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1.  Structurally related nucleotides as selective agonists and antagonists at P2Y1 receptors 
The P2Y1 receptor responds to adenine nucleotides and is present in platelets, heart, smooth muscles prostate, ovary, and brain. A selective antagonist may be useful as an antithrombotic agent. We have analyzed the binding site of this G protein-coupled receptor using ligand design, site-directed mutagenesis, and homology modeling based on rhodopsin. We have designed and synthesized a series of deoxyadenosine 3′,5′-bisphosphate derivatives that act as antagonists, or, in some cases with small structural changes, as agonists or partial agonists. The 2-position accommodates Cl or thioethers, whereas the N6-position is limited to Me or Et. 2′-Substitution with OH or OMe increases agonist efficacy over 2′-H. Using molecular modeling of the binding site, the oxygen atoms of the ribose moiety were predicted to be non-essential, i.e. no specific H-bonds with the receptor protein appear in the model. We have, therefore, substituted this moiety with carbocylics, smaller and larger rings, conformationally constrained rings, and acyclics, with retention of affinity for the receptor. With simplified pharmacophores we are exploring the steric and electronic requirements of the receptor binding site, and the structural basis of receptor activation.
PMCID: PMC4313380  PMID: 11347970
G protein-coupled receptors; Nucleotides; P2Y1; Molecular modeling
2.  Methanocarba Analogues of Purine Nucleosides as Potent and Selective Adenosine Receptor Agonists 
Journal of medicinal chemistry  2000;43(11):2196-2203.
Adenosine receptor agonists have cardioprotective, cerebroprotective, and antiinflammatory properties. We report that a carbocyclic modification of the ribose moiety incorporating ring constraints is a general approach for the design of A1 and A3 receptor agonists having favorable pharmacodynamic properties. While simple carbocyclic substitution of adenosine agonists greatly diminishes potency, methanocarba-adenosine analogues have now defined the role of sugar puckering in stabilizing the active adenosine receptor-bound conformation and thereby have allowed identification of a favored isomer. In such analogues a fused cyclopropane moiety constrains the pseudosugar ring of the nucleoside to either a Northern (N) or Southern (S) conformation, as defined in the pseudorotational cycle. In binding assays at A1, A2A, and A3 receptors, (N)-methanocarba-adenosine was of higher affinity than the (S)-analogue, particularly at the human A3 receptor (N/S affinity ratio of 150). (N)-Methanocarba analogues of various N6-substituted adenosine derivatives, including cyclopentyl and 3-iodobenzyl, in which the parent compounds are potent agonists at either A1 or A3 receptors, respectively, were synthesized. The N6-cyclopentyl derivatives were A1 receptor-selective and maintained high efficacy at recombinant human but not rat brain A1 receptors, as indicated by stimulation of binding of [35S]GTP-γ-S. The (N)-methanocarba-N6-(3-iodobenzyl)adenosine and its 2-chloro derivative had Ki values of 4.1 and 2.2 nM at A3 receptors, respectively, and were highly selective partial agonists. Partial agonism combined with high functional potency at A3 receptors (EC50 < 1 nM) may produce tissue selectivity. In conclusion, as for P2Y1 receptors, at least three adenosine receptors favor the ribose (N)-conformation.
PMCID: PMC3471159  PMID: 10841798
3.  Induction of Novel Agonist Selectivity for the ADP-Activated P2Y1 Receptor Versus the ADP-Activated P2Y12 and P2Y13 Receptors by Conformational Constraint of an ADP Analog 
ADP is the cognate agonist of the P2Y1, P2Y12, and P2Y13 receptors. With the goal of identifying a high potency agonist that selectively activates the P2Y1 receptor, we examined the pharmacological selectivity of the conformationally constrained non-nucleotide analog (N)-methanocarba-2MeSADP [(1′S,2′R, 3′S,4′R,5′S)-4-[(6-amino-2-methylthio-9H-purin-9-yl)-1-diphosphoryloxymethyl]bicyclo[3.1.0]hexane-2,3-diol] among the three ADP-activated receptors. Each P2Y receptor was expressed transiently in COS-7 cells, and inositol lipid hydrolysis was quantified as a measure of receptor activity. In the case of the Gi-linked P2Y12 and P2Y13 receptors, a chimeric G protein, Gαq/i, was coexpressed to confer a capacity of these Gi-linked receptors to activate phospholipase C. 2MeSADP (2-methylthio-ADP) was a potent agonist at all three receptors exhibiting EC50 values in the sub to low nanomolar range. In contrast, whereas (N)-methanocarba-2MeSADP was an extremely potent (EC50 = 1.2 ± 0.2 nM) agonist at the P2Y1 receptor, this non-nucleotide analog exhibited no agonist activity at the P2Y12 receptor and very low activity at the P2Y13 receptor. (N)-Methanocarba-2MeSADP also failed to block the action of 2MeSADP at the P2Y12 and P2Y13 receptors, indicating that the (N)-methanocarba analog is not an antagonist at these receptors. The P2Y1 receptor selectivity of (N)-methanocarba-2MeSADP was confirmed in human platelets where it induced the shape change promoted by P2Y1 receptor activation without inducing the sustained platelet aggregation that requires simultaneous activation of the P2Y12 receptor. These results provide the first demonstration of a high-affinity agonist that discriminates among the three ADP-activated P2Y receptors, and therefore, introduce a potentially important new pharmacological tool for delineation of the relative biological action of these three signaling proteins.
doi:10.1124/jpet.104.068650
PMCID: PMC3459333  PMID: 15345752

Results 1-3 (3)