Sesquiterpene Lactones and their Anti-Tumor Activity from the Flowers of Inula Britannica

A new sesquiterpene lactone, 6β-O-isobutyrylbritannilactone (5) and five known sesquiterpene lactones; britannilactone (1), 1-O-acetylbritannilactone (2), Hydroxy alantolactone (3), 8-epi-ivangustin (4) and 1,6-O,Odiacetylbritannilactone (6), were isolated from the flowers of Inula britannica. In the known sesquiterpene lactones, (3) and (4) were isolated for the first time from Inula britannica. The structures of these compounds were established unambiguously by UV, MS and a series of 1D and 2D NMR analyses. Compounds 3, 4, 5 and 6 exhibited significant cytotoxicity for tumor cells in vitro in bioassay.