α-REDUCTION OF THE 20-CARBONYL GROUP IN C-21 STEROIDS BY RHODOTORULA LONGISSIMA

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Abstract
The microbiological synthesis of several 20α-dihydro reference steroids is described. The influence of various substituent groups on α-reduction of the C-20 carbonyl group by a yeast, Rhodotorula longissima, has been investigated for compounds related to progesterone and corticosterone. Reduction at C-20 is enhanced by the presence of a 17α-hydroxyl group, but retarded by the presence of hydroxyl groups at C-11 and C-21. In those instances where 20α-conversion proceeds at a slow rate, oxygenation at C-11 appears to be essential for the preservation of the Δ4-3-ketone structure.