Antioxidative Indenone and Benzophenone Derivatives from the Mangrove-Derived Fungus Cytospora heveae NSHSJ-2

Seven new polyketides, including four indenone derivatives, cytoindenones A-C (1, 3-4), 3 '-methoxycytoindenone A (2), a benzophenone derivative, cytorhizophin J (6), and a pair of tetralone enantiomers, (+/-)-4,6-dihydroxy-5-methoxy-alpha-tetralone (7), together with a known compound (5) were obtained from the endophytic fungus Cytospora heveae NSHSJ-2 isolated from the fresh stem of the mangrove plant Sonneratia caseolaris. Compound 3 represented the first natural indenone monomer substituted by two benzene moieties at C-2 and C-3. Their structures were determined by the analysis of 1D and 2D NMR, as well as mass spectroscopic data, and the absolute configurations of (+/-)-7 were determined on the basis of the observed specific rotation value compared with those of the tetralone derivatives previously reported. In bioactivity assays, compounds 1, 4-6 showed potent DPPH center dot scavenging activities, with EC50 values ranging from 9.5 to 16.6 mu M, better than the positive control ascorbic acid (21.9 mu M); compounds 2-3 also exhibited DPPH center dot scavenging activities comparable to ascorbic acid.