Synthesis and potency of novel uracil nucleotides and derivatives as P2Y2 and P2Y6 receptor agonists

Absence of P2Y2 Receptor Does Not Prevent Bone Destruction in a Murine Model of Muscle Paralysis-Induced Bone Loss

Increased incidence of bone fractures in the elderly is associated with gradual sarcopenia. Similar deterioration of bone quality is seen with prolonged bed rest, spinal cord injuries or in astronauts exposed to microgravity and, preceded by loss of muscle mass. Signaling mechanisms involving uridine-5'-triphosphate (UTP) regulate bone homeostasis via P2Y₂ receptors on osteoblasts and osteoclasts, whilst dictating the bone cells' response to mechanical loading. We hypothesized that muscle paralysis-induced loss of bone quality would be prevented in P2Y₂ receptor knockout (KO) mice. Female mice injected with botulinum toxin (BTX) in the hind limb developed muscle paralysis and femoral DXA analysis showed reduction in bone mineral density (<10%), bone mineral content (<16%) and bone area (<6%) in wildtype (WT) compared to KO littermates (with <13%, <21%, <9% respectively). The femoral metaphyseal strength was reduced equally in both WT and KO (<37%) and <11% in diaphysis region of KO, compared to the saline injected controls. Tibial micro-CT showed reduced cortical thickness (12% in WT vs. 9% in KO), trabecular bone volume (38% in both WT and KO), trabecular thickness (22% in WT vs. 27% in KO) and increased SMI (26% in WT vs. 19% in KO) after BTX. Tibial histomorphometry showed reduced formation in KO (16%) but unchanged resorption in both WT and KO. Furthermore, analyses of DXA and bone strength after regaining the muscle function showed partial bone recovery in the KO but no difference in the bone recovery in WT mice. Primary osteoblasts from KO mice displayed increased viability and alkaline phosphatase activity but, impaired bone nodule formation. Significantly more TRAP-positive osteoclasts were generated from KO mice but displayed reduced resorptive function. Our data showed that hind limb paralysis with a single dose of BTX caused profound bone loss after 3 weeks, and an incomplete reversal of bone loss by week 19. Our findings indicate no role of the P2Y₂ receptor in the bone loss after a period of skeletal unloading in mice or, in the bone recovery after restoration of muscle function.

Role of the Purinergic P2Y2 Receptor in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH), group 1 pulmonary hypertension (PH), is a fatal disease that is characterized by vasoconstriction, increased pressure in the pulmonary arteries, and right heart failure. PAH can be described by abnormal vascular remodeling, hyperproliferation in the vasculature, endothelial cell dysfunction, and vascular tone dysregulation. The disease pathomechanisms, however, are as yet not fully understood at the molecular level. Purinergic receptors P2Y within the G-protein-coupled receptor family play a major role in fluid shear stress transduction, proliferation, migration, and vascular tone regulation in systemic circulation, but less is known about their contribution in PAH. Hence, studies that focus on purinergic signaling are of great importance for the identification of new therapeutic targets in PAH. Interestingly, the role of P2Y2 receptors has not yet been sufficiently studied in PAH, whereas the relevance of other P2Ys as drug targets for PAH was shown using specific agonists or antagonists. In this review, we will shed light on P2Y receptors and focus more on the P2Y2 receptor as a potential novel player in PAH and as a new therapeutic target for disease management.

Structure-activity relationships of pyrimidine nucleotides containing a 5'-α,β-methylene diphosphonate at the P2Y6 receptor

The Gq-coupled P2Y6 receptor (P2Y6R) is a component of the purinergic signaling system and functions in inflammatory, cardiovascular and metabolic processes. UDP, the native P2Y6R agonist and P2Y14R partial agonist, is subject to hydrolysis by ectonucleotidases. Therefore, we have synthesized UDP/CDP analogues containing a stabilizing α,β-methylene bridge as P2Y6R agonists and identified compatible affinity-enhancing pyrimidine modifications. A distal binding region on the receptor was explored with 4-benzyloxyimino cytidine 5'-diphosphate analogues and their potency determined in a calcium mobilization assay. A 4-trifluoromethyl-benzyloxyimino substituent in 25 provided the highest human P2Y6R potency (MRS4554, 0.57 µM), and a 5-fluoro substitution of the cytosine ring in 28 similarly enhanced potency, with >175- and 39-fold selectivity over human P2Y14R, respectively. However, 3-alkyl (31-33, 37, 38), β-d-arabinofuranose (39) and 6-aza (40) substitution prevented P2Y6R activation. Thus, we have identified new α,β-methylene bridged N4-extended CDP analogues as P2Y6R agonists that are highly selective over the P2Y14R.

The role of P2Y receptors in regulating immunity and metabolism

P2Y receptors are G protein-coupled receptors whose physiological agonists are the nucleotides ATP, ADP, UTP, UDP and UDP-glucose. Eight P2Y receptors have been cloned in humans: P2Y₁R, P2Y₂R, P2Y₄R, P2Y₆R, P2Y₁₁R, P2Y₁₂R, P2Y₁₃R and P2Y₁₄R. P2Y receptors are expressed in lymphoid tissues such as thymus, spleen and bone marrow where they are expressed on lymphocytes, macrophages, dendritic cells, neutrophils, eosinophils, mast cells, and platelets. P2Y receptors regulate many aspects of immune cell function, including phagocytosis and killing of pathogens, antigen presentation, chemotaxis, degranulation, cytokine production, and lymphocyte activation. Consequently, P2Y receptors shape the course of a wide range of infectious, autoimmune, and inflammatory diseases. P2Y₁₂R ligands have already found their way into the therapeutic arena, and we envision additional ligands as future drugs for the treatment of diseases caused by or associated with immune dysregulation.

Overview of Biologically Active Nucleoside Phosphonates

The use of the phosphonate motif featuring a carbon-phosphorous bond as bioisosteric replacement of the labile P–O bond is widely recognized as an attractive structural concept in different areas of medicinal chemistry, since it addresses the very fundamental principles of enzymatic stability and minimized metabolic activation. This review discusses the most influential successes in drug design with special emphasis on nucleoside phosphonates and their prodrugs as antiviral and cancer treatment agents. A description of structurally related analogs able to interfere with the transmission of other infectious diseases caused by pathogens like bacteria and parasites will then follow. Finally, molecules acting as agonists/antagonists of P2X and P2Y receptors along with nucleotidase inhibitors will also be covered. This review aims to guide readers through the fundamentals of nucleoside phosphonate therapeutics in order to inspire the future design of molecules to target infections that are refractory to currently available therapeutic options.

Therapeutic potential of uracil and its derivatives in countering pathogenic and physiological disorders

Uracil is one of the most notable pharmacophores in medicinal chemistry as the pyrimidine nucleobase forms an integral part of many commercial drugs. Though the name uracil is usually associated with cancer drugs, there are many uracil-based compounds which can treat different diseases when they are employed. So far, there has been no in-depth review concerning uracil drugs in the market, or in the different stages of clinical trials, including those approved or discontinued. The current work focuses on the importance of uracil and its derivatives in treating different diseases. The use of uracil compounds in treating viral infections, cancer, diabetic, thyroid and autosomal recessive disorders are discussed in the review. The mechanism of action of each uracil drug with emphasis on their structure and properties are discussed in detail. The targeted action of these drugs on sites or on the different stages of a disorder/pathogenic life cycle are also discussed. This review encompasses uracil drugs approved as well as those in development from the 1950's onwards. The utility of uracil in drug discovery and its association with a wide range of diseases is brought forth within this review to demonstrate its potential to a wider audience.

Update of P2Y receptor pharmacology: IUPHAR Review 27

Eight G protein-coupled P2Y receptor subtypes respond to extracellular adenine and uracil mononucleotides and dinucleotides. P2Y receptors belong to the δ group of rhodopsin-like GPCRs and contain two structurally distinct subfamilies: P2Y₁ , P2Y₂ , P2Y₄ , P2Y₆ , and P2Y₁₁ (principally G_q protein-coupled P2Y₁ -like) and P2Y_12-14 (principally G_i protein-coupled P2Y₁₂ -like) receptors. Brain P2Y receptors occur in neurons, glial cells, and vasculature. Endothelial P2Y₁ , P2Y₂ , P2Y₄ , and P2Y₆ receptors induce vasodilation, while smooth muscle P2Y₂ , P2Y₄ , and P2Y₆ receptor activation leads to vasoconstriction. Pancreatic P2Y₁ and P2Y₆ receptors stimulate while P2Y₁₃ receptors inhibits insulin secretion. Antagonists of P2Y₁₂ receptors, and potentially P2Y₁ receptors, are anti-thrombotic agents, and a P2Y₂ /P2Y₄ receptor agonist treats dry eye syndrome in Asia. P2Y receptor agonists are generally pro-inflammatory, and antagonists may eventually treat inflammatory conditions. This article reviews recent developments in P2Y receptor pharmacology (using synthetic agonists and antagonists), structure and biophysical properties (using X-ray crystallography, mutagenesis and modelling), physiological and pathophysiological roles, and present and potentially future therapeutic targeting.

Synthetic Strategies for Dinucleotides Synthesis

Dinucleoside 5′,5′-polyphosphates (DNPs) are endogenous substances that play important intra- and extracellular roles in various biological processes, such as cell proliferation, regulation of enzymes, neurotransmission, platelet disaggregation and modulation of vascular tone. Various methodologies have been developed over the past fifty years to access these compounds, involving enzymatic processes or chemical procedures based either on P(III) or P(V) chemistry. Both solution-phase and solid-support strategies have been developed and are reported here. Recently, green chemistry approaches have emerged, offering attracting alternatives. This review outlines the main synthetic pathways for the preparation of dinucleoside 5′,5′-polyphosphates, focusing on pharmacologically relevant compounds, and highlighting recent advances.

Nucleoside Tetra- and Pentaphosphates Prepared Using a Tetraphosphorylation Reagent Are Potent Inhibitors of Ribonuclease A

Adenosine and uridine 5'-tetra- and 5'-pentaphosphates were synthesized from an activated tetrametaphosphate ([PPN]₂[P₄O₁₁], [PPN]₂[1], PPN = bis(triphenylphosphine)iminium) and subsequently tested for inhibition of the enzymatic activity of ribonuclease A (RNase A). Reagent [PPN]₂[1] reacts with unprotected uridine and adenosine in the presence of a base under anhydrous conditions to give nucleoside tetrametaphosphates. Ring opening of these intermediates with tetrabutylammonium hydroxide ([TBA][OH]) yields adenosine and uridine tetraphosphates (p₄A, p₄U) in 92% and 85% yields, respectively, from the starting nucleoside. Treatment of ([PPN]₂[1]) with AMP or UMP yields nucleoside-monophosphate tetrametaphosphates (cp₄pA, cp₄pU) having limited aqueous stability. Ring opening of these ultraphosphates with [TBA][OH] yields p₅A and p₅U in 58% and 70% yield from AMP and UMP, respectively. We characterized inorganic and nucleoside-conjugated linear and cyclic oligophosphates as competitive inhibitors of RNase A. Increasing the chain length in both linear and cyclic inorganic oligophosphates resulted in improved binding affinity. Increasing the length of oligophosphates on the 5' position of adenosine beyond three had a deleterious effect on binding. Conversely, uridine nucleotides bearing 5' oligophosphates saw progressive increases in binding with chain length. We solved X-ray cocrystal structures of the highest affinity binders from several classes. The terminal phosphate of p₅A binds in the P₁ enzymic subsite and forces the oligophosphate to adopt a convoluted conformation, while the oligophosphate of p₅U binds in several extended conformations, targeting multiple cationic regions of the active-site cleft.

Pharmacology of P2Y receptors

P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular nucleotides. There are eight mammalian P2Y receptor subtypes divided into two subgroups (P2Y₁, P2Y₂, P2Y₄, P2Y₆, and P2Y₁₁) and (P2Y₁₂, P2Y₁₃, and P2Y₁₄). The P2Y receptors are expressed in various cell types and play important roles in physiology and pathophysiology including inflammatory responses and neuropathic pain. The antagonism of P2Y₁₂ receptors is used in pharmacotherapy for the prevention and therapy of cardiovascular events. The nucleoside analogue ticagrelor and active metabolites of the thienopyridine compounds ticlopidine, clopidogrel and prasugrel inhibit platelet P2Y₁₂ receptors and reduce thereby platelet aggregation. The P2Y₂ receptor agonist diquafosol is used for the treatment of the dry eye syndrome. The P2Y receptor subtypes differ in their amino acid sequences, their pharmacological profiles and their signaling transduction pathways. Recently, selective receptor ligands have been developed for all subtypes. The published crystal structures of the human P2Y₁ and P2Y₁₂ receptors as well as receptor models will facilitate the development of novel drugs for pharmacotherapy.

Synthesis of Nucleoside-5'-O-Tetraphosphates from Activated Trimetaphosphate and Nucleoside-5'-O-Monophosphates

This article describes a straight-forward chemical method for the synthesis of nucleoside-5'-O-tetraphosphates, such as cytosine-, guanosine-, adenosine-, and uridine-5'-O-tetraphosphates, starting from the corresponding nucleoside monophosphates and trimetaphosphate, a readily available and inexpensive starting material. The procedure involves reacting the tri(tetrabutylammonium) salt of trimetaphosphate with mesitylenesulfonyl chloride and N-methylimidazole. The resulting activated cyclic trimetaphosphate is reacted with the tetrabutylammonium salts of nucleoside monophosphates. After quenching the reaction with buffer and high-performance liquid chromatography purification, the desired nucleoside-5'-O-tetraphosphates were obtained in yields of 84% to 86%. © 2018 by John Wiley & Sons, Inc.

Tools and drugs for uracil nucleotide-activated P2Y receptors

P2Y receptors (P2YRs) are a family of G protein-coupled receptors activated by extracellular nucleotides. Physiological P2YR agonists include purine and pyrimidine nucleoside di- and triphosphates, such as ATP, ADP, UTP, UDP, nucleotide sugars, and dinucleotides. Eight subtypes exist, P2Y₁, P2Y₂, P2Y₄, P2Y₆, P2Y₁₁, P2Y₁₂, P2Y₁₃, and P2Y₁₄, which represent current or potential future drug targets. Here we provide a comprehensive overview of ligands for the subgroup of the P2YR family that is activated by uracil nucleotides: P2Y₂ (UTP, also ATP and dinucleotides), P2Y₄ (UTP), P2Y₆ (UDP), and P2Y₁₄ (UDP, UDP-glucose, UDP-galactose). The physiological agonists are metabolically unstable due to their fast hydrolysis by ectonucleotidases. A number of agonists with increased potency, subtype-selectivity and/or enzymatic stability have been developed in recent years. Useful P2Y₂R agonists include MRS2698 (6-01, highly selective) and PSB-1114 (6-05, increased metabolic stability). A potent and selective P2Y₂R antagonist is AR-C118925 (10-01). For studies of the P2Y₄R, MRS4062 (3-15) may be used as a selective agonist, while PSB-16133 (10-06) is a selective antagonist. Several potent P2Y₆R agonists have been developed including 5-methoxyuridine 5'-O-((R_p)α-boranodiphosphate) (6-12), PSB-0474 (3-11), and MRS2693 (3-26). The isocyanate MRS2578 (10-08) is used as a selective P2Y₆R antagonist, although its reactivity and low water-solubility are limiting. With MRS2905 (6-08), a potent and metabolically stable P2Y₁₄R agonist is available, while PPTN (10-14) represents a potent and selective P2Y₁₄R antagonist. The radioligand [³H]UDP can be used to label P2Y₁₄Rs. In addition, several fluorescent probes have been developed. Uracil nucleotide-activated P2YRs show great potential as drug targets, especially in inflammation, cancer, cardiovascular and neurodegenerative diseases.

Current knowledge on the nucleotide agonists for the P2Y2 receptor

P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular nucleotides. There are eight mammalian P2Y receptor subtypes (P2Y1, P2Y2, P2Y4, P2Y6, P2Y11, P2Y12, P2Y13, and P2Y14). P2Y2 receptors are widely expressed and play important roles in multiple functionalities. Diquafosol tetrasodium, known as INS365, which was the first P2Y2 receptor agonists that had been approved in April 2010 and launched in Japan by Santen Pharmaceuticals. Besides, a series of similar agonists for the P2Y2 receptor are undergoing development to cure different diseases related to the P2Y2 receptor. This article illustrated the structure and functions of the P2Y2 receptor and focused on several kinds of agonists about their molecular structures, research progress and chemical synthesis methods. Last but not the least, we summarized the structures-activity relationship (SAR) of agonists for the P2Y2 receptor and expected more efficient agonists for the P2Y2 receptor.

Pyrimidine Nucleotides Containing a (S)-Methanocarba Ring as P2Y6 Receptor Agonists

Both agonists and antagonists of the UDP-activated P2Y₆ receptor (P2Y₆R) have been proposed for therapeutic use, in conditions such as cancer, inflammation, neurodegeneration and diabetes. Uracil nucleotides containing a South-bicyclo[3.1.0]hexane ((S)-methanocarba) ring system in place of the ribose ring were synthesized and shown to be potent P2Y₆R agonists in a calcium mobilization assay. The (S)-methanocarba modification was compatible with either a 5-iodo or 4-methoxyimino group on the pyrimidine, but not with a α,β-methylene 5´-diphosphate. (S)-Methanocarba dinucleotide potency was compatible with a N⁴-methoxy modification on the proximal nucleoside that is assumed to bind at the P2Y₆R similarly to UDP; (N)-methanocarba was preferred on the distal nucleoside moiety. This suggests that the distal dinucleotide P2Y₆R binding site prefers a ribose-like group that can attain a (N) conformation, rather than (S). Dinucleotide binding was modeled by homology modeling, docking and molecular dynamics simulations, which suggested the same ribose conformational preferences found empirically.

Effects of 4(1H)-quinolinone derivative, a novel non-nucleotide allosteric purinergic P2Y 2 agonist, on cardiomyocytes in neonatal rats

Purinergic P2Y₂ receptors, G-protein coupled receptors that primarily couple with Gα_q/11-proteins, are activated equipotently by adenosine-5′-triphosphate (ATP) and uridine-5′-triphosphate. Evidence suggests that P2Y₂ agonists make potential drug candidates for the treatment of cardiovascular diseases. However, selective non-nucleotide, small-molecule P2Y₂ agonists have yet to be developed. In this report, we discuss Compound 89, a novel non-nucleotide allosteric P2Y₂ agonist that was active in signal transduction and gene induction, and in our in vitro cardiac hypertrophy model. Compound 89 exhibited selective P2Y₂ agonistic activity and potentiated responses to the endogenous agonist ATP, while exhibiting no agonistic activities for four other Gα_q/11-coupled human P2Y (hP2Y) receptors and one representative Gα_i/o-coupled hP2Y₁₂ receptor. Its P2Y₂ agonistic effect on mouse P2Y₂ receptors suggested non-species-specific activity. Compound 89 acted as a pure positive allosteric modulator in a Ca²⁺ mobilization assay of neonatal rat cardiomyocytes; it potentiated ATP-induced expression of genes in the nuclear receptor 4A family (negative regulators of hypertrophic stimuli in cardiomyocytes). Additionally, Compound 89 attenuated isoproterenol-induced cardiac hypertrophy, presumably through dose-dependent interaction with pericellular ATP. These results indicate that Compound 89 is potentially efficacious against cardiomyocytes and therefore a good proof-of-concept tool for elucidating the therapeutic potential of P2Y₂ activation in various cardiovascular diseases.

Prostaglandin E2 glyceryl ester is an endogenous agonist of the nucleotide receptor P2Y6

Cyclooxygenase-2 catalyses the biosynthesis of prostaglandins from arachidonic acid but also the biosynthesis of prostaglandin glycerol esters (PG-Gs) from 2-arachidonoylglycerol. Previous studies identified PG-Gs as signalling molecules involved in inflammation. Thus, the glyceryl ester of prostaglandin E₂, PGE₂-G, mobilizes Ca²⁺ and activates protein kinase C and ERK, suggesting the involvement of a G protein-coupled receptor (GPCR). To identify the endogenous receptor for PGE₂-G, we performed a subtractive screening approach where mRNA from PGE₂-G response-positive and -negative cell lines was subjected to transcriptome-wide RNA sequencing analysis. We found several GPCRs that are only expressed in the PGE₂-G responder cell lines. Using a set of functional readouts in heterologous and endogenous expression systems, we identified the UDP receptor P2Y₆ as the specific target of PGE₂-G. We show that PGE₂-G and UDP are both agonists at P2Y₆, but they activate the receptor with extremely different EC₅₀ values of ~1 pM and ~50 nM, respectively. The identification of the PGE₂-G/P2Y₆ pair uncovers the signalling mode of PG-Gs as previously under-appreciated products of cyclooxygenase-2.

P2Y6 Receptor Antagonist MRS2578 Inhibits Neutrophil Activation and Aggregated Neutrophil Extracellular Trap Formation Induced by Gout-Associated Monosodium Urate Crystals

Human neutrophils (polymorphonuclear leukocytes [PMNs]) generate inflammatory responses within the joints of gout patients upon encountering monosodium urate (MSU) crystals. Neutrophil extracellular traps (NETs) are found abundantly in the synovial fluid of gout patients. The detailed mechanism of MSU crystal-induced NET formation remains unknown. Our goal was to shed light on possible roles of purinergic signaling and neutrophil migration in mediating NET formation induced by MSU crystals. Interaction of human neutrophils with MSU crystals was evaluated by high-throughput live imaging using confocal microscopy. We quantitated NET levels in gout synovial fluid supernatants and detected enzymatically active neutrophil primary granule enzymes, myeloperoxidase, and human neutrophil elastase. Suramin and PPADS, general P2Y receptor blockers, and MRS2578, an inhibitor of the purinergic P2Y6 receptor, blocked NET formation triggered by MSU crystals. AR-C25118925XX (P2Y2 antagonist) did not inhibit MSU crystal-stimulated NET release. Live imaging of PMNs showed that MRS2578 represses neutrophil migration and blocked characteristic formation of MSU crystal-NET aggregates called aggregated NETs. Interestingly, the store-operated calcium entry channel inhibitor (SK&F96365) also reduced MSU crystal-induced NET release. Our results indicate that the P2Y6/store-operated calcium entry/IL-8 axis is involved in MSU crystal-induced aggregated NET formation, but MRS2578 could have additional effects affecting PMN migration. The work presented in the present study could lead to a better understanding of gouty joint inflammation and help improve the treatment and care of gout patients.

Recent Trends in Nucleotide Synthesis

Focusing on the recent literature (since 2000), this review outlines the main synthetic approaches for the preparation of 5'-mono-, 5'-di-, and 5'-triphosphorylated nucleosides, also known as nucleotides, as well as several derivatives, namely, cyclic nucleotides and dinucleotides, dinucleoside 5',5'-polyphosphates, sugar nucleotides, and nucleolipids. Endogenous nucleotides and their analogues can be obtained enzymatically, which is often restricted to natural substrates, or chemically. In chemical synthesis, protected or unprotected nucleosides can be used as the starting material, depending on the nature of the reagents selected from P(III) or P(V) species. Both solution-phase and solid-support syntheses have been developed and are reported here. Although a considerable amount of research has been conducted in this field, further work is required because chemists are still faced with the challenge of developing a universal methodology that is compatible with a large variety of nucleoside analogues.

How To Form a Phosphate Anhydride Linkage in Nucleotide Derivatives

The fundamental roles of nucleoside triphosphates and nucleotide cofactors such as NAD(+) in biochemistry are well known. In recent decades, continuing research has revealed the key role of 5'-capped RNA and 5',5'-dinucleoside polyphosphates in the regulation of vitally important physiological processes. Last but not least, the commercial potential of nucleoside triphosphate synthesis can hardly be overestimated. Nevertheless, despite decades of investigation and the obvious topicality of the research on the chemical synthesis of the nucleotide compounds containing phosphate anhydride linkages, none of the existing procedures can be considered an up-to-date "gold standard". However, there are a number of fruitful synthetic approaches to forming phosphate anhydride linkages in satisfactory yield. These are summarized in this concise review, organized by the type of active phosphorous intermediate and reagents used.

Pharmacology and structure of P2Y receptors

P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular nucleotides. There are eight mammalian P2Y receptor subtypes (P2Y1, P2Y2, P2Y4, P2Y6, P2Y11, P2Y12, P2Y13, and P2Y14). P2Y receptors are widely expressed and play important roles in physiology and pathophysiology. One important example is the ADP-induced platelet aggregation mediated by P2Y1 and P2Y12 receptors. Active metabolites of the thienopyridine compounds ticlopidine, clopidogrel and prasugrel as well as the nucleoside analogue ticagrelor block P2Y12 receptors and thereby platelet aggregation. These drugs are used for the prevention and therapy of cardiovascular events. Moreover, P2Y receptors play important roles in the nervous system. Adenine nucleotides modulate neuronal activity and neuronal fibre outgrowth by activation of P2Y1 receptors and control migration of microglia by P2Y12 receptors. UDP stimulates microglial phagocytosis through activation of P2Y6 receptors. There is evidence for a role for P2Y2 receptors in Alzheimer's disease pathology. The P2Y receptor subtypes are highly diverse in both their amino acid sequences and their pharmacological profiles. Selective receptor ligands have been developed for the pharmacological characterization of the receptor subtypes. The recently published three-dimensional crystal structures of the human P2Y1 and P2Y12 receptors will facilitate the development of therapeutic agents that selectively target P2Y receptors. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Calcium signaling and the novel anti-proliferative effect of the UTP-sensitive P2Y11 receptor in rat cardiac myofibroblasts

During myocardial ischemia and reperfusion both purines and pyrimidines are released into the extracellular milieu, thus creating a signaling wave that propagates to neighboring cells via membrane-bound P2 purinoceptors activation. Cardiac fibroblasts (CF) are important players in heart remodeling, electrophysiological changes and hemodynamic alterations following myocardial infarction. Here, we investigated the role UTP on calcium signaling and proliferation of CF cultured from ventricles of adult rats. Co-expression of discoidin domain receptor 2 and α-smooth muscle actin indicate that cultured CF are activated myofibroblasts. Intracellular calcium ([Ca(2+)]i) signals were monitored in cells loaded with Fluo-4 NW. CF proliferation was evaluated by the MTT assay. UTP and the selective P2Y4 agonist, MRS4062, caused a fast desensitizing [Ca(2+)]i rise originated from thapsigargin-sensitive internal stores, which partially declined to a plateau providing the existence of Ca(2+) in the extracellular fluid. The biphasic [Ca(2+)]i response to UTP was attenuated respectively by P2Y4 blockers, like reactive blue-2 and suramin, and by the P2Y11 antagonist, NF340. UTP and the P2Y2 receptor agonist MRS2768 increased, whereas the selective P2Y11 agonist NF546 decreased, CF growth; MRS4062 was ineffective. Blockage of the P2Y11 receptor or its coupling to adenylate cyclase boosted UTP-induced CF proliferation. Confocal microscopy and Western blot analysis confirmed the presence of P2Y2, P2Y4 and P2Y11 receptors. Data indicate that besides P2Y4 and P2Y2 receptors which are responsible for UTP-induced [Ca(2+)]i transients and growth of CF, respectively, synchronous activation of the previously unrecognized P2Y11 receptor may represent an important target for anti-fibrotic intervention in cardiac remodeling.

Pyrimidinergic Receptor Activation Controls Toxoplasma gondii Infection in Macrophages

Infection by the protozoan parasite Toxoplasma gondii is highly prevalent worldwide and may have serious clinical manifestations in immunocompromised patients. T. gondii is an obligate intracellular parasite that infects almost any cell type in mammalian hosts, including immune cells. The immune cells express purinergic P2 receptors in their membrane--subdivided into P2Y and P2X subfamilies--whose activation is important for infection control. Here, we examined the effect of treatment with UTP and UDP in mouse peritoneal macrophages infected with T. gondii tachyzoites. Treatment with these nucleotides reduced parasitic load by 90%, but did not increase the levels of the inflammatory mediators NO and ROS, nor did it modulate host cell death by apoptosis or necrosis. On the other hand, UTP and UDP treatments induced early egress of tachyzoites from infected macrophages, in a Ca2+-dependent manner, as shown by scanning electron microscopy analysis, and videomicroscopy. In subsequent infections, prematurely egressed parasites had reduced infectivity, and could neither replicate nor inhibit the fusion of lysosomes to the parasitophorous vacuole. The use of selective agonists and antagonists of the receptor subtypes P2Y2 and P2Y4 and P2Y6 showed that premature parasite egress may be mediated by the activation of these receptor subtypes. Our results suggest that the activity of P2Y host cell receptors controls T. gondii infection in macrophages, highlighting the importance of pyrimidinergic signaling for innate immune system response against infection. Finally the P2Y receptors should be considered as new target for the development of drugs against T. gondii infection.

Synthesis and structure-activity relationship of uracil nucleotide derivatives towards the identification of human P2Y6 receptor antagonists

P2Y6 receptor (P2Y6-R) is involved in various physiological and pathophysiological events. With a view to set rules for the design of UDP-based reversible P2Y6-R antagonists as potential drugs, we established structure-activity relationship of UDP analogues, bearing modifications at the uracil ring, ribose moiety, and the phosphate chain. For instance, C5-phenyl- or 3-NMe-uridine-5'-α,β-methylene-diphosphonate, 16 and 23, or lack of 2'-OH, in 12-15, resulted in loss of both agonist and antagonist activity toward hP2Y6-R. However, uridylyl phosphosulfate, 19, selectively inhibited hP2Y6-R (IC50 112 μM) versus P2Y2/4-Rs. In summary, we have established a comprehensive SAR for hP2Y6-R ligands towards the development of hP2Y6-R antagonists.

Nucleotides Acting at P2Y Receptors: Connecting Structure and Function

Eight G protein-coupled P2Y receptor (P2YR) subtypes are important physiologic mediators. The human P2YRs are fully activated by ATP (P2Y2 and P2Y11), ADP (P2Y1, P2Y12, and P2Y13), UTP (P2Y2 and P2Y4), UDP (P2Y6 and P2Y14), and UDP glucose (P2Y14). Their structural elucidation is progressing rapidly. The X-ray structures of three ligand complexes of the Gi-coupled P2Y12R and two of the Gq-coupled P2Y1Rs were recently determined and will be especially useful in structure-based ligand design at two P2YR subfamilies. These high-resolution structures, which display unusual binding site features, complement mutagenesis studies for probing ligand recognition and activation. The structural requirements for nucleotide agonist recognition at P2YRs are relatively permissive with respect to the length of the phosphate moiety, but less so with respect to base recognition. Nucleotide-like antagonists and partial agonists are also known for P2Y1, P2Y2, P2Y4, and P2Y12Rs. Each P2YR subtype has the ability to be activated by structurally bifunctional agonists, such as dinucleotides, typically, dinucleoside triphosphates or tetraphosphates, and nucleoside polyphosphate sugars (e.g., UDP glucose) as well as the more conventional mononucleotide agonists. A range of dinucleoside polyphosphates, from triphosphates to higher homologs, occurs naturally. Earlier modeling predictions of the P2YRs were not very accurate, but recent findings have provided much detailed structural insight into this receptor family to aid in the rational design of new drugs.

2-Thiouracil deprived of thiocarbonyl function preferentially base pairs with guanine rather than adenine in RNA and DNA duplexes

2-Thiouracil-containing nucleosides are essential modified units of natural and synthetic nucleic acids. In particular, the 5-substituted-2-thiouridines (S2Us) present in tRNA play an important role in tuning the translation process through codon-anticodon interactions. The enhanced thermodynamic stability of S2U-containing RNA duplexes and the preferred S2U-A versus S2U-G base pairing are appreciated characteristics of S2U-modified molecular probes. Recently, we have demonstrated that 2-thiouridine (alone or within an RNA chain) is predominantly transformed under oxidative stress conditions to 4-pyrimidinone riboside (H2U) and not to uridine. Due to the important biological functions and various biotechnological applications for sulfur-containing nucleic acids, we compared the thermodynamic stabilities of duplexes containing desulfured products with those of 2-thiouracil-modified RNA and DNA duplexes. Differential scanning calorimetry experiments and theoretical calculations demonstrate that upon 2-thiouracil desulfuration to 4-pyrimidinone, the preferred base pairing of S2U with adenosine is lost, with preferred base pairing with guanosine observed instead. Therefore, biological processes and in vitro assays in which oxidative desulfuration of 2-thiouracil-containing components occurs may be altered. Moreover, we propose that the H2U-G base pair is a suitable model for investigation of the preferred recognition of 3'-G-ending versus A-ending codons by tRNA wobble nucleosides, which may adopt a 4-pyrimidinone-type structural motif.

Synthesis of Dinucleoside Triphosphates with Pyrimidine Bases

A facile and efficient method for the synthesis of dinucleoside triphosphates with pyrimidine bases (Up3U, Cp3C, and Up3C) from the corresponding nucleoside 5′-phosphoropiperidates has been developed. The experimental results indicated that the employment of 4,5-dicyanoimidazole (DCI) as the activator could notably promote the coupling reaction.

4-Alkyloxyimino derivatives of uridine-5'-triphosphate: distal modification of potent agonists as a strategy for molecular probes of P2Y2, P2Y4, and P2Y6 receptors

Extended N(4)-(3-arylpropyl)oxy derivatives of uridine-5'-triphosphate were synthesized and potently stimulated phospholipase C stimulation in astrocytoma cells expressing G protein-coupled human (h) P2Y receptors (P2YRs) activated by UTP (P2Y2/4R) or UDP (P2Y6R). The potent P2Y4R-selective N(4)-(3-phenylpropyl)oxy agonist was phenyl ring-substituted or replaced with terminal heterocyclic or naphthyl rings with retention of P2YR potency. This broad tolerance for steric bulk in a distal region was not observed for dinucleoside tetraphosphate agonists with both nucleobases substituted. The potent N(4)-(3-(4-methoxyphenyl)-propyl)oxy analogue 19 (EC50: P2Y2R, 47 nM; P2Y4R, 23 nM) was functionalized for chain extension using click tethering of fluorophores as prosthetic groups. The BODIPY 630/650 conjugate 28 (MRS4162) exhibited EC50 values of 70, 66, and 23 nM at the hP2Y2/4/6Rs, respectively, and specifically labeled cells expressing the P2Y6R. Thus, an extended N(4)-(3-arylpropyl)oxy group accessed a structurally permissive region on three Gq-coupled P2YRs, and potency and selectivity were modulated by distal structural changes. This freedom of substitution was utilized to design of a pan-agonist fluorescent probe of a subset of uracil nucleotide-activated hP2YRs.

Investigation of the functional expression of purine and pyrimidine receptors in porcine isolated pancreatic arteries

Receptors for purines and pyrimidines are expressed throughout the cardiovascular system. This study investigated their functional expression in porcine isolated pancreatic arteries. Pancreatic arteries (endothelium intact or denuded) were prepared for isometric tension recording and preconstricted with U46619, a thromboxane A(2) mimetic; adenosine-5'-diphosphate (ADP), uridine-5'-triphosphate (UTP) and MRS2768, a selective P2Y(2) agonist, were applied cumulatively, while adenosine-5'-triphosphate (ATP) and αβ-methylene-ATP (αβ-meATP) response curves were generated from single concentrations per tissue segment. Antagonists/enzyme inhibitors were applied prior to U46619 addition. ATP, αβ-meATP, UTP and MRS2768 induced vasoconstriction, with a potency order of αβ-meATP > MRS2768 > ATP ≥ UTP. Contractions to ATP and αβ-meATP were blocked by NF449, a selective P2X(1) receptor antagonist. The contraction induced by ATP, but not UTP, was followed by vasorelaxation. Endothelium removal and DUP 697, a cyclooxygenase-2 inhibitor, had no significant effect on contraction to ATP but attenuated that to UTP, indicating actions at distinct receptors. MRS2578, a selective P2Y(6) receptor antagonist, had no effect on contractions to UTP. ADP induced endothelium-dependent vasorelaxation which was inhibited by MRS2179, a selective P2Y(1) receptor antagonist, or SCH58261, a selective adenosine A(2A) receptor antagonist. The contractions to ATP and αβ-meATP were attributed to actions at P2X(1) receptors on the vascular smooth muscle, whereas it was shown for the first time that UTP induced an endothelium-dependent vasoconstriction which may involve P2Y(2) and/or P2Y(4) receptors. The relaxation induced by ADP is mediated by P2Y(1) and A(2A) adenosine receptors. Porcine pancreatic arteries appear to lack vasorelaxant P2Y(2) and P2Y(4) receptors.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Pharmacological characterization of the P2 receptors profile in the podocytes of the freshly isolated rat glomeruli

Calcium flux in the podocytes is critical for normal and pathophysiological regulation of these types of cells, and excessive calcium signaling results in podocytes damage and improper glomeruli function. Purinergic activation of P2 receptors is a powerful and rapid signaling process; however, the exact physiological identity of P2 receptors subtypes in podocytes remains essentially unknown. The goal of this study was to determine the P2 receptor profile in podocytes of the intact Sprague-Dawley rat glomeruli using available pharmacological tools. Glomeruli were isolated by differential sieving and loaded with Fluo-4/Fura Red cell permeable calcium indicators, and the purinergic response in the podocytes was analyzed with ratiometric confocal fluorescence measurements. Various P2 receptors activators were tested and compared with the effect of ATP, specifically, UDP, MRS 2365, bzATP, αβ-methylene, 2-meSADP, MRS 4062, and MRS 2768, were analyzed. Antagonists (MRS 2500, 5-BDBD, A438079, and NF 449) were tested when 10 μM ATP was applied as the EC50 for ATP activation of the calcium influx in the podocytes was determined to be 10.7 ± 1.5 μM. Several agonists including MRS 2365 and 2-meSADP caused calcium flux. Importantly, only the P2Y1-specific antagonist MRS 2500 (1 nM) precluded the effects of ATP concentrations of the physiological range. Immunohistochemical analysis confirmed that P2Y1 receptors are highly expressed in the podocytes. We conclude that P2Y1 receptor signaling is the predominant P2Y purinergic pathway in the glomeruli podocytes and P2Y1 might be involved in the pathogenesis of glomerular injury and could be a target for treatment of kidney diseases.

P2X and P2Y nucleotide receptors as targets in cardiovascular disease

Endogenous nucleotides have widespread actions in the cardiovascular system, but it is only recently that the P2X and P2Y receptor subtypes, at which they act, have been identified and subtype-selective agonists and antagonists developed. These advances have greatly increased our understanding of the physiological and pathophysiological functions of P2X and P2Y receptors, but investigation of the clinical usefulness of selective ligands is at an early stage. Nonetheless, the evidence considered in this review demonstrates clearly that various cardiovascular disorders, including vasospasm, hypertension, congestive heart failure and cardiac damage during ischemic episodes, may be viable targets. With further development of novel, selective agonists and antagonists, our understanding will continue to improve and further therapeutic applications are likely to be discovered.

The activation of P2Y6 receptor in cultured spinal microglia induces the production of CCL2 through the MAP kinases-NF-κB pathway

Rat primary cultures of spinal microglia were stimulated by UTP, a known P2Y2/4 receptor agonist, which resulted in the production and release of the C-C chemokine CCL2 (monocyte chemoattractant protein-1; MCP-1) measured by real-time PCR and ELISA, respectively. In an in vitro preparation of rat spinal microglia, with regard to the P2Y subtypes, the expression of P2Y1, 2, 6, 12, 13 and P2Y14, but not P2Y4, were detected by RT-PCR. The subtype of microglial P2Y receptor which could be involved in the production of CCL2 was also determined. The UTP-induced production of CCL2 was significantly blocked by pretreatment with reactive blue 2 and suramin, nonselective P2Y receptor antagonists, and MRS2578, a selective P2Y6 receptor antagonist. By contrast, knockdown of the P2Y2 receptor by RNA interference had no effect. The stimulatory effect of UTP was inhibited by phospholipase C (PLC) inhibitor U73122 and Src tyrosine kinase inhibitor PP2. A potential role of mitogen activated protein kinases was suggested since UTP-induced CCL2 production was significantly blocked by both U0126 and SB 202190, which are potent inhibitors of extracellular signal-regulated kinase (ERK) and p38, respectively. Moreover, UTP-stimulated phosphorylation of these kinases involved the activation of the P2Y6 receptor. Lastly, activation of nuclear factor-κB (NF-κB) by UTP is likely to be essential in the expression of CCL2. Together, these findings suggest that stimulation of spinal microglia P2Y6 receptors induce the production of CCL2 through either PLC-mediated ERK or p38 phosphorylation and the subsequent activation of NF-κB.

P2Y2 receptor agonist with enhanced stability protects the heart from ischemic damage in vitro and in vivo

Extracellular nucleotides acting via P2 receptors play important roles in cardiovascular physiology/pathophysiology. Pyrimidine nucleotides activate four G protein-coupled P2Y receptors (P2YRs): P2Y2 and P2Y4 (UTP-activated), P2Y6, and P2Y14. Previously, we showed that uridine 5'-triphosphate (UTP) activating P2Y2R reduced infarct size and improved mouse heart function after myocardial infarct (MI). Here, we examined the cardioprotective role of P2Y2R in vitro and in vivo following MI using uridine-5'-tetraphosphate δ-phenyl ester tetrasodium salt (MRS2768), a selective and more stable P2Y2R agonist. Cultured rat cardiomyocytes pretreated with MRS2768 displayed protection from hypoxia [as revealed by lactate dehydrogenase (LDH) release and propidium iodide (PI) binding], which was reduced by P2Y2R antagonist, AR-C118925 (5-((5-(2,8-dimethyl-5H-dibenzo[a,d][7]annulen-5-yl)-2-oxo-4-thioxo-3,4-dihydropyrimidin-1(2H)-yl)methyl)-N-(1H-tetrazol-5-yl)furan-2-carboxamide). In vivo, echocardiography and infarct size staining of triphenyltetrazolium chloride (TTC) in 3 groups of mice 24 h post-MI: sham, MI, and MI+MRS2768 indicated protection. Fractional shortening (FS) was higher in MRS2768-treated mice than in MI alone (40.0 ± 3.1 % vs. 33.4 ± 2.7 %, p < 0.001). Troponin T and tumor necrosis factor-α (TNF-α) measurements demonstrated that MRS2768 pretreatment reduced myocardial damage (p < 0.05) and c-Jun phosphorylation increased. Thus, P2Y2R activation protects cardiomyocytes from hypoxia in vitro and reduces post-ischemic myocardial damage in vivo.

P2Y receptors in the mammalian nervous system: pharmacology, ligands and therapeutic potential

P2Y receptors for extracellular nucleotides are coupled to activation of a variety of G proteins and stimulate diverse intracellular signaling pathways that regulate functions of cell types that comprise the central nervous system (CNS). There are 8 different subtypes of P2Y receptor expressed in cells of the CNS that are activated by a select group of nucleotide agonists. Here, the agonist selectivity of these 8 P2Y receptor subtypes is reviewed with an emphasis on synthetic agonists with high potency and resistance to degradation by extracellular nucleotidases that have potential applications as therapeutic agents. In addition, the recent identification of a wide variety of subtype-selective antagonists is discussed, since these compounds are critical for discerning cellular responses mediated by activation of individual P2Y receptor subtypes. The functional expression of P2Y receptor subtypes in cells that comprise the CNS is also reviewed and the role of each subtype in the regulation of physiological and pathophysiological responses is considered. Other topics include the role of P2Y receptors in the regulation of blood-brain barrier integrity and potential interactions between different P2Y receptor subtypes that likely impact tissue responses to extracellular nucleotides in the CNS. Overall, current research suggests that P2Y receptors in the CNS regulate repair mechanisms that are triggered by tissue damage, inflammation and disease and thus P2Y receptors represent promising targets for the treatment of neurodegenerative diseases.

Synthesis of nucleoside tetraphosphates and dinucleoside pentaphosphates via activation of cyclic trimetaphosphate

A procedure for the synthesis of dinucleoside 5'-pentaphosphates (Np5N) and nucleoside 5'-tetraphosphates (Np4) is described. The procedure relies on the activation of cyclic trimetaphosphate followed by a reaction with a nucleoside 5'-monophosphate (NMP) to give intermediates of type 3. Reaction of 3 with water or an NMP gives the desired products in yields ranging from 77 to 86%.

AMP-activated protein kinase as regulator of P2Y(6) receptor-induced insulin secretion in mouse pancreatic β-cells

5'-AMP-activated protein kinase (AMPK) and its pharmacological modulators have been targeted for treating type 2 diabetes. Extracellular uridine 5'-diphosphate (UDP) activates P2Y6 receptors (P2Y6Rs) in pancreatic β-cells to release insulin and reduce apoptosis, which would benefit diabetes. Here, we studied the role of P2Y6R in activation of AMPK in MIN6 mouse pancreatic β-cells and insulin secretion. Treatment with a potent P2Y6R dinucleotide agonist MRS2957 (500nM) activated AMPK, which was blocked by P2Y6R-selective antagonist MRS2578. Also, MRS2957 induced phosphorylation of acetyl-coenzyme A carboxylase (ACC), a marker of AMPK activity. Calcium chelator BAPTA-AM, calmodulin-dependent protein kinase kinase (CaMKK) inhibitor STO-069 and IP3 receptor antagonist 2-APB attenuated P2Y6R-mediated AMPK phosphorylation revealing involvement of intracellular Ca(2+) pathways. P2Y6R agonist induced insulin secretion at high glucose, which was reduced by AMPK siRNA. Thus, P2Y6R has a crucial role in β-cell function, suggesting its potential as a therapeutic target in diabetes.

Purinergic receptors regulate myogenic tone in cerebral parenchymal arterioles

Myogenic tone is a fundamental aspect of vascular behavior in resistance arteries. This contractile response to changes in intravascular pressure is critically involved in blood flow autoregulation in tissues such as the brain, kidneys, and heart. Myogenic tone also helps regulate precapillary pressure and provides a level of background tone upon which vasodilator stimuli act to increase tissue perfusion when appropriate. Despite the importance of these processes in the brain, little is known about the mechanisms involved in control of myogenic tone in the cerebral microcirculation. Here, we report that pharmacological inhibition of P2Y4 and P2Y6 pyrimidine receptors nearly abolished myogenic tone in cerebral parenchymal arterioles (PAs). Molecular suppression of either P2Y4 or P2Y6 receptors using antisense oligodeoxynucleotides reduced myogenic tone by 44%±8% and 45%±7%, respectively. These results indicate that both receptor isoforms are activated by increased intravascular pressure, which enhances the activity of voltage-dependent calcium channels and increases myogenic tone in PAs. Enhancement or inhibition of ectonucleotidase activity had no effect on parenchymal arteriolar myogenic tone, indicating that this response is not mediated by local release of nucleotides, but rather may involve direct mechanical activation of P2Y receptors in the smooth muscle cells.

4-Alkyloxyimino-cytosine nucleotides: tethering approaches to molecular probes for the P2Y6 receptor

4-Alkyloxyimino derivatives of pyrimidine nucleotides display high potency as agonists of certain G protein-coupled P2Y receptors (P2YRs). In an effort to functionalize a P2Y₆R agonist for fluorescent labeling, we probed two positions (N⁴ and γ-phosphate of cytidine derivatives) with various functional groups, including alkynes for click chemistry. Functionalization of extended imino substituents at the 4 position of the pyrimidine nucleobase of CDP preserved P2Y₆R potency generally better than γ-phosphoester formation in CTP derivatives. Fluorescent Alexa Fluor 488 conjugate 16 activated the human P2Y₆R expressed in 1321N1 human astrocytoma cells with an EC₅₀ of 9 nM, and exhibited high selectivity for this receptor over other uridine nucleotide-activated P2Y receptors. Flow cytometry detected specific labeling with 16 to P2Y₆R-expressing but not to wild-type 1321N1 cells. Additionally, confocal microscopy indicated both internalized 16 (t_1/2 of 18 min) and surface-bound fluorescence. Known P2Y₆R ligands inhibited labeling. Theoretical docking of 16 to a homology model of the P2Y₆R predicted electrostatic interactions between the fluorophore and extracellular portion of TM3. Thus, we have identified the N⁴-benzyloxy group as a structurally permissive site for synthesis of functionalized congeners leading to high affinity molecular probes for studying the P2Y₆R.

An efficient synthesis of pyrimidine specific 2'-deoxynucleoside-5'-tetraphosphates

An efficient chemical synthesis of pyrimidine specific 2'-deoxynucleoside-5'-tetraphosphates, such as 2'-deoxycytidine-5'-tetraphosphate (dC4P) and thymidine-5'-tetraphosphate (T4P) is described. The present three-step synthetic strategy involves monophosphorylation of 2'-deoxynucleoside using phosphorous oxychloride, conversion of 5'-monophosphate into the corresponding imidazolide salt, followed by reaction with tris[tributylammonium] triphosphate leading to the 2'-deoxynucleoside-5'-tetraphosphate in good yields.

An improved strategy for the synthesis of [¹⁸F]-labeled arabinofuranosyl nucleosides

The expression of the herpes simplex virus type-1 thymidine kinase (HSV1-tk) gene can be imaged efficaciously using a variety of 2'-[(18)F]fluoro-2'-deoxy-1-b-D-arabinofuranosyl-uracil derivatives [[(18)F]-FXAU, X=I(iodo), E(ethyl), and M(methyl)]. However, the application of these derivatives in clinical and translational studies has been impeded by their complicated and long syntheses (3-5h). To remedy these issues, in the study at hand we have investigated whether microwave or combined catalysts could facilitate the coupling reaction between sugar and nucleobase and, further, have probed the feasibility of establishing a novel approach for [(18)F]-FXAU synthesis. We have demonstrated that the rate of the trimethylsilyl trifluoromethanesulfonate (TMSOTf)-catalyzed coupling reaction between the 2-deoxy-sugar and uracil derivatives at 90 °C can be significantly accelerated by microwave-driven heating or by the addition of Lewis acid catalyst (SnCl(4)). Further, we have observed that the stability of the α- and β-anomers of [(18)F]-FXAU derivatives differs during the hydrolysis step. Using the microwave-driven heating approach, overall decay-corrected radiochemical yields of 19%-27% were achieved for [(18)F]-FXAU in 120min at a specific activity of >22MBq/nmol (595Ci/mmol). Ultimately, we believe that these high yielding syntheses of [(18)F]-FIAU, [(18)F]-FMAU and [(18)F]-FEAU will facilitate routine production for clinical applications.

UDP made a highly promising stable, potent, and selective P2Y6-receptor agonist upon introduction of a boranophosphate moiety

P2Y(6) nucleotide receptor (P2Y(6)-R) plays important physiological roles, such as insulin secretion and reduction of intraocular pressure. However, this receptor is still lacking potent and selective agonists to be used as potential drugs. Here, we synthesized uracil nucleotides and dinucleotides, substituted at the C5 and/or P(α) position with methoxy and/or borano groups, 18-22. Compound 18A, R(p) isomer of 5-OMe-UDP(α-B), is the most potent and P2Y(6)-R selective agonist currently known (EC(50) 0.008 μM) being 19-fold more potent than UDP and showing no activity at uridine nucleotide receptors, P2Y(2)- and P2Y(4)-R. Analogue 18A was highly chemically stable under conditions mimicking gastric juice acidity (t(1/2) = 16.9 h). It was more stable to hydrolysis by nucleotide pyrophosphatases (NPP1,3) than UDP (15% and 28% hydrolysis by NPP1 and NPP3, respectively, vs 50% and 51% hydrolysis of UDP) and metabolically stable in blood serum (t(1/2) = 17 vs 2.4, 11.9, and 21 h for UDP, 5-OMe-UDP, and UDP(α-B), respectively). This newly discovered highly potent and physiologically stable P2Y(6)-R agonist may be of future therapeutic potential.

General procedure for the synthesis of dinucleoside polyphosphates

Dinucleoside 5',5'-polyphosphates (N(p)(n)N) play important roles in biological processes and have been developed into drugs. However, their synthesis still remains a challenge. Here we report a rapid and general approach to the synthesis of dinucleoside 5',5'-polyphosphates by coupling highly reactive nucleoside 5'-monophosphate-N-methylimidazolium salts donors with nucleoside 5'-mono-, -di-, and -triphosphate acceptors.

Pyrimidine nucleotides with 4-alkyloxyimino and terminal tetraphosphate δ-ester modifications as selective agonists of the P2Y(4) receptor

P2Y(2) and P2Y(4) receptors are G protein-coupled receptors, activated by UTP and dinucleoside tetraphosphates, which are difficult to distinguish pharmacologically for lack of potent and selective ligands. We structurally varied phosphate and uracil moieties in analogues of pyrimidine nucleoside 5'-triphosphates and 5'-tetraphosphate esters. P2Y(4) receptor potency in phospholipase C stimulation in transfected 1321N1 human astrocytoma cells was enhanced in N(4)-alkyloxycytidine derivatives. OH groups on a terminal δ-glucose phosphoester of uridine 5'-tetraphosphate were inverted or substituted with H or F to probe H-bonding effects. N(4)-(Phenylpropoxy)-CTP 16 (MRS4062), Up(4)-[1]3'-deoxy-3'-fluoroglucose 34 (MRS2927), and N(4)-(phenylethoxy)-CTP 15 exhibit ≥10-fold selectivity for human P2Y(4) over P2Y(2) and P2Y(6) receptors (EC(50) values 23, 62, and 73 nM, respectively). δ-3-Chlorophenyl phosphoester 21 of Up(4) activated P2Y(2) but not P2Y(4) receptor. Selected nucleotides tested for chemical and enzymatic stability were much more stable than UTP. Agonist docking at CXCR4-based P2Y(2) and P2Y(4) receptor models indicated greater steric tolerance of N(4)-phenylpropoxy group at P2Y(4). Thus, distal structural changes modulate potency, selectivity, and stability of extended uridine tetraphosphate derivatives, and we report the first P2Y(4) receptor-selective agonists.

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 EC(50) value of 1.3 μM 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 (EC(50) 4.98 μM, >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, EC(50) = 0.604 μM, >100-fold selective). In an attempt to obtain metabolically stable UTP analogues, β,γ-dichloro- and β,γ-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-β,γ-difluoromethylene-UTP (14g) was a potent P2Y(2) agonist with an EC(50) value of 0.134 μM and >50-fold selectivity. N3-Phenacyl-β,γ-dichloromethylene-UTP (14b) proved to be a potent P2Y(6) receptor agonist (EC(50) 0.142 μM) with high selectivity versus P2Y(4) (50-fold) and moderate selectivity versus P2Y(2) receptors (6-fold).

P1,P2-diimidazolyl derivatives of pyrophosphate and bis-phosphonates--synthesis, properties, and use in preparation of dinucleoside tetraphosphates and analogs

P(1),P(2)-Diimidazolyl derivatives of pyrophosphate and halomethylene-bis-phosphonates have been synthesized and characterized, and the mechanism of their formation was studied. These reagents enable synthesis of dinucleoside tetraphosphates and tetraphosphonates conveniently and in high yields.