Abstract
Three novel macrocyclic tetralactams, gunnilactam A (1), gunnilactam B (2), and gunnilactam C (3), were isolated from the submerged fermentation broth of Paecilomyces gunnii, an entomogenous fungus identified as the anamorph of Cordyceps gunnii. Their structures were determined using NMR data, HREIMS, and single-crystal X-ray crystallography. Gunnilactam A exhibited selective cytotoxic activity against human prostate cancer C42B cells with an IC50 value of 5.4 μM.