good supply of blood to the biting insect; such compounds could be useful in the treatment
of stroke secondary to blood clots within the brain. Amphibian evolution has enabled
the biosynthesis of antibacterial peptides on the skins of frogs so that they can avoid
infections as they swim through stagnant swamp waters; peptides such as these could
be a good starting point for the peptidomimetic design of novel antibacterial agents.
Reptile evolution has culminated in the biosynthesis of neuroactive venoms for pur-
poses of hunting and defense; these molecules have been fine-tuned by evolution as
agents specific for neurotransmitter receptors. Plant evolution has culminated in a wide
variety of biomolecules that affect any animal that may choose to eat them: it is bio-
logically advantageous for some plants to be eaten so that their seeds can be dispersed
in the stool of the animal that ate them; conversely, it is biologically advantageous for
other plants to produce noxious chemicals to decrease the likelihood of their being
eaten. Because of these diverse biological activities, any of these non-human biosyn-
thetic molecules could, in principle, be a lead compound for human drug discovery.
Another promising feature of animal- or plant-based natural products is that they are
a superb source of molecular diversity. As a synthetic chemist, Nature is much more
creative and is not constrained to the same finite number of synthetic reactions typically
employed by human synthetic organic chemists. When designing new innovative
therapies, molecular diversity is important. Furthermore, when developing compound
libraries for high throughput screening (see section 3.2.6), it is important to have
libraries that capture molecular diversity and are not merely large collections of struc-
turally similar analogs.
Although ethnopharmacology, the scientific investigation of natural products, folk
medicine, and traditional remedies, has led to some bona fide drugs (e.g., reserpine (3.1),
quinine (3.2), ephedrine (3.3)), it has not proven to be a reliable or efficient source of
leads. However, natural products have always been and still are an inexhaustible source
of drug leads as well as drugs. Renewed interest in natural products and the novel struc-
tures they provide is especially noticeable in marine pharmacology, a practically virgin
116 MEDICINAL CHEMISTRY