Cardiac glycosides, development from natural

Natural products are generally classified by a number of criteria functional, structural and biosynthetic. Despite the reservations expressed above, certain functional subdivisions are useful in certain applications. Such terms as antibiotics, hormones or cardiac glycosides are commonly used. The grouping of natural products on the basis of common carbon skeletons is perhaps the most attractive for the chemist. The realization that many natural products fall into distinct structural groups which could be, at least formally, derived from much simpler molecules was an important development in that it led to the proposal of speculative biogenetic hypotheses which were largely responsible for stimulating the rapid development of the field of biosynthesis. However, such an approach is not entirely satisfactory since it is now clear that many compounds which are of similar structural types are derived by quite different routes in vivo. 

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