Evolution of Indole Alkaloids in Apocynaceae

Abstract

The indole alkaloids are outstanding among secondary plant metabolites in their structural intricacy and diversity. Tryptophan and secologanin, through their condensation product vincoside (code I, Table 9.1) as intermediate, are responsible for the biosynthesis of three indole alkaloid groups, characterized by different basic carbon skeletons, the corynanthe (codes prefixed I → V), aspidosperma (codes prefixed VI →, except for VI.3 →), and iboga (codes VI.3 types. The code of each skeleton of the indole alkaloids (Table 9.1) indicates its position on a biogenetic map. Comments on the construction of such maps, as well as their use in the determination of specialization values (S) for skeleta, together with rules for the determination of oxidation values (O) of compounds, are presented in Chapter 6. With reference to the latter topic, the point value for a carboxyl, which is of course (oxy- + oxo-functions) 3, is included even for skeletons which have lost this group during their biosynthesis, since such loss does not imply diminution of oxidation level (cf. Chap. 5).