N-(2-Phenoxy)ethyl imidazo[1,2-a]pyridine-3-carboxamides containing various amine moieties: Design, synthesis and antitubercular activity

Design, synthesis and biological evaluation of phenanthridine amide and 1,2,3-triazole analogues against Mycobacterium tuberculosis

The phenanthridine core exhibits antitubercular activity, according to reports from the literature. Several 1,2,3-triazole-based heterocyclic compounds are well-known antitubercular agents. A series of twenty-five phenanthridine amide and 1,2,3-triazole derivatives are synthesized and analyzed using ESI-MS, 1HNMR, and 13CNMR on the basis of our earlier findings that phenanthridine and 1,2,3-triazoles shown good antitubercular activity. The synthesized phenanthridine amide and 1,2,3-triazole analogues were tested in vitro against Mycobacterium tuberculosis H37Rv and minimum inhibitory concentration (MIC) values were determined utilizing non-replicating and replicating low-oxygen recovery assay (LORA) and microplate Alamar Blue assay (MABA) methodologies. The phenanthridine amide derivative PA-01 had an MIC of 61.31 μM in MABA and 62.09 μM in the LORA technique, showing intense anti-TB activity. Amongst the phenanthridine triazole derivatives, PT-09, with MICs of 41.47 and 78.75 μM against the tested strain of Mtb in both MABA and LORA was the most active one. The final analogues' drug-likeness is predicted using absorption, distribution, metabolism, excretion, and toxicity (ADMET) studies. The most active compounds PA-01 and PT-09 were further subjected to in silico docking studies. Using the Glide module of Schrodinger, molecular docking analysis was carried out to estimate the plausible binding pattern of PA-01 and PT-09 at the active site of Mycobacterial DNA topoisomerase II (PDB code: 5BS8). Further, molecular dynamics studies of PA-01 and PT-09 were also carried out.

Synthesis and biological evaluation of esculetin derivatives as potential anti-HBV agents

Previous in vivo and in vitro studies revealed that esculetin (Fig. 1) has anti-hepatitis B virus (anti-HBV) activity as well as a protective effect on liver damage caused by duck hepatitis B virus. We designed and synthesized a series of esculetin derivatives, introduced side chains containing various amino groups into site 7 of the parent structure, and synthesized C-4 and C-8 substituted derivatives with the goal of investigating their anti-HBV activities. In vitro anti-HBV activity was performed against HepG2.2.15 cells by using Enzyme-Linked Immunosorbent Assay(ELISA) kit and cytotoxicity was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay with lamivudine as the positive control. The results demonstrated that several compounds showed moderate anti-HBV activity, while the introduction of morpholine groups could significantly inhibit the expression of hepatitis B e antigen (HBeAg) and the introduction of the 2-methylimidazole group could significantly inhibit the expression of Hepatitis B surface antigen (HBsAg). Among all tested compounds, compound 4a demonstrated the best anti-HBeAg activity (IC₅₀ = 15.8 ± 4.2 μM), while compound 6d demonstrated the best anti-HBsAg activity (IC₅₀ = 21.4 ± 2.8 μM). Compounds 6b and 6c showed moderate anti-HBV activity and HBsAg inhibition. Compounds 4b showed moderate anti-HBV activity and an inhibitory effect on HBeAg. In addition, compounds 4a, 4c, 4d, 6b, 6c and 6d showed improved metabolic stability. This study provides useful guidance for the discovery of anti-HBV drugs, which merits further investigation.

On drug discovery against infectious diseases and academic medicinal chemistry contributions

This perspective is an attempt to document the problems that medicinal chemists are facing in drug discovery. It is also trying to identify relevant/possible, research areas in which academics can have an impact and should thus be the subject of grant calls. Accordingly, it describes how hit discovery happens, how compounds to be screened are selected from available chemicals and the possible reasons for the recurrent paucity of useful/exploitable results reported. This is followed by the successful hit to lead stories leading to recent and original antibacterials which are, or about to be, used in human medicine. Then, illustrated considerations and suggestions are made on the possible inputs of academic medicinal chemists. This starts with the observation that discovering a "good" hit in the course of a screening campaign still rely on a lot of luck - which is within the reach of academics -, that the hit to lead process requires a lot of chemistry and that if public-private partnerships can be important throughout these stages, they are absolute requirements for clinical trials. Concerning suggestions to improve the current hit success rate, one academic input in organic chemistry would be to identify new and pertinent chemical space, design synthetic accesses to reach these and prepare the corresponding chemical libraries. Concerning hit to lead programs on a given target, if no new hits are available, previously reported leads along with new structural data can be pertinent starting points to design, prepare and assay original analogues. In conclusion, this text is an actual plea illustrating that, in many countries, academic research in medicinal chemistry should be more funded, especially in the therapeutic area neglected by the industry. At the least, such funds would provide the intensive to secure series of hopefully relevant chemical entities which appears to often lack when considering the results of academic as well as industrial screening campaigns.

Design, synthesis and anti-mycobacterial evaluation of imidazo[1,2-a]pyridine analogues

Based on the molecular hybridization strategy, thirty-four imidazo[1,2-a]pyridine amides (IPAs) and imidazo[1,2-a]pyridine sulfonamides (IPSs) were designed and synthesized. The structures of the target compounds were characterized using ¹H NMR, ¹³C NMR, LCMS, and elemental analyses. The synthesized compounds were evaluated in vitro for anti-tubercular activity using the microplate Alamar Blue assay against Mycobacterium tuberculosis H37Rv strain and the MIC was determined. The evaluated compounds exhibited MIC in the range 0.05-≤100 μg mL^-1. Among these derivatives, IPA-6 (MIC 0.05 μg mL^-1), IPA-9 (MIC 0.4 μg mL^-1), and IPS-1 (MIC 0.4 μg mL^-1) displayed excellent anti-TB activity, whereas compounds IPA-5, IPA-7 and IPS-16 showed good anti-TB activity (MIC 0.8-3.12 μg mL^-1). The most active compounds with MIC of <3.125 μg mL^-1 were screened against human embryonic kidney cells to check their cytotoxicity to normal cells. It was observed that these compounds were nontoxic (SI value ≥66). The ADMET characteristics of the final compounds were also predicted in silico. Further, using the Glide module of Schrodinger software, a molecular docking study of IPA-6 was carried out to estimate the binding pattern at the active site of enoyl acyl carrier protein reductase from Mycobacterium tuberculosis (PDB 4TZK). Finally, molecular dynamics simulations were performed for 100 ns to elucidate the stability, conformation, and intermolecular interactions of the co-crystal ligand and significantly active compound IPA-6 on the selected target protein. IPA-6, the most active compound, was found to be 125 times more potent than the standard drug ethambutol (MIC 6.25 μg mL^-1).

Design, synthesis and biological evaluation of nitrofuran-1,3,4-oxadiazole hybrids as new antitubercular agents

Three series of novel nitrofuran-1,3,4-oxadiazole hybrids were designed and synthesized as new anti-TB agents. The structure activity relationship study indicated that the linkers and the substituents on the oxadiazole moiety greatly influence the activity, and the substituted benzenes are more favoured than the cycloalkyl or heterocyclic groups. Besides, the optimal compound in series 2 was active against both MTB H₃₇Rv strain and MDR-MTB 16883 clinical isolate and also displayed low cytotoxicity, low inhibition of hERG and good oral PK, indicating its promising potential to be a lead for further structural modifications.

Design, synthesis and biological activity of N-(amino)piperazine-containing benzothiazinones against Mycobacterium tuberculosis

A series of novel benzothiazinone derivatives containing a N-(amino)piperazine moiety, based on the structure of WAP-1902 discovered in our lab, were designed and synthesized as new anti-TB agents. Many of the compounds exhibited excellent in vitro activity against both drug-sensitive MTB strain H37Rv and multidrug-resistant clinical isolates (MIC: < 0.016 μg/mL), and good safety index (CC₅₀: >64 μg/mL). Especially compound 1o displayed low hERG cardiac toxicity and acceptable oral pharmacokinetic profiles, indicating its promising potential to be a lead compound for future antitubercular drug discovery.

Design, synthesis and biological evaluation of novel 1,2,3-triazole analogues of Imidazo-[1,2-a]-pyridine-3-carboxamide against Mycobacterium tuberculosis

Twenty-eight novel 1,2,3-triazole analogues of imidazo-[1,2-a]-pyridine-3-carboxamide were designed and synthesized based on hybridization approach. The structure of the final compounds are characterized using ¹HNMR, ¹³CNMR, LCMS and elemental analyses and are screened in vitro for anti-tubercular activity using low-oxygen recovery assay (LORA) non-replicating and using microplate alamar blue assay (MABA) against replicating M. tuberculosis. MIC was determined. From the obtained results, it was observed that, among (2,7-dimethylimidazo[1,2-a]pyridin-3-yl)(4-((1-subtituted phenyl-1H-1,2,3-triazol-4-yl)methyl)piperazin-1-yl)methanones and (6-chloro-2-methylimidazo[1,2-a]pyridin-3-yl)(4-((1-substituted phenyl-1H-1,2,3-triazol-4-yl)methyl)piperazin-1-yl)methanones, compounds with substitution at para position with electron electron releasing groups exhibited the best activity (< 34 μg/mL). Amidst, (2,7-dimethylimidazo[1,2-a]pyridin-3-yl)(4-(2-(4-alkyl/substituted aryl-1H-1,2,3-triazol-1-yl)ethyl)piperazin-1-yl)methanones and (6-chloro-2-methylimidazo[1,2-a]pyridin-3-yl)(4-(2-(4- alkyl/substituted aryl -1H-1,2,3-triazol-1-yl)ethyl)piperazin-1-yl)methanones, compounds with long alkyl chain or cyclo propyl group were most active (< 21 μg/mL) in MABA method against the tested strain of MTB. Compound 10b emerged to be the most active compound in MABA and LORA with MIC values 13.74 and 24.63 μg/mL respectively. In-silico ADMET parameters were also predicted for the significantly active compound. Finally, molecular docking study was carried out to predict the feasible binding pattern of the most active compound at the active site of enoyl acyl carrier protein reductase from Mycobacterium tuberculosis (PDB-4TZK) using Glide module of Schrodinger software.

Telacebec (Q203): Is there a novel effective and safe anti-tuberculosis drug on the horizon?

High prevalence and stronger emergency of various forms of drug-resistant tuberculosis (DR-TB), including the multidrug-resistant (MDR-TB) as well as extensively drug-resistant (XDR-TB) ones, caused by variously resistant Mycobacterium tuberculosis pathogens, make first-line anti-tuberculosis (anti-TB) agents therapeutically more and more ineffective. Therefore, there is an imperative to develop novel highly efficient (synthetic) agents against both drug-sensitive-TB and DR-TB. The exploration of various heterocycles as prospective core scaffolds for the discovery, development and optimization of anti-TB drugs remains an intriguing scientific endeavour. Telacebec (Q203; TCB), a molecule containing an imidazo[1,2-a]pyridine-3-carboxamide (IPA) structural motif, is considered a novel very promising anti-TB agent showing a unique mechanism of action. The compound blocks oxidative phosphorylation by inhibiting a mycobacterial respiratory chain due to interference with a specific cytochrome b subunit (QcrB) of transmembrane bc1 menaquinol-cytochrome c oxidoreductase as an essential component for transporting electrons across the membrane from menaquinol to other specific subunit, cytochrome c (QcrC). Thus, the ability of mycobacteria to synthesize adenosine-5´-triphosphate is limited and energy generating machinery is disabled. The TCB molecule effectively fights drug-susceptible, MDR as well as XDR M. tuberculosis strains. The article briefly explains a mechanism of an anti-TB action related to the compounds containing a variously substituted IPA scaffold and is focused on their fundamental structure-anti-TB activity relationships as well. Special consideration is paid to TCB indicating the importance of particular structural fragments for maintaining (or even improving) favourable pharmacodynamic, pharmacokinetic and/or toxicological properties. High lipophilicity of TCB might be regarded as one of the key physicochemical properties with positive impact on anti-TB effect of the drug. In January 2021, the TCB molecule was also involved in phase-II clinical trials focused on the treatment of Coronavirus Disease-19 caused by Severe Acute Respiratory Syndrome Coronavirus 2.