New Diterpenoids and Isocoumarin Derivatives from the Mangrove-Derived Fungus Hypoxylon sp.

Two new diterpenoids, hypoxyterpoids A (1) and B (2), and four new isocoumarin derivatives, hypoxymarins A-D (4-7), together, with seven known metabolites (3 and 8-13) were obtained from the crude extract of the mangrove-derived fungus Hypoxylon sp. The structures of the new compounds were elucidated on the basis of 1- and 2-dimensional (1D/2D) nuclear magnetic resonance (NMR) spectroscopic and mass spectrometric analysis. The absolute configurations of compounds 1, 2, 4, 5, and 7 were determined by comparison of experimental and calculated electronic circular dichroism (ECD) spectra, and the absolute configurations of C-4 ' in 6 and C-9 in 7 were determined by [Rh-2(OCOCF3)(4)]-induced ECD spectra. Compound 1 showed moderate alpha-glucosidase inhibitory activities with IC50 values of 741.5 +/- 2.83 mu M. Compounds 6 and 11 exhibited DPPH scavenging activities with IC50 values of 15.36 +/- 0.24 and 3.69 +/- 0.07 mu M, respectively.