Optimization of 2-Amino-4,6-diarylpyrimidine-5-carbonitriles as Potent and Selective A1 Antagonists

Abstract

We herein document a large collection of 108 2-amino-4,6-disubstituted-pyrimidine derivatives as potent, structurally simple, and highly selective A₁AR ligands. The most attractive ligands were confirmed as antagonists of the canonical cyclic adenosine monophosphate pathway, and some pharmacokinetic parameters were preliminarilly evaluated. The library, built through a reliable and efficient three-component reaction, comprehensively explored the chemical space allowing the identification of the most prominent features of the structure-activity and structure-selectivity relationships around this scaffold. These included the influence on the selectivity profile of the aromatic residues at positions R⁴ and R⁶ of the pyrimidine core but most importantly the prominent role to the unprecedented A₁AR selectivity profile exerted by the methyl group introduced at the exocyclic amino group. The structure-activity relationship trends on both A₁ and A_2AARs were conveniently interpreted with rigorous free energy perturbation simulations, which started from the receptor-driven docking model that guided the design of these series.

Figure 1

Structure of representative A₁ adenosine receptor antagonists.^,−

Figure 2

Structure of the model (2- or 4-)-aminopyrimidines (15–17) and herein documented A₁ antagonists (18–20).⁻

Scheme 1. Three-Component Assembly of the Novel 2-Amino-4,6-diaryl-5-carbonitriles (18–20)

Figure 3

Concentration-response curves of the effect of 19ao, 19l, 19v, and XAC on 3 μM forskolin-stimulated cAMP production in the presence of NECA 100 nM.

Figure 4

Affinity-selectivity plot for the 2-amino-4,6-diaryl-5-carbonitriles of series I (18a–18 am) and series II (19a–19bn). Inverted triangles show dual A_2A/A_2B compounds.

Figure 5

Affinity-selectivity plot of a selection of 2-amino-4,6-diaryl-5-carbonitriles from series II (the shape indicates the substituent on R², and the color indicates the substituent on R⁴).

Figure 6

(A) Two binding modes considered for this series (conformation A, orange; conformation B, magenta) illustrated on compound 19ao on the A₁AR (PDB: 5N2S). (B) Scatter plot of the predicted (vertical axis) vs experimental (horizontal axis) binding free energies for the A₁AR, as determined by FEP calculations using conformation A. The dots are colored according to the SEM of the associated FEP simulations after cycle closure correction (see Experimental Section).

Figure 7

Binding mode to the A₁AR (A–C, PDB: 5N2S) and the A_2AAR (D, PDB: 4EIY with closed conformation, red; D–F, PDB: 3UZC, open conformation, gray) of N-substituted compounds: 19l, R² = Me, orange (A, D); 19m, R² = Et, green (B, E); 19n, R² = Ph, blue (C, F).