Xanthone-derived polyketides from the Thai mangrove endophytic fungus Phomopsis sp. xy21

Abstract Six new xanthone-derived polyketides, named phomoxanthones F—K ( 1 – 6 ), along with three known ones, were isolated from Phomopsis sp. xy21, which was isolated as an endophytic fungus from the Thai mangrove Xylocarpus granatum . Phomoxanthone F ( 1 ) represents the first xanthone-derived polyketide containing a 10a-decarboxylated benzopyranone nucleus that was substituted by a 4-methyldihydrofuran-2(3 H )-one moiety at C10a. Phomoxanthones G ( 2 ) and H ( 3 ) are highly oxidized xanthone-derived polyketides containing a novel 5-methyl-6-oxabicyclo[3.2.1]octane motif. This is the first report of a C6- O -C12 bridge in xanthone-derived polyketides. Additionally, a plausible biogenetic pathway for these xanthone-derived polyketides is proposed.