Four New Isocoumarins from the Mangrove Fungus Alternaria Malorum with Antimicrobial Activities

Abstract Four new isocoumarins, alternariethers A–C ( 1 – 3 ) and alternariester ( 4 ) were separated from the fermentation of the fungus Alternaria malorum FL39, purified from Myoporum bontioides . Their structures were ascertained using NMR and HR‐ESI‐MS spectroscopy. For compound 4 , the absolute configuration was solved with the help of ECD calculation and the DP4+ method. Compared with the positive control triadimefon, compound 1 showed more potent antifungal effects on Colletotrichum musae . The antifungal effects of compounds 1 , 2 , and 3 on Fusarium oxysporum and Fusarium graminearum , of compound 4 on F. oxysporum , were equal to those of triadimefon. Except for compound 4 which was inactive against Escherichia coli with O78 serotype, all compounds showed moderate or weak antibacterial activity against Staphylococcus aureus ATCC 6538 and E. coli with O6 or O78 serotype.