Absolute stereostructure of carabrane-type sesquiterpene and vasorelaxant-active sesquiterpenes from Zedoariae Rhizoma

The aqueous acetone extract of Zedoariae Rhizoma was found to show inhibitory effects on contractions induced by high concentrations of potassium cation (K+) in isolated rat aortic strips. From the extract, two new carabrane-type sesquiterpenes, curcarabranols A and B, were isolated together with a few carabrane-type sesquiterpenes, such as curcumenone and 4S-dihydrocurcumenone. Their absolute stereostructures were determined on the basis of chemical and physicochemical evidence, which included the application of the modified Mosherʹs method and chemical conversion from curcumenone to curcarabranols A and B. In addition, several sesquiterpenes and diarylheptanoids (e.g. germacrone, glechomanolide, isocurucmenol, β-eudesmol, and β-dictyopterol) showed potent inhibitory effects on contractions induced by high concentrations of K+ in isolated rat aortic strips (inhibition >80% at 100 μM), while they did not inhibit norepinephrine-induced contractions, so that the vasorelaxant activities of these sesquiterpenes were presumed to be dependent on their calcium channel-blocking activity.