Molecular recognition in purinergic receptors. 2. Diastereoselectivity of the h-P2Y₁-receptor

In the companion paper, part 1, we described the construction of an improved molecular model for the h-P2Y₁ receptor (h-P2Y ₁-R) and proposed a rational for the stereoelectronic selectivity of the receptor. Here, we extend our studies on the molecular recognition of the h-P2Y₁-R to the exploration of the diastereoselectivity of this receptor. For this purpose, we implemented an integrative approach combining synthesis, spectral analysis, biochemical assays, and computational analysis. Specifically, we selected and synthesized novel ATP analogues bearing a chiral center on the phosphate chain. We analyzed the conformation of the chiral ATP analogues in solution by ¹H/¹³C NMR and assigned the absolute configuration of the diastereoisomers. The coordination mode of these analogues with a Mg²⁺ ion was evaluated by ³¹P NMR. These chiral analogues were biochemically evaluated and found to be potent h-P2Y ₁-R ligands. An EC₅₀ difference of ca. 20-fold was observed between the diastereoisomers. Their spectral absolute configuration assignment was confirmed by comparison of the biochemical results to those of ATP-α-S diastereoisomers whose chirality is known. Finally, a computational analysis was performed for the elucidation of molecular recognition employing molecular mechanics (docking) studies on the receptor:ligands complexes. On the basis of the current results, we hypothesize that h-P2Y₁-R's chiral discrimination originates from the requirement that the nucleotide analogue interacts with a Mg²⁺ ion within the receptor binding site. This Mg2+ ion is possibly coordinated with both Asp204 and the ATP's α, β, γ-phosphates in a Λ configuration.