Furostanol Bisglycosides Corresponding to Dioscin and Gracillin

Two compounds, positive (red) to the Ehrlich reagent and predominant in the methanol extracts of the fresh rhizomes of Dioscorea gracillima MIQ., were isolated. Their structures were established as 26-O-β-D-glucopyranosyl 22-methoxyfurost-5-ene-3β, 26-diol 3-O-β-chacotrioside (I), mp 187-191°(decomp.), [α]D-95.6°, and its 22-hydroxy analog (I'), mp 190-196°(decomp.), [α]D-79.8°, the furostanol bisglycosides corresponding to 25D-spirost-5-en-3β-ol (diosgenin) 3-O-β-chacotrioside (dioscin) (III), the major component of the stored materials. I is regarded as an artifact formed from I', and I'and I are named proto-dioscin and methyl proto-dioscin, respectively. Smilax-saponin B, which had been assigned a structure, diosgenin hexaglycoside, was identical with I and the structure is revised. Among the Ehrlich positive compounds in the methanol extracts of the fresh rhizomes of D. septemloba THUNB., the major, mp 249-251°(decomp.), [α]D-76.9°, was isolated and characterized as the analog (II) of I, chacotriose being replaced by gracillimtriose, corresponding to gracillin (IV). One of the minor components was identified with the 22-hydroxy compound (II') of II, mp 235-238°(decomp.), [α]D-57.8°. II'and II are named proto-gracillin and methyl proto-gracillin, respectively. Kikuba-saponin, which had been assigned the structure, IV monoglucoside, was identical with II and the structure is revised.