Structural investigation and biological activity of sesquiterpene lactones from the traditional Chinese herb Inula racemosa

Five new sesquiterpene lactones, racemosalactones A-E (1-5), along with 19 known sesquiterpene latones (6-24), were isolated from the roots of Inula racemosa. Their structures were elucidated by extensive spectroscopic analysis, and the absolute configuration of 2 was deduced from X-ray diffraction analysis. Compounds 1, 6, 8, 10, 12, 14, and 17 exhibited antiproliferative activities with IC50 values ranging from 0.38 to 4.19 μg/mL against human non-small-cell lung Cancer A549, hepatocellular carcinoma HepG2, and human fibrosarcoma HT1080 cells. Compounds 6 and 8 exhibited antiproliferative activities against endothelial cells with IC50 values of 2.4 and 2.5 μg/mL, respectively. Furthermore, compounds 6 and 8 both inhibited endothelial cell tube formation at 1.0 μg/mL. A method for the rapid and straightforward preparative-scale isolation of compound 6 from alantolides is described.