Pterocarpan Profiles for Soybean Leaves at Different Growth Stages and Investigation of Their Glycosidase Inhibitions

Abstract

Soybean leaves are eaten as seasonal edible greens in Korea. Analysis of the ethyl acetate extract of these leaves showed that it exhibited potent and selective neuraminidase inhibition, which began at the R3 stage and peaked at R7. Ten pterocarpans, including the new 6a-hydroxypterocarpan 10, were isolated from soybean leaves and their inhibition activities tested against a range of glycosidases. The relationship between structure and enzyme inhibition was investigated: 6a-hydroxypterocarpans exhibited much higher inhibition against neuraminidase (IC50 = 2.4-89.4 mu M) than alpha-glucosidase (IC50 = 90.4- >100 mu M). Glyceollin VII (7) displayed 40-fold greater activity (IC50 = 2.4 mu M) against neuraminidase than alpha-glucosidase (IC50 = 90.4 mu M). On the other hand, coumestanes (1-3) were good alpha-glucosidase inhibitors (IC50 = 6.0-42.6 mu M). In kinetic analysis, the most potent neuraminidase inhibitors (5-10) were noncompetitive. HPLC analysis indicated that most pterocarpan synthesis began from the R3 stage, and a rapid change of pterocarpan concentrations was observed between the R4 and R7 stages.