Berkeleyamide B is a 4-pyrone isolated from the extremophilic fungus, Penicillium rubrum, collected from the Berkeley Pit Lake, Butte by Stierle and colleagues, University of Montana in 2007. Berkeleyamide B was speculated to be formed biosynthetically from the condensation of a phenyl triketide with leucine, differing from the other berkeleyamides by the presence of a 4-pyrone core structure. Berkeleyamide B has demonstrated in vitro activity against caspase-1 and matrix metalloproteinase-3, which are regulated in many tumors.