Studies on Monoterpene Glucosides and Related Natural Products. LII. Mechanism for Iridane Skeleton Formation from Acyclic Monoterpenes in the Biosynthesis of Secoiridoid Glucosides and Indole Alkaloids

Abstract

Administration of various ³H-labeled monoterpenes to Catharanthus roseus and Lonicera morrowii demonstrated that secoiridoid glucosides and indole alkaloids of these plants are formed through cyclization of 10-oxoneral or 10-oxogeranial to iridodial followed by further elaboration. This result is contradictory with the report by Kurz et al. which indicated the intermediacy of 9, 10-dihydroxygeraniol and its oxo-derivatives for the biosynthesis of secologanin and indole alkaloids of C. roseus suspension cultures.