Human A3 Adenosine Receptor Antagonists Research Articles

Design and Synthesis of 2,6-Disubstituted-4'-Selenoadenosine-5'-N,N-Dimethyluronamide Derivatives as Human A3 Adenosine Receptor Antagonists.

A new series of 4′-selenoadenosine-5′-N,N-dimethyluronamide derivatives as highly potent and selective human A3 adenosine receptor (hA3AR) antagonists, is described. The highly selective A3AR agonists, 4′-selenoadenosine-5′-N-methyluronamides were successfully converted into selective antagonists by adding a second N-methyl group to the 5′-uronamide position. All the synthesized compounds showed medium to high binding affinity at the hA3AR. Among the synthesized compounds, 2-H-N6-3-iodobenzylamine derivative 9f exhibited the highest binding affinity at hA3AR. (Ki = 22.7 nM). The 2-H analogues generally showed better binding affinity than the 2-Cl analogues. The cAMP functional assay with 2-Cl-N6-3-iodobenzylamine derivative 9l demonstrated hA3AR antagonist activity. A molecular modelling study suggests an important role of the hydrogen of 5′-uronamide as an essential hydrogen bonding donor for hA3AR activation.

Discovery of simplified N2-substituted pyrazolo[3,4-d]pyrimidine derivatives as novel adenosine receptor antagonists: Efficient synthetic approaches, biological evaluations and molecular docking studies

In the present study, a molecular simplification approach was employed to design novel bicyclic pyrazolo[3,4-d]pyrimidine (PP) derivatives from tricyclic pyrazolo[4,3-e]-1,2,4-triazolo-[1,5-c]pyrimidines (PTP) as promising human A3 adenosine receptor (hA3AR) antagonists. All the target compounds were synthesized using novel and efficient synthetic schemes and the structure–activity relationship studies of these PPs were explored through the synthesis of a series of PTP analogues with various substituents. Substituents with different lipophilicity and steric hindrance (e.g., alkyl and aryl–alkyl) functions were introduced at N2 position of the pyrazole ring, while acyl groups with different electronic properties were introduced at C6 position of the bicyclic nucleus to probe both electronic and positional effects. Most of the synthesized derivatives of the PP series presented good affinity at the hA3AR, as indicated by the low micromolar range of Ki values and among them, compound 63 with N2 neopentyl substituents showed most potent hA3AR affinity with Ki value of 0.9μM and high selectivity (hA1AR/hA3AR=>111 & hA2AAR/hA3AR=>111) towards other adenosine receptor subtypes. Interestingly, small isopropyl groups at N2 position displayed high affinity at another receptor subtype (hA2AAR, e.g., compound 55, with Ki hA2AAR=0.8μM), while they were less favorable at the hA3AR. Molecular docking analysis was also performed to predict the possible binding mode of target compounds inside the hA3AR and hA2AAR. Overall, PP derivatives represent promising starting points for new AR antagonists.

2-Arylpyrazolo[4,3-d]pyrimidin-7-amino Derivatives As New Potent and Selective Human A3 Adenosine Receptor Antagonists. Molecular Modeling Studies and Pharmacological Evaluation

On the basis of our previously reported 2-arylpyrazolo[4,3-d]pyrimidin-7-ones, a set of 2-arylpyrazolo[4,3-d]pyrimidin-7-amines were designed as new human (h) A3 adenosine receptor (AR) antagonists. Lipophilic groups with different steric bulk were introduced at the 5-position of the bicyclic scaffold (R5 = Me, Ph, CH2Ph), and different acyl and carbamoyl moieties (R7) were appended on the 7-amino group, as well as a para-methoxy group inserted on the 2-phenyl ring. The presence of acyl groups turned out to be of paramount importance for an efficient and selective binding at the hA3 AR. In fact, most of the 7-acylamino derivatives showed low nanomolar affinity (Ki = 2.5-45 nM) and high selectivity toward this receptor. A few selected pyrazolo[4,3-d]pyrimidin-7-amides were effective in counteracting oxaliplatin-induced apoptosis in rat astrocyte cell cultures, an in vitro model of neurotoxicity. Through an in silico receptor-driven approach the obtained binding data were rationalized and the molecular bases of the observed hA3 AR affinity and hA3 versus hA2A AR selectivity were explained.

Pharmacophore elucidation for a new series of 2-aryl-pyrazolo-triazolo-pyrimidines as potent human A3 adenosine receptor antagonists

A ligand-based pharmacophore was obtained for a new series of 2-unsubstituted and 2-(para-substituted)phenyl-pyrazolo-triazolo-pyrimidines as potent human A(3) adenosine receptor antagonists. Through comparative molecular field analysis-based quantitative structure-activity relationship studies, structural features at the N(5)-, N(8)- and C(2)-positions of the tricyclic nucleus were deeply investigated, with emphasis given to the unprecedentedly explored C(2)-position. The resulting model showed good correlation and predictability (r(2)=0.936; q(2)=0.703; r(pred)(2)=0.663). Overall, the contribution of steric effect was found relatively more predominant for the optimal interaction of these antagonists to the human A(3) receptor.

Pyrido[2,3-e]-1,2,4-triazolo[4,3-a]pyrazin-1-one as a New Scaffold To Develop Potent and Selective Human A3 Adenosine Receptor Antagonists. Synthesis, Pharmacological Evaluation, and Ligand−Receptor Modeling Studies

The paper describes a new class of human (h) A(3) adenosine receptor antagonists, the 2-arylpyrido[2,3-e]-1,2,4-triazolo[4,3-a]pyrazin-1-one derivatives (PTP), either 4-oxo (1-6, series A) or 4-amino-substituted (7-20, series B). In both series A and B, substituents able to act as hydrogen bond acceptors (OMe, OH, F, COOEt) were inserted on the 2-phenyl ring. In series B, cycloalkyl and acyl residues were introduced on the 4-amino group. Some of the new derivatives showed high hA(3) AR affinities (K(i) < 50 nM) and selectivities vs both hA(1) and hA(2A) receptors. The selected 4-benzoylamino-2-(4-methoxyphenyl)pyrido[2,3-e]-1,2,4-triazolo[4,3-a]pyrazin-1-one (18), tested in an in vitro rat model of cerebral ischemia, proved to be effective in preventing the failure of synaptic activity induced by oxygen and glucose deprivation in the hippocampus. Molecular docking of this new class of hA(3) AR antagonists was carried out to depict their hypothetical binding mode to our refined model of hA(3) receptor.

Structure–activity relationships of 2-chloro-N6-substituted-4′-thioadenosine-5′-N,N-dialkyluronamides as human A3 adenosine receptor antagonists

On the basis of potent and selective A(3) adenosine receptor (AR) antagonist, 2-chloro-N(6)-(3-iodobenzyl)-4'-thioadenosine-5'-N,N-dimethyluronamide, structure-activity relationships were studied for a series of 5'-N,N-dialkyluronamide derivatives, synthesized from D-gulonic gamma-lactone. From this study, it was revealed that removal of the hydrogen bond-donating ability of the 5'-uronamide was essential for the pure A(3)AR antagonism. 5'-N,N-Dimethyluronamide derivatives exhibited higher binding affinity than larger 5'-N,N-dialkyl or 5'-N,N-cycloalkylamide derivatives, indicating that steric factors are crucial in binding to the human A(3)AR. A N(6)-(3-bromobenzyl) derivative 6c (K(i)=9.32 nM) exhibited the highest binding affinity at the human A(3)AR with very low binding affinities to other AR subtypes.

Scouting Human A3 Adenosine Receptor Antagonist Binding Mode Using a Molecular Simplification Approach: From Triazoloquinoxaline to a Pyrimidine Skeleton as a Key Study

The concept of molecular simplification as a drug design strategy to shorten synthetic routes, while keeping or enhancing the biological activity of the lead drug, has been applied to design new classes of human A3 adenosine receptor (AR) antagonists. Over the past decade, we have focused a part of our research on the study of AR antagonists belonging to strictly correlated classes of tricyclic compounds. One of these classes is represented by the 2-aryl-1,2,4-triazolo[4,3-a]quinoxalin-1-one derivatives, either 4-amino or 4-oxo-substituted, which were intensively investigated by evaluating the effect of different substituents on the 2-phenyl ring and on the 4-amino group. Using an in silico molecular simplification approach, a new series of easily synthesizable 2-amino/2-oxoquinazoline-4-carboxamido derivatives have been discovered, presenting high affinity and selectivity against human A3 AR.

New 2-Arylpyrazolo[3,4-c]quinoline Derivatives as Potent and Selective Human A3Adenosine 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.

Response Surface Analysis as Alternative 3D-QSAR Tool: Human A3 Adenosine Receptor Antagonists as a Key Study

Response Surface Analysis as Alternative 3D-QSAR Tool: Human A3 Adenosine Receptor Antagonists as a Key Study

Quantitative structure-activity relationship study of human A3 adenosine receptor antagonists: Derivatives of 2-aryl-1,2,4-triazolo[4,3-α]quinoxaline

A quantitative structure-activity relationship (QSAR) study was conducted on the antagonistic activities of derivatives of 2-aryl-1,2,4-triazolo[4,3-α]quinoxaline at the human A3 adenosine receptor. As per the structural framework, the title analogues were subdivided into two congeneric series, namely the 1,4-dione and the 4-amino-1-one series. A majority of substituents occurred at the R- and a limited number at the X-positions in both of these series. In the case of the 1,4-dione series, the derived significant QSAR equation revealed that those substituents exhibiting a larger field effect at R renders the molecule to more efficiently bind at the receptor site. The study also extrapolated the requirement of electron-donor substituents at the X-position which, at present, is regarded as insensitive to any interaction due to limited substitution. However, the X-position may be explored in a further synthetic study. From the derived correlation equation for the 4-amino-1-one series, it appeared that a strong electron-withdrawing substituent at R will enhance the pKi value of a compound while a strong electron-donor at this position will have a detrimental effect on it. Based on correlation equations, derived using different electronic parameters, it may be interpreted that the two series of compounds attain different orientation inside the recognition site of the receptor.

Pyrazolo-triazolo-pyrimidines as adenosine receptor antagonists: A complete structure-activity profile.

In the last 5 years, many efforts have been conducted searching potent and selective human A3 adenosine antagonists. In this field several different classes of compounds, possessing very good affinity (nM range) and with a broad range of selectivity, have been proposed. Recently, our group synthesized a new series of pyrazolo-triazolo-pyrimidines bearing different substitutions at the N5 and N8 positions, which have been described as highly potent and selective human A3 adenosine receptor antagonists. The present review summarizes available data and provides an overview of the structure–activity relationships found for this class of human A3 adenosine receptor antagonists.

4-Amido-2-aryl-1,2,4-triazolo[4,3-a]quinoxalin-1-ones as New Potent and Selective Human A3 Adenosine Receptor Antagonists. Synthesis, Pharmacological Evaluation, and Ligand−Receptor Modeling Studies

A structural investigation on some 4-amido-2-phenyl-1,2-dihydro-1,2,4-triazolo[4,3-a]quinoxalin-1-one derivatives, designed as human A3 adenosine receptor (hA3 AR) antagonists, is described. In the new derivatives, some acyl residues with different steric bulk were introduced on the 4-amino group, and their combination with the 4-methoxy group on the 2-phenyl moiety, and/or the 6-nitro/6-amino substituent on the fused benzo ring, was also evaluated. Most of the new derivatives were potent and selective hA3 AR antagonists. SAR analysis showed that hindering and lipophilic acyl moieties not only are well tolerated but even ameliorate the hA3 affinity. Interestingly, the 4-methoxy substituent on the appended 2-phenyl moiety, as well as the 6-amino group, always exerted a positive effect, shifting the affinity toward the hA3 receptor subtype. In contrast, the 6-nitro substituent exerted a variable effect. An intensive molecular modeling investigation was performed to rationalize the experimental SAR findings.

1,2,4-Triazolo[1,5-a]quinoxaline as a Versatile Tool for the Design of Selective Human A3 Adenosine Receptor Antagonists: Synthesis, Biological Evaluation, and Molecular Modeling Studies of 2-(Hetero)aryl- and 2-Carboxy-Substitued Derivatives

A number of 4-oxo-substituted 1,2,4-triazolo[1,5-a]quinoxaline derivatives bearing at position-2 the claimed (hetero)aryl moiety (compounds 1-15) but also a carboxylate group (16-28, 32-36) or a hydrogen atom (29-31) were designed as human A3 (hA3) adenosine receptor (AR) antagonists. This study produced some interesting compounds and among them the 2-(4-methoxyphenyl)-1,2,4-triazolo[1,5-a]quinoxalin-4-one (8), which can be considered one of the most potent and selective hA3 adenosine receptor antagonists reported till now. Moreover, as a new finding, replacement of the classical 2-(hetero)aryl moiety with a 2-carboxylate function (compounds 16-28 and 32-36) maintained good hA3 AR binding activity but, most importantly and interestingly, produced a large increase in hA3 versus hA1 selectivity. A receptor-based SAR analysis provided new interesting insights about the steric and electrostatic requirements that are important for the anchoring of these derivatives at the hA3 receptor recognition site, thus highlighting the versatility of the triazoloquinoxaline scaffold for obtaining potent and selective hA3 AR antagonists.

Autocorrelation of Molecular Electrostatic Potential Surface Properties Combined with Partial Least Squares Analysis as Alternative Attractive Tool to Generate Ligand-Based 3D-QSARs

A database of 106 human A3 adenosine receptor antagonists was used to derive two alternative PLS models: one starting from CoMFA descriptors and the other starting from the autocorrelation descriptors. The peculiarity of this work is the introduction of autocorrelation vectors as molecular descriptors for the PLS analysis. The autocorrelation allows comparing molecules (and their properties) with different structures and with different spatial orientation without any previous alignment. In particular, Molecular Electrostatic Potential (MEP) was the property computed and its information encoded in autocorrelation vectors. The 3D spatial distribution and the values of the electrostatic potential is in fact largely responsible for the binding of a substrate to its receptor binding site. Validation was done with an external test set and the results of the two models were compared. Interestingly, our preliminary results seem to indicate that this new alternative approach could robustly compete with the already well consolidated CoMFA approach. In particular, we have suggested that it could be a very interesting tool to filter large structural database in several virtual screening applications.

Pyrazolo[4,3‐e]1,2,4‐triazolo[1,5‐c]pyrimidine derivatives: A new pharmacological tool for the characterization of the human A3 adenosine receptor

AbstractAdenosine regulates many physiological functions by interaction with four different G‐protein‐coupled receptors classified as A1, A2A, A2B, and A3. While adenosine A1 and A2A receptor subtypes have been pharmacologically characterized through the use of selective ligands, the A2B and A3 adenosine receptor subtypes are presently under study in order to better understand their physio‐pathological functions. In particular, activation of adenosine A3 receptors has been shown to stimulate phospholipase C and D and to inhibit adenylate cyclase. Activation of A3 adenosine receptors also causes the release of inflammatory mediators such as histamine from mast cells, which are responsible for processes such as inflammation and hypotension. For these reasons, it has been suggested that A3 adenosine receptor antagonists can be considered potential drugs for the treatment of asthma and inflammation. In the last few years different classes of heterocyclic compounds have been identified as A3 adenosine antagonists, but none of the tested compounds showed significant selectivity for A3 adenosine receptor subtype. Herein, we report our recent results on a class of pyrazolo[4,3‐e]1,2,4‐triazolo[1,5‐c]pyrimidine derivatives as a new class of potent and selective human A3 adenosine receptor antagonists. The full characterization of the first high‐affinity radioligand antagonist for this receptor subtype, designated [3H] MRE3008F20, is briefly summarized. Drug Dev. Res. 52:406–415, 2001. © 2001 Wiley‐Liss, Inc.

Molecular modeling studies of human A3 adenosine antagonists: structural homology and receptor docking.

Molecular modeling studies were conducted on various chemically diverse classes of human A3 adenosine receptor antagonists (hA3ANTs), such as adenines, xanthines, triazoloquinazolines, flavonoids, thiazolopyridines, 6-phenyl-1, 4-dihydropyridines, and 6-phenylpyridines. Using a combination of ab initio quantum mechanical calculations, electrostatic potential map comparison, and the steric and electrostatic alignment (SEAL) method, a general pharmacophore map for hA3ANTs has been derived. Based on the proposed pharmacophore map, we hypothesize that the receptor binding properties of different A3 antagonist derivatives are due to recognition at a common region inside the receptor binding site and, consequently, a common electrostatic potential profile. A model of the human A3 receptor, docked with the triazoloquinazoline reference ligand CGS 15953 (9-chloro-2-(2-furyl)[1,2,4]triazolo[1,5-c]quinazolin-5-amine), was built and analyzed to help interpret these results. All other antagonist structures were docked inside the receptor according to the results obtained through the steric and electrostatic alignment (SEAL) approach using the structure of CGS 15953 as a template. The receptor model was derived from primary sequence comparison, secondary structure predictions, and three-dimensional homology building, using rhodopsin as a template. An energetically refined 3D structure of the ligand-receptor complex was obtained using our recently introduced cross-docking procedure (J. Med. Chem. 1998, 41, 1456-1466), which simulates the ligand-induced reorganization of the native receptor structure.