Cynanchum komarovii Al. Iljinski. (Asclepiadaceae) is a wild shrub, widely distributed in the northwest part of the People's Republic of China. The alcoholic extract from the aerial parts of C. komarovii was found to show potent antiviral activity against tobacco mosaic virus (TMV), potato virus Y(PVY) and turnip mosaic virus (TuMV). Using a bioassay- directed fractionation approach, the phenanthroindolizidine alkaloids (G), including two known compounds, 7-demethoxytylophorine (antofine) (1) and N-oxide-7- demethoxytylophorine (N-oxide antofine) (2), were isolated rom the extract. The structures of 1 and 2 were established by comparison with authentic spectra. Compound 1 was confirmed to be the major active component against TMV among the alkaloids G. Bioassay performed by the conventional half-leaf method revealed that the alkaloid G showed highly inhibitory activity against TMV, PVY and TuMV. The major active alkaloid 1, exhibited 60% inhibition against TMV at a concentration of 1.0 μg/mL, while a commercial antiviral 2, 4-dioxo-hexahydro-1, 3, 5-triazine (DHT) only showed 50% inhibition at 500 μg/mL under the same conditions.

Key words: PESTICIDES, CHEMICAL COMPOSITION, BIOLOGICAL ACTIVITY, PLANT VIRUS DISEASES, INDOLE ALKALOIDS, ALKALOID, TYLOPHORA OVATA, TOBACCO MOSAIC VIRUS, POTATO X DISEASE VIRUS, LONING