Amaurones A-K: Polyketides from the Fish Gut-Derived Fungus Amauroascus sp. CMB-F713.

Using a molecular networking guided strategy, chemical analysis of the Australian mullet fish gastrointestinal tract-derived fungus Amauroascus sp. CMB-F713 yielded a family of polyketide pyrones, amaurones A-I (1-9), featuring an unprecedented carbon skeleton. Structures were assigned to 1-9 by detailed spectroscopic analysis (including X-ray analysis of 1), biosynthetic considerations, and chemical interconversions. For example, the orthoacetate 5 was unstable when stored dry at room temperature, transforming to the monoacetates 2 and 3, while mild heating (40 °C) prompted quantitative conversion of 3 to 2, via an intramolecular trans-acetylation. Likewise, during handling, the monoacetate 1 was prone to intramolecular trans-acetylation, leading to an equilibrium mixture with the isomeric monoacetate amaurone J (10), confirmed when partial hydrolysis of the diacetate 2 yielded the monoacetates 1 and 10 and the triol amaurone K (11).