Studies on the Biosynthetic Conversion of Cholesterol into Pregnenolone
SIDE CHAIN CLEAVAGE OF SOME 20-p-TOLYL ANALOGS OF CHOLESTEROL AND 20α-HYDROXYCHOLESTEROL
- From the Departments of Biochemistry, of Obstetrics and Gynecology, and the International Institute for the Study of Human Reproduction, College of Physicians and Surgeons, Columbia University, New York, New York 10032
- From the Departments of Biochemistry, of Obestetrics and Gynecology, and the International Institute for the Study of Human Reproduction, College of Physicians and Surgeons, Columbia University, New York, New York 10032
Abstract
Some 20-p-tolyl analogs of 20α-hydroxycholesterol and cholesterol have been synthesized and tested as precursors of pregnenolone. As in the previously synthesized t-butyl analog, (20R)-20-t-butyl-5-pregnene-3β,20-diol, C-22 in these synthetic compounds is completely substituted and therefore unavailable for biological hydroxylation (1). (20R)-20-(p-Tolyl)-5-pregnene-3β,20-diol, 1, when incubated with an acetone powder preparation of bovine adrenal mitochondria forms pregnenolone and progesterone in good yield (more than 23%). (20S)-20-(p-Tolyl)-5-pregnen-3β-ol, 2, prepared by Raney nickel hydrogenation of 1, when incubated in a similar fashion yields 1 in large quantity in addition to small amounts of pregnenolone and progesterone. This is the first reported instance of substantial in vitro 20α-hydroxylation of a 22-desoxy substrate, natural or artificial. The styrene 20-(p-tolyl)-5,20-pregnadien-3β-ol, 3, made by dehydration of 1, is not a substrate for side chain cleavage. The results support the previously advanced hypothesis that the true intermediates in the side chain cleavage of cholesterol are reactive complexes of a metalloenzyme and oxygenated steroidal species, and not free hydroxylated compounds. Two reaction mechanisms consistent with these findings are proposed.
- Received June 28, 1973.
- © 1974, by the American Society of Biological Chemists, Inc.
