Studies on the Biosynthetic Conversion of Cholesterol into Pregnenolone

• Published in: The Journal of biological chemistry Vol. 249; no. 4; pp. 1277 - 1285
• Main Authors: Hochberg, Richard B., McDonald, Patrick D., Feldman, Mark, Lieberman, Seymour
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 25.02.1974; American Society for Biochemistry and Molecular Biology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(19)42972-4

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.