Sonja Kachler

The significance of 2-furyl ring substitution with a 2-(para-substituted) aryl group in a new series of pyrazolo-triazolo-pyrimidines as potent and highly selective hA3 adenosine receptors antagonists: new insights into structure-affinity relationship and receptor-antagonist recognition

Among the heterocyclic structures identified as potent human A(3) (hA(3)) adenosine receptors antagonists, we have demonstrated that the new pyrazolo-triazolo-pyrimidines, bearing an aryl group in replacement of the C(2)-furyl ring, not only confer a good pharmacological profile (with significantly enhanced selectivity against other adenosine receptor subytpes) but also overcome the metabolic transformation of the furan ring into toxic intermediates. All the synthesized [2-(para-substituted) phenyl]-pyrazolo-triazolo-pyrimidines showed affinity at the hA(3) receptor in the low nanomolar range. The most potent derivative of the series presented better affinity and excellent selectivity (compound 31, K(i) hA(3) = 0.108 nM; hA(1)/hA(3) = 5200; hA(2A)/hA(3) = 7200), in comparison to the C(2)-furyl counterpart. A receptor-driven molecular modeling investigation, based on a recently proposed model of A(3) receptor derived from the crystallographic structure of human A(2A) receptor, has been carried out in order to support the experimental binding data and to justify the enhanced selectivity against the other receptor subtypes.

Discovery of novel A3 adenosine receptor ligands based on chromone scaffold.

A project focused on the discovery of new chemical entities (NCEs) as AR ligands that incorporate a benzo-γ-pyrone [(4H)-1-benzopyran-4-one] substructure has been developed. Accordingly, two series of novel chromone carboxamides placed at positions C2 (compounds 2-13) and C3 (compounds 15-26) of the γ-pyrone ring were synthesized using chromone carboxylic acids (compounds 1 or 14) as starting materials. From this study and on the basis of the obtained structure-activity relationships it was concluded that the chromone carboxamide scaffold represent a novel class of AR ligands. The most remarkable chromones were compounds 21 and 26 that present a better affinity for A3AR (Ki = 3680 nM and Ki = 3750 nM, respectively). Receptor-driven molecular modeling studies provide information on the binding/selectivity data of the chromone. The data so far acquired are instrumental for future optimization of chromone carboxamide as a selective A3AR antagonist.

Chalcone-based derivatives as new scaffolds for hA3 adenosine receptor antagonists

With the aim of finding new adenosine receptor (AR) ligands based on the chalcone scaffold, we report the synthesis of a new series of coumarin–chalcone hybrids and the pharmacological characterization of their actions at four subtypes of AR.

New insight into adenosine receptors selectivity derived from a novel series of [5-substituted-4-phenyl-1,3-thiazol-2-yl] benzamides and furamides.

A series of [5-substituted-4-phenyl-1,3-thiazol-2-yl] benzamide and furamide analogues were investigated in radioligand binding studies at adenosine receptor subtypes with an aim to obtain potent and selective adenosine receptor ligands. Benzamide and furamide linked to thiazole was found to be crucial for high adenosine receptor affinity. The most potent compound indentified in this study was 5d with low nanomolar affinity for all four adenosine receptor subtypes. Compounds 5a and 5g showed moderate selectivity for A2A adenosine receptors. Molecular docking versus all four human adenosine receptors combined with membrane molecular dynamics studies were performed to rationalise the peculiar selectivity profile of 5d antagonist.

Combining selectivity and affinity predictions using an integrated Support Vector Machine (SVM) approach: An alternative tool to discriminate between the human adenosine A(2A) and A(3) receptor pyrazolo-triazolo-pyrimidine antagonists binding sites.

G Protein-coupled receptors (GPCRs) selectivity is an important aspect of drug discovery process, and distinguishing between related receptor subtypes is often the key to therapeutic success. Nowadays, very few valuable computational tools are available for the prediction of receptor subtypes selectivity. In the present study, we present an alternative application of the Support Vector Machine (SVM) and Support Vector Regression (SVR) methodologies to simultaneously describe both A(2A)R versus A(3)R subtypes selectivity profile and the corresponding receptor binding affinities. We have implemented an integrated application of SVM-SVR approach, based on the use of our recently reported autocorrelated molecular descriptors encoding for the Molecular Electrostatic Potential (autoMEP), to simultaneously discriminate A(2A)R versus A(3)R antagonists and to predict their binding affinity to the corresponding receptor subtype of a large dataset of known pyrazolo-triazolo-pyrimidine analogs. To validate our approach, we have synthetized 51 new pyrazolo-triazolo-pyrimidine derivatives anticipating both A(2A)R/A(3)R subtypes selectivity and receptor binding affinity profiles.

Targeting adenosine receptors with coumarins: synthesis and binding activities of amide and carbamate derivatives.

Objectives  With the aim of finding the structural features governing binding activity and selectivity against adenosine receptors (ARs), several 3‐subtituted coumarins with amide (compounds 3–6) and carbamate (7–9) functions were synthesized. To study its possible influence on the binding activity and selectivity, a hydroxyl substituent was also introduced at position 4 of the coumarin moiety.

Does the combination of optimal substitutions at the C2-, N5- and N8-positions of the pyrazolo-triazolo-pyrimidine scaffold guarantee selective modulation of the human A3 adenosine receptors?

In an attempt to study the optimal combination of a phenyl ring at the C(2)-position and different substituents at the N(5)- and N(8)-positions towards the selective modulation of human A(3) adenosine receptors (hA(3)AR), we synthesized a new series of 2-para-(un)substituted-phenyl-pyrazolo-triazolo-pyrimidines bearing either a methyl or phenylethyl at N(8) and chains of variable length at N(5). Through biological evaluation, it was found that the majority of the compounds had good affinities towards the hA(3)AR in the low nanomolar range. Compound 16 possessed the best hA(3)AR affinity and selectivity profile (K(i)hA(3)=1.33 nM; hA(1)/hA(3)=4880; hA(2A)/hA(3)=1100) in the present series of 2-(substituted)phenyl-pyrazolo-triazolo-pyrimidine derivatives. In addition to pharmacological characterization, a molecular modeling investigation on these compounds further elucidated the effect of different substituents at the pyrazolo-triazolo-pyrimidine scaffold on affinity and selectivity to hA(3)AR.

Novel 8-(p-substituted-phenyl/benzyl)xanthines with selectivity for the A2A adenosine receptor possess bronchospasmolytic activity

A new series of 8-(p-substituted-phenyl/benzyl)xanthines has been synthesized and evaluated in vitro for adenosine receptor binding affinity and in vivo for bronchospasmolytic effects. It was observed that the nature of substituent at para-position of 8-phenyl/benzyl group on the xanthine scaffold remarkably affects the binding affinity and selectivity of xanthine derivatives for various adenosine receptor subtypes and also their bronchospasmolytic effects. Newly synthesized 8-phenylxanthines displayed potent binding affinity and significant selectivity for A2A receptors and also produced potent bronchospasmolytic effects. Replacement of phenyl ring with benzyl moiety at C8 of xanthine skeleton resulted in notable reduction in adenosine receptor affinity and broncholytic effects.

Navigating in chromone chemical space: discovery of novel and distinct A3 adenosine receptor ligands

One of the major hurdles in the development of safe and effective drugs targeting G-protein coupled receptors (GPCRs) is finding ligands that are highly selective for a specific receptor subtype. The search for novel compounds with therapeutic value by targeting the A3 adenosine receptor (A3AR) is still in its early stages. The increasing knowledge about the biological, physiological and pathological role of the A3AR subtype was accompanied by the design and development of the A3AR ligands, but the particular role of A3AR agonists and antagonists is still an open issue. Among the large variety of chemical classes screened towards ARs flavonoids have been indicated as remarkable A3AR antagonists. However, the search of A3AR ligands based on this framework seems to be discontinued. In this context, our research group focused its investigation into the discovery and development of novel, potent and selective AR ligands based on the chemical core of flavonoids, the chromone scaffold. The ongoing research has shown that chromone-2-phenylcarboxamide derivatives display a remarkable preference for hA3AR. In this work we report stimulating results, supported by A2A/A3 molecular docking simulations and structure–affinity-relationship (SAR) studies by which N-(4,5-methylthiazol-2-yl)-4-oxo-4H-chromene-2-carboxamide (compound 31) emerged as the most potent and selective compound, displaying an hA3 Ki of 167 nM and a selectivity ratio of 590 vs. the hA1 and 480 vs. the hA2AAR subtypes. The chromone-based ligand was obtained by a simple synthetic approach and will enter in a lead optimization program to enhance its potency and drug-like properties.

Novel thiazole-thiophene conjugates as adenosine receptor antagonists: synthesis, biological evaluation and docking studies.

Here we report novel thiazole-thiophene conjugates as adenosine receptor antagonists. All the molecules were evaluated for their binding affinity for adenosine receptors. Most of the molecules were found to interact with the A1, A2A and A3 adenosine receptor subtypes with good affinity values. The most potent and selective compound 8n showed an A3Ki value of 0.33μM with selectivity ratios of >90 versus the A1 and >30 versus the A2 subtypes. For compound 8n docking studies into the binding site of the A3 adenosine receptor are provided to visualize its binding mode.