Effect of Nitrogen Atom Substitution in A₃ Adenosine Receptor Binding: <i>N</i>‑(4,6-Diarylpyridin-2-yl)acetamides as Potent and Selective Antagonists

We report the first family of 2-acetamidopyridines as potent and selective A₃ adenosine receptor (AR) antagonists. The computer-assisted design was focused on the bioisosteric replacement of the N1 atom by a CH group in a previous series of diarylpyrimidines. Some of the generated 2-acetamidopyridines elicit an antagonistic effect with excellent affinity (<i>K</i>_i < 10 nM) and outstanding selectivity profiles, providing an alternative and simpler chemical scaffold to the parent series of diarylpyrimidines. In addition, using molecular dynamics and free energy perturbation simulations, we elucidate the effect of the second nitrogen of the parent diarylpyrimidines, which is revealed as a stabilizer of a water network in the binding site. The discovery of 2,6-diaryl-2-acetamidopyridines represents a step forward in the search of chemically simple, potent, and selective antagonists for the hA₃AR, and exemplifies the benefits of a joint theoretical–experimental approach to identify novel hA₃AR antagonists through succinct and efficient synthetic methodologies

Enantiospecific Recognition at the A_2B Adenosine Receptor by Alkyl 2‑Cyanoimino-4-substituted-6-methyl-1,2,3,4-tetrahydropyrimidine-5-carboxylates

A novel family of structurally simple, potent, and selective nonxanthine A_2BAR ligands was identified, and its antagonistic behavior confirmed through functional experiments. The reported alkyl 2-cyanoimino-4-substituted-6-methyl-1,2,3,4-tetrahy-dropyrimidine-5-carboxylates (<b>16</b>) were designed by bioisosteric replacement of the carbonyl group at position 2 in a series of 3,4-dihydropyrimidin-2-ones. The scaffold (<b>16</b>) documented herein contains a chiral center at the heterocycle. Accordingly, the most attractive ligand of the series [(±)<b>16b</b>, <i>K</i>_i <b>=</b> 24.3 nM] was resolved into its two enantiomers by chiral HPLC, and the absolute configuration was established by circular dichroism. The biological evaluation of both enantiomers demonstrated enantiospecific recognition at A_2BAR, with the (<i>S</i>)-<b>16b</b> enantiomer retaining all the affinity (<i>K</i>_i <b>=</b> 15.1 nM), as predicted earlier by molecular modeling. This constitutes the first example of enantiospecific recognition at the A_2B adenosine receptor and opens new possibilities in ligand design for this receptor

Effect of Nitrogen Atom Substitution in A₃ Adenosine Receptor Binding: <i>N</i>‑(4,6-Diarylpyridin-2-yl)acetamides as Potent and Selective Antagonists

We report the first family of 2-acetamidopyridines as potent and selective A₃ adenosine receptor (AR) antagonists. The computer-assisted design was focused on the bioisosteric replacement of the N1 atom by a CH group in a previous series of diarylpyrimidines. Some of the generated 2-acetamidopyridines elicit an antagonistic effect with excellent affinity (<i>K</i>_i < 10 nM) and outstanding selectivity profiles, providing an alternative and simpler chemical scaffold to the parent series of diarylpyrimidines. In addition, using molecular dynamics and free energy perturbation simulations, we elucidate the effect of the second nitrogen of the parent diarylpyrimidines, which is revealed as a stabilizer of a water network in the binding site. The discovery of 2,6-diaryl-2-acetamidopyridines represents a step forward in the search of chemically simple, potent, and selective antagonists for the hA₃AR, and exemplifies the benefits of a joint theoretical–experimental approach to identify novel hA₃AR antagonists through succinct and efficient synthetic methodologies