Stereoselectivities of microbial epoxide hydrolases

Epoxide hydrolases from bacterial and fungal sources are highly versatile biocatalysts for the asymmetric hydrolysis of epoxides on a preparative scale. Besides kinetic resolution, which yields the corresponding enantiomerically enriched vicinal diol and the remaining nonconverted epoxide, enantioconvergent processes are also possible, which lead to the formation of a single enantiomeric diol from a racemic oxirane. The data available to date indicate that the enantioselectivities of enzymes from certain microbial sources can be correlated to the substitutional pattern of various types of substrates: red yeasts (e.g. Rhodotorula or Rhodosporidium sp.) give best enantioselectivities with monosubstituted oxiranes; fungal cells (e.g. from Aspergillus and Beauveria sp.) are best suited for styrene oxide-type substrates; bacterial enzymes, on the other hand (in particular from Actinomycetes such as Rhodococcus and Nocardia sp.) are the biocatalysts of choice for more highly substituted 2,2- and 2,3-disubstituted epoxides.