Three new isocoumarin derivatives from the mangrove endophytic fungus Penicillium sp. YYSJ-3

Three new isocoumarin derivatives, (S)-6,8-dihydroxy-5-(methoxymethyl)-3,7-dimethylisochroman-1-one (1), (S)-6,8-dihydroxy-3,5,7-trimethyl-isochroman-1-one (2) and (R)-2-chloro-3-(8-hydroxy-6-methoxy-1-oxo-1H-isochromen-3-yl) propyl acetate (3), along with four known compounds (4-7) were isolated from a mangrove endophytic fungus Penicillium sp. YYSJ-3. Their structures were established on the basis of the extensive spectroscopic data and HR-ESI-MS analysis. The absolute configurations of 1-3 were further determined by X-ray diffraction analysis and optical rotations. Compounds 3, 6 and 7 showed promising inhibitory activity against alpha-glucosidase, which were stronger than that of the positive control 1-deoxynojirimycin (IC50 141.2 mu mol.L-1).