Tetrahedron Asymmetry

Editorial board ()
Publication date: 15 August 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 8
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Graphical contents list ()
Publication date: 15 August 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 8
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Contributors to this issue ()
Publication date: 15 August 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 8
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Applications of sharpless asymmetric dihydroxylation in the total synthesis of natural products ()
Publication date: 15 August 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 8 Author(s): Majid M. Heravi, Vahideh Zadsirjan, Maryam Esfandyari, Tahmineh Baie Lashaki Sharpless asymmetric dihydroxylation involves the reaction of an alkene with osmium tetroxide in the presence of a chiral quinine ligand to form an optically active vicinal diol. This reaction was primarily developed by Sharpless based on the already known racemic Upjohn dihydroxylation. The chiral diols obtained by Sharpless asymmetric dihydroxylation are important intermediates in organic synthesis. Herein, we emphasise the applications of Sharpless asymmetric dihydroxylation in the total synthesis of natural products. Graphical abstract image
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Asymmetric synthesis of spirocyclohexanone-pyrrolidine via AgI-catalysed asymmetric 1,3-dipolar cycloaddition of azomethine ylides ()
Publication date: 15 August 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 8 Author(s): Bilel Bdiri, Chuan Li, Zhi-Ming Zhou Cinchonine was effectively used in an AgOAc-catalysed asymmetric 1,3-dipolar cycloaddition of azomethine ylides with 2,6-bis(arylmethylidene) cyclohexanones, affording spiropyrrolidine derivatives with excellent yields (up to 99%), diastereoselectivities (up to 96:04 dr), and enantioselectivities (up to 99% ee). Graphical abstract image
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Stereoselective allylation reactions of acyclic and chiral α-amino-β-hydroxy aldehydes ()
Publication date: 15 August 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 8 Author(s): In-Soo Myeong, Yong-Taek Lee, Sang-Hyun Lee, Changyoung Jung, Jin-Seok Kim, Seok-Hwi Park, Jihun Kang, Seung-Jong Lee, In-Hae Ye, Won-Hun Ham Stereoselective allylation reactions of acyclic and chiral α-amino-β-hydroxy aldehydes affording chiral β-amino-α,γ-diols are described. Several Lewis acids (BF3·OEt2, SnCl4, TiCl4, ZnCl2, and MgBr2·OEt2) were employed to mediate the allylation reactions. The reactions of anti-α-NHCbz-β-OTBS substrates mediated by SnCl4 afforded syn-selective products. The same reaction conditions also gave satisfactory results for the reactions of syn-α-NHCbz-β-OTBS substrates. The mechanism involves α-chelation between the amido group and aldehyde oxygen. Graphical abstract image
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Sulfated cyclodextrins as water-soluble chiral NMR solvating agents for cationic compounds ()
Publication date: 15 August 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 8 Author(s): Brielle E. Dalvano, Thomas J. Wenzel The utility of a series of sulfated cyclodextrins as water-soluble chiral NMR solvating agents for cationic substrates is described. Sulfated α-, β- and γ-cyclodextrin with degrees of substitution of 12, 13 and 14, respectively, a sulfated β-cyclodextrin with a degree of substitution of 9 and a sulfobutyl ether β-cyclodextrin with a degree of substitution of 6.3 are examined. Results with 33 water-soluble cationic organic salts are reported. Chiral differentiation with the sulfated cyclodextrins is compared to prior results obtained with anionic carboxymethylated and phosphated cyclodextrins. The highly sulfated cyclodextrins are often more effective at causing enantiomeric differentiation in 1H NMR spectra than the sulfobutyl ether, carboxymethylated and phosphated cyclodextrins, and are recommended as the first choice of a chiral solvating agent for the analysis of chiral cationic organic salts in aqueous solution. Graphical abstract image
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Ammonium chiral borate salt catalyzed asymmetric Friedel-Crafts alkylation of indoles with α,β-disubstituted enals ()
Publication date: 15 August 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 8 Author(s): Mitsuhiro Ueda, Yoshitaka Yagyu, Ilhyong Ryu In the presence of a catalytic amount of ammonium chiral borate salt, asymmetric Friedel-Crafts alkylation of indoles with α,β-disubstituted enals proceeded to give the corresponding 1,4-addition products with moderate enantioselectivities. Graphical abstract image
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Comparison of resolution methods for racemic 8-(phenylsulfinyl)-1-naphthoic acid ()
Publication date: 15 August 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 8 Author(s): Anikó Nemes, Dénes Szabó, József Rábai Despite of the fact that resolution is an extremely important process in the pharmaceutical and agrochemical industries, the development of the separation of enantiomers is still based on trial-and-error experiments. In order to compare the different procedures, the resolution of 8-(phenylsulfinyl)-1-naphthoic acid 1 was carried out by chiral organic bases using heat facilitated diastereomeric crystallization, enantioselective liquid–liquid extraction and chiroselective transport. The results give valuable information about the interactions in the racemate/resolving agent/solvent system, which helps with the understanding and development of resolution processes. Diastereomeric crystallization with brucine as a resolving agent afforded enantiomerically pure (−)-1. Graphical abstract image
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Enantioselective total synthesis of a natural hydrocarbazolone alkaloid, identification of its stereochemistry, and revision of its spectroscopic data ()
Publication date: 15 August 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 8 Author(s): Siyuan Wu, Shinji Harada, Takahiro Morikawa, Atsushi Nishida The natural hydrocarbazolone alkaloid (1R,2R,3R)-3-hydroxy-1,2-dimethyl-1,2,3,9-tetrahydro-4H-carbazol-4-one has been synthesized in a catalytic and enantioselective manner. A key hydrocarbazole derivative was constructed by the holmium-catalyzed Diels-Alder reaction of (silyloxyvinyl)indole as the diene. Total synthesis of the natural product clarified the ambiguity in the spectroscopic data reported for natural products. Graphical abstract image
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Preparation of α-galactooligoglycosides by cell walls from Cryptococcus laurentii using a novel α-galactosyl donor ()
Publication date: 15 August 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 8 Author(s): Vladimír Mastihuba, Mária Mastihubová, Miroslav Belák, Jana Dudíková, Elena Karnišová Potocká, Ladislav Petruš The cell walls of an acapsular strain of the yeast Cryptococcus laurentii catalyze the regioselective formation of α-galactooligosaccharides through self-condensation of 4-nitrophenyl α-d-galactopyranoside and of a novel activated α-galactosyl donor 2,2,2-trifluoroethyl α-d-galactopyranoside. The latter substance can be easily prepared by several methods and is highly soluble in water and therefore can be used in higher initial concentrations suppressing secondary product hydrolysis. The preparative reaction catalyzed by cell walls provided 17.4% and 2% of corresponding 2,2,2-trifluoroethyl galactobioside and galactotrioside, respectively, while the reaction with 4-nitrophenyl α-d-galactopyranoside provided the corresponding 4-nitrophenyl galactobioside and galactotrioside in 6.6 and 2.5% yields, respectively. The reactions proceeded with strict α-(1→6)-regioselectivity. Graphical abstract image
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Stereochemistry abstracts ()
Publication date: 15 August 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 8
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Tetrahedron: Asymmetry Reports ()
Publication date: 15 August 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 8
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Cumulative author index ()
Publication date: 15 August 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 8
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Solid state conformations of α,β-unsaturated hydroxamates derived from the ‘chiral Weinreb amide’ auxiliary (S)-N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine ()
Publication date: Available online 14 August 2017 Source:Tetrahedron: Asymmetry Author(s): Stephen G. Davies, James A. Lee, Paul M. Roberts, James E. Thomson, Jingda Yin α,β-Unsaturated hydroxamates derived from the ‘chiral Weinreb amide’ auxiliary (S)-N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine consistently adopt a defined conformation and undergo highly diastereoselective conjugate addition reactions with lithium amide reagents. The configuration of the N-1-(1′-naphthyl)ethyl group dictates the position of the O-tert-butyl group and also the configuration adopted by the pyramidal nitrogen atom via a ‘chiral relay’ effect. Conjugate addition of lithium amide reagents to these substrates proceeds on the face opposite to both the O-tert-butyl group and nitrogen lone-pair with high levels of diastereoselectivity. Graphical abstract image
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Traceless chirality transfer from a norbornene β-amino acid to pyrimido[2,1-a]isoindole enantiomers ()
Publication date: Available online 11 August 2017 Source:Tetrahedron: Asymmetry Author(s): Ferenc Miklós, Kristóf Bozó, Zsolt Galla, Matti Haukka, Ferenc Fülöp The synthesis of two enantiomeric pairs of pyrimidoisoindoles 9a, 9b and 10a, 10b is reported. During a domino ring-closure reaction, followed by cycloreversion, the chirality of diendo-(−)-(1R,2S,3R,4S)-3-aminobicyclo[2.2.1]hept-5-ene-2-carboxamide [(−)-1] was successfully transfered to heterocycles (+)-9a, (+)-10a, (−)-9b, (−)-10b and (−)-10c. Graphical abstract image
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Best practice and pitfalls in absolute structure determination ()
Publication date: Available online 8 August 2017 Source:Tetrahedron: Asymmetry Author(s): Anthony Linden In routine small-molecule single crystal structure determination, accurate absolute structure determination has sometimes been challenging. Developments in diffractometers, X-ray sources, detectors and software, along with new concepts for the elucidation of the absolute structure have seen the greatest advances in recent times. Nonetheless, determining the absolute structure of a crystal, particularly when only light atoms are present, requires some thought in the planning of the experiment in order to obtain the best possible data and some care in modelling the structure and interpreting the results so as not to draw incorrect or unsupported conclusions. Some practical recommendations for best practice and how to avoid pitfalls and misinterpretations are presented as a guide, particularly for those new to the field of crystal structure analysis. Graphical abstract image
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Editorial board ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7
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Graphical contents list ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7
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Contributors to this issue ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7
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Advances on asymmetric organocatalytic 1,4-conjugate addition reactions in aqueous and semi-aqueous media ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7 Author(s): Anirban Mondal, Sudipto Bhowmick, Ayndrila Ghosh, Tanmoy Chanda, Kartick C. Bhowmick Asymmetric Michael addition reactions or 1,4-conjugate addition reactions are considered to be the fundamental C–C bond-forming reaction for the construction of chiral β-nitro, β-carbonyl and several other important structural motifs in organic synthesis. After the development of many chiral metal complexes as catalysts, a tremendous growth in the design and applications of variety of new chiral organocatalysts for asymmetric 1,4-conjugate addition reactions has been witnessed over the last two decades. Initially, asymmetric organocatalysis has been performed in organic solvents, but gradually performing the same catalysis in aqueous and semi-aqueous media became a necessity due to environmental aspects as well as to achieve better reactivity and selectivity. The structural and functional diversity of the chiral organocatalysts derived from natural and synthetic sources utilized differently the water either as the sole solvent, co-solvent or additive for optimising their best performances. In the present review, we discuss a detailed and comprehensive report on the advancement in the field of asymmetric organocatalytic 1,4-conjugate addition reactions in aqueous and semi-aqueous media. Graphical abstract image
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Recent advances in the enantioselective 1,3-dipolar cycloaddition of azomethine ylides and dipolarophiles ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7 Author(s): Bilel Bdiri, Boa-Jing Zhao, Zhi-Ming Zhou The synthesis of diastereo- and enantiopure heterocyclic molecules via catalytic asymmetric 1,3-dipolar cycloaddition reaction between azomethine ylides, generated in situ from α-amino acid-derived iminoesters and dipolarophiles is considered one of the most powerful and versatile techniques. In this review, we make a detailed overview of the latest developments in this area since 2014 and highlight the recent improvements in the structural scope of dipolarophiles, azomethine ylide precursors, and chiral ligands. Graphical abstract image
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Isoskeletomerism as an intermediate concept for mediating between stereoisomerism and isomerism. A remedy for conceptual defects of organic chemistry ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7 Author(s): Shinsaku Fujita After isoskeletomerism is introduced as an intermediate concept for mediating between stereoisomerism and isomerism, so-called ‘constitutional isomerism’ is critically discussed as one of the roots of confusion in organic chemistry. The convention that isomerism is subdivided into stereoisomerism and ‘constitutional isomerism’ is concluded to be misleading, because these concepts are conceptually distinct from a viewpoint of the concepts of equivalence relationships and equivalence classes. The indifference toward these concepts is one of the conceptual defects of organic chemistry. A new flowchart for judging enantiomerism, RS-stereoisomerism, stereoisomerism, isoskeletomerism, and isomerism is discussed to generate an isomer-classification diagram, where RS-stereoisomerism and isoskeletomerism are contained as new matters for remedying the conceptual defects. Skeletons are derived from basic skeletons by three operations (the bond operation, the replacement operation, and the substitutive operation), and they are used to examine the action of isoskeletomeric relationships. Equivalent molecular entities under an isoskeletomeric relationship are collected to give a set of isoskeletomers, which is concluded to be an equivalence class. The confusion caused by so-called ‘constitutional isomerism’ and its subcategories (‘skeletal isomerism’, ‘positional isomerism’, and so on) is critically discussed from the viewpoint of isoskeletomerism as a missing link. The double-entendre of the term constitution is examined when applied to both a 3D entity (a set of stereoisomers) and a 2D entity (a graph). Taxonomy of organic compounds and rational formulas, nomenclature of organic compounds, and combinatorial enumeration of chemical compounds are discussed from the viewpoint of isoskeletomerism. Graphical abstract image
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Chloramphenicol base chemistry. Part 11:1 chloramphenicol base-derived thiourea-catalyzed enantioselective Michael addition of malononitrile to α,β-unsaturated ketones ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7 Author(s): Linjie Yan, Haifeng Wang, Fangjun Xiong, Yuan Tao, Yan Wu, Fener Chen The first chloramphenicol base-derived thiourea-catalyzed enantioselective Michael addition of malononitrile to α,β-unsaturated ketones is reported. The Michael adducts were obtained in good to excellent yields (up to 98% yield) and enantioselectivities (up to 94% ee). This reaction has a broad substrate scope to various α,β-unsaturated ketones. With this in mind, this methodology was successfully applied to the synthesis of a chiral piperidone, an advanced building block for dihydropyridinone P2X7 receptor antagonists. Graphical abstract image
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A class of α-amino acids-derived multifunctional amidophosphane precatalysts: application to the highly enantio- and diastereoselective silver(I)-catalyzed 1,3-dipolar cycloaddition reaction ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7 Author(s): Yihui Hou, Zhipeng Zhou, Pingle Liu, Jiankang Wang, Qinglin Hou, Pushan Wen, Haifei Wang A class of multifunctional amidophosphanes derived from chiral α-amino acids have been developed with two amide bonds, a tertiary amine and a phosphine. In combination with Ag(I) salts, these amidophosphanes have been demonstrated as highly efficient multifunctional catalysts in the asymmetric 1,3-dipolar cycloaddition of azomethine ylides as well as the three-component reaction of the α-iminoesters in situ generated. Under optimal conditions, highly functionalized endo-8 pyrrolidines were obtained with good to excellent yields (up to 99% yield) and enantioselectivities (up to 98% ee). Graphical abstract image
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Extractive biocatalysis in the asymmetric reduction of α-alkyl, β-aryl enones by Baker’s yeast ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7 Author(s): Rafaela M. Silva, Laura T. Okano, J. Augusto R. Rodrigues, Giuliano C. Clososki We prepared various chiral α-alkyl, β-aryl ketones with good to excellent enantiomeric excess through the Baker’s yeast asymmetric double-bond reduction of the corresponding α,β-unsaturated substrates adsorbed onto the resin Amberlite XAD-7. This methodology was compatible with substrates bearing both electron-donating and withdrawing groups attached to the aromatic ring. Elongation of the α-alkyl substituent of the starting material strongly affected the reactivity and enantioselectivity of the reaction. Graphical abstract image
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3-Menthoxybiphenyl-4-carboxylic acid: a versatile resolving agent and reagent for determination of the absolute configuration of benzylic alcohols ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7 Author(s): Shunsuke Kuwahara, Nobuyoshi Tasaki, Yuri Suzuki, Mizuki Nakagawa, Mari Ikeda, Yoichi Habata A versatile reagent for the chiral resolution and determination of the absolute configuration of benzylic alcohols, (−)-3-menthoxybiphenyl-4-carboxylic acid, is reported. (−)-3-menthoxybiphenyl-4-carboxylic acid was condensed with racemic benzylic alcohols to yield diastereomeric 3-menthoxybiphenyl-4-carboxylic esters, which were separated by reversed-phase HPLC. The absolute configurations of the 3-menthoxybiphenyl-4-carboxylic esters were unambiguously determined by exciton-coupled circular dichroism. Hydrolysis of the 3-menthoxybiphenyl-4-carboxylic esters yielded enantiopure alcohols, and their absolute configurations were simultaneously determined. Graphical abstract image
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The synthesis of chiral tridentate ligands from l-proline and their application in the copper(II)-catalyzed enantioselective Henry reaction ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7 Author(s): Daqian Xu, Qiangsheng Sun, Zhengjun Quan, Wei Sun, Xicun Wang A series of chiral tridentate ligands derived from readily available enantiopure l-proline were designed and synthesized. The ligands together with Cu(OAc)2 were successfully used in asymmetric Henry reactions. Various structurally divergent aldehydes and nitromethane were converted into versatile β-nitro alcohols in MeOH at room temperature with very good yields (up to 85%) and enantioselectivities (up to 86%). Graphical abstract image
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Chemo-enzymatic synthesis of (R)-5-hydroxymethyl-2-isopropyl-5-methylcyclopent-1-en-1-yl trifluoromethylsulfonate, a potential chiral building block for multicyclic terpenoids ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7 Author(s): Kazuaki Kuwata, Kengo Hanaya, Takeshi Sugai, Mitsuru Shoji The chemo-enzymatic synthesis of (R)-5-hydroxymethyl-2-isopropyl-5-methylcyclopent-1-en-1-yl trifluoromethylsulfonate, a potential chiral building block for polycyclic terpenoids containing a five–membered ring having isopropyl and angular methyl substituents, such as erinacin A and dolatriol, was achieved over 11 steps from ethyl 2-oxocyclopentane-1-carboxylate. The key synthetic precursor for this triflate was ethyl (1S,2R)-2-hydroxycyclopentanecarboxylate (>99% ee), which was prepared by a lipase-catalyzed enantioselective hydrolysis of the corresponding racemic acetate. The antipodal (S)-triflate is expected to be the synthetic intermediate for another group of terpenoids involving hamigeran B and stolonidiol. Enantiomerically pure (1R,2S)-hydroxyester (>99% ee) was prepared in high yield using the asymmetric reduction of the oxoester with commercially available carbonyl reductase, “Chiralscreen® OH”-E001. Graphical abstract image
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Catalytic asymmetric syntheses of (−)-oudemanisin A and its diastereomer ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7 Author(s): Yun Zhou, Qinghua Bian, Pengfei Yang, Lifeng Wang, Shuoning Li, Xiao Sun, Mingan Wang, Min Wang, Jiangchun Zhong The first asymmetric catalytic synthesis of (−)-oudemanisin A 1a and its diastereomer 1b has been achieved. The key steps of our strategy involved the asymmetric alkynylation of an unsaturated aliphatic aldehyde catalyzed by Trost’s ProPhenol ligand, chemoselective oxidation of the olefinic diol, base-induced ring opening of the lactone, and acylation–alkylation of the ester. Graphical abstract image
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Catalytic asymmetric synthesis of β-triazolyl amino alcohols by asymmetric transfer hydrogenation of α-triazolyl amino alkanones ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7 Author(s): Vijyesh K. Vyas, Bhalchandra M. Bhanage The synthesis of optically active β-triazolyl amino alcohols was carried out via ruthenium catalyzed asymmetric transfer hydrogenation of α-triazolyl amino alkanones. This reaction proceeds under mild reaction conditions with up to 99% yield and 99.9% enantiomeric excess (ee). This protocol was applied to the synthesis of an enantiopure antitubercular agent and its arylated product with retention in enantiomeric purity. The absolute configuration at the stereogenic center of the chiral product as found to be (S). Graphical abstract image
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An efficient synthesis of the opioid analgesic (R)-phenampromide via an aziridinium ion ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7 Author(s): Mohammad Mujahid, Prashant Mujumdar, Murugesan Sasikumar, Shirish P. Deshmukh, Murugan Muthukrishnan A simple and efficient synthesis of the opioid analgesic agent (R)-phenampromide with high enantiopurity (>99% ee) via the formation of an aziridinium ion as a key step using commercially available starting material is described. Graphical abstract image
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Stereochemistry abstracts ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7
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Tetrahedron: Asymmetry Reports ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7
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Cumulative author index ()
Publication date: 15 July 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 7
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Editorial board ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6
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Graphical contents list ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6
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Contributors to this issue ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6
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Asymmetric biosynthesis of intermediates of anti-HIV drugs ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6 Author(s): Yiyuan Wang, Yingxiu Cao, Yuanxiu Li, Jiayu Jin, Jinliang Li, Hao Song Human immunodeficiency virus (HIV) infection is the fifth most common cause of death and many new HIV infections occur every year. The prevalence of HIV also seriously affects the quality of a patient’s life. More than forty anti-HIV drugs have been put into clinical uses, many of which are chiral molecules with multiple stereogenic centers, for example abacavir, lamivudine, zidovudine, stavudine, tenofovir, atazanavir. However, the chemical synthesis of these chiral intermediates have the disadvantages of low enantiomeric purity and complex synthetic steps. The benefits of asymmetric biosynthesis of chiral drugs include high enantiomeric excess (e.e.), good product selectivity, mild reaction conditions, and less side effects. The biosynthesis of the chiral intermediates of these anti-HIV drugs is thus particularly important. Herein, we review the different sources of enzymes and microbial cells for the asymmetric biosynthesis of the above chiral anti-HIV drug intermediates. We also review recent biotechnology progress in engineering these enzymes and microbial cells with improved biocatalytic activities, including enzyme and cell immobilization, surface display of enzymes, and directed evolution of enzymes. These biotechnology processes enable the efficient biosynthesis of these chiral intermediates, facilitating the industrial production of anti-HIV drugs with reduced costs. Graphical abstract image
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Synthesis of the enantiomers of (3Z,9Z)-cis-6,7-epoxy-3,9-octadecadiene, one of the major components of the sex pheromone of Ectropis oblique Prout ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6 Author(s): Jie Yu, Feng Guo, Yun-Qiu Yang, Hui-Hui Gao, Ru-Yan Hou, Xiao-Chun Wan Both enantiomers of (3Z,9Z)-cis-6,7-epoxy-3,9-octadecadiene, one of which is the major component of the sex pheromone of Ectropis oblique Prout, were synthesized in 23% overall yield for the (−)-(6S,7R)-enantiomer and 18% yield for the (+)-(6R,7S)-isomer. This protocol uses a sequential regioselective ring-opening strategy and provides a convenient and reliable access to other structurally related insect sex pheromones. Preliminary biological studies revealed that (−)-(6S,7R)-2a was roughly as active as the natural pheromone, while racemic (±)-2 was less bioactive and (+)-2b was much less bioactive. Graphical abstract image
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2-Cyano-2-indolylpropanoic acid as a chiral derivatizing agent for the absolute configuration assignment of secondary alcohols and primary amines by 1H NMR and VCD ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6 Author(s): Claudia I. Bautista-Hernández, Nayely Trejo-Carbajal, Erick A. Zúñiga-Estrada, Alberto Aristeo-Dominguez, Myriam Meléndez-Rodríguez, Oscar R. Suárez-Castillo, Maricruz Sánchez-Zavala, Julián Cruz-Borbolla, Martha S. Morales-Ríos, Pedro Joseph-Nathan A convenient approach for the absolute configuration assignment of secondary alcohols in the (8R,1′R,2′S,5′R)-15,25, (8S,1′R,2′S,5′R)-15,25, (8R,1′R)-21–24, and (8S,1′R)-21–24 ester series, and of primary amines in the (8R,1′R)-32–37 and (8S,1′R)-32–37 amide series, by means of 1H NMR and VCD spectroscopy, using 2-cyano-2-indolylpropanoic acid as a chiral derivatizing agent is presented. DFT calculations were carried out to demonstrate the anisotropic effect of the indole skeleton on the chiral alcohol or the amine fragment. Vibrational circular dichroism (VCD) measurements of the above series indicated a VCD bisignated couplet resulting from the interaction of the ester carbonyl group and the CN group. The absolute configuration assignments were further tested by X-ray diffraction analysis. Graphical abstract image
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Synthesis of [2.2]paracyclophane-based bidentate oxazoline–carbene ligands for the asymmetric 1,2-silylation of N-tosylaldimines ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6 Author(s): Xichao Wang, Zhen Chen, Wenzeng Duan, Chun Song, Yudao Ma A series of novel oxazoline-substituted imidazolium salts with planar and central chirality has been successfully synthesized and applied to copper-catalyzed enantioselective 1,2-silylation of N-tosylaldimines. The oxazoline–carbene copper complex generated in situ by the reaction of the oxazoline-substituted imidazolium and Cu2O demonstrated an exceptionally high catalytic activity in the asymmetric 1,2-silylation of N-tosylaldimines, affording chiral α-amino silanes with excellent yields and enantioselectivities. Graphical abstract image
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Copper(II) complexes of 2-(pyridine-2-yl)imidazolidine-4-thione derivatives for asymmetric Henry reactions ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6 Author(s): Gabriela Nováková, Pavel Drabina, Jan Svoboda, Miloš Sedlák The preparation of a new series of 2-(pyridine-2-yl)imidazolidine-4-thione derivatives is described. Their corresponding copper(II) complexes were found to be highly enantioselective catalysts for asymmetric Henry reactions (up to 98% ee). Immobilization of these complexes by anchoring onto Merrifield™ resin with respect to their use as recyclable catalysts was subsequently performed. The heterogeneous catalysts prepared in this way were tested in the asymmetric Henry reactions and showed high catalytic activity; they can be easily recycled, although their enantioselectivities were only moderate (∼50% ee). Graphical abstract image
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A convenient stereoselective synthesis of 5-hydroxy-3-oxoesters and 3-hydroxy-5-oxoesters ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6 Author(s): Anna Żądło-Dobrowolska, Joerg H. Schrittwieser, Barbara Grischek, Dominik Koszelewski, Wolfgang Kroutil, Ryszard Ostaszewski A biocatalytic approach was employed for the asymmetric reduction of sterically demanding ketones to prepare 3-hydroxy-5-oxo-5-phenylpentanoates and 5-hydroxy-3-oxo-5-phenylpentanoates. Screening a collection of microorganisms led to the identification of stereocomplementary microbial strains that provide access to both enantiomers of 3-hydroxy-5-oxo-5-phenylpentanoates and 5-hydroxy-3-oxo-5-phenylpentanoates with high enantiomeric excess (up to 99% ee). Moreover, the application of Saccharomyces cerevisiae gave two diastereomers of 3,5-dihydroxy-5-phenylpentanoates with high enantiomeric excess (up to 99% ee). The applicability of the identified strains was demonstrated by transforming the obtained dihydroxy ester into the chemically valuable lactone (4S,6R)-tetrahydro-4-hydroxy-6-phenyl-pyran-2-one. Graphical abstract image
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Stereoselective Michael-alkylation and Michael-oxidation reactions of chiral 1,3-dioxolanones ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6 Author(s): Hao-Chun Liao, Kuan-Jen Yao, Yi-Chou Tsai, Biing-Jiun Uang A highly diastereoselective Michael-alkylation/oxidation methodology has been developed for the synthesis of optically active α-hydroxy-1,5-diester subunits. Inverse stereochemistry at the C2′ position could be achieved by using a Michael acceptor equipped with a suitable group followed by a highly stereoselective protonation. This methodology has been applied to the enantioselective synthesis of the upper fragment of (+)-retusine. Graphical abstract image
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Enzyme mediated kinetic resolution of δ-hydroxy-α,β-unsaturated esters as a route to optically active δ-lactones ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6 Author(s): Dominik Koszelewski, Daniel Paprocki, Anna Brodzka, Ryszard Ostaszewski A novel synthetic route to optically active saturated and unsaturated δ-lactones based on enzymatic kinetic resolution and ring-closing metathesis reactions has been proposed. The influence of temperature, co-solvent, organic additives and the substrate structure on the catalytic behavior of selected hydrolases was studied. The substantial impact of the organic co-solvent and surfactant type on the enzymatic activity and enantioselectivity was observed providing enantiomerically pure δ-hydroxy-α,β-unsaturated esters. The established protocol combining enzymatic kinetic resolution with ring closing metathesis was successfully applied in the synthesis of the enantiomerically pure (6R)-phenyl-5,6-dihydro-2H-pyran-2-one which plays crucial role in the synthesis of the number of bioactive compounds. Graphical abstract image
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Study of a new ‘chiral proton’ organocatalyst with hydrolase activity: application in azlactone racemic dynamic resolution ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6 Author(s): Ángel L. Fuentes de Arriba, Omayra H. Rubio, Luis Simón, Victoria Alcázar, Laura M. Monleón, Francisca Sanz, Joaquin R. Morán For the first time, a 1,3-ketoenol system is described as an acid catalyst with hydrolytic activity. The combination of an enol and a pyridine/benzimidazole supported on a benzofuran skeleton allowed the creation of a novel bifunctional organocatalyst, which has been applied in azlactone racemic dynamic resolution. In spite of the moderate enantioselectivities obtained, the catalyst constitutes a novel concept in the field of chiral Brønsted acid catalysis. Graphical abstract image
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A planar chiral six-membered cyclic (amino)(ferrocenyl)carbene and its sulfur adduct ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6 Author(s): Risa Yasue, Masaru Miyauchi, Kazuhiro Yoshida A planar chiral ferrocene-fused cyclic aldimine was synthesized and a series of iminium salts were divergently prepared from it. The new carbene was generated from a salt by simple deprotonation with a strong base and identified by a carbene trapping experiment with sulfur. The sulfur adduct was fully characterized and its crystal structure implied that the new carbene would create an excellent chiral environment when used as a catalyst or a ligand in catalytic asymmetric synthesis. Graphical abstract image
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Conformationally rigid chiral ferrocene derivative: Synthesis, resolution and stereochemical assignment ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6 Author(s): Kamsali Murali Mohan Achari, Chinnasamy Ramaraj Ramanathan A conformationally rigid chiral molecule LB-I with Lewis basic site has been designed and synthesized in racemic form from ferrocene via Lewis acid mediated diastereoselective cyclization of hydroxy lactam. Both isomers were successfully obtained in enantiomerically pure form through classical resolution using dibenzoyl-d-tartaric acid as the chiral resolving agent in acetone. The nature of the diastereomeric salt formed in the resolution process was investigated by single crystal X-ray crystallographic studies. The absolute configuration of (+)-LB-I was unambiguously assigned as (S,Rp ) by single crystal analysis of the salt I obtained from precipitate fraction containing (+)-LB-I and dibenzoyl-d-tartaric acid. Graphical abstract image
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A carbohydrate-derived trifunctional scaffold for DNA-encoded libraries ()
Publication date: 15 June 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 6 Author(s): Amalia M. Estévez, Felix Gruber, Alexander L. Satz, Rainer E. Martin, Hans Peter Wessel For the generation of DNA-encoded libraries, a central scaffold containing three exit vectors with defined chirality was devised starting from commercially available tri-O-acetyl-glucal. This scaffold may be connected to the DNA barcode at any of the three different exit vectors, thus making it a versatile approach as this readily leads to three different libraries. For one of the three possibilities, the compatibility with the DNA tag was demonstrated. The reactions include amide bond formation, Boc deprotection, urea formation, azide reduction and reductive alkylation. Graphical abstract image
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