Cladoxanthones A and B, Xanthone-Derived Metabolites with a Spiro[cyclopentane-1,2'-[3,9a]ethanoxanthene]-2,4',9',11'-tetraone Skeleton from a sp.

Cladoxanthones A () and B (), two xanthone-derived metabolites featuring a new spiro[cyclopentane-1,2'-[3,9a]ethanoxanthene]-2,4',9',11'(4a')-tetraone skeleton, were isolated from cultures of the ascomycete fungus sp., together with the known mangrovamide J (). Their structures were elucidated primarily by NMR experiments. The absolute configurations of and were assigned by X-ray crystallography using Cu Kα radiation. Compound could be generated from the hypothetical precursors related to α-methylene ketone and dihydro-xanthone via a Diels-Alder reaction, while could be an oxidative coupling product resulting from and . Compounds and showed weakly cytotoxic effects.