Developing novel classes of protein kinase CK1δ inhibitors by fusing [1,2,4]triazole with different bicyclic heteroaromatic systems.

Protein kinase CK1δ expression and activity is involved in different pathological situations that include neuroinflammatory and neurodegenerative diseases. For this reason, protein kinase CK1δ has become a possible therapeutic target for these conditions. 5,6-fused bicyclic heteroaromatic systems that resemble adenine of ATP represent optimal scaffolds for the development of a new class of ATP competitive CK1δ inhibitors. In particular, a new series of [1,2,4]triazolo[1,5-c]pyrimidines and [1,2,4]triazolo[1,5-a][1,3,5]triazines was developed. Some crucial interactors have been identified, such as the presence of a free amino group able to interact with the residues of the hinge region at the 5- and 7- positions of the [1,2,4]triazolo[1,5-c]pyrimidine and [1,2,4]triazolo[1,5-a][1,3,5]triazine scaffolds, respectively; or the presence of a 3-hydroxyphenyl or 3,5-dihydroxyphenyl moiety at the 2- position of both nuclei. Molecular modeling studies identified the key interactions involved in the inhibitor-protein recognition process that appropriately fit with the outlined structure-activity relationship. Considering the fact that the CK1 protein kinase is involved in various pathologies in particular of the central nervous system, the interest in the development of new inhibitors permeable to the blood-brain barrier represents today an important goal in the pharmaceutical field. The best potent compound of the series is the 5-(7-amino-5-(benzylamino)-[1,2,4]triazolo[1,5-a][1,3,5]triazin-2-yl)benzen-1,3-diol (compound 51, IC50 = 0.18 µM) that was predicted to have an intermediate ability to cross the membrane in our in vitro assay and represents an optimal starting point to both studies the therapeutic value of protein kinase CK1δ inhibition and to develop new more potent derivatives.

A Triazolotriazine-Based Dual GSK-3ß/CK-1δ Ligand as a Potential Neuroprotective Agent Presenting Two Different Mechanisms of Enzymatic Inhibition.

Glycogen synthase kinase 3ß (GSK-3ß) and casein kinase 1δ (CK-1δ) are emerging targets for the treatment of neuroinflammatory disorders, including Parkinson's disease. An inhibitor able to target these two kinases was developed by docking-based design. Compound 12, 3-(7-amino-5-(cyclohexylamino)-[1,2,4]triazolo[1,5-a][1,3,5]triazin-2-yl)-2-cyanoacrylamide, showed combined inhibitory activity against GSK-3ß and CK-1δ [IC50 (GSK-3ß)=0.17 µm; IC50 (CK-1δ)=0.68 µm]. In particular, classical ATP competition was observed against CK-1δ, and a co-crystal of compound 12 inside GSK-3ß confirmed a covalent interaction between the cyanoacrylamide warhead and Cys199, which could help in the development of more potent covalent inhibitors of GSK-3ß. Preliminary studies on in vitro models of Parkinson's disease revealed that compound 12 is not cytotoxic and shows neuroprotective activity. These results encourage further investigations to validate GSK-3ß/CK-1δ inhibition as a possible new strategy to treat neuroinflammatory/degenerative diseases.

Pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines and Structurally Simplified Analogs. Chemistry and SAR Profile as Adenosine Receptor Antagonists.

Adenosine was defined as a neuromodulator which exerts its action by interaction with specific G-protein coupled receptor termed adenosine receptors. Adenosine receptors are expressed in several tissues and cells of our body and exist as four different subtypes of these receptors: A1, A2, A2B and A3. In the last years significant efforts were made to obtain highly potent and selective ligands for the four adenosine receptors subtypes. Both agonists and antagonists were used as pharmacological tools to study therapeutic implications of enhancing or blocking the adenosine receptors activity, and some of these compounds have reached clinical phases. The pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines (PTPs) represent one of the several templates designed as adenosine receptor antagonists. A lot of synthetic work was made on this scaffold in order to obtain potent A2 and A3 antagonists. Here were reviewed the synthetic approaches followed by both academia and industry to introduce different substituents at different positions of the PTP nucleus, in particular at the 2, 5, 7, 8 and 9 positions. Nevertheless PTP derivatives are tricyclic compounds with a high molecular weight which exhibit limitations such as poor aqueous solubility and difficult synthetic preparation. With the aim to obtain derivatives with the same potency and selectivity of PTP but with better drug-like properties, researchers made structural simplification of this scaffold. Replacement of the pyrazole or triazole rings of PTP led to the [1,2,4]triazolo[1,5-c]pyrimidine and pyrazolo[3,4- d]pyrimidine derivatives, respectively. Synthetic strategies for these compounds were reported, combined with the SAR profile on the adenosine receptors.

5,7-Disubstituted-[1,2,4]triazolo[1,5-a][1,3,5]triazines as pharmacological tools to explore the antagonist selectivity profiles toward adenosine receptors.

The structure-activity relationship of new 5,7-disubstituted-[1,2,4]triazolo[1,5-a][1,3,5]triazines as adenosine receptors (ARs) antagonists has been explored. The introduction of a benzylamino group at C5 with a free amino group at C7 increases the affinity toward all the ARs subtypes (10: KihA1 = 94.6 nM; KihA2A = 1.11 nM; IC50hA2B = 2214 nM; KihA3 = 30.8 nM). Replacing the free amino group at C7 with a phenylureido moiety yields a potent and quite selective hA2A AR antagonist (14: hA2A AR Ki = 1.44 nM; hA1/hA2A = 216.0; hA3/hA2A = 20.6). This trend diverges from the analysis on the pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine series previously reported. With the help of an in silico receptor-driven approach, we have rationalized these observations and elucidated from a molecular point of view the role of the benzylamino group at C5 in determining affinity toward the hA2A AR.

The Influence of the 1-(3-Trifluoromethyl-Benzyl)-1H-Pyrazole-4-yl Moiety on the Adenosine Receptors Affinity Profile of Pyrazolo[4,3-e][1,2,4]Triazolo[1,5-c]Pyrimidine Derivatives.

A new series of pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine (PTP) derivatives has been developed in order to explore their affinity and selectivity profile at the four adenosine receptor subtypes. In particular, the PTP scaffold was conjugated at the C2 position with the 1-(3-trifluoromethyl-benzyl)-1H-pyrazole, a group believed to confer potency and selectivity toward the human (h) A2B adenosine receptor (AR) to the xanthine ligand 8-(1-(3-(trifluoromethyl)benzyl)-1H-pyrazol-4-yl)-1,3-dimethyl-1H-purine-2,6(3H,7H)-dione (CVT 6975). Interestingly, the synthesized compounds turned out to be inactive at the hA2B AR but they displayed affinity at the hA3 AR in the nanomolar range. The best compound of the series (6) shows both high affinity (hA3 AR Ki = 11 nM) and selectivity (A1/A3 and A2A/A3 > 9090; A2B/A3 > 909) at the hA3 AR. To better rationalize these results, a molecular docking study on the four AR subtypes was performed for all the synthesized compounds. In addition, CTV 6975 and two close analogues have been subjected to the same molecular docking protocol to investigate the role of the 1-(3-trifluoromethyl-benzyl)-1H-pyrazole on the binding at the four ARs.

Scaffold decoration at positions 5 and 8 of 1,2,4-triazolo[1,5-c]pyrimidines to explore the antagonist profiling on adenosine receptors: a preliminary structure-activity relationship study.

The structure-activity relationship (SAR) of new 5,8-disubstituted-1,2,4-triazolo[1,5-c]pyrimidines as adenosine receptors (ARs) antagonists has been explored. All the synthesized compounds show affinity for the hA2A and hA3 ARs depending on the substitution patterns at the 5 and 8 positions. In particular, a free amino group at the 5 position with an ethoxycarbonyl group at the 8 position leads to potent and quite selective hA2A antagonists (compound 12: hA2A AR Ki=3.32 nM; hA1/hA2A=55.6; hA2A/hA3=0.01), whereas the introduction of a methylamino function at the 5 position yields a good binding profile at the hA3 AR (compound 23: hA3 AR Ki=4.14 nM, hA1/hA3=236; hA2A/hA3=25). Through an in silico receptor-driven approach, we have determined the most favorable orientation of the substitutions at the 5 and 8 positions of the 1,2,4-triazolo[1,5-c]pyrimidine (TP) scaffold and, accordingly, we have elucidated the observed SAR.