关键词: 不对称还原, 酶抑制剂, 酶抑制剂, 立体选择性, 催化机理

Abstract: In the process of asymmetric reduction of b-ketoesters by baker￠s yeast, the enantioselectivity of yeast cells could be controlled by allyl compounds added in the reaction system. 4-Chrolo-3-oxobutanoate (COBE) was used as the model substrate. After yeast cells were pretreated with acrylamide and allyl alcohol, the enantiomeric excess (e.e.) of S-CHBE increased to 94%, while pretreated with allyl bromide, R-CHBE could be detected. The allyl compounds were proved to be toxic to the cells and intracellular enzymes by DNS and API ZYM system respectively. Furthermore, the toxicity was determined by the groups the allyl carried. Washed with PBS buffer for several times, the activity of pretreated yeasts could be recovered gradually. As the concentration of substrate increased, the e.e. of S-CHBE catalyzed by ally alcohol-pretreated yeast remained at 90%. On the other hand, the e.e. of R-CHBE catalyzed by allyl bromide-pretreated yeast dropped from 90% to 45%. These results suggested that allyl compounds acted as competitive enzyme inhibitors adsorbed on the active site of enzymes, and different groups of allyl compounds determined the types of subjected enzymes. The result in pretreatment of the yeast with inhibitor analogs showed that the enzymes had steric hindrance for both inhibitor and substrate.

Key words: asymmetric reduction, 4-chrolo-3-oxobutanoate (COBE, enzyme inhibitor, enantioselectivity, catalysis mechanism