Abstract
Three A(3) adenosine receptor (AR) antagonists (1-3) selected from 4-acylamino-6-alkyloxy-2-alkylthiopyrimidines previously investigated by us were modified by inserting a methyl group on their ether or thioether side chains. These compounds gave us the chance to evaluate whether their higher lipophilicity, reduced conformational freedom and chirality might improve the potency towards the A(3) AR. Racemic mixtures of 1-3 were resolved using chiral HPLC methods and the absolute configurations of the enantiomers were assigned by chiroptical spectroscopy and density functional theory calculations. We measured the affinity for human A(1), A(2A), A(2B) and A(3) ARs of the racemic mixtures and the pure enantiomers of 1-3 by radioligand competition binding experiments. Cell-based assays of the most potent enantiomers confirmed their A(3) AR antagonist profiles. Our research led to the identification of (S)-1 with high potency (0.5 nM) and selectivity as an A(3) AR antagonist. Moreover we built a docking-model useful to design new pyrimidine derivatives.