Heterocycles as Drugs and Drug Design Targets

Natural product exogenous (exogenous to humans, but endogenous to other life forms) heterocycles 

Each of these four categories is rich in drug discovery lead candidates. 

This chapter focuses primarily on endogenous molecules as nonmessenger targets for drug design. There are many such molecules. As discussed earlier, amino acid derivatives, 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 exogenous heterocycles. Nature is a great source of molecular diversity, especially for bioactive 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 administered 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 belladonna and other genera of the Solanaceae plant family the plant was called belladonna [ beautiful woman ] since it was used by 

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