Eremophilane-Type Sesquiterpenoids with Diverse Skeletons from Ligularia sagitta

Five new highly oxygenated eremophilane-type
sesquiterpenoids,
possessing C19 (1 and 2), C15 (3 and 4), and C14 (8) skeletons, along with eight known eremophilenolides were
obtained from the aerial parts of Ligularia sagitta. The absolute configuration of 1 was assigned by X-ray
diffraction analysis and that of 3 by ECD spectroscopy.
Compounds 1–10 were evaluated for
their antibacterial activities against Staphyloccocus
aureus, Bacillus subtilis, Escherichia coli, Bacillus cereus, and Erwinia carotovora. Compounds 4 and 5 displayed broad-spectrum
inhibitory activity against these bacteria with MIC values of approximately
7.25 μg/mL, followed by 3 and 6 with
MIC values in the range of 23.0–125.0 μg/mL. Compounds 3 and 8 showed mild activity against three human
tumor cell lines (IC50 ≈ 13 μM). Preliminary
structure–activity relationships for these eremophilenolides
are reported.