Cytotoxic germacrane-type sesquiterpene lactones from the whole plant of Inula cappa

Phytochemical investigation on the whole plant of Inula cappa led to the isolation of two new germacrane-type sesquiterpene lactones, ineupatolides D and E (1 and 2), together with three known analogs. The structures of the new compounds were established by extensive analysis of 1D and 2D NMR spectra, as well as MS data. Their absolute configurations were determined by CD spectra. All compounds showed moderate inhibitory effects on A431, A549, BGC-823, HL-60, HT-29, and MCF-7 cancer cell lines with IC50 values ranging from 2.1 to 36.3 μM.