2-Arylpyrazolo[4,3-d]pyrimidin-7-amino Derivatives As New Potent and Selective Human A3 Adenosine Receptor Antagonists. Molecular Modeling Studies and Pharmacological Evaluation

On the basis of our previously reported 2-arylpyrazolo[4,3-d]pyrimidin-7-ones, a set of 2-arylpyrazolo[4,3- d]pyrimidin-7-amines were designed as new human (h) A(3) adenosine receptor (AR) antagonists. Lipophilic groups with different steric bulk were introduced at the 5-position of the bicyclic scaffold (R-5 = Me, Ph, CH2Ph), and different acyl and carbamoyl moieties (R-7) were appended on the 7-amino group, as well as a para-methoxy group inserted on the 2-phenyl ring. The presence of acyl groups turned out to be of paramount importance for an efficient and selective binding at the hA(3) AR In fact, most of the 7-acylamino derivatives showed low nanomolar affinity (K-l, = 2.5-45 nM) and high selectivity toward this receptor. A few selected pyrazolo[4,3-d]pyrimidin-7-amides were effective in counteracting oxaliplatin-induced apoptosis in rat astrocyte cell cultures, an in vitro model of neurotoxicity. Through an in silica receptor-driven approach the obtained binding data were rationalized and the molecular bases of the observed hA(3) AR affinity and hA(3) versus hA(2A) AR selectivity were explained.