Cinnamic acid intermediates as precursors to mesembrine and some observations on the late stages in the biosynthesis of the mesembrine alkaloids

Abstract

Experiments with various labelled cinnamic acid derivatives establish, in conjunction with previous work, that the incorporation of phenylalanine into the 3a-aryl octahydroindole ring system of the mesembrine alkaloids occurs via the intermediacy of cinnamic acid and 4′-hydroxycinnamic acid. The major pathway to the 3′,4′-di-oxyaryl substituted alkaloids proceeds via 4′-hydroxydihydrocinnamic acid (4′-phloretic acid), and 3′4′-dioxy-genated cinnamic acids are not involved as intermediates on this major pathway. In accord with this latter finding, the 3′-aryl oxygen substituent is introduced at a late state in the biosynthesis as evidenced by the bioconversion in S. strictum of sceletenone to mesembrenol and other related alkaloids. The late stages in the biosynthesis of the alkaloids are shown to involve the sequence: sceletenone, 4′- O-demethylmesembrenone, mesembrenone. Mesembrenone is converted to mesembrine, mesembrenol and mesembranol.