Koumine-type alkaloids

Koumine (70) is a principal alkaloid of G. elegans Benth. (35-39). Recent clinical experiments showed the effect of koumine on malignant tumors and its analgesic activity with no additive side effects (2). Because of the novelty of its hexacyclic cage structure, many chemical and synthetic studies have been conducted (1). 

The presence of koumine Nb-oxide (71) in the leaves of G. elegans was reported (Fig. 4) (6). Oxidation of koumine (70) with /n-chloroperbenzoic acid (/n-CPBA) produced two diastereomeric iVb-oxides, one of which was identical with the natural A -oxide (71). From the H-NMR spectral analysis, the configuration on can be deduced to be (5) in the natural N-oxide. Unnatural N-oxide gave crystals suitable for X-ray analysis, whose result confirmed the structural conclusion obtained from H-NMR analysis. 

The isolation of a pair of 19-hydroxydihydro derivatives of koumine from 

elegans was independently reported by two research groups. The Beijing 

2-Dihydrokoumine (74) was isolated as a natural product 42), although it had been prepared from koumine (70) during its structure elucidation 43). In this report, modified Hofmann degradation of koumine derivative was also described. 

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Koumine-type Alkaloids from Gelsemium Species... 

Sakai S, Yamanaka E, Kitajima M, Yokota M, Aimi N, Wongserpipatana S, Ponglux D 1986 Biomimetic synthesis of koumine skeleton partial synthesis of 11-methoxykoumine (Gelsemium-type alkaloid) from 18-hydroxygardnerine. Tetrahedron Lett 27 4585-4588... 

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