Structure of Curdione

From zedoary, Curcuma zedoaria (Zingiberaceae), a sesquiterpenoid curdione, C15H24O2, has been isolated and shown to be germacr-1 (10)-ene-5, 8-dione (I) based on the following evidence. The presence of a β-methyl-β, γ-unsaturated ketone and an isolated ketone group in the germacrane skeleton has been indicated by spectral determinations of curdione and its reduction product, the diol (IV), which is reversible to curdione on oxidation, and by dehydrogenation of the diol (IV) to S-guaiazulene (VII). The location of the two carbonyls has been established by the transformation of its dihydro-derivative (III) to the enone (VIII) whose structure has been confirmed by its spectral properties and by its conversion into vetivazulene (XI).