SOME ASPECTS OF THE CHEMISTRY OF CATHARANTHINE AND CLEAVAMINE

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Abstract
Chemical and spectroscopic evidence is presented for an interesting acid-catalyzed rearrangement of the alkaloid catharanthine. Four reaction products (descarbomethoxycatharanthine and cleavamine and its two dihydro derivatives) were isolated, and their formation is rationalized by a mechanism involving ring-opened intermediates. Evidence is presented in support of the proposed mechanism and, in particular, a novel transannular cyclization leading to the Iboga alkaloid skeleton is shown in support of the steps postulated for the formation of descarbomethoxycatharanthine.The X-ray analysis of cleavamine methiodide established the absolute configuration of the lone asymmetric center present in the molecule and, from these results, the absolute configuration of the Iboga alkaloids can be derived.