Studies on the Biosynthetic Conversion of Cholesterol into Pregnenolone SIDE CHAIN CLEAVAGE OF A t-BUTYL ANALOG OF 20α-HYDROXYCHOLESTEROL, (20R)-20-t-BUTYL-5PREGNENE-3β,20-DIOL, A COMPOUND COMPLETELY SUBSTITUTED AT C-22

Brian Luttrell; Richard B. Hochberg; W. Ross Dixon; Patrick D. McDonald; Seymour Lieberman

Studies on the Biosynthetic Conversion of Cholesterol into Pregnenolone

SIDE CHAIN CLEAVAGE OF A t-BUTYL ANALOG OF 20α-HYDROXYCHOLESTEROL, (20R)-20-t-BUTYL-5PREGNENE-3β,20-DIOL, A COMPOUND COMPLETELY SUBSTITUTED AT C-22

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

Abstract

(20R)-20-t-Butyl-5-pregnene-3β,20-diol, an analog of 20α-hydroxycholesterol, has been synthesized and its metabolism studied. Since C-22 in this synthetic compound is completely substituted, this position is unavailable for biological oxygenation. When injected intravenously into a rabbit, the t-butyl analog is metabolized to urinary pregnanediol. When incubated with sonicated mitochondria from bovine adrenal glands, it is converted into pregnenolone. Two mechanisms consistent with these findings are proposed; both predict the involvement of reactive, transient, intermediate complexes which are represented simply either as radical or ionic species. However, the actual mechanism may best be imagined to be some hybrid of these two extreme processes. These and other results form the basis of a new hypothesis for the pathways used for the biosynthesis of pregnenolone from cholesterol. In this scheme, the traditional side chain-hydroxylated compounds are not obligatory intermediates; rather, they are considered to be by-products resulting from competitive reactions of short lived, reactive species.