Inhibitory Activity of 4-O-Benzoyl-3′-O-(OMethylsinapoyl) Sucrose from Polygala tenuifolia on Escherichia coli β-Glucuronidase

Bacterial β-glucuronidase in the intestine is involved in the conversion of 7-ethyl-10- hydroxycamptochecin glucuronide (derived from irinotecan) to 7-ethyl-10-hydroxycamptothecin, which causes intestinal bleeding and diarrhea (side effects of anti-cancer drugs). Twelve compounds (1–12) from Polygala tenuifolia were evaluated in terms of β-glucuronidase inhibition in vitro. 4-O-Benzoyl-3′-O-(O-methylsinapoyl) sucrose (C3) was highly inhibitory at low concentrations. C3 (an uncompetitive inhibitor) exhibited a k(i) value of 13.4 μM; inhibitory activity increased as the substrate concentration rose. Molecular simulation revealed that C3 bound principally to the Gln158–Tyr160 enzyme loop. Thus, C3 will serve as a lead compound for development of new β-glucuronidase inhibitors.