Synthesis of carbohydrazides and carboxamides as anti-tubercular agents

Tackling Nontuberculous Mycobacteria by Repurposable Drugs and Potential Leads from Natural Products

Nontuberculous Mycobacteria (NTM) refer to bacteria other than all Mycobacterium species that do not cause tuberculosis or leprosy, excluding the species of the Mycobacterium tuberculosis complex, M. leprae and M. lepromatosis. NTM are ubiquitous and present in soils and natural waters. NTM can survive in a wide range of environmental conditions. The direct inoculum of the NTM from water or other materials is most likely a source of infections. NTMs are responsible for several illnesses, including pulmonary alveolar proteinosis, cystic fibrosis, bronchiectasis, chronic obstructive pneumoconiosis, and pulmonary disease. Recent reports suggest that NTM species have become insensitive to sterilizing agents, antiseptics, and disinfectants. The efficacy of existing anti-NTM regimens is diminishing and has been compromised due to drug resistance. New and recurring cases of multidrug-resistant NTM strains are increasing. Thus, there is an urgent need for ant-NTM regimens with novel modes of action. This review sheds light on the mode of antimicrobial resistance in the NTM species. Then, we discussed the repurposable drugs (antibiotics) that have shown new indications (activity against NTM strains) that could be developed for treating NTM infections. Also, we have summarised recently identified natural leads acting against NTM, which have the potential for treating NTM-associated infections.

Targeting Mycobacterium tuberculosis iron-scavenging tools: a recent update on siderophores inhibitors

Among the various bacterial infections, tuberculosis (TB) remains a life-threatening infectious disease responsible as the most significant cause of mortality and morbidity worldwide. The co-infection of human immunodeficiency virus (HIV) in association with TB burdens the healthcare system substantially. Notably, M.tb possesses defence against most antitubercular antibiotic drugs, and the efficacy of existing frontline anti-TB drugs is waning. Also, new and recurring cases of TB from resistant bacteria such as multidrug-resistant TB (MDR), extensively drug-resistant TB (XDR), and totally drug-resistant TB (TDR) strains are increasing. Hence, TB begs the scientific community to explore the new therapeutic class of compounds with their novel mechanism. M.tb requires iron from host cells to sustain, grow, and carry out several biological processes. M.tb has developed strategic methods of acquiring iron from the surrounding environment. In this communication, we discuss an overview of M.tb iron-scavenging tools. Also, we have summarized recently identified MbtA and MbtI inhibitors, which prevent M.tb from scavenging iron. These iron-scavenging tool inhibitors have the potential to be developed as anti-TB agents/drugs.

Targeting mycobacterial membranes and membrane proteins: Progress and limitations

Among the various bacterial infections, tuberculosis continues to hold center stage. Its causative agent, Mycobacterium tuberculosis, possesses robust defense mechanisms against most front-line antibiotic drugs and host responses due to their complex cell membranes with unique lipid molecules. It is now well-established that bacteria change their membrane composition to optimize their environment to survive and elude drug action. Thus targeting membrane or membrane components is a promising avenue for exploiting the chemical space focussed on developing novel membrane-centric anti-bacterial small molecules. These approaches are more effective, non-toxic, and can attenuate resistance phenotype. We present the relevance of targeting the mycobacterial membrane as a practical therapeutic approach. The review highlights the direct and indirect targeting of membrane structure and function. Direct membrane targeting agents cause perturbation in the membrane potential and can cause leakage of the cytoplasmic contents. In contrast, indirect membrane targeting agents disrupt the function of membrane-associated proteins involved in cell wall biosynthesis or energy production. We discuss the chronological chemical improvements in various scaffolds targeting specific membrane-associated protein targets, their clinical evaluation, and up-to-date account of their ''mechanisms of action, potency, selectivity'' and limitations. The sources of anti-TB drugs/inhibitors discussed in this work have emerged from target-based identification, cell-based phenotypic screening, drug repurposing, and natural products. We believe this review will inspire the exploration of uncharted chemical space for informing the development of new scaffolds that can inhibit novel mycobacterial membrane targets.

Design and synthesis of new indanol-1,2,3-triazole derivatives as potent antitubercular and antimicrobial agents

In a search of new antitubercular agents, herein we have reported a series of new thirty-two indanol-1,2,3-triazole derivatives. The synthesized compounds were screened for their in vitro antitubercular and antimicrobial activities. Among the screened compounds, most of the compounds have displayed good antitubercular activity against Mycobacterium tuberculosis H37Rv. The compound 5g has been identified as potent antitubercular agent with MIC value 1.56 µM. The most active compounds of the series were further studied for their cytotoxicity against HEK 293 cells using MTT assay and found to be nontoxic. In addition, ten compounds were shown good antimicrobial activities against both antibacterial and antifungal pathogens. A molecular docking study against Mycobacterial enoyl-ACP-reductase (InhA) was performed to gain an insight into the molecular mechanism of antitubercular action. The pharmacokinetic parameters of these compounds were studied and displayed acceptable drug-likeness score.

Repurposed drug candidates for antituberculosis therapy

Antibiotics have been a key part of clinical treatments for more than 70 years. Long-term use of antimicrobial treatments has led to the development of severe bacterial resistance, which has become increasingly serious due to antibiotic abuse, resulting in the treatment of bacterial infections becoming challenging. The repurposing of approved drugs presents a promising strategy to address current bottlenecks in the development of novel antibacterial agents. Drug repurposing is a cost-effective emerging strategy, which aims to treat resistant infectious diseases by identifying known drugs with predicted efficacy for diseases other than the target disease. This strategy has potential in the treatment of tuberculosis (TB), particularly drug-resistant TB. In recent years, a panel of drugs approved for clinical use or clinical trials, such as linezolid, vancomycin and celecoxib, have been found to have anti-TB activities. However, the utility of drug repurposing is limited by the number of candidate compounds and their low activities. The low activities of repurposed drugs have slowed the development of a drug-repurposing strategy for anti-TB drugs. The present review discusses progress in the discovery of new anti-TB agents through drug repurposing since 2014. We also discuss the challenges faced and analyze the innovative ways that are being used to overcome these difficulties. This review may provide a useful guide for researchers in the field of drug repurposing.

Synthesis and amide imidic prototropic tautomerization in thiophene-2-carbohydrazide: XRD, DFT/HSA-computation, DNA-docking, TG and isoconversional kinetics via FWO and KAS models

Thiophene-2-carbohydrazide as a novel small-molecule amide tautomer has been synthesized with an acceptable yield under microwave radiation (MW) conditions. The amide imidic thiophene-2-carbohydrazide prototropic tautomerization via single proton intramigration was computed using the DFT B3LYP/6-311G(d,p) level of theory. The endo-isomer amide structure of thiophene-2-carbohydrazide was proved by XRD and is considered to be the kinetically favored isomer. The DFT-structure parameters were compared to their corresponding XRD-experimental parameters. Several H-bond interactions were detected in the crystal lattice experimentally using the XRD-packing model then correlated to MEP and HSA calculations. The manual and calculated electronic parameters such as, frontier molecular orbital energies, excitation energy, absorption, dipole moment, DOS, GRD quantum parameters and TD-SCF/B3LYP were DFT computed. The thiophene-2-carbohydrazide isomers together with their prototropic (E)/(Z)-thiophene-2-carbohydrazonic acid tautomers were docked against 1BNA DNA. FWO and KAS isoconversional kinetic methods were applied, and the thermal behavior and estimated E_a–α relations were determined.

Thiophene-2-carbohydrazide as a novel small-molecule amide tautomer has been synthesized with an acceptable yield under microwave radiation (MW) conditions.

Discovery of hydrazone containing thiadiazoles as Mycobacterium tuberculosis growth and enoyl acyl carrier protein reductase (InhA) inhibitors

Tuberculosis, caused by Mycobacterium tuberculosis, is a serious infectious disease and remains a global health problem. There is an increasing need for the discovery of novel therapeutic agents for its treatment due to the emerging multi-drug resistance. Herein, we present the rational design and the synthesis of eighteen new thiadiazolylhidrazones (TDHs) which were synthesized by intramolecular oxidative N-S bond formation reaction of 2-benzylidene-N-(phenylcarbamothioyl)hydrazine-1-carboximidamide derivatives by phenyliodine(III) bis(trifluoroacetate) (PIFA) under mild conditions. The compounds were characterized by various spectral techniques including FTIR, ¹H NMR, ¹³C NMR and HRMS. Furthermore, the proposed structure of TDH12 was resolved by single-crystal X-ray analysis. The compounds were evaluated for their in vitro antitubercular activity against M. tuberculosis H37Rv. Among them, some compounds exhibited remarkable antimycobacterial activity, MIC = 0.78-6.25 μg/mL, with low cytotoxicity. Additionally, the most active compounds were screened for their biological activities against M. tuberculosis in the nutrient starvation model. Enzyme inhibition assays and molecular docking studies revealed enoyl acyl carrier protein reductase (InhA) as the possible target enzyme of the compounds to show their antitubercular activities.