Potential Antituberculosis Agents Research Articles

Synthesis, In silico and In vitro Analysis of Hydrazones as Potential Antituberculosis Agents

Synthesis, In silico and In vitro Analysis of Hydrazones as Potential Antituberculosis Agents

A Simple Work-Up-free, Solvent-free Approach to Novel Amino Acid Linked 1,4-Disubstituted 1,2,3-Triazoles as Potent Antituberculosis Agents.

An efficient, green strategy for synthesis of 1,4-disubstituted-1,2,3-triazole has been developed using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) acetate ionic liquid (200 μL) under a solvent- and external base-free condition. This protocol is further applied for the synthesis of novel amino acid containing 1,2,3-triazole molecules, which were then evaluated for potential antitubercular and antibacterial activities. Cytotoxicity assay of the compounds was also performed. In silico analysis of the promising compounds selected through experimental analysis was thereafter performed for visualizing molecular interactions and predicting binding affinities between our synthesized molecules, which exhibited good activity in experimental studies and the DprE1 target protein of Mycobacterium tuberculosis. Durg-likeness studies also show potential of the synthesized molecules as drug candidates.

P.296 Interhemispheric imbalance of motor cortex excitability in affective disorders – a systematic review and meta-analysis

Tuberculosis (TB) is of one the most infectious disease caused by Mycobacterium tuberculosis which remains a serious public health problem. Emergence of multi-drug resistant strains of M. tuberculosis led to development of new and more potent anti-tuberculosis agents. The aim of this study was to correlate the chemical structures of the inhibitory compounds with their experimental activities. In this study, analogs of 2,4-disubstituted quinoline derivatives as potent anti-tubercular agents was subjected to quantitative structure–activity relationship (QSAR) analysis in order to build a QSAR model for predicting the activities of these compounds. In order to build the regression model, Genetic Function Approximation (GFA) and Multi-linear Regression approach were used to predict the activities of inhibitory compounds. Based on the prediction, the best validation model was found to have squared correlation coefficient (R2) of 0.9367, adjusted squared correlation coefficient (R2 adj) value of 0.9223 and cross validation coefficient (Qcv2) value of 0.8752. The chosen model was subjected to external validations and the model was found to have (R2 test) of 0.8215 and Y-randomization Coefficient (cRp2) of 0.6633. The proposed QSAR model provides a valuable approach for designing more potent anti-tubercular agents.

Synthesis, Spectroscopic, In-vitro and Computational Analysis of Hydrazones as Potential Antituberculosis Agents: (Part-I).

Since the last few decades, the healthcare sector is facing the problem of the development of multidrug-resistant (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) infections all over the world. Regardless of the current healthcare progress for the treatment of mycobacterial infections, we are still unable to control addition of every year 9 million new cases of tuberculosis (TB). We had an objective to synthesize some novel hydrazones, which were further subjected to characterization, Photoluminescence study, in vitro anti-mycobacterium testing and in silico ADMET predictions. Some new hydrazone derivatives have been successfully prepared by the condensation reaction in the present study. All the compounds were characterized by using FTIR, NMR, UV, Fluorescence spectroscopic techniques. All our newly synthesized compounds showed strong electronic excitation at 292.6 - 319.0 nm and displayed more intense emissions in the 348 - 365 nm regions except compound 3i. The newly synthesized hydrazones 3a, 3b, 3f and 3g were found to be the most active compounds and showed MIC (Minimum inhibitory concentrations) values of 12.5 μg/mL. In the realm of development of more potent, effective, safer and less toxic antituberculosis agents; our current study would definitely help the medicinal chemists to develop potent analogues containing hydrazine motifs in them.

Backbone resonance assignment and dynamics of 110 kDa hexameric inorganic pyrophosphatase from Mycobacterium tuberculosis.

Family I soluble inorganic pyrophosphatases (PPases; EC 3.6.1.1) are enzymes essential for all organisms. They hydrolyze inorganic pyrophosphate, thus providing the driving force for numerous biosynthetic reactions. Soluble PPases retain enzymatic activity only in multimeric forms. PPases from various organisms are extensively studied by X-ray crystallography but until now there was no information on their structure and dynamics in solution. Hexameric 110 kDa (6×18.3 kDa) PPase from Mycobacterium tuberculosis (Mt-PPase) is a promising target for the rational design of potential anti-tuberculosis agents. In order to use NMR techniques in functional studies of Mt-PPase and rational design of the inhibitors for this enzyme, it is necessary to have information on the backbone 1H, 13C and 15N resonance assignments. Samples of Mt-PPase enriched with 99% of 13C and 15N isotopes, and 95% of 2H were obtained using recombinant protein expression in an isotopically-labeled medium and effective heat-shock protocol for the deuterium-to-hydrogen exchange of the amide groups. Backbone resonance assignment was achieved for more than 95% of the residues. It was found that the secondary structure of Mt-PPase in solution corresponds well to the crystal structure of this protein. Protein backbone dynamics were studied using 15N NMR relaxation experiments. Determined resonance assignments and dynamic properties provide the basis for the subsequent structure-based design of novel inhibitors of Mt-PPase-potential anti-tuberculosis drugs.

Synthesis and molecular docking study of 6-chloropyrazine-2-carboxylic acid derivatives

One of the most lethal and frequent infectious diseases worldwide is tuberculosis. Multi and extensively tuberculosis drug-resistant constitutes a serious problem and emphasizes the need for novel anti-tubercular agents. Accordingly, various pyrazine-2-carboxamides were synthesized and evaluated as potential anti-tuberculosis agents. The synthesis involved reaction of pyrazinoic acids with thionyl chloride to yield acyl chlorides which on treatment with various anilines gave various pyrazine-2-carboxamides. Based on structure-activity relationships extracted from previously published, this paper reported the synthesis and molecular docking study of 6-chloropyrazine-2-carboxamides. Synthesis involved reaction of 6-chloropyrazinoic acid with 2,4,6-trichlorobenzoyl chloride instead of thionyl chloride which listed under the Chemical Weapons Convention as it may use for the production of chemical weapons. Structure identification of 6-chloropyrazine-2-carboxamides was carried out by 1H NMR, 13C NMR, FTIR, and high-resolution mass spectroscopy. It is predicted that 6-chloro-N-octylpyrazine-2-carboxamide has better bioactivity against Mycobacterium tuberculosis, based on molecular docking study.

Synthesis, In silico and In vitro Analysis of Hydrazones as Potential Antituberculosis Agents

The objective of our current study is to design and synthesise more potent hydrazide- hydrazones, containing anti-tubercular agents. In the current study, we synthesized 10 hydrazones (3a-3j) by stirring corresponding benzohydrazides (2) with substituted aldehydes (1a-j) in ethanol as a solvent and acetic acid as a catalyst at room temperature. All synthesized compounds were characterized by various spectroscopic techniques including elemental analysis, ultraviolet-visible spectroscopy, fluorescence, fourier- transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. Compounds (3a-3j) were tested for in vitro anti-TB activity using Microplate Alamar Blue Assay (MABA). All our synthesized compounds (3a-3j) were found to be potent against Mycobacteria tuberculosis (H37RV strain) with MIC (minimum inhibitory concentrations) values of 3.125-50 μg/mL. The hydrazide CO-NH protons in (3a-j) compounds are highly deshielded and showed broad singlet at 9.520-9.168 ppm. All the compounds were found to have more intense emission in the 416 - 429 nm regions and strong absorption in the regions of 316 - 327 nm. Synthesized compounds were also tested for in silico analysis using different software for their Absorption, Distribution, Metabolism, Excretion and Toxicity (ADMET) analysis. All the compounds were found to be in silico non-carcinogenic. It will be worth saying that our in silico and in vitro approaches used in the current study will become a guide for medicinal chemists to make structural modifications and synthesize more effective and potent hydrazone containing anti-tubercular agents.

Protein kinases as antituberculosis targets: The case of thymidylate kinases.

This review is a concise summary of studies involving the design, synthesis and characterization of potential inhibitors against thymidylate kinase of Mycobacterium tuberculosis. Tuberculosis inspite of being an ancient disease still continues to be a leading cause of death in the world. The increasing emergence of drug resistant Mycobacterium tuberculosis is one of the challenges in the complete elimination of tuberculosis. Thus, there is an undeniable need to develop novel treatment strategies to combat this deadly pathogen. Several protein targets are being investigated in Mycobacterium tuberculosis with an aim to develop the most potent and selective antituberculosis agents. It is not surprising that protein kinases, the key regulators of metabolism in almost all organisms are one of the major targets explored in antituberculosis drug discovery. Thymidylate kinases, a well established antiviral and anticancer target has garnered significant attention in the past twenty years in the development of prospective antituberculosis agents. A comprehensive analysis of such studies will provide a better understanding on the druggability of thymidylate kinase and also, will enable to refine the future drug designing studies on this attractive drug target of Mycobacterium tuberculosis.

Discovery of New and Potent InhA Inhibitors as Antituberculosis Agents: Structure-Based Virtual Screening Validated by Biological Assays and X-ray Crystallography.

The enoyl-acyl carrier protein reductase InhA of Mycobacterium tuberculosis is an attractive, validated target for antituberculosis drug development. Moreover, direct inhibitors of InhA remain effective against InhA variants with mutations associated with isoniazid resistance, offering the potential for activity against MDR isolates. Here, structure-based virtual screening supported by biological assays was applied to identify novel InhA inhibitors as potential antituberculosis agents. High-speed Glide SP docking was initially performed against two conformations of InhA differing in the orientation of the active site Tyr158. The resulting hits were filtered for drug-likeness based on Lipinski's rule and avoidance of PAINS-like properties and finally subjected to Glide XP docking to improve accuracy. Sixteen compounds were identified and selected for in vitro biological assays, of which two (compounds 1 and 7) showed MIC of 12.5 and 25 μg/mL against M. tuberculosis H37Rv, respectively. Inhibition assays against purified recombinant InhA determined IC50 values for these compounds of 0.38 and 0.22 μM, respectively. A crystal structure of the most potent compound, compound 7, bound to InhA revealed the inhibitor to occupy a hydrophobic pocket implicated in binding the aliphatic portions of InhA substrates but distant from the NADH cofactor, i.e., in a site distinct from those occupied by the great majority of known InhA inhibitors. This compound provides an attractive starting template for ligand optimization aimed at discovery of new and effective compounds against M. tuberculosis that act by targeting InhA.

Refined homology model of cytochrome bcc complex B subunit for virtual screening of potential anti-tuberculosis agents

Cytochrome bcc complex is important for ATP synthesis and cellular activity, as a crucial step in the terminal reduction of oxygen in aerobic electron transport chains. The b subunit of cytochrome bcc complex (QcrB) has been reported as a promising anti-tuberculosis target, with many novel anti-tuberculosis scaffolds reported. However, the 3D structure of mycobacterium tuberculosis (M. tuberculosis) QcrB has not been released, making it hard to understand the interactions between QcrB and its inhibitors as well as to develop novel anti-tuberculosis scaffolds. Herein we built the optimal homology model of M. tuberculosis QcrB using the M. smegmatis QcrB structure as template, which was refined through all-atom molecular dynamics simulation. Then, the binding modes of known inhibitors were predicted through molecular docking method, along with molecular dynamics simulation and binding free energy calculation to verify the accuracy of docking results and stability of the protein-inhibitor complexes. The informative key residues within QcrB site enabled us to perform structure-based virtual library screening to obtain potential M. tuberculosis QcrB inhibitors, which were validated through molecular dynamics simulation and MM-GBSA calculation and analyzed through pharmacokinetic properties prediction. Our research would provide a deeper insight into the interactions between M. tuberculosis QcrB and its inhibitors, which boosts to develop novel therapy against tuberculosis.Communicated by Ramaswamy H. Sarma

Exploration of 5-(5-nitrothiophen-2-yl)-4,5-dihydro-1H-pyrazoles as selective, multitargeted antimycobacterial agents.

We report the biological evaluation of 5-(5-nitrothiophen-2-yl)-4,5-dihydro-1H-pyrazole derivatives against bacteria, eukaryotic cell lines and the assessment of their mechanisms of action to determine their prospects of being developed into potent antituberculosis agents. The compounds were evaluated for their antibacterial property against Mycobacterium tuberculosis H37Rv, multidrug-resistant M.tuberculosis, Mycobacterium bovis BCG, Mycobacteriumaurum, Escherichia coli, and Staphylococcus aureus using high-throughput spot-culture growth inhibition assay. They were found to be selective toward slow-growing mycobacteria and Gram-positive bacteria. In M.bovis BCG, they exhibited a bactericidal mode of action. Cytotoxicity was assessed in human THP-1 and murine RAW 264.7 cell lines, and the compounds showed a lower cytotoxicity potential whencompared with their antibacterial activity. They were found to be excellent whole-cell efflux pump inhibitors of the mycobacterial surrogate M.aurum, performing better than known efflux pump inhibitor verapamil. The 5-nitrothiophene moiety was identified for the first time as a prospective inhibitor scaffold of mycobacterial arylamine N-acetyltransferase enzyme, which is the key enzyme in metabolizing isoniazid, a first-line antituberculosis drug. The two aforementioned findings make the compounds potential hits in the development of adjunctive tuberculosis therapy.

Hydrazone, benzohydrazones and isoniazid-acylhydrazones as potential antituberculosis agents.

Aim: To evaluate the potential of three benzohydrazones (1-3), four acylhydrazones derived from isoniazid (INH-acylhydrazones) (4-7) and one hydrazone (8) as antituberculosis agents.Materials & methods: Inhibitory and bactericidal activities were determined for the reference Mycobacterium tuberculosis (Mtb) strain and clinical isolates. Cytotoxicity, drug combinations and ethidium bromide accumulation assays were also performed. Results: The tested compounds (1-8) presented excellent antituberculosis activity with surprisingly inhibitory (0.12-250μg/ml) and bactericidal values, even against multidrug-resistant Mtb clinical isolates. Compounds showed high selectivity index, with values reaching 1833.33, and a limited spectrum of activity. Some of the compounds (2 & 8) are also great inhibitors of bacillus efflux pumps. Conclusion: Benzohydrazones and INH-acylhydrazones may be considered scaffolds for the development of new anti-Mtb drugs.

The synthesis and evaluation of quinolinequinones as anti-mycobacterial agents

A library of thirty-two quinolinequinones (QQs) with various amine substituents at the 6- and 7-positions were synthesised efficiently and in good yields for evaluation as potential anti-tuberculosis agents. Mycobacterium tuberculosis growth inhibition assays demonstrated that QQs bearing moderate length alkyl chains (i.e. heptylphenylamino- and octylamino-QQs), and aryl groups (i.e. phenylethylamino- and benzylamino-QQs) exhibited encouraging inhibitory activity, while QQ analogue 7-chloro-6-propargylamino-quinoline-5,8-dione (16b) had excellent inhibitory activity (MIC = 8 μM). The cLogP values and redox activities of the QQs were determined, and neither readout correlated with the anti-mycobacterial activities of the compounds. Notwithstanding, mode of action studies of 16b revealed that treatment of M. tuberculosis with this compound led to activation of NADH-dependent oxygen consumption suggesting a redox cycling mechanism. To this end, the promising anti-mycobacterial activity of several QQs and their ability to perturb oxygen management leading to an uncontrolled respiratory burst, as identified in this work and by others, demonstrates the merit of further optimising the anti-mycobacterial activity of this readily synthesised class of compound.

A Derived QSAR Model for Predicting Some Compounds as Potent Antagonist against Mycobacterium tuberculosis: A Theoretical Approach.

Development of more potent antituberculosis agents is as a result of emergence of multidrug resistant strains of M. tuberculosis. Novel compounds are usually synthesized by trial approach with a lot of errors, which is time consuming and expensive. QSAR is a theoretical approach, which has the potential to reduce the aforementioned problem in discovering new potent drugs against M. tuberculosis. This approach was employed to develop multivariate QSAR model to correlate the chemical structures of the 2,4-disubstituted quinoline analogues with their observed activities using a theoretical approach. In order to build the robust QSAR model, Genetic Function Approximation (GFA) was employed as a tool for selecting the best descriptors that could efficiently predict the activities of the inhibitory agents. The developed model was influenced by molecular descriptors: AATS5e, VR1_Dzs, SpMin7_Bhe, TDB9e, and RDF110s. The internal validation test for the derived model was found to have correlation coefficient (R2) of 0.9265, adjusted correlation coefficient (R2 adj) value of 0.9045, and leave-one-out cross-validation coefficient (Q_cv∧2) value of 0.8512, while the external validation test was found to have (R2 test) of 0.8034 and Y-randomization coefficient (cR_p∧2) of 0.6633. The proposed QSAR model provides a valuable approach for modification of the lead compound and design and synthesis of more potent antitubercular agents.

3,5-Dialkoxypyridine analogues of bedaquiline are potent antituberculosis agents with minimal inhibition of the hERG channel.

Bedaquiline is a new drug of the diarylquinoline class that has proven to be clinically effective against drug-resistant tuberculosis, but has a cardiac liability (prolongation of the QT interval) due to its potent inhibition of the cardiac potassium channel protein hERG. Bedaquiline is highly lipophilic and has an extremely long terminal half-life, so has the potential for more-than-desired accumulation in tissues during the relatively long treatment durations required to cure TB. The present work is part of a program that seeks to identify a diarylquinoline that is as potent as bedaquiline against Mycobacterium tuberculosis, with lower lipophilicity, higher clearance, and lower risk for QT prolongation. Previous work led to the identification of compounds with greatly-reduced lipophilicity compounds that retain good anti-tubercular activity in vitro and in mouse models of TB, but has not addressed the hERG blockade. We now present compounds where the C-unit naphthalene is replaced by a 3,5-dialkoxy-4-pyridyl, demonstrate more potent in vitro and in vivo anti-tubercular activity, with greatly attenuated hERG blockade. Two examples of this series are in preclinical development.

Geometrical and Topological Descriptors for Activities Modeling of some Potent Inhibitors against Mycobacterium Tuberculosis: A Genetic Functional Approach

Abstract: : Improvement on more potent anti-tuberculosis agents is as a result of emergence of multi-drug resistant strains of M. Tuberculosis. Syntheses of novel compounds are usually by trial approach with lots of errors which is time consuming and expensive. QSAR is a theoretical approach, which has the potential to reduce the aforementioned problem in discovering new potent drugs against M. Tuberculosis. This approach was employed to develop multivariate QSAR model to correlate the chemical structures of the 1,2,4-triazole analogues with their observed activities using a theoretical approach. In order to build the robust QSAR model, the best descriptors that could efficiently predict the activities of the inhibitory agents were selected by employing Genetic Function Approximation (GFA) as a modeling tool. Correlation coefficient (R2) of 0.9142, cross validation coefficient (Q_cv^2) value of 0.8324 and adjusted correlation coefficient (R2 adj) value of 0.8851 were the internal validation test conducted to access the derived model while (R2test) of 0.7495 and Y-randomization Coefficient (cR_p^2) of 0.7334 were the external validation tests to confirmed the robustness of the built model. The proposed QSAR model provides a valuable approach for modification of the lead compound, design and synthesizing of more potent anti-tubercular agents.

Pyrazole and imidazo[1,2-b]pyrazole Derivatives as New Potential Antituberculosis Agents.

We screened a large library of differently decorated imidazo-pyrazole and pyrazole derivatives as possible new antitubercular agents and this preliminary screening showed that many compounds are able to totally inhibit Mycobacterium growth (>90 %). Among the most active compounds, we selected some new possible hits based on their similarities and, at the same time, on their novelty with respect to the pipeline drugs. In order to increase the potency and obtain more information about structure-activity relationship (SAR), we designed and synthesized three new series of compounds (2a-e, 3a-e, and 4a-l). Performed tests confirmed that both new pyrazoles and imidazo-pyrazoles could represent a new starting point to obtain more potent compounds and further work is now underway to identify the protein targets of this new class of anti-TB agents.

Design, synthesis, and bioevaluation of a novel class of (E)-4-oxo-crotonamide derivatives as potent antituberculosis agents

A series of novel (E)-4-oxo-2-crotonamide derivatives were designed and synthesized to find potent antituberculosis agents. All the target compounds were evaluated for their in vitro activity against Mycobacterium tuberculosis H37Rv(MTB). Results reveal that 4-phenyl moiety at part A and short methyl group at part C were found to be favorable. Most of the derivatives displayed promising activity against MTB with MIC ranging from 0.125 to 4 µg/mL. Especially, compound IIIa16 was found to have the best activity with MIC of 0.125 μg/mL against MTB and with MIC in the range of 0.05–0.48 µg/mL against drug-resistant clinical MTB isolates.

Rational design of coumarin derivatives as antituberculosis agents.

A series of coumarin derivatives was designed as potential antituberculosis agents. The compounds were screened against active and dormant Mycobacterium tuberculosis (Mtb). Compounds 3k and 3n were found to have the most promising activity against replicating MtbH37Rv exhibiting minimum inhibitory concentration of 4.63 and 9.75μM respectively. The compounds were also effective against dormant MtbH37Rv exhibiting more potency than the standard drugs, isoniazid and rifampicin. The compounds were found to be non-cytotoxic against human cell lines. This study provides promising antituberculosis agents that are effective against replicating as well as dormant Mtb and can thus act as potential leads for further development.

Theoretical modeling for predicting the activities of some active compounds as potent inhibitors against Mycobacterium tuberculosis using GFA-MLR approach

Tuberculosis (TB) is of one the most infectious disease caused by Mycobacterium tuberculosis which remains a serious public health problem. Emergence of multi-drug resistant strains of M. tuberculosis led to development of new and more potent anti-tuberculosis agents. The aim of this study was to correlate the chemical structures of the inhibitory compounds with their experimental activities. In this study, analogs of 2,4-disubstituted quinoline derivatives as potent anti-tubercular agents was subjected to quantitative structure–activity relationship (QSAR) analysis in order to build a QSAR model for predicting the activities of these compounds. In order to build the regression model, Genetic Function Approximation (GFA) and Multi-linear Regression approach were used to predict the activities of inhibitory compounds. Based on the prediction, the best validation model was found to have squared correlation coefficient (R2) of 0.9367, adjusted squared correlation coefficient (R2 adj) value of 0.9223 and cross validation coefficient (Qcv2) value of 0.8752. The chosen model was subjected to external validations and the model was found to have (R2 test) of 0.8215 and Y-randomization Coefficient (cRp2) of 0.6633. The proposed QSAR model provides a valuable approach for designing more potent anti-tubercular agents.