Pyrazolo[1,5-c]quinazoline derivatives and their simplified analogues as adenosine receptor antagonists: Synthesis, structure–affinity relationships and molecular modeling studies

A number of 5-oxo-pyrazolo[1,5-c]quinazolines (series B-1), bearing at position-2 the claimed (hetero) aryl moiety (compounds 1–8) but also a carboxylate group (9–14), were designed as hA3 AR antagonists. This study produced some interesting compounds endowed with good hA3 receptor affinity and high selectivity, being totally inactive at all the other AR subtypes. In contrast, the corresponding 5- ammino derivatives (series B-2) do not bind or bind with very low affinity at the hA3 AR, the only exception being the 5-N-benzoyl compound 19 that shows a hA3 Ki value in the high l-molar range. Evaluation of the synthetic intermediates led to the identification of some 5(3)-(2-aminophenyl)-3(5)-(hetero)arylpyrazoles 20–24 with modest affinity but high selectivity toward the hA3 AR subtype. Molecular docking of the herein reported tricyclic and simplified derivatives was carried out to depict their hypothetical binding mode to our model of hA3 receptor