Synthesis and biological evaluation of a new series of 2-amino-3-aroyl thiophene derivatives as agonist allosteric modulators of the A1 adenosine receptor. A position-dependent effect study.

The 2-amino-3-(p-chlorobenzoyl)thiophene scaffold has been widely employed as a pharmacophore for the identification of small molecules acting as allosteric modulators at the adenosine A1 receptor. A new series of 2-amino-3-(p-chlorobenzoyl)-4-benzyl-5-arylthiophene derivatives, characterized by the absence as well as the presence of electron-releasing or electron-withdrawing groups on the phenyl ring at the 4- and 5-positions of the thiophene ring, were identified as positive allosteric enhancers at the adenosine A1 receptor in binding (saturation, competition and dissociation kinetics) and functional assays. To better understand the positional requirements of substituents on the 2-amino-3-(p-chlorobenzoyl)thiophene core, the corresponding regioisomeric 4-aryl-5-benzylthiophene analogues were synthesized and found to possess reduced allosteric enhancer activity.

Current status of A1 adenosine receptor allosteric enhancers.

Adenosine is an ubiquitous nucleoside involved in various physiological and pathological functions by stimulating A1, A2A, A2B and A3 adenosine receptors (ARs). Allosteric enhancers to A1ARs may represent novel therapeutic agents because they increase the activity of these receptors by mediating a shift to their active form in the A1AR-G protein ternary complex. In this manner, they are able to amplify the action of endogenous adenosine, which is produced in high concentrations under conditions of metabolic stress. A1AR allosteric enhancers could be used as a justifiable alternative to the exogenous agonists that are characterized by receptor desensitization and downregulation. In this review, an analysis of some of the most interesting allosteric modulators of A1ARs has been reported.

History and perspectives of A2A adenosine receptor antagonists as potential therapeutic agents.

Growing evidence emphasizes that the purine nucleoside adenosine plays an active role as a local regulator in different pathologies. Adenosine is a ubiquitous nucleoside involved in various physiological and pathological functions by stimulating A1 , A2A , A2B , and A3 adenosine receptors (ARs). At the present time, the role of A2A ARs is well known in physiological conditions and in a variety of pathologies, including inflammatory tissue damage and neurodegenerative disorders. In particular, the use of selective A2A antagonists has been reported to be potentially useful in the treatment of Parkinson's disease (PD). In this review, A2A AR signal transduction pathways, together with an analysis of the structure-activity relationships of A2A antagonists, and their corresponding pharmacological roles and therapeutic potential have been presented. The initial results from an emerging polypharmacological approach are also analyzed. This approach is based on the optimization of the affinity and/or functional activity of the examined compounds toward multiple targets, such as A1 /A2A ARs and monoamine oxidase-B (MAO-B), both closely implicated in the pathogenesis of PD.

Synthesis and biological evaluation of novel allosteric enhancers of the A1 adenosine receptor based on 2-amino-3-(4'-chlorobenzoyl)-4-substituted-5-arylethynyl thiophene.

A Sonogashira coupling strategy was employed to synthesize a new series of allosteric modulators for the A1 adenosine receptor based on the 2-amino-3-(p-chlorobenzoyl)-4-substituted thiophene skeleton, with a two-carbon (rigid or flexible) linker between the 5-position of the thiophene ring and a (hetero)aryl or alkyl moiety. Among the compounds characterized by the presence of a common phenylacetylene moiety at the 5-position of the thiophene ring, the neopentyl substitution at the 4-position supported a strong activity. In the series of 4-neopentyl derivatives, the presence of an acetylene spacer at the 5-position of the thiophene is optimal for activity, whereas reduction of the acetylene to an ethyl moiety decreased activity, both in functional and binding assays. Derivatives 4e, 4g-h, 4j, 4l, and 4m were the most promising compounds in binding (saturation and competition) and functional cAMP studies, being able to potentiate agonist [(3)H]CCPA binding to the A1 receptor, with 4e as the best compound of the series. The latter compound also retarded the dissociation of another radiolabeled agonist, [(3)H]NECA, from the receptor.

Synthesis and biological evaluation of novel 2-amino-3-aroyl-4-neopentyl-5-substituted thiophene derivatives as allosteric enhancers of the A1 adenosine receptor.

2-Amino-3-benzoyl thiophenes have been widely reported to act as allosteric enhancers at the A1 adenosine receptor. Their activity can be increased considerably by appropriate substitutions at the 4- and 5-positions of the thiophene ring. Substituent size at the thiophene C-4 position seemed to be a factor closely related to activity, with the 4-neopentyl (2,2-dimethylpropyl) substitution showing the greatest enhanced activity. A wide series of 2-amino-3-aroyl-4-neopentylthiophene derivatives with general structure 3, characterized by the presence of different substituents (bromine, aryl and heteroaryl) at the 5-position of the thiophene ring, have been identified as potent AEs at the A1AR. With only one exception, all of the synthesized compounds proved to be superior to the reference compound PD 81,723 in a functional assay. Derivatives 3p, 3u, 3am, 3ap and 3ar were the most active compounds in binding (saturation and competition) and functional cAMP studies, being able to potentiate agonist [(3)H]CCPA binding to the A1 receptor.

Synthesis and biological effects of novel 2-amino-3-(4-chlorobenzoyl)-4-substituted thiophenes as allosteric enhancers of the A1 adenosine receptor.

Allosteric enhancers for the A1 adenosine receptor represent a novel and unique drug design strategy to augment the response to endogenous adenosine in a site- and event-specific manner. We have previously investigated a detailed structure-activity relationship study around a wide series of 2-amino-3-aroyl-4-[(4-arylpiperazin-1-yl)methyl]thiophene derivatives as potent allosteric enhancers of the A1 adenosine receptor. In this manuscript we report our investigation on the influence on allosteric enhancer activity of further substitution at the 4-position of the 2-amino-3-(4-chlorobenzoyl)-thiophene system to explore bulk tolerance by replacement of the arylpiperazine moiety with a series of fused indole nuclei corresponding to 1,2,3,4-tetrahydropyrazino[1,2-a]indole, 1,2,3,4,10,10a-hexahydropyrazino[1,2-a]indole, tetrahydro-γ-carboline, tetrahydroisoquinoline, spiro-1,3-benzodioxolepiperidine, aliphatic tertiary amine, N-alkylaniline, aryl ether and aryl thioether templates. The 1,2,3,4-tetrahydropyrazino[1,2-a]indole derivatives 3a-c and 3e were the most active compounds in binding (saturation and competition) and functional cAMP studies, being able to potentiate agonist [(3)H]CCPA binding to the A1 receptor. This study also shows that it is possible to obtain a good separation between allosteric enhancement and antagonistic activity at the A1 adenosine receptor.

Discovery of 7-oxopyrazolo[1,5-a]pyrimidine-6-carboxamides as potent and selective CB(2) cannabinoid receptor inverse agonists.

We recently described the medicinal chemistry of a new series of heteroaryl-4-oxopyridine/7-oxopyrimidines as CB2 receptor partial agonists, showing that the functionality of these ligands is controlled by the nature of the heteroaryl function condensed with the pyridine ring. We describe herein the design and synthesis of the 7-oxopyrazolo[1,5-a]pyrimidine-6-carboxamides, structural isomers of our previously reported pyrazolo[3,4-b]pyridines. All of the new compounds showed high affinity and selectivity for the CB2 receptor in the nanomolar range. In 3,5-cyclic adenosine monophosphate (cAMP) assays, the novel series shows stimulatory effects on forskolin-induced cAMP production acting as inverse agonists.

Design, synthesis, and pharmacological properties of new heteroarylpyridine/heteroarylpyrimidine derivatives as CB(2) cannabinoid receptor partial agonists.

Recent developments indicate that CB(2) receptor ligands have the potential to become therapeutically important. To explore this potential, it is necessary to develop compounds with high affinity for the CB(2) receptor. Very recently, we have identified the oxazinoquinoline carboxamides as a novel class of CB(2) receptor full agonists. In this paper we describe the medicinal chemistry of a new series of heteroaryl-4-oxopyridine/7-oxopyrimidine derivatives. Some of the reported compounds showed high affinity and potency at the CB(2) receptor while showing only modest affinity for the centrally expressed CB(1) cannabinoid receptor. Moreover, we found that the functionality of these ligands is controlled by the nature of the heteroaryl function condensed with the pyridine ring. In 3,5-cyclic adenosine monophosphate (cAMP) assays, the novel series show dose-dependent effects on the modulation of forskolin-induced cAMP production, revealing different behaviors as full agonists, partial agonists, and inverse agonists.

Skin permeability and pharmacokinetics of diclofenac epolamine administered by dermal patch in Yorkshire-Landrace pigs.

PURPOSE: This study compared the pharmacokinetic profile, and systemic and local absorption of diclofenac, following dermal patch application and oral administration in Yorkshire-Landrace pigs. PATIENTS AND METHODS: Twelve anesthetized, female, Yorkshire-Landrace pigs were randomized to receive either the dermal patch (FLECTOR(®) patch, 10 × 14 cm; Alpharma Pharmaceuticals, a subsidiary of Pfizer Inc, New York, NY) or 50 mg oral diclofenac (Voltaren(®); Novartis, East Hanover, NJ). Tissue (skin area of 2 × 2 cm and underlying muscles approximately 2-3 cm in depth) and blood (10 mL) samples were collected at timed intervals up to 11.5 hours after initial patch application or oral administration. The concentrations of diclofenac in plasma, skin, and muscle samples were analyzed using validated ultra performance liquid chromatography tandem mass spectrometric methods. RESULTS: Peak systemic exposure of diclofenac was very low by dermal application compared with oral administration (maximum concentration [C(max)] values of 3.5 vs 9640 ng/mL, respectively). Absorption of diclofenac into underlying muscles beneath the dermal patch was sustained, and followed apparently zero-order kinetics, with the skin serving as a depot with elevated concentrations of diclofenac. Concentrations of diclofenac in muscles beneath the patch application site were similar to corresponding tissues after oral administration (C(max) values of 879 and 1160 ng/mL, respectively). In contrast to the wide tissue distribution of diclofenac after oral administration, dermal patch application resulted in high concentrations of diclofenac only on the treated skin and immediate tissue underneath the patch. Low concentrations of diclofenac were observed in the skin and muscles collected from untreated areas contralateral to the site of dermal patch application. CONCLUSION: Dermal patch application resulted in low systemic absorption and high tissue penetration of diclofenac compared with oral administration.

Synthesis and biological evaluation of 2-amino-3-(4-chlorobenzoyl)-4-[(4-arylpiperazin-1-yl)methyl]-5-substituted-thiophenes. effect of the 5-modification on allosteric enhancer activity at the A1 adenosine receptor.

We have recently reported a detailed structure-activity relationship study around a wide series of 2-amino-3-(4-chlorobenzoyl)-4-[(4-arylpiperazin-1-yl)methyl]thiophene derivatives as potent allosteric enhancers of the A(1) adenosine receptor. In the current study, we have continued to explore the potential of these molecules by synthesizing of a novel series of analogues that share a common 2-amino-3-(4-chlorobenzoyl)thiophene nucleus. Modifications were focused on varying the nature and the position of electron-withdrawing or electron-releasing groups on the phenyl of an arylpiperazine moiety attached at the 4-position of the thiophene ring by a methylene chain, combined with the presence of small alkyl groups (methyl or ethyl), bromine, or aryl moieties at the thiophene C-5 position. In this series of compounds, substitution at the 5-position had a fundamental effect on activity, with the 5-aryl group contributing additively to the allosteric enhancer activity. The thiophene C-5 aryl derivatives 4ad, 4ak, and 4al were the most active compounds in binding and functional experiments.

7-Oxo-[1,4]oxazino[2,3,4-ij]quinoline-6-carboxamides as selective CB(2) cannabinoid receptor ligands: structural investigations around a novel class of full agonists.

Cannabinoid receptor agonists have gained attention as potential therapeutic targets of inflammatory and neuropathic pain. Here, we report the identification and optimization of a series of 7-oxo-[1,4]oxazino[2,3,4-ij]quinoline-6-carboxamide derivatives as a novel chemotype of selective cannabinoid CB(2) receptor agonists. Structural modifications led to the identification of several compounds as potent and selective cannabinoid receptor agonists (20, hCB(2)K(i) = 2.5 nM, SI = 166; 21, hCB(2)K(i) = 0.81 nM, SI = 383; 38, hCB(2)K(i) = 15.8 nM, SI > 633; 56, hCB(2)K(i) = 8.12 nM, SI > 1231; (R)-58, hCB(2)K(i) = 9.24 nM, SI > 1082). The effect of a chiral center on the biological activity was also investigated, and it was found that the (R)-enantiomers exhibited greater affinity at the CB(2) receptor than the (S)-enantiomers. In 3,5-cyclic adenosine monophosphate assays, the novel series behaved as agonists, exhibiting functional activity at the human CB(2) receptor.

Water-soluble pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines as human A3 adenosine receptor antagonists.

A relevant problem of the pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine nucleus, an attractive scaffold for the preparation of adenosine receptor antagonists, is the low water solubility. We originally functionalized the C(5) position with a salifiable 4-pyridylcarbamoyl moiety that conferred good water solubility at low pH (<4.0) but poor solubility at physiologic pH, indicative of the dissociation of the pyridinium species. Here we replaced the pyridin-4-yl moiety with a 1-(substituted)piperidin-4-yl ring to exploit the higher basicity of this nucleus and for the the possibility to generate stable, water-soluble salts. The hydrochloride salt of the 1-(cyclohexylmethyl)piperidin-4-yl derivative (10, K(i)(hA(3)) = 9.7 nM, IC(50)(hA(3)) = 30 nM, K(i)(hA(1)/hA(3)) = 351, K(i)(hA(2A)/hA(3)) > 515, IC(50)(hA(2B)) > 5 µM) showed a solubility of 8 mg/mL at physiological pH and gave a stable aqueous system suitable for intravenous infusion. Molecular modeling studies were helpful in rationalizing the available structure-activity relationships and the selectivity profile of the new ligands.

Structure-activity relationships of 2-amino-3-aroyl-4-[(4-arylpiperazin-1-yl)methyl]thiophenes. Part 2: Probing the influence of diverse substituents at the phenyl of the arylpiperazine moiety on allosteric enhancer activity at the A1 adenosine receptor.

In a preliminary article, we reported the potent allosteric enhancer activity at the A(1) adenosine receptor of a small series of 2-amino-3-(4-chlorobenzoyl)-4-[4-(aryl)piperazin-1-yl)methyl]thiophene derivatives bearing electron-withdrawing or electron-releasing groups at the para-position of the phenylpiperazine moiety. In the present study, we report the development of the compounds previously studied by modifying both the number and position of substituents on the phenylpiperazine moiety, aimed at establishing a structure-activity relationship identifying additional compounds with improved activity. The nature and the position of substituents on the phenyl ring tethered to the piperazine seemed to exert a fundamental influence on the allosteric enhancer activity, with the 3,4-difluoro 4i, 3-chloro-4-fluoro 4o, and 4-trifluoromethoxy 4ak derivatives being the most active compounds in binding (saturation and competition experiments) and functional cAMP studies. This study shows that it is also possible to obtain a good separation between allosteric enhancement and antagonistic activity at the A(1) adenosine receptor.

Pyrrolo- and pyrazolo-[3,4-e][1,2,4]triazolo[1,5-c]pyrimidines as adenosine receptor antagonists.

The discovery and development of adenosine receptor antagonists have represented for years an attractive field of research from the perspective of identifying new drugs for the treatment of widespread disorders such as inflammation, asthma and Parkinson's disease. The present work can be considered as an extension of our structure-activity relationship studies on the pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine (PTP) nucleus, extensively investigated by us as a useful template, in particular, for the identification of A(2A) and A(3) adenosine receptor antagonists. In order to explore the role of the nitrogen at the 7-position, we performed a new synthetic strategy for the preparation of pyrrolo[3,4-e][1,2,4]triazolo[1,5-c]pyrimidine derivatives which can be considered as 7-deaza analogues of the parent PTPs. We also synthesised a novel series of pyrazolo[3,4-e][1,2,4]triazolo[1,5-c]pyrimidines as junction isomers of the reference compounds. In both cases we obtained some examples of potent antagonists (K(i) in the low nanomolar range) with variable selectivity profiles in relation to the nature of substituents introduced at the C(5)-, N(8)- and/or N(9)-positions. The pyrrolo-triazolo-pyrimidine derivative 9b appeared to be a potent A(3) adenosine receptor antagonist (K(i)=10 nM) with good selectivity over hA(1) (74-fold) and hA(2A) (20-fold) adenosine receptors combined with low activity at the hA(2B) subtype (IC(50)=906 nM). Moreover, some examples of high-affinity A(1)/A(2A) dual antagonists have been identified in both series. This work constitutes a new and important contribution for the comprehension of the interaction between PTPs and adenosine receptors.

Novel 1,3-dipropyl-8-(3-benzimidazol-2-yl-methoxy-1-methylpyrazol-5-yl)xanthines as potent and selective A2B adenosine receptor antagonists.

Molecular modeling studies, including the comparative molecular field analysis (CoMFA) method, on 52 antagonists of the A(2B) adenosine receptor with known biological activity were performed to identify the three-dimensional features responsible for A(2B) adenosine receptor antagonist activity. On the basis of these and previous results on the potent antagonist effect of 8-pyrazolyl-xanthines at human A(2B)AR, a new series of compounds was synthesized and evaluated in binding studies against the human A(1), A(2A), A(3), and A(2B)ARs. A remarkable improvement in selectivity with respect to the previous series, maintaining the potency at human A(2B) receptor, was achieved, as exemplified by the 8-[3-(4-chloro-6-trifluoromethyl-1H-benzoimidazol-2-yl-methoxy)-1-methyl-1H-pyrazol-5-yl]-1,3-dipropyl-3,7-dihydro-purine-2,6-dione derivative 66: K(i) A(2B) = 9.4 nM, IC(50) hA(2B) = 26 nM hA(1)/hA(2B) = 269, hA(2A)/hA(2B) > 106, hA(3)/hA(2B) >106. This study also led to the identification of a series of pyrazole-xanthine compounds with a simplified structure, exemplified by 8-(3-hydroxy-1-methyl-1H-pyrazol-5-yl)-xanthine 80 displaying very high affinity at A(2B)AR with good selectivity over AR subtypes (K(i) = 4.0 nM, IC(50) hA(2B) = 20 nM hA(1)/hA(2B) = 183, hA(2A),hA(3)/hA(2B) > 250).

New 2-heterocyclyl-imidazo[2,1-i]purin-5-one derivatives as potent and selective human A3 adenosine receptor antagonists.

A series of 4-allyl/benzyl-7,8-dihydro-8-methyl/ethyl-2-[(substituted)isoxazol/pyrazol-3/5-yl]-1H-imidazo[2,1-i]purin-5(4H)-ones has been synthesized and evaluated in radioligand binding assays to determine their affinities at the human A(1), A(2A), and A(3) adenosine receptors. Efficacy at the hA(2B) AR and antagonism of selected ligands at the hA(3) AR were also assessed through cAMP experiments. All of the synthesized molecules exhibited high affinity at the hA(3) AR (K(i) values ranging from 1.46 to 44.8 nM), as well as remarkable selectivity versus A(1), A(2A), and A(2B) AR subtypes. Compound (R)-4-allyl-8-ethyl-7,8-dihydro-2-(3-methoxy-1-methyl-1H-pyrazol-5-yl)-1H-imidazo[2,1-i]purin-5(4H)-one (R-33) was found to be the most potent and selective ligand of the series (K(i) hA(3) = 1.46 nM, K(i) hA(2A)/K(i) hA(3) > 3425; IC(50) hA(2B)/K(i) hA(3) > 3425; K(i) hA(1)/K(i) hA(3) = 1729). Molecular modeling studies were helpful in rationalizing the available structure-activity relationships along with the selectivity profiles of the new series of ligands.

Synthesis and biological evaluation of 2-amino-3-(4-chlorobenzoyl)-4-[N-(substituted) piperazin-1-yl]thiophenes as potent allosteric enhancers of the A1 adenosine receptor.

The synthesis and evaluation of a series of 2-amino-3-(4-chlorobenzoyl)-4-[4-(alkyl/aryl)piperazin-yl]thiophene derivatives as allosteric enhancers of the A 1-adenosine receptor are described. The nature of substituents on the phenyl ring tethered to the piperazine seem to exert a fundamental influence on the allosteric enhancer activity, with the 4-chlorophenyl 8f and 4-trifluoromethyl 8j derivatives being the most active compounds in binding (saturation and displacement experiments) and functional cAMP studies.

1,3-Dipropyl-8-(1-phenylacetamide-1H-pyrazol-3-yl)-xanthine derivatives as highly potent and selective human A(2B) adenosine receptor antagonists.

A new series of 1,3-dipropyl-8-(1-phenylacetamide-1H-pyrazol-3-yl)-xanthine derivatives has been identified as potent A(2B) adenosine receptor antagonists. The products have been evaluated for their binding affinities for the human A(2B), A(1), A(2A), and A(3) adenosine receptors. N-(4-chloro-phenyl)-2-[3-(2,6-dioxo-1,3-dipropyl-2,3,6,7-tetrahydro-1H-purin-8-yl)-5-methyl-pyrazol-1-yl] (11c) showed a high affinity for the human A(2B) adenosine receptor K(i)=7nM and good selectivity (A(1), A(2A), A(3)/A(2B)>140). Synthesis and SAR of this novel class of compounds is presented herein.

From tyrosine to glycine: synthesis and biological activity of potent antagonists of the purinergic P2X7 receptor.

The characterization of the native and recombinant P2X7 receptor continues to be hindered by the lack of specific and subtype-selective antagonists with a "druglike" profile. However, a tyrosine derivative named KN-62 exhibits selective P2X7 receptor-blocking properties. As a molecular simplification of KN-62, the present study was designed to evaluate the functional antagonistic properties of a novel series of glycine derivatives characterized by the presence of different phenyl-substituted piperazine moieties. Antagonistic activity of these glycine derivatives was tested on HEK293 cells transfected with the human P2X7 receptor. The most potent P2X7 receptor antagonist identified in this study (compound 4g) contains an o-fluorine substituent on the phenylpiperazine moiety and had an IC50 of 12.1 nM. The biological responses investigated were ATP-dependent Ca2+ influx across the plasma membrane and ethidium bromide uptake.

Allosteric enhancers for A1 adenosine receptor.

Allosteric enhancers at the adenosine A(1) receptor have received attention as anti-arrhythmic cardiac agents, and, more recently, as anti-lipolytic agents. In addition, allosteric modulators at the adenosine A(1) receptor have therapeutic potential as analgesics and neuroprotective agents. In particular, the compounds with improved potency as enhancers and reduced antagonist properties are mentioned.