Saponin and Sapogenol. XIII. Structures of Three Soybean Saponins : Soyasaponin I, Soyasaponin II, and Soyasaponin III

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Soyasaponin I (major), II and III, all of which possess soyasapogenol B (2) as the common aglycone, have been isolated from the MeOH extractive of soybean (Glycine max MERRILL, Leguminosae). On the basis of chemical and physicochemical evidence, the structure of soyasaponin I has been elucidated to be 3-O-[α-L-rhamnopyranosyl (1→2)-β-D-galactopyranosyl (1→2)-β-D-glucuronopyranosyl]-soyasapogenol B (7) and the structures of soyasaponin II and III to be 3-O-[α-L-rhamnopyranosyl (1→2)-α-L-arabinopyranosyl (1→2)-β-D-glucuronopyranosyl]-soyasapogenol B (8) and 3-O-[β-D-galactopyranosyl (1→2)-β-D-glucuronopyranosyl]-soyasapogenol B (9), respectively.