A spiro[chroman-3,7'-isochromene]-4,6'(8'H)-dione from the Cordyceps-colonizing fungus Fimetariella sp.

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