Synthesis and Antiproliferative Activity of 2,6-Disubstituted Imidazo[4,5-b]pyridines Prepared by Suzuki Cross Coupling.

A series of novel 2,6-diphenyl substituted imidazo[4,5-b]pyridines was designed and synthesized using optimized Suzuki cross coupling to evaluate their biological activity in vitro. The conditions of the Suzuki coupling were evaluated and optimized using a model reaction. To study the influence of the substituents on the biological activity, we prepared N-unsubstituted and N-methyl substituted imidazo[4,5-b]pyridines with different substituents at the para position on the phenyl ring placed at position 6 on the heterocyclic scaffold. Antiproliferative activity was determined on diverse human cancer cell lines, and the selectivity of compounds with promising antiproliferative activity was determined on normal peripheral blood mononuclear cells (PBMC). Pronounced antiproliferative activity was observed for p-hydroxy substituted derivatives 13 and 19, both displaying strong activity against most of the tested cell lines (IC50 1.45-4.25 µM). The unsubstituted N-methyl derivative 19 proved to be the most active derivative. There was a dose-dependent accumulation of G2/M arrested cells in several cancer cell lines after exposure to compound 19, implying a cell cycle-phase-specific mechanism of action. Additionally, the novel series of derivatives was evaluated for antiviral activity against a broad panel of viruses, yet the majority of tested compounds did not show antiviral activity.

Biological Activity of Amidino-Substituted Imidazo [4,5-b]pyridines.

A series of cyano- and amidino-substituted imidazo[4,5-b]pyridines were synthesized using standard methods of organic synthesis, and their biological activity was evaluated. Biological evaluation included in vitro assessment of antiproliferative effects on a diverse selection of human cancer cell lines, antibacterial activity against chosen Gram-positive and Gram-negative bacterial strains, and antiviral activity on a broad panel of DNA and RNA viruses. The most pronounced antiproliferative activity was observed for compound 10, which contained an unsubstituted amidino group, and compound 14, which contained a 2-imidazolinyl amidino group; both displayed selective and strong activity in sub-micromolar inhibitory concentration range against colon carcinoma (IC50 0.4 and 0.7 µM, respectively). All tested compounds lacked antibacterial activity, with the exception of compound 14, which showed moderate activity against E. coli (MIC 32 µM). Bromo-substituted derivative 7, which contained an unsubstituted phenyl ring (EC50 21 µM), and para-cyano-substituted derivative 17 (EC50 58 µM) showed selective but moderate activity against respiratory syncytial virus (RSV).

Design and synthesis of novel imidazo[4,5-b]pyridine based compounds as potent anticancer agents with CDK9 inhibitory activity.

New imidazo[4,5-b]pyridine derivatives were designed, synthesized and screened for their anticancer activity against breast (MCF-7) and colon (HCT116) cancer cell lines. Nine compounds (I, II, IIIa, IIIb, IV, VI, VIIa, VIII, IX) showed significant activity against MCF-7, while six compounds (I, VIIc, VIIe, VIIf, VIII, IX) elicited a remarkable activity against HCT116. Compounds showing significant anticancer activity revealed remarkable CDK9 inhibitory potential (IC50 = 0.63-1.32 µM) relative to sorafenib (IC50 = 0.76 µM). Moreover, a molecular docking study was performed to illustrate the binding mode of the most active compounds in the active site of CDK9 where it revealed superior binding affinity relative to the natural ligand (T3C).

Design, Synthesis, Antitumor Activity and NMR-Based Metabolomics of Novel Amino Substituted Tetracyclic Imidazo[4,5-b]Pyridine Derivatives.

Newly prepared tetracyclic imidazo[4,5-b]pyridine derivatives were synthesized to study their antiproliferative activity against human cancer cells. Additionally, the structure-activity was studied to confirm the impact of the N atom position in pyridine nuclei as well as the chosen amino side chains on antiproliferative activity. Targeted amino substituted regioisomers were prepared by using uncatalyzed amination from corresponding chloro substituted precursors. The most active compounds 6 a, 8 and 10 showed improved activity in comparison to standard drug etoposide with IC50 values in a nanomolar range of concentration (0.2-0.9 µM). NMR-based metabolomics is a powerful instrument to elucidate activity mechanism of new chemotherapeutics. Multivariate and univariate statistical analysis of metabolic profiles of non-small cell lung cancer cells before and after exposure to 6 a revealed significant changes in metabolism of essential amino acids, glycerophospholipids and oxidative defense. Insight into the changes of metabolic pathways that are heavily involved in cell proliferation and survival provide valuable guidelines for more detailed analysis of activity metabolism and possible targets of this class of bioactive compounds.

Novel acrylonitrile derived imidazo[4,5-b]pyridines as antioxidants and potent antiproliferative agents for pancreatic adenocarcinoma.

We present the design, synthesis, computational analysis, and biological assessment of several acrylonitrile derived imidazo[4,5-b]pyridines, which were evaluated for their anticancer and antioxidant properties. Our aim was to explore how the number of hydroxy groups and the nature of nitrogen substituents influence their biological activity. The prepared derivatives exhibited robust and selective antiproliferative effects against several pancreatic adenocarcinoma cells, most markedly targeting Capan-1 cells (IC50 1.2-5.3 µM), while their selectivity was probed relative to normal PBMC cells. Notably, compound 55, featuring dihydroxy and bromo substituents, emerged as a promising lead molecule. It displayed the most prominent antiproliferative activity without any adverse impact on the viability of normal cells. Furthermore, the majority of studied derivatives also exhibited significant antioxidative activity within the FRAP assay, even surpassing the reference molecule BHT. Computational analysis rationalized the results by highlighting the dominance of the electron ionization for the antioxidant features with the trend in the computed ionization energies well matching the observed activities. Still, in trihydroxy derivatives, their ability to release hydrogen atoms and form a stable O-H⋯O•⋯H-O fragment upon the H• abstraction prevails, promoting them as excellent antioxidants in DPPH• assays as well.

Novel amino substituted tetracyclic imidazo[4,5-b]pyridine derivatives: Design, synthesis, antiproliferative activity and DNA/RNA binding study.

A novel series of tetracyclic imidazo[4,5-b]pyridine derivatives was designed and synthesized as potential antiproliferative agents. Their antiproliferative activity against human cancer cells was influenced by the introduction of chosen amino side chains on the different positions on the tetracyclic skeleton and particularly, by the position of N atom in the pyridine nuclei. Thus, the majority of compounds showed improved activity in comparison to standard drug etoposide. Several compounds showed pronounced cytostatic effect in the submicromolar range, especially on HCT116 and MCF-7 cancer cells. The obtained results have confirmed the significant impact of the position of N nitrogen in the pyridine ring on the enhancement of antiproliferative activity, especially for derivatives bearing amino side chains on position 2. Thus, regioisomers 6, 7 and 9 showed noticeable enhancement of activity in comparison to their counterparts 10, 11 and 13 with IC50 values in a nanomolar range of concentration (0.3-0.9 µM). Interactions with DNA (including G-quadruplex structure) and RNA were influenced by the position of amino side chains on the tetracyclic core of imidazo[4,5-b]pyridine derivatives and the ligand charge. Moderate to high binding affinities (logKs = 5-7) obtained for selected imidazo[4,5-b]pyridine derivatives suggest that DNA/RNA are potential cell targets.

New imidazopyridines with phosphodiesterase 4 and 7 inhibitory activity and their efficacy in animal models of inflammatory and autoimmune diseases.

Herein, we describe the rapid synthesis of a focused library of trisubstituted imidazo[4,5-b]pyridines and imidazo[4,5-c]pyridines from 2,4-dichloro-3-nitropyridine using the combination of solution-phase/solid-phase chemistry as new potential anti-inflammatory agents in the treatment of autoimmune diseases. Structure-activity relationship studies, followed by the structure optimization, provided hit compounds (17 and 28) which inhibited phosphodiesterase 4 (PDE4) with IC50 values comparable to rolipram and displayed different inhibitory potency against phosphodiesterase 7 (PDE7). Among them, compound 17 showed a beneficial effect in all the studied animal models of inflammatory and autoimmune diseases (concanavalin A-induced hepatitis, lipopolysaccharide-induced endotoxemia, collagen-induced arthritis, and MOG35-55-induced encephalomyelitis). In addition, compound 17 showed a favorable pharmacokinetic profile after intraperitoneal administration; it was characterized by a fast absorption from the peritoneal cavity and a relatively long terminal half-life in rats. It was found to penetrate brain barrier in mice. The performed experiments sheds light on the impact of PDE7A inhibition for the efficacy of PDE4 inhibitors in these disease conditions.

Directed solid-phase synthesis of trisubstituted imidazo[4,5-c]pyridines and imidazo[4,5-b]pyridines.

An efficient method is described for the solid-supported synthesis of imidazo[4,5-b]pyridines and imidazo[4,5-c]pyridines from 2,4-dichloro-3-nitropyridine. The key pyridine building block was reacted with polymer-supported amines, followed by replacement of the second chlorine with amines, nitro group reduction, and imidazole ring closure with aldehydes. Depending on the combination of polymer-supported and solution-phase reagents, the strategy allowed for the simple preparation of the target trisubstituted derivatives with variable positioning of the pyridine nitrogen atom. Additionally, after a slight modification of the method, the preparation of strictly isomeric imidazopyridines was possible.

Discovery of Disubstituted Imidazo[4,5-b]pyridines and Purines as Potent TrkA Inhibitors.

Trk receptor tyrosine kinases have been implicated in cancer and pain. A crystal structure of TrkA with AZ-23 (1a) was obtained, and scaffold hopping resulted in two 5/6-bicyclic series comprising either imidazo[4,5-b]pyridines or purines. Further optimization of these two fusion series led to compounds with subnanomolar potencies against TrkA kinase in cellular assays. Antitumor effects in a TrkA-driven mouse allograft model were demonstrated with compounds 2d and 3a.