Benzophenones as xanthine oxidase inhibitors

Eight synthetic bezophenones were tested for their inhibitory effects on xanthine oxidase (XO). The enzyme, XO catalyses the oxidation of hypoxanthine to xanthine and of xanthine to uric acid, which has a λ max of 295 nm, forming the basis for a spectrophotometric assay for the activity of XO. The results showed that 2,2',4,4'-tetrahydroxybenzophenone (6), 3,4,5,2',3',4'-hexahydroxybenzophenone (8) and 4,4'-dihydroxybenzophenone (3) displayed the inhibitory effects on XO with an order of activity of IC50 = 47.59, 69.40 and 82.94 μM, respectively. The apparent inhibition constants (Ki) of (8) and (3) were 15.61 and 64.86 μM respectively, and both of them induced mixed type (non-competitive-uncompetitive) inhibitions of the substrate xanthine.