Abstract
Asymmetric dihydroxylation of (20(22) E)-cholesta-5,20(22)-dien-3β-ol acetate ( 2a), prepared from pregnenolone, gave a 1:1 mixture (67% yield) of (20 R,22 R)-cholest-5-ene-3β,20,22-triol 3-acetate ( 3a) and its 20 S,22 S isomer 3b. Highly purified 3a and 3b were obtained by semipreparative silver ion high performance liquid chromatography. Saponification of 3a and 3b gave (20 R,22 R)-cholest-5-ene-3β,20,22-triol ( 4a) and its 20 S,22 S isomer 4b. This simple approach provided the natural isomer 4a more efficiently than previously described chemical or enzymatic syntheses. Full 1H and 13C nuclear magnetic resonance data were presented for triols 4a and 4b and their synthetic precursors. Side-chain conformations of 2a, its 20(22)Z isomer, 4a, and 4b were studied by molecular mechanics and nuclear Overhauser effect difference spectroscopy.
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