Novel 3-[4-alkoxy-3-(1H-tetrazol-1-yl) phenyl]-1,2,4-oxadiazol-5(4H)-ones as promising xanthine oxidase inhibitors: Design, synthesis and biological evaluation.

Xanthine oxidase (XO) is a critical target for the therapy of hyperuricemia and gout. In this study, a number of 3-[4-alkoxy-3-(1H-tetrazol-1-yl) phenyl]-1,2,4-oxadiazol-5(4H)-ones (3a-3w) were newly designed by a bioisosteric replacement and hybrid strategy with the hope of obtaining novel and effective nonpurine XO inhibitors. Subsequently, these compounds were synthesized through a three-step procedure, with good yields. In addition, the in vitro bovine XO inhibitions were measured by spectrophotometric determination of uric acid formation at 295 nm using allopurinol as a positive control. As a result, compound 3j was found to be the most potent XO inhibitor, with an IC50 value of 0.121 µM, which was approximately 63-fold more potent than allopurinol, and the analysis of the structure-activity relationships indicated that the hydrophobic group at 4'-position was essential for inhibitory potency. Additionally, the molecular modeling results showed that the 1,2,4-oxadiazol-5(4H)-one moiety binds to XO active site via various hydrogen bonds with Arg880 and Thr1010. Moreover, the compound 3j was demonstrated to be a mixed-type nonpurine XO inhibitor. Furthermore, the hypouricemic studies on a rat model, induced by potassium oxonate, demonstrated that serum uric acid levels could be effectually reduced by compound 3j at an oral dose of 15 mg/kg. Therefore, compound 3j could be a promising lead compound for the treatment of hyperuricemia and gout.