Mushroom alkaloids are of a considerable interest as a consequence of their unique secondary metabolites. This work describes the isolation and identification of brotasic acid methyl ester (1) from the fruiting bodies of the mushroom Auricularia sp. After isolation using a series of chromatographic steps, compound 1 was identified by analysis of spectroscopic data and has a novel carbon skeleton. The structure of 1 is related to the structure of the histone deacetylase inhibitor SAHA.