Steroidal glycoalkaloids: nature and consequences of bioactivity.

Abstract

Of the many compounds that make up the secondary compound profile of plants, the steroidal glycoalkaloids figure amongst the more interesting not only for chemical and biological reasons, but also because they have exerted an important influence on various aspects of human activity and behaviour. Glycoalkaloids are present in more than 350 plant species mainly of the family Solanaceae (and to a lesser extent the Liliaceae). In excess of 75 naturally occurring aglycone structures (alkamines) are known which are based on a C27 cholestane skeleton with additional nitrogen-containing rings or groups that impart basicity and some of the biological activity. In addition, a significant portion of the biological activity of glycoalkaloids derives from an oligosaccharide moiety (comprising up to five monosaccharides and usually C 3 attached) which renders the molecule amphipathic. Some important structures referred to in the text are shown in Figure 1. The chemistry and taxonomic distribution of glycoalkaloids has been comprehensively reviewed by Schreibers1 and Ripperger and Schreiber2, and other aspects by various authors3–11. Thus, although usually referred to as glycoalkaloids, many of these compounds also possess characteristics of plant monodesmosidic saponins. Many glycoalkaloids exhibit two main types of biological activity which very much reflect this ‘dual’ chemical nature, viz. antiacetylcholinesterase activity reminiscent of some alkaloids, and membrane-lytic properties similar to those of saponins.