A Spiro[chroman-3,7′-isochromene]-4,6′(8′<i>H</i>)-dione from the Cordyceps-Colonizing Fungus Fimetariella sp.

Fimetarone A (<b>1</b>), a metabolite with the new spiro[chroman-3,7′-isochromene]-4,6′(8′<i>H</i>)-dione skeleton, was isolated from cultures of the Cordyceps-colonizing fungus Fimetariella sp. Compound <b>1</b> was a 1:1 atropdiastereomeric mixture in NMR data, and a<i>S</i>,9<i>S</i> and a<i>R</i>,9<i>R</i> enantiomers were found and confirmed by X-ray crystallography. Compound <b>1</b> could be derived from the hypothetical precursors 3,4,5-trihydroxy-2-(2-methylene-3,5-dioxohexanoyl)benzoic acid (<b>5</b>) and lapidosin (<b>6</b>)