Steroidal Free Radicals as Possible Intermediates in the Biosynthesis of C 19 -△ 16 -Steroids

Treatment of deoxycorticosterone with reagents that abstract a hydrogen atom from the C-21-hydroxyl group leads to the formation of androsta-4,16-dien-3-one. In vitro incubations of [1,2- 3 H]deoxycorticosterone with homogenates of boar testis tissue produce the tritiated dienone. This reaction can be formulated as an abstraction of hydrogen from the C-21-hydroxyl group to form a C-21-alkoxy radical, followed by a 1,5-H·shift from the C-16 atom and β-scission of the C-16-alkoxy radical leading to the loss of a C 2 fragment (C-20 and C-21) with the formation of the double bond between C-16 and C-17. Both the chemical model and the in vitro experiment support further the thesis [Lieberman, S., L. Bandy, V. Lippman, and K. D. Roberts, Biochem. Biophys. Res. Commun. , 34, 367 (1969)] that biosynthetic reactions in which molecular oxygen reacts with steroids (for example, side-chain cleavage or hydroxylation) involve steroidal free radicals.