Structure and Physiological Activity of DDMP Saponins in Leguminous Plant

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The composition and the structures of group B saponins in native soybean seeds were investigated. Five kinds of saponins named soyasaponins alphag, betag, betaa, gammag and gammaa according to elution order from HPLC were isolated, and the structures were characterized as having a 2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP) group attached by acetal linkage to C-22 of the aglycones soyasaponines V,I,II,III and IV,respectively. These DDMP cojugated saponins are considered to be the genuine saponins in native soybean seeds, and soyasaponins I,II,III,IV and V are artifacts produced by heating during the extraction or concentration process. The DDMP saponins are widely distributed in the leguminous plant such as soyasaponin betag isolated from rootstock of the American groundnut. And new DDMP saponins were isolated from Phaseolus coccineus and Dolichos lablab, named as soyasaponin alphaa and lablab saponine I respectively. A high concentration of DDMP saponin was observed around the cell in fibrovascular bundles connecting the stem to the plumule.The chemiluminescence (CL) of catechins were measured in the presence of active oxygen species and acetaldehyde (MeCHO). (-)-Epigallocatechin (EGC) exhibited the strongest CL among flavonoids, anthocyanins and catechins. The CL intensity, P,was dependent on the concentrations of active oxygen species, X,such as H_2O_2, catalytic species, Y,such as EGC and receptive species, Z,such as MeCHO as follows ; p=k[X][Y][Z] (k, photon constant). DDMP saponins showed oxygen-radical-scavenging activity assayd by using the xanthin oxidase-NH2OH methods, ESR and chemiluminescence. One milligram of DDMP saponin/mg exhibited superoxide-scavenging activity of a degree equvalent to 17.1 units of superoxide dismutase/ml measured by the ESR spin trapping method. We have found that group A and DDMP saponins are Y equivalent to EGC and Z equivalent to MeCHO,respectively.