Syntheses of 1,2,4-triazolo[4,3-c]pteridines.: Potential substrates for xanthine oxidase

A synthetic route for the preparation of 9-phenyl-1,2,4-triazolo[4,3-c]pteridines 8 is described. Their reactivities towards xanthine oxidase from Arthrobacter M-4 are determined and compared with the pteridine derivatives 6-phenylpteridin-4[3H]-thione 5, 6-phenyl-4-thiomethylpteridine 6, 4-hydrazino-6-phenylpteridine 7, 3-N-methyl-6-phenylpteridin-4[3H]-thione 19, 4-amino-6-phenylpteridine 22 and 1-N-methyl-6-phenylpteridin-4[1H]-one 24, in order to inspect a possible influence of pyrimidine ring substitution pattern on their interaction with the bacterial enzyme. It has been suggested that a planar structure of the pteridine moiety and the substituents could be an important factor that so far has been overlooked when considering the enzyme activity. Some literature data are also discussed in view of revision of structure assignment of the compounds 12, 14, and 17.