Absolute Stereostructures of Alismalactone 23-Acetate and Alismaketone-A 23-Acetate, New seco-Protostane and Protostane-Type Triterpenes with Vasorelaxant Effects from Chinese Alismatis Rhizoma.

New bioactive seco-protostane and protostane-type triterpenes, alismalactone 23-acetate and alismaketone-A 23-acetate, were isolated from Chinese Alismatis Rhizoma originating from Fukien province, the dried rhizoma of Alisma orientale JUZEP. Absolute stereostructures of the new triterpenes were determined on the basis of chemical and physicochemical evidence, which included chemical correlations with the known triterpene alisol B monoacetate. Alismalactone W-acetate and alismaketone-A 23-acetate were found to show inhibitory activity on the contractions induced by a high concentration of K+ in isolated aortic strips from rats.