First discovery and stucture-activity relationship study of phenanthroquinolizidines as novel antiviral agents against tobacco mosaic virus (TMV).

A series of phenanthroquinolizidine alkaloids 1-24 were prepared and first evaluated for their antiviral activity against tobacco mosaic virus (TMV). The bioassay results showed that most of these compounds exhibited good to excellent in vivo anti-TMV activity, of which compounds 1, 2, 15 and 16 displayed significantly higher activity than (R)-antofine and commercial Ningnanmycin at the same test condition. The substituents on the phenanthrene moiety play an important role for maintaining high in vivo antiviral activity. The introduction of 6-hydroxyl, which is proposed to interact with TMV RNA, did increased anti-TMV activity. The 14aR-configuration was confirmed to be the preferred antiviral configuration for phenanthroquinolizidine alkaloids. Introduction of hydroxy group at 15-position of phenanthroquinolizidine alkaloids increased activity for S-configuration but decreased activity for R-configuration. Present study provides fundamental support for development and optimization of phenanthroquinolizidine alkaloids as potential inhibitors of plant virus.