8-Amino-1,2,4-triazolo[4,3-a]pyrazin-3-one derivatives hybridized with antioxidants: new highly potent and selective human A2A adenosine receptor antagonists as useful agents against cerebral ischemia

Cerebral ischemia is a complex pathology resulting from the interplay of diverse mechanisms including the massive release of adenosine and the consequent activation of its receptors. Among them, the A2A adenosine receptor (AR) plays a significant role. Much evidence showed that selective A2A AR antagonists reduce excitotoxicity and exert neuroprotective activity in animal models of cerebral ischemia. Oxidative stress contributes to ischemic brain injury; thus, antioxidants have been intensively investigated as neuroprotective against ischemic stroke. This work focuses on the identification of dual-acting derivatives able to block the A2A AR and exert antioxidant effects because they could be more potent neuroprotective than single-acting compounds. Thus, a set of 8-amino-6-aryl-2-phenyl-1,2,4-triazolo[4,3-a]pyrazin-3-ones hybridized with the antioxidant edaravone (EDA) (1–5) and (S)-2-oxothiazolidine-4-carboxylic acid (OTC) (6–8) were synthesized. The new derivatives were potent hA2A AR antagonists (Ki = 1.7–117 nM), endowed with good selectivity versus the other AR subtypes. Molecular docking studies revealed that these derivatives bind optimally to the A2A AR, with the 2-phenyl ring positioned deep within the receptor cavity and the 6-substituent located near the entrance. Selected compounds, hybridized with EDA and OTC, were effective in reducing neuronal damage caused by oxygen and glucose deprivation in rat hippocampal models of cerebral ischemia. The findings suggested that the neuroprotective effects of EDA-based derivatives 3 and 4 may result from both their antioxidant properties and their ability to antagonize the A2A AR. These results highlighted the therapeutic potential of dual-acting compounds, combining antioxidant activity and A2A AR antagonism, for the treatment of cerebral ischemia and other oxidative stress-related disorders.