Three new anthraquinones from the twigs of Cassia fistula and their bioactivities

Three previously unreported anthraquinones, fistulaquinones A–C (1–3), together with three known ones (4–6) were isolated from the twigs of Cassia fistula. Their structures were determined by means of extensive NMR and MS spectroscopic analyses. All the isolated compounds were tested for their anti-tobacco mosaic virus (anti-TMV) activity, and compound 3 showed significant activity with inhibition rate of 34.5% at 20μm concentration, even more potent than positive control. Additionally, compounds 1–6 exhibited moderate cytotoxicity with IC50values ranging from 2.8 to 9.4μm for some tested human tumor cell lines.