Isocoumarin and pyranone derivatives isolated from the mangrove-associated fungus Exserohilum rostratum NS-KS-3 as α-glucosidase inhibitors.

Six new polyketides including three isocoumarins (1-3) and three α-pyranone derivatives (4-6) were isolated from culture of the mangrove-derived fungus Exserohilum rostratum NS-KS-3, together with the known compounds (7-9). The planar structures of these new compounds were determined on the basis of NMR and mass spectroscopic data analyses. The absolute configurations of the new compounds were determined by comparing the experimental ECD spectra with the calculated ECD spectra. The new compounds 1, 2, 4, and the known compound 7 showed α-glucosidase inhibition activities with IC values of 0.093, 0.168, 0.250, and 0.154 mM, respectively.