Saponin and Sapogenol. XLIII. : Acetyl-soyasaponins A₄, A₅, and A₆, New Astringent Bisdesmosides of Soyasapogenol A, from Japanese Soybean, the Seeds of Glycine max MERRILL.

Abstract

In addition to soyasaponins I, II, and III, three new bitter and astringent bisdesmosides named acetyl-soyasaponin A₄(2), acetyl-soyasaponin A₅ (3), and acetyl-soyasaponin A₆ (4) which are characterized by having a fully acetylated terminal xylosyl moiety, have been isolated from a Japanese species of soybean (Tamanishiki strain), the seeds of Glycine max MERRILL, cultivated in Hokkaido Prefecture. By means of photochemical degradation (a selective cleavage method for the glucuronide linkage), and on the basis of physicochemical evidence including ¹H- and ¹³C-nuclear magnetic resonance analysis, the structures of acetyl-soyasaponins A₄, A₅, and A₆ have been elucidated as 3-O-[β-D-glucopyranosyl(1→2)-β-D-galactopyranosyl(1→2)-β-D-glucuronopyranosyl]-22-O-[2, 3, 4-tri-O-acetyl-β-D-xylopyranosyl(1→3)-α-L-arabinopyranosyl]soyasapogenol A (2), 3-O-[β-D-galactopyranosyl(1→2)-β-D-glucuronopyranosyl]-22-O-[2, 3, 4-tri-O-acetyl-β-D-xylopyranosyl(1→3)-α-L-arabinopyranosyl]soyasapogenol A (3), and 3-O-[α-L-arabinopyranosyl-(1→2)-β-D-glucuronopyranosyl]-22-O-[2, 3, 4-tri-O-acetyl-β-D-xylopyranosyl(1→3)-α-L-arabinopyranosyl]soyasapogenol A (4), respectively.