Microbiological transformations .33. Fungal epoxide hydrolases applied to the synthesis of enantiopure para-substituted styrene oxides. A mechanistic approach

The biohydrolysis of differently para-substituted styrene oxide derivatives was studied, using whole cells of the fungi Aspergillus niger or Beauveria sulfurescens. These microorganisms proved to be equipped with epoxide hydrolases which are able to achieve these hydrolyses with high enantioselectivity. This allowed the preparation of the optically active epoxides and of the corresponding vicinal diols which were obtained with good to excellent enantiomeric purity. These two microorganisms proved to be enantiocomplementary. A mechanistic study, carried out using a crude lyophilized enzymatic extract from A. niger, indicated via Hammet coefficient plotting that this hydrolysis is very probably due to a general base-catalyzed process.