QSAR and docking studies of novel β-carboline derivatives as anticancer

Quantitative structure–activity relationship (QSAR) studies were performed on β-carboline derivatives for prediction of anticancer activity. The statistically significant 2D-QSAR model having r ² = 0.726 and q ² = 0.654 with pred_r ² = 0.763 was developed by stepwise multiple linear regression method. In order to understand the structural requirement of these β-carboline derivatives, a ligand-based pharmacophore 3D-QSAR model was developed. The five-point pharmacophore hypothesis yielded a 3D-QSAR model with good partial least-square statistics results (r ² = 0.73, Q _ext ²  = 0.755, F = 67.5, SD = 0.245, RMSE = 0.241, Pearson-R = 0.883). A docking study revealed the binding orientations of these derivatives at the active site amino residues of DNA intercalate (PDB ID: 1D12). The results of 2D-QSAR, atom-based 3D-QSAR, and docking studies gave detailed structural insights as well as highlighted important binding features of β-carboline derivatives as anticancer agent which provided guidance for the rational design of novel potent anticancer agents.     

Patent Evaluation: Arylethanolamine derivatives and their use as β3-adrenoceptor agonists

Summary

Novelty: Novel arylethanolamine derivatives are claimed to be β₃-adrenoreceptor agonists. They are stated to show good selectivity for β₃-rather than β1- or β2-adrenoreceptors. They are potentially useful for the treatment of hyperglycaemia and obesity.

Biology: Lipolysis stimulated by β-agonists was demonstrated in rat white adipocytes, according to the method of Rodbell (J. Biol. Chem. (1964) 239:375–380) and the modification of Honnor et al. (J. Biol. Chem. (1985) 260:15122–15129). The specified compound had an EC₅₀ of 41.7nM (intrinsic activity = 1.0). In vitro, β1- and β2- adrenoceptor agonist activity was studied using rat atrial preparations and rat uterine preparations, respectively. The specified compound demonstrated K_i values of 7610nM and 3656nM for β1- and β2- adrenoceptors, respectively.

Chemistry: Five compounds are disclosed and are exemplified by synthesis. Yields, mps, optical rotations and nmr data are given. Two compounds are specifically claimed including the (R)-4-[2-[N-[2-(3-chlorophenyl)-2-hydroxyethyl]amino]ethyl]phenoxyacetic acid, sodium salt.     

Synthesis of biphenyl derivatives as ACE and α-amylase inhibitors

Angiotensin converting enzyme (ACE) and α-amylase inhibitors were synthesized using 4′-(bromomethyl)-biphenyl-2-carbonitrile 1 and various cyclic secondary amines (a–h). The nitrile group appended to biphenyl was converted into tetrazole 3a–3h and the tetrazole was ring transformed into 1,3,4-oxadiazole derivatives 4a–4h. Some of the compounds have exhibited significant ACE and α-amylase inhibition.     

3D-QSAR study of tyrosine and propanoic acid derivatives as PPARα/γ dual agonists using CoMSIA

The peroxisome proliferator-activated receptors (PPARs) have increasingly become attractive targets for developing novel therapeutics for Type 2 Diabetes. Three dimensional-quantitative structure–activity relationship approach has been applied to a series of α-substituted 3-phenylpropanoic acid and tyrosine derivatives, reported as PPARα/γ dual agonists. Comparative molecular similarity indices analysis has been employed in correlating pharmacological data available for single enantiomer at individual receptor subtype. Three models: PPARα, PPARγ and PPARdual-model, using sum of individual activities as dependent parameter, are developed with statistically significant r _cv ²  > 0.5 and r _ncv ²  > 0.9 and lower values of standard error of estimation. This information can be used to design and prediction of enantioselective novel PPAR agonists. Activities of two sets of designed new molecules have also been predicted using generated models.     

Agonistic and antagonistic effects of various α-adrenergic agonists in human platelets

Summary In human platelets, the effects of various -adrenergic agonists were studied on platelet aggregation and adenylate cyclase activity. Out of many phenylethylamine derivatives tested, only some catecholamines were able to act as -adrenergic agonists inducing platelet aggregation and inhibition of adenylate cyclase with the order of potency: adrenaline > noradrenaline>-methylnoradrenaline. Other phenylethylamine and imidazoline derivatives, which act as potent -adrenergic agonists in various systems, neither induced primary aggregation nor adenylate cyclase inhibition, when tested at concentrations up to 1 mM. Since binding studies indicated high affinities of these agents to the platelet -adrenergic receptor, their effects on adrenaline-induced aggregation and adenylate cyclase inhibition were studied.Both types of -adrenergic agonists tested, phenylethylamine and imidazoline derivatives, prevented adrenaline-induced aggregation and adenylate cyclase inhibition. The imidazolines, xylometazoline, oxymetazoline, naphazoline, clonidine and tetryzolin, were the most effective antagonists with similar potencies as observed with the typical -adrenergic antagonists, phentolamine and yohimbine. Phenylethylamine derivatives such as phenylephrine, methoxamine, synephrine and norfenefrine, similarly antagonized the adrenaline-induced responses but higher concentrations were required. The potencies of these phenylethylamine derivatives were similar to those of the classical -adrenergic antagonists, phenoxybenzamine and azapetine. The results indicate that the platelet -adrenergic receptor, which has many similarities with the ₂-adrenergic receptor with regard to affinities of various -adrenergic agonists, completely differs from that found in other tissues, inasmuch as only some catecholamines acted as agonists whereas other phenylethylamine derivatives and imidazoline derivatives acted as antagonists.A preliminary report of these studies has been presented (Jakobs, 1978)     

Pharmacophore modeling of some novel indole β-diketo acid and coumarin-based derivatives as HIV integrase inhibitors

To design new chemotypes with enhanced potencies against the HIV integrase enzyme, 3D pharmacophore models were generated and QSAR study was carried out on 44 novel indole β-diketo acid derivatives and coumarin-based Inhibitors. A five-point pharmacophore with two hydrogen bond acceptors (A) and three aromatic rings (R) as pharmacophore features was developed by PHASE module of Schrodinger suite. The pharmacophore hypothesis yielded a statistically significant 3D-QSAR model, with a correlation coefficient of R ² = 0.81 for training set compounds. The model generated showed excellent predictive power, with a correlation coefficient of Q ² = 0.69 for a randomly chosen test set of eight compounds. The 3D-QSAR plots illustrated insights into the structure activity relationship of these compounds which may helps in the design and development of novel integrase inhibitors.     

Synthesis of β-hydroxy-propenamide derivatives and the inhibition of human dihydroorotate dehydrogenase

Novel beta-hydroxy propenamides as analogues of the active metabolite of leflunomide (A 771726) were synthesized and evaluated for their inhibitory activity on dihydroorotate dehydrogenase (DHODH) in an investigation into their immunosuppressive activity. Compounds 2a, 3a, and 3h were approximately 4-40 times more potent than leflunomide in their activity while they were-less active than A 771726.     

Protective effects of glycyrrhizin against β₂-adrenergic receptor agonist-induced receptor internalization and cell apoptosis

It has been reported that treatment with β? adrenergic receptor (β?AR) agonist bronchodilators may result in airway β?ARs internalization and cardiac muscle cells apoptosis. This could lead to the loss of pharmacological effect of β?AR agonists and increase adverse cardiovascular events in asthma patients receiving β?AR agonist therapy. Glycyrrhizin, the major bioactive component of licorice root extract, has been reported to exhibit protective effect on respiratory system. Here, we investigate the effects of glycyrrhizin against β?AR agonist salbutamol-induced receptor internalization and cell apoptosis. In our study, the live cell confocal imaging and fixed-cell enzyme-linked immunosorbent assay (ELISA) assay revealed that glycyrrhizin significantly inhibited salbutamol-induced surface β?AR internalization. The underlying mechanisms were then identified to be that glycyrrhizin could reduce the association of β?ARs with β-arrestins and clathrin heavy chain as well as the level of G protein-coupled receptor kinase (GRK) mediated phosphorylation of β?ARs. The inhibition of receptor internalization by glycyrrhizin further lead to stabilization of the β?AR mRNA and protein expression, thus amplified the transmembrane signaling via the β?ARs. We also proved that glycyrrhizin could profoundly attenuate salbutamol-induced early cellular apoptosis by regulating the expressions of B-cell lymphoma 2 (Bcl-2) family genes. Taken together, our results suggest that glycyrrhizin exhibits protective effects against β?AR agonist-induced receptor internalization and cell apoptosis. These findings might have practical implications for future strategies of combined application of glycyrrhizin with β?AR receptor agonists to improve the efficacy of bronchodilators in patients with asthma and chronic obstructive pulmonary disease (COPD).     

Inhaled corticosteroids as combination therapy with β-adrenergic agonists in airways disease: present and future

Inhaled corticosteroid (ICS) therapy in combination with long-acting β-adrenergic agonists represents the most important treatment for chronic airways diseases such as asthma and chronic obstructive pulmonary disease (COPD). ICS therapy forms the basis for treatment of asthma of all severities, improving asthma control, lung function and preventing exacerbations of disease. Use of ICS has also been established in the treatment of COPD, particularly symptomatic patients, who experience useful gains in quality of life, likely from an improvement in symptoms such as breathlessness and in reduction in exacerbations, and an attenuation of the yearly rate of deterioration in lung function. The addition of long-acting β-agonist (LABA) therapy with ICS increases the efficacy of ICS effects in moderate-to-severe asthma. Thus, a 800 μg daily dose of the ICS budesonide reduced severe exacerbation rates by 49% compared to a low dose of 200 μg daily, and addition of the LABA formoterol to budesonide (800 μg) led to a 63% reduction. In COPD, the effects of ICS are less prominent but there are beneficial effects on the decline in FEV₁ and the rate of exacerbations. A reduction in the rate of decline in FEV₁ of 16 ml/year with a 25% reduction in exacerbation rate has been reported with the salmeterol and fluticasone combination. A non-significant 17.5% reduction in all-cause mortality rate with ICS and LABA is reported. Chronic inflammation is a feature of both asthma and COPD, although there are site and characteristic differences. ICS targets this inflammation although this effect of ICS is less effective in patients with severe asthma and with COPD; however, addition of LABA may potentiate the anti-inflammatory effects of ICS. An important consideration is the presence of corticosteroid insensitivity in these patients. Currently available ICS have variably potent binding activities to specific glucocorticoid receptors, leading to inhibition of gene expression by either binding to DNA and inducing anti-inflammatory genes or by repressing the induction of pro-inflammatory mediators. Local side effects of ICS include oral candidiasis, hoarseness and dysphonia, while systemic side effects, such as easy bruising and reduction in growth velocity or bone mineral densitometry, are usually restricted to doses above maximally recommended doses. Use of LABA alone in patients with asthma increases the risk of asthma-related events including deaths, but this is less observed with the combination of ICS and LABA. Therefore, use of LABA alone is not recommended for asthma therapy. Future progress in ICS development will be characterised by the introduction of ICS with greater efficacy with a limited side-effect profile, and by longer-acting ICS that can be used in combination with once-daily LABAs. Other agents that could improve the efficacy of corticosteroids or reverse corticosteroid insensitivity may be added to ICS. ICS in combination with LABAs will continue to remain the main focus of treatment of airways diseases.     

Antitumor activity of a novel series of α-aryloxy-α-methylhydrocinnamic acid derivatives as PPAR gamma agonists against a panel of human cancer cell lines

Summary  Peroxisome proliferator-activated receptor gamma (PPARγ) agonists have shown benefit in treating diabetes mellitus, atherosclerosis and cancer. However, widespread use of thiazolidinediones (TZDs), the clinically used synthetic PPARγ agonists, has been limited by adverse cardiovascular effects. Consequently, numerous novel non-TZD compounds were synthesized and antidiabetic efficacy was evaluated to identify PPARγ agonists for potential clinical use. On the other hand, many studies have documented that the antitumor activity of PPARγ agonists is PPARγ independent. Here we hypothesized that there might exist some compounds with less PPARγ agonistic activity or antidiabetic efficacy but potent antitumor activity. In this study, we evaluated the PPARγ agonistic and antitumor activity of several newly synthesized α-aryloxy-α-methylhydrocinnamic acid derivatives as PPARγ agonists in a panel of human cancer cell lines, which showed promising antitumor activity without appreciable PPARγ agonistic activity. The results of MTT assay revealed that cell viability was inhibited in a dose dependent manner with IC₅₀ 17.1–55.1 μM for all the novel compounds and rosiglitazone (17.2–165 μM). They induced cell cycle arrest and apoptosis tested by Flow Cytometry. In conclusion, our findings demonstrate that these compounds have potent in vitro cytotoxicity, the possible mechanism of which is through induction of apoptosis and cell cycle arrest Xishan Xiong and Yangliang Ye contributed equally to this work.     

Comparative pharmacology of human β-adrenergic receptor subtypes—characterization of stably transfected receptors in CHO cells

Although many ₁-receptor antagonists and ₂-receptor agonists have been used in pharmacotherapy for many years their pharmacological properties at all three known subtypes of -adrenergic receptors are not always well characterized. The aim of this study was, therefore, to provide comparative binding characteristics of agonists (epinephrine, norepinephrine, isoproterenol, fenoterol, salbutamol, salmeterol, terbutalin, formoterol, broxaterol) and antagonists (propranolol, alprenolol, atenolol, metoprolol, bisoprolol, carvedilol, pindolol, BRL 37344, CGP 20712, SR 59230A, CGP 12177, ICI 118551) at all three subtypes of human -adrenergic receptors in an identical cellular background. We generated Chinese hamster ovary (CHO) cells stably expressing the three -adrenergic receptor subtypes at comparable levels. We characterized these receptor subtypes and analyzed the affinity of routinely used drugs as well as experimental compounds in competition binding studies, using the non-selective antagonist ¹²⁵I-cyanopindolol as a radioligand. Furthermore, we analyzed the -receptor-mediated adenylyl cyclase activity in isolated membranes from these cell lines. The results from our experiments show that all compounds exhibit distinct patterns of selectivity and activity at the three -receptor subtypes. In particular, a number of ₂- or ₃-receptor agonists that are inverse agonists at the other subtypes were identified. In addition, ₁-receptor antagonists with agonistic activity at ₂- and ₃-receptors were found. These specific mixtures of agonism, antagonism, and inverse agonism at different subtypes may have important implications for the therapeutic use of the respective compounds.     

Discriminative stimulus properties of β-carbolines characterized as agonists and inverse agonists at central benzodiazepine receptors

The discriminative stimulus properties of three -carboline derivatives were studied in three groups of rats trained, respectively, to discriminate diazepam (2.5 mg/kg IP), chlordiazepoxide (CDP, 5 mg/kg IP) or pentylenetetrazol (PTZ, 15 mg/kg IP) from saline in standard procedures employing two-lever operant chambers. Two -carbolines, ZK 91296 and ZK 93423, substituted for the benzodiazepines in both CDP- and diazepam-trained rats. The neutral benzodiazepine antagonist Ro 15-1788 blocked the diazepam discriminative stimulus and the ability of ZK 91296 to substitute for diazepam. A third -carboline, FG 7142, was not identified as benzodiazepine-like in generalization tests in either diazepam- or CDP-trained rats, but when administered together with CDP antagonized the benzodiazepine discriminative stimulus. In rats trained to discriminate PTZ from saline (a discrimination which is thought to depend on the anxiogenic properties of PTZ) the PTZ cue was antagonized by diazepam and ZK 93423, and partially antagonized by ZK 91296. The PTZ cue generalized to FG 7142 and this generalization was partially antagonized by Ro 15-1788. These results suggest that the three -carbolines provide more than one kind of discriminative stimulus, consistent with the classification of ZK 93423 as an agonist at central benzodiazepine receptors, with ZK 91 296 as a partial agonist, and with FG 7142 as an inverse agonist. Pharmacologically, ZK 93 423 and ZK 91 296 may exhibit anxiolytic qualities, whereas FG 7142 produces anxiogenic effects.     

The pharmacogenetics of β-adrenergic receptor antagonists in the treatment of hypertension and heart failure

INTRODUCTION: β-Blockers have an important therapeutic role throughout the cardiovascular continuum. However, there is considerable variation in response to these drugs, which may be related to genetic influences on their pharmacokinetics and pharmacodynamic effects. AREAS COVERED: This review focuses on genetic variations in the drug metabolizing enzymes which influence the pharmacokinetics and potentially the pharmacodynamics of some β-blockers. It also reviews the polymorphisms in the adrenergic receptors (ARs) and their related pathways which are likely to influence the responses to β-blockers. EXPERT OPINION: The CYP2D6 genotypes influence the pharmacokinetics of some β-blockers but the effects on β-blocker responses have been inconsistent and there is currently no general role for CYP2D6 genotyping prior to choosing a particular β-blocker or dose. The common polymorphisms producing changes in the β(1)-ARs, and their signaling pathways, have been associated with clinical outcomes in several studies in hypertension and heart failure. Treatment with β-blockers, especially with higher doses, appears to have greater benefits in patients with the genetic forms of the β(1)-ARs which are more responsive to both agonists and antagonists. However, current data are not sufficiently consistent to support genotyping for these polymorphisms before selecting or initiating β-blocker treatment and further study results are needed to clarify the situation.     

Metabolism and disposition of a β3-adrenergic receptor agonist LY368842 in male Fisher 344 rats

The metabolism and disposition of LY368842, a β₃-adrenergic receptor agonist, were characterized in F344 rats following oral or intravenous administration of [¹⁴C]LY368842. These studies were conducted as part of the investigation of the mechanism of dark liver pigmentation in LY368842-treated F344 rats. The maximum plasma concentration of LY368842 was reached at 3?h after an oral dose, with an elimination half-life of 4?h. The oral bioavailability of LY368842 was determined as 8%. A tissue distribution study by quantitative whole-body autoradiography indicated high concentrations of radiocarbon in gastrointestinal contents and moderate concentrations in liver. The radiocarbon was rapidly eliminated in rats, with approximately 3% of the dose recovered in urine and 90% in faeces over 168?h. In bile duct-cannulated rats, about 42% of the dose was recovered in bile and 41% remained in the faeces. Metabolites of LY368842 were identified in rat urine, faeces, bile and plasma samples. Oxidative metabolism of LY368842 led to the formation of a hydroxy metabolite, an indole-2,3-dione metabolite and oxidative cleavage products such as amine and diol metabolites. Several glucuronide conjugates were also identified in rat bile. These data suggest that LY368842 is not completely absorbed but is widely distributed, extensively metabolized and rapidly eliminated in rats after oral administration.     

Pharmacokinetics and absolute bioavailability of carteolol,a new β-adrenergic receptor blocking agent

Summary The pharmacokinetics and absolute bioavailability of a new nonselective -adrenoreceptor blocking agent, carteolol, were investigated after administration of single intravenous and oral doses to eight normal volunteers. Plasma and urine drug concentrations were measured by an HPLC method. The pharmacokinetic parameters after intravenous dosing were obtained by a two-compartment analysis: elimination or -phase t_1/2 4.7±0.3 h; Vc, 0.74±0.101/kg; Vd, 4.05±0.48 l/kg; Cl, 10.13±0.94 ml/min/kg; Cl_R, 6.56±0.58 ml/min/kg; and Cl_NR, 3.57±0.40 ml/min/kg. The absolute bioavailability obtained from plasma data was 83.7±8.0%, which was consistent with that derived from analysis of urine of 82.7±4.2%. The amounts excreted unchanged in urine up to 48 h after the intravenous and oral doses were 65.0±1.5% and 53.8±3.2% of the administered doses, respectively. The t_1/2 for removal of the drug derived from plasma and urine findings after intravenous and oral dosing were similar, which indicates that the main route of elimination of carteolol is via the kidneys. As the Cl_R of carteolol exceeded the Cl of creatinine there may be renal tubular secretion of the drug.     

Valerenic acid derivatives as novel subunit-selective GABAA receptor ligands �Cin vitro and in vivo characterization

BACKGROUND AND PURPOSE

Subunit-specific modulators of γ-aminobutyric acid (GABA) type A (GABA_A) receptors can help to assess the physiological function of receptors with different subunit composition and also provide the basis for the development of new drugs. Valerenic acid (VA) was recently identified as a β_2/3 subunit-specific modulator of GABA_A receptors with anxiolytic potential. The aim of the present study was to generate VA derivatives as novel GABA_A receptor modulators and to gain insight into the structure–activity relation of this molecule.

EXPERIMENTAL APPROACH

The carboxyl group of VA was substituted by an uncharged amide or amides with different chain length. Modulation of GABA_A receptors composed of different subunit compositions by the VA derivatives was studied in Xenopus oocytes by means of the two-microelectrode voltage-clamp technique. Half-maximal stimulation of GABA-induced chloride currents (I_GABA) through GABA_A receptors (EC₅₀) and efficacies (maximal stimulation of I_GABA) were estimated. Anxiolytic activity of the VA derivatives was studied in mice, applying the elevated plus maze test.

KEY RESULTS

Valerenic acid amide (VA-A) displayed the highest efficacy (more than twofold greater I_GABA enhancement than VA) and highest potency (EC₅₀= 13.7 ± 2.3 µM) on α₁β₃ receptors. Higher efficacy and potency of VA-A were also observed on α₁β₂γ_2s and α₃β₃γ_2s receptors. Anxiolytic effects were most pronounced for VA-A.

CONCLUSIONS AND IMPLICATIONS

Valerenic acid derivatives with higher efficacy and affinity can be generated. Greater in vitro action of the amide derivative correlated with a more pronounced anxiolytic effect in vivo. The data give further confidence in targeting β₃ subunit containing GABA_A receptors for development of anxiolytics.     

Characterization of α- and β-adrenergic receptors linked to human platelet adenylate cyclase

Summary Adrenaline and noradrenaline cause aggregation of human platelets through -adrenergic receptors, whereas isoprenaline through -adrenergic receptors can inhibit aggregation. Either type of adrenergic receptors is coupled to platelet adenylate cyclase. Stimulation and inhibition of adenylate cyclase by -and -adrenergic stimulants, respectively, had been demonstrated in human platelet lysates. These effects were characterized with regard to the effectiveness of various agonists and antagonists.Reduction of platelet adenylate cyclase activity was observed only with L-adrenaline and L-noradrenaline. This inhibitory effect, which was increased in the presence of a -adrenergic blocking agent, was half-maximal at about 1 to 2×10^–6 M adrenaline, and maximal inhibition (by 50–60%) was observed at about 3×10^–5M. Various other catecholamine and imidazoline derivatives that act as -adrenergic agonists in other cell types neither induced aggregation nor affected the enzyme activity.Adrenaline-induced inhibition of platelet adenylate cyclase was prevented by -adrenergic blocking agents. These compounds inhibited the effects of adrenaline on aggregation and on adenylate cyclase with similar efficacies. Dihydrogenated ergot alkaloids were more effective than phentolamine and yohimbine; phenoxybenzamine, tolazoline and azapetine were least effective. Adrenaline-induced inhibition of platelet adenylate cyclase was reversed by phentolamine without apparent lag phase.In the presence of -adrenergic blocking agents, adrenaline was capable of increasing adenylate cyclase activity between 20 and 50%. Only adrenaline and isoprenaline stimulated adenylate cyclase activity; other compounds that stimulate -adrenergic receptors in other cell types, including -adrenergic stimulants, had no effect on the activity of the platelet enzyme. The stimulatory effect of adrenaline was prevented by various -adrenergic blocking agents including pindolol and propranolol. Preferentially -adrenergic receptor blocking agents such as practolol and atenolol were without effect.These findings indicate that the spectrum of compounds capable of exhibiting intrinsic activity through - and -adrenergic receptors of human platelets is very narrow and that either type of platelet adrenergic receptors appears to differ from those found in other cell types.     

Discovery of isoxazole analogues of sazetidine-A as selective α4β2-nicotinic acetylcholine receptor partial agonists for the treatment of depression

Depression, a common neurological condition, is one of the leading causes of disability and suicide worldwide. Standard treatment, targeting monoamine transporters selective for the neurotransmitters serotonin and noradrenaline, is not able to help many patients that are poor responders. This study advances the development of sazetidine-A analogues that interact with α4β2 nicotinic acetylcholine receptors (nAChRs) as partial agonists and that possess favorable antidepressant profiles. The resulting compounds that are highly selective for the α4β2 subtype of nAChR over α3β4-nAChRs are partial agonists at the α4β2 subtype and have excellent antidepressant behavioral profiles as measured by the mouse forced swim test. Preliminary absorption, distribution, metabolism, excretion, and toxicity (ADMET) studies for one promising ligand revealed an excellent plasma protein binding (PPB) profile, low CYP450-related metabolism, and low cardiovascular toxicity, suggesting it is a promising lead as well as a drug candidate to be advanced through the drug discovery pipeline.     

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.