Synthesis and Biological Activity of Novel Oxazinyl Flavonoids as Antiviral and Anti-Phytopathogenic Fungus Agents

A series of oxazinyl flavonoids were synthesized on the basis of flavone. The structures of all target compounds were characterized by 1H NMR, 13C NMR, and HRMS. The effect of the different substituent on the N-position of oxazinyl flavonoids against tobacco mosaic virus (TMV) activities and plant pathogen activities was systematically investigated. In vivo anti-TMV activity showed that most of the compounds showed moderate-to-excellent antiviral activities against TMV at 500 μg/mL. Compounds 6b, 6d, 6j–6k, and 6n–6q showed better antiviral activities than ribavirin (a commercially available antiviral agent) and apigenin. In particular, compounds 6n and 6p even displayed slightly higher activities than ningnanmycin, which were expected to become new antiviral candidates. Antiviral mechanism research by molecular docking exhibited that compounds 6n and 6p could interact with TMV CP and inhibit virus assembly. Then, the antifungal activities of these compounds against six kinds of plant pathogenic fungi were tested, and the results showed that these oxazinyl flavonoids had broad-spectrum fungicidal activities. Compounds 6h exhibited antifungal activity of up to 91% against Physalospora piricola and might become a candidate drug for new fungicides.