Pyrazolo[4,3-e][1,2,4]triazines:: Purine analogues with electronic absorption in the visible region

Synthesis of several pryrazolo[4,3-e][1,2,4]-triazines is described. The absorption spectrum of some 5-substituted derivatives was found to extend to the visible region. These compounds were found to inhibit some enzymes of purine metabolism, like xanthine oxidase or bacterial purine-nucleoside phosphorylase with K-i values in the 10(-3) 10(-5) M range.