Stereoselectivities of microbial epoxide hydrolases

Epoxide hydrolases from bacterial and fungal sources are highly versatile b iocatalysts for the asymmetric hydrolysis of epoxides on a preparative scal e. Besides kinetic resolution, which yields the corresponding enantiomerica lly enriched vicinal diol and the remaining nonconverted epoxide, enantioco nvergent processes are also possible, which lead to the formation of a sing le enantiomeric diol from a racemic oxirane. The data available to date ind icate that the enantioselectivities of enzymes from certain microbial sourc es can be correlated to the substitutional pattern of various types of subs trates: red yeasts (e.g. Rhodotorula or Rhodosporidium sp.) give best enant ioselectivities with monosubstituted oxiranes; fungal cells (e.g. from Aspe rgillus and Beauveria sp.) are best suited for styrene oxide-type substrate s; bacterial enzymes, on the other hand (in particular from Actinomycetes s uch as Rhodococcus and Nocardia sp.) are the biocatalysts of choice for mor e highly substituted 2,2- and 2,3-disubstituted epoxides.