Aromatization and microbial hydroxylation of 3-18O-testosterone

3-18O-Testosterone (1) is transformed to estradiol (4) by human placental microsomes, and to the 6β- and 11α-hydroxy derivatives 2 and 3 by Rhizopusarrhizus, without significant loss of label. Neither process is therefore one which involves reversible Schiff base formation at C-3 at any stage.