Cytotoxic sesquiterpene lactones from Campuloclinium macrocephalum (=Eupatorium macrocephalum)

Three undescribed germacranolide sesquiterpene lactones, named macrocephalides A-C, along with known steroids, triterpenes and flavonoids were isolated from the aerial parts of Campuloclinium macrocephalum. The structures of the undescribed compounds were elucidated with basis on their 1D and 2D-NMR, and HR-ESI-MS data. Their absolute configurations were assigned by comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Additionally, macrocephalides A-C were evaluated for their in vitro cytotoxic activities against nine human cancer cell lines. Macrocephalides A and B exhibited moderate to potent cytotoxic activity, inhibiting 50% of cell growth (GI₅₀) at concentrations ranging from 0.576 to 6.37 μM.