How Substrate Solvation Contributes to the Enantioselectivity of Subtilisin toward Secondary Alcohols
摘要:
The current rule to predict the enantiopreference of subtilisin toward secondary alcohols is based on the size of the substituents at the stereocenter and implies that the active site contains two differently sized pockets for these substituents. Several experiments are inconsistent with the current rule. First, the X-ray structures of subtilisin show there is only one pocket (the S1' pocket) approximately the size of a phenyl group to bind secondary alcohols. Second, the rule often predicts the incorrect enantiomer for reactions in water. To resolve these contradictions, we refine the current rule to show that subtilisin binds only one substituent of a secondary alcohol and leaves the other in solvent. To test this refined empirical rule, we show that the enantioselectivity of a series of secondary alcohols in water varied linearly with the difference in hydrophobicity (log P/P0) of the substituents. This hydrophobicity difference accounts for the solvation of one substituent in water.
Conversion of α,β-Unsaturated Aldehydes into Saturated Esters: An Umpolung Reaction Catalyzed by Nucleophilic Carbenes
作者:Audrey Chan、Karl A. Scheidt
DOI:10.1021/ol050100f
日期:2005.3.1
species from alpha,beta-unsaturated aldehydes. These nucleophilic intermediates can be protonated, and the resulting activated carbonyl unit is trapped with an alcohol nucleophile, thereby promoting a highly efficient conversion of an alpha,beta-unsaturated aldehyde into a saturated ester. A kinetic resolution of secondary alcohols can be achieved using chiral imidazoylidene catalysts. [reaction: see text]
Acetate aldol reactions of chiral oxocarbenium ions
作者:Sandeep Kanwar、Sanjay Trehan
DOI:10.1016/j.tetlet.2004.12.116
日期:2005.2
Chiral oxocarbeniumions have been exploited to carry out highly diastereoselective and enantioselective acetate aldol addition reactions. The chiral auxiliary has been optimized to give the product with good diastereoselectivity.
Kinetic Resolution of Racemic Secondary Benzylic Alcohols by the Enantioselective Esterification Using Pyridine-3-carboxylic Anhydride (3-PCA) with Chiral Acyl-Transfer Catalysts
production of chiralcarboxylic esters by the combination of chiral nucleophilic catalyst, such as tetramisole (=2,3,5,6‐tetrahydro‐6‐phenylimidazo[2,1‐b][1,3]thiazole) derivatives. An efficient kineticresolution of racemic benzylic alcohols with achiralcarboxylicacids was achieved by using 3‐PCA in the presence of (R)‐benzotetramisole ((R)‐BTM), and a variety of optically active carboxylic esters were
发现吡啶-3-羧酸酐(3-PCA)是一种有效的偶联剂,可在温和的条件下通过简单的实验程序从各种羧酸与醇制备羧酸酯。这种新型缩合剂3-PCA不仅适用于由4-(二甲氨基)吡啶(DMAP)催化的非手性羧酸酯的合成,而且还适用于通过手性亲核催化剂(如四甲酚( = 2,3,5,6-四氢-6-苯基咪唑[2,1- b ] [1,3]噻唑)衍生物。在(R)-苯并四咪唑((R)-BTM),并且通过这种新的手性诱导系统在不使用叔胺的情况下生产了具有高对映体过量的多种旋光羧酸酯。
The Specificity of the Nucleophilic Site of α-Chymotrypsin and its Potential for the Resolution of Alcohols. Enzyme-catalyzed Hydrolyses of Some (+)-, (−)-, and (±)-2-Butyl, -2-Octyl, and -α-Phenethyl Esters
作者:Yong Yeng Lin、David N. Palmer、J. Bryan Jones
DOI:10.1139/v74-075
日期:1974.2.1
The α-chymotrypsin-catalyzedhydrolyses of a representative spectrum of (R)- and (S)-2-butyl, -2-octyl, and -α-phenethyl esters of N-acetyl-L-phenylalanine, N-acetylglycine, α-hydroxy-β-phenyl-propionic, dihydrocinnamic, and hippuric acids have been examined. The kinetic studies were carried out in order to provide data on the practicability of exploiting the stereospecificity of the nucleophilic region
2,2-Disubstituted Propionic Anhydrides: Effective Coupling Reagents for the Kinetic Resolution of Secondary Benzylic Alcohols Using BTM
作者:Isamu Shiina、Kenya Nakata、Masuhiro Sugimoto、Yu-suke Onda、Takashi Iizumi、Keisuke Ono
DOI:10.3987/com-08-s(f)75
日期:——
variety of opticallyactive benzylic alcohols possessing aliphatic substituents at the C-1 position are produced by the kinetic resolution of racemic secondary alcohols using free carboxylicacids with 2,2-disubstituted propionic anhydrides and (+)-benzotetramisole (BTM). Evaluation of the efficiency of this asymmetric esterification using several anhydrides derived from aliphatic carboxylicacids were carried