Studies on the Constituents of the Dioscorea tokoro Rhizome

: The rhizome of Dioscorea tokoro has been used in China to alleviate the pain of rheumatic disorders of the knees and hips, but the active component has not been clarified. In order to determine its pharmacological activity, we isolated and characterized the structure of the constituents of the Dioscorea tokoro rhizome by means of column chromatography and spectral analysis. As a result, two new furostanol saponins, protoyononin （ D8 ） and protocompound x （ D12 ） , were isolated from the Dioscorea tokoro rhizome, along with ten known spirostanol and furostanol derivatives, namely, dioscin, gracillin, yononin, tokorogenin, tokoronin, compound x, protoyonogenin, protodioscin, protogra cillin and prototokoronin. The structures of D8 and D12 were determined based on chemical and spectral methods and characterized as 26- O - β - D -glucopyranosyl （ 25 R ） -2 β ,3 α ,22 ξ ,26-tetrahydroxyfurost-2- O - α - L -arabinopyranside （ protoyononin ） and 26- O - β - D -glucopyranosyl （ 25 R ） -1 β ,2 β ,3 α ,22 ξ ,26-pentahydroxyfurost-1- O - β - D -glucopyranside （ protocompound x ） .