Chapter 9 The Iboga and Voacanga Alkaloids
This chapter describes the iboga and voacanga alkaloids. The iboga alkaloids presently number twelve, if their oxidation products are excluded, all from apocynaceous plants of the genera Conopharyngia (Plumeria), Ervatamia, Gabunea, Stemmadenia, Tabernaemontana, Voacanga, Vinca (Lochnera, Catharanthus), and Tabernanthe. It was from the last genus that the parent pentacyclic heterocycle, ibogamine, was first obtained. The structures of these compounds depend entirely on their interrelationships with ibogaine, whose structure was derived by degradation and X-ray analysis. The absolute stereochemistry has not been rigorously determined, and none of the bases, at the time of writing, had been synthesized. The alkaloids can be conveniently grouped as shown in the table presented in the chapter, and it should be noted that the trivial names currently used obscure their similarities. Many of the alkaloids suffer facile autoxidation to yield hydroperoxyand hydroxyindolenines, whose further degradation products are 4-hydroxyquinolines and pseudoindoxyls. Therefore, the isolation of these products from the plant cannot by itself be taken as proof of their natural occurrence. This situation is similar to that which exists for several of the tertiary bases obtained from Hunteria eburnea Pichon and possibly for some of the dimeric curare alkaloids derived from the Wieland-Gumlich aldehyde
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