Discovery of picomolar slow tight-binding inhibitors of α-fucosidase

Glycosidase inhibitors have shown great medicinal and pharmaceutical values as exemplified by the therapeutic treatment of influenza virus and non-insulin-dependent diabetes. We herein report the discovery of picomolar slow tight-binding inhibitors 2-5 against the α-fucosidase from Corynebacterium sp. by a rapid screening for an optimal aglycon attached to 1-aminomethyl fuconojirimycin (1). The time-dependent inhibition displays the progressive tightening of enzyme-inhibitor complex from a low nanomolar K _i to picomolar K_i* value. Particularly compound 2 with a K_i* of 0.46 pM represents the most potent glycosidase inhibitor to date. The effect of compound 3 on the intrinsic fluorescence of α-fucosidase is both time- and concentration-dependent in a saturation-type manner, which is consistent with the initial formation of a rapid equilibrium complex of enzyme and inhibitor (E·I), followed by the slower formation of a tightly bound enzyme-inhibitor complex (E·I*). The binding affinity increases 3.5 × 10 ⁴-fold from 1 (K_i = 16.3 nM) to 2 (K_i* = 0.46 pM). This work clearly demonstrates the effectiveness of our combinatorial approach leading to the rapid discovery of potent inhibitors.