Highly Modified Sesquiterpene Lactones with Cytotoxic Activities from Strobocalyx chunii .

Three new germacranolide sesquiterpene lactones (SLs), strochunolides A-C (-, respectively), and a new guaianolide SL, strochunolide D (), were isolated from and structurally characterized. Compound is the first example of a dihomo-germacranolide SL, characterized by an unprecedented 6/10/5 tricyclic scaffold incorporating an additional fused δ-lactone C-ring. The structure of a known germacranolide SL, spicatolide C (), was revised as its 8-epimer. Compound exhibited potent cytotoxic activity against the HL-60 cell line, with an IC value of 0.18 ± 0.01 μM.