Ainsliatriolides A and B, Two Guaianolide Trimers from <i>Ainsliaea fragrans</i> and Their Cytotoxic Activities

Ainsliatriolides A (1) and B (2), two guaianolide sesquiterpenoid trimers possessing an unprecedented skeleton, were isolated from Ainsliaea fragrans. Their structures were elucidated through extensive analysis of spectroscopic data and confirmed by single-crystal X-ray diffraction experiment. Ainsliatriolides A and B are first examples of compound trimerized from guaianolide sesquiterpenoids through two different C–C linkages (type A, 4–2′/15–14′; type B, 15′-15″). Ainsliatriolide A displayed potent cytotoxicity with an averaged IC50 value of 1.17 μM against four cancer cells.