Merrillianin, a unique seco-prezizaane-type sesquiterpene, and (6R)-pseudomajucin from Illicium merrillianum

Novel sesquiterpene lactones, (6R)-pseudomajucin () and merrillianin (), have been isolated from the pericarps of Illicium merrillianum, and their structures have been elucidated on the basis of the spectral data. A methanol solution of (6R)-pseudomajucin coexisted with (6R)-pseudomajucinone () in a keto/acetal equilibrium, whereas the crystals solely consisted of a keto-type , the structure of which was established by X-ray crystallographic analysis. The absolute stereochemistry of was determined by the X-ray crystallographic analysis of its 7-O-methyl-3-O-p-bromophenylcarbamate. Merrillianin () is a unique seco-prezizaane-type sesquiterpene with an unprecedented dilactone moiety, which may be biosynthesized from pseudomajucin () or (6R)-pseudomajucin () by oxidative cleavage of the C-6/C-7 bond.