Bioactive sesquiterpenes from Inula helenium

Twenty-one eudesmane-type sesquiterpenes, including five new compounds, were isolated from the roots of Inula helenium. The structures of the new compounds (1–5) were determined by extensive spectroscopic data interpretation, single-crystal X-ray diffraction analysis and ECD calculations. Six compounds can synergistically enhance cisplatin effect against ovarian cancer cells, the structure − activity relationship for the synergistic effect of these compounds with cisplatin was revealed for the first time, which provides useful clues to develop novel sensitizers to overcome drug resistance in cancer. In addition, fifteen sesquiterpenes exhibited significant anti-inflammatory activity, which provided promising candidates for development of anti-inflammatory agent.