The components of several Petasites species have been investigated and shown to include petasin furanopetasin derivatives belonging to the eremophilane type of sesquiterpene, and bakkenolide derivatives. It has been reported that the petasin derivatives have spasmolytic properties and bakkenolide-A has cytotoxic activity. Natural is (+)-isopetasol. It was also isolated from the rhizomes of Ligularia fischeri grown in Henan province of China. Isopetasol derivatives with an unsaturated acid ester moiety will selectively inhibit RNA synthesis in the ascites tumor of mouse.