ALKALOID BIOSYNTHESIS .14. SECOLOGANIN - ITS CONVERSION INTO IPECOSIDE AND ITS ROLE AS BIOLOGICAL PRECURSOR OF INDOLE ALKALOIDS

The preparation of secologanin (V) is described and this product is used for the partial synthesis of desacetylipeco-side (XX) and of ipecoside (XXI). The isomers (XXIII) and (XXIV) were also obtained. Tracer experiments on Vinca rosea plants establish that secologanin is a specific precursor of representative indole alkaloids from the Corynanthe. Aspidosperma, and Iboga families. The further requirement for a true precursor, that its presence in the living system should be demonstrated, is met by isolation of secologanin from Vinca rosea plants both by radiochemical dilution analysis and by macro-isolation. The biosynthesis of secologanin from loganin is established in Vinca rosea and Menyanthes trifoliate plants. A preliminary account of this work has been published.