Voacamine Voacangine

The second component of voacamine, voacangine (142), has been unambiguously correlated with catharanthine (152). The latter is converted by reductive demethoxycarbonylation to cleavamine (153), whose absolute stereochemistry has been determined by X-ray analysis cf. ref. 77). 

V. braceata has been identified as an African botanical with hallucigenogenic potential. Stem barks of V. braceata contain 2.46% of alkaloids mainly voacamine/voacamine N-oxide, 20- epi voacamine and voacangine, although these alkaloids are related with ibogaine, it was concluded that there is no evidence of hallucinogenic properties reported De Smet 21). 

Voacamine readily undergoes mono-demethoxycarbonylation in which the methoxycarbonyl group of the voacangine half (a-indolylacetic acid derivative) is lost. 

From the same plant voacamine V( )-oxide (159) has also been isolated. Acid-catalysed hydrolysis gives voacangine (142) and catalytic hydrogenation gives 19,20-dihydrovoacamine (146). The important n.m.r. signals of voacamine are present with the same chemical shifts in the spectrum of the N(j,)-oxide apart from the singlet which is shifted downfield by 0.7 p.p.m., typical... 

Voacamidine (145) has been isolated from both V. africana and Conopharyngia durissima Stapf. On acid treatment it is converted partly to voacamine (141) and partly to voacangine (142) along with the vobasinol decomposition products. As mentioned (see Voacamine, p. 244) it can be partially synthesised along with voacamine (141) by acid-catalysed condensation of voacangine (142) and vobasinol (144) as the kinetically-controlled product (see refs. 77 and 85). In contrast to that of voacamine (141) its n.m.r. spectrum shows two doublets at... 

A partial synthesis of voacamine (and voacamidine, XXVI) was carried out by condensing voacangine and vobasinol in refluxing 1.5% methanolic hydrochloric acid 45, 49). This vinylogous Mannich type condensation (Chart VI) has an analogy in the known dimerization of 1-hydroxy-1,2,3,4-tetrahydrocarbazole 45, 50). 

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