Bioactivity Isochromenes from Cigar Tobacco-Derived Endophytic Fungus Aspergillus fumigatus

Two new isochromenes, 1-(8-methoxy-3-methyl-1H-isochromen-6-yl)propan-1-one (1) and 3-hydroxy-1-(8- methoxy-3-methyl-1H-isochromen-7-yl)propan-1-one (2), along with five known ones, (3–7) were isolated from the fermentation products of a cigar tobacco-derived endophytic fungus Aspergillus fumigatus. Their structures were elucidated by spectroscopic methods, including extensive 1D and 2D NMR techniques. Compounds 1 and 2 were evaluated for their antibacterial activities against Pseudomonas syringae (the main pathogenic sources of tobacco angular spot disease). Compounds 1 and 2 showed activity with MIC50 values of 6.8 and 8.4 μg/mL, respectively, whereas the MIC50 value of the positive control (agricultural streptomycin) is 2.2 μg/mL. The efficiencies of 1 and 2 are lower than that of the positive control.