A novel class of highly potent and selective A1 adenosine antagonists: structure-affinity profile of a series of 1,8-naphthyridine derivatives

Synthesis of 1,8-Naphthyridines by the Ionic Liquid-Catalyzed Friedlander Reaction and Application in Corrosion Inhibition

A several of basic ionic liquids (ILs) were synthesized as green solvents and catalysts for the preparation of 1,8-naphthyridyl derivatives via the Friedlander reaction. [Bmmim][Im] exhibited remarkable catalytic activity to achieve the synthetic targets, and the reaction conditions were optimized. The model product 2,3-diphenyl-1,8-naphthyridine (1,8-Nap), with carboxyethylthiosuccinic acid (CETSA) to form an IL corrosion inhibitor ([1,8-Nap][CETSA]), and its corrosion inhibition performance for Q235 steel in 1 M HCl were researched by weight loss measurements, and the results showed that the inhibition efficiency was 96.95% when the concentration of [1,8-Nap][CETSA] was 1 mM at 35 °C. The electrochemical test verified that [1,8-Nap][CETSA] acted as a mixed-type inhibitor but mainly exhibited cathodic behavior. The inhibitor adsorbed on the metal surface was further proved by surface topography analysis.

Crystal structure of 2-(naphthalen-2-yl)-1,8-naphthyridine, C18H12N2

C18H12N2, monoclinic, P21/c (no. 14), a = 27.514(5) Å, b = 6.3231(11) Å, c = 7.4175(13) Å, β = 95.805(2)°, V = 1283.8(4) Å3, Z = 4, R gt(F) = 0.0439, wR ref(F 2) = 0.1233, T = 296(2) K.

Crystal structure of 2-(4-chlorophenyl)-3-phenyl-1,8-naphthyridine, C20H13N2Cl

C20H13N2Cl, monoclinic, P21/n (no. 14), a = 6.179(4) Å, b = 11.666(8) Å, c = 22.460(15) Å, β = 95.837°, V = 1610.6(19) Å3, Z = 4, Rgt(F) = 0.0507, wRref(F2) = 0.1599, T = 296(2) K.

Crystal structure of 2-(3,4-dimethylphenyl)-1,8-naphthyridine, C16H14N2

C16H14N2, orthorhombic, P212121, a = 6.449(8) Å, b = 10.548(14) Å, c = 17.84(2) Å, V = 1213(3) Å3, Z = 4, R gt(F) = 0.0406, wR ref(F 2) = 0.0933, T = 296(2) K.

New potent and selective A1 adenosine receptor antagonists as potential tools for the treatment of gastrointestinal diseases

The synthesis of 9-alkyl substituted adenine derivatives presenting aromatic groups and cycloalkyl rings in 8- and N⁶-position, respectively, is reported. The compounds were tested with radioligand binding studies showing, in some cases, a low nanomolar A₁ adenosine receptor affinity and a very good selectivity versus the other adenosine receptor subtypes. Functional assays at human adenosine receptors and at a mouse ileum tissue preparation clearly demonstrate the antagonist profile of these molecules, with inhibitory potency at nanomolar level. A molecular modeling study, consisting in docking analysis at the recently reported A₁ adenosine receptor crystal structure, was performed for the interpretation of the obtained pharmacological results. The N⁶-cyclopentyl-9-methyl-8-phenyladenine (17), resulting the most active derivative of the series (K_i = 2.8 nM and IC₅₀ = 14 nM), was also very efficacious in counteracting the effect of the agonist CCPA on mouse ileum contractility. This new compound represents a tool for the development of new agents for the treatment of intestinal diseases as constipation and postoperative ileus.

Ring transformation of unsaturated N-bridgehead fused pyrimidin-4(3H)-ones: role of repulsive electrostatic nonbonded interaction

Thermal ring transformation ability of unsaturated N-bridgehead fused pyrimidin-4(3H)-ones A is governed by both the steric and the electrostatic interactions between the oxygen of the carbonyl group and the substituent in the peri position.

New 2-arylpyrazolo[3,4-c]quinoline derivatives as potent and selective human A3 adenosine receptor antagonists. Synthesis, pharmacological evaluation, and ligand-receptor modeling studies

This paper reports the study of some 2-arylpyrazolo[3,4-c]quinolin-4-ones, 4-amines, and 4-amino-substituted derivatives designed as human A3 adenosine receptor (AR) antagonists. Most of the herein reported compounds showed a nanomolar affinity toward the hA3 receptor subtype and different degrees of selectivity that resulted to be strictly dependent on the presence and nature of the substituent on the 4-amino group. Bulky and lipophilic acyl groups, as well as the benzylcarbamoyl residue, afforded highly potent and selective hA3 receptor antagonists. The selected 4-diphenylacetylamino-2-phenylpyrazoloquinoline (25) and 4-dibenzoylamino-2-(4-methoxyphenyl)pyrazoloquinoline (36), tested in an in vitro rat model of cerebral ischemia, prevented the irreversible failure of synaptic activity induced by oxygen and glucose deprivation in the hippocampus. The observed structure-affinity relationships of this class of antagonists were also exhaustively rationalized using the recently published ligand-based homology modeling (LBHM) approach.

Tricyclic imidazoline derivatives as potent and selective adenosine A1 receptor antagonists

Novel tricyclic imidazoline antagonists of the adenosine A1 receptor are described. For key compounds, the selectivity level over other adenosine receptor subtypes is examined along with their in vivo effects in a rat diuresis model. Compound 14, the (R)-isomer of 7,8-dihydro-8-ethyl-2-(4-bicyclo[2.2.2]octan-1-ol)-4-propyl-1H-imidazo[2,1-i]purin-5(4H)-one, is a particularly potent adenosine A1 receptor antagonist with good selectivity over the other three adenosine receptor subtypes: A1 (human) Ki=22 nM; A2A (human) Ki=4400 nM; A2B (human) Ki=580 nM; A3 (human) Ki>or=10,000 nM. Imidazoline 14 is a competitive adenosine A1 receptor antagonist with a pA2 value of 8.88 and is highly soluble in water (>100 mg/mL). In addition, it has an oral bioavailability of 84% and an oral half-life of 3.8 h in rats. When orally administered in a rat diuresis model, compound 14 promoted sodium excretion (ED50=0.01 mg/kg). This level of efficacy is comparable to that of BG9928, a selective adenosine A1 receptor antagonist that is currently in clinical trials as a treatment for congestive heart failure. Additional modifications to 14 also showed that the bridgehead hydroxyl group could be replaced with a propionic acid (compound 36) without a significant loss in binding affinity or in vivo activity.

Progress in the pursuit of therapeutic adenosine receptor antagonists

Ever since the discovery of the hypotensive and bradycardiac effects of adenosine, adenosine receptors continue to represent promising drug targets. First, this is due to the fact that the receptors are expressed in a large variety of tissues. In particular, the actions of adenosine (or methylxanthine antagonists) in the central nervous system, in the circulation, on immune cells, and on other tissues can be beneficial in certain disorders. Second, there exists a large number of ligands, which have been generated by introducing several modifications in the structure of the lead compounds (adenosine and methylxanthine), some of them highly specific. Four adenosine receptor subtypes (A1, A2A, A2B, and A3) have been cloned and pharmacologically characterized, all of which are G protein-coupled receptors. Adenosine receptors can be distinguished according to their preferred mechanism of signal transduction: A1 and A3 receptors interact with pertussis toxin-sensitive G proteins of the Gi and Go family; the canonical signaling mechanism of the A2A and of the A2B receptors is stimulation of adenylyl cyclase via Gs proteins. In addition to the coupling to adenylyl cyclase, all four subtypes may positively couple to phospholipase C via different G protein subunits. The development of new ligands, in particular, potent and selective antagonists, for all subtypes of adenosine receptors has so far been directed by traditional medicinal chemistry. The availability of genetic information promises to facilitate understanding of the drug-receptor interaction leading to the rational design of a potentially therapeutically important class of drugs. Moreover, molecular modeling may further rationalize observed interactions between the receptors and their ligands. In this review, we will summarize the most relevant progress in developing new therapeutic adenosine receptor antagonists.

Synthesis and pharmacology of pyrido[2,3-d]pyrimidinediones bearing polar substituents as adenosine receptor antagonists

Amino-substituted pyrido[2,3-d]pyrimidinediones have previously been found to bind to adenosine A1 and A2A receptors in micromolar concentrations. The present study was aimed at studying the structure-activity relationships of this class of compounds in more detail. Most of the investigated compounds were provided with polar substituents, such as ethoxycarbonyl groups and basic amino functions, in order to improve their water-solubility. The compounds were synthesized starting from 6-amino-1,3-dimethyluracil via different reaction sequences involving (cyano)acetylation, Vilsmeier formylation, or reaction with diethyl ethoxymethylenemalonate (EMME). The most potent and selective compound of the present series was 6-carbethoxy-1,2,3,4-tetrahydro-1,3-dimethyl-5-(2-naphthylmethyl)aminopyrido[2,3-d]pyrimidine-2,4-dione (11c) with a Ki value of 5 nM at rat and 25 nM at human A1 receptors. The compound was more than 60-fold selective versus A3 and more than 300-fold selective versus A2A receptors. It showed an over 300-fold improvement with respect to the lead compound. In GTPgammaS binding studies at membranes of Chinese hamster ovary cells recombinantly expressing the human adenosine A1 receptor, 11c behaved as an antagonist with inverse agonistic activity. A regioisomer of 11c, 6-carbethoxy-1,2,3,4-tetrahydro-1,3-dimethyl-7-(2- naphthylmethyl)aminopyrido[2,3-d]pyrimidine-2,4-dione (7a) in which the 2-naphthylmethylamino substituent at position 5 of 11c was moved to the 7-position, was a relatively potent (Ki=226 nM) and selective (>20-fold) A3 ligand. In the series of compounds lacking an electron-withdrawing ethoxycarbonyl or cyano substituent in the 6-position, compounds with high affinity for adenosine A2A receptors were identified, such as 1,2,3,4-tetrahydro-1,3-dimethyl-5-(1-naphthyl)aminopyrido[2,3-d]pyrimidine-2,4-dione 16b (Ki human A2A=81.3 nM, Ki human A1=153 nM, and Ki human A3>10,000 nM).

1,8-Naphthyridin-4-one derivatives as new ligands of A2A adenosine receptors

A series of 1,8-naphthyridine derivatives bearing various substituents in position 3, 4, and 7 of the heterocyclic nucleus have been synthesized and evaluated for their affinity at the bovine and human adenosine receptors. The new compounds were found to lack the affinity toward A(1)AR, whereas many of them are able to acquire an interesting affinity and selectivity for the A(2A)AR.

2,4,6-trisubstituted pyrimidines as a new class of selective adenosine A1 receptor antagonists

Adenosine receptor antagonists usually possess a bi- or tricyclic heteroaromatic structure at their core with varying substitution patterns to achieve selectivity and/or greater affinity. Taking into account molecular modeling results from a series of potent adenosine A1 receptor antagonists, a pharmacophore was derived from which we show that a monocyclic core can be equally effective. To achieve a compound that may act at the CNS we propose imposing a restriction related to its polar surface area (PSA). In consequence, we have synthesized two novel series of pyrimidines, possessing good potency at the adenosine A1 receptor and desirable PSA values. In particular, compound 30 (LUF 5735) displays excellent A1 affinity (Ki = 4 nM) and selectivity (< or =50% displacement of 1 muM concentrations of the radioligand at the other three adenosine receptors) and has a PSA value of 53 A2.

Study on Affinity Profile toward Native Human and Bovine Adenosine Receptors of a Series of 1,8-Naphthyridine Derivatives

A new series of 1,8-naphthyridine derivatives (29-44 and 46-52) bearing various substituents in different positions on the heterocyclic nucleus were synthesized in order to analyze the effects produced on the affinity toward the bovine adenosine receptors. These derivatives represent an extension of our previous work on this class of compounds with high affinity toward A(1) adenosine receptors.(19) The results of radioligand binding assays indicate that a large number of the 1,8-naphthyridine derivatives proved to be A(1) selective, with a high affinity toward bovine adenosine receptors in the low nanomolar range, and one (29) in the subnanomolar range. Furthermore, the new series of 1,8-naphthyridine derivatives (29-44 and 46-52), together with the analogous derivatives 1-28 previously studied,(19) were tested to evaluate their affinity toward human cortical A(1) receptors and human striatal A(2A) receptors. The results indicate that all the 1,8-naphthyridine compounds generally possess a higher affinity toward the bovine A(1) receptor compared with the human A(1) receptor. As regards the affinity toward the A(2A) bovine receptor, only a few compounds possess a moderate affinity, which for some compounds remained approximately the same toward the A(2A) human receptor. A molecular modeling study of the docking of the 1,8-naphthyridine compounds with both the bovine and the human A(1) adenosine receptors was carried out with the aim of explaining the marked decrease in the affinity toward human A(1) adenosine receptors in comparison with bovine A(1) adenosine receptors. This study indicated that the structural differences, albeit small, of the active sites of the two receptors make differences in the dimensions of the site and this influenced the ability of the title compounds to interact with the two A(1) receptors.

Cytoskeletal protein 4.1G binds to the third intracellular loop of the A1 adenosine receptor and inhibits receptor action

To identify binding partners of the A1AR (A1 adenosine receptor), yeast two-hybrid screening of a rat embryonic cDNA library was performed. This procedure led to the identification of erythrocyte membrane cytoskeletal protein (represented as 4.1G) as an A1AR-binding partner. Truncation studies revealed that the C-terminal domain of 4.1G was essential for binding to A1ARs and that the C-terminal domain of 4.1G and the third intracellular loop of A1ARs interacted. A1AR-4.1G interaction was also confirmed in studies using brain tissue. Studies in HEK-293 (human embryonic kidney 293) cells and Chinese-hamster ovary cells showed that 4.1G interfered with A1AR signal transduction, as 4.1G reduced A1AR-mediated inhibition of cAMP accumulation and intracellular calcium release. 4.1G also altered cell-surface A1AR expression. These observations identify 4.1G as a novel A1AR-binding partner that can regulate adenosine action.

Synthesis, molecular modeling studies, and pharmacological activity of selective A(1) receptor antagonists

We present a combined computational study aimed at identifying the three-dimensional structural properties required for different classes of compounds to show antagonistic activity toward the A(1) adenosine receptor (AR). Particularly, an approach combining pharmacophore mapping, molecular alignment, and pseudoreceptor generation was applied to derive a hypothesis of the interaction pathway between a set of A(1) AR antagonists taken from the literature and a model of the putative A(1) receptor. The pharmacophore model consists of seven features and represents an improvement of the N(6)-C8 model, generally reported as the most probable pharmacophore model for A(1) AR agonists and antagonists. It was used to build up a pseudoreceptor model able to rationalize the relationships between structural properties and biological data of, and external to, the training set. In fact, to further assess its statistical significance and predictive power, the pseudoreceptor was employed to predict the free energy of binding associated with compounds constituting a test set. While part of these molecules was also taken from the literature, the remaining compounds were designed and synthesized by our research group. All of the new compounds were tested for their affinity toward A(1), A(2a), and A(3) AR, showing interesting antagonistic activity and A(1) selectivity.

4-[6-(Dansylamino)hexylamino]-7-methyl-2-phenyl-1,8-naphthyridine as a new potential fluorescent probe for studying A1-adenosine receptor

A new fluorescent ligand for adenosine receptors, obtained by the insertion of a dansylamino-moiety with a linear hexyl spacer in the N4 position of a 1,8-naphthyridine adenosine receptor ligand, proved to possess a high affinity and selectivity for the A1 receptor subtype.

Substituted 4-phenyl-2-(phenylcarboxamido)-1,3-thiazole derivatives as antagonists for the adenosine A(1) receptor

The synthesis and receptor binding of novel adenosine receptor antagonists is described. We found that non-xanthine 4-phenyl-2-(phenylcarboxamido)-1,3-thiazole derivatives may have high affinity and substantial selectivity for the adenosine A(1) receptor.