Petasins from the R hizomes of Ligularia fischeri and I ts D erivatives

Five eremophilane sesquiterpenoids were isolated from the rhizomes of Ligularia fischeri grown in Henan province of China and identified as 3α-Tigloyloxyeremophila-9,11-dien-8-one (3), Isopetasan (4), Neopetasan (5), Isopetasol(6) and Petasol (7), by spectroscopic methods. Petasin (1) previously isolated was analyzed to determine its absolute configuration by X-ray single crystal diffraction. Five petasin derivatives including three new compounds (2a, 6a and 6b) were synthesized. 12 eremophilane sesquiterpenoids including the derivatives except for 4 (minor amount) were assessed against human neuroblastoma (SKN-SH) by the SRB method. 1 was also tested on inhibiting prostate carcinoma (Bc3) cell lines. The results showed 1 has the strong inhibitory activity against SKN-SH and Bc3 cell lines and other compounds with α-isopropylidene group also have the strong activity against the human neuroblastoma (SKN-SH). The above results indicated the α - isopropylidene group might be the active center against pulmonary carcinoma (SKN-SH) in the same eremophilane-type skeleton. Petasins may be interesting for their good bioactivities.