Discovery of Potent and Highly Selective A_2B Adenosine Receptor Antagonist Chemotypes

Three novel families of A_2B adenosine receptor antagonists were identified in the context of the structural exploration of the 3,4-dihydropyrimidin-2­(1H)-one chemotype. The most appealing series contain imidazole, 1,2,4-triazole, or benzimidazole rings fused to the 2,3-positions of the parent diazinone core. The optimization process enabled identification of a highly potent (3.49 nM) A_2B ligand that exhibits complete selectivity toward A₁, A_2A, and A₃ receptors. The results of functional cAMP experiments confirmed the antagonistic behavior of representative ligands. The main SAR trends identified within the series were substantiated by a molecular modeling study based on a receptor-driven docking model constructed on the basis of the crystal structure of the human A_2A receptor.