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In this work, we describe the identification of the 1,2,4-triazolo[4,3-a]pyrazin-3-one as a new versatile scaffold for the development of adenosine human (h) receptor antagonists. The new chemotype ensued from a molecular simplification approach applied to our previously reported 1,2,4-triazolo[4,3-a]quinoxalin-1-one series. Hence, a set of novel 8-amino-2-aryl-1,2,4-triazolopyrazin-3-one derivatives, featured by different substituents on the 2-phenyl ring (R) and at position 6 (R6), was synthesized with the main purpose of targeting the hA2A adenosine receptor (AR). Several compounds possessed nanomolar affinity for the hA2A AR (Ki = 2.9-10 nM) and some, very interestingly, also showed high selectivity for the target. One selected potent hA2A AR antagonist (12, R = H, R6 = 4-methoxyphenyl) demonstrated some ability to counteract MPP+-induced neurotoxicity in cultured human neuroblastoma SH-SY5Y cells, a widely used in vitro Parkinson's disease model. Docking studies at hAR structures were performed to rationalize the observed affinity data. [ABSTRACT FROM AUTHOR]

New 7-amino-2-phenylpyrazolo[4,3-d]pyrimidine derivatives, substituted at the 5-position with aryl(alkyl)amino- and 4-substituted-piperazin-1-yl- moieties, were synthesized with the aim of targeting human (h) adenosine A1and/or A2Areceptor subtypes. On the whole, the novel derivatives1–24shared scarce or no affinities for the off-target hA2Band hA3ARs. The 5-(4-hydroxyphenethylamino)- derivative12showed both good affinity (Ki= 150 nM) and the best selectivity for the hA2AAR while the 5-benzylamino-substituted5displayed the best combined hA2A(Ki= 123 nM) and A1AR affinity (Ki= 25 nM). The 5-phenethylamino moiety (compound6) achieved nanomolar affinity (Ki= 11 nM) and good selectivity for the hA1AR. The 5-(N4-substituted-piperazin-1-yl) derivatives15–24bind the hA1AR subtype with affinities falling in the high nanomolar range. A structure-based molecular modeling study was conducted to rationalize the experimental binding data from a molecular point of view using both molecular docking studies and Interaction Energy Fingerprints (IEFs) analysis. [ABSTRACT FROM PUBLISHER]

In this study, we determined the crystal structure of an engineered human adenosine A 2A receptor bound to a partial agonist and compared it to structures cocrystallized with either a full agonist or an antagonist/inverse agonist. The interaction between the partial agonist, belonging to a class of dicyanopyridines, and amino acids in the ligand binding pocket inspired us to develop a small library of derivatives and assess their affinity in radioligand binding studies and potency and intrinsic activity in a functional, label-free, intact cell assay. It appeared that some of the derivatives retained the partial agonist profile, whereas other ligands turned into inverse agonists. We rationalized this remarkable behavior with additional computational docking studies.

New 8-amino-6-aryl-1,2,4-triazolo[4,3- a ]pyrazin-3-ones were designed to obtain dual antioxidant-human A 2A adenosine receptor (hA 2A AR) antagonists. Two sets of compounds were synthesized, the first featuring phenol rings at the 6-position, the second bearing the lipoyl and 4-hydroxy-3,5-di- tert but-benzoyl residues appended by different linkers on the 6-phenyl ring. Several new triazolopyrazines ( 1-21 ) were potent and selective hA 2A AR antagonists ( K i = 0.17-54.5 nM). Compounds 11 , 15 , and 21 , featuring antioxidant moieties, and compound 12 , lacking the antioxidant functionality, reduced oxaliplatin-induced toxicity in microglia cells, the most active being the lipoyl-derivative 15 and the (4-hydroxy-3,5-di- tert -butyl)benzoyl-analogue 21 which were effective in reducing the oxygen free radical level. The lipoyl-derivative 15 was also able to revert oxaliplatin-induced neuropathy in the mouse. In vivo efficacy of 15 makes it a promising neuroprotective agent in oxidative stress-related diseases.

New 7-amino-2-phenylpyrazolo[4,3-d]pyrimidine derivatives, substituted at the 5-position with aryl(alkyl)amino- and 4-substituted-piperazin-1-yl- moieties, were synthesized with the aim of targeting human (h) adenosine A 1 and/or A 2A receptor subtypes. On the whole, the novel derivatives 1-24 shared scarce or no affinities for the off-target hA 2B and hA 3 ARs. The 5-(4-hydroxyphenethylamino)- derivative 12 showed both good affinity (K i = 150 nM) and the best selectivity for the hA 2A AR while the 5-benzylamino-substituted 5 displayed the best combined hA 2A (K i = 123 nM) and A 1 AR affinity (K i = 25 nM). The 5-phenethylamino moiety (compound 6) achieved nanomolar affinity (K i = 11 nM) and good selectivity for the hA 1 AR. The 5-(N 4 -substituted-piperazin-1-yl) derivatives 15-24 bind the hA 1 AR subtype with affinities falling in the high nanomolar range. A structure-based molecular modeling study was conducted to rationalize the experimental binding data from a molecular point of view using both molecular docking studies and Interaction Energy Fingerprints (IEFs) analysis.[Formula: see text].

In this work, we describe the identification of the 1,2,4-triazolo[4,3-a]pyrazin-3-one as a new versatile scaffold for the development of adenosine human (h) receptor antagonists. The new chemotype ensued from a molecular simplification approach applied to our previously reported 1,2,4-triazolo[4,3-a]quinoxalin-1-one series. Hence, a set of novel 8-amino-2-aryl-1,2,4-triazolopyrazin-3-one derivatives, featured by different substituents on the 2-phenyl ring (R) and at position 6 (R 6 ), was synthesized with the main purpose of targeting the hA 2A adenosine receptor (AR). Several compounds possessed nanomolar affinity for the hA 2A AR (K i = 2.9-10 nM) and some, very interestingly, also showed high selectivity for the target. One selected potent hA 2A AR antagonist (12, R = H, R 6 = 4-methoxyphenyl) demonstrated some ability to counteract MPP + -induced neurotoxicity in cultured human neuroblastoma SH-SY5Y cells, a widely used in vitro Parkinson's disease model. Docking studies at hAR structures were performed to rationalize the observed affinity data.

In this study, we describe the design and synthesis of new N 5 -substituted-2-(2-furanyl) thiazolo[5,4-d]pyrimidine-5,7-diamines (2-18) and their pharmacological characterization as A 2A adenosine receptor (AR) antagonists by using in vitro and in vivo assays. In competition binding experiments two derivatives (13 and 14) emerged as outstanding ligands showing two different affinity values (KH and KL) for the hA 2A receptor with the high affinity KH value in the femtomolar range. The in vitro functional activity assays, performed by using cyclic AMP experiments, assessed that they behave as potent inverse agonists at the hA 2A AR. Compounds 13 and 14 were evaluated for their antinociceptive activity in acute experimental models of pain showing an effect equal to or greater than that of morphine. Overall, these novel inverse agonists might represent potential drug candidates for an alternative approach to the management of pain.