Penicillide is a tetracycle with a central 8-membered lactone ring, produced by Penicillium, Talaromyces and other sp. first reported by Miura and co-workers, Yamagata University Japan, in 1974. Penicillide, an oxytocin inhibitor, also inhibits calpain, a calcium-activated papain-like protease with an IC50 of 7 μM becoming ineffective at 200 μM. Like its acetyl derivative, purpactin A, penicillide is a potent acyl CoA:cholesterol acyltransferase inhibitor. Penicillide is reported to be a plant growth inhibitor.