Aristolochic acid B is one of the major components of the carcinogenic plant extract aristolochic acid, is known to be mutagenic and to form DNA adducts in vitro and in vivo.

Cyclo(Pro-Pro) tasted bitter.Verpacamides A-D, a sequence of C11N5 diketopiperazines relating cyclo(Pro-Pro) to cyclo(Pro-Arg), from the marine sponge Axinella vaceleti is possible biogenetic precursors of pyrrole-2-aminoimidazole alkaloids.

Imidazole is a planar 5-membered ring and a highly polar compound. It has been used extensively as a corrosion inhibitor. Imidazole is incorporated into many important biological molecules.