Isolation and mass spectrometric identification of two metabolites of FK 506 from rat liver microsomal incubation media.

A transient epoxide in equilibrium with its possible isomeric forms, most probably induced easily by neighboring-group assistance of a hydroxy group, and a dihydrodiol formed under the influence of the hydrase enzymic activity and/or by simple hydrolysis were isolated by HPLC and identified by FAB/MS from rat liver microsomal incubation media.