Saponin and Sapogenol. XLII. : Structures of Acetyl-soyasaponins A1, A2, and A3, Astringent Partially Acetylated Bisdesmosides of Soyasapogenol A, from American Soybean, the Seeds of Glycine max MERRILL

By means of high performance liquid chromatography and other methods, three new partially acetylated soyasaponins, named acetyl-soyasaponin A1 (6a), acetyl-soyasaponin A2 (7a), and acetyl-soyasaponin A3 (8a), were isolated from American soybeans, the seeds of Glycine max MERRILL., together with hitherto known soyasaponins I (3), II (4), and III (5). Acetyl-soyasaponins A1, A2, and A3 are noteworthy due to their bitter and astringent tastes, although their parent saponins, soyasaponins A1 (6), A2 (7), and A3 (8), do not show such tastes.By virtue of the photochemical degradation method for the glucuronide linkage and on the basis of 1H- and 13C-nuclear magnetic resonance and secondary ion mass spectrum analyses, structures of acetyl-soyasaponins A1, A2, and A3 have been elucidated as 3-O-[β-D-glucopyranosyl-(1→2)-β-D-galactopyranosyl(1→2)-β-D-glucuronopyranosyl]-22-O-[2, 3, 4, 6-tetra-O-acetyl-β-D-glucopyranosyl(1→3)-α-L-arabinopyranosyl]soyasapogenol A (6a), 3-O-[β-D-galactopyranosyl-(1→2)-β-D-glucuronopyranosyl]-22-O-[2, 3, 4, 6-tetra-O-acetyl-β-D-glucopyranosyl(1→3)-α-L-arabinopyranosyl]soyasapogenol A (7a), and 3-O-[α-L-arabinopyranosyl(1→2)-β-D-glucuronopy-ranosyl]-22-O-[2, 3, 4, 6-tetra-O-acetyl-β-D-glucopyranosyl(1→3)-α-L-arabinopyranosyl]soya-sapogenol A (8a), respectively.