2-Aryl-Benzoimidazoles as Type II NADH Dehydrogenase Inhibitors of Mycobacterium tuberculosis

The nonproton pumping type II NADH dehydrogenase in Mycobacterium tuberculosis is essential for meeting the energy needs in terms of ATP under normal aerobic and stressful hypoxic environmental states. Type II NADH dehydrogenase conduits electrons into the electron transport chain in Mycobacterium tuberculosis, which results in ATP synthesis. Therefore, the inhibition of NDH-2 ensures the abolishment of the entire ATP synthesis machinery. Also, type II NADH dehydrogenase is absent in the mammalian genome, thus making it a potential target for antituberculosis drug discovery. Herein, we have screened a commercially available library of drug-like molecules and have identified a hit having a benzimidazole core moiety (6, H37Rv mc26230; minimum inhibitory concentration (MIC) = 16 μg/mL and ATP IC50 = 0.23 μg/mL) interfering with the oxidative phosphorylation pathway. Extensive medicinal chemistry optimization resulted in analogue 8, with MIC = 4 μg/mL and ATP IC50 = 0.05 μg/mL against the H37Rv mc26230 strain of Mycobacterium tuberculosis. Compounds 6 and 8 were found to be active against mono- and multidrug-resistant mycobacterium strains and demonstrated a bactericidal response. The Peredox-mCherry experiment and identification of single-nucleotide polymorphisms in mutants of CBR-5992 (a known type II NADH dehydrogenase inhibitor) were used to confirm the molecules as inhibitors of the type II NADH dehydrogenase enzyme. The safety index >10 for the test active molecules revealed the safety of test molecules.

Development and Evaluation of Bis-benzothiazoles as a New Class of Benzothiazoles Targeting DprE1 as Antitubercular Agents

Benzothiazole-bearing compounds have emerged as potential noncovalent DprE1 (decaprenylphosphoryl-β-d-ribose-2'-epimerase) inhibitors active against Mycobacterium tuberculosis. Based on structure-based virtual screening (PDB ID: 4KW5), a focused library of thirty-one skeletally diverse benzothiazole amides was prepared, and the compounds were assessed for their antitubercular activity against M.tb H37Ra. Most potent compounds 3b and 3n were further evaluated against the M.tb H37Rv strain by the microdilution assay method. Among the compounds evaluated, bis-benzothiazole amide 3n emerged as a hit molecule and demonstrated promising antitubercular activity with minimum inhibitory concentration (MIC) values of 0.45 μg/mL and 8.0 μg/mL against H37Ra and H37Rv, respectively. Based on the preliminary hit molecule (3n), a focused library of 12 more bis-benzothiazole amide derivatives was further prepared by varying the substituents on either side to obtain new leads and generate a structure-activity relationship (SAR). Among these compounds, 6a, 6c, and 6d demonstrated remarkable antitubercular activity with MIC values of 0.5 μg/mL against H37Ra and 1.0, 2.0, and 8.0 μg/mL against H37Rv, respectively. The most active compound, 6a, also displayed significant efficacy against four drug-resistant tuberculosis strains. Compound 6a was assessed for in vitro cytotoxicity against the HepG2 cell line, and it displayed insignificant cytotoxicity. Furthermore, time-kill kinetic studies demonstrated time- and dose-dependent bactericidal activity of this compound. The GFP release assay revealed that compound 6a targets the inhibition of a cell wall component. SNPs in dprE-1 gene assessment revealed that compound 6a binds to tyrosine at position 314 of DprE1 and replaces it with histidine, causing resistance similar to that of standard TCA1. In silico docking studies further suggest that the strong noncovalent interactions of these compounds may lead to the development of potent noncovalent DprE1 inhibitors.

Access to Isoxazoles via Photo-oxygenation of Furan Tethered α-Azidoketones

Photocatalyst-free visible light-enabled direct oxygenation of furan-tethered α-azidoketones was studied. The reaction yielded various products depending on the substituents, with isoxazoles forming as the major products. The findings suggest that singlet oxygen was generated during the reaction and reacted with α-azidoketones in a [4 + 2] fashion to yield endoperoxides, which rearranged in multiple ways to generate isoxazoles. Some of the synthesized isoxazoles were evaluated as α-glucosidase inhibitors, and three of them 5bi, 5bj, and 5bl exhibited good activity with IC50 values of 454.57 ± 29.34, 147.84 ± 2.28, and 272.58 ± 42.06 μM, respectively, when compared with the standard drug acarbose (IC50 = 1224.33 ± 126.72 μM).

Antitubercular activity of 2-mercaptobenzothiazole derivatives targeting Mycobacterium tuberculosis type II NADH dehydrogenase

Mycobacterium tuberculosis (Mtb) type II NADH dehydrogenase (NDH-2) transports electrons into the mycobacterial respiratory pathway at the cost of reduction of NADH to NAD+ and is an attractive drug target. Herein, we have synthesised a series of 2-mercaptobenzothiazoles (C1-C14) and evaluated their anti-tubercular potential as Mtb NDH-2 inhibitors. The synthesised compounds C1-C14 were evaluated for MIC90 and ATP depletion against Mtb H37Ra, M. bovis, and Mtb H37Rv mc2 6230. Compounds C3, C4, and C11 were found to be the active molecules in the series and were further evaluated for their MIC90 against Mtb-resistant strains and for their bactericidal potential against Mtb H37Rv mc26230. The Peredox-mCherry-expressing Mtb strain was used to examine whether C3, C4, and C11 possess NDH-2 inhibitory potential. Furthermore, cytotoxicity analysis against HepG2 displayed a safety index (SI) of >10 for C3 and C4. To get an insight into the mode of interaction at NDH-2, we have performed computational analysis of our active compounds.

Third Generation Solid Dispersion-Based Formulation of Novel Anti-Tubercular Agent Exhibited Improvement in Solubility, Dissolution and Biological Activity

The long treatment period and development of drug resistance in tuberculosis (TB) necessitates the discovery of new anti-tubercular agents. The drug discovery program of the institute leads to the development of an anti-tubercular lead (IIIM-019), which is an analogue of nitrodihydroimidazooxazole and exhibited promising anti-tubercular action. However, IIIM-019 displays poor aqueous solubility (1.2 µg/mL), which demands suitable dosage form for its efficient oral administration. In the present study, third generation solid dispersion-based formulation was developed to increase the solubility and dissolution of IIIM-019. The solubility profile of IIIM-019 using various polymeric carriers was determined and subsequently, PVP K-30 and P-407 were selected for preparation of binary and ternary solid dispersion. The third-generation ternary solid dispersion comprising PVP K-30 and P-407 revealed a remarkable enhancement in the aqueous solubility of IIIM-019. Physicochemical characterization of the developed formulations was done by employing FTIR spectroscopy, scanning electron microscopy, X-ray diffraction analysis, differential scanning calorimetry, and dynamic light scattering analysis. The dissolution study indicated an impressive release profile with the optimized formulation. The optimized formulation was further examined for cytotoxicity, cellular uptake, and hemolytic activity. The results indicated that the formulation had no apparent cytotoxicity on Caco-2 cells and was non-hemolytic in nature. Moreover, the optimized formulation showed significantly improved anti-tubercular activity compared to the native molecule. These findings showed that the developed third generation ternary solid dispersion could be a promising option for the oral delivery of investigated anti-tubercular molecule.

Unraveling Dilemmas and Lacunae in the Escalating Drug Resistance of Mycobacterium tuberculosis to Bedaquiline, Delamanid, and Pretomanid

Delamanid, bedaquiline, and pretomanid have been recently added in the anti-tuberculosis (anti-TB) treatment regimens and have emerged as potential solutions for combating drug-resistant TB. These drugs have proven to be effective in treating drug-resistant TB when used in combination. However, concerns have been raised about the eventual loss of these drugs due to evolving resistance mechanisms and certain adverse effects such as prolonged QT period, gastrointestinal problems, hepatotoxicity, and renal disorders. This Perspective emphasizes the properties of these first-in-class drugs, including their mechanism of action, pharmacokinetics/pharmacodynamics profiles, clinical studies, adverse events, and underlying resistance mechanisms. A brief coverage of efforts toward the generation of best-in-class leads in each class is also provided. The ongoing clinical trials of new combinations of these drugs are discussed, thus providing a better insight into the use of these drugs while designing an effective treatment regimen for resistant TB cases.

Emerging impact of triazoles as anti-tubercular agent

Tuberculosis, a disease of poverty is a communicable infection with a reasonably high mortality rate worldwide. 10 Million new cases of TB were reported with approx 1.4 million deaths in the year 2019. Due to the growing number of drug-sensitive and drug-resistant tuberculosis cases, there is a vital need to develop new and effective candidates useful to combat this deadly disease. Despite tremendous efforts to identify a mechanism-based novel antitubercular agent, only a few have entered into clinical trials in the last six decades. In recent years, triazoles have been well explored as the most valuable scaffolds in drug discovery and development. Triazole framework possesses favorable properties like hydrogen bonding, moderate dipole moment, enhanced water solubility, and also the ability to bind effectively with biomolecular targets of M. tuberculosis and therefore this scaffold displayed excellent potency against TB. This review is an endeavor to summarize an up-to-date innovation of triazole-appended hybrids during the last 10 years having potential in vitro and in vivo antitubercular activity with structure activity relationship analysis. This review may help medicinal chemists to explore the triazole scaffolds for the rational design of potent drug candidates having better efficacy, improved selectivity and minimal toxicity so that these hybrid NCEs can effectively be explored as potential lead to fight against M. tuberculosis.

Recent advancement in drug development of nitro(NO2 )-heterocyclic compounds as lead scaffolds for the treatment of Mycobacterium tuberculosis

Tuberculosis (TB) is an infectious disease caused predominantly by Mycobacterium tuberculosis (Mtb). It was responsible for approximately 1.4 million deaths worldwide in 2019. The lack of new drugs to treat drug-resistant strains is a principal factor for the slow rise in TB infections. Our aim is to aid the development of new TB treatments by describing improvements (last decade, 2011-2021) to nitro(NO₂ )-based compounds that have shown activity or pharmacological properties (e.g., anti-proliferative, anti-kinetoplastid) against Mtb. For all compounds, we have included final correlations of minimum inhibitory concentrations against Mtb (H₃₇ Rv).

Synthesis of sorafenib analogues incorporating a 1,2,3-triazole ring and cytotoxicity towards hepatocellular carcinoma cell lines

A series of 1,2,3-triazole-containing Sorafenib analogues, in which the aryl urea moiety of Sorafenib (1) was replaced with a 1,2,3-triazole ring linking a substituted phenoxy fragment, were prepared successfully via Huisgen 1,3-dipolar cycloaddition and nucleophilic aromatic substitution. The studies of cytotoxicity towards human hepatocellular carcinoma (HCC) cell lines, HepG2 and Huh7, indicated that p-tert-butylphenoxy analogue 2m showed significant inhibitory activity against Huh7 with IC₅₀ = 5.67 ± 0.57 µM. More importantly, 2m showed low cytotoxicity against human embryonal lung fibroblast cell line, MRC-5, with IC₅₀ > 100 µM, suggesting its highly selective cytotoxic activity (SI > 17.6) towards Huh7 which is much superior to that of Sorafenib (SI = 6.73). The molecular docking studies revealed that the analogue 2m bound B-RAF near the binding position of Sorafenib, while it interacted VEGFR2 efficiently at the same binding position of Sorafenib. However, 2m exhibited moderate inhibitory activity toward B-RAF, implying that its anti-Huh7 effect might not strictly relate to inhibition of B-RAF. Wound healing and BrdU cell proliferation assays confirmed anti-cell migration and anti-cell proliferative activities towards Huh7. With its inhibitory efficiency and high safety profile, 2m has been identified as a promising candidate for the treatment of HCC.

Recent Progress in the Discovery and Development of 2-Nitroimidazooxazines and 6-Nitroimidazooxazoles to Treat Tuberculosis and Neglected Tropical Diseases

Nitroimidazole drugs have a long history as therapeutic agents to treat bacterial and parasitic diseases. The discovery in 1989 of a bicyclic nitroimidazole lead, displaying in vitro and in vivo antitubercular activity, spurred intensive exploration of this and related scaffolds, which led to the regulatory approval of pretomanid and delamanid as a new class of tuberculosis drugs. Much of the discovery work related to this took place over a 20-year period ending in 2010, which is covered in a number of cited reviews. This review highlights subsequent research published over the 2011–August 2020 timeframe, and captures detailed structure–activity relationship studies and synthetic strategies directed towards uncovering newer generation drugs for both tuberculosis and selected neglected tropical diseases. Additionally, this review presents in silico calculations relating to the drug-like properties of lead compounds and clinical agents, as well as chemical development and manufacturing processes toward providing bulk drug supplies.

Tyrosol 1,2,3-triazole analogues as new acetylcholinesterase (AChE) inhibitors

The present work proposed the preparation of triazolic analogues of tyrosol, a biophenol found in olive oil and whose wide range of bioactivities has been the target of many studies. We obtained fifteen novel tyrosol derivatives and the compounds of the series were later evaluated as acetylcholinesterase (AChE) inhibitors. The study of AChE inhibition is important for the development of new drugs and pesticides, and especially the research for managing Alzheimer's disease. The most active compound, namely 7-({1-[2-(4-hydroxyphenyl)ethyl]-1H-1,2,3-triazol-4-yl}methoxy)-4-methyl-2H-chromen-2-one (30), showed IC₅₀ value of 14.66 ± 2.29 μmol L^-1. Docking experiments corroborated by kinetic assay are suggestive of a competitive inhibition mechanism. Derivatives interacted with amino acids from the AChE active site associated to the development of Alzheimer's disease. The results indicate that the compounds synthesized have a high potential as prototypes for the development of new acetylcholinesterase inhibitors.

Formulation technologies and advances for oral delivery of novel nitroimidazoles and antimicrobial peptides

Antibiotic resistance has become a global crisis, driving the exploration for novel antibiotics and novel treatment approaches. Among these research efforts two classes of antibiotics, bicyclic nitroimidazoles and antimicrobial peptides, have recently shown promise as novel antimicrobial agents with the possibility to treat multi-drug resistant infections. However, they suffer from the issue of poor oral bioavailability due to disparate factors: low solubility in the case of nitroimidazoles (BCS class II drugs), and low permeability in the case of peptides (BCS class III drugs). Moreover, antimicrobial peptides present another challenge as they are susceptible to chemical and enzymatic degradation, which can present an additional pharmacokinetic hurdle for their oral bioavailability. Formulation technologies offer a potential means for improving the oral bioavailability of poorly permeable and poorly soluble drugs, but there are still drawbacks and limitations associated with this approach. This review discusses in depth the challenges associated with oral delivery of nitroimidazoles and antimicrobial peptides and the formulation technologies that have been used to overcome these problems, including an assessment of the drawbacks and limitations associated with the technologies that have been applied. Furthermore, the potential for supercritical fluid technology to overcome the shortcomings associated with conventional drug formulation methods is reviewed.

A concise and sequential synthesis of the nitroimidazooxazole based drug, Delamanid and related compounds

A concise, protection-group free and sequential route has been developed for the synthesis of the nitroimidazole based FDA-approved multi-drug resistant anti-tuberculosis drug, Delamanid and anti-leishmanial lead candidate VL-2098. The synthesis required chiral epoxides (11 and 17) as key intermediates. The chiral epoxide 11 was synthesised by sequential reaction cascades viz., allylation, selective N-arylation, Mitsunobu etherification, Sharpless asymmetric dihydroxylation and epoxidation, which do not require any special/dry reaction conditions. The steps involved towards the synthesis of epoxide also worked nicely in gram scales. After the synthesis of epoxide 11, the synthesis of Delamanid was achieved by reaction with 2-bromo-4-nitroimidazole 12 with an overall yield of 27%. Similarly, anti-leishmanial lead candidate VL-2098 was also synthesized in an overall yield of 36%.

A concise, protection-group free and sequential route has been developed for the synthesis of the nitroimidazole based FDA-approved multi-drug resistant anti-tuberculosis drug, Delamanid and anti-leishmanial lead candidate VL-2098.

14-Residue peptaibol velutibol A from Trichoderma velutinum: its structural and cytotoxic evaluation

Velutibol A (1), a new 14-residue peptaibol was isolated from the Himalayan cold habitat fungus Trichoderma velutinum. The structural characterization was carried out by 1D and 2D NMR studies, and tandem mass studies, and Marfey's method aided in determining the stereochemistry of the amino acids. The CD analysis revealed folding of the peptide in a 3₁₀-helical conformation. The intramolecular H-bonding was determined by an NMR-VT experiment. Cytotoxic evaluation was carried out against a panel of cancer cell lines. The cell cycle assay was carried out on human myeloid leukaemia (HL-60) cells and revealed the formation of apoptotic bodies and DNA damage in a dose-dependent manner. Three other peptaibols namely velutibol B (2), velutibol C (3), and velutibol D (4) were also isolated in trace amounts from the psychotropic fungus and characterized through tandem mass spectroscopy and Marfey's analysis.

Velutibol A (1), a new 14-residue peptaibol isolated from the Himalayan cold habitat fungus Trichoderma velutinum.

Advances in Drug Discovery of New Antitubercular Multidrug-Resistant Compounds

Tuberculosis (TB), a disease caused mainly by the Mycobacterium tuberculosis (Mtb), is according to the World Health Organization (WHO) the infectious disease responsible for the highest number of deaths worldwide. The increased number of multidrug-resistant (MDR-TB) and extensively drug-resistant (XDR-TB) strains, and the ineffectiveness of the current treatment against latent tuberculosis are challenges to be overcome in the coming years. The scenario of drug discovery becomes alarming when it is considered that the number of new drugs does not increase proportionally to the emergence of drug resistance. In this review, we will demonstrate the current advances in antitubercular drug discovery, focusing on the research of compounds with potent antituberculosis activity against MDR-TB strains. Herein, active compounds against MDR-TB with minimum inhibitory concentrations (MICs) less than 11 µM and low toxicity published in the last 4 years in the databases PubMed, Web of Science and Scopus will be presented and discussed.

Preclinical comprehensive physicochemical and pharmacokinetic profiling of novel nitroimidazole derivative IIIM-019 - A potential oral treatment for tuberculosis

New compounds against tuberculosis are urgently needed to combat the crisis of drug resistance in tuberculosis (TB). We have identified a nitrodihydroimidazooxazole analog, IIIM-019 as a new anti-tubercular agent with a MIC of 0.23 μM against H37Rv. Physicochemical properties, in-vitro pharmacokinetics and in-vivo multiple-doses pharmacokinetics were studied for the compound. In silico physicochemical parameters and Lipinski's violations were determined for drug like properties. Lipophilicity was determined experimentally as Octanol-PBS partition coefficient (log P). Passive and active permeability of the compound was determined by PAMPA and Caco-2 cell permeability analysis, respectively. Plasma protein binding was determined by Rapid equilibrium dialysis. Metabolism by liver microsomes revealed the t1/2 and intrinsic clearance of the compound. Hepatotoxicity of IIIM-019 was determined alone and in combination to first line anti-tubercular drugs. The compound was also estimated for nuclear DNA damage. Single doses of IIIM-019 (2.5, 10, 25 and 100 mg/kg) were administered orally to Balb/c mice and the blood samples were analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS). IIIM-019 exhibited very good lipophilicity (log P) of 2.47 which makes it optimal for oral administration. The compound showed low solubility and permeability and high plasma protein binding. However, it was highly stable in rat liver microsomes with t1/2 > 2 h and very low intrinsic clearance. It was found to be non-hepatotoxic and did not induce any significant DNA damage at high concentrations even up to 100 μM. IIIM-019 showed satisfactory in-vivo pharmacokinetic properties. By increasing the dose from 2.5 mg/kg to 10 mg/kg, AUC0-t increased from 14935 ng h/ml to 81,478 ng h/ml. However the exposure of IIIM-019 in plasma suggested that the levels reached saturation at higher concentrations. The compound showed a good oral bioavailability of 58.7%. The results insinuate that IIIM-019 should undergo further development as a potential treatment for tuberculosis.

Development and validation of a highly sensitive LC-MS/MS-ESI method for quantification of IIIM-019-A novel nitroimidazole derivative with promising action against Tuberculosis: Application to drug development

The study aims to illustrate an analytical validation of a rapid and sensitive liquid chromatography (LC) coupled to tandem mass spectrometry (MS-MS) and electrospray ionization (ESI) method for quantification of IIIM-019 (a novel nitroimidazole derivative with potential activity against Tuberculosis) in mice plasma. The extraction of the analyte and the internal standard (Tolbutamide) from the plasma samples involves protein precipitation using acetonitrile. The chromatographic separation was accomplished using a gradient mode and the mobile phase comprised of acetonitrile and 0.1% formic acid in water. The flow rate used was 0.7 ml/min on a C18e high performance Chromolith column. IIIM-019 and Tolbutamide (IS) were analyzed by combined reversed-phase LC/MS-MS with positive ion electrospray ionization. The MS-MS ion transitions used were 533>170.1, 533>198 for IIIM-019 and 271>74, 271>155 for internal standard (IS) respectively. The method was linear over a concentration range of 0.5-1000 ng/ml and the lower limit of quantification was 0.50 ng/ml. The entire study was validated for accuracy, precision, linearity, range, selectivity, lower limit of quantification (LLOQ), recovery, and matrix effect in accordance with the FDA guidelines of method validation. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The intra and inter-day precisions were in the range of 0.51-11.18% and 0.51-7.55%. The pharmacokinetics was performed on male Balb/c mice by oral (2.5mg/kg), intraperitoneal (2.5mg/kg) and intravenous (1mg/kg) routes. The oral bioavailability of IIIM-019 was 51.6%. The method was also applied successfully in determining microsomal stability wherein the compound was found to be very slightly metabolized by rat liver microsomes.

Synthesis and Biological Evaluation of Polar Functionalities Containing Nitrodihydroimidazooxazoles as Anti-TB Agents

Novel polar functionalities containing 6-nitro-2,3-dihydroimidazooxazole (NHIO) analogues were synthesized to produce a compound with enhanced solubility. Polar functionalities including sulfonyl, uridyl, and thiouridyl-bearing NHIO analogues were synthesized and evaluated against Mycobacterium tuberculosis (MTB) H37Rv. The aqueous solubility of compounds with MIC values ≤0.5 μg/mL were tested, and six compounds showed enhanced aqueous solubility. The best six compounds were further tested against resistant (Rif(R) and MDR) and dormant strains of MTB and tested for cytotoxicity in HepG2 cell line. Based on its overall in vitro characteristics and solubility profile, compound 6d was further shown to possess high microsomal stability, solubility under all tested biological conditions (PBS, SGF and SIF), and favorable oral in vivo pharmacokinetics and in vivo efficacy.