Phenolic Compounds from Cassia siamea and Their Anti-Tobacco Mosaic Virus Activity

Two new phenolic compounds, 6-hydroxy-7-methoxy-3-(4-methoxyphenyl)-2H-chromen-2-one (1) and 7-hydroxy-6-methoxy-3-(4-methoxyphenyl)-2H-chromen-2-one (2), together with six known phenols (3–8), were isolated from the stems of Cassia siamea. The structure of 1–8 was elucidated by spectroscopic methods including extensive 1D and 2D NMR techniques. Compounds 1–8 were evaluated for their anti-tobacco mosaic virus (anti-TMV) activity. The results showed that compounds 1 and 2 have potential anti-TMV activity with inhibition rates of 28.2 and 23.5%, respectively. Compounds 3–8 also showed anti-TMV activity with inhibition rates in the range of 11.6–19.8%.