5-Substituted N-(9H-purin-6-yl)-1,2-oxazole-3-carboxamides as xanthine oxidase inhibitors

Synthetic 6-substituted purine derivatives are known to exhibit diverse bioactivity. In this paper, a series of N-(9H-purin-6-yl)-1,2-oxazole-3-carboxamide derivatives were synthesized and evaluated in vitro against xanthine oxidase, an enzyme of purine catabolism. The introduction of aryl substituent at position 5 of the oxazole ring was found to increase the inhibition efficiency. Some of the inhibitors containing 5-substituted isoxazole and purine moieties were characterized by IC50 values in the nanomolar range. According to the kinetic data, the most active N-(9H-purin-6-yl)-5-(5,6,7,8-tetrahydronaphthalen-2-yl)-1,2-oxazole-3-carboxamide demonstrated a competitive type of inhibition with respect to the enzyme-substrate. Molecular docking was carried out to elucidate the mechanism of enzyme-inhibitor complex formation. The data obtained indicate that xanthine oxidase may be one of the possible targets for the bioactive purine carboxamides.