Identification and structure-activity relationship studies of osthol, a cytotoxic principle from Cnidium monnieri

Osthol (1) was isolated from the fruit of Cnidium monnieri as a cytotoxic principle. Its structure-activity relationship study reveals that the 3,4-olefinic bond is essential for its cytotoxic activity, and the prenyl (C5) unit attached at the 8 position enhances the cytotoxicity. Analogues 7 and 8 that have a longer alkoxy unit at the 7 position showed ten times higher cytotoxicity than 1.