Design, Synthesis, and Evaluation of a New Chemotype Fluorescent Ligand for the P2Y₂ Receptor

The P2Y₂ receptor (P2Y₂R) is a target for diseases including cancer, idiopathic pulmonary fibrosis, and atherosclerosis. However, there are insufficient P2Y₂R antagonists available for validating P2Y₂R function and future drug development. Evaluation of how (R)-5-(7-chloro-2-((2-ethoxyethyl)amino)-4H-benzo[5,6]cyclohepta[1,2-d]thiazol-4-yl)-1-methyl-4-thioxo-3,4-dihydropyrimidin-2(1H)-one, a previously published thiazole-based analogue of AR-C118925, binds in a P2Y₂R homology model was used to design new P2Y₂R antagonist scaffolds. One P2Y₂R antagonist scaffold retained millimolar affinity for the P2Y₂R and upon further functionalization with terminal carboxylic acid groups affinity was improved over 100-fold. This functionalized P2Y₂R antagonist scaffold was employed to develop new chemotype P2Y₂R fluorescent ligands, that were attainable in a convergent five-step synthesis. One of these fluorescent ligands demonstrated micromolar affinity (pK _d = 6.02 ± 0.12, n = 5) for the P2Y₂R in isolated cell membranes and distinct pharmacology from an existing P2Y₂R fluorescent antagonist, suggesting it may occupy a different binding site on the P2Y₂R.