Antiproliferative Sesquiterpenoids from Ligularia rumicifolia with Diverse Skeletons

Twenty-two new sesquiterpenoids with four skeletal types and 15 known analogues were isolated from the whole plants of Ligularia rumicifolia. The structures of the isolates were elucidated based on comprehensive spectroscopic data analysis. Compound 1 is a C14 nor-sesquiterpenoid featuring a 6/6/6 tricyclic skeleton with a 9,13-ether bridge. The absolute configuration of 2 was established through single-crystal X-ray diffraction data. Compounds 13–16 exhibited in vitro antiproliferative activity against the four human tumor cell lines A-549, HGC-27, HeLa, and MV4-11. Specifically, compounds 13 and 16 showed antiproliferative activity against the MV4-11 cell line with IC50 values of 0.5 ± 0.2 and 1.1 ± 0.5 μM, respectively.