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.

Abstract

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.