Beside other pharmaceutical benefits, flavonoids are known for their potent α-glucosidase inhibition. In the present study, we investigated α-glucosidase inhibitory effects of structurally related 11 flavonols, among which quercetin-3-O-(3″-O-galloyl)-β-galactopyranoside (8) and quercetin 3-O-(6″-O-galloyl)-β-glucopyranoside (9) showed significant inhibition compared to the positive control, acarbose, with IC50 values of 0.97 ± 0.02 and 1.35 ± 0.06 µM, respectively. It was found that while sugar substitution to C3-OH of C ring reduced the α-glucosidase inhibitory effect, galloyl substitution to these sugar units increased it. An enzyme kinetics analysis revealed that 7 was competitive, whereas 1, 2, 8, and 9 were uncompetitive inhibitors. In the light of these findings, we performed molecular docking studies to predict their inhibition mechanisms at atomic level.
Keywords: Enzyme kinetics; Flavonoid; Flavonol; Molecular docking; α-glucosidase.
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