Two New Alkaloids from the Seeds of Cassia alata and Their Anti-Tobacco Mosaic Virus Activity

Two new alkaloids, 3-(hydroxymethyl)-6,9-dimethyl-7H-benzo[de]quinolin-7-one (1) and 3-(hydroxymethyl)-8-methoxy-6,9-dimethyl-7H-benzo[de]quinolin-7-one (2), together with two known alkaloids (3 and 4) were isolated from the seeds of Cassia alata. Their structures were determined by means of HR-ESI-MS and extensive 1D and 2D NMR spectroscopic studies. Compounds 1–4 were tested for their anti-tobacco mosaic virus (anti-TMV) activity. The results revealed that compounds 1–4 have potential anti-TMV activity with inhibition rates of 29.2, 38.5, 24.2, and 28.8% at the concentration of 20 μM, respectively. The inhibition rates of 1 and 2 are higher than that of the postive control.