The most abundant polyphenol of soy leaves, coumestrol, displays potent α-glucosidase inhibitory activity

The leaves of soybean (Glycine max) were extracted into four different polar solvents: ethylacetate, butanol, ethanol and water. The ethylacetate extract (EE) showed the lowest IC50 value against α-glucosidase (70.1 μg/ml). To investigate the compounds responsible for this effect, activity guided fractionation of soybean leaves by chromatography yielded seven phenolic compounds which were identified as formononetin (1), afromosin (2), coumestrol (3), isotrifoliol (4), phaseol (5), glyceofuran (6) and a new compound, glyceollin V (7). Importantly, coumestrol 3 was not only the most potent component with IC50 = 6.0 μM, but also the most abundant polyphenol in soybean leaves. There was shown to be an increasing inhibition across the developmental stage of the plant, which correlated strongly with an increase in compound 3 in the leaves. In fact, we have shown it can comprise up to 65% of the polyphenols in the leaves by HPLC analysis.