Abstract
Five new unusual C17/C15 sesquiterpene lactone dimers, carabrodilactones A–E (1–5), along with four known common C15/C15 SLDs, carpedilactones A and B (6 and 7), faberidilactone A (8), and faberidilactone C (9), were isolated from the whole plants of Carpesium abrotanoides. The structures of 1–5 featured a flexible C-11/C-13′ linked single bond between two sesquiterpene units and a tailed acetyl connected to the C-13 position. The preferential conformation of 1–5 was elucidated by the diagnostic NMR data of geminal proton of H-13. The biogenetic pathway of 1–5 was proposed to involve Stetter and Michael addition reactions. In addition, compound 1 exhibited significant cytotoxicities against the four cell lines (A549, HCT116, MDA-MB, and BEL7404 cells) with IC50 value in the range of 3.08–8.05 μM, while compounds 2–5 showed weak cytotoxicities.
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