Alkaloid studies. Part LXVI. Reactions of some Aspidosperma alkaloids with m-chloroperbenzoic acid. Removal of the angular ethyl group of aspidospermine

Abstract

The oxidation of 20-oxoaspidospermine (6) and other Aspidosperma alkaloids (2c) and (13b) with m-chloroperbenzoic acid resulted in the formation of the 19-hydroxy-10-ketones (8a), (11 a), and (14). Acetic anhydride–sulphuric acid treatment of (8a) afforded the 5(19)-en-10-one (9a), which with diborane gave N-deacetyl-5-de-ethylaspidospermine (10), an analogue of aspidospermine lacking the angular ethyl group. Alternative attempts to achieve this aim through degradation of the angular methoxycarbonyl group in cylindrocarine (2a) are also reported. The mass spectral fragmentation of several aspidospermine-type alkaloids has been studied with the aid of deuterium-labelled analogues.