Germacranolides from Helianthus californicus

Five germacranolide sesquiterpene lactones and a trachylobane diterpene were isolated from the hexaploid species Helianthus californicus. Four of the sesquiterpene lactones are new, including a 1-oxo-3,10-diol without any carbon-carbon double bonds in the main ring whose structure was confirmed by X-ray crystallography. These results require revision of the structures of several previously published compounds. Two of the germacranolides have alkyl ether functions at a position β to a ketone and are believed to be artifacts of the isolation process. Based on terpenoid chemistry, there are no obvious progenitors of H. californicus among the diploid species of Helianthus examined to date.