Selective and potent P2Y(11) receptor antagonists have yet to be developed, thus impeding an evaluation of this G protein-coupled receptor mainly expressed on immune cells. Taking suramin with moderate inhibitory potency as a template, 18 ureas with variations of the methyl groups of suramin and their precursors were functionally tested at P2Y(11), P2Y(1), and P2Y(2) receptors. Fluorine substitution of the methyl groups of suramin led to the first nanomolar P2Y(11) antagonist (8f, NF157, pK(i): 7.35). For selectivity, 8f was also tested at various P2X receptors. 8f displayed selectivity for P2Y(11) over P2Y(1) (>650-fold), P2Y(2) (>650-fold), P2X(2) (3-fold), P2X(3) (8-fold), P2X(4) (>22-fold), and P2X(7) (>67-fold) but no selectivity over P2X(1). QSAR studies confirm that residues with favored resonance and size parameters in the aromatic linker region can indeed lead to an increased potency as is the case for 8f. A symmetric structure linking two anionic clusters seems to be required for bioactivity. 8f may be helpful for studies evaluating the physiological role of P2Y(11) receptors.

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Extracellular adenine and uracil 5'-nucleotides are important signalling molecules that exert a great variety of effects in numerous tissues and cell types through the activation of P2 receptors. In the past eight years, an extended series of P2 receptors (P2X(17), ionotropic subunits; P2Y(1,2,4,6,11,12), metabotropic receptors) has been cloned from vertebrate tissues. In this rapidly expanding field, one of the main current challenges is to relate the cloned P2 receptor subtypes to the diverse physiological responses mediated by the pharmacological phenotypes of native P2 receptors. Unfortunately, subtype-selective P2 ligands, especially potent and selective antagonists, have been only slowly forthcoming, and this acts as a considerable impediment to progress. However, a number of new P2 receptor antagonists have recently been described which to some degree are more potent and more selective than earlier antagonists like suramin or pyridoxal-5'-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS). This work moves us closer to the ideal goal of classifying the recombinant and native P2 receptor subtypes on the basis of antagonist profiles. This review begins with a brief account of the current status of P2 receptors and their ligands. It then focuses on structure-activity relationships of PPADS and suramin analogues and will finish with a brief discussion of some related therapeutic possibilities.