STEREOCHEMISTRY OF ENZYMATIC CONVERSION OF A DELTA4-3-OXOSTEROID INTO A 3-OXO-5BETA-STEROID - BILE ACIDS AND STEROIDS 208

The synthesis of [4‐3H,4‐14C]7α‐hydroxycholest‐4‐en‐3‐one is described. The transformation of this compound into cholic acid in the bile fistula rat occurred with retention of the tritium label. The position of the tritium label in the isolated cholic acid was established by oxidation at the C‐3 position of the methylated derivative followed by dehydrogenation with selenium dioxide yielding methyl 7α,12α‐dihydroxy‐3‐oxo‐chol‐4‐enoate. This compound retained most of the tritium label. Since selenium dioxide dehydrogenation of a 3‐oxo‐5β‐steroid could be shown to involve a preferential loss of a 4α‐hydrogen, it was concluded that the tritium label in the cholic acid isolated from bile was located in the 4β‐position. The enzymatic reduction of the Δ4 double bond in 7α‐hydroxycholest‐4‐en‐3‐one in its conversion into cholic acid thus involves a trans diaxial addition of hydrogens. Copyright © 1969, Wiley Blackwell. All rights reserved