Plants, insects, and marine invertebrates utilize natural
products as a means whereby they defend themselves
chemically against predation and consumption (e.g., herbivory).
A fascinating example is provided by the pupae of
the coccinellid beetle, Epilachna borealis, which exert a
chemical defensive mechanism against predators through the
secretion from their glandular hairs of droplets containing a
library of hundreds of large-ring (up to 98 members)
macrocyclic polyamines, with the simplest example having
the generic formula shown (8; Scheme 2).17 The use of three
simple (2-hydroxyethylamino)alkanoic acid precursors in the
building of these libraries provides clear evidence that
combinatorial chemistry was pioneered and widely used in
Nature for the synthesis of biologically active compound
libraries.