New furoisocoumarins and isocoumarins from the mangrove endophytic fungus <i>Aspergillus</i> sp. 085242

Abstract

The chemical investigation of the mangrove endophytic fungus <i>Aspergillus</i> sp. 085242 afforded eight isocoumarin derivatives <b>1</b>-<b>8</b> and one isoquinoline <b>9</b>. Asperisocoumarins A and B (<b>1</b> and <b>2</b>) were new furoisocoumarins, and asperisocoumarins E and F (<b>5</b> and <b>6</b>) were new isocoumarins. Their structures were established by analysis of their spectroscopic data and the absolute configuration of compound <b>2</b> was unambiguously determined by X-ray structure analysis and ECD calculation. Moreover, the absolute configurations of compounds <b>3</b>-<b>5</b> were assigned by comparison of their ECD spectra with isocoumarins described in the literature. Asperisocoumarins C and D (<b>3</b> and <b>4</b>) were fully characterized spectroscopically and isolated from a natural source for the first time. Asperisocoumarins A-D (<b>1</b>-<b>4</b>) related to the class of furo[3,2-<i>h</i>]isocoumarins are rarely occurring in natural sources. Compounds <b>2</b>, <b>5</b>, and <b>6</b> showed moderate α-glucosidase inhibitory activity with IC₅₀ of 87.8, 52.3, and 95.6 μM, respectively. In addition, compounds <b>1</b> and <b>3</b> exhibited weak radical scavenging activity with EC₅₀ values of 125 and 138 μM, respectively.