A SAPONIN CONJUGATED WITH 2,3-DIHYDRO-2,5-DIHYDROXY-6-METHYL-4H-PYRAN-4-ONE FROM DOLICHOS-LABLAB

A new 2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP)-conjugated saponin, lablab saponin I, was isolated from the hypocotyl of hyacinth bean (Dolichos lablab). The structure was elucidated by H-1 NMR and C-13 NMR spectroscopy and chemical techniques as 3-O-[alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-galactopyranosyl(1 --> 2)-beta-D-glucuronopyranosyl(1 -->)]-22-O-[2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one(2' -->)]-3 beta,22 beta,24-trihydroxyolean-12-en-28-al. SOD (superoxide dismutase)-like activity depended upon the DDMP group and the aldehyde group (C-28) of the aglycone was observed in the order of lablab saponin I > glutathione > soyasaponin beta g > maltol. The soybean saponin Bb, lacking the DDMP moiety was found not to exhibit the SOD-like activity.