Side chain modified sterols as probes into insect molting hormone metabolism. II: Synthesis of monofluorocholesterols

The hydroxylations of the cholesterol side chain at C-20, 22, and 25 are key terminal events in ecdysone biogenesis. We have prepared the C-20, C-22, C-24, and C-25 monofluorinated cholesterols as potential inhibitors of these hydroxylation events, and preliminary bioassay results in Manduca sexta are reported. The synthesis of [26 14C]-20-fluorocholesterol is also described. Although the 20-, 22-,and 25-monofluorocholesterols do not appear to affect larval growth and development, the 24-fluoro isomer shows a moderate retardation of growth and a modest increase in mortality.