Stages in the biosynthesis of the epoxy lactol side chain of Nic-1, insect antifeedant steroid of Nicandra physaloides

Abstract

Isotopic labelling experiments with Nicandra physaloides plants show that the insect antifeedant steroid Nic-1 1 is formed from 24(28)-methylenecholesterol 2a; in the double bond isomerisation to 24-methylcholesta-5,24(25)-dien-3β-ol 3a, the 25-(pro-R) methyl becomes C-27, the pro-Z methyl in 3a. Hydroxylations lead through the diol 4a to the triol 6a, and hence to the lactol 7a, with retention of the 26-hydrogen.