Chemotaxonomic studies of mesembrine-type alkaloids in Sceletium plant species

Abstract

Complementary medicines containing the succulent herb Sceletium are being sold without information regarding their phytochemical contents, which is essential for the quality control of medicines. Furthermore, several different Sceletium species exist and little has been reported on the alkaloidal identities and contents of the various species. We therefore conducted phytochemical investigations on six selected Sceletium specimens, identified on the basis of their venation pattern as either 'emarcidum' or 'tortuosum' type. The tortuosum type consisted of S. tortuosum, S. expansum and S. strictum, whereas the emarcidum type consisted of S. emarcidum, S. exalatum and S. rigidum. Analysis was conducted by high-performance liquid chromatography with UV and alkaloids were identified by online mass spectroscopy. S. tortuosum and S. expansum samples contained mesembrine together with mesembrenone, mesembranol and epimesembranol, although the latter two alkaloids were present in low concentrations in S. expansum. S. strictum contained mesembrenone, mesembrine and either 4'-O-demethylmesembrenone or 4'-O-demethylmesembrenol. The emarcidum type specimens showed a complete absence of the major alkaloid mesembrine, as well as the other alkaloids usually associated with these species. In only one of the species of the emarcidum type - S. exalatum - two peaks corresponded to either 4'-O-demethylmesembrenone or O-methyljoubertiamine and either 4'-O-demethylmesembrenol or N-demethylmesembrenol, respectively. This study clearly indicates that not all Sceletium species contain the mesembrine-type alkaloids usually associated with Sceletium. It is thus important to identify the correct Sceletium species to ensure correct alkaloidal content for the manufacture and quality control of products containing this plant material. © 2013. The Authors. Published under a Creative Commons Attribution Licence.