Conversion of an androgen epoxide into 17β-estradiol by human placental microsomes

: Three androgen epoxides, 17beta-hydroxy-4beta,5-oxido-5beta-androstan-3-one (II), 3beta,19-dihydroxy-5,6beta-oxido-5beta-androstan-17-one 3-acetate (VIII), and 19-hydroxy-4beta,5-oxido-5beta-androstane-3,17-dione (V), were synthesized and subsequently evaluated as potential precursors in the biosynthesis of estrogens by incubation with human placental microsomes. One of these epoxides (V) was converted into 17beta-estradiol, whereas the other two were metabolized to unidentified products. The possible intermediacy of an androgen epoxide in the biosynthesis of estrone and of 17beta-estradiol is discussed and a mechanism is proposed for the aromatization process.