(–)-Peniisocoumarin D, an unreported isocoumarin derivative isolated from the coculture of marine algicolous fungal strains <i>Trichoderma flagellatum</i> 12A1N and <i>Fusarium proliferatum</i> 1023F

(-)-Peniisocoumarin D (<b>1a</b>), a new isocoumarin derivative, together with its enantiomer (+)-peniisocoumarin D (<b>1b</b>) and nine other known isolates (<b>2-10</b>), was obtained from the coculture of two marine algicolous fungi <i>Trichoderma flagellatum</i> 12A1N and <i>Fusarium proliferatum</i> 1023 F. The structure identification of <b>1a</b> was conducted by spectroscopic analysis (including 1D/2D NMR and HR-MS experiments) and comparison with the ECD and optical rotation data of its enantiomer <b>1b</b> in the literature. Some isolates (<b>1a</b>, <b>1b</b> and <b>2-5</b>) were assessed for growth inhibition of three plant-pathogenic fungi (<i>Colletotrichum gloeosporioides</i>, <i>Fusarium oxysporum</i> f. sp. <i>cubense</i> and <i>Glomerella cingulata</i>). Compounds <b>3</b> and <b>4</b> exhibited weak inhibitory effects against <i>G. cingulata</i> with MICs of 64 <i>μ</i>g/mL.