Synthesis of 24,28-didehydroaplysterol and X-ray crystal structure of aplysterol: unusual marine sterols

Abstract

The synthesis of 26-methyl-24-methylenecholesterol establishes this as the 24,28-didehydroaplysterol, isolated from the sponge Verongia aerophoba; the structure of 24,26-dimethylcholesterol, previously suggested for aplysterol, occurring in the same sponge as the principal sterol, has been confirmed by single-crystal X-ray diffraction studies of its p-iodobenzoate derivative, which also showed the stereochemistry to be 24R,25S.