The role of 5-arylalkylamino- and 5-piperazino- moieties on the 7-aminopyrazolo[4,3-d]pyrimidine core in affecting adenosine A and A receptor affinity and selectivity profiles.

New 7-amino-2-phenylpyrazolo[4,3-d]pyrimidine derivatives, substituted at the 5-position with aryl(alkyl)amino- and 4-substituted-piperazin-1-yl- moieties, were synthesized with the aim of targeting human (h) adenosine A and/or A receptor subtypes. On the whole, the novel derivatives 1-24 shared scarce or no affinities for the off-target hA and hA ARs. The 5-(4-hydroxyphenethylamino)- derivative 12 showed both good affinity (K = 150 nM) and the best selectivity for the hA AR while the 5-benzylamino-substituted 5 displayed the best combined hA (K = 123 nM) and A AR affinity (K = 25 nM). The 5-phenethylamino moiety (compound 6) achieved nanomolar affinity (K = 11 nM) and good selectivity for the hA AR. The 5-(N-substituted-piperazin-1-yl) derivatives 15-24 bind the hA AR subtype with affinities falling in the high nanomolar range. A structure-based molecular modeling study was conducted to rationalize the experimental binding data from a molecular point of view using both molecular docking studies and Interaction Energy Fingerprints (IEFs) analysis.[Formula: see text].