Isolation, Structure Elucidation, and Absolute Configuration of Highly Oxygenated Germacranolides from Carpesium cernuum

The new highly oxygenated germacranolides cernuumolides A–J (1–10) and the known compounds 11–20 were isolated from Carpesium cernuum. Among these compounds, 1–4 are 11-methoxymethyl­germacranolides and 5–7 as well as 11–17 are 2,9-hemiacetal-linked germacranolides. Their structures were elucidated using NMR and HRESIMS analyses, and X-ray diffraction studies were used to confirm the absolute configurations of 1, 2, 5, 6, 8, and 9. Cernuumolides A–J were evaluated for their in vitro cytotoxicity against the A549, HCT116, MDA-MB-231, and BEL7404 cell lines, and 8 exhibited moderate cytotoxicity with IC50 values in the 0.87–2.02 μM range.