Enantiospecific Recognition at the A 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 AAR 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 (16) were designed by bioisosteric replacement of the carbonyl group at position 2 in a series of 3,4-dihydropyrimidin-2-ones. The scaffold (16) documented herein contains a chiral center at the heterocycle. Accordingly, the most attractive ligand of the series [(±)16b, K = 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 AAR, with the (S)-16b enantiomer retaining all the affinity (K = 15.1 nM), as predicted earlier by molecular modeling. This constitutes the first example of enantiospecific recognition at the A adenosine receptor and opens new possibilities in ligand design for this receptor.