Two New Antibacterial Benzoazepines from a Cigar-Tobacco-Derived Endophytic Aspergillus fumigatus

In this study, two new benzoazepines (1 and 2), together with five known analogs (3–7) were isolated from the cigar-tobacco-derived endophytic Aspergillus fumigatus. Their structures were determined by means of HR-ESI-MS and extensive 1D and 2D NMR spectroscopic studies. All compounds were evaluated for their antibacterial activities against five nitrosobacteria strains Nitrosomonas communis, Nitrosomonas nitrosa, Nitrosospira multiformis, Nitrobacter winogradskyi, and Nitrospira inopinata. Interestingly, compounds 1–7 exhibited notable antibacterial activity with bacteriostatic diameters within the range 13.8 ± 1.9–26.3 ± 2.5 mm against five nitrosobacteria strains, and most of the bacteriostatic diameters are higher than that of positive controls. Owing to the nitrosobacteria having the ability to convert nitrogen components into nitrite in tobacco, and then converting to tobacco-specific nitrosamines (TSNAs), the above compounds have the potential to reduce TSNAs in tobacco by inhibiting nitrosobacteria during the fermentation process of tobacco leaves.