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A number of 8-substituted-9-deazaxanthine derivatives (1,3-dialkyl-6-substituted-1H-pyrrolo[3,2-d]pyrimidine-2,4(3H,5H)-diones) were prepared and tested for their antagonistic activity at the recombinant human adenosine receptors, in particular at the A_2B and A_2A receptor subtypes. Compounds endowed with micromolar to nanomolar binding affinities, but with poor A_2B/A_2A selectivity, were obtained. Preliminary quantitative structure–affinity relationships suggested that the binding potency at the A_2B receptor is mainly modulated by the electronic and lipophilic properties of the ligands.