Sesquiterpenes from the whole plants of Parasenecio roborowskii

Six eremophilane-type (parasenolide A-F) and an eudesmane-type (parasenin) sesquiterpenoids, along with eight known sesquiterpenes, were isolated from the whole plants of Parasenecio roborowskii. The structures and absolute configurations of new compounds were elucidated using extensive spectroscopic analysis, including HRESIMS, 1D and 2D NMR experiments, the CD exciton chirality methods, and single-crystal X-ray crystallography. All isolated compounds were evaluated for cytotoxicity against five human cancer (HeLa, HepG2, K562, MDA231, and NCI-H460) cell lines and a murine melanoma B16 F10 cell line by MTT assay. Compounds 1-15 showed cytotoxic activities, especially compounds 3, 4, 8, 10, and 12. These five compounds showed broad spectrum activities against all the tested cancer cell lines with IC₅₀ ranging from 9.2 to 35.5μM. The study supports that eremophilenolides and eudesmane-type sesquiterpenes occur mainly in the genus Parasenecio and can be used as a chemosystematic marker of the genus.