Inhibition of adenosine deaminase by novel 5:7 fused heterocycles containing the imidazo[4,5-e][1,2,4]triazepine ring system:: A structure-activity relationship study

As part of a program to explore structure-activity relationships for the extremely tight binding inhibition characteristics of coformycins to adenosine deaminase, a series of analogues (1a-1h) containing the imidazo[4,5-e][1,2,4]triazepine ring system has been synthesized and screened in vitro against a mammalian adenosine deaminase for inhibitory activity. While compounds 1a and 1b, were synthesized in five steps starting from 4-nitroimidazole, others were derived from la through simple exchange reactions with the appropriate alcohols. The observed kinetics profiles and K-i values suggest that the target compounds are competitive inhibitors that bind 6-9 orders of magnitude less tightly to the enzyme. Compounds 1c and 1d were the most active in the series with K-i's ranging from 12 to 15 muM.