Selective inhibition of xanthine oxidase by substituted pyridopyrimidines

Six 2-methyl-3-substituted-pyrido-(2,3-d)-pyrimidine 4 (3H)-ones were synthesized and evaluated for their ability to inhibit xanthine oxidase and other purine catabolizing enzymes of rat liver. All compounds inhibited xanthine oxidase selectively when tested at a final concentration of 0.5 mM in vitro. Adenosine deaminase, guanosine deaminase and guanine deaminase were unaffected. The inhibition of xanthine oxidase was found to be competitive in nature.