Deracemization of (±)-2,3-disubstituted oxiranes via biocatalytic hydrolysis using bacterial epoxide hydrolases: kinetics of an enantioconvergent process

Abstract

Asymmetric biocatalytic hydrolysis of (±)-2,3-disubstituted oxiranes leading to the formation of vicinal diols in up to 97% ee at 100% conversion was accomplished by using the epoxide hydrolase activity of various bacterial strains. The mechanism of this deracemization was elucidated by ¹⁸OH₂-labelling experiments using a partially purified epoxide hydrolase from Nocardia EH1. The reaction was shown to proceed in an enantioconvergent fashion by attack of OH^– at the (S)-configured oxirane carbon atom with concomitant inversion of configuration. A mathematical model developed for the description of the kinetics was verified by the determination of the four relative rate constants governing the regio- and enantio-selectivity of the process.