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Discovery and Redesign of a Family VIII Carboxylesterase with High (S)-Selectivity toward Chiral sec-Alcohols
Highly enantioselective lipase has been widely utilized in the preparation of versatile enantiopure chiral sec-alcohols through kinetic or dynamic kinetic resolution. Lipase is intrinsically (R)-selective, and it is difficult to obtain (S)-selective lipase. Recent crystal structures of a family VIII carboxylesterase have revealed that the spatial array of its catalytic triad is the mirror image of that of lipase but with a catalytic triad that is distinct from lipase. We, therefore, hypothesized that the family VIII carboxylesterase may exhibit (S)-enantioselectivity toward sec-alcohols similar to (S)-selective serine protease, whose catalytic triad is also spatially arrayed as its mirror image. In this study, a homologous enzyme (carboxylesterase from Proteobacteria bacterium SG_bin9, PBE) of a known family VIII carboxylesterase (pdb code: 4IVK) was prepared, which showed not only moderate (S)-selectivity toward sec-alcohols such as 3-butyn-2-ol and 1-phenylethyl alcohol but also (R)-selectivity toward particular sec-alcohols among the substrates explored. Furthermore, the (S)-selectivity of PBE has been significantly improved by rational redesign based on molecular modeling. Molecular modeling identified a binding pocket composed of Ser381, Ala383, and Arg408 for the methyl substituent of (R)-1-phenylethyl acetate and suggested that larger residues may increase the enantioselectivity by interfering with the binding of the slow-reacting enantiomer. As predicted, substituting Ser381with larger residues (Phe, Tyr, and Trp) significantly improved the (S)-selectivity of PBE toward all sec-alcohols explored, even the substrates toward which the wild-type PBE exhibits (R)-selectivity. For instance, the enantioselectivity toward 3-butyn-2-ol and 1-phenylethyl alcohol was improved from E = 5.5 and 36.1 to E = 2001 and 882, respectively, by single mutagenesis (S381F).
Park, Areum,Park, Seongsoon
p. 2397 - 2402
(2022/02/17)

Enantioselective oxidation of secondary alcohols by the flavoprotein alcohol oxidase from Phanerochaete chrysosporium
The enantioselective oxidation of secondary alcohols represents a valuable approach for the synthesis of optically pure compounds. Flavoprotein oxidases can catalyse such selective transformations by merely using oxygen as electron acceptor. While many flavoprotein oxidases preferably act on primary alcohols, the FAD-containing alcohol oxidase from Phanerochaete chrysosporium was found to be able to perform kinetic resolutions of several secondary alcohols. By selective oxidation of the (S)-alcohols, the (R)-alcohols were obtained in high enantiopurity. In silico docking studies were carried out in order to substantiate the observed (S)-selectivity. Several hydrophobic and aromatic residues in the substrate binding site create a cavity in which the substrates can comfortably undergo van der Waals and pi-stacking interactions. Consequently, oxidation of the secondary alcohols is restricted to one of the two enantiomers. This study has uncovered the ability of an FAD-containing alcohol oxidase, that is known for oxidizing small primary alcohols, to perform enantioselective oxidations of various secondary alcohols.
Tjallinks, Gwen,Martin, Caterina,Fraaije, Marco W.
(2021/05/03)

Ester Synthesis in Water: Mycobacterium smegmatis Acyl Transferase for Kinetic Resolutions
The acyl transferase from Mycobacterium smegmatis (MsAcT) catalyses transesterification reactions in aqueous media because of its hydrophobic active site. Aliphatic cyanohydrin and alkyne esters can be synthesised in water with excellent and strikingly opposite enantioselectivity [(R);E>37 and (S);E>100, respectively]. When using this enzyme, the undesired hydrolysis of the acyl donor is an important factor to take into account. Finally, the choice of acyl donor can significantly influence the obtained enantiomeric excesses. (Figure presented.).
de Leeuw, Nicolas,Torrelo, Guzman,Bisterfeld, Carolin,Resch, Verena,Mestrom, Luuk,Straulino, Emanuele,van der Weel, Laura,Hanefeld, Ulf
p. 242 - 249
(2017/11/16)

Application of homochiral alkylated organic cages as chiral stationary phases for molecular separations by capillary gas chromatography
Molecular organic cage compounds have attracted considerable attention due to their potential applications in gas storage, catalysis, chemical sensing, molecular separations, etc. In this study, a homochiral pentyl cage compound was synthesized from a condensation reaction of (S,S)-1,2-pentyl-1,2-diaminoethane and 1,3,5-triformylbenzene. The imine-linked pentyl cage diluted with a polysiloxane (OV-1701) was explored as a novel stationary phase for high-resolution gas chromatographic separation of organic compounds. Some positional isomers were baseline separated on the pentyl cage-coated capillary column. In particular, various types of enantiomers including chiral alcohols, esters, ethers and epoxides can be resolved without derivatization on the pentyl cage-coated capillary column. The reproducibility of the pentyl cage-coated capillary column for separation was investigated using nitrochlorobenzene and styrene oxide as analytes. The results indicate that the column has good stability and separation reproducibility after being repeatedly used. This work demonstrates that molecular organic cage compounds could become a novel class of chiral separation media in the near future.
Xie, Shengming,Zhang, Junhui,Fu, Nan,Wang, Bangjin,Hu, Cong,Yuan, Liming
(2016/12/03)

Enantioconvergent Nucleophilic Substitution Reaction of Racemic Alkyne-Dicobalt Complex (Nicholas Reaction) Catalyzed by Chiral Br?nsted Acid
Catalytic enantioselective syntheses enable a practical approach to enantioenriched molecules. While most of these syntheses have been accomplished by reaction at the prochiral sp2-hybridized carbon atom, little attention has been paid to enantioselective nucleophilic substitution at the sp3-hybridized carbon atom. In particular, substitution at the chiral sp3-hybridized carbon atom of racemic electrophiles has been rarely exploited. To establish an unprecedented enantioselective substitution reaction of racemic electrophiles, enantioconvergent Nicholas reaction of an alkyne-dicobalt complex derived from racemic propargylic alcohol was developed using a chiral phosphoric acid catalyst. In the present enantioconvergent process, both enantiomers of the racemic alcohol were transformed efficiently to a variety of thioethers with high enantioselectivity. The key to achieving success is dynamic kinetic asymmetric transformation (DYKAT) of enantiomeric cationic intermediates generated via dehydroxylation of the starting racemic alcohol under the influence of the chiral phosphoric acid catalyst. The present fascinating DYKAT involves the efficient racemization of these enantiomeric intermediates and effective resolution of these enantiomers through utilization of the chiral conjugate base of the phosphoric acid.
Terada, Masahiro,Ota, Yusuke,Li, Feng,Toda, Yasunori,Kondoh, Azusa
supporting information
p. 11038 - 11043
(2016/09/09)

Coupling biocatalysis and click chemistry: One-pot two-step convergent synthesis of enantioenriched 1,2,3-triazole-derived diols
A fully convergent one-pot two-step synthesis of different chiral 1,2,3-triazole-derived diols in high yields and excellent enantio- and diastereoselectivities has been achieved under very mild conditions in aqueous medium by combining a single alcohol dehydrogenase (ADH) with a Cu-catalysed 'click' reaction. The Royal Society of Chemistry 2013.
Cuetos, Aníbal,Bisogno, Fabricio R.,Lavandera, Iván,Gotor, Vicente
supporting information
p. 2625 - 2627
(2013/04/23)

Asymmetric hydrogenation of alkynyl ketones with the η6- arene/TsDPEN-ruthenium(II) catalyst
Enantioselective hydrogenation of alkynyl ketones catalyzed by Ru(OTf)(TsDPEN)(η6-p-cymene) (TsDPEN = N-(p-toluenesulfonyl)-1,2- diphenylethylenediamine) affords the propargylic alcohols in up to 97% ee. The alkynyl moieties are left intact in most cases. The reaction can be conducted with a substrate-to-catalyst molar ratio as high as 5000 under 10 atm of H 2. The mode of enantioselection is elucidated with the transition state models directed by the CH/π attractive interaction between the substrate and the catalytic species.
Arai, Noriyoshi,Satoh, Hironori,Utsumi, Noriyuki,Murata, Kunihiko,Tsutsumi, Kunihiko,Ohkuma, Takeshi
supporting information
p. 3030 - 3033
(2013/07/26)

Electrical and mechanical anharmonicities from NIR-VCD spectra of compounds exhibiting axial and planar chirality: The cases of (S)-2,3-pentadiene and methyl-d3 (R)- and (S)-[2.2]paracyclophane-4-carboxylate
The IR and Near infrared (NIR) vibrational circular dichroism (VCD) spectra of molecules endowed with noncentral chirality have been investigated. Data for fundamental, first, and second overtone regions of (S)-2,3-pentadiene, exhibiting axial chirality, and methyl-d3 (R)- and (S)-[2.2]paracyclophane-4-carboxylate, exhibiting planar chirality have been measured and analyzed. The analysis of NIR and IR VCD spectra was based on the local-mode model and the use of density functional theory (DFT), providing mechanical and electrical anharmonic terms for all CH-bonds. The comparison of experimental and calculated spectra is satisfactory and allows one to monitor fine details in the asymmetric charge distribution in the molecules: these details consist in the harmonic frequencies, in the principal anharmonicity constants, in both the atomic polar and axial tensors and in their first and second derivatives with respect to the CH-stretching coordinates. Chirality, 2011. 2011 Wiley Liss, Inc. Copyright
Abbate, Sergio,Longhi, Giovanna,Gangemi, Fabrizio,Gangemi, Roberto,Superchi, Stefano,Caporusso, Anna Maria,Ruzziconi, Renzo
experimental part
p. 841 - 849
(2012/02/06)

Inclusion of aliphatic alcohols in pockets of (S)-threonyl-(S)- phenylglycine using grinding method
Inclusion compounds of a dipeptide, (S)-threonyl-(S)-phenylglycine (Thr-Phg), with several aliphatic alcohols were easily prepared by grinding them in a mortar. Thr-Phg molecules arranged in antiparallel to construct a sheet, and guest alcohols were accommodated in a chiral pocket between the sheets. 3-Butyn-2-ol and 2-butanol were included with moderate enantioselectivity, 57% ee (R) and 49% ee (R), respectively. The role of the hydroxy group of Thr-Phg is not only to construct the unique pocket but also to capture guest alcohols by hydrogen bonding.
Akazome, Motohiro,Toma, Shusaku,Horiguchi, Tatsunori,Megumi, Ken,Matsumoto, Shoji
experimental part
p. 2844 - 2848
(2011/05/06)

PROCESS FOR THE PREPARATIN OF ALKYNOLS
Process for the preparation of an alkynol with formula HC=C-C(OH)-R2 (formula 2) wherein R2 represents methyl, halomethyl or ethyl, wherein the corresponding silyl-protected alkynol ester with formula 1 (1) wherein R1 represents H, or an optionally substituted alkyl, an optionally substituted alkenyl or an optionally substituted (hetero)aryl group, R2 is as defined above and A3Si represents a trisubstituted silyl group wherein each A independently represents anoptionally substituted alkyl or an optionally substituted (hetero)aryl group, in the presence of water and at least an equivalent amount of amine functionalities is converted into the alkynol with formula 2. Preferably, the amount of water is between 0.5 and 3 equivalents calculated with respect to the amount of silyl-protected alkynol ester with formula (1).
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Page/Page column 8-9

(2008/06/13)

PROCESS FOR THE PRODUCTION OF A HYDROXYALKYNE BY COUPLING REACTION BETWEEN ACETALDEHYDE AND A TERMINAL ALKYNE
A process for performing a coupling reaction between acetaldehyde and a terminal alkyne to yield a hydroxyalkyne is described comprising the steps of; (i) reacting without solvent, a terminal alkyne with a Lewis acidic metal salt in the presence of a alkanolamine ligand and a cyclic amine base to form a metal-alkyne complex, and (ii) adding a solution of acetaldehyde to the metal-alkyne complex.
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Page 8

(2010/02/09)

PMHS-mediated couplings of alkynes or benzothiazoles with various electrophiles: Application to the synthesis of (-)-akolactone A
Polymethylhydrosiloxane (PMHS) in combination with CsF facilitates the cross-coupling of alkynes or benzothiazoles with an array of vinyl, styryl, and aryl halides or nonaflates as well as acid chlorides. Experimental and spectroscopic evidence indicates that these reactions involve the in situ generation of a siloxyl intermediate. These cross-couplings proceed relatively quickly at room temperature and under amine-free conditions. To demonstrate the applicability of the method, a total synthesis of the cyctotoxic butanolide (-)-akolactone A was carried out.
Gallagher, William P.,Maleczka Jr., Robert E.
p. 6775 - 6779
(2007/10/03)

The effect of catechin derivatives on the enantioselectivity of lipase-catalyzed hydrolyses of alkynol benzoate esters
Polyphenols, such as (+)-catechin and pyrogallol could be used to enhance stereochemical control in the lipase-catalyzed hydrolysis of alkynol benzoate esters, leading to increased enantioselectivities in the kinetic resolution of alkynols with lipase Amano AH.
Nakamura, Kaoru,Takenaka, Keishi
p. 415 - 422
(2007/10/03)

A high-throughput-screening method for the identification of active and enantioselective hydrolases
A rapid and reliable test for the determination of hydrolase activity and enantioselectivity comprises the conversion of acetic acid released from acetates to NADH by using a commercially available enzymatic test-kit (see scheme). The NAHDH is spectrophotometrically quantified in a microtiter plate format.
Baumann, Markus,Stuermer, Rainer,Bornscheuer, Uwe T.
p. 4201 - 4204
(2007/10/03)

Synthesis of stereopentad analogues of the C14-C22 segment of callystatin A through additions of chiral allenylzinc reagents to stereotriads
The addition of (P)- and (M)-allenylzinc reagents, prepared in situ through Pd-catalyzed metalation of(R)- and (S)-3-butyn-2-ol mesylates, to diastereomeric stereotriad aldehydes 8, 13, 18, and 23 of syn,syn, syn,anti, anti,anti, and anti,syn stereochemis
Marshall,Schaaf
p. 7825 - 7831
(2007/10/03)

FR901464: Total synthesis, proof of structure, and evaluation of synthetic analogues
The natural product FR901464 (1) was isolated by the Fujisawa Pharmaceutical Co. and shown to have intriguing biological properties including impressive antitumor activity. In this paper we describe the first total synthesis of 1 in full detail. A chiral building block synthetic strategy was used to assemble the target: optically active components were generated using asymmetric catalytic reactions, and these fragments were coupled together at a late stage in a convergent synthesis. In particular, a versatile, asymmetric hetero-Diels-Alder (HDA) reaction was developed in the context of this synthesis and used with great effectiveness for the preparation of the two densely functionalized pyran rings. The flexible nature of the synthetic route also allowed us to prepare a series of analogues of 1. These compounds were used to prove the relative stereochemistry of the natural product as well as to probe the importance of certain structural features of FR901464 with regard to biological activity.
Thompson,Jamison,Jacobsen
p. 9974 - 9983
(2007/10/03)

New chiral hosts derived from dimeric tartaric acid: Efficient optical resolution of aliphatic alcohols by inclusion complexation
The novel, chiral, host compounds 8 and 9 were derived from tartaric acid. Inclusion complexation with these host compounds permitted highly efficient resolution of some aliphatic alcohols (10-13). The symmetrical dimer host compound 8 is effective for optical resolution of alcohols 10, 12, and 13 by a combination of enantioselective inclusion complexation and distillation techniques. The unsymmetrical dimer host compound 9 is effective for optical resolution of cyanohydrin 11. The crystal structures of the inclusion complexes were analyzed by X-ray diffraction methods in order to elucidate the mechanism of the efficient chiral recognition in the inclusion crystals.
Tanaka, Koichi,Honke, Shinji,Urbanczyk-Lipkowska, Zofia,Toda, Fumio
p. 3171 - 3176
(2007/10/03)

Rapid screening of hydrolases for the enantioselective conversion of 'difficult-to-resolve' substrates
Hydrolases showing high enantioselectivity towards three racemic alcohols (1-methoxy-2-propanol, 3-hydroxy-tetrahydrofuran, 3-butyn-2-ol) and pantolactone were identified by a step-wise screening procedure. Initially, those biocatalysts, which exhibited hydrolytic activity towards the corresponding acetates or butyrates, were selected out of >100 enzymes. Here, rapid screening was performed in a pH-indicator-based format in microtiter plates. Subsequently, enantioselectivity of active hydrolases was determined in small scale reactions (～1 mg substrate per reaction) by means of gas chromatography using chiral columns. Enzymes exhibiting highest enantioselectivities were then chosen for preparative scale resolution. Using this strategy, at least one suitable hydrolase was found for 3 out of the 4 model compounds examined, allowing efficient kinetic resolution. Moreover, in all cases enantiocomplementary enzymes were identified thus enabling access to both enantiomers of all substrates.
Baumann, Markus,Hauer, Bernhard H.,Bornscheuer, Uwe T.
p. 4781 - 4790
(2007/10/03)

Lipase-catalyzed kinetic resolution of 3-butyn-2-ol
Optically active 3-butyn-2-ol, an important building block, was synthesized successfully using lipase-catalyzed kinetic resolution. Starting from the thus obtained 3-butyn-2-ol, several 4-aryl-substituted compounds were synthesized enantioselectively.
Nakamura, Kaoru,Takenaka, Keishi,Ohno, Atsuyoshi
p. 4429 - 4439
(2007/10/03)

Asymmetric synthesis of (R)-N-3-butyn-2-yl-N-hydroxyurea, a key intermediate for 5-lipoxygenase inhibitors
An efficient asymmetric synthesis of (R)-N-3-butyn-2-yl-N-hydroxyurea from crotyl alcohol is described. The process involves asymmetric Sharpless epoxidation to establish the stereochemistry, formation of (S)-3-butynol and hydroxyl substitution with inversion by the masked N-hydroxyurea reagent N,O-bis(phenoxycarbonyl)hydroxylamine in a Mitsunobu reaction.
Kolasa, Teodozyj,Stewart, Andrew O.,Brooks, Clint D. W.
p. 729 - 736
(2007/10/03)

Antiulcer compounds having a substituted alkynyl or quinoxaline nucleus and methods of making thereof
This invention relates to a novel compound which is useful as a drug in preventing and/or treating peptic ulcer-related diseases, to a production process thereof and to a pharmaceutical composition containing the same. Particularly, it provides a compound which has a specified substituted alkynylpyrazine nucleus or a specified substituted alkynylquinoxaline nucleus, represented by the following formula (I) STR1 wherein A is represented by the following formula (II) or (III) STR2 and R1 is represented by the following formula (IV), STR3 and the salts thereof, a production process thereof and a pharmaceutical composition containing the same. The inventive compound is useful as a drug in preventing and/or treating peptic ulcer-related diseases.
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(2008/06/13)

Practical preparation of both optically pure enantiomers of but-1-yn-3-ol, oct-1-yn-3-ol and 6-methylhept-2-yn-4-ol using biocartol as resolving agent
A new facile preparation of optically pure secondary alkynols has been developed. This involves resolution of the corresponding racemic alcohols using biocartol as the resolving agent.
Michelet,Besnier,Tanier,Touzin,Genet,Demoute
p. 165 - 167
(2007/10/02)

Convenient Preparation of Optically Pure Propargylic Alcohols Using 2-(Trimethylsilyl)vinyl Sulfoxide As A Novel Chiral Synthon
Both enentiomers of optically pure propargylic alcohols are conveniently prepared by the reaction of α-vinyl anion of 2-(trimethylsilyl)vinyl p-tolyl sulfoxide with aldehydes and subsequent either desilylsulfination or thermal elimination of the sulfinyl group.
Kusuda, Shinya,Kawamura, Kiyoshi,Ueno, Yoshio,Toru, Takeshi
p. 6587 - 6590
(2007/10/02)

Synthesis of Enantioenriched Homopropargylic Alcohols through Diastereoselective SE' Additions of Chiral Allenylstannanes to Aldehydes
Allenylstannanes (S)-4 and (R)-4, available in ca. 90percent ee from alkynones 1 through reduction with the LiAlH4-Darvon alcohol or -ent-Darvon alcohol complex, followed by SN2' displacement on the derived mesylates (R)-3 or (S)-3 with Bu3SnLi*CuBr*Me2S, readily add to various aldehydes under Lewis acid catalysis to afford optically active homopropargylic alcohols with good to excellent syn diastereoselectivity.With 2-(benzyloxy)propanal (48), MgBr2-catalyzed reactions are highly stereoselective, affording the syn adduct 49 from the (S)-stannane (S)-4 and the anti adduct 52 from the (R)-stannane (R)-4.BF3-promoted additions give mainly or exclusively the syn adducts 49 and 51.Additions of (S)- and (R)-4 to (R)-3-(benzyloxy)-2-methylpropanal (61) yield the syn adducts 62 and 64 as major or exclusive products.
Marshall, James A.,Wang, Xiao-jun
p. 1242 - 1252
(2007/10/02)

Selective Reductions. 46. Effect of the Steric Requirement at the 2-Position of Apopinene on chiral Reductions. B-(Iso-2-ethylapopinocampheyl)- and B-(Iso-2-n-propylapopinocampheyl)-9-borabicyclononanes as Improved Reagents for the Chiral Reduction of α,β-Acetylenic Ketones ...
B-(Iso-2-ethylapopinocampheyl)-9-borabicyclononane (Eapine-Borane, 7), and B-(Iso-2-n-propylapopinocampheyl)-9-borabicyclononane (Prapine-Borane, 9), prepared via the hydroboration of 2-ethylapopinene (6) or 2-n-propylapopinene (8), respectively, with 9-borabicyclononane, reduce prochiral α,β-acetylenic ketones and α-keto esters to the corresponding alcohols with significantly higher optical induction than does Alpine-Borane (1). (-)-2-n-Propylapopinene was synthesized by treating nopyl tosylate with dimethyl cuprate prepared in situ from methyllithium and cuprous iodide. (+)-2-n-Propylapopinene was synthesized by Schlosser metalation of (+)-α-pinene followed by treatment with ethyl iodide. 4-Phenyl-3-butyne-2-one was reduced to the corresponding propargylic alcohol in 89percent ee and 96percent ee by Eapine-Borane and Prapine-Borane, respectively, as compared to 82percent ee with Alpine-Borane.Similar improved results were realized in the reduction of other acetylenic ketones by Eapine-Borane and Prapine-Borane.Similar improvements in the optical yields were realized in the reduction of α-keto esters by Eapine-Borane.For example, while Alpine-Borane produced methyl and ethyl lactate in 92percent and 91percent ee, respectively, Eapine-Borane gave these alcohols in 97percent and 96percent ee, respectively.Unfortunately, Prapine-Borane shows no improvement in percent ee for the reduction of α-keto esters.The increase in the percent ee realized is tentatively attributed to the increased steric requirements of the alkyl group at the 2-position of apopinene.
Brown, Herbert C.,Ramachandran, P. Veeraraghavan,Weissman, Steven A.,Swaminathan, S.
p. 6328 - 6333
(2007/10/02)

Chiral 2,2-Disubstituted Cyclohexanones; Annulation via Claisen Rearrangement Products
The methyl enol ether of 2-methylcyclohexanone reacts regiospecifically with the optical active forms of but-3-yn-2-ol and but-3-en-2-ol. (R)-But-3-yn-2-ol yields an approximately 4:1 mixture of (R)-2-methyl-2-(R-buta-1,2-dienyl)cyclohexanone and the corresponding SR compound.By contrast the but-3-en-2-ol reaction is ca. 96percent enantioselective; (R)-but-3-en-2-ol gives (R)-2-(trans-but-2-enyl)-2-methylcyclohexanone and (S)-but-3-en-2-ol gives the corresponding (S)-cyclohexanone.These Claisen rearrangement products have been transformed into Robinson-type annulated ketones.Cleavage of some highly hindered esters has been carried out efficiently by sodium methylsulphinyl-methanide in dimethyl sulphoxide.
Grattan, T. J.,Whitehurst, J. S.
p. 11 - 18
(2007/10/02)

Chemoenzymatic Synthesis of Chiral Isoxazole Derivatives
The synthesis of the two enantiomers of 1-(3-bromo-5-isoxazolyl)-2-(tert-butylamino)ethanol (1), a potent and selective β2-adrenergic stimulant, has been efficiently accomplished by enzyme-catalyzed transformations.The absolute configurations are attributed to (+)- and (-)-1 by correlation with (S)-3-butyn-2-ol.The S enantiomer was prepared in >98percent enantiomeric excess by reducing α-bromo ketone 4 in the presence of alcohol dehydrogenase from Thermoanaerobium brockii and the R enantiomer was obtained in 97percent ee through a kinetic resolution of the racemic bromohydrin(+/-)-5, in organic solvents, catalyzed by lipase P from Pseudomonas fluorescens.The experimental conditions for the lipase-catalyzed asymmetric transesterifications were optimized in order to improve reaction rates and the enantiomeric excess of the products.
Amici, Marco De,Micheli, Carlo De,Carrea, Giacomo,Spezia, Sandro
p. 2646 - 2650
(2007/10/02)

PRACTICAL METHOD FOR SYNTHESIS OF OPTICALLY PURE PROPARGYLIC ALCOHOLS
Highly efficient practical method for synthesis of optically pure propargylic alcohols is described which involves the synthesis of chiral γ-iodo allylic alcohols by the Sharpless kinetic resolution of secondary γ-hetero substituted allylic alcohols and their 1,2-dehydrohalogenation reaction.
Ito, Takayori,Okamoto, Sentaro,Sato, Fumie
p. 7083 - 7086
(2007/10/02)

Stereoisomers of Allenic Amines as Inactivators of Monoamine Oxidase Type B. Stereochemical Probes of the Active Site
The kinetics of inactivation of mitochondrial monoamine oxidase type B (MAO-B) by a series of 18 stereoisomers of tertiary α-allenic amines have been investigated in detail.The chirality of the allene group in N-methyl-N-aralkylpenta-2,3-dienamines was found to have a profound effect on the inactivation rate, with the (R)-allenes being up to 200-fold more potent than their (S)-allenic counterparts.The ability of (S)-allenes to inactivate MAO was severely compromised by the presence of N-phenethyl or N-α-substituted-aralkyl substituents.The opposing chiralities in both the allene and aralkyl groups of (R,R)- and (S,S)-N-methyl-N-(1,2,3,4-tetrahydro-1-naphthyl)-penta-2,3-dieneamine resulted in a difference of more than 3 oredrs of magnitude in inactivation rates.The stereoselectivity of MAO-B was examined further with a series of reversible aralkylamine inhibitors; thus (R)-1,2,3,4-tetrahydro-1-naphthylamine was determined to be 150-fold more potent than its enantiomer.
Smith, Roger A.,White, Robert L.,Krantz, Allen
p. 1558 - 1566
(2007/10/02)

Selective Reductions. 37. Asymmetric Reduction of Prochiral Ketones with B-(3-Pinanyl)-9-borabicyclononane
The chiral trialkylborane B-(3-pinanyl)-9-borabicyclononane, either with the neat reagents or concentrated solutions, 2 M, reduces a wide range of prochiral carbonyl compounds with good to excellent asymmetric induction.Reduction of simple dialkyl ketones, 2-butanone, 2-octanone, 3-methyl-2-butanone, and 3,3-dimethyl-2-butanone, yields the corresponding alcohols with 43percent, 48percent, 62percent, and 0.7percent asymmetric induction.Acetophenone is reduced to 1-phenylethanol in 85percent ee.The α,β-unsaturated ketones 3-buten-2-one, 1-acetyl-1-cyclohexene, 3-methyl-2-cyclohexenone, and trans-4-phenyl-3-buten-2-one are reduced to the corresponding allylic alcohols with 57percent, 64percent, 11percent, and 97percent asymmetric induction, respecticvely.The α,β-conjugated acetylenic ketones 3-butyn-2-one, 4-methyl-1-pentyn-3-one, and 4-phenyl-3-butyn-2-one underwent a rapid reduction to afford the corresponding propargylic alcohols with 79percent, 99percent, and 91percent enantiomeric purities.The α-haloalkyl aromatic ketones α-chloroacetophenone, α-bromoacetophenone, α-iodoacetophenone, α,p-dibromoacetophenone, α-bromo-p-cyanoacetophenone,α-bromo-2'-acetonaphthone,and α,α,α-trifluoroacetophenone afforded the corresponding halohydrins with 96percent,93percent,93percent,96percent,96percent,90percent,and35percent enantiomeric purities, respectively.The corresponding aliphatic analogue 1-bromo-3-methyl-butanone gave the halohydrin in 66percent ee.The other isomer of this ketone, 3-bromo-3-methyl-2-butanone, failed to undergo reduction.Both the aliphatic and aromatic α-keto esters underwent rapid reduction to give the corresponding α-hydroxy esters with excellentenantiomeric excesses.Thus, methyl, ethyl, isopropyl, and tert-butyl pyruvates afforded the corresponding lactates with 86percent,83percent,78percent, and 92percent ee at 25 deg C,respectively.Lowering the reaction temperature to 0 deg C gave the tert-butyl lactate in 100percent ee.Other aliphatic α-keto esters such as metyl and ethyl 2-oxopentanoates, methyl 3-methyl-2-oxobutanoate, and ethyl 4-methyl-2-oxopentanoate were reduced to the corresponding α-hydroxy esters with 96percent, 96percent, 11percent, and 82percent ee.The methyl, isopropyl, and tert-butyl benzoylformates were reduced to the corresponding mendelic esters with 90percent, 96percent and 100percent ee, respectively.The reduction of the β-keto esters, however, proceeded slowly and ethyl acetoacetate gave the corresponding alcohol with 55percent ee.
Brown, Herbert C.,Pai, G. Ganesh
p. 1384 - 1394
(2007/10/02)

Improved Procedure for the Asymmetric Reduction of Prochiral Ketones by B-(3-Pinanyl)-9-borabicyclononane
An improved experimental procedure gives good optical induction in the reduction of nonacetylenic prochiral ketones, using the chiral trialkylborane B-(3-pinanyl)-9-borabicyclononane (Midland's reagent).
Brown, Herbert C.,Pai, Ganesh G.
p. 1606 - 1608
(2007/10/02)