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

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