Cyclopenin is one of an unusual family of benzodiazepine metabolites produced by a number of Penicillium species. Often mistakenly referred to as a mycotoxin, cyclopenin shows little toxicity against mammalian cells, bacteria or fungi in vitro. Cyclopenin is an intermediate in the biosynthesis of 3-O-methyl viridicatin, a strong inhibitor of TNFα-induced replication HIV. Lack of availability has hitherto restricted a more intensive investigation of this interesting metabolite.