Biosynthesis of the nicandrenoids: stages in the oxidative elaboration of the side chain and the fate of the diastereotopic 25-methyl groups of 24-methylenecholesterol

Abstract

Experiments with Nicandra physaloides plants show that the insect antifeedant steroid Nic-1 (1) is formed from 24-methylenecholesterol: in double bond isomerisation to 24-methylcholesta-5,24-dien-3β-ol, the 25-(pro-S) methyl in (2) becomes the 25-(pro-Z) methyl, in (3); further oxidations lead to triol (6) and hence to lactol (1) with partial retention of 26-hydrogen.