Plants and cardiac glycosides.

It is often asked why plants contain such remarkable compounds, sometimes beyond the practical reach of the synthetic chemist. What use are these compounds to the plant itself? Defence against predators is one answer although it has to be said that many of today's predators did not exist when the flowering plants, the angiosperms, evolved 80-100 million years ago. It has been shown for example that the methylxanthines in tea and coffee have static and cidal activity against insect pests.' Glycosides are usually compounds of plant origin. They are made up of one or more sugars combined with an alcohol, a phenol, or a complex molecule such as a steroid nucleus. The non-sugar moiety or aglycone is also called a genin. Because they do not contain nitrogen it is wrong to call them alkaloids. In addition to the cardiac glycosides with their cyclopentanoperhydrophenanthrene nucleus in the genin moiety there are other glycosidal plant substances such as the anthraquinone derivatives senna, rhubarb, aloe, and cascara; saponins; cyanogenetic glycosides such as amygdalin from bitter almond; terpene and sterol glycosides; glycosidal dyes and pigments; and finally gums and tannins. The venom glands of the skin of the toad (Bufo) contain digitalis like compounds and this animal gives its name to that group of the glycosides which have a steroid skeleton of 24 carbon atoms (C24), the bufadienolides. A few plant glycosides also belong to this group, notably those from squill, but all others have a C23 skeleton and belong to the cardenolides group. The genus Digitalis is named after the shape of the flowers (digitus, a finger). Although ingenious alternatives have been proposed to explain the common name, foxglove, there is no doubt that this title does mean the glove of a fox. The genus comprises biennial or perennial herbs, or rarely small shrubs, with leaves which are simple, arranged alternately, and sometimes with the lowest leaves forming a rosette. They are natives of Europe, North Africa, and West Asia but not of China. The formerly named