7α-Methyl-19-hydroxy-testosterone-17β-acetate (2a) was transformed by Arthrobacter simplex to 7α-methyl-estradiol- 17β-acetate (3a) in 65% yield and 7α-methyl-estrone (1e) in 20% yield. Apparently 1e was produced through the hydrolysis of 2a or 3a followed by oxidation. Since 7α-methyl-19-nor-testosterone (4a) or its Δ5 - isomer (4b) was transformed by A. simplex under the same condition to give mainly 1e and it is known that A. simplex is capable of hydrolyzing the acetate. However, in case of 2a, the 17β acetate is probably hindered by C13-methyl group, so it was hydrolysed only to a limited extent. In agreement with this assumption 7β-methyl-19-hydroxy-testosterone-17β-acetate (2b) was converted to 3b with the 17β-acetate group intact. The structure of 3b was proved by IR, ^1H NMR and MS.

Key words: TESTOSTERONE, ESTROGEN, STEROL, ARTHROBACTER, ESTRONE, MICROBIAL TRANSFORMATION, AROMATIZATION