Voacanga alkaloids

The first reported preparation of a binary alkaloid of the vinblastine type came from the efforts of J. Harley-Mason and Atta-ur-Rahman 15,16). In accord with a proposal for the synthesis of vinblastine-type alkaloids (77), their synthetic strategy was based on a coupling reaction previously developed by G. Biichi et al. for the synthesis of Voacanga alkaloids (75), as shown in Scheme 1. There, acid-catalyzed ionization... 

Under this heading are collected the alkaloids from the plants given in Table I, with the exception of the iboga bases already considered and those dealt with under Voacanga alkaloids. 

Gonopharyngia durissima has afforded iboga bases, two dimeric alkaloids discussed under Voacanga alkaloids, and a trace of a base, alkaloid E, mp 191°-193°, pif a 7.26, UV-maxima at 210 and 305 mp, which differed from the other isolates in having no carbonyl absorption in the IR-spectrum (14). Gonopharyngia pachysiphon, in contrast to C. durissima, has yielded only steroidal bases (45). 

From a pharmacological point of view, the Voacanga alkaloids are relatively nontoxic, rapidly eliminated, and of no great interest (68). The reported potent cardiotonic properties (9, 54, 69) of some of these alkaloids have apparently not withstood the test of time (52). 

In the past decades, many stndies were condncted and reported that focused on the identification of the wide array of V. africana alkaloids and the main ergot alkaloids have been isolated. With the improvement of the isolation procedures many minor components have been identified (Table IV). Voacanga alkaloids have been isolated from leaves, seeds (mature and inmature), tmnk and root bark (Table IV). 

Table V. Voacanga Alkaloids Reported in Other Speeies of the Apoeyaneeae Family...

Details of the Czech group s chiroptical studies of the Iboga and Voacanga alkaloids, summarized previously, " have now been published. ... 

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