Beauvetetraones A-C, phomaligadione-derived polyketide dimers from the entomopathogenic fungus, Beauveria bassiana

We report the isolation of two novel epimeric phomaligadione-derived polyketides, beauvetetraones A-B (1-2), from the entomopathogenic fungus Beauveria bassiana. Beauvetetraones A and B feature an unprecedented methylene-bridged phloroglucinol skeleton with a highly rearranged scaffold. In addition, a dimer of two phomaligadiones, named beauvetetraone C, was isolated for the first time from a natural source. The structures of compounds 1-3 including their absolute configurations were unambiguously assigned by NMR spectroscopic analyses, phenylglycine methyl ester (PGME) analysis, and quantum chemical ECD calculations. A putative biosynthetic pathway for beauvetetraones A-C is proposed.