Antibacterial Naphthoquinones from a Nicotiana tabacum Derived Endophytic Fusarium solani

In this study, two new (1 and 2), together with five known (3–4) naphthoquinones were isolated from the Nicotiana tabacum-derived endophytic Fusarium solani. 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 the bacteriostatic diamater in the range of 3.2 ± 1.7~25.4 ± 2.3 mm against five nitrosobacteria strains, and most of the bacteriostatic diamaters were higher than that of positive control. Due to the nitrosobacteria having the ability to convert nitrogen components into nitrosamines in tobacco, and then convert them into 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.