| Summary: | Three new dibenzo-<i>α</i>-pyrone derivatives, alternolides A–C (<b>1</b>–<b>3</b>), and seven known congeners (<b>4</b>–<b>10</b>) were isolated from the marine-derived fungus of <i>Alternaria alternata</i> LW37 assisted by the one strain-many compounds (OSMAC) strategy. The structures of <b>1</b>–<b>3</b> were established by extensive spectroscopic analyses, and their absolute configurations were determined by modified Snatzke′s method and electronic circular dichroism (ECD) calculations. Compounds <b>6</b> and <b>7</b> showed good 1,1-diphenyl-2-picrylhydrazyl (DPPH) antioxidant scavenging activities with IC<sub>50</sub> values of 83.94 ± 4.14 and 23.60 ± 1.23 µM, respectively. Additionally, <b>2</b>, <b>3</b> and <b>7</b> exhibited inhibitory effects against <i>α</i>-glucosidase with IC<sub>50</sub> values of 725.85 ± 4.75, 451.25 ± 6.95 and 6.27 ± 0.68 µM, respectively. The enzyme kinetics study indicated <b>2</b> and <b>3</b> were mixed-type inhibitors of <i>α</i>-glucosidase with <i>K</i><sub>i</sub> values of 347.0 and 108.5 µM, respectively. Furthermore, the interactions of <b>2</b>, <b>3</b> and <b>7</b> with <i>α</i>-glucosidase were investigated by molecular docking.
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