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Trifluorinated Pyrimidine-Based A2B Antagonists: Optimization and Evidences of Stereospecific Recognition.

We report the identification of two subsets of fluorinated nonxanthine A2B adenosine receptor antagonists. The novel derivatives explore the effect of fluorination at different positions of two pyrimidine-based scaffolds. The most interesting ligands combine excellent hA2B affinity (Ki < 15 nM) and remarkable subtype selectivity. The results of functional cAMP experiments confirmed the antagonistic behavior of representative ligands. The compounds were design on the basis of previous molecular models of the stereoselective binding of the parent scaffolds to the hA2B receptor, and we herein provide refinement of such models with the fluorinated compounds, which allow the explanation of the spurious effects of the fluorination at the different positions explored. These models are importantly confirmed by a synergistic study combining chiral HPLC, circular dichroism, diastereoselective synthesis, molecular modeling and X-ray crystallography, providing experimental evidence towards the stereospecific interaction between optimized trifluorinated stereoisomers and the hA2B receptor.