Novel 8-amino-1,2,4-triazolo[4,3-a]pyrazin-3-one derivatives as potent human adenosine A1 and A2A receptor antagonists. Evaluation of their protective effect against β-amyloid-induced neurotoxicity in SH-SY5Y cells

In this work, an enlarged series of 1,2,4-triazolo[4,3-a]pyrazin-3-ones was designed to target the human (h) A2A adenosine receptor (AR) or both hA1 and hA2A ARs. The novel 8-amino-1,2,4-triazolopyrazin-3-one derivatives 1–25 featured a phenyl or a benzyl pendant at position 2 while different aryl/heteroaryl substituents were placed at position 6. Two compounds (8 and 10) endowed with high affinity (Ki = 7.2 and 10.6 nM) and a complete selectivity for the hA2A AR were identified. Moreover, several derivatives possessed nanomolar affinity for both hA1 and hA2A ARs (both Ki < 20 nM) and different degrees of selectivity versus the hA3 AR. Two selected compounds (10 and 25) demonstrated ability in preventing β-amyloid peptide (25–35)-induced neurotoxicity in SH-SY5Y cells. Results of docking studies at the hA2A and hA1 AR crystal structures helped us to rationalize the observed affinity data and to highlight that the steric hindrance of the substituents at the 2- and 6-position of the bicyclic core affects the binding mode in the receptor cavity.