Exploring the 2- and 5-positions of the pyrazolo[4,3-d]pyrimidin-7-amino scaffold to target human A1 and A2A adenosine receptors

• Published in: Bioorganic & medicinal chemistry 2016-06, Vol.24 (12), p.2794-2808
• Main Authors: Squarcialupi, Lucia, Falsini, Matteo, Catarzi, Daniela, Varano, Flavia, Betti, Marco, Varani, Katia, Vincenzi, Fabrizio, Dal Ben, Diego, Lambertucci, Catia, Volpini, Rosaria, Colotta, Vittoria
• Format: Article
• Language: English
• Subjects: A1 and A2A adenosine receptor antagonists; Amination; G protein-coupled receptors; Humans; Ligand–adenosine receptor modeling studies; Molecular Docking Simulation; Purinergic P1 Receptor Antagonists - chemistry; Purinergic P1 Receptor Antagonists - pharmacology; Pyrazoles - chemistry; Pyrazoles - pharmacology; Pyrazolo[4,3-d]pyrimidines; Pyrimidines - chemistry; Pyrimidines - pharmacology; Receptor, Adenosine A1 - metabolism; Receptor, Adenosine A2A - metabolism
• ISSN: 0968-0896; 1464-3391
• DOI: 10.1016/j.bmc.2016.04.048

[Display omitted] •New pyrazolopyrimidines were designed to target hA1 and hA2A adenosine receptors.•Different groups were evaluated at the 2- and 5-positions of the scaffold.•The 2-(2-methoxybenzyl) moiety afforded the highest hA2A AR affinities.•The 5-(5-methylfuran-2-yl) group achieved the best hA2A affinities.•The hA2A and hA1 affinities were rationalized by molecular docking investigations. A new series of 7-aminopyrazolo[4,3-d]pyrimidine derivatives (1–31) were synthesized to evaluate some structural modifications at the 2- and 5-positions aimed at shifting affinity towards the human (h) A2A adenosine receptor (AR) or both hA2A and hA1 ARs. The most active compounds were those featured by a 2-furyl or 5-methylfuran-2-yl moiety at position 5, combined with a benzyl or a substituted-benzyl group at position 2. Several of these derivatives (22–31) displayed nanomolar affinity for the hA2A AR (Ki=3.62–57nM) and slightly lower for the hA1 ARs, thus showing different degrees (3–22 fold) of hA2A versus hA1 selectivity. In particular, the 2-(2-methoxybenzyl)-5-(5-methylfuran-2-yl) derivative 25 possessed the highest hA2A and hA1 AR affinities (Ki=3.62nM and 18nM, respectively) and behaved as potent antagonist at both these receptors (cAMP assays). Its 2-(2-hydroxybenzyl) analog 26 also showed a high affinity for the hA2A AR (Ki=5.26nM) and was 22-fold selective versus the hA1 subtype. Molecular docking investigations performed at the hA2A AR crystal structure and at a homology model of the hA1 AR allowed us to represent the hypothetical binding mode of our derivatives and to rationalize the observed SARs.