Biosynthesis of 16 alpha, 17 alpha-epoxy-4-androsten-3-one in rat liver microsomes.

4,16-Androstadien-3-one was incubated with the microsomal fraction of male rat liver in the presence of a NADPH generating system and oxygen. The metabolites formed were extracted from the incubation medium and purified by thin-layer chromatography (tlc). Final identification was performed by combined gas liquid chromatography-mass spectrometry. Incubation of 4,16-androstadien-3-one resulted in the formation of a non-polar metabolite which proved to be 16 alpha, 17 alpha-epoxy-4-androsten-3-one. This epoxide is a shortlived intermediate which is rapidly hydrolysed by the microsomal epoxide hydratase to 16 beta, 17 alpha-dihydroxy-4-androsten-3-one. In order to increase the amounts of epoxide in the incubation mixtures, styrene oxide which is a potent inhibitor of the epoxide hydratase was added. Under these conditions, up to 8% of the 16-dehydro-steroid incubated was transferred to the 16 alpha, 17 alpha-epoxy-compound.