Saponin and Sapogenol. XLVI. : On the Constituents in Aerial Part of American Alfalfa, Medicago sativa L. : The Structure of Dehydrosoyasaponin I

From the aerial part of North American alfalfa, Medicago sativa L. (Leguminosae), a new glucuronide-saponin named dehydrosoyasaponin I (7) and two glycero-glycolipids (8, 9) were isolated together with three known glucuronide-saponins, soyasaponin I (6), azukisaponin II (4), and azukisaponin V (5). the structure of dehydrosoyasaponin I has been determined as 3-O-[α-L-rhamnopyranosyl-(1→2)-β-D-galactopyranosyl-(1→2)-β-D-glucuronopyranosyl]soyasapogenol E (7) from the chemical and spectral evidence. Two glycero-glycolipids have been elucidated respectively as 1-O-β-D-galactopyranosyl-2, 3-di-O-acyl-D-glycerol, in which the acyl group comprises linolenoyl (90%), linoleoyl (8%), and palmitoyl (2%) residues (8), and 1-O-[α-D-galactopyranosyl-(l→6)-β-D-galactopyranosyl]-2, 3-di-O-acyl-D-glycerol, in which the acyl group comprises linolenoyl (85%), linoleoyl (5%), palmitoyl (5%), oleoyl (3%), and stearoyl (2%) residues (9). On the structure elucidation of 9, the lead-tetraacetate degradation method, which is one of selective cleavage methods for the glucuronide linkage in glucuronide-saponins, has been shown to be applicable for the cleavage of the galacturonide linkage in 9.