, it is compatible with safely handled aqueous cyanide salts, and is thus adaptable to large-scale synthesis. This new methodology can be applied to the efficient syntheses of

  6. Asymmetric, Three-Component, One-Pot Synthesis of Spiropyrazolones and 2,5-Chromenediones from Aldol Condensation/NHC-Catalyzed Annulation Reactions.

    PubMed

    Wang, Lei; Li, Sun; Chauhan, Pankaj; Hack, Daniel; Philipps, Arne R; Puttreddy, Rakesh; Rissanen, Kari; Raabe, Gerhard; Enders, Dieter

    2016-04-01

    A novel one-pot, three-component diastereo- and enantioselective synthesis of spiropyrazolones has been developed involving the aldol condensation of an enal to generate α,β-unsaturated pyrazolones, which react with a second equivalent of enal through an N-heterocyclic carbene (NHC)-catalyzed [3+2] annulation. The desired spirocyclopentane pyrazolones are obtained in moderate to good yields and good to excellent stereoselectivities. Alternatively, starting from cyclic 1,3-diketones, 2,5-chromenediones are available through [2+4] annulation.

  7. Hydrodehalogenation of alkyl iodides with base-mediated hydrogenation and catalytic transfer hydrogenation: application to the asymmetric synthesis of N-protected α-methylamines.

    PubMed

    Mandal, Pijus K; Birtwistle, J Sanderson; McMurray, John S

    2014-09-01

    We report a very mild synthesis of N-protected α-methylamines from the corresponding amino acids. Carboxyl groups of amino acids are reduced to iodomethyl groups via hydroxymethyl intermediates. Reductive deiodination to methyl groups is achieved by hydrogenation or catalytic transfer hydrogenation under alkaline conditions. Basic hydrodehalogenation is selective for the iodomethyl group over hydrogenolysis-labile protecting groups, such as benzyloxycarbonyl, benzyl ester, benzyl ether, and 9-fluorenyloxymethyl, thus allowing the conversion of virtually any protected amino acid into the corresponding N-protected α-methylamine.

  8. Rh2 (S-1,2-NTTL)4 : A novel Rh2 (S-PTTL)4 analog with lower ligand symmetry for asymmetric synthesis of chiral cyclopropylphosphonates.

    PubMed

    Adly, Frady G; Maddalena, Johncarlo; Ghanem, Ashraf

    2014-11-01

    A new series of dirhodium(II) tetracarboxylate was derived from N-1,2-naphthaloyl-(S)-amino acid ligands. In terms of enantioselectivity, Rh2 (S-1,2-NTTL)4 () derived from N-1,2-naphthaloyl-(S)-tert-leucine, was the best-performing catalyst among the new series in the enantioselective synthesis of cyclopropylphosphonate derivatives (up to >99% enantiomeric excess). A predictive model was proposed to justify the observed high enantiomeric induction exhibited by Rh2 (S-1,2-NTTL)4 with donor-acceptor phosphonate carbenoids.

  9. Asymmetric, Three-Component, One-Pot Synthesis of Spiropyrazolones and 2,5-Chromenediones from Aldol Condensation/NHC-Catalyzed Annulation Reactions.

    PubMed

    Wang, Lei; Li, Sun; Chauhan, Pankaj; Hack, Daniel; Philipps, Arne R; Puttreddy, Rakesh; Rissanen, Kari; Raabe, Gerhard; Enders, Dieter

    2016-04-01

    A novel one-pot, three-component diastereo- and enantioselective synthesis of spiropyrazolones has been developed involving the aldol condensation of an enal to generate α,β-unsaturated pyrazolones, which react with a second equivalent of enal through an N-heterocyclic carbene (NHC)-catalyzed [3+2] annulation. The desired spirocyclopentane pyrazolones are obtained in moderate to good yields and good to excellent stereoselectivities. Alternatively, starting from cyclic 1,3-diketones, 2,5-chromenediones are available through [2+4] annulation. PMID:26864437

  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 α,β-unsaturated aldehydes (e.g., cinnamaldehyde). The structure and absolute configuration of a product were confirmed by X-ray analysis of an appropriate derivative.

  11. 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

  12. Thou shalt versus thou shalt not: a meta-synthesis of GPs' attitudes to clinical practice guidelines

    PubMed Central

    Carlsen, Benedicte; Glenton, Claire; Pope, Catherine

    2007-01-01

    Background GPs' adherence to clinical practice guidelines is variable. Barriers to guideline implementation have been identified but qualitative studies have not been synthesised to explore what underpins these attitudes. Aim To explore and synthesise qualitative research on GPs' attitudes to and experiences with clinical practice guidelines. Design of study Systematic review and meta-synthesis of qualitative studies. Method PubMed, CINAHL, EMBASE, Social Science Citation Index, and Science Citation Index were used as data sources, and independent data extraction was carried out. Discrepancies were resolved by consensus. Initial thematic analysis was conducted, followed by interpretative synthesis. Results Seventeen studies met the inclusion criteria. Five were excluded following quality appraisal. Twelve papers were synthesised which reported research in the UK, US, Canada, and the Netherlands, and covered different clinical guideline topics. Six themes were identified: questioning the guidelines, GPs' experience, preserving the doctor–patient relationship, professional responsibility, practical issues, and guideline format. Comparative analysis and synthesis revealed that GPs' reasons for not following guidelines differed according to whether the guideline in question was prescriptive, in that it encouraged a certain type of behaviour or treatment, or proscriptive, in that it discouraged certain treatments or behaviours. Conclusion Previous analyses of guidelines have focused on professional attitudes and organisational barriers to adherence. This synthesis suggests that the purpose of the guideline, whether its aims are prescriptive or proscriptive, may influence if and how guidelines are received and implemented. PMID:18252073

  13. Widely applicable synthesis of enantiomerically pure tertiary alkyl-containing 1-alkanols by zirconium-catalyzed asymmetric carboalumination of alkenes and palladium- or copper-catalyzed cross-coupling.

    PubMed

    Xu, Shiqing; Lee, Ching-Tien; Wang, Guangwei; Negishi, Ei-ichi

    2013-08-01

    A highly enantioselective and widely applicable method for the synthesis of various chiral 2-alkyl-1-alkanols, especially those of feeble chirality, has been developed. It consists of zirconium-catalyzed asymmetric carboalumination of alkenes (ZACA), lipase-catalyzed acetylation, and palladium- or copper-catalyzed cross-coupling. By virtue of the high selectivity factor (E) associated with iodine, either (S)- or (R)-enantiomer of 3-iodo-2-alkyl-1-alkanols (1), prepared by ZACA reaction of allyl alcohol, can be readily purified to the level of ≥99% ee by lipase-catalyzed acetylation. A variety of chiral tertiary alkyl-containing alcohols, including those that have been otherwise difficult to prepare, can now be synthesized in high enantiomeric purity by Pd- or Cu-catalyzed cross-coupling of (S)-1 or (R)-2 for introduction of various primary, secondary, and tertiary carbon groups with retention of all carbon skeletal features. These chiral tertiary alkyl-containing alcohols can be further converted into the corresponding acids with full retention of the stereochemistry. The synthetic utility of this method has been demonstrated in the highly enantioselective (≥99% ee) and efficient syntheses of (R)-2-methyl-1-butanol and (R)- and (S)-arundic acids.

  14. Remote electronic control in the regioselective reduction of succinimides: a practical, scalable synthesis of Ep4 antagonist MF-310.

    PubMed

    Molinaro, Carmela; Gauvreau, Danny; Hughes, Gregory; Lau, Stephen; Lauzon, Sophie; Angelaud, Rémy; O'Shea, Paul D; Janey, Jacob; Palucki, Michael; Hoerrner, Scott R; Raab, Conrad E; Sidler, Rick R; Belley, Michel; Han, Yongxin

    2009-09-01

    A practical large-scale chromatography-free synthesis of EP4 antagonist MF-310, a potential new treatment for chronic inflammation, is presented. The synthetic route provided MF-310 as its sodium salt in 10 steps and 17% overall yield from commercially available pyridine dicarboxylate 7. The key features of this sequence include a unique regioselective reduction of succinimide 2 controlled by the electronic properties of a remote pyridine ring, preparation of cyclopropane carboxylic acid 3 via a Corey-Chaykovsky cyclopropanation, and a short synthesis of sulfonamide 5.

  15. 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.

  16. Asymmetric catalysis: An enabling science

    PubMed Central

    Trost, Barry M.

    2004-01-01

    Chirality of organic molecules plays an enormous role in areas ranging from medicine to material science, yet the synthesis of such entities in one enantiomeric form is one of the most difficult challenges. The advances being made stem from the convergence of a broader understanding of theory and how structure begets function, the developments in the interface between organic and inorganic chemistry and, most notably, the organic chemistry of the transition metals, and the continuing advancements in the tools to help define structure, especially in solution. General themes for designing catalysts to effect asymmetric induction are helping to make this strategy more useful, in general, with the resultant effect of a marked enhancement of synthetic efficiency. PMID:14990801

  17. Chemistry of Renieramycins. Part 14: Total Synthesis of Renieramycin I and Practical Synthesis of Cribrostatin 4 (Renieramycin H)

    PubMed Central

    Yokoya, Masashi; Kobayashi, Keiichiro; Sato, Mitsuhiro; Saito, Naoki

    2015-01-01

    The first total synthesis of (±)-renieramycin I, which was isolated from the Indian bright blue sponge Haliclona cribricutis, is described. The key step is the selenium oxide oxidation of pentacyclic bis-p-quinone derivative (3) stereo- and regioselectively. We also report a large-scale synthesis of cribrostatin 4 (renieramycin H) via the C3-C4 double bond formation in an early stage based on the Avendaño’s protocol, from readily available 1-acetyl-3-(3-methyl-2,4,5-trimethylphenyl)methyl-piperazine-2,5-dione (8) in 18 steps (8.3% overall yield). The synthesis provides unambiguous evidence supporting the original structure of renieramycin I. PMID:26287215

  18. Practical synthesis of (20S)-10-(3-aminopropyloxy)-7-ethylcamptothecin, a water-soluble analogue of camptothecin.

    PubMed

    Watanabe, Tatsuya; Tsuboi, Yasunori; Nomura, Sumihiro

    2013-03-01

    A robust, practical synthesis of (20S)-10-(3-aminopropyloxy)-7-ethylcamptothecin (T-2513, 5), which is a water-soluble analogue of camptothecin, has been developed. The key step in this synthesis is a highly diastereoselective ethylation at the C20 position by using N-arylsulfonyl-(R)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid ester as a chiral auxiliary, which affords the key intermediate ethyl-(S)-2-acyloxy-2-(6-cyano-5-oxo-1,2,3,5-tetrahydroindolizin-7-yl)butanoate (8k) in 93% yield and 87% de. Optically pure compound 8k was obtained by a single recrystallization from acetone and its further elaboration through Friedlander condensation afforded compound 5. This synthesis does not require any chromatographic purification steps and can provide compound 5 on a multi-gram scale in 6.3% overall yield (16 steps). PMID:23281180

  19. Synthesis of Silver(I) and Gold(I) Complexes Containing Enantiopure Pybox Ligands. First Assays on the Silver(I)-Catalyzed Asymmetric Addition of Alkynes to Imines.

    PubMed

    Borrajo-Calleja, Gustavo M; de Julián, Eire; Bayón, Esther; Díez, Josefina; Lastra, Elena; Merino, Isabel; Gamasa, M Pilar

    2016-09-01

    Dinuclear complexes [Ag2(CF3SO3){(S,S)-(i)Pr-pybox}2][CF3SO3] (1), [Ag2(R-pybox)2][X]2 [R-pybox = 2,6-bis[4-(S)-isopropyloxazolin-2-yl]pyridine (S,S)-(i)Pr-pybox and X = PF6 (2) and BF4 (3); R-pybox = 2,6-bis[(3aS,8aR)-8,8a-dihydro-3aH-indeno[1,2-d]oxazol-2-yl]pyridine (3aS,3a'S,8aR,8a'R)-indane-pybox and X = CF3SO3 (4)], [Ag2{(S,S)-(i)Pr-pybox}{(3aS,3a'S,8aR,8a'R)-indane-pybox}][CF3SO3]2 (5), and [Ag2(R-pybox)3][X]2 [R-pybox = (3aS,3a'S,8aR,8a'R)-indane-pybox and X = CF3SO3 (10), SF6 (11), and PF6 (12)] as well as mononuclear complexes [Ag(R-pybox)2][X] [R-pybox = (S,S)-(i)Pr-pybox and X = SbF6 (6), PF6 (7), and BF4 (8); R-pybox = (3aS,3a'S,8aR,8a'R)-indane-pybox) and X = BF4 (9)] have been prepared by the reaction of the corresponding silver salts and pybox ligands using the appropriate molar ratio conditions. The first gold(I)/pybox complex [Au6Cl4{(S,S)-(i)Pr-pybox}4][AuCl2]2 (13) has been synthesized by the reaction of [AuCl{S(CH3)2}] and (S,S)-(i)Pr-pybox (1:1 molar ratio) in acetonitrile. The structures of the dinuclear (1, 4, 5, 10, and 11) and mononuclear (6 and 9) silver complexes and the hexanuclear gold complex 13 have been determined by single-crystal X-ray diffraction analysis. These studies have been complemented with a solution-state study by NMR spectroscopy, which included structure elucidation, variable-temperature measurements, and diffusion studies using diffusion-ordered spectroscopy (DOSY; for complexes 1, 4, 10, and 12). Complexes 1, 2, 4, and 10 have been assayed as catalysts in the asymmetric addition of phenylacetylene to N-benzylideneaniline.

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

    NASA Astrophysics Data System (ADS)

    Shebl, Magdy

    2014-01-01

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

  1. Synthesis of Silver(I) and Gold(I) Complexes Containing Enantiopure Pybox Ligands. First Assays on the Silver(I)-Catalyzed Asymmetric Addition of Alkynes to Imines.

    PubMed

    Borrajo-Calleja, Gustavo M; de Julián, Eire; Bayón, Esther; Díez, Josefina; Lastra, Elena; Merino, Isabel; Gamasa, M Pilar

    2016-09-01

    Dinuclear complexes [Ag2(CF3SO3){(S,S)-(i)Pr-pybox}2][CF3SO3] (1), [Ag2(R-pybox)2][X]2 [R-pybox = 2,6-bis[4-(S)-isopropyloxazolin-2-yl]pyridine (S,S)-(i)Pr-pybox and X = PF6 (2) and BF4 (3); R-pybox = 2,6-bis[(3aS,8aR)-8,8a-dihydro-3aH-indeno[1,2-d]oxazol-2-yl]pyridine (3aS,3a'S,8aR,8a'R)-indane-pybox and X = CF3SO3 (4)], [Ag2{(S,S)-(i)Pr-pybox}{(3aS,3a'S,8aR,8a'R)-indane-pybox}][CF3SO3]2 (5), and [Ag2(R-pybox)3][X]2 [R-pybox = (3aS,3a'S,8aR,8a'R)-indane-pybox and X = CF3SO3 (10), SF6 (11), and PF6 (12)] as well as mononuclear complexes [Ag(R-pybox)2][X] [R-pybox = (S,S)-(i)Pr-pybox and X = SbF6 (6), PF6 (7), and BF4 (8); R-pybox = (3aS,3a'S,8aR,8a'R)-indane-pybox) and X = BF4 (9)] have been prepared by the reaction of the corresponding silver salts and pybox ligands using the appropriate molar ratio conditions. The first gold(I)/pybox complex [Au6Cl4{(S,S)-(i)Pr-pybox}4][AuCl2]2 (13) has been synthesized by the reaction of [AuCl{S(CH3)2}] and (S,S)-(i)Pr-pybox (1:1 molar ratio) in acetonitrile. The structures of the dinuclear (1, 4, 5, 10, and 11) and mononuclear (6 and 9) silver complexes and the hexanuclear gold complex 13 have been determined by single-crystal X-ray diffraction analysis. These studies have been complemented with a solution-state study by NMR spectroscopy, which included structure elucidation, variable-temperature measurements, and diffusion studies using diffusion-ordered spectroscopy (DOSY; for complexes 1, 4, 10, and 12). Complexes 1, 2, 4, and 10 have been assayed as catalysts in the asymmetric addition of phenylacetylene to N-benzylideneaniline. PMID:27500504

  2. 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.

  3. Skinner Meets Piaget on the Reggio Playground: Practical Synthesis of Applied Behavior Analysis and Developmentally Appropriate Practice Orientations

    ERIC Educational Resources Information Center

    Warash, Bobbie; Curtis, Reagan; Hursh, Dan; Tucci, Vicci

    2008-01-01

    We focus on integrating developmentally appropriate practices, the project approach of Reggio Emilia, and a behavior analytic model to support a quality preschool environment. While the above practices often are considered incompatible, we have found substantial overlap and room for integration of these perspectives in practical application. With…

  4. 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

  5. Prediction of Multi-Target Networks of Neuroprotective Compounds with Entropy Indices and Synthesis, Assay, and Theoretical Study of New Asymmetric 1,2-Rasagiline Carbamates

    PubMed Central

    Romero Durán, Francisco J.; Alonso, Nerea; Caamaño, Olga; García-Mera, Xerardo; Yañez, Matilde; Prado-Prado, Francisco J.; González-Díaz, Humberto

    2014-01-01

    In a multi-target complex network, the links (Lij) represent the interactions between the drug (di) and the target (tj), characterized by different experimental measures (Ki, Km, IC50, etc.) obtained in pharmacological assays under diverse boundary conditions (cj). In this work, we handle Shannon entropy measures for developing a model encompassing a multi-target network of neuroprotective/neurotoxic compounds reported in the CHEMBL database. The model predicts correctly >8300 experimental outcomes with Accuracy, Specificity, and Sensitivity above 80%–90% on training and external validation series. Indeed, the model can calculate different outcomes for >30 experimental measures in >400 different experimental protocolsin relation with >150 molecular and cellular targets on 11 different organisms (including human). Hereafter, we reported by the first time the synthesis, characterization, and experimental assays of a new series of chiral 1,2-rasagiline carbamate derivatives not reported in previous works. The experimental tests included: (1) assay in absence of neurotoxic agents; (2) in the presence of glutamate; and (3) in the presence of H2O2. Lastly, we used the new Assessing Links with Moving Averages (ALMA)-entropy model to predict possible outcomes for the new compounds in a high number of pharmacological tests not carried out experimentally. PMID:25255029

  6. Asymmetric hydrolytic kinetic resolution with recyclable macrocyclic Co(III)-salen complexes: a practical strategy in the preparation of (R)-mexiletine and (S)-propranolol.

    PubMed

    Sadhukhan, Arghya; Khan, Noor-ul H; Roy, Tamal; Kureshy, Rukhsana I; Abdi, Sayed H R; Bajaj, Hari C

    2012-04-23

    A chiral cobalt(III) complex (1e) was synthesized by the interaction of cobalt(II) acetate and ferrocenium hexafluorophosphate with a chiral dinuclear macrocyclic salen ligand that was derived from 1R,2R-(-)-1,2-diaminocyclohexane with trigol bis-aldehyde. A variety of epoxides and glycidyl ethers were suitable substrates for the reaction with water in the presence of chiral macrocyclic salen complex 1e at room temperature to afford chiral epoxides and diols by hydrolytic kinetic resolution (HKR). Excellent yields (47% with respect to the epoxides, 53% with respect to the diols) and high enantioselectivity (ee>99% for the epoxides, up to 96% for the diols) were achieved in 2.5-16 h. The Co(III) macrocyclic salen complex (1e) maintained its performance on a multigram scale and was expediently recycled a number of times. We further extended our study of chiral epoxides that were synthesized by using HKR to the synthesis of chiral drug molecules (R)-mexiletine and (S)-propranolol. PMID:22422658

  7. Exploring the Relevance of Qualitative Research Synthesis to Higher Education Research and Practice

    ERIC Educational Resources Information Center

    Major, Claire; Savin-Baden, Maggi

    2010-01-01

    This paper proposes the importance of qualitative research synthesis to the field of higher education. It examines seven key texts that undertake synthesis in this field and compares essential features and elements across studies. The authors indicate strengths of the approaches and highlight ways forward for using qualitative research synthesis…

  8. Asymmetrical field emitter

    DOEpatents

    Fleming, James G.; Smith, Bradley K.

    1995-01-01

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

  9. 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.

  10. 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.

  11. Asymmetric ion trap

    DOEpatents

    Barlow, Stephan E.; Alexander, Michael L.; Follansbee, James C.

    1997-01-01

    An ion trap having two end cap electrodes disposed asymmetrically about a center of a ring electrode. The inner surface of the end cap electrodes are conformed to an asymmetric pair of equipotential lines of the harmonic formed by the application of voltages to the electrodes. The asymmetry of the end cap electrodes allows ejection of charged species through the closer of the two electrodes which in turn allows for simultaneously detecting anions and cations expelled from the ion trap through the use of two detectors charged with opposite polarity.

  12. 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.

  13. Isolation of Rhodococcus sp. Strain ECU0066, a New Sulfide Monooxygenase-Producing Strain for Asymmetric Sulfoxidation▿ †

    PubMed Central

    Li, Ai-Tao; Zhang, Jian-Dong; Xu, Jian-He; Lu, Wen-Ya; Lin, Guo-Qiang

    2009-01-01

    A new and efficient sulfide monooxygenase-producing strain, ECU0066, was isolated and identified as a Rhodococcus sp. that could transform phenylmethyl sulfide (PMS) to (S)-sulfoxide with 99% enantiomeric excess via two steps of enantioselective oxidations. Its enzyme activity could be effectively induced by adding PMS or phenylmethyl sulfoxide (PMSO) directly to a rich medium at the early log phase (6 h) of fermentation, resulting in over 10-times-higher production of the enzyme. This bacterial strain also displayed fairly good activity and enantioselectivity toward seven other sulfides, indicating a good potential for practical application in asymmetric synthesis of chiral sulfoxides. PMID:18836022

  14. 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.

  15. The meaning and perceived value of mind-body practices for people living with HIV: a qualitative synthesis.

    PubMed

    Donald, Graeme; Lawrence, Maggie; Lorimer, Karen; Stringer, Jacqui; Flowers, Paul

    2015-01-01

    Mind-body practices (MBPs) are a subset of complementary medicine that represents a selection of self-care activities that may promote the health of people living with HIV (PLWH). No synthesis of qualitative research in this context, which might inform service provision and research priorities, has yet been published. A systematic search of electronic databases was conducted, identifying papers exploring the experience of MBPs in PLWH. During thematic synthesis, all text under the headings "results" or "findings" was scanned line by line, and discrete, meaningful units of text were extracted as data items. Categories were identified, and second- and third-order constructs were developed. Concerns related to control and self-management appeared in the convergence of participants' worlds with the medical world and in being pragmatic about selecting MBPs and goal setting. The themes developed suggest a desire for more holistic and person-centered care, arguably marginalized as a result of effective antiretroviral therapy.

  16. One-step catalytic asymmetric synthesis of all-syn deoxypropionate motif from propylene: Total synthesis of (2R,4R,6R,8R)-2,4,6,8-tetramethyldecanoic acid

    PubMed Central

    Ota, Yusuke; Murayama, Toshiki; Nozaki, Kyoko

    2016-01-01

    In nature, many complex structures are assembled from simple molecules by a series of tailored enzyme-catalyzed reactions. One representative example is the deoxypropionate motif, an alternately methylated alkyl chain containing multiple stereogenic centers, which is biosynthesized by a series of enzymatic reactions from simple building blocks. In organic synthesis, however, the majority of the reported routes require the syntheses of complex building blocks. Furthermore, multistep reactions with individual purifications are required at each elongation. Here we show the construction of the deoxypropionate structure from propylene in a single step to achieve a three-step synthesis of (2R,4R,6R,8R)-2,4,6,8-tetramethyldecanoic acid, a major acid component of a preen-gland wax of the graylag goose. To realize this strategy, we focused on the coordinative chain transfer polymerization and optimized the reaction condition to afford a stereo-controlled oligomer, which is contrastive to the other synthetic strategies developed to date that require 3–6 steps per unit, with unavoidable byproduct generation. Furthermore, multiple oligomers with different number of deoxypropionate units were isolated from one batch, showing application to the construction of library. Our strategy opens the door for facile synthetic routes toward other natural products that share the deoxypropionate motif. PMID:26908873

  17. Copper-catalyzed intermolecular asymmetric propargylic dearomatization of indoles.

    PubMed

    Shao, Wen; Li, He; Liu, Chuan; Liu, Chen-Jiang; You, Shu-Li

    2015-06-22

    The first copper-catalyzed intermolecular dearomatization of indoles by an asymmetric propargylic substitution reaction was developed. This method provides a highly efficient synthesis of versatile furoindoline and pyrroloindoline derivatives containing a quaternary carbon stereogenic center and a terminal alkyne moiety with up to 86 % yield and 98 % ee. PMID:25968474

  18. Reducing obesity and related chronic disease risk in children and youth: a synthesis of evidence with 'best practice' recommendations.

    PubMed

    Flynn, M A T; McNeil, D A; Maloff, B; Mutasingwa, D; Wu, M; Ford, C; Tough, S C

    2006-02-01

    Childhood obesity is a global epidemic and rising trends in overweight and obesity are apparent in both developed and developing countries. Available estimates for the period between the 1980s and 1990s show the prevalence of overweight and obesity in children increased by a magnitude of two to five times in developed countries (e.g. from 11% to over 30% in boys in Canada), and up to almost four times in developing countries (e.g. from 4% to 14% in Brazil). The goal of this synthesis research study was to develop best practice recommendations based on a systematic approach to finding, selecting and critically appraising programmes addressing prevention and treatment of childhood obesity and related risk of chronic diseases. An international panel of experts in areas of relevance to obesity provided guidance for the study. This synthesis research encompassed a comprehensive search of medical/academic and grey literature and the Internet covering the years 1982-2003. The appraisal approach developed to identify best practice was unique, in that it considered not only methodological rigour, but also population health, immigrant health and programme development/evaluation perspectives in the assessment. Scores were generated based on pre-determined criteria with programmes scoring in the top tertile of the scoring range in any one of the four appraisal categories included for further examination. The synthesis process included identification of gaps and an analysis and summary of programme development and programme effectiveness to enable conclusions to be drawn and recommendations to be made. The results from the library database searches (13,158 hits), the Internet search and key informant surveys were reduced to a review of 982 reports of which 500 were selected for critical appraisal. In total 158 articles, representing 147 programmes, were included for further analysis. The majority of reports were included based on high appraisal scores in programme development

  19. 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.

  20. 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.

  1. Asymmetric information and economics

    NASA Astrophysics Data System (ADS)

    Frieden, B. Roy; Hawkins, Raymond J.

    2010-01-01

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

  2. Social skills interventions for individuals with autism: evaluation for evidence-based practices within a best evidence synthesis framework.

    PubMed

    Reichow, Brian; Volkmar, Fred R

    2010-02-01

    This paper presents a best evidence synthesis of interventions to increase social behavior for individuals with autism. Sixty-six studies published in peer-reviewed journals between 2001 and July 2008 with 513 participants were included. The results are presented by the age of the individual receiving intervention and by delivery agent of intervention. The findings suggest there is much empirical evidence supporting many different treatments for the social deficits of individuals with autism. Using the criteria of evidence-based practice proposed by Reichow et al. (Journal of Autism and Developmental Disorders, 38:1311-1318, 2008), social skills groups and video modeling have accumulated the evidence necessary for the classifications of established EBP and promising EBP, respectively. Recommendations for practice and areas of future research are provided. PMID:19655240

  3. 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.

  4. 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 Prisoner’s 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

  5. 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.

  6. Asymmetric Synthesis of First Generation Molecular Motors

    PubMed Central

    2014-01-01

    A general enantioselective route to functionalized first generation molecular motors is described. An enantioselective protonation of the silyl enol ethers of indanones by a Au(I)BINAP complex sets the stage for a highly diastereoselective McMurry coupling as a second enhancement step for enantiomeric excess. In this way various functionalized overcrowded alkenes could be synthesized in good yields (up to 78%) and good to excellent enantiomeric excess (85% ee–>98% ee) values. PMID:25079823

  7. A practical and efficient route for the highly enantioselective synthesis of mexiletine analogues and novel beta-thiophenoxy and pyridyl ethers.

    PubMed

    Huang, Kun; Ortiz-Marciales, Margarita; Stepanenko, Viatcheslav; De Jesús, Melvin; Correa, Wildeliz

    2008-09-01

    A practical and efficient procedure for the enantioselective synthesis of mexiletine analogues with use of 10% of spiroborate ester 6 as chirality transfer agent is presented. A variety of mexiletine analogues were prepared in good yield with excellent enantioselectivities (91-97% ee) from readily available starting materials. The developed methodology was also successfully applied for the synthesis of novel beta-amino ethers containing thiophenyl and pyridyl fragments. PMID:18690744

  8. Pyrosequencing on templates generated by asymmetric nucleic acid sequence-based amplification (asymmetric-NASBA).

    PubMed

    Jia, Huning; Chen, Zhiyao; Wu, Haiping; Ye, Hui; Yan, Zhengyu; Zhou, Guohua

    2011-12-21

    Pyrosequencing is an ideal tool for verifying the sequence of amplicons. To enable pyrosequencing on amplicons from nucleic acid sequence-based amplification (NASBA), asymmetric NASBA with unequal concentrations of T7 promoter primer and reverse transcription primer was proposed. By optimizing the ratio of two primers and the concentration of dNTPs and NTPs, the amount of single-stranded cDNA in the amplicons from asymmetric NASBA was found increased 12 times more than the conventional NASBA through the real-time detection of a molecular beacon specific to cDNA of interest. More than 20 bases have been successfully detected by pyrosequencing on amplicons from asymmetric NASBA using Human parainfluenza virus (HPIV) as an amplification template. The primary results indicate that the combination of NASBA with a pyrosequencing system is practical, and should open a new field in clinical diagnosis.

  9. Intramolecular benzyl protection delivery: a practical synthesis of DMDP and DGDP from D-fructose.

    PubMed

    García-Moreno, M Isabel; Aguilar, Matilde; Ortiz Mellet, Carmen; García Fernández, José M

    2006-01-19

    [reaction: see text] A two-step protection of 1,2-diols as the corresponding o-xylylene cyclic ethers, involving an intramolecular ring-closing O-benzylation reaction, has been developed to overcome the problems associated to regioselective benzylation reactions. The strategy has been applied to the high-yielding synthesis of the pyrrolidine glycosidase inhibitors DMDP and DGDP.

  10. What Works in the Community Colleges: A Synthesis of the Literature on Best Practices.

    ERIC Educational Resources Information Center

    Bourdon, Carrie M., Ed.; Carducci, Rozana, Ed.

    This paper offers a synthesis of 27 community college issues derived from recent books, journals, and ERIC documents. It presents single-page statements that each include a research finding, comments, and references. The findings are divided into nine topics: administration and governance, faculty, student achievement and persistence, curriculum…

  11. A practical improvement, enhancing the large-scale synthesis of (+)-discodermolide: a third-generation approach.

    PubMed

    Smith, Amos B; Freeze, B Scott; Brouard, Ignacio; Hirose, Tomoyasu

    2003-11-13

    [reaction: see text] A significant improvement to the Penn one-gram synthesis of (+)-discodermolide (1) has been achieved. Specifically, reduction of the steric bulk of the C(11) hydroxyl protecting group permits formation of the requisite AB Wittig salt at the expense of the undesired intramolecular cyclization upon treatment with PPh(3) at ambient pressure.

  12. The Theory and Practice of Culturally Relevant Education: A Synthesis of Research across Content Areas

    ERIC Educational Resources Information Center

    Aronson, Brittany; Laughter, Judson

    2016-01-01

    Many teachers and educational researchers have claimed to adopt tenets of culturally relevant education (CRE). However, recent work describes how standardized curricula and testing have marginalized CRE in educational reform discourses. In this synthesis of research, we sought examples of research connecting CRE to positive student outcomes across…

  13. Synthesis and polymerization of bicyclic ketals: a practical route to high-molecular weight polyketals.

    PubMed

    Whiting, Bryan T; Coates, Geoffrey W

    2013-07-31

    Polyketals are an important class of materials for drug delivery to sensitive tissues as they degrade in vivo to nonacidic species. We report the synthesis of high-molecular weight cyclic polyketals by the cationic ring-opening polymerization of bicyclic ketal monomers, which were prepared by the metal-catalyzed rearrangement of epoxy ketones. Three different cyclic polyketals with high molecular weights were synthesized using this protocol.

  14. 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.

  15. Distributed Practice in Verbal Recall Tasks: A Review and Quantitative Synthesis

    ERIC Educational Resources Information Center

    Cepeda, Nicholas J.; Pashler, Harold; Vul, Edward; Wixted, John T.; Rohrer, Doug

    2006-01-01

    The authors performed a meta-analysis of the distributed practice effect to illuminate the effects of temporal variables that have been neglected in previous reviews. This review found 839 assessments of distributed practice in 317 experiments located in 184 articles. Effects of spacing (consecutive massed presentations vs. spaced learning…

  16. The quest for a practical synthesis of morphine alkaloids and their derivatives by chemoenzymatic methods.

    PubMed

    Reed, Josephine W; Hudlicky, Tomas

    2015-03-17

    We became interested in approaches to morphine in the early 1990s following our immersion into the new program on the enzymatic dihydroxylation of aromatics. Larry Kwart, a former classmate of one of us at Rice University, who worked with our group at Virginia Tech in the mid-1980s, introduced to us the use of blocked mutants of Pseudomonas putida (Pp39D) for the production of arene-cis-dihydrodiols. Larry had gained expertise in microbiology from a postdoctoral stay with David Gibson, who discovered this unique enzymatic transformation, and he helped us to establish a strong program in chemoenzymatic synthesis that continues to this day. Without his pioneering effort, none of our accomplishments in chemoenzymatic synthesis, including the various approaches to morphine, would have materialized. Here we trace the evolution of our approaches to morphine alkaloids and some commercial opiate-derived medicinal agents. The design features and chronology of our approaches are discussed in a way that allows the reader to appreciate a number of errors that were made in conception as well as in execution. Experience acquired from many failed or less-than-effective attempts has finally led to an "almost reasonable" total synthesis, the key concept being based on our very first but unsuccessful attempt more than two decades ago. The irony of this accomplishment has not been lost on us. Each section of this Account presents a summary of distinctly different approaches to morphine alkaloids. Each ends with a short and philosophical lesson that was (or should have been) learned in the process. We intend for this Account to offer more than the history of a search for the perfect design solution to a synthetic problem. In today's era of rapid and often careless publication of results, it should serve also as a reminder that the success and the integrity of synthetic ventures depends on perseverance, adjustment of strategy, improvements of previous attempts, and serious attention to

  17. Asymmetric inclusion process.

    PubMed

    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. PMID:22181081

  18. Practical synthesis of pyrazoles via a copper-catalyzed relay oxidation strategy.

    PubMed

    Tang, Xiaodong; Huang, Liangbin; Yang, Jidan; Xu, Yanli; Wu, Wanqing; Jiang, Huanfeng

    2014-12-01

    Various 1,3- and 1,3,4-substituted pyrazoles are smoothly formed via copper-catalyzed cascade reactions of oxime acetates, amines and aldehydes. This relay oxidative process involves copper-promoted N-O bond cleavage and C-C/C-N/N-N bond formations to furnish pyrazolines, and sequential Cu-O2 system-involved oxidative dehydrogenation of pyrazolines to afford pyrazoles. This transformation provides a novel and versatile approach for the synthesis of pyrazoles, with an inexpensive copper catalyst and green oxidants. It is atom- and step-economical, and possesses a good functional group tolerance, as well as operational simplicity. PMID:25319768

  19. Developing clinical practice guidelines: types of evidence and outcomes; values and economics, synthesis, grading, and presentation and deriving recommendations

    PubMed Central

    2012-01-01

    Clinical practice guidelines are one of the foundations of efforts to improve healthcare. In 1999, we authored a paper about methods to develop guidelines. Since it was published, the methods of guideline development have progressed both in terms of methods and necessary procedures and the context for guideline development has changed with the emergence of guideline clearinghouses and large scale guideline production organisations (such as the UK National Institute for Health and Clinical Excellence). It therefore seems timely to, in a series of three articles, update and extend our earlier paper. In this second paper, we discuss issues of identifying and synthesizing evidence: deciding what type of evidence and outcomes to include in guidelines; integrating values into a guideline; incorporating economic considerations; synthesis, grading, and presentation of evidence; and moving from evidence to recommendations. PMID:22762158

  20. Preparation of asymmetric porous materials

    DOEpatents

    Coker, Eric N.

    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.

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

    NASA Astrophysics Data System (ADS)

    Makó, Attila; Menyhárd, Dóra K.; Bakó, Péter; Keglevich, György; Tőke, László

    2008-12-01

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

  2. 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.

  3. Asymmetric twin Dark Matter

    SciTech Connect

    Farina, Marco

    2015-11-01

    We study a natural implementation of Asymmetric Dark Matter in Twin Higgs models. The mirroring of the Standard Model strong sector suggests that a twin baryon with mass around 5 GeV is a natural Dark Matter candidate once a twin baryon number asymmetry comparable to the SM asymmetry is generated. We explore twin baryon Dark Matter in two different scenarios, one with minimal content in the twin sector and one with a complete copy of the SM, including a light twin photon. The essential requirements for successful thermal history are presented, and in doing so we address some of the cosmological issues common to many Twin Higgs models. The required interactions we introduce predict signatures at direct detection experiments and at the LHC.

  4. 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.

  5. Evidence-Based Practices for Teachers: A Synthesis of Trustworthy Online Sources

    ERIC Educational Resources Information Center

    Ecker, Andrew J.

    2016-01-01

    The purpose of this study was to identify evidence-based practices (EBPs) for teachers of students with disabilities. A review of 13 trustworthy websites yielded 61 EBPs relevant, as determined by this author, to teachers of students with disabilities. The EBPs were organized into six categories: schoolwide framework, literacy instruction, math…

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

    NASA Astrophysics Data System (ADS)

    Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Röse, Philipp; Chen, Liang-An; Harms, Klaus; Marsch, Michael; Hilt, Gerhard; Meggers, Eric

    2014-11-01

    Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the `green' synthesis of non-racemic chiral molecules.

  7. Practical and Efficient Synthesis of α-Aminophosphonic Acids Containing 1,2,3,4-Tetrahydroquinoline or 1,2,3,4-Tetrahydroisoquinoline Heterocycles.

    PubMed

    Ordóñez, Mario; Arizpe, Alicia; Sayago, Fracisco J; Jiménez, Ana I; Cativiela, Carlos

    2016-01-01

    We report here a practical and efficient synthesis of α-aminophosphonic acid incorporated into 1,2,3,4-tetrahydroquinoline and 1,2,3,4-tetrahydroisoquinoline heterocycles, which could be considered to be conformationally constrained analogues of pipecolic acid. The principal contribution of this synthesis is the introduction of the phosphonate group in the N-acyliminium ion intermediates, obtained from activation of the quinoline and isoquinoline heterocycles or from the appropriate δ-lactam with benzyl chloroformate. Finally, the hydrolysis of phosphonate moiety with simultaneous cleavage of the carbamate afforded the target compounds. PMID:27589713

  8. Introducing Freshmen Students to the Practice of Solid-Phase Synthesis

    NASA Astrophysics Data System (ADS)

    Taralp, Alpay; Hulusi Türkseven, Can; Özgür Çakmak, Atilla; Çengel, Ömer

    2002-01-01

    A one-semester laboratory project on solid-phase peptide chemistry was designed pedagogically to cater to freshman science students. The approach not only permitted multistep syntheses that would be considered impractical in solution, but also gave students insight into fundamental aspects of research at an early stage of development. Young scientists prepared Bz-Asn-Asn-Phe and Bz-Asn-Gln-Phe--peptides envisaged as potential competitive inhibitors of chymotrypsin. The synthesis, defined by an attachment-deprotection cycle, two elongation-deprotection cycles, and a benzoyl-capping protocol, was completed manually on Wang resin using Fmoc chemistry. Students quantified the yield of each condensation and deprotection reaction by measuring levels of dibenzylfulvene chromophore, a stoichiometrically afforded by-product. Benzoylation of the N-terminus was confirmed by employing a cadmium-ninhydrin reagent. The group also ascertained, through use of a chromogenic substrate, that chymotrypsin-catalyzed hydrolysis was impeded slightly when carried out in the presence of target peptides. Supplementary analyses supporting peptide purity and composition were given to students. Grading was based on laboratory participation, project proposals, reports, and a concluding slide-show presentation made to peers and colleagues. While the project was time-consuming overall, students acquired an impression of research work and an appreciation of the utility of solid-phase methods.

  9. Communication about serious illness care goals: a review and synthesis of best practices.

    PubMed

    Bernacki, Rachelle E; Block, Susan D

    2014-12-01

    An understanding of patients' care goals in the context of a serious illness is an essential element of high-quality care, allowing clinicians to align the care provided with what is most important to the patient. Early discussions about goals of care are associated with better quality of life, reduced use of nonbeneficial medical care near death, enhanced goal-consistent care, positive family outcomes, and reduced costs. Existing evidence does not support the commonly held belief that communication about end-of-life issues increases patient distress. However, conversations about care goals are often conducted by physicians who do not know the patient, do not routinely address patients' nonmedical goals, and often fail to provide patients with sufficient information about prognosis to allow appropriate decisions; in addition, they tend to occur so late in the patient's illness that their impact on care processes is reduced. This article (1) reviews the evidence and describes best practices in conversations about serious illness care goals and (2) offers practical advice for clinicians and health care systems about developing a systematic approach to quality and timing of such communication to assure that each patient has a personalized serious illness care plan. Best practices in discussing goals of care include the following: sharing prognostic information, eliciting decision-making preferences, understanding fears and goals, exploring views on trade-offs and impaired function, and wishes for family involvement. Several interventions hold promise in systematizing conversations with patients about serious illness care goals: better education of physicians; systems to identify and trigger early discussions for appropriate patients; patient and family education; structured formats to guide discussions; dedicated, structured sections in the electronic health record for recording information; and continuous measurement. We conclude that communication about serious

  10. Activation of carboxylic acids in asymmetric organocatalysis.

    PubMed

    Monaco, Mattia Riccardo; Poladura, Belén; Diaz de Los Bernardos, Miriam; Leutzsch, Markus; Goddard, Richard; List, Benjamin

    2014-07-01

    Organocatalysis, catalysis using small organic molecules, has recently evolved into a general approach for asymmetric synthesis, complementing both metal catalysis and biocatalysis. Its success relies to a large extent upon the introduction of novel and generic activation modes. Remarkably though, while carboxylic acids have been used as catalyst directing groups in supramolecular transition-metal catalysis, a general and well-defined activation mode for this useful and abundant substance class is still lacking. Herein we propose the heterodimeric association of carboxylic acids with chiral phosphoric acid catalysts as a new activation principle for organocatalysis. This self-assembly increases both the acidity of the phosphoric acid catalyst and the reactivity of the carboxylic acid. To illustrate this principle, we apply our concept in a general and highly enantioselective catalytic aziridine-opening reaction with carboxylic acids as nucleophiles.

  11. Asymmetric synthesis of chiral β-alkynyl carbonyl and sulfonyl derivatives via sequential palladium and copper catalysis† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c6sc01724j Click here for additional data file.

    PubMed Central

    Masters, James T.; Taft, Benjamin R.; Lumb, Jean-Philip

    2016-01-01

    We present a full account detailing the development of a sequential catalysis strategy for the synthesis of chiral β-alkynyl carbonyl and sulfonyl derivatives. A palladium-catalyzed cross coupling of terminal alkyne donors with acetylenic ester, ketone, and sulfone acceptors generates stereodefined enynes in high yield. These compounds are engaged in an unprecedented, regio- and enantioselective copper-catalyzed conjugate reduction. The process exhibits a high functional group tolerance, and this enables the synthesis of a broad range of chiral products from simple, readily available alkyne precursors. The utility of the method is demonstrated through the elaboration of the chiral β-alkynyl products into a variety of different molecular scaffolds. Its value in complex molecule synthesis is further validated through a concise, enantioselective synthesis of AMG 837, a potent GPR40 receptor agonist. PMID:27746892

  12. A Global Synthesis of Jatropha Cultivation: Insights into Land Use Change and Management Practices.

    PubMed

    Walmsley, David C; Bailis, Rob; Klein, Alexandra-Maria

    2016-09-01

    Despite setbacks, interest in Jatropha cultivation remains high. This study addressed the question to what extent Jatropha cultivation has replaced specific vegetation and land use types and how the existing areas are managed. Major forms of land use change and management practices were identified based on cluster analysis of data from 106 interviewee's responses to a comprehensive global survey. Of the 1.04 × 10(6) ha cultivated with Jatropha in 2011 40% were established on land that was cleared of vegetation as a result of logging activities unrelated to Jatropha cultivation, 34% was defined as unused, and the remainder was attributable to areas previously used for crops or animal husbandry. With the exception of croplands, these areas were dominated (90-98%) by a few internationally active companies whose cultivation models were almost exclusively based on outgrower schemes. Management practices were largely extensive in nature (low mechanical input and infrequent use of fertilizers, pesticides and herbicides), and also dominated by large projects. Broad surveys, such as this, are useful in identifying general trends in this emerging global industry, but detailed case studies, particularly of large projects, are needed in order to draw more informed conclusions about the site-specific impacts of Jatropha cultivation. PMID:27508463

  13. Earthworm Is a Versatile and Sustainable Biocatalyst for Organic Synthesis

    PubMed Central

    Guan, Zhi; Chen, Yan-Li; Yuan, Yi; Song, Jian; Yang, Da-Cheng; Xue, Yang; He, Yan-Hong

    2014-01-01

    A crude extract of earthworms was used as an eco-friendly, environmentally benign, and easily accessible biocatalyst for various organic synthesis including the asymmetric direct aldol and Mannich reactions, Henry and Biginelli reactions, direct three-component aza-Diels-Alder reactions for the synthesis of isoquinuclidines, and domino reactions for the synthesis of coumarins. Most of these reactions have never before seen in nature, and moderate to good enantioselectivities in aldol and Mannich reactions were obtained with this earthworm catalyst. The products can be obtained in preparatively useful yields, and the procedure does not require any additional cofactors or special equipment. This work provides an example of a practical way to use sustainable catalysts from nature. PMID:25148527

  14. 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

  15. High-throughput methods for the development of new catalytic asymmetric reactions.

    PubMed

    Traverse, John F; Snapper, Marc L

    2002-10-01

    Chiral, single enantiomer pharmaceuticals have become increasingly more important. Therefore, research aimed at providing new methods for their selective preparation has taken on an even greater importance. One of the most efficient strategies for the synthesis of non-racemic, chiral molecules is asymmetric catalysis. There are many variables involved in the discovery of a new catalytic asymmetric transformation; hence, methods for the rapid screening of large numbers of catalysts have been developed. Herein, these techniques and strategies for the rapid discovery of novel asymmetric catalysts are reviewed.

  16. Cp2ZrMeCl: A Reagent for Asymmetric Methyl Addition.

    PubMed

    Garrec, Kilian; Fletcher, Stephen P

    2016-08-01

    The use of Cp2ZrMeCl is described as a source of nucleophilic methyl in asymmetric catalysis. This easily prepared reagent is bench stable, weighable in air, and generally useful in highly enantioselective copper-catalyzed addition reactions at room temperature. Methyl is successfully (generally >90% ee) added in 1,4-additions to cyclic and acyclic α,β-unsaturated ketones to provide tertiary and quaternary centers. Examples of catalyst controlled diastereoselective 1,6-addition and dynamic kinetic asymmetric allylic alkylation reactions are also reported. The reagent is used in the catalytic asymmetric synthesis of naturally occurring fragrance (R)-(-)-muscone (82% yield, 91% ee). PMID:27458650

  17. Synthesis and characterizations of microwave sintered ferrite powders and their composite films for practical applications

    NASA Astrophysics Data System (ADS)

    Shannigrahi, S. R.; Pramoda, K. P.; Nugroho, F. A. A.

    2012-01-01

    Phase pure single phase ferrite powders of (NixR1-x)0.5Zn0.5Fe2O4 (R=Mn, Co, Cu; x=0, 0.5) were manufactured using microwave sintering at 930 °C for 10 min in air atmosphere. The powders were characterized for their structure, microstructure, thermal, and magnetic properties. Selected powders were used as fillers to prepare their composite films using polymethyl methacrylate polymers as matrix. The composite films were prepared using the melt blending approach and were tested for their microstructure, thermal, and magnetic hysteresis loop as well as 3D magnetic field space mappings using an electromagnetic compatibility scanner. Among the studied ferrites, cobalt doped ferrites and their composites showed the best electromagnetic interference (EMI) shielding effectiveness value and have potential for practical EMI shielding applications.

  18. Total synthesis of bistramide A.

    PubMed

    Lowe, Jason T; Wrona, Iwona E; Panek, James S

    2007-01-18

    An asymmetric synthesis of the marine metabolite bistramide A is reported. The synthesis relies on the utility of three different organosilane reagents to construct all principle fragments and 8 of the 11 stereogenic centers of the natural product. [structure: see text].

  19. Pyrrolidinyl-camphor derivatives as a new class of organocatalyst for direct asymmetric Michael addition of aldehydes and ketones to beta-nitroalkenes.

    PubMed

    Ting, Ying-Fang; Chang, Chihliang; Reddy, Raju Jannapu; Magar, Dhananjay R; Chen, Kwunmin

    2010-06-18

    Practical and convenient synthetic routes have been developed for the synthesis of a new class of pyrrolidinyl-camphor derivatives (7 a-h). These novel compounds were screened as catalysts for the direct Michael addition of symmetrical alpha,alpha-disubstituted aldehydes to beta-nitroalkenes. When this asymmetric transformation was catalyzed by organocatalyst 7 f, the desired Michael adducts were obtained in high chemical yields, with high to excellent stereoselectivities (up to 98:2 diastereomeric ratio (d.r.) and 99 % enantiomeric excess (ee)). The scope of the catalytic system was expanded to encompass various aldehydes and ketones as the donor sources. The synthetic application was demonstrated by the synthesis of a tetrasubstituted-cyclohexane derivative from (S)-citronellal, with high stereoselectivity.

  20. Experimental Quantification of Asymmetric Einstein-Podolsky-Rosen Steering.

    PubMed

    Sun, Kai; Ye, Xiang-Jun; Xu, Jin-Shi; Xu, Xiao-Ye; Tang, Jian-Shun; Wu, Yu-Chun; Chen, Jing-Ling; Li, Chuan-Feng; Guo, Guang-Can

    2016-04-22

    Einstein-Podolsky-Rosen (EPR) steering describes the ability of one observer to nonlocally "steer" the other observer's state through local measurements. EPR steering exhibits a unique asymmetric property; i.e., the steerability can differ between observers, which can lead to one-way EPR steering in which only one observer obtains steerability in the steering process. This property is inherently different from the symmetric concepts of entanglement and Bell nonlocality, and it has attracted increasing interest. Here, we experimentally demonstrate asymmetric EPR steering for a class of two-qubit states in the case of two measurement settings. We propose a practical method to quantify the steerability. We then provide a necessary and sufficient condition for EPR steering and clearly demonstrate one-way EPR steering. Our work provides new insight into the fundamental asymmetry of quantum nonlocality and has potential applications in asymmetric quantum information processing.

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

    PubMed

    Molander, Gary A; Wisniewski, Steven R; Hosseini-Sarvari, Mona

    2013-10-11

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

  2. Iron-, Cobalt-, and Nickel-Catalyzed Asymmetric Transfer Hydrogenation and Asymmetric Hydrogenation of Ketones.

    PubMed

    Li, Yan-Yun; Yu, Shen-Luan; Shen, Wei-Yi; Gao, Jing-Xing

    2015-09-15

    Chiral alcohols are important building blocks in the pharmaceutical and fine chemical industries. The enantioselective reduction of prochiral ketones catalyzed by transition metal complexes, especially asymmetric transfer hydrogenation (ATH) and asymmetric hydrogenation (AH), is one of the most efficient and practical methods for producing chiral alcohols. In both academic laboratories and industrial operations, catalysts based on noble metals such as ruthenium, rhodium, and iridium dominated the asymmetric reduction of ketones. However, the limited availability, high price, and toxicity of these critical metals demand their replacement with abundant, nonprecious, and biocommon metals. In this respect, the reactions catalyzed by first-row transition metals, which are more abundant and benign, have attracted more and more attention. As one of the most abundant metals on earth, iron is inexpensive, environmentally benign, and of low toxicity, and as such it is a fascinating alternative to the precious metals for catalysis and sustainable chemical manufacturing. However, iron catalysts have been undeveloped compared to other transition metals. Compared with the examples of iron-catalyzed asymmetric reduction, cobalt- and nickel-catalyzed ATH and AH of ketones are even seldom reported. In early 2004, we reported the first ATH of ketones with catalysts generated in situ from iron cluster complex and chiral PNNP ligand. Since then, we have devoted ourselves to the development of ATH and AH of ketones with iron, cobalt, and nickel catalysts containing novel chiral aminophosphine ligands. In our study, the iron catalyst containing chiral aminophosphine ligands, which are expected to control the stereochemistry at the metal atom, restrict the number of possible diastereoisomers, and effectively transfer chiral information, are successful catalysts for enantioselective reduction of ketones. Among these novel chiral aminophosphine ligands, 22-membered macrocycle P2N4

  3. Copper(II) coordination chain complex with the 2,5-bis(2-pyridyl)-1,3,4-thiadiazole ligand and an asymmetric μ2-1,1-azido double-bridged: Synthesis, crystal structure and magnetic properties

    NASA Astrophysics Data System (ADS)

    Laachir, Abdelhakim; Guesmi, Salaheddine; Saadi, Mohamed; El Ammari, Lahcen; Mentré, Olivier; Vezin, Hervé; Colis, Silviu; Bentiss, Fouad

    2016-11-01

    A new asymmetric μ2-1,1-azido double bridged cooper (II), with 2,5-bis(2-pyridyl)-1,3,4-thiadiazole (L), has been synthesized and characterized using single crystal X-ray diffraction, FT-IR, UV-Visible spectroscopic and magnetic measurements. The asymmetric unit of the title compound contains half molecule of formula, C12H8CuN10S, which crystallizes in the triclinic system, space group P 1 bar , with a = 6.5916 (4)Å, b = 10.6905 (7) Å, c = 11.5037 (7) Å, α = 106.508 (3)°, β = 105.538 (3)°, γ = 90.233 (4)°, V = 745.99 (8) Å3 and Z = 2. The structure consists of two [CuN5] prismatic polyhedra linked together by edge-sharing to build up a [Cu2N8] dimer arranged in chain. The connectivity along the chain is performed by Nsbnd N edge sharing between dimers. In the crystal, the molecules are linked together by Csbnd H⋯N hydrogen bonds and by π---π interactions between parallel pyridyl rings of neighboring molecules. The interpretation of FT-IR and UV-Vis spectra is consistent with the crystal structure determined by X-ray diffraction. The magnetic properties of the complex confirm the picture of an alternated … Cu-J1-Cu ….J2 … Cu-J1-Cu … magnetic chains. We found in the dimers weak antiferromagnetic exchange interactions J1/k = -5.9 (1) k and between them J2/k = -2.3 k.

  4. Practice and power: a review and interpretive synthesis focused on the exercise of discretionary power in policy implementation by front-line providers and managers.

    PubMed

    Gilson, Lucy; Schneider, Helen; Orgill, Marsha

    2014-12-01

    Tackling the implementation gap is a health policy concern in low- and middle-income countries (LMICs). Limited attention has so far been paid to the influence of power relations over this gap. This article presents, therefore, an interpretive synthesis of qualitative health policy articles addressing the question: how do actors at the front line of health policy implementation exercise discretionary power, with what consequences and why? The article also demonstrates the particular approach of thematic synthesis and contributes to discussion of how such work can inform future health policy research. The synthesis drew from a broader review of published research on any aspect of policy implementation in LMICs for the period 1994-2009. From an initial set of 50 articles identified as relevant to the specific review question, a sample of 16 articles were included in this review. Nine report experience around decentralization, a system-level change, and seven present experience of implementing a range of reproductive health (RH) policies (new forms of service delivery). Three reviewers were involved in a systematic process of data extraction, coding, analysis, synthesis and article writing. The review findings identify: the practices of power exercised by front-line health workers and their managers; their consequences for policy implementation and health system performance; the sources of this power and health workers' reasons for exercising power. These findings also provide the basis for an overarching synthesis of experience, highlighting the importance of actors, power relations and multiple, embedded contextual elements as dimensions of health system complexity. The significance of this synthesis lies in its insights about: the micropractices of power exercised by front-line providers; how to manage this power through local level strategies both to influence and empower providers to act in support of policy goals; and the focus and nature of future research on

  5. Adherence to clinical practice guidelines among three primary contact professions: a best evidence synthesis of the literature for the management of acute and subacute low back pain

    PubMed Central

    Amorin-Woods, Lyndon G.; Beck, Randy W.; Parkin-Smith, Gregory F.; Lougheed, James; Bremner, Alexandra P.

    2014-01-01

    Aim: To determine adherence to clinical practice guidelines in the medical, physiotherapy and chiropractic professions for acute and subacute mechanical low back pain through best-evidence synthesis of the healthcare literature. Methods: A structured best-evidence synthesis of the relevant literature through a literature search of relevant databases for peer-reviewed papers on adherence to clinical practice guidelines from 1995 to 2013. Inclusion of papers was based on selection criteria and appraisal by two reviewers who independently applied a modified Downs & Black appraisal tool. The appraised papers were summarized in tabular form and analysed by the authors. Results: The literature search retrieved 23 potentially relevant papers that were evaluated for methodological quality, of which 11 studies met the inclusion criteria. The main finding was that no profession in the study consistently attained an overall high concordance rating. Of the three professions examined, 73% of chiropractors adhered to current clinical practice guidelines, followed by physiotherapists (62%) and then medical practitioners (52%). Conclusions: This review showed that quality papers in this area of research are very limited. Notwithstanding, chiropractors appear to adhere to clinical practice guidelines more so than physiotherapists and medical practitioners, although there is scope for improvement across all three professions. PMID:25202150

  6. Generation of Trityl Radicals by Nucleophilic Quenching of Tris(2,3,5,6-tetrathiaaryl)methyl Cations and Practical and Convenient Large-Scale Synthesis of Persistent Tris(4-carboxy-2,3,5,6-tetrathiaaryl)methyl Radical

    PubMed Central

    Rogozhnikova, Olga Yu.; Vasiliev, Vladimir G.; Troitskaya, Tatiana I.; Trukhin, Dmitry V.; Mikhalina, Tatiana V.; Halpern, Howard J.; Tormyshev, Victor M.

    2014-01-01

    Tris(2,3,5,6-tetrathiaaryl)methyl cations, which were generated from the corresponding triarylmethanols in the presence of strong acids, underwent reaction with nucleophiles to give trityl radicals, as the product of a one-electron reduction of the carbocation. Depending on the nature of the nucleophile, the only byproducts were either diamagnetic quinone methides or asymmetrical monosubstituted trityl radicals. Herein, we report a protocol for the large-scale synthesis of the Finland trityl, which has the advantage of high overall yield and reproducibility. PMID:24772001

  7. Limit laws for the asymmetric inclusion process.

    PubMed

    Reuveni, Shlomi; Eliazar, Iddo; Yechiali, Uri

    2012-12-01

    The Asymmetric Inclusion Process (ASIP) is a unidirectional lattice-gas flow model which was recently introduced as an exactly solvable 'Bosonic' counterpart of the 'Fermionic' asymmetric exclusion process. An iterative algorithm that allows the computation of the probability generating function (PGF) of the ASIP's steady state exists but practical considerations limit its applicability to small ASIP lattices. Large lattices, on the other hand, have been studied primarily via Monte Carlo simulations and were shown to display a wide spectrum of intriguing statistical phenomena. In this paper we bypass the need for direct computation of the PGF and explore the ASIP's asymptotic statistical behavior. We consider three different limiting regimes: heavy-traffic regime, large-system regime, and balanced-system regime. In each of these regimes we obtain-analytically and in closed form-stochastic limit laws for five key ASIP observables: traversal time, overall load, busy period, first occupied site, and draining time. The results obtained yield a detailed limit-laws perspective of the ASIP, numerical simulations demonstrate the applicability of these laws as useful approximations.

  8. Limit laws for the asymmetric inclusion process.

    PubMed

    Reuveni, Shlomi; Eliazar, Iddo; Yechiali, Uri

    2012-12-01

    The Asymmetric Inclusion Process (ASIP) is a unidirectional lattice-gas flow model which was recently introduced as an exactly solvable 'Bosonic' counterpart of the 'Fermionic' asymmetric exclusion process. An iterative algorithm that allows the computation of the probability generating function (PGF) of the ASIP's steady state exists but practical considerations limit its applicability to small ASIP lattices. Large lattices, on the other hand, have been studied primarily via Monte Carlo simulations and were shown to display a wide spectrum of intriguing statistical phenomena. In this paper we bypass the need for direct computation of the PGF and explore the ASIP's asymptotic statistical behavior. We consider three different limiting regimes: heavy-traffic regime, large-system regime, and balanced-system regime. In each of these regimes we obtain-analytically and in closed form-stochastic limit laws for five key ASIP observables: traversal time, overall load, busy period, first occupied site, and draining time. The results obtained yield a detailed limit-laws perspective of the ASIP, numerical simulations demonstrate the applicability of these laws as useful approximations. PMID:23367919

  9. 1-Magnesiotetrahydroisoquinolyloxazolines as Chiral Nucleophiles in Stereoselective Additions to Aldehydes: Auxiliary Optimization, Asymmetric Synthesis of (+)-Corlumine, (+)-Bicuculline, (+)-Egenine, and (+)-Corytensine, and Preliminary (13)C NMR Studies of 1-Lithio- and 1-Magnesiotetrahydroisoquinolyloxazolines.

    PubMed

    Gawley, Robert E.; Zhang, Pingsheng

    1996-11-15

    Transmetalation of 1-lithiotetrahydroisoquinolyloxazolines with magnesium halides affords Grignard reagents that add to aldehydes with up to 80% selectivity for one of the four possible diastereomeric products. An oxazoline chiral auxiliary derived from camphor provides an optimal blend of diastereoselectivity and isomer separability. Synthetic applications of the optimal auxiliary, patterned after a literature approach in the racemic series, comprise an improved (formal) synthesis of bicuculline, egenine, and corytensine, as well as an efficient synthesis of corlumine. Preliminary NMR studies show that both 1-lithio- and 1-magnesiotetrahydroisoquinolyloxazolines are dynamic mixtures in THF solution at low temperatures. The barrier to pyramidal inversion of the secondary Grignard reagent is in the 9.8-10.1 kcal/mol range, while an upper limit of about 8.2 kcal/mol can be assigned to the barrier to the organolithium inversion. PMID:11667797

  10. Development of chiral sulfoxide ligands for asymmetric catalysis.

    PubMed

    Trost, Barry M; Rao, Meera

    2015-04-20

    Nitrogen-, phosphorus-, and oxygen-based ligands with chiral backbones have been the historic workhorses of asymmetric transition-metal-catalyzed reactions. On the contrary, sulfoxides containing chirality at the sulfur atom have mainly been used as chiral auxiliaries for diastereoselective reactions. Despite several distinct advantages over traditional ligand scaffolds, such as the proximity of the chiral information to the metal center and the ability to switch between S and O coordination, these compounds have only recently emerged as a versatile class of chiral ligands. In this Review, we detail the history of the development of chiral sulfoxide ligands for asymmetric catalysis. We also provide brief descriptions of metal-sulfoxide bonding and strategies for the synthesis of enantiopure sulfoxides. Finally, insights into the future development of this underutilized ligand class are discussed.

  11. [Asymmetric intramolecular conjugate addition of chiral enolates via non-equilibrium].

    PubMed

    Monguchi, Daiki

    2006-08-01

    Optically active alpha,alpha-disubstituted alpha-amino acids belong to an important class of unnatural amino acids. Since the synthesis of such amino acids involves the creation of a quaternary stereocenter, methods for their synthesis have been extensively studied. We have reported that N-t-butoxycarbonyl(Boc)-N-methoxymethyl(MOM)-amino acid derivatives undergo asymmetric alpha-alkylation in up to 93% ee. Original chiral information on an amino acid is preserved in axially chiral enolate intermediates, and thus asymmetric induction is achieved without the aid of external chiral sources (i.e., memory of chirality). Recently, we have reported a new protocol for the asymmetric cyclization of amino acid derivatives, which enables straightforward synthesis of cyclic amino acids with a tetrasubstituted carbon center from the usual alpha-amino acids in up to 98% ee. Here we report the asymmetric construction of highly substituted chiral nitrogen heterocycles via intramolecular conjugate addition of chiral enolates generated from N-Boc-N-alkylylamino acid derivatives. This method is applicable to the asymmetric construction of pyrrolidine, piperidine, tetrahydroisoquinoline, and indoline derivatives with contiguous quaternary and tertiary stereocenters.

  12. Vertical asymmetric double quantum dots

    NASA Astrophysics Data System (ADS)

    Roßbach, R.; Reischle, M.; Beirne, G. J.; Schweizer, H.; Jetter, M.; Michler, P.

    2007-01-01

    Two layers of differently sized self-assembled InP-quantum dots (QDs) separated by a GaInP spacer layer with varying thickness were grown by metal organic vapor phase epitaxy (MOVPE). Photoluminescence measurements of the QD ensembles and of individual asymmetric double QDS show coupling due to the tunnelling of carriers.

  13. 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…

  14. A practical synthesis of 3,4-diethoxybenzthioamide based on Friedel-Crafts reaction with potassium thiocyanate in methanesulfonic acid.

    PubMed

    Aki, Shinji; Fujioka, Takafumi; Ishigami, Masashi; Minamikawa, Jun-ichi

    2002-09-01

    The synthesis of 3,4-diethoxybenzthioamide, the key intermediate for OPC-6535, is achieved by employing Friedel-Crafts reaction of 1,2-diethoxybenzene with potassium thiocyanate in methanesulfonic acid at ambient temperature.

  15. (E)-2-boryl-1,3-butadiene derivatives of the 10-TMS-9-BBDs: highly selective reagents for the asymmetric synthesis of anti-1,2-disubstituted 3,4-pentadien-1-ols.

    PubMed

    González, Javier R; González, Ana Z; Soderquist, John A

    2009-07-29

    The efficient stepwise construction of optically pure trans-4-substituted 2-boryl-1,3-butadienes 6 is described. Hydroboration of 1-alkynes with either enantiomeric form of 3 leads to the pure trans-1-alkenylboranes 4 which undergo addition of alpha-ethoxyvinyllithium followed by a BF(3)-mediated 1,2-B-->C vinylic group migration to provide 6. These organoboranes 6 serve as a new type of asymmetric allylborating agent providing an extremely selective protocol for the preparation of anti-1,2-disubstituted 3,4-pentadien-1-ols 8 as essentially single diastereomers in enantiomerically pure form. One example of a cis-2-boryl-1,3-butadiene (9) was prepared through a Grignard procedure. It was found to provide the corresponding syn-alcohol 11. The utility of 8 was demonstrated in their conversion to substituted beta-hydroxy acids 12 through ozonolysis and to substituted alpha,beta-unsaturated-delta-lactones 13 through Ru-catalyzed cyclocarbonylation. PMID:19580266

  16. A Simple Modeling of Asymmetric Rolling

    NASA Astrophysics Data System (ADS)

    Halloumi, A.; Desrayaud, Ch.; Montheillet, F.

    2010-06-01

    Two complementary analytical approaches and the finite difference method are proposed for modeling asymmetric rolling (ASR) of metal sheet. The first analytical model is an upper bound method based on a uniform strain field depending on one single optimization parameter, viz. the entry velocity of the sheet. Its results can be straightforwardly used for practical applications. The second model uses a more refined analytical velocity field based on the classical parabolic estimation of the material flow lines in rolling. It involves an additional optimization parameter associated with the precise form of the velocity field. Local values of strain, strain rate and self-heating temperature are easily calculated, as well as the rolling force. Finally, the finite difference method is applied to compute heat transfers between the rolls and the sheet. In conclusion, the respective advantages of the three methods are discussed.

  17. 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

  18. Asymmetric 1,4-bis(ethynyl)bicyclo[2.2.2]octane rotators via monocarbinol functionalization. Ready access to polyrotors.

    PubMed

    Lemouchi, Cyprien; Batail, Patrick

    2015-01-01

    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.

  19. Selective fowler reductions: asymmetric total syntheses of isofagomine and other 1-azasugars from methyl nicotinate.

    PubMed

    Zhao, G; Deo, U C; Ganem, B

    2001-01-25

    [figure: see text] An efficient, high-yielding strategy has been developed for the asymmetric synthesis of 1-N-iminosugars (1-azasugars), a new class of glycosidase inhibitors with promising biomedical applications. A highly regioselective procedure for the 1,2-reduction of substituted pyridines was employed to transform methyl nicotinate into several representative 1-azasugars.

  20. One-pot sequential asymmetric hydrogenation of β-aryl-β-aryloxy acroleins.

    PubMed

    Liu, Yufeng; Chen, Jianzhong; Zhang, Zhenfeng; Qin, Jian; Zhao, Min; Zhang, Wanbin

    2016-08-01

    A one-pot sequential asymmetric hydrogenation of β-aryl-β-aryloxy acroleins has been realized for the preparation of chiral 3-aryl-3-aryloxy alcohols with excellent yields and good enantioselectivities. This methodology can be employed in new synthetic routes for the synthesis of fluoxetine, atomoxetine, and related analogues. PMID:27439010

  1. 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

  2. Synthesis and crystal structure of new dicopper(II) complexes having asymmetric N,N'-bis(substituted)oxamides with DNA/protein binding ability: In vitro anticancer activity and molecular docking studies.

    PubMed

    Zheng, Kang; Zhu, Ling; Li, Yan-Tuan; Wu, Zhi-Yong; Yan, Cui-Wei

    2015-08-01

    Two new dicopper(II) complexes bridged by asymmetric N,N'-bis(substituted)oxamide ligands: N-(5-chloro-2-hydroxyphenyl)-N'-[2-(dimethylamino)ethyl]oxamide (H3chdoxd) and N-hydroxypropyl-N'-(2-carboxylatophenyl)oxamide (H3oxbpa), and end-capped with 2,2'-bipyridine (bpy), namely [Cu2(ClO4)(chdoxd)(CH3OH)(bpy)]·H2O (1) and [Cu2(pic)(oxbpa)(CH3OH)(bpy)]·0.5CH3OH (2) (pic denotes picrate anion), have been synthesized and characterized by elemental analysis, molar conductivity measurement, IR and electronic spectral studies, and single-crystal X-ray diffraction. The X-ray diffraction analysis revealed that both the copper(II) ions bridged by the cis-oxamido ligands in dicopper(II) complexes 1 and 2 are all in square-pyramidal environments with the corresponding Cu⋯Cu separations of 5.194(3) and 5.1714(8)Å, respectively. In the crystals of the two complexes, there are abundant hydrogen bonds and π-π stacking interactions contributing to the supramolecular structure. The reactivities toward herring sperm DNA (HS-DNA) and bovine serum albumin (BSA) of the two complexes are studied both theoretically and experimentally, indicating that both the two complexes can interact with the DNA in the mode of intercalation, and effectively bind to BSA via the favored binding sites Trp134 for the complex 1 and Trp213 for the complex 2. Interestingly, the in vitro anticancer activities of the two complexes against the selected tumor cell lines are consistent with their DNA/BSA-binding affinities following the order of 1>2. The effects of coordinated counterions in the two complexes on DNA/BSA-binding ability and in vitro anticancer activity are preliminarily discussed.

  3. 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.

  4. 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

  5. Stable walking with asymmetric legs.

    PubMed

    Merker, Andreas; Rummel, Juergen; Seyfarth, Andre

    2011-12-01

    Asymmetric leg function is often an undesired side-effect in artificial legged systems and may reflect functional deficits or variations in the mechanical construction. It can also be found in legged locomotion in humans and animals such as after an accident or in specific gait patterns. So far, it is not clear to what extent differences in the leg function of contralateral limbs can be tolerated during walking or running. Here, we address this issue using a bipedal spring-mass model for simulating walking with compliant legs. With the help of the model, we show that considerable differences between contralateral legs can be tolerated and may even provide advantages to the robustness of the system dynamics. A better understanding of the mechanisms and potential benefits of asymmetric leg operation may help to guide the development of artificial limbs or the design novel therapeutic concepts and rehabilitation strategies.

  6. Electron jet of asymmetric reconnection

    NASA Astrophysics Data System (ADS)

    Khotyaintsev, Yu. V.; Graham, D. B.; Norgren, C.; Eriksson, E.; Li, W.; Johlander, A.; Vaivads, A.; André, M.; Pritchett, P. L.; Retinò, A.; Phan, T. D.; Ergun, R. E.; Goodrich, K.; Lindqvist, P.-A.; Marklund, G. T.; Le Contel, O.; Plaschke, F.; Magnes, W.; Strangeway, R. J.; Russell, C. T.; Vaith, H.; Argall, M. R.; Kletzing, C. A.; Nakamura, R.; Torbert, R. B.; Paterson, W. R.; Gershman, D. J.; Dorelli, J. C.; Avanov, L. A.; Lavraud, B.; Saito, Y.; Giles, B. L.; Pollock, C. J.; Turner, D. L.; Blake, J. D.; Fennell, J. F.; Jaynes, A.; Mauk, B. H.; Burch, J. L.

    2016-06-01

    We present Magnetospheric Multiscale observations of an electron-scale current sheet and electron outflow jet for asymmetric reconnection with guide field at the subsolar magnetopause. The electron jet observed within the reconnection region has an electron Mach number of 0.35 and is associated with electron agyrotropy. The jet is unstable to an electrostatic instability which generates intense waves with E∥ amplitudes reaching up to 300 mV m-1 and potentials up to 20% of the electron thermal energy. We see evidence of interaction between the waves and the electron beam, leading to quick thermalization of the beam and stabilization of the instability. The wave phase speed is comparable to the ion thermal speed, suggesting that the instability is of Buneman type, and therefore introduces electron-ion drag and leads to braking of the electron flow. Our observations demonstrate that electrostatic turbulence plays an important role in the electron-scale physics of asymmetric reconnection.

  7. Asymmetrical hypersensitivity to bovine collagen.

    PubMed

    Somerville, P; Wray, R C

    1993-05-01

    We report a unique patient with true asymmetrical hypersensitivity to bovine collagen. Hypersensitivity is the development of an inflammatory response at a treatment site after a negative skin test. She developed an inflammatory response in only one of two simultaneously injected sites. About 1.5% of patients with a negative skin test have a hypersensitivity reaction consisting of firmness, erythema, and swelling. The signs and symptoms generally resolve spontaneously in a few months.

  8. 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).

  9. Sulfonyl Azoles in the Synthesis of 3-Functionalized Azole Derivatives.

    PubMed

    Palmieri, Alessandro; Petrini, Marino

    2016-06-01

    Sulfonyl indoles, as well as related azolyl derivatives, have been recently introduced in synthesis as stable precursors of reactive indolenine intermediates. This personal account reports on the discovery of sulfonyl azoles and their practical utilization in many synthetic processes for the preparation of functionalized 3-substituted indoles, indazoles, and pyrroles. The indolenine intermediates obtained by treatment of sulfonyl azoles with Brønsted bases or Lewis acids can be considered as vinylogous imino derivatives that can be made to react with different nucleophilic reagents. These include organometallic reagents, reducing agents, stabilized carbanions, and heteronucleophiles. The controlled and mild conditions for the generation of indolenines from sulfonyl azoles make these substrates particularly useful in asymmetric synthesis, exploiting organo- or metal-catalyzed processes. Although less exploited, sulfonyl indoles can also be involved in photochemical processes for the preparation of polycyclic derivatives. PMID:27147297

  10. Precision synthesis, structure and function of helical polymers

    PubMed Central

    OKAMOTO, Yoshio

    2015-01-01

    Helical structures are chiral, which means that if we can synthesize a polymer having a stable one-handed helicity, the polymer is optically active. In 1979, we succeeded in the synthesis of a one-handed helical polymer from an optically inactive achiral monomer, triphenylmethyl methacrylate (TrMA). This is the first example of the asymmetric synthesis of an optically active one-handed helical polymer. The polymer (PTrMA) exhibited an unexpected high chiral recognition ability and afforded a practically useful chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC) by coating it on silica gel. In addition, we also succeeded in the development of very useful CSPs for HPLC using the phenylcarbamate derivatives of polysaccharides, cellulose and amylose. These CSPs can efficiently resolve a broad range of chiral compounds, and have been used all over the world for separating and analyzing chiral compounds. PMID:26062738

  11. Precision synthesis, structure and function of helical polymers.

    PubMed

    Okamoto, Yoshio

    2015-01-01

    Helical structures are chiral, which means that if we can synthesize a polymer having a stable one-handed helicity, the polymer is optically active. In 1979, we succeeded in the synthesis of a one-handed helical polymer from an optically inactive achiral monomer, triphenylmethyl methacrylate (TrMA). This is the first example of the asymmetric synthesis of an optically active one-handed helical polymer. The polymer (PTrMA) exhibited an unexpected high chiral recognition ability and afforded a practically useful chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC) by coating it on silica gel. In addition, we also succeeded in the development of very useful CSPs for HPLC using the phenylcarbamate derivatives of polysaccharides, cellulose and amylose. These CSPs can efficiently resolve a broad range of chiral compounds, and have been used all over the world for separating and analyzing chiral compounds. PMID:26062738

  12. Expediting analog design retargeting by design knowledge re-use and circuit synthesis: a practical example on a Delta-Sigma modulator

    NASA Astrophysics Data System (ADS)

    Webb, Matthew; Tang, Hua

    2016-08-01

    In the past decade or two, due to constant and rapid technology changes, analog design re-use or design retargeting to newer technologies has been brought to the table in order to expedite the design process and improve time-to-market. If properly conducted, analog design retargeting could significantly cut down design cycle compared to designs starting from the scratch. In this article, we present an empirical and general method for efficient analog design retargeting by design knowledge re-use and circuit synthesis (CS). The method first identifies circuit blocks that compose the source system and extracts the performance parameter specifications of each circuit block. Then, for each circuit block, it scales the values of design variables (DV) from the source design to derive an initial design in the target technology. Depending on the performance of this initial target design, a design space is defined for synthesis. Subsequently, each circuit block is automatically synthesised using state-of-art analog synthesis tools based on a combination of global and local optimisation techniques to achieve comparable performance specifications to those extracted from the source system. Finally, the overall system is composed of those synthesised circuit blocks in the target technology. We illustrate the method using a practical example of a complex Delta-Sigma modulator (DSM) circuit.

  13. Catalytic enantioselective synthesis of naturally occurring butenolides via hetero-allylic alkylation and ring closing metathesis.

    PubMed

    Mao, Bin; Geurts, Koen; Fañanás-Mastral, Martín; van Zijl, Anthoni W; Fletcher, Stephen P; Minnaard, Adriaan J; Feringa, Ben L

    2011-03-01

    An efficient catalytic asymmetric synthesis of chiral γ-butenolides was developed based on the hetero-allylic asymmetric alkylation (h-AAA) in combination with ring closing metathesis (RCM). The synthetic potential of the h-AAA-RCM protocol was illustrated with the facile synthesis of (-)-whiskey lactone, (-)-cognac lactone, (-)-nephrosteranic acid, and (-)-roccellaric acid.

  14. 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-γ-butyrolactone, is described, that proceeds through a D-proline-catalyzed asymmetric aminooxylation, indium-mediated Reformatsky-Claisen rearrangement of an α,α-dibromoacetate derivative, and diastereoselective dihydroxylation. The route requires no protective group manipulation and allows the concise seven-step synthesis of 1 from n-octanal.

  15. Catalytic enantioselective synthesis of naturally occurring butenolides via hetero-allylic alkylation and ring closing metathesis.

    PubMed

    Mao, Bin; Geurts, Koen; Fañanás-Mastral, Martín; van Zijl, Anthoni W; Fletcher, Stephen P; Minnaard, Adriaan J; Feringa, Ben L

    2011-03-01

    An efficient catalytic asymmetric synthesis of chiral γ-butenolides was developed based on the hetero-allylic asymmetric alkylation (h-AAA) in combination with ring closing metathesis (RCM). The synthetic potential of the h-AAA-RCM protocol was illustrated with the facile synthesis of (-)-whiskey lactone, (-)-cognac lactone, (-)-nephrosteranic acid, and (-)-roccellaric acid. PMID:21268603

  16. Social Skills Interventions for Individuals with Autism: Evaluation for Evidence-Based Practices within a Best Evidence Synthesis Framework

    ERIC Educational Resources Information Center

    Reichow, Brian; Volkmar, Fred R.

    2010-01-01

    This paper presents a best evidence synthesis of interventions to increase social behavior for individuals with autism. Sixty-six studies published in peer-reviewed journals between 2001 and July 2008 with 513 participants were included. The results are presented by the age of the individual receiving intervention and by delivery agent of…

  17. Psychotropic Medications in Children with Autism Spectrum Disorders: A Systematic Review and Synthesis for Evidence-Based Practice

    ERIC Educational Resources Information Center

    Siegel, Matthew; Beaulieu, Amy A.

    2012-01-01

    This paper presents a systematic review, rating and synthesis of the empirical evidence for the use of psychotropic medications in children with autism spectrum disorders (ASD). Thirty-three randomized controlled trials (RCTs) published in peer-reviewed journals qualified for inclusion and were coded and analyzed using a systematic evaluative…

  18. Combining a Laboratory Practical Class with a Computer Simulation: Studies on the Synthesis of Urea in Isolated Hepatocytes.

    ERIC Educational Resources Information Center

    Bender, David A.

    1986-01-01

    Describes how a computer simulation is used with a laboratory experiment on the synthesis of urea in isolated hepatocytes. The simulation calculates the amount of urea formed and the amount of ammonium remaining as the concentrations of ornithine, citrulline, argininosuccinate, arginine, and aspartate are altered. (JN)

  19. A concise and stereoselective synthesis of squalamine.

    PubMed

    Zhang, Dong-Hui; Cai, Feng; Zhou, Xiang-Dong; Zhou, Wei-Shan

    2003-09-01

    [reaction: see text] A short and highly stereoselective synthesis of the novel steroid squalamine (1) was accomplished in nine steps from easily available methyl chenodeoxylcholanate 2. Our synthesis featured improved dehydrogenation of 4 followed by conjugate reduction to construct the trans AB-ring system and efficient asymmetric isopropylation of aldehyde 6 to introduce the C-24R-hydroxyl group. PMID:12943401

  20. Theory and Modeling of Asymmetric Catalytic Reactions.

    PubMed

    Lam, Yu-Hong; Grayson, Matthew N; Holland, Mareike C; Simon, Adam; Houk, K N

    2016-04-19

    Modern density functional theory and powerful contemporary computers have made it possible to explore complex reactions of value in organic synthesis. We describe recent explorations of mechanisms and origins of stereoselectivities with density functional theory calculations. The specific functionals and basis sets that are routinely used in computational studies of stereoselectivities of organic and organometallic reactions in our group are described, followed by our recent studies that uncovered the origins of stereocontrol in reactions catalyzed by (1) vicinal diamines, including cinchona alkaloid-derived primary amines, (2) vicinal amidophosphines, and (3) organo-transition-metal complexes. Two common cyclic models account for the stereoselectivity of aldol reactions of metal enolates (Zimmerman-Traxler) or those catalyzed by the organocatalyst proline (Houk-List). Three other models were derived from computational studies described in this Account. Cinchona alkaloid-derived primary amines and other vicinal diamines are venerable asymmetric organocatalysts. For α-fluorinations and a variety of aldol reactions, vicinal diamines form enamines at one terminal amine and activate electrophilically with NH(+) or NF(+) at the other. We found that the stereocontrolling transition states are cyclic and that their conformational preferences are responsible for the observed stereoselectivity. In fluorinations, the chair seven-membered cyclic transition states is highly favored, just as the Zimmerman-Traxler chair six-membered aldol transition state controls stereoselectivity. In aldol reactions with vicinal diamine catalysts, the crown transition states are favored, both in the prototype and in an experimental example, shown in the graphic. We found that low-energy conformations of cyclic transition states occur and control stereoselectivities in these reactions. Another class of bifunctional organocatalysts, the vicinal amidophosphines, catalyzes the (3 + 2) annulation

  1. Asymmetric gold nanoparticle reduction into polydimethylsiloxane thin films

    NASA Astrophysics Data System (ADS)

    Dunklin, Jeremy R.; Forcherio, Gregory T.; Berry, Keith R.; Roper, D. Keith

    2014-09-01

    Polymer thin films embedded with plasmonic gold nanoparticles (AuNPs) are of significant interest in biomedicine, optics, photovoltaic, and nanoelectromechanical systems. Thin polydimethylsiloxane (PDMS) films containing 3-7 micron layers of AuNPs that were fabricated with a novel diffusive-reduction synthesis technique attenuated up to 85% of incoming laser light at the plasmon resonance. Rapid diffusive reduction of AuNPs into asymmetric PDMS thin films provided superior optothermal capabilities relative to thicker films in which AuNPs were reduced throughout. A photonto- heat conversion of up to 3000°C/watt was demonstrated, which represents a 3-230-fold increase over previous AuNPfunctionalized systems. Optical attenuation and thermal response increased in proportion to order of magnitude increases in tetrachloroaurate (TCA) solution concentration. Optical and thermoplasmonic responses were observed with and without an adjacent mesh support, which increased attenuation but decreased thermal response. Morphological, optical, and thermoplasmonic properties of asymmetric AuNP-PDMS films varied significantly with diffusive TCA concentration. Gold nanoparticles, networks, and conglomerates were formed via reduction as the amount of dissolved TCA increased across a log10-scale. Increasing TCA concentrations caused polymer surface cratering, leading to a larger effective surface area. This method, utilizing the diffusion of TCA into a single exposed partially cured PDMS interface, could be used to replace expensive lithographic or solution synthesis of plasmon-functionalized systems.

  2. 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

  3. Mechanistic Insights into Homogeneous and Heterogeneous Asymmetric Iron Catalysis

    NASA Astrophysics Data System (ADS)

    Sonnenberg, Jessica

    Our group has been focused on replacing toxic and expensive precious metal catalysts with iron for the synthesis of enantiopure compounds for industrial applications. During an investigation into the mechanism of asymmetric transfer hydrogenation with our first generation iron-(P-N-N-P) catalysts we found substantial evidence for zero-valent iron nanoparticles coated in chiral ligand acting as the active site. Extensive experimental and computational experiments were undertaken which included NMR, DFT, reaction profile analysis, substoichiometric poisoning, electron microscope imaging, XPS and multiphasic analysis, all of which supported the fact that NPs were the active species in catalysis. Reversibility of this asymmetric reaction on the nanoparticle surface was then probed using oxidative kinetic resolution of racemic alcohols, yielding modest enantiopurity and high turnover frequencies (TOF) for a range of aromatic alcohols. Efficient dehydrogenation of ammonia-borane for hydrogen evolution and the formation of B-N oligomers was also shown using the NP system, yielding highly active systems, with a maximum TOF of 3.66 H2/s-1 . We have also begun to focus on the development of iron catalysts for asymmetric direct hydrogenation of ketones using hydrogen gas. New chiral iron-(P-N-P) catalysts were developed and shown to be quite active and selective for a wide range of substrates. Mechanistic investigations primarily using NMR and DFT indicated that a highly active trans-dihydride species was being formed during catalyst activation. Lastly, a new library of chiral P-N-P and P-NH-P ligands were developed, as well as their corresponding iron complexes, some of which show promise for the development of future generations of active asymmetric direct hydrogenation catalysts.

  4. Catalytic Asymmetric Arylation of α-Aryl-α-diazoacetates with Aniline Derivatives.

    PubMed

    Xu, Bin; Li, Mao-Lin; Zuo, Xiao-Dong; Zhu, Shou-Fei; Zhou, Qi-Lin

    2015-07-15

    The asymmetric arylation of diazo compounds with aniline derivatives cooperatively catalyzed by an achiral dirhodium complex and a chiral spiro phosphoric acid is reported. The reaction provides a new method for the facile synthesis of α-diarylacetates, versatile building blocks with a diaryl tertiary chiral center, in good yields (up to 95%) with high enantioselectivities (up to 97% ee). Preliminary mechanistic studies suggest that the arylation reaction proceeds via a stepwise process, in which the enantioselectivity is controlled by a chiral spiro phosphoric acid-promoted proton shift in a zwitterionic intermediate. This work represents the first asymmetric intermolecular C(sp(2))-H bond insertion reaction with arenes.

  5. Practical synthesis of a chromene analog for use as a retinoic acid receptor alpha antagonist lead compound.

    PubMed

    Jetson, Rachael; Malik, Neha; Luniwal, Amarjit; Chari, Venkatesh; Ratnam, Manohar; Erhardt, Paul

    2013-05-01

    Retinoic acid receptor alpha (RARα) selective compounds may guide the design of drugs that can be used in conjunction with hormonal adjuvant therapy in the treatment of breast cancer. Herein we report a modified synthesis of a known RARα antagonist, 2-fluoro-4-[[[8-bromo-2,2-dimethyl-4-(4-methylphenyl)chroman-6-yl]carbonyl]amino]benzoic acid and a synthesis of its unknown, desfluoro analog, 4-[[[8-bromo-2,2-dimethyl-4-(4-methylphenyl)chroman-6-yl]carbonyl]amino]benzoic acid. The modified route allows for facile reaction workups, increased yields, lower cost and incorporates a green alternative step. Structure-activity relationship studies determined through functional cell-based assays, demonstrated antagonism to RARα for both compounds. Molecular modeling within the RARα binding pocket was used to compare binding interactions of the desfluoro analog to a known RAR antagonist.

  6. A practical synthesis of a high-loading solid-supported IBX amide for the oxidation of alcohols.

    PubMed

    Lecarpentier, Patrick; Crosignani, Stefano; Linclau, Bruno

    2005-01-01

    A straightforward three-step synthesis of a solid-supported IBX amide resin was achieved using inexpensive and commercially available 2-iodobenzoic acid chloride and Merrifield resin. A high apparent loading of 0.63 mmol g(-1) was obtained. Oxidation of a range of alcohols to the corresponding carbonyl compounds proved very straightforward using 1.2 equiv of the resin. Recycling of the resin was also possible with minimal loss of activity after two reoxidations.

  7. Migration in asymmetric, random environments

    NASA Astrophysics Data System (ADS)

    Deem, Michael; Wang, Dong

    Migration is a key mechanism for expansion of communities. As a population migrates, it experiences a changing environment. In heterogeneous environments, rapid adaption is key to the evolutionary success of the population. In the case of human migration, environmental heterogeneity is naturally asymmetric in the North-South and East-West directions. We here consider migration in random, asymmetric, modularly correlated environments. Knowledge about the environment determines the fitness of each individual. We find that the speed of migration is proportional to the inverse of environmental change, and in particular we find that North-South migration rates are lower than East-West migration rates. Fast communication within the population of pieces of knowledge between individuals, similar to horizontal gene transfer in genetic systems, can help to spread beneficial knowledge among individuals. We show that increased modularity of the relation between knowledge and fitness enhances the rate of evolution. We investigate the relation between optimal information exchange rate and modularity of the dependence of fitness on knowledge. These results for the dependence of migration rate on heterogeneity, asymmetry, and modularity are consistent with existing archaeological facts.

  8. Asymmetric Laguerre-Gaussian beams

    NASA Astrophysics Data System (ADS)

    Kovalev, A. A.; Kotlyar, V. V.; Porfirev, A. P.

    2016-06-01

    We introduce a family of asymmetric Laguerre-Gaussian (aLG) laser beams. The beams have been derived via a complex-valued shift of conventional LG beams in the Cartesian plane. While propagating in a uniform medium, the first bright ring of the aLG beam becomes less asymmetric and the energy is redistributed toward peripheral diffraction rings. The projection of the orbital angular momentum (OAM) onto the optical axis is calculated. The OAM is shown to grow quadratically with increasing asymmetry parameter of the aLG beam, which equals the ratio of the shift to the waist radius. Conditions for the OAM becoming equal to the topological charge have been derived. For aLG beams with zero radial index, we have deduced an expression to define the intensity maximum coordinates and shown the crescent-shaped intensity pattern to rotate during propagation. Results of the experimental generation and rotation of aLG beams agree well with theoretical predictions.

  9. Excitons in asymmetric quantum wells

    NASA Astrophysics Data System (ADS)

    Grigoryev, P. S.; Kurdyubov, A. S.; Kuznetsova, M. S.; Ignatiev, I. V.; Efimov, Yu. P.; Eliseev, S. A.; Petrov, V. V.; Lovtcius, V. A.; Shapochkin, P. Yu.

    2016-09-01

    Resonance dielectric response of excitons is studied for the high-quality InGaAs/GaAs heterostructures with wide asymmetric quantum wells (QWs). To highlight effects of the QW asymmetry, we have grown and studied several heterostructures with nominally square QWs as well as with triangle-like QWs. Several quantum confined exciton states are experimentally observed as narrow exciton resonances. A standard approach for the phenomenological analysis of the profiles is generalized by introducing different phase shifts for the light waves reflected from the QWs at different exciton resonances. Good agreement of the phenomenological fit to the experimentally observed exciton spectra for high-quality structures allowed us to reliably obtain parameters of the exciton resonances: the exciton transition energies, the radiative broadenings, and the phase shifts. A direct numerical solution of the Schrödinger equation for the heavy-hole excitons in asymmetric QWs is used for microscopic modeling of the exciton resonances. Remarkable agreement with the experiment is achieved when the effect of indium segregation is taken into account. The segregation results in a modification of the potential profile, in particular, in an asymmetry of the nominally square QWs.

  10. Seismic demand of plan-asymmetric structures: a revisit

    NASA Astrophysics Data System (ADS)

    Roy, Rana; Chakroborty, Suvonkar

    2013-03-01

    In view of the recognition of the importance of the interdependent behavior of strength and stiffness of walltype structural elements, the seismic demand of plan-asymmetric systems is revisited. Useful strength distribution strategies, i.e., `Center of Strength-Center of Mass (CV-CM) coinciding' and `Balanced Center of Strength-Center of Resistance (CVCR)' are adopted. Design charts for the seismic demand of classical uni-directionally and bi-directionally asymmetric systems are developed in a simple unified format. A conceptual framework is also outlined to conveniently apply the design charts. Illustrations are included to explain the use of the current recommendations in practical design. The study also highlights the relative performance of `CV-CM coinciding' and `Balanced CV-CR' criteria.

  11. Rotational Control of Asymmetric Molecules: Dipole- versus Polarizability-Driven Rotational Dynamics.

    PubMed

    Damari, Ran; Kallush, Shimshon; Fleischer, Sharly

    2016-09-01

    We experimentally study the optical- and terahertz-induced rotational dynamics of asymmetric molecules in the gas phase. Terahertz and optical fields are identified as two distinct control handles over asymmetric molecules, as they couple to the rotational degrees of freedom via the molecular dipole and polarizability selectively. The distinction between those two rotational handles is highlighted by different types of quantum revivals observed in long-duration (>100  ps) field-free rotational evolution. The experimental results are in excellent agreement with random phase wave function (RPWF) simulations [Phys. Rev. A 91, 063420 (2015)] and provide verification of the RPWF as an efficient method for calculating asymmetric molecular dynamics at ambient temperatures, where exact calculation methods are practically not feasible. Our observations and analysis pave the way for orchestrated excitations by both optical and terahertz fields as complementary rotational handles that enable a plethora of new possibilities in three-dimensional rotational control of asymmetric molecules. PMID:27636471

  12. Rotational Control of Asymmetric Molecules: Dipole- versus Polarizability-Driven Rotational Dynamics

    NASA Astrophysics Data System (ADS)

    Damari, Ran; Kallush, Shimshon; Fleischer, Sharly

    2016-09-01

    We experimentally study the optical- and terahertz-induced rotational dynamics of asymmetric molecules in the gas phase. Terahertz and optical fields are identified as two distinct control handles over asymmetric molecules, as they couple to the rotational degrees of freedom via the molecular dipole and polarizability selectively. The distinction between those two rotational handles is highlighted by different types of quantum revivals observed in long-duration (>100 ps ) field-free rotational evolution. The experimental results are in excellent agreement with random phase wave function (RPWF) simulations [Phys. Rev. A 91, 063420 (2015)] and provide verification of the RPWF as an efficient method for calculating asymmetric molecular dynamics at ambient temperatures, where exact calculation methods are practically not feasible. Our observations and analysis pave the way for orchestrated excitations by both optical and terahertz fields as complementary rotational handles that enable a plethora of new possibilities in three-dimensional rotational control of asymmetric molecules.

  13. Total synthesis of ochnaflavone.

    PubMed

    Ndoile, Monica M; van Heerden, Fanie R

    2013-01-01

    The first total syntheses of ochnaflavone, an asymmetric biflavone consisting of apigenin and luteolin moieties, and the permethyl ether of 2,3,2'',3''-tetrahydroochnaflavone have been achieved. The key steps in the synthesis of ochnaflavone were the formation of a diaryl ether and ring cyclization of an ether-linked dimeric chalcone to assemble the two flavone nuclei. Optimal experimental conditions for the oxidative cyclization to form ochnaflavone were established.

  14. Total synthesis of ochnaflavone

    PubMed Central

    Ndoile, Monica M

    2013-01-01

    Summary The first total syntheses of ochnaflavone, an asymmetric biflavone consisting of apigenin and luteolin moieties, and the permethyl ether of 2,3,2'',3''-tetrahydroochnaflavone have been achieved. The key steps in the synthesis of ochnaflavone were the formation of a diaryl ether and ring cyclization of an ether-linked dimeric chalcone to assemble the two flavone nuclei. Optimal experimental conditions for the oxidative cyclization to form ochnaflavone were established. PMID:23946830

  15. Vaginal practices as women's agency in sub-Saharan Africa: a synthesis of meaning and motivation through meta-ethnography.

    PubMed

    Martin Hilber, Adriane; Kenter, Elise; Redmond, Shelagh; Merten, Sonja; Bagnol, Brigitte; Low, Nicola; Garside, Ruth

    2012-05-01

    This paper reports on a systematic review of qualitative research about vaginal practices in sub-Saharan Africa, which used meta-ethnographic methods to understand their origins, their meanings for the women who use them, and how they have evolved in time and place. We included published documents which were based on qualitative methods of data collection and analysis and contained information on vaginal practices. After screening, 16 texts were included which dated from 1951 to 2008. We found that practices evolve and adapt to present circumstances and that they remain an important source of power for women to negotiate challenges that they face. Recent evidence suggests that some practices may increase a woman's susceptibility to HIV and other sexually transmitted infections. The success of new female-controlled prevention technologies, such as microbicides, might be determined by whether they can and will be used by women in the course of their daily life. PMID:22401645

  16. Vaginal practices as women's agency in sub-Saharan Africa: a synthesis of meaning and motivation through meta-ethnography.

    PubMed

    Martin Hilber, Adriane; Kenter, Elise; Redmond, Shelagh; Merten, Sonja; Bagnol, Brigitte; Low, Nicola; Garside, Ruth

    2012-05-01

    This paper reports on a systematic review of qualitative research about vaginal practices in sub-Saharan Africa, which used meta-ethnographic methods to understand their origins, their meanings for the women who use them, and how they have evolved in time and place. We included published documents which were based on qualitative methods of data collection and analysis and contained information on vaginal practices. After screening, 16 texts were included which dated from 1951 to 2008. We found that practices evolve and adapt to present circumstances and that they remain an important source of power for women to negotiate challenges that they face. Recent evidence suggests that some practices may increase a woman's susceptibility to HIV and other sexually transmitted infections. The success of new female-controlled prevention technologies, such as microbicides, might be determined by whether they can and will be used by women in the course of their daily life.

  17. Palladium-catalyzed cross-coupling of aryl chlorides and triflates with sodium cyanate: A practical synthesis of unsymmetrical ureas

    PubMed Central

    Vinogradova, Ekaterina V.; Fors, Brett P.; Buchwald, Stephen L.

    2012-01-01

    An efficient method for palladium-catalyzed cross-coupling of aryl chlorides and triflates with sodium cyanate is reported. The protocol allows for the synthesis of unsymmetrical N,N'-di- and N,N,N'-trisubstituted ureas in one pot, and is tolerant of a wide range of functional groups. Insight into the mechanism of aryl isocyanate formation is gleaned through studies of the transmetallation and reductive elimination steps of the reaction, including the first demonstration of reductive elimination from an arylpalladium isocyanate complex to produce an aryl isocyanate. PMID:22716197

  18. Mechanochemistry assisted asymmetric organocatalysis: A sustainable approach

    PubMed Central

    Chauhan, Pankaj

    2012-01-01

    Summary 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

  19. Defect-free ultrahigh flux asymmetric membranes

    DOEpatents

    Pinnau, Ingo; Koros, William J.

    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.

  20. New asymmetric quantum codes over Fq

    NASA Astrophysics Data System (ADS)

    Ma, Yuena; Feng, Xiaoyi; Xu, Gen

    2016-07-01

    Two families of new asymmetric quantum codes are constructed in this paper. The first family is the asymmetric quantum codes with length n=qm-1 over Fq, where qge 5 is a prime power. The second one is the asymmetric quantum codes with length n=3m-1. These asymmetric quantum codes are derived from the CSS construction and pairs of nested BCH codes. Moreover, let the defining set T1=T2^{-q}, then the real Z-distance of our asymmetric quantum codes are much larger than δ _max+1, where δ _max is the maximal designed distance of dual-containing narrow-sense BCH code, and the parameters presented here have better than the ones available in the literature.

  1. Asymmetric Cherenkov acoustic reverse in topological insulators

    NASA Astrophysics Data System (ADS)

    Smirnov, Sergey

    2014-09-01

    A general phenomenon of the Cherenkov radiation known in optics or acoustics of conventional materials is a formation of a forward cone of, respectively, photons or phonons emitted by a particle accelerated above the speed of light or sound in those materials. Here we suggest three-dimensional topological insulators as a unique platform to fundamentally explore and practically exploit the acoustic aspect of the Cherenkov effect. We demonstrate that by applying an in-plane magnetic field to a surface of a three-dimensional topological insulator one may suppress the forward Cherenkov sound up to zero at a critical magnetic field. Above the critical field the Cherenkov sound acquires pure backward nature with the polar distribution differing from the forward one generated below the critical field. Potential applications of this asymmetric Cherenkov reverse are in the design of low energy electronic devices such as acoustic ratchets or, in general, in low power design of electronic circuits with a magnetic field control of the direction and magnitude of the Cherenkov dissipation.

  2. Asymmetric Electrostatic Radiation Shielding for Spacecraft

    NASA Technical Reports Server (NTRS)

    Metzger, Philip T.; Youngquist, Robert C.; Lane, John E.

    2005-01-01

    A paper describes the types, sources, and adverse effects of energetic-particle radiation in interplanetary space, and explores a concept of using asymmetric electrostatic shielding to reduce the amount of such radiation impinging on spacecraft. Typically, such shielding would include a system of multiple inflatable, electrically conductive spheres deployed in clusters in the vicinity of a spacecraft on lightweight structures that would maintain the spheres in a predetermined multipole geometry. High-voltage generators would maintain the spheres at potential differences chosen in conjunction with the multipole geometry so that the resulting multipole field would gradually divert approaching energetic atomic nuclei from a central region occupied by the spacecraft. The spheres nearest the center would be the most positive, so as to repel the positively charged impinging nuclei from the center. At the same time, the monopole potential of the overall spacecraft-and-shielding system would be made negative so as to repel thermal electrons. The paper presents results of computational simulations of energetic-particle trajectories and shield efficiency for a trial system of 21 spheres arranged in three clusters in an overall linear quadrupole configuration. Further development would be necessary to make this shielding concept practical.

  3. Obstacles to implementing evidence-based practice in Belgium: a context-specific qualitative evidence synthesis including findings from different health care disciplines.

    PubMed

    Hannes, K; Goedhuys, J; Aertgeerts, B

    2012-01-01

    A number of barriers to the implementation of evidence-based practice have already been inventoried. However, little attention has been given to their context-specific nature. This qualitative evidence synthesis examines commonalities in the obstacles perceived by different groups of health care practitioners working in the Belgian health care system and sets out to discuss potential strategies to bridge some of these barriers. We actively searched for primary studies addressing our topic of interest in international and national databases (1990 to May 2008), consulted experts and screened references of retrieved studies. We opted for the meta-aggregative approach, developed by the Joanna Briggs Institute, to analyse our findings. The findings indicate that (1) evidence might have a limited role in decision-making processes; (2) aspects other than quality of care steer the evidence-based practice agenda; (3) some health care providers benefit less from evidence-based practice than others and (4) there is a lack of competences to put the evidence-based principles in practice. Belgian policy makers might consider health care system characteristics from and strategies developed or suggested by others to respond to country-specific obstacles. Examples include but are not limited to; (a) providing incentives for patient-centred care coordination and patient communication, (b) supporting practitioners interested in applying research-related activities, (c) considering direct access systems and interprofessional learning to respond to the demand for autonomous decision-making from satellite professional groups, (d) systematically involving allied health professionals in important governmental advisory boards, (e) considering pharmaceutical companies perceived as 'the enemy' an ally in filling in research gaps, (f) embedding the evaluation of evidence-based knowledge and skills in examinations (g) moving from (in)formative learning to transformative learning and (h

  4. Baseline Testing of the Club Car Carryall With Asymmetric Ultracapacitors

    NASA Technical Reports Server (NTRS)

    Eichenberg, Dennis J.

    2003-01-01

    The NASA John H. Glenn Research Center initiated baseline testing of the Club Car Carryall with asymmetric ultracapacitors as a way to reduce pollution in industrial settings, reduce fossil fuel consumption, and reduce operating costs for transportation systems. The Club Car Carryall provides an inexpensive approach to advance the state of the art in electric vehicle technology in a practical application. The project transfers space technology to terrestrial use via non-traditional partners, and provides power system data valuable for future space applications. The work was done under the Hybrid Power Management (HPM) Program, which includes the Hybrid Electric Transit Bus (HETB). The Carryall is a state of the art, ground up, electric utility vehicle. A unique aspect of the project was the use of a state of the art, long life ultracapacitor energy storage system. Innovative features, such as regenerative braking through ultracapacitor energy storage, are planned. Regenerative braking recovers much of the kinetic energy of the vehicle during deceleration. The Carryall was tested with the standard lead acid battery energy storage system, as well as with an asymmetric ultracapacitor energy storage system. The report concludes that the Carryall provides excellent performance, and that the implementation of asymmetric ultracapacitors in the power system can provide significant performance improvements.

  5. Professional Leadership Practices and Diversity Issues in the U.S. Higher Education System: A Research Synthesis

    ERIC Educational Resources Information Center

    Karkouti, Ibrahim Mohamad

    2016-01-01

    This paper examines the effects of negligence toward diversity issues on campus racial climate, describes how exclusionary practices affect minority students' (i.e., Asian American, Hispanic, Black, and Native American) educational experiences, and addresses faculty issues relevant to diversity. In addition, the paper identifies the factors that…

  6. The Dialectic of Creativity: A Synthesis of Neurobiological, Psychological, Cultural and Practical Aspects of the Creative Process

    ERIC Educational Resources Information Center

    Holm-Hadulla, Rainer M.

    2013-01-01

    In the beginning of the 21st century, creativity has been highly esteemed not only in the arts and sciences, but also in economy, politics, and individual welfare. Most theories and practical applications stem from individual sciences and frequently conclude with generalizations that cannot be derived from the specific scientific paradigm. It…

  7. Goals, Principles, and Practices for Community-Based Adult Education through the Lens of a Hatcher-Assagioli Synthesis

    ERIC Educational Resources Information Center

    Ayvazian, Andrea S.

    2012-01-01

    This study examines how adult education can facilitate learning towards the full realization of human potential. It synthesizes two theories of human development, and applies this to the practice of community-based adult education carried out by trained facilitators who do not have formal degrees in the field of mental health. The first part of…

  8. Educational Practice in India and its Foundations in Indian Heritage: A Synthesis of the East and West?

    ERIC Educational Resources Information Center

    Singh, Madhu

    2013-01-01

    The paper examines education practice in India in terms of the division between indigenous cultures on the one hand, and the formal culture of learning and knowledge systems inherited from colonial times on the other. These "two Indias" are still reflected in the modern educational system in India, seen in the vast differences between the formal…

  9. Asymmetric Construction of 2,3-Dihydroisoxazoles via an Organocatalytic Formal [3 + 2] Cycloaddition of Enynes with N-Hydroxylamines.

    PubMed

    Li, Wenbo; Yu, Xiuzhao; Yue, Zhenting; Zhang, Junliang

    2016-08-19

    An organocatalytic asymmetric formal [3 + 2] cycloaddition of enynones with N-hydroxylamines has been described. A newly designed multifunctional organocatalyst was found to be highly effective, and the method allowed the synthesis of a variety of 2,3-dihydroisoxazoles in good yields with excellent enantioselectivity. PMID:27482852

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

    NASA Astrophysics Data System (ADS)

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

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

  11. Synthesis of Enantiomerically Pure Anthracyclinones

    NASA Astrophysics Data System (ADS)

    Achmatowicz, Osman; Szechner, Barbara

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

  12. Recent Developments in the Catalytic, Asymmetric Construction of Pyrroloindolines Bearing All-Carbon Quaternary Stereocenters

    PubMed Central

    Repka, Lindsay M.; Reisman, Sarah E.

    2014-01-01

    Pyrroloindoline alkaloids constitute a large family of natural products that has inspired the development of an impressive array of new reactions to prepare the key heterocyclic motif. This synopsis will address catalytic, asymmetric reactions developed to synthesize pyrroloindolines bearing C3a all-carbon quaternary stereocenters. The methods described herein include both transition metal-catalyzed and organocatalyzed reactions that have been demonstrated suitable for the synthesis of the pyrroloindoline framework. PMID:24295135

  13. Unidirectional optical Bloch oscillations in asymmetric waveguide arrays.

    PubMed

    Kumar, Pradeep; Levy, Miguel

    2011-11-15

    We present an analytical proof of the existence of unidirectional optical Bloch oscillations in a waveguide array system. It is shown that the presence of nonreciprocity in the system allows for a complete normal-mode dephasing in one of the propagation directions, resulting in a unidirectional breakdown in Bloch oscillations. A model system consisting of an array of transversely magnetized asymmetric Si/SiO2 waveguides with a magneto-optic cover layer is presented. Large index contrasts between film and cover are critical for practical realizations.

  14. Nondeterministic self-assembly with asymmetric interactions

    NASA Astrophysics Data System (ADS)

    Tesoro, S.; Göpfrich, K.; Kartanas, T.; Keyser, U. F.; Ahnert, S. E.

    2016-08-01

    We investigate general properties of nondeterministic self-assembly with asymmetric interactions, using a computational model and DNA tile assembly experiments. By contrasting symmetric and asymmetric interactions we show that the latter can lead to self-limiting cluster growth. Furthermore, by adjusting the relative abundance of self-assembly particles in a two-particle mixture, we are able to tune the final sizes of these clusters. We show that this is a fundamental property of asymmetric interactions, which has potential applications in bioengineering, and provides insights into the study of diseases caused by protein aggregation.

  15. Regenerating a symmetry in asymmetric dark matter.

    PubMed

    Buckley, Matthew R; Profumo, Stefano

    2012-01-01

    Asymmetric dark matter theories generically allow for mass terms that lead to particle-antiparticle mixing. Over the age of the Universe, dark matter can thus oscillate from a purely asymmetric configuration into a symmetric mix of particles and antiparticles, allowing for pair-annihilation processes. Additionally, requiring efficient depletion of the primordial thermal (symmetric) component generically entails large annihilation rates. We show that unless some symmetry completely forbids dark matter particle-antiparticle mixing, asymmetric dark matter is effectively ruled out for a large range of masses, for almost any oscillation time scale shorter than the age of the Universe. PMID:22304253

  16. Regenerating a symmetry in asymmetric dark matter.

    PubMed

    Buckley, Matthew R; Profumo, Stefano

    2012-01-01

    Asymmetric dark matter theories generically allow for mass terms that lead to particle-antiparticle mixing. Over the age of the Universe, dark matter can thus oscillate from a purely asymmetric configuration into a symmetric mix of particles and antiparticles, allowing for pair-annihilation processes. Additionally, requiring efficient depletion of the primordial thermal (symmetric) component generically entails large annihilation rates. We show that unless some symmetry completely forbids dark matter particle-antiparticle mixing, asymmetric dark matter is effectively ruled out for a large range of masses, for almost any oscillation time scale shorter than the age of the Universe.

  17. Nondeterministic self-assembly with asymmetric interactions.

    PubMed

    Tesoro, S; Göpfrich, K; Kartanas, T; Keyser, U F; Ahnert, S E

    2016-08-01

    We investigate general properties of nondeterministic self-assembly with asymmetric interactions, using a computational model and DNA tile assembly experiments. By contrasting symmetric and asymmetric interactions we show that the latter can lead to self-limiting cluster growth. Furthermore, by adjusting the relative abundance of self-assembly particles in a two-particle mixture, we are able to tune the final sizes of these clusters. We show that this is a fundamental property of asymmetric interactions, which has potential applications in bioengineering, and provides insights into the study of diseases caused by protein aggregation. PMID:27627332

  18. Nondeterministic self-assembly with asymmetric interactions.

    PubMed

    Tesoro, S; Göpfrich, K; Kartanas, T; Keyser, U F; Ahnert, S E

    2016-08-01

    We investigate general properties of nondeterministic self-assembly with asymmetric interactions, using a computational model and DNA tile assembly experiments. By contrasting symmetric and asymmetric interactions we show that the latter can lead to self-limiting cluster growth. Furthermore, by adjusting the relative abundance of self-assembly particles in a two-particle mixture, we are able to tune the final sizes of these clusters. We show that this is a fundamental property of asymmetric interactions, which has potential applications in bioengineering, and provides insights into the study of diseases caused by protein aggregation.

  19. Comparison of electrophilic amination reagents for N-amination of 2-oxazolidinones and application to synthesis of chiral hydrazones.

    PubMed

    Shen, Yuehai; Friestad, Gregory K

    2002-08-23

    Comparison of several hydroxylamine-based electrophilic ammonia equivalents in the N-amination of 2-oxazolidinones revealed that O-(p-nitrobenzoyl)hydroxylamine (NbzONH(2)) and sodium hydride in dioxane is a superior reagent combination for this purpose. Practical preparations of a variety of chiral N-acylhydrazones by this method gave yields ranging from 45 to 95%. Methods for exchange or removal of the aldehyde component have been developed, making this a general route to chiral N-acylhydrazones of interest for asymmetric synthesis applications. PMID:12182669

  20. A Practical and General Base-Catalyzed Carbonylation of Amines for the Synthesis of N-Formamides.

    PubMed

    Li, Wanfang; Wu, Xiao-Feng

    2015-10-12

    A highly practical and general base-catalyzed carbonylation of amines to the corresponding N-formamides has been realized. Cheap inorganic bases, including Group IA and IIA metal hydroxides, alkoxides, carbonates, and phosphates, were effective catalysts for the transformation. In the presence of 10-40 mol % of KOH or K2 CO3 , various amines were converted into the corresponding N-formamides in good-to-excellent yields using CO as the formylation reagents.

  1. Twin Higgs Asymmetric Dark Matter.

    PubMed

    García García, Isabel; Lasenby, Robert; March-Russell, John

    2015-09-18

    We study asymmetric dark matter (ADM) in the context of the minimal (fraternal) twin Higgs solution to the little hierarchy problem, with a twin sector with gauged SU(3)^{'}×SU(2)^{'}, a twin Higgs doublet, and only third-generation twin fermions. Naturalness requires the QCD^{'} scale Λ_{QCD}^{'}≃0.5-20  GeV, and that t^{'} is heavy. We focus on the light b^{'} quark regime, m_{b^{'}}≲Λ_{QCD}^{'}, where QCD^{'} is characterized by a single scale Λ_{QCD}^{'} with no light pions. A twin baryon number asymmetry leads to a successful dark matter (DM) candidate: the spin-3/2 twin baryon, Δ^{'}∼b^{'}b^{'}b^{'}, with a dynamically determined mass (∼5Λ_{QCD}^{'}) in the preferred range for the DM-to-baryon ratio Ω_{DM}/Ω_{baryon}≃5. Gauging the U(1)^{'} group leads to twin atoms (Δ^{'}-τ^{'}[over ¯] bound states) that are successful ADM candidates in significant regions of parameter space, sometimes with observable changes to DM halo properties. Direct detection signatures satisfy current bounds, at times modified by dark form factors. PMID:26430985

  2. Twin Higgs Asymmetric Dark Matter.

    PubMed

    García García, Isabel; Lasenby, Robert; March-Russell, John

    2015-09-18

    We study asymmetric dark matter (ADM) in the context of the minimal (fraternal) twin Higgs solution to the little hierarchy problem, with a twin sector with gauged SU(3)^{'}×SU(2)^{'}, a twin Higgs doublet, and only third-generation twin fermions. Naturalness requires the QCD^{'} scale Λ_{QCD}^{'}≃0.5-20  GeV, and that t^{'} is heavy. We focus on the light b^{'} quark regime, m_{b^{'}}≲Λ_{QCD}^{'}, where QCD^{'} is characterized by a single scale Λ_{QCD}^{'} with no light pions. A twin baryon number asymmetry leads to a successful dark matter (DM) candidate: the spin-3/2 twin baryon, Δ^{'}∼b^{'}b^{'}b^{'}, with a dynamically determined mass (∼5Λ_{QCD}^{'}) in the preferred range for the DM-to-baryon ratio Ω_{DM}/Ω_{baryon}≃5. Gauging the U(1)^{'} group leads to twin atoms (Δ^{'}-τ^{'}[over ¯] bound states) that are successful ADM candidates in significant regions of parameter space, sometimes with observable changes to DM halo properties. Direct detection signatures satisfy current bounds, at times modified by dark form factors.

  3. Chaos suppression through asymmetric coupling

    NASA Astrophysics Data System (ADS)

    Bragard, J.; Vidal, G.; Mancini, H.; Mendoza, C.; Boccaletti, S.

    2007-12-01

    We study pairs of identical coupled chaotic oscillators. In particular, we have used Roessler (in the funnel and no funnel regimes), Lorenz, and four-dimensional chaotic Lotka-Volterra models. In all four of these cases, a pair of identical oscillators is asymmetrically coupled. The main result of the numerical simulations is that in all cases, specific values of coupling strength and asymmetry exist that render the two oscillators periodic and synchronized. The values of the coupling strength for which this phenomenon occurs is well below the previously known value for complete synchronization. We have found that this behavior exists for all the chaotic oscillators that we have used in the analysis. We postulate that this behavior is presumably generic to all chaotic oscillators. In order to complete the study, we have tested the robustness of this phenomenon of chaos suppression versus the addition of some Gaussian noise. We found that chaos suppression is robust for the addition of finite noise level. Finally, we propose some extension to this research.

  4. Structural basis of arginine asymmetrical dimethylation by PRMT6.

    PubMed

    Wu, Hong; Zheng, Weihong; Eram, Mohammad S; Vhuiyan, Mynol; Dong, Aiping; Zeng, Hong; He, Hao; Brown, Peter; Frankel, Adam; Vedadi, Masoud; Luo, Minkui; Min, Jinrong

    2016-10-01

    PRMT6 is a type I protein arginine methyltransferase, generating the asymmetric dimethylarginine mark on proteins such as histone H3R2. Asymmetric dimethylation of histone H3R2 by PRMT6 acts as a repressive mark that antagonizes trimethylation of H3 lysine 4 by the MLL histone H3K4 methyltransferase. PRMT6 is overexpressed in several cancer types, including prostate, bladder and lung cancers; therefore, it is of great interest to develop potent and selective inhibitors for PRMT6. Here, we report the synthesis of a potent bisubstrate inhibitor GMS [6'-methyleneamine sinefungin, an analog of sinefungin (SNF)], and the crystal structures of human PRMT6 in complex, respectively, with S-adenosyl-L-homocysteine (SAH) and the bisubstrate inhibitor GMS that shed light on the significantly improved inhibition effect of GMS on methylation activity of PRMT6 compared with SAH and an S-adenosyl-L-methionine competitive methyltransferase inhibitor SNF. In addition, we also crystallized PRMT6 in complex with SAH and a short arginine-containing peptide. Based on the structural information here and available in the PDB database, we proposed a mechanism that can rationalize the distinctive arginine methylation product specificity of different types of arginine methyltransferases and pinpoint the structural determinant of such a specificity. PMID:27480107

  5. Lithium Titanate Confined in Carbon Nanopores for Asymmetric Supercapacitors.

    PubMed

    Zhao, Enbo; Qin, Chuanli; Jung, Hong-Ryun; Berdichevsky, Gene; Nese, Alper; Marder, Seth; Yushin, Gleb

    2016-04-26

    Porous carbons suffer from low specific capacitance, while intercalation-type active materials suffer from limited rate when used in asymmetric supercapacitors. We demonstrate that nanoconfinement of intercalation-type lithium titanate (Li4Ti5O12) nanoparticles in carbon nanopores yielded nanocomposite materials that offer both high ion storage density and rapid ion transport through open and interconnected pore channels. The use of titanate increased both the gravimetric and volumetric capacity of porous carbons by more than an order of magnitude. High electrical conductivity of carbon and the small size of titanate crystals allowed the composite electrodes to achieve characteristic charge and discharge times comparable to that of the electric double-layer capacitors. The proposed composite synthesis methodology is simple, scalable, and applicable for a broad range of active intercalation materials, while the produced composite powders are compatible with commercial electrode fabrication processes.

  6. Lithium Titanate Confined in Carbon Nanopores for Asymmetric Supercapacitors.

    PubMed

    Zhao, Enbo; Qin, Chuanli; Jung, Hong-Ryun; Berdichevsky, Gene; Nese, Alper; Marder, Seth; Yushin, Gleb

    2016-04-26

    Porous carbons suffer from low specific capacitance, while intercalation-type active materials suffer from limited rate when used in asymmetric supercapacitors. We demonstrate that nanoconfinement of intercalation-type lithium titanate (Li4Ti5O12) nanoparticles in carbon nanopores yielded nanocomposite materials that offer both high ion storage density and rapid ion transport through open and interconnected pore channels. The use of titanate increased both the gravimetric and volumetric capacity of porous carbons by more than an order of magnitude. High electrical conductivity of carbon and the small size of titanate crystals allowed the composite electrodes to achieve characteristic charge and discharge times comparable to that of the electric double-layer capacitors. The proposed composite synthesis methodology is simple, scalable, and applicable for a broad range of active intercalation materials, while the produced composite powders are compatible with commercial electrode fabrication processes. PMID:26950509

  7. Power spectra of a constrained totally asymmetric simple exclusion process

    NASA Astrophysics Data System (ADS)

    Cook, L. Jonathan; Zia, R. K. P.

    2010-07-01

    In nature, all biological systems function in a far-from-equilibrium state. Here, we study the process of translation in protein synthesis, using the totally asymmetric simple exclusion process (TASEP) as a model. In particular, we explore the effects of a finite supply of particles for the TASEP, as in a living cell with a finite pool of ribosomes. Specifically, we investigate the power spectrum associated with total occupancy, utilizing both Monte Carlo simulations and theoretical analysis. New features arise, such as large suppressions at low frequencies, due to the added constraint. A theory is formulated based on a Langevin approach with discrete space and time. With good agreement between the simulation and theory, we gain some insights into the effects of finite resources on the TASEP.

  8. A second-generation total synthesis of (+)-discodermolide: the development of a practical route using solely substrate-based stereocontrol.

    PubMed

    Paterson, Ian; Delgado, Oscar; Florence, Gordon J; Lyothier, Isabelle; O'Brien, Matthew; Scott, Jeremy P; Sereinig, Natascha

    2005-01-01

    A novel total synthesis of the complex polyketide (+)-discodermolide, a promising anticancer agent of sponge origin, has been completed in 7.8% overall yield over 24 linear steps, with 35 steps altogether. This second-generation approach was designed to rely solely on substrate control for introduction of the required stereochemistry, eliminating the use of all chiral reagents or auxiliaries. The common 1,2-anti-2,3-syn stereotriad found in each of three subunits, aldehyde 9 (C(1)-C(5)), ester 40 (C(9)-C(16)), and aldehyde 13 (C(17)-C(24)), was established via a boron-mediated aldol reaction of ethyl ketone 15 and formaldehyde, followed by hydroxyl-directed reduction to give 1,3-diol 14. Alternatively, a surrogate aldehyde 22 was employed for formaldehyde in this aldol reaction, leading to the beta-hydroxy aldehyde 20 as a common building block, corresponding to the discodermolide stereotriad. Key fragment unions were achieved by a lithium-mediated anti aldol reaction of ester 40 and aldehyde 13 under Felkin-Anh control to provide (16S,17S)-adduct 51 and a boron-mediated aldol reaction between enone 10 and aldehyde 9, exploiting unprecedented remote 1,6-stereoinduction, to give the (5S)-adduct 57.

  9. Molecular counting by photobleaching in protein complexes with many subunits: best practices and application to the cellulose synthesis complex

    PubMed Central

    Chen, Yalei; Deffenbaugh, Nathan C.; Anderson, Charles T.; Hancock, William O.

    2014-01-01

    The constituents of large, multisubunit protein complexes dictate their functions in cells, but determining their precise molecular makeup in vivo is challenging. One example of such a complex is the cellulose synthesis complex (CSC), which in plants synthesizes cellulose, the most abundant biopolymer on Earth. In growing plant cells, CSCs exist in the plasma membrane as six-lobed rosettes that contain at least three different cellulose synthase (CESA) isoforms, but the number and stoichiometry of CESAs in each CSC are unknown. To begin to address this question, we performed quantitative photobleaching of GFP-tagged AtCESA3-containing particles in living Arabidopsis thaliana cells using variable-angle epifluorescence microscopy and developed a set of information-based step detection procedures to estimate the number of GFP molecules in each particle. The step detection algorithms account for changes in signal variance due to changing numbers of fluorophores, and the subsequent analysis avoids common problems associated with fitting multiple Gaussian functions to binned histogram data. The analysis indicates that at least 10 GFP-AtCESA3 molecules can exist in each particle. These procedures can be applied to photobleaching data for any protein complex with large numbers of fluorescently tagged subunits, providing a new analytical tool with which to probe complex composition and stoichiometry. PMID:25232006

  10. A Practical Guide on the Synthesis of Metal Chelates for Molecular Imaging and Therapy by Means of Click Chemistry.

    PubMed

    Notni, Johannes; Wester, Hans-Jürgen

    2016-08-01

    The copper-catalyzed cycloaddition of organic azides and alkynes (CuAAC) is one of the most popular reactions for rapid assembly of multifunctional molecular frameworks from commercially available building blocks. It is also attractive for synthesis of conjugates of multidentate chelate ligands (chelators) with molecular targeting vectors, such as peptides or proteins, which serve as precursors for labeling with metal radionuclides or are useful as MRI contrast agents after Gd(III) complexation. However, applicability of CuAAC for such purposes is complicated by formation of unwanted copper chelates. The alternative use of copper-free click chemistry, for example, the strain-promoted alkyne-azide cycloaddition (SPAAC) or the Diels-Alder reaction of tetrazines and strained alkenes, entails other specific challenges: Introduction of large, isomerically non-homogeneous and hydrophobic linker groups affects product homogeneity and can severely change pharmacokinetic profiles. Against this background, this review elucidates scope and applicability of both Cu-catalyzed and Cu-free alkyne-azide cycloadditions pertinent to the elaboration of radiometal chelates and MRI contrast agents, with an emphasis on strategies to tackle the problem of copper complexation during CuAAC. PMID:27333118

  11. 1H-Imidazol-4(5H)-ones and thiazol-4(5H)-ones as emerging pronucleophiles in asymmetric catalysis

    PubMed Central

    Mielgo, Antonia

    2016-01-01

    Summary Asymmetric catalysis represents a very powerful tool for the synthesis of enantiopure compounds. In this context the main focus has been directed not only to the search for new efficient chiral catalysts, but also to the development of efficient pronucleophiles. This review highlights the utility and first examples of 1H-imidazol-4(5H)-ones and thiazol-4(5H)-ones as pronucleophiles in catalytic asymmetric reactions. PMID:27340482

  12. Organocatalytic Asymmetric Tandem Nazarov Cyclization/Semipinacol Rearrangement: Rapid Construction of Chiral Spiro[4.4]nonane-1,6-diones.

    PubMed

    Yang, Bin-Miao; Cai, Pei-Jun; Tu, Yong-Qiang; Yu, Zhi-Xiang; Chen, Zhi-Min; Wang, Shuang-Hu; Wang, Shao-Hua; Zhang, Fu-Min

    2015-07-01

    A novel organocatalytic asymmetric tandem Nazarov cyclization/semipinacol rearrangement reaction using "unactivated" substrates has been developed, generating a series of chiral spiro[4.4]nonane-1,6-diones in up to 96% yield and 97% enantiomeric excess. Significantly, it is the first direct example for asymmetric synthesis of cyclopentanones with four stereocenters using Nazarov cyclization. DFT calculations have been applied to understand the reaction mechanism, stereochemistry, and substituent effects. PMID:26076169

  13. Understanding success and failure in multimorbidity: protocol for using realist synthesis to identify how social learning and workplace practices can be optimised

    PubMed Central

    2013-01-01

    analysis and synthesis of credible and trustworthy data judged to be relevant to our research question. Discussion Findings will be submitted for peer-reviewed publication. Identification of how mechanisms of social learning and workplace practices could be optimised to improve quality and utility of patient care in multimorbidity is important. This can inform the future research regarding interventions that will produce a sustainable medical workforce equipped to provide healthcare, when the possibility of cure is absent. PMID:24066719

  14. Asymmetrically charged carbon nanotubes by controlled functionalization.

    PubMed

    Peng, Qiang; Qu, Liangti; Dai, Liming; Park, Kyoungweon; Vaia, Richard A

    2008-09-23

    Surface modification of carbon nanotubes (CNTs) has been widely studied for some years. However, the asymmetric modification of individual CNTs with different molecular species/nanoparticles at the two end-tips or along the nanotube length is only a recent development. As far as we are aware, no attempt has so far been made to asymmetrically functionalize individual CNTs with moieties of opposite charges. In this paper, we have demonstrated a simple, but effective, asymmetric modification of the sidewall of CNTs with oppositely charged moieties by plasma treatment and pi-pi stacking interaction. The as-prepared asymmetrically sidewall-functionalized CNTs can be used as a platform for bottom-up self-assembly of complex structures or can be charge-selectively self-assembled onto and/or between electrodes with specific biases under an appropriate applied voltage for potential device applications. PMID:19206422

  15. Asymmetric cryptography based on wavefront sensing.

    PubMed

    Peng, Xiang; Wei, Hengzheng; Zhang, Peng

    2006-12-15

    A system of asymmetric cryptography based on wavefront sensing (ACWS) is proposed for the first time to our knowledge. One of the most significant features of the asymmetric cryptography is that a trapdoor one-way function is required and constructed by analogy to wavefront sensing, in which the public key may be derived from optical parameters, such as the wavelength or the focal length, while the private key may be obtained from a kind of regular point array. The ciphertext is generated by the encoded wavefront and represented with an irregular array. In such an ACWS system, the encryption key is not identical to the decryption key, which is another important feature of an asymmetric cryptographic system. The processes of asymmetric encryption and decryption are formulized mathematically and demonstrated with a set of numerical experiments.

  16. GPM Sees Tropical Storm Danny's Asymmetric Rainfall

    NASA Video Gallery

    On Aug. 19, GPM saw Danny's rain structure was still asymmetric as noted by the large rain band (identified by the green arc indicating moderate rain) being located mainly on the eastern side of th...

  17. Conveying Equipoise during Recruitment for Clinical Trials: Qualitative Synthesis of Clinicians’ Practices across Six Randomised Controlled Trials

    PubMed Central

    Jepson, Marcus; Strong, Sean; Wilson, Caroline; Beard, David; Blazeby, Jane M.; Birtle, Alison; Halliday, Alison

    2016-01-01

    Background Randomised controlled trials (RCTs) are essential for evidence-based medicine and increasingly rely on front-line clinicians to recruit eligible patients. Clinicians’ difficulties with negotiating equipoise is assumed to undermine recruitment, although these issues have not yet been empirically investigated in the context of observable events. We aimed to investigate how clinicians conveyed equipoise during RCT recruitment appointments across six RCTs, with a view to (i) identifying practices that supported or hindered equipoise communication and (ii) exploring how clinicians’ reported intentions compared with their actual practices. Methods and Findings Six pragmatic UK-based RCTs were purposefully selected to include several clinical specialties (e.g., oncology, surgery) and types of treatment comparison. The RCTs were all based in secondary-care hospitals (n = 16) around the UK. Clinicians recruiting to the RCTs were interviewed (n = 23) to understand their individual sense of equipoise about the RCT treatments and their intentions for communicating equipoise to patients. Appointments in which these clinicians presented the RCT to trial-eligible patients were audio-recorded (n = 105). The appointments were analysed using thematic and content analysis approaches to identify practices that supported or challenged equipoise communication. A sample of appointments was independently coded by three researchers to optimise reliability in reported findings. Clinicians and patients provided full written consent to be interviewed and have appointments audio-recorded. Interviews revealed that clinicians’ sense of equipoise varied: although all were uncertain about which trial treatment was optimal, they expressed different levels of uncertainty, ranging from complete ambivalence to clear beliefs that one treatment was superior. Irrespective of their personal views, all clinicians intended to set their personal biases aside to convey trial treatments

  18. The cosmology of asymmetric brane modified gravity

    SciTech Connect

    O'Callaghan, Eimear; Gregory, Ruth; Pourtsidou, Alkistis E-mail: ppxap1@nottingham.ac.uk

    2009-09-01

    We consider the asymmetric branes model of modified gravity, which can produce late time acceleration of the universe and compare the cosmology of this model to the standard ΛCDM model and to the DGP braneworld model. We show how the asymmetric cosmology at relevant physical scales can be regarded as a one-parameter extension of the DGP model, and investigate the effect of this additional parameter on the expansion history of the universe.

  19. Metallic organophosphates as catalysts in asymmetric synthesis: a return journey.

    PubMed

    Parra, Alejandro; Reboredo, Silvia; Martín Castro, Ana M; Alemán, José

    2012-07-14

    This perspective article provides a general overview of the most relevant topics in the applications of chiral metallic organophosphates. A brief introduction along with a historic comparative profile of the BINOL and phosphoric acid analogues are given. Next, a selection of the most outstanding uses of the catalysts according to the employed metal is presented.

  20. Organocatalytic Asymmetric Synthesis of Dihydrobenzoxazinones Bearing Trifluoromethylated Quaternary Stereocenters.

    PubMed

    Lou, Hengqiao; Wang, Yongtao; Jin, Enze; Lin, Xufeng

    2016-03-01

    Chiral phosphoric acid-catalyzed enantioselective aza-Friedel-Crafts reaction of trifluoromethyl benzoxazinones with pyrroles is reported. Under mild conditions, a range of enantioenriched dihydrobenzoxazinones bearing trifluoromethylated quaternary stereocenters could be obtained in good to excellent yield and ee. A remarkable fluorine effect is observed, and preliminary mechanistic studies combined with theory calculations suggest that triple-hydrogen-bonding interactions hold the transition structure rigidly and allow the bulky substituents of the catalyst to influence the enantioselectivity. PMID:26882280

  1. Silyl Ketene Imines: Highly Versatile Nucleophiles for Catalytic, Asymmetric Synthesis

    PubMed Central

    Denmark, Scott E.; Wilson, Tyler W.

    2012-01-01

    This Minireview provides an overview on the development of silyl ketene imines and their recent applications in catalytic, enantioselective reactions. The unique structure of the ketene imine allows a diverse range of reactivity patterns and provides solutions to existing challenges in the enantioselective construction of quaternary stereogenic carbon centers and cross-benzoin adducts. A variety of reactions for which silyl ketene imines have been applied are presented with an overall goal of inspiring new uses for these underutilized nucleophiles. PMID:22968901

  2. Asymmetric Methods for the Synthesis of Flavanones, Chromanones, and Azaflavanones

    PubMed Central

    Nibbs, Antoinette E.

    2012-01-01

    Flavanones, chromanones, and related structures are privileged natural products that display a wide variety of biological activities. Although flavanoids are abundant in nature, there are a limited number of available general and efficient synthetic methods for accessing molecules of this class in a stereoselective manner. Their structurally simple architectures belie the difficulties involved in installation and maintenance of the stereogenic configuration at the C2 position, which can be sensitive and can undergo epimerization under mildly acidic, basic, and thermal reaction conditions. This review presents the methods currently used to access these related structures. The synthetic methods include manipulation of the flavone/flavanone core, carbon-carbon bond formation, and carbon–heteroatom bond formation. PMID:22876166

  3. Computer graphics synthesis for inferring artist studio practice: an application to Diego Velázquez's Las Meninas[

    NASA Astrophysics Data System (ADS)

    Stork, David G.; Furuichi, Yasuo

    2009-02-01

    Diego Velázquez's Las meninas (1656) has been called by some art experts "the most important painting of the 17th century," "a theology of painting," and even "the world's greatest painting"; it has been the subject of intensive study. The work depicts a complex scene in the Alcázar palace of King Philip IV of Spain, and includes mirror reflections of the king and queen, apparently standing in place of the viewer, as well as the artist himself standing before an enormous canvas on an easel. Nevertheless, questions remain about the studio and the proper viewing configuration: Is the artist looking toward the perspectivally correct position of the viewer in the museum space (center of projection), outside the picture space? Does the perspectivally correct position correspond to the locations of the king and queen seen reflected in the mirror? Is the bright illumination on the king and queen (as revealed in the mirror) consistent with the lighting in the tableau itself? We addressed these questions in a new way: by building a full computer graphics model of the figures and tableau as well as the viewer's space outside the painting. In our full model, the painting itself is represented as a translucent window onto which the picture space is projected toward the center of projection, that is, the viewer. Our geometric and (new) lighting evidence confirm Janson's and Snyder's contention that the plane mirror on the back wall reflects the other side of the large painting depicted within the tableau, not the king and queen themselves in the studio. We believe our computer graphics synthesis of both the tableau within the painting and the viewer's space in the real world is the first of its kind to address such problems in the history of art.

  4. A Practical Green Synthesis, and Biological Evaluation of Benzimidazoles Against Two Neglected Tropical Diseases: Chagas and Leishmaniasis.

    PubMed

    Bandyopadhyay, Debasish; Samano, Selina; Villalobos-Rocha, Juan C; Sanchez-Torres, Luvia E; Nogueda-Torres, Benjamín; Rivera, Gildardo; Banik, Bimal K

    2013-01-01

    Antimicrobial resistance is an ever-increasing problem throughout the world and has already reached severe proportions. Two very common neglected tropical diseases are Chagas' disease and leishmaniasis. Chagas' disease is a severe health problem, mainly in Latin America, causing approximately 50000 deaths a year and millions of people are infected. About 25-30% of the patients infected with Trypanosoma cruzi develop the chronic form of the disease. On the other hand, Leishmaniasis represents a complex of diseases with an important clinical and epidemiological diversity. It is endemic in 88 countries 72 of which are developing countries and its estimated there are 12 million people infected and 350 million are in areas with infection risk. On this basis, research on organic compounds that can be used against these two diseases is an important target. A very simple, green, and efficient protocol is developed in which bismuth nitrate pentahydrate is employed as a Lewis acid catalyst in aqueous media under microwave irradiation for the synthesis of various 2-aryl substituted benzimidazoles from aldehydes and o-phenylenediamine. Other salient features of this protocol include milder conditions, atom-economy, easy extraction, and no wastes. Nine 1H-benzimidazole derivatives (1-9) with substituents at positions 2 and 5 were synthesized and the structure of the compounds was elucidated by spectroscopic methods. The compounds were screened to identify whether they posses pharmacological activity against Chagas' disease and leishmaniasis. Compound 8 showed better activity than the control Nifurtimox against INC-5 Trypanosoma cruzi strain whereas compounds 3 and 9 have demonstrated potent leshmanicidal activity. A systematic green synthetic procedure and in vitro biological evaluation of nine 1H-benzimidazoles are described. PMID:23317160

  5. Asymmetric Magnetic Reconnection in the Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Murphy, N. A.; Miralles, M. P.; Ranquist, D. A.; Pope, C. L.; Raymond, J. C.; Lukin, V. S.; McKillop, S.; Shen, C.; Winter, H. D.; Reeves, K. K.; Lin, J.

    2013-12-01

    Models of solar flares and coronal mass ejections typically predict the development of an elongated current sheet in the wake behind the rising flux rope. In reality, reconnection in these current sheets will be asymmetric along the inflow, outflow, and out-of-plane directions. We perform resistive MHD simulations to investigate the consequences of asymmetry during solar reconnection. We predict several observational signatures of asymmetric reconnection, including flare loops with a skewed candle flame shape, slow drifting of the current sheet into the strong field upstream region, asymmetric footpoint speeds and hard X-ray emission, and rolling motions within the erupting flux rope. There is net plasma flow across the magnetic field null along both the inflow and outflow directions. We compare simulations to SDO/AIA, Hinode/XRT, and STEREO observations of flare loop shapes, current sheet drifting, and rolling motions during prominence eruptions. Simulations of the plasmoid instability with different upstream magnetic fields show that the reconnection rate remains enhanced even during the asymmetric case. The islands preferentially grow into the weak field upstream region. The islands develop net vorticity because the outflow jets impact them obliquely rather than directly. Asymmetric reconnection in the chromosphere occurs when emerging flux interacts with pre-existing overlying flux. We present initial results on asymmetric reconnection in partially ionized chromospheric plasmas. Finally, we discuss how comparisons to observations are necessary to understand the role of three-dimensional effects.

  6. Asymmetric Magnetic Reconnection in the Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Murphy, N. A.; Miralles, M. P.; Ranquist, D. A.; Pope, C. L.; Raymond, J. C.; Lukin, V. S.; McKillop, S. C.; Shen, C.; Winter, H. D.; Reeves, K. K.; Lin, J.

    2013-12-01

    Models of solar flares and coronal mass ejections typically predict the development of an elongated current sheet in the wake behind the rising flux rope. In reality, reconnection in these current sheets will be asymmetric along the inflow, outflow, and out-of-plane directions. We perform resistive MHD simulations to investigate the consequences of asymmetry during solar reconnection. We predict several observational signatures of asymmetric reconnection, including flare loops with a skewed candle flame shape, slow drifting of the current sheet into the strong field upstream region, asymmetric footpoint speeds and hard X-ray emission, and rolling motions within the erupting flux rope. There is net plasma flow across the magnetic field null along both the inflow and outflow directions. We compare simulations to SDO/AIA, Hinode/XRT, and STEREO observations of flare loop shapes, current sheet drifting, and rolling motions during prominence eruptions. Simulations of the plasm! oid instability with different upstream magnetic fields show that the reconnection rate remains enhanced even during the asymmetric case. The islands preferentially grow into the weak field upstream region. The islands develop net vorticity because the outflow jets impact them obliquely rather than directly. Asymmetric reconnection in the chromosphere occurs when emerging flux interacts with pre-existing overlying flux. We present initial results on asymmetric reconnection in partially ionized chromospheric plasmas. Finally, we discuss how comparisons to observations are necessary to understand the role of three-dimensional effects.

  7. The Reception of J. H. van't Hoff's Theory of the Asymmetric Carbon Atom

    ERIC Educational Resources Information Center

    Snelders, H. A. M.

    1974-01-01

    Discusses Jacobus Henricus van't Hoff's revolutionary theory of the asymmetric carbon atom and its early reception among his contemporaries in the Netherlands. Indicates that the extension of the new idea to practical problems gives the impetus to the development of stereochemistry. (CC)

  8. Method and apparatus for controlling LCL converters using asymmetric voltage cancellation techniques

    DOEpatents

    Wu, Hunter; Sealy, Kylee Devro; Sharp, Bryan Thomas; Gilchrist, Aaron

    2016-01-26

    A method and apparatus for LCL resonant converter control utilizing Asymmetric Voltage Cancellation is described. The methods to determine the optimal trajectory of the control variables are discussed. Practical implementations of sensing load parameters are included. Simple PI, PID and fuzzy logic controllers are included with AVC for achieving good transient response characteristics with output current regulation.

  9. Multilingual Label Quests: A Practice for the "Asymmetrical" Multilingual Classroom

    ERIC Educational Resources Information Center

    Bonacina-Pugh, Florence

    2013-01-01

    Research on multilingual classrooms usually focuses on contexts where both teachers and pupils share the same linguistic repertoire; what can be called "symmetrical" multilingual classrooms. This paper sets out to investigate whether (and how) pupils' multilingual resources can be used in classrooms where the teacher does not share pupils'…

  10. Glycals in enantiospecific synthesis

    NASA Astrophysics Data System (ADS)

    Tolstikov, Alexander G.; Tolstikov, Genrikh A.

    1993-06-01

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

  11. Performance-Enhancing Asymmetric Separator for Lithium-Sulfur Batteries.

    PubMed

    Conder, Joanna; Forner-Cuenca, Antoni; Gubler, Elisabeth Müller; Gubler, Lorenz; Novák, Petr; Trabesinger, Sigita

    2016-07-27

    Asymmetric separators with polysulfide barrier properties consisting of porous polypropylene grafted with styrenesulfonate (PP-g-PLiSS) were characterized in lithium-sulfur cells to assess their practical applicability. Galvanostatic cycling at different C-rates with and without an electrolyte additive and cyclic voltammetry were used to probe the electrochemical performance of the cells with the PP-g-PLiSS separators and to compare it with the performance of the cells utilizing state-of-the-art separator, Celgard 2400. Overall, it was found that regardless of the applied cycling rate, the use of the grafted separators greatly enhances the Coulombic efficiency of the cell. An appropriate Li-exchange-site (-SO3(-)) concentration at and near the surface of the separator was found to be essential to effectively suppress the polysulfide shuttle without sacrificing the Li-ion mobility through the separator and to improve the practical specific charge of the cell. PMID:27367443

  12. Total Synthesis of Mycalolides A and B through Olefin Metathesis.

    PubMed

    Kita, Masaki; Oka, Hirotaka; Usui, Akihiro; Ishitsuka, Tomoya; Mogi, Yuzo; Watanabe, Hidekazu; Tsunoda, Masaki; Kigoshi, Hideo

    2015-11-16

    An asymmetric total synthesis of the trisoxazole marine macrolides mycalolides A and B is described. This synthesis involves the convergent assembly of highly functionalized C1-C19 trisoxazole and C20-C35 side-chain segments through the use of olefin metathesis and esterification as well as Julia-Kocienski olefination and enamide formation as key steps.

  13. Total Synthesis of Mycalolides A and B through Olefin Metathesis.

    PubMed

    Kita, Masaki; Oka, Hirotaka; Usui, Akihiro; Ishitsuka, Tomoya; Mogi, Yuzo; Watanabe, Hidekazu; Tsunoda, Masaki; Kigoshi, Hideo

    2015-11-16

    An asymmetric total synthesis of the trisoxazole marine macrolides mycalolides A and B is described. This synthesis involves the convergent assembly of highly functionalized C1-C19 trisoxazole and C20-C35 side-chain segments through the use of olefin metathesis and esterification as well as Julia-Kocienski olefination and enamide formation as key steps. PMID:26450520

  14. Asymmetric catalytic cascade reactions for constructing diverse scaffolds and complex molecules.

    PubMed

    Wang, Yao; Lu, Hong; Xu, Peng-Fei

    2015-07-21

    With the increasing concerns about chemical pollution and sustainability of resources, among the significant challenges facing synthetic chemists are the development and application of elegant and efficient methods that enable the concise synthesis of natural products, drugs, and related compounds in a step-, atom- and redox-economic manner. One of the most effective ways to reach this goal is to implement reaction cascades that allow multiple bond-forming events to occur in a single vessel. This Account documents our progress on the rational design and strategic application of asymmetric catalytic cascade reactions in constructing diverse scaffolds and synthesizing complex chiral molecules. Our research is aimed at developing robust cascade reactions for the systematic synthesis of a range of interesting molecules that contain structural motifs prevalent in natural products, pharmaceuticals, and biological probes. The strategies employed to achieve this goal can be classified into three categories: bifunctional base/Brønsted acid catalysis, covalent aminocatalysis/N-heterocyclic carbene catalysis, and asymmetric organocatalytic relay cascades. By the use of rationally designed substrates with properly reactive sites, chiral oxindole, chroman, tetrahydroquinoline, tetrahydrothiophene, and cyclohexane scaffolds were successfully assembled under bifunctional base/Brønsted acid catalysis from simple and readily available substances such as imines and nitroolefins. We found that some of these reactions are highly efficient since catalyst loadings as low as 1 mol % can promote the multistep sequences affording complex architectures with high stereoselectivities and yields. Furthermore, one of the bifunctional base/Brønsted acid-catalyzed cascade reactions for the synthesis of chiral cyclohexanes has been used as a key step in the construction of the tetracyclic core of lycorine-type alkaloids and the formal synthesis of α-lycorane. Guided by the principles of

  15. Overcoming asymmetric goals in teams: the interactive roles of team learning orientation and team identification.

    PubMed

    Pearsall, Matthew J; Venkataramani, Vijaya

    2015-05-01

    Although members of teams share a common, ultimate objective, they often have asymmetric or conflicting individual goals that shape the way they contribute to, and pursue, the shared goal of the team. Compounding this problem, they are frequently unaware of the nature of these goal asymmetries or even the fact that such differences exist. Drawing on, and integrating, social interdependence and representational gaps theories, we identify 2 emergent states that combine interactively to enable teams to overcome asymmetric goals: team identification and team learning orientation. Using data from long-term, real-life teams that engaged in a computer simulation designed to create both asymmetric goals and representational gaps about those goals, we found that teams were most effective when they had a high learning orientation coupled with high team identification and that this effect was mediated by teams' ability to form more accurate team goal mental models and engage in effective planning processes. Implications for theory and practice are discussed.

  16. Seeing left- or right-asymmetric tail wagging produces different emotional responses in dogs.

    PubMed

    Siniscalchi, Marcello; Lusito, Rita; Vallortigara, Giorgio; Quaranta, Angelo

    2013-11-18

    Left-right asymmetries in behavior associated with asymmetries in the brain are widespread in the animal kingdom, and the hypothesis has been put forward that they may be linked to animals' social behavior. Dogs show asymmetric tail-wagging responses to different emotive stimuli-the outcome of different activation of left and right brain structures controlling tail movements to the right and left side of the body. A crucial question, however, is whether or not dogs detect this asymmetry. Here we report that dogs looking at moving video images of conspecifics exhibiting prevalent left- or right-asymmetric tail wagging showed higher cardiac activity and higher scores of anxious behavior when observing left- rather than right-biased tail wagging. The finding that dogs are sensitive to the asymmetric tail expressions of other dogs supports the hypothesis of a link between brain asymmetry and social behavior and may prove useful to canine animal welfare theory and practice.

  17. Enantioselective Total Synthesis of (+)-Psiguadial B.

    PubMed

    Chapman, Lauren M; Beck, Jordan C; Wu, Linglin; Reisman, Sarah E

    2016-08-10

    The first enantioselective total synthesis of the cytotoxic natural product (+)-psiguadial B is reported. Key features of the synthesis include (1) the enantioselective preparation of a key cyclobutane intermediate by a tandem Wolff rearrangement/asymmetric ketene addition, (2) a directed C(sp(3))-H alkenylation reaction to strategically forge the C1-C2 bond, and (3) a ring-closing metathesis to build the bridging bicyclo[4.3.1]decane terpene framework. PMID:27452034

  18. Asymmetric soft-error resistant memory

    NASA Technical Reports Server (NTRS)

    Buehler, Martin G. (Inventor); Perlman, Marvin (Inventor)

    1991-01-01

    A memory system is provided, of the type that includes an error-correcting circuit that detects and corrects, that more efficiently utilizes the capacity of a memory formed of groups of binary cells whose states can be inadvertently switched by ionizing radiation. Each memory cell has an asymmetric geometry, so that ionizing radiation causes a significantly greater probability of errors in one state than in the opposite state (e.g., an erroneous switch from '1' to '0' is far more likely than a switch from '0' to'1'. An asymmetric error correcting coding circuit can be used with the asymmetric memory cells, which requires fewer bits than an efficient symmetric error correcting code.

  19. Asymmetric Magnon Excitation by Spontaneous Toroidal Ordering

    NASA Astrophysics Data System (ADS)

    Hayami, Satoru; Kusunose, Hiroaki; Motome, Yukitoshi

    2016-05-01

    The effects of spontaneous toroidal ordering on magnetic excitation are theoretically investigated for a localized spin model that includes a staggered Dzyaloshinsky-Moriya interaction and anisotropic exchange interactions, which arise from the antisymmetric spin-orbit coupling and the multiorbital correlation effect. We show that the model exhibits a Néel-type antiferromagnetic order, which simultaneously accompanies a ferroic toroidal order. We find that the occurrence of toroidal order modulates the magnon dispersion in an asymmetric way with respect to the wave number: a toroidal dipole order on the zigzag chain leads to a band-bottom shift, while a toroidal octupole order on the honeycomb lattice gives rise to a valley splitting. These asymmetric magnon excitations could be a source of unusual magnetic responses, such as nonreciprocal magnon transport. A variety of modulations are discussed while changing the lattice and magnetic symmetries. The implications regarding candidate materials for asymmetric magnon excitations are presented.

  20. Active cavitation detection of asymmetrical inertial cavitation

    NASA Astrophysics Data System (ADS)

    Everbach, E. Carr

    2001-05-01

    The active cavitation detector (ACD) developed in Bob Apfel's laboratory has often been employed to quantify pressure thresholds for inception of symmetrical inertial cavitation of microbubbles. In the current application, however, a 30-MHz ACD interrogates individual echo-contrast agent bubbles adhering to a Mylar(TM) sheet that are driven into asymmetrical (jet-producing) collapse by a 1-MHz toneburst (>1 MPa pp). The resulting ACD output suggests that asymmetrical bubble collapse is slower than symmetrical collapse, producing less total radiated acoustic power. ACD output mixed with reference sinusoids at 30 MHz and low pass filtered yields Doppler signals that may be useful in quantifying asymmetrical collapses under biomedically relevant conditions, such as on endothelial walls.

  1. Asymmetric Membrane Osmotic Capsules for Terbutaline Sulphate

    PubMed Central

    Gobade, N. G.; Koland, Marina; Harish, K. H.

    2012-01-01

    The aim of the present study was to design an asymmetric membrane capsule, an osmotic pump-based drug delivery system of ethyl cellulose for controlled release of terbutaline sulphate. asymmetric membrane capsules contains pore-forming water soluble additive, sorbitol in different concentrations in the capsule shell membrane, which after coming in contact with water, dissolves, resulting in an in situ formation of a microporous structure. The terbutaline sulphate is a β-adrenoreceptor agonist widely used in the treatment of asthma. The oral dosage regimen of terbutaline sulphate is 5 mg twice or thrice daily, the plasma half-life is approximate 3-4 h and it produces GI irritation with extensive first pass metabolism. Hence, terbutaline sulphate was chosen as a model drug with an aim to develop controlled release system. Different formulations of ethyl cellulose were prepared by phase inversion technique using different concentrations of sorbitol as pore forming agent. It was found that the thickness of the prepared asymmetric membrane capsules was increased with increase in concentration of ethyl cellulose and pore forming agent, i.e. sorbitol. The dye release study in water and 10% sodium chloride solution indicates that, the asymmetric membrane capsules follow osmotic principle to release content. The pores formed due to sorbitol were confirmed by microscopic observation of transverse section of capsule membrane. Data of in vitro release study of terbutaline sulphate from asymmetric membrane capsules indicated that, the capsules prepared with 10% and 12.5% of ethyl cellulose and 25% of sorbitol released as much as 97.44% and 76.27% in 12 h, respectively with zero order release rate. Hence asymmetric membrane capsule of 10% ethyl cellulose and 25% of sorbitol is considered as optimum for controlled oral delivery of terbutaline sulphate. PMID:23204625

  2. Asymmetric membrane osmotic capsules for terbutaline sulphate.

    PubMed

    Gobade, N G; Koland, Marina; Harish, K H

    2012-01-01

    The aim of the present study was to design an asymmetric membrane capsule, an osmotic pump-based drug delivery system of ethyl cellulose for controlled release of terbutaline sulphate. asymmetric membrane capsules contains pore-forming water soluble additive, sorbitol in different concentrations in the capsule shell membrane, which after coming in contact with water, dissolves, resulting in an in situ formation of a microporous structure. The terbutaline sulphate is a β-adrenoreceptor agonist widely used in the treatment of asthma. The oral dosage regimen of terbutaline sulphate is 5 mg twice or thrice daily, the plasma half-life is approximate 3-4 h and it produces GI irritation with extensive first pass metabolism. Hence, terbutaline sulphate was chosen as a model drug with an aim to develop controlled release system. Different formulations of ethyl cellulose were prepared by phase inversion technique using different concentrations of sorbitol as pore forming agent. It was found that the thickness of the prepared asymmetric membrane capsules was increased with increase in concentration of ethyl cellulose and pore forming agent, i.e. sorbitol. The dye release study in water and 10% sodium chloride solution indicates that, the asymmetric membrane capsules follow osmotic principle to release content. The pores formed due to sorbitol were confirmed by microscopic observation of transverse section of capsule membrane. Data of in vitro release study of terbutaline sulphate from asymmetric membrane capsules indicated that, the capsules prepared with 10% and 12.5% of ethyl cellulose and 25% of sorbitol released as much as 97.44% and 76.27% in 12 h, respectively with zero order release rate. Hence asymmetric membrane capsule of 10% ethyl cellulose and 25% of sorbitol is considered as optimum for controlled oral delivery of terbutaline sulphate. PMID:23204625

  3. Representing Practice: Practice Models, Patterns, Bundles

    ERIC Educational Resources Information Center

    Falconer, Isobel; Finlay, Janet; Fincher, Sally

    2011-01-01

    This article critiques learning design as a representation for sharing and developing practice, based on synthesis of three projects. Starting with the findings of the Mod4L Models of Practice project, it argues that the technical origins of learning design, and the consequent focus on structure and sequence, limit its usefulness for sharing…

  4. Reconstitution of a eukaryotic replisome reveals the mechanism of asymmetric distribution of DNA polymerases

    PubMed Central

    Yurieva, Olga; O'Donnell, Mike

    2016-01-01

    ABSTRACT Eukaryotes require 3 DNA polymerases for normal replisome operations, DNA polymerases (Pol) α, delta and epsilon. Recent biochemical and structural studies support the asymmetric use of these polymerases on the leading and lagging strands. Pol epsilon interacts with the 11-subunit CMG helicase, forming a 15-protein leading strand complex that acts processively in leading strand synthesis in vitro, but Pol epsilon is inactive on the lagging strand. The opposite results are observed for Pol delta with CMG. Pol delta is highly active on the lagging strand in vitro, but has only feeble activity with CMG on the leading strand. Pol α also functions with CMG to prime both strands, and is even capable of extending both strands with CMG present. However, extensive DNA synthesis by Pol α is sharply curtailed by the presence of either Pol epsilon or Pol delta, which limits the role of the low fidelity Pol α to the initial priming of synthesis. PMID:27416113

  5. Exploring and Implementing Participatory Action Synthesis

    ERIC Educational Resources Information Center

    Wimpenny, Katherine; Savin-Baden, Maggi

    2012-01-01

    This article presents participatory action synthesis as a new approach to qualitative synthesis which may be used to facilitate the promotion and use of qualitative research for policy and practice. The authors begin by outlining different forms of qualitative research synthesis and then present participatory action synthesis, a collaborative…

  6. Asymmetric acoustic transmission in multiple frequency bands

    NASA Astrophysics Data System (ADS)

    Sun, Hong-xiang; Yuan, Shou-qi; Zhang, Shu-yi

    2015-11-01

    We report both experimentally and numerically that the multi-band device of the asymmetric acoustic transmission is realized by placing two periodic gratings with different periods on both sides of two brass plates immersed in water. The asymmetric acoustic transmission can exist in four frequency bands below 1500 kHz, which arises from the interaction between various diffractions from the two gratings and Lamb modes in the brass plates immersed in water. The results indicate that the device has the advantages of multiple band, broader bandwidth, and simpler structure. Our finding should have great potential applications in ultrasonic devices.

  7. Asymmetric counter propagation of domain walls

    NASA Astrophysics Data System (ADS)

    Andrade-Silva, I.; Clerc, M. G.; Odent, V.

    2016-07-01

    Far from equilibrium systems show different states and domain walls between them. These walls, depending on the type of connected equilibria, exhibit a rich spatiotemporal dynamics. Here, we investigate the asymmetrical counter propagation of domain walls in an in-plane-switching cell filled with a nematic liquid crystal. Experimentally, we characterize the shape and speed of the domain walls. Based on the molecular orientation, we infer that the counter propagative walls have different elastic deformations. These deformations are responsible of the asymmetric counter propagating fronts. Theoretically, based on symmetry arguments, we propose a simple bistable model under the influence of a nonlinear gradient, which qualitatively describes the observed dynamics.

  8. Asymmetric and Unilateral Hearing Loss in Children

    PubMed Central

    Vila, Peter; Lieu, Judith E. C.

    2015-01-01

    Asymmetric and unilateral hearing losses in children have traditionally been underappreciated, but health care practitioners are now beginning to understand their effect on development and the underlying pathophysiologic mechanisms. The common wisdom among medical and educational professionals has been that at least one normal hearing or near-normal hearing ear was sufficient for typical speech and language development in children. The objective of this review is to illustrate to the non-otolaryngologist the consequences of asymmetric and unilateral hearing loss in children on developmental and educational outcomes. In the process, etiology, detection, and management are discussed. Lastly, implications for further research are considered. PMID:26004144

  9. Asymmetric acoustic transmission in multiple frequency bands

    SciTech Connect

    Sun, Hong-xiang; Yuan, Shou-qi; Zhang, Shu-yi

    2015-11-23

    We report both experimentally and numerically that the multi-band device of the asymmetric acoustic transmission is realized by placing two periodic gratings with different periods on both sides of two brass plates immersed in water. The asymmetric acoustic transmission can exist in four frequency bands below 1500 kHz, which arises from the interaction between various diffractions from the two gratings and Lamb modes in the brass plates immersed in water. The results indicate that the device has the advantages of multiple band, broader bandwidth, and simpler structure. Our finding should have great potential applications in ultrasonic devices.

  10. Asymmetric multiscale behavior in PM2.5 time series: Based on asymmetric MS-DFA

    NASA Astrophysics Data System (ADS)

    Zhang, Chen; Ni, Zhiwei; Ni, Liping

    2016-11-01

    Particulate matter with an aerodynamic diameter of 2.5 mm or less (PM2.5) is one of the most serious air pollution, considered most harmful for people by World Health Organisation. In this paper, we utilized the asymmetric multiscale detrended fluctuation analysis (A-MSDFA) method to explore the existence of asymmetric correlation properties for PM2.5 daily average concentration in two USA cities (Fresno and Los Angeles) and two Chinese cities (Hong Kong and Shanghai), and to assess the properties of these asymmetric correlations. The results show the existences of asymmetric correlations, and the degree of asymmetric for two USA cities is stronger than that of two Chinese cities. Further, most of the local exponent β(n) are smaller than 0.5, which indicates the existence of anti-persistent long-range correlation for PM2.5 time series in four cities. In addition, we reanalyze the asymmetric correlation by the A-MSDFA method with secant rolling windows of different sizes, which can investigate dynamic changes in the multiscale correlation for PM2.5 time series with changing window size. Whatever window sizes, the correlations are asymmetric and display smaller asymmetries at small scales and larger asymmetries at large scales. Moreover, the asymmetries become increasingly weaker with the increase of window sizes.

  11. Effectiveness of the Picture Exchange Communication System as a Functional Communication Intervention for Individuals with Autism Spectrum Disorders: A Practice-Based Research Synthesis

    ERIC Educational Resources Information Center

    Tien, Kai-Chien

    2008-01-01

    This research synthesis verifies the effectiveness of the Picture Exchange Communication System (PECS) for improving the functional communication skills of individuals with autism spectrum disorders (ASD). The research synthesis was focused on the degree to which variations in PECS training are associated with variations in functional…

  12. Catalytic enantioselective synthesis of vicinal dialkyl arrays.

    PubMed

    van Zijl, Anthoni W; Szymanski, Wiktor; López, Ferrnando; Minnaard, Adriaan J; Feringa, Ben L

    2008-09-19

    With a consecutive "asymmetric allylic alkylation (AAA)/cross-metathesis (CM)/conjugate addition (CA)" protocol it is possible to synthesize either stereoisomer of compounds containing a vicinal dialkyl array with excellent stereoselectivity. The versatility of this protocol in natural product synthesis is demonstrated in the preparation of the ant pheromones faranal and lasiol. PMID:18683977

  13. Stereoselective Synthesis of Quaternary Proline Analogues

    PubMed Central

    Calaza, M. Isabel

    2009-01-01

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

  14. Total synthesis of aeruginosin 98B.

    PubMed

    Trost, Barry M; Kaneko, Toshiyuki; Andersen, Neil G; Tappertzhofen, Christoph; Fahr, Bruce

    2012-11-21

    The first total synthesis of aeruginosin 98B was accomplished. The key step is a highly diastereoselective Pd-catalyzed intramolecular asymmetric allylic alkylation reaction of a diastereomeric mixture of allylic carbonates that is enabled by the use of racemic phosphine ligand L1.

  15. Total Synthesis of (-)-Daphenylline.

    PubMed

    Yamada, Ryosuke; Adachi, Yohei; Yokoshima, Satoshi; Fukuyama, Tohru

    2016-05-10

    Total synthesis of (-)-daphenylline, a hexacyclic Daphniphyllum alkaloid, was achieved. Construction of the tricyclic DEF ring system was initiated by asymmetric Negishi coupling followed by an intramolecular Friedel-Crafts reaction. Installation of a side chain onto the tricyclic core was carried out through Sonogashira coupling, stereocontrolled Claisen rearrangement by taking advantage of the characteristic conformation of the tricyclic DEF core, and the stereoselective alkylation of a lactone. After the introduction of a glycine unit, the ABC ring system was stereoselectively constructed through intramolecular cycloaddition of the cyclic azomethine ylide. PMID:27062676

  16. Asymmetric Alternating Copolymerization of Meso-epoxides and Cyclic Anhydrides: Efficient Access to Enantiopure Polyesters.

    PubMed

    Li, Jie; Liu, Ye; Ren, Wei-Min; Lu, Xiao-Bing

    2016-09-14

    Synthesis of stereoregular polyesters with main-chain chirality was achieved for the first time by the asymmetric copolymerization of meso-epoxides and cyclic anhydrides using catalyst systems based on enantiopure bimetallic complexes. The combination of the biphenol-linked dinuclear aluminum complex with tert-butyl groups in the phenolate ortho-positions and a nucleophilic co-catalyst was found to be more efficient in catalyzing this asymmetric copolymerization, affording enantiomerically enriched polyesters (up to 91% ee) with completely alternating structure and narrow molecular weight distribution. It was discovered that the isotactic-enriched poly(cyclopentene phthalate) is a typical semicrystalline material with a melting endothermic peak at 221 °C. This study is expected to provide a promising route to prepare various stereoregular polyesters having a wide variety of physical properties and degradability. PMID:27562940

  17. Catalytic asymmetric carbon-carbon bond formation via allylic alkylations with organolithium compounds

    NASA Astrophysics Data System (ADS)

    Pérez, Manuel; Fañanás-Mastral, Martín; Bos, Pieter H.; Rudolph, Alena; Harutyunyan, Syuzanna R.; Feringa, Ben L.

    2011-05-01

    Carbon-carbon bond formation is the basis for the biogenesis of nature's essential molecules. Consequently, it lies at the heart of the chemical sciences. Chiral catalysts have been developed for asymmetric C-C bond formation to yield single enantiomers from several organometallic reagents. Remarkably, for extremely reactive organolithium compounds, which are among the most broadly used reagents in chemical synthesis, a general catalytic methodology for enantioselective C-C formation has proven elusive, until now. Here, we report a copper-based chiral catalytic system that allows carbon-carbon bond formation via allylic alkylation with alkyllithium reagents, with extremely high enantioselectivities and able to tolerate several functional groups. We have found that both the solvent used and the structure of the active chiral catalyst are the most critical factors in achieving successful asymmetric catalysis with alkyllithium reagents. The active form of the chiral catalyst has been identified through spectroscopic studies as a diphosphine copper monoalkyl species.

  18. Developments in asymmetric catalysis by metal complexes of chiral chelating nitrogen-donor ligands.

    PubMed

    Caputo, Christine A; Jones, Nathan D

    2007-11-01

    In part because of their straightforward and modular syntheses from readily available enantiopure starting materials, and their capacity to bind a wide variety of transition metals, chiral, chelating nitrogen-donor ligands have played a prominent role in asymmetric catalysis. A large number of highly enantioselective transformations rely upon these ligands whose reported classes are built around amine, imine, pyrrole, pyrrolidine, oxazoline and oxazolidine donor groups, among others. In this Perspective, we examine a selection of transformative developments in asymmetric catalysis by metal complexes of bi- and polydentate members of this ligand family. We describe approaches to ligand design and synthesis, structure and bonding in coordination complexes, and limitations and future challenges. PMID:17940641

  19. Mach bands change asymmetrically during solar eclipses.

    PubMed

    Ross, John; Diamond, Mark R; Badcock, David R

    2003-01-01

    Observations made during two partial eclipses of the Sun show that the Mach bands on shadows cast by the Sun disappear and reappear asymmetrically as an eclipse progresses. These changes can be explained as due to changes in the shape of the penumbras of shadows as the visible portion of the Sun forms crescents of different orientation. PMID:12892435

  20. Mach bands change asymmetrically during solar eclipses.

    PubMed

    Ross, John; Diamond, Mark R; Badcock, David R

    2003-01-01

    Observations made during two partial eclipses of the Sun show that the Mach bands on shadows cast by the Sun disappear and reappear asymmetrically as an eclipse progresses. These changes can be explained as due to changes in the shape of the penumbras of shadows as the visible portion of the Sun forms crescents of different orientation.