Pyrimidine Ribonucleotides with Enhanced Selectivity as P2Y6 Receptor Agonists: Novel 4-Alkyloxyimino, (S)-Methanocarba, and 5′-Triphosphate γ-Ester Modifications

The P2Y6 receptor is a cytoprotective G-protein-coupled receptor (GPCR) activated by UDP (EC50 = 0.30 μM). We compared and combined modifications to enhance P2Y6 receptor agonist selectivity, including ribose ring constraint, 5-iodo and 4-alkyloxyimino modifications, and phosphate modifications such as α,β-methylene and extension of the terminal phosphate group into γ-esters of UTP analogues. The conformationally constrained (S)-methanocarba-UDP is a full agonist (EC50 = 0.042 μM). 4-Methoxyimino modification of pyrimidine enhanced P2Y6, preserved P2Y2 and P2Y4, and abolished P2Y14 receptor potency, in the appropriate nucleotide. N4-Benzyloxy-CDP (15, MRS2964) and N4-methoxy-Cp3U (23, MRS2957) were potent, selective P2Y6 receptor agonists (EC50 of 0.026 and 0.012 μM, respectively). A hydrophobic binding region near the nucleobase was explored with receptor modeling and docking. UTP-γ-aryl and cycloalkyl phosphoesters displayed only intermediate P2Y6 receptor potency but had enhanced stability in acid and ...