Epicoccarines A, B and epipyridone: tetramic acids and pyridone alkaloids from an Epicoccum sp. associated with the tree fungus Pholiota squarrosa

Abstract

Investigation of the metabolic profile of a fungus (Epicoccum sp.) isolated from the fruiting body of the tree fungus Pholiota squarrosa led to the discovery of two novel tetramic acid derivatives, epicoccarine A (2) and B (3), as well as a new pyridone alkaloid, epipyridone (1), with an unusually cyclized side chain. It appears that 1 is biogenetically derived from the ring expansion of 2 followed by a proposed hetero-Diels–Alder reaction. 2 shows selective antibacterial activity against Gram positive bacteria, in particular Mycobacterium vaccae.