This chapter focuses primarily on endogenous molecules as nonmessenger targets for
drug design. There are many such molecules. As discussed earlier, amino acid deriva-
tives, lipids (eicosanoids), nucleoside/nucleotide derivatives, and carbohydrates all
afford heterocyclic leads for drug design. The discussion will not be repeated here.
In addition to endogenous heterocycles, there are also medically important exoge-
nous heterocycles. Nature is a great source of molecular diversity, especially for bioac-
tive molecules. Nature provides a rich source of peptidic (penicillin), lipid (terpenes),
and other (alkaloid) heterocyclic natural products. These compounds are produced in
plants or nonhuman animals, but may exert profound biological effects when adminis-
tered to humans.
Heterocycles which are not biosynthesized in humans, but which are natural products
produced by other life forms, are very important in the history of drug design. This is
particularly true of alkaloids containing a piperidine ring. These include coniine (8.87,
extracted from poison hemlock,Conium maculatum, a member of the Umbelliferae carrot
family), atropine (from Atropa belladonnaand other genera of the Solanaceae plant
family; the plant was calledbelladonna[“beautiful woman”] since it was used by
530 MEDICINAL CHEMISTRY