Structural Modifications of UMP, UDP, and UTP Leading to Subtype-Selective Agonists for P2Y2, P2Y4, and P2Y6 Receptors

A large series of derivatives and analogues of the uracil nucleotides UMP, UDP, and UTP with modifications in various positions of the uracil moiety and/or the phosphate groups were synthesized and evaluated at human P2Y(2), P2Y(4), and P2Y(6) receptors. 2-(Ar)alkylthio substitution of UMP and UDP was best tolerated by the P2Y(2) receptor, 2-Phenethylthio-UMP (13e) showed an EC50 value of 1.3 mu M at P2Y(2) and > 70-fold selectivity versus P2Y(4) and P2Y(6) receptors. Substitution of the 2-keto group in UMP by NH (13g, iso-CMP) resulted in the first potent and selective P2Y(4) agonist (EC50 4.98 mu M > 20-fold selective vs P2Y(2) and P2Y(6)). In contrast, :replacement of the 2-keto function in UDP by NH yielded a potent P2Y(2) agonist (12g, iso-CDP, EC50 = 0.604 mu M, > 100-fold selective). In an attempt to obtain metabolically stable UTP analogues, beta,gamma-dichloro- and beta,gamma-difluoro-methylene-UTP derivatives were synthesized. The triphosphate modifications were much better tolerated by P2Y(2), and in some cases also by P2Y(6), than by P2Y(4) receptors. 4-Thio-beta,gamma-difluoromethylene-UTP (14g) was a potent P2Y(2) agonist with an EC50 value of 0.134 mu M and > 50-fold selectivity. N3-Phenacyl-beta,gamma-dichloromethylene-UTP (14b) proved to be a potent P2Y(6) receptor agonist (EC50 0.142 mu M) with high selectivity versus P2Y(4) (50-fold) and moderate selectivity versus P2Y(2) receptors (6-fold).