William R. Nes

The H-migration in the alkylation of sterols at C-24☆

Abstract 1. 1. 24-Tritiolanosterol was prepared from lanosterol. 2. 2. Incubation in vivo of 24-tritiolanosterol with seeds of Pinus pinea yielded labeled 24-ethylidenecholesterol which was identified by ozonolysis to labeled 24-ketocholesterol. 3. 3. The position of the label in 24-ketocholesterol was shown to be C-25 by reduction to the labeled 24-hydroxy derivative followed by dehydration to desmosterol with loss of label. 4. 4. The results are in agreement with the predicted 1,2-H-migration3 during alkylation of the Δ24-bond.

The configuration at C-20 of a natural Δ5-C26-sterol

The (20R)- and (20S)-epimers of halosterol, a naturally occurring C26-analogue of cholesterol, have been synthesized; the (20R)-epimer was identical with and the (20S)-epimer different from the sterol derived from the naturally occurring 22-dehydro derivative.