SAR studies on trisubstituted benzimidazoles as inhibitors of Mtb FtsZ for the development of novel antitubercular agents

Rational molecular design converting fascaplysin derivatives to potent broad-spectrum inhibitors against bacterial pathogens via targeting FtsZ

The filamentous temperature-sensitive mutant Z protein (FtsZ), a key player in bacterial cell division machinery, emerges as an attractive target to tackle the plight posed by the ever growing antibiotic resistance over the world. Therefore in this regard, agents with scaffold diversities and broad-spectrum antibacterial activity against Gram-positive and Gram-negative pathogens are highly needed. In this study, a new class of marine-derived fascaplysin derivatives has been designed and synthesized by Suzuki-Miyaura cross-coupling. Some compounds exhibited potent bactericidal activities against a panel of Gram-positive (MIC = 0.024-6.25 μg/mL) and Gram-negative (MIC = 1.56-12.5 μg/mL) bacteria including methicillin-resistant S. aureus (MRSA). They exerted their effects by dual action mechanism via disrupting the integrity of the bacterial cell membrane and targeting FtsZ protein. These compounds stimulated polymerization of FtsZ monomers and bundling of the polymers, and stabilized the resulting polymer network, thus leading to the dysfunction of FtsZ in cell division. In addition, these agents showed negligible hemolytic activity and low cytotoxicity to mammalian cells. The studies on docking and molecular dynamics simulations suggest that these inhibitors bind to the hydrophilic inter-domain cleft of FtsZ protein and the insights obtained in this study would facilitate the development of potential drugs with broad-spectrum bioactivities.

A Review of Approaches to the Metallic and Non-Metallic Synthesis of Benzimidazole (BnZ) and Their Derivatives for Biological Efficacy

Heterocyclic compounds are significant lead drug candidates based on their various structure-activity relationships (SAR), and their use in pharmaceutics is constantly developing. Benzimidazole (BnZ) is synthesized by a condensation reaction between benzene and imidazole. The BnZ structure consists of two nitrogen atoms embedded in a five-membered imide ring which is fused with a benzene ring. This review examines the conventional and green synthesis of metallic and non-metallic BnZ and their derivatives, which have several potential SARs, along with a wide range of pharmacological properties, including anti-cancer, anti-inflammatory, anti-microbial, anti-tubercular, and anti-protozoal properties. These compounds have been proven by pharmacological investigations to be efficient against different strains of microbes. Therefore, in this review, the structural variations of BnZ are listed along with various applications, predominantly related to their biological activities.

Molecular Design and In-Silico Analysis of Trisubstituted Benzimidazole Derivatives as Ftsz Inhibitor

Tuberculosis (TB) is the fastest spreading infectious disease and one of the top ten diseases that kill millions of people annually. The rapid spread of a multidrug-resistant strain of Mycobacterium tuberculosis leads to multidrug-resistance tuberculosis (MDR-TB), which is very difficult to treat. Filament temperature-sensitive protein ring-Z (Ftsz) protein could be the best target to inhibit bacterial cytokinesis. This research is conducted to predict the antitubercular activity of trisubstituted benzimidazole derivatives targeting FtsZ protein by an in-silico approach (molecular docking, pharmacokinetic parameter, drug likeliness, toxicity prediction, and biological activity prediction). Amine and aldehyde substitutions are used as primary scaffolds to design 20 trisubstituted benzimidazole derivatives for molecular docking. AutoDock vina v.1.2.0 software was used to predict the binding interaction between ligand and receptor (FtsZ, PDB ID : 1RQ7). The drug-likeliness properties and toxicity of ligands were predicted from SwissADMET and ToxiM web servers, respectively. Compound A15 (2,3,5,6-tetrafluoro-N1-{6-fluoro-5-[4-(1H-imidazole-1-yl) phenoxy]-1H-1,3-benzodiazol-2-yl} benzene-1,4-diamine) showed the best binding energy (ΔG = −10.2 kcal/mol/) along with four hydrogen bond interactions (GLY107, PHE180, ASP 184). Similarly, compounds A19 and A20 have the best binding score of −9.8 kcal/mol, with excellent pharmacokinetic parameters. It is found that the binding energy of all ligands (ΔG = −8.0 to −10.2 kcal/mol) is better than the reference compound Moxifloxacin (ΔG = −7.7 kcal/mol). None of the ligands violate Lipinski’s rule, but all ligands’ toxicity is slightly high (>0.8 score). It is reported that the amine-substituted benzimidazole derivatives have better binding energy than the aldehyde substitution. Therefore, it is concluded that compounds A19 and A20 can be the best candidate as Ftsz protein inhibitors but an in-vitro animal study and toxicity study are necessary to validate these data.

Synthetic approaches to potent heterocyclic inhibitors of tuberculosis: A decade review

Tuberculosis (TB) continues to be a significant global health concern with about 1.5 million deaths annually. Despite efforts to develop more efficient vaccines, reliable diagnostics, and chemotherapeutics, tuberculosis has become a concern to world health due to HIV, the rapid growth of bacteria that are resistant to treatment, and the recently introduced COVID-19 pandemic. As is well known, advances in synthetic organic chemistry have historically enabled the production of important life-saving medications that have had a tremendous impact on patients’ lives and health all over the world. Small-molecule research as a novel chemical entity for a specific disease target offers in-depth knowledge and potential therapeutic targets. In this viewpoint, we concentrated on the synthesis of a number of heterocycles reported in the previous decade and the screening of their inhibitory action against diverse strains of Mycobacterium tuberculosis. These findings offer specific details on the structure-based activity of several heterocyclic scaffolds backed by their in vitro tests as a promising class of antitubercular medicines, which will be further useful to build effective treatments to prevent this terrible illness.

Bacterial FtsZ inhibition by benzo[d]imidazole-2-carboxamide derivative with anti-TB activity

Aims: The present study aimed to assess the mode of action of previously reported anti- Mycobacterium tuberculosis benzo[ d]imidazole-2-carboxamides against FtsZ along with their antibacterial potential. Materials & methods: The anti-mycobacterial action of benzo[ d]imidazole-2-carboxamides against FtsZ was evaluated using inhibition of Bacillus subtilis 168, light scattering assay, circular dichroism spectroscopy, in silico molecular docking and molecular dynamics simulations. Results & conclusion: Three compounds (1k, 1o and 1e) were active against isoniazid-resistant strains. Four compounds (1h, 1i, 1o and 4h) showed >70% inhibition against B. subtilis 168. Compound 1o was the most potent inhibitor (91 ± 5% inhibition) of  B. subtilis 168 FtsZ and perturbed its secondary structure. Molecular docking and molecular dynamics simulation of complexed 1o suggested M. tuberculosis FtsZ as a possible target for antitubercular activity.

Investigating the Antituberculosis Activity of Selected Commercial Essential Oils and Identification of Active Constituents Using a Biochemometrics Approach and In Silico Modeling

Tuberculosis (TB) is a disease caused by Mycobacterium tuberculosis which has become prevalent due to the emergence of resistant M. tuberculosis strains. The use of essential oils (EOs) as potential anti-infective agents to treat microbial infections, including TB, offers promise due to their long historical use and low adverse effects. The current study aimed to investigate the in vitro anti-TB activity of 85 commercial EOs, and identify compounds responsible for the activity, using a biochemometrics approach. A microdilution assay was used to determine the antimycobacterial activity of the EOs towards some non-pathogenic Mycobacterium strains. In parallel, an Alamar blue assay was used to investigate antimycobacterial activity towards the pathogenic M. tuberculosis strain. Chemical profiling of the EOs was performed using gas chromatography-mass spectrometry (GC-MS) analysis. Biochemometrics filtered out putative biomarkers using orthogonal projections to latent structures discriminant analysis (OPLS-DA). In silico modeling was performed to identify potential therapeutic targets of the active biomarkers. Broad-spectrum antimycobacterial activity was observed for Cinnamomum zeylanicum (bark) (MICs = 1.00, 0.50, 0.25 and 0.008 mg/mL) and Levisticum officinale (MICs = 0.50, 0.5, 0.5 and 0.004 mg/mL) towards M. smegmatis, M. fortuitum, M. gordonae and M. tuberculosis, respectively. Biochemometrics predicted cinnamaldehyde, thymol and eugenol as putative biomarkers. Molecular docking demonstrated that cinnamaldehyde could serve as a scaffold for developing a novel class of antimicrobial compounds by targeting FtsZ and PknB from M. tuberculosis.

Design and synthesis of benzimidazole derivatives as antimycobacterial agents

A series of 2,5-disubstituted benzimidazole derivatives was synthesized with the aim to identify compounds with potent anti-TB activity. All the compounds were screened in vitro against cultured Mycobacterium tuberculosis H₃₇ Rv strain and found to be exhibiting MIC₉₉ values in the range of 0.195-100 µM. Out of 43 synthesized compounds, two compounds 11h and 13e showed better anti-TB activity than the reference drug isoniazid.

Structure-based virtual screening and biological evaluation of novel inhibitors of mycobacterium Z-ring formation

The major part of commercial prodrugs against Mycobacterium tuberculosis (Mtb) demonstrated a significant inhibitory effect on cell division and inhibition of bacterial growth in vitro. However, further implementation often failed to overcome the compensatory system of interchangeable cascades. This is the most common situation for the compounds, which hit the key enzymes activities involved in all basic stages of the cell cycle. We decided to find more compounds, which could affect a cytoskeleton complex playing important role in sensing the external signals, intracellular transport, and cell division. In general, the bacterial cytoskeleton is crucial for response to the environment and participates in cell-to-cell communication. In turn, filamentous temperature-sensitive Z (FtsZ) protein, a mycobacterial tubulin homolog, is essential for Z-ring formation and further bacteria cell division. We predicted the most preferable binding-sites and conducted a high-throughput virtual screening. Modeling results suggest that some compounds bind in a specific region on the surface Mtb FtsZ, which is absent in human, and other could hit GTPase activity of the FtsZ. Further in vitro studies confirmed that these novel molecules can efficiently bind to these pockets, demonstrating an effect on the polymerization state and kinetics mechanisms. The rescaling of the experiment on the cell line revealed that reported compounds are able to alter the polymerization level of the filamentous and, therefore, prevent mycobacteria reproduction.

Synthesis of 4-[(1H-Benzimidazol-2-yl)sulfanyl]benzaldehyde and 2-({4-[(1H-Benzimidazol-2-yl)sulfanyl]phenyl}methylidene)hydrazine-1-carbothioamide

Here we describe the preparation of 2-(4-((1H-benzo[d]imidazol-2-yl)thio)-benzylidene)-hydrazine-1-carbothioamide in two steps. In the first step, 1,3-dihydro-2H-1,3-benzimidazole-2-thione was reacted with 4-fluorobenzaldehyde in DMSO to get 4-[(1H-benzimidazol-2-yl)sulfanyl]benzaldehyde in high yield. The reaction of the obtained aldehyde with thiosemicarbazide in ethanol at reflux temperature yielded 2-({4-[(1H-benzimidazol-2-yl)sulfanyl]phenyl}methylidene)hydrazine-1-carbothioamide. The structure of the synthesized compounds was established by NMR spectroscopy (1H, 13C), mass spectrometry, and infrared spectroscopy.

Recent advancements on Benzimidazole: A versatile scaffold in medicinal chemistry

Benzimidazole is nitrogen containing fused heterocycle which has been extensively explored in medicinal chemistry. Benzimidizole nucleus has been found to possess various biological activities such as anticancer, antimicrobial, anti-inflammatory, antiviral, antitubercular and antidiabetic. A number of benzimidazoles such as bendamustine, pantoprazole have been approved for the treatment of various illnesses whereas galeterone and GSK461364 are in clinical trials. The present review article gives an overview about the different biological activities exhibited by the benzimidazole derivatives as well as different methods used for the synthesis of benzimidazole derivatives for the past ten years.

Tuberculosis Drug Discovery: A Decade of Hit Assessment for Defined Targets

More than two decades have elapsed since the publication of the first genome sequence of Mycobacterium tuberculosis (Mtb) which, shortly thereafter, enabled methods to determine gene essentiality in the pathogen. Despite this, target-based approaches have not yielded drugs that have progressed to clinical testing. Whole-cell screening followed by elucidation of mechanism of action has to date been the most fruitful approach to progressing inhibitors into the tuberculosis drug discovery pipeline although target-based approaches are gaining momentum. This review discusses scaffolds that have been identified over the last decade from screens of small molecule libraries against Mtb or defined targets where mechanism of action investigation has defined target-hit couples and structure-activity relationship studies have described the pharmacophore.

The study of 9,10-dihydroacridine derivatives as a new and effective molecular scaffold for antibacterial agent development

The emergence of worldwide spreading drug-resistant bacteria has been a serious threat to public health during the past decades. The development of new and effective antibacterial agents to address this critical issue is an urgent action. In the present study, we investigated the antibacterial activity of two 9,10-dihydroacridine derivatives and their mechanism. Both compounds were found possessing strong antibacterial activity against some selected Gram-positive bacteria including MRSA, VISA and VRE. The biological study suggests that the compounds promoted FtsZ polymerization and also disrupted Z-ring formation at the dividing site and consequently, the bacterial cell division is interrupted and causing cell death.

Structure-activity relationship studies on 2,5,6-trisubstituted benzimidazoles targeting Mtb-FtsZ as antitubercular agents

Filamenting temperature sensitive protein Z (FtsZ) is an essential bacterial cell division protein and a promising target for the development of new antibacterial therapeutics. As a part of our ongoing SAR studies on 2,5,6-trisubstituted benzimidazoles as antitubercular agents targeting Mtb-FtsZ, a new library of compounds with modifications at the 2 position was designed, synthesized and evaluated for their activity against Mtb-H37Rv. This new library of trisubstituted benzimidazoles exhibited MIC values in the range of 0.004-50 μg mL-1. Compounds 6b, 6c, 20f and 20g showed excellent growth inhibitory activities ranging from 0.004-0.08 μg mL-1. This SAR study has led to the discovery of a remarkably potent compound 20g (MIC 0.0039 μg mL-1; normalized MIC 0.015 μg mL-1). Our 3DQSAR model predicted 20g as the most potent compound in the library.

Design, synthesis, and biological evaluation of benzo[d]imidazole-2-carboxamides as new anti-TB agents

Tuberculosis is the leading cause of death globally among infectious diseases. Due to the development of resistance of Mycobacterium tuberculosis to currently used anti-TB medicines and the TB-HIV synergism the urgent need to develop novel anti-mycobacterial agents has been realized. The drug-to-target path has been the successful strategy for new anti-TB drug development. All the six drug candidates that have shown promise during the clinical trials and some of these being approved for treatment against MDR TB are the results of phenotype screening of small molecule compound libraries. In search of compounds belonging to novel pharmacophoric class that could be subjected to whole cell assay to generate new anti-TB leads the benzo[d]imidazole-2-carboxamide moiety has been designed as a novel anti-TB scaffold. The design was based on the identification of the benzimidazole ring as a prominent substructure of the FDA approved drugs, the structural analysis of reported anti-TB benzimidazoles, and the presence of the C-2 carboxamido functionality in novel bioisoteric anti-TB benzothiazoles. Twenty seven final compounds have been prepared via NH₄Cl-catalyzed amidation of ethyl benzo[d]imidazole-2-carboxylates, as the required intermediates, obtained through a green "all water" one-pot synthetic route following a tandem N-arylation-reduction-cyclocondensation procedure. All of the synthesised target compounds were assessed for anti-TB potential using H₃₇Rv ATCC27294 strain. Thirteen compounds were found with better MIC (0.78-6.25 µg/mL) than the standard drugs and being non-cytotoxic nature (<50% inhibition against RAW 264.7 cell lines at 50 µg/mL). The compound 8e exhibited best anti-TB activity (MIC: 2.15 µM and selectivity index: > 60) and a few others e.g., 8a, 8f, 8k and 8o are the next best anti-TB hits (MIC: 1.56 µg/mL). The determination and analysis of various physiochemical parameters revealed favorable druglike properties of the active compounds. The compounds 8a-l and 8o, with MIC values of ≤ 6.25 μg/mL, have high LipE values (10.66-11.77) that are higher than that of the suggested value of > 6 derived from empirical evidence for quality drug candidates and highlight their therapeutic potential. The highest LipE value of 11.77 of the best active compound 8e with the MIC of 0.78 μg/mL indicates its better absorption and clearance as a probable clinical candidate for anti-TB drug discovery. These findings highlight the discovery of benzimidazole-2-carboxamides for further development as new anti-TB agents.

Computational studies of the properties and activities of selected trisubstituted benzimidazoles as potential antitubercular drugs inhibiting MTB-FtsZ polymerization

Trisubstituted benzimidazoles (trisbenz) are significantly active against nonreplicating Mycobacterium tuberculosis (MTB) by inhibiting the polymerization of Filamentous Temperature Sensitive Mutant Z (FtsZ), an essential bacteria cell division protein. In-depth in-silico study of 5 of the most active trisubstituted benzimidazoles; trisbenz 1, 2, 3, 4 and 5, giving insight into their properties, such as stability, bioavailability, interactions with residues at the binding site of MTB-FtsZ and their influence on structural dynamics of the protein have been conducted. This was achieved through the application of in-silico methods including density functional theory (DFT) calculations, ADME properties calculations, molecular docking and molecular dynamics simulations. A DFT approach was applied to predict reactivity properties of potent FtsZ inhibitors, and the results reveal the relative reactivity of these inhibitors as bioactive moieties. The estimated ADME properties predicted all 5 compounds to be bioavailable and suitable for oral administration. Molecular docking, binding free energy, RMSD, RMSF, and hydrogen bond analysis confirmed these 5 compounds as potent MTB-FtsZ inhibitors. Although analyses proved these compounds to be bioactive and potent MTB-FtsZ inhibitors, however, trisbenz 1 appeared to be the most active against this protein while trisbenz 5 was the least active. This study further confirms the experimental study while also giving insight on the compounds mechanism of action and presents their bioavailability properties.

2-Aryl benzazole derived new class of anti-tubercular compounds: Endowed to eradicate mycobacterium tuberculosis in replicating and non-replicating forms

The high mortality rate and the increasing prevalence of Mtb resistance are the major concerns for the Tuberculosis (TB) treatment in this century. To counteract the prevalence of Mtb resistance, we have synthesized 2-aryl benzazole based dual targeted molecules. Compound 9m and 9n were found to be equally active against replicating and non-replicating form of Mtb (MIC_(MABA) 1.98 and 1.66 μg/ml; MIC_(LORA) 2.06 and 1.59 μg/ml respectively). They arrested the cell division (replicating Mtb) by inhibiting the GTPase activity of FtsZ with IC₅₀ values 45 and 64 μM respectively. They were also capable of kill Mtb in non-replicating form by inhibiting the biosynthesis of menaquinone which was substantiated by the MenG inhibition (IC₅₀ = 11.62 and 7.49 μM respectively) followed by the Vit-K2 rescue study and ATP production assay.

Recent progress of bacterial FtsZ inhibitors with a focus on peptides

In recent years, the rise of antibiotic resistance has become a primary health problem. With the emergence of bacterial resistance, the need to explore and develop novel antibacterial drugs has become increasingly urgent. Filamentous temperature-sensitive mutant Z (FtsZ), a crucial cell division protein of bacteria, has become a vital antibacterial target. FtsZ is a filamentous GTPase; it is highly conserved in bacteria and shares less than 20% sequence identity with the eukaryotic cytoskeleton protein tubulin, indicating that FtsZ-targeting antibacterial agents may have a low cytotoxicity toward eukaryotes. FtsZ can form a dynamic Z-ring in the center of the cell resulting in cell division. Furthermore, disturbance in the assembly of FtsZ may affect cellular dynamics and bacterial cell survival, making it a fascinating target for drug development. This review focuses on the recent discovery of FtsZ inhibitors, including peptides, natural products, and other synthetic small molecules, as well as their mechanism of action, which could facilitate the discovery of novel FtsZ-targeting clinical drugs in the future.

Synthesis and Antimycobacterial Activity of 2,5-Disubstituted and 1,2,5-Trisubstituted Benzimidazoles

The appearance of drug-resistant strains of Mycobacterium tuberculosis and the dramatic increase in infection rates worldwide evidences the urgency of developing new and effective compounds for treating tuberculosis. Benzimidazoles represent one possible source of new compounds given that antimycobacterial activity has already been documented for some derivatives, such as those bearing electron-withdrawing groups. The aim of this study was to synthesize two series of benzimidazoles, di- and trisubstituted derivatives, and evaluate their antimycobacterial activity. Accordingly, 5a and 5b were synthesized from hydroxymoyl halides 3a and 3b, and nitro-substituted o-phenylenediamine 4. Compound 11 was synthesized from an aromatic nitro compound, 4-chloro-1,2-phenylenediamine 9, mixed with 3-nitrobenzaldehyde 10, and bentonite clay. Although the synthesis of 11 has already been reported, its antimycobacterial activity is herein examined for the first time. 1,2,5-trisubstituted benzimidazoles 7a, 7b, and 12 were obtained from N-alkylation of 5a, 5b, and 11. All benzimidazole derivatives were characterized by FT-IR, NMR, and HR-MS, and then screened for their in vitro antimycobacterial effect against the M. tuberculosis H37Rv strain. The N-alkylated molecules (7a, 7b, and 12) generated very limited in vitro inhibition of mycobacterial growth. The benzimidazoles (5a, 5b, and 11) showed in vitro potency against mycobacteria, reflected in minimal inhibitory concentration (MIC) values in the range of 6.25-25 μg/mL. Consequently, only the 2,5-disubstituted benzimidazoles were assessed for biological activity on mouse macrophages infected with M. tuberculosis. A good effect was found for the three compounds. The cytotoxicity assay revealed very low toxicity for all the test compounds against the macrophage cell line. According to the docking study, 2,5-disubstituted benzimidazoles exhibit high affinity for an interdomain cleft that plays a key role in the GTP-dependent polymerization of the filamentous temperature-sensitive Z (FtsZ) protein. The ability of different benzimidazoles to impede FtsZ polymerization is reportedly related to their antimycobacterial activity. On the other hand, the 1,2,5-trisubstituted benzimidazoles docked to the N-terminal of the protein, close to the GTP binding domain, and did not show strong binding energies. Overall, 5a, 5b, and 11 proved to be good candidates for in vivo testing to determine their potential for treating tuberculosis.

Cell division protein FtsZ: from structure and mechanism to antibiotic target

Antimicrobial resistance to virtually all clinically applied antibiotic classes severely limits the available options to treat bacterial infections. Hence, there is an urgent need to develop and evaluate new antibiotics and targets with resistance-breaking properties. Bacterial cell division has emerged as a new antibiotic target pathway to counteract multidrug-resistant pathogens. New approaches in antibiotic discovery and bacterial cell biology helped to identify compounds that either directly interact with the major cell division protein FtsZ, thereby perturbing the function and dynamics of the cell division machinery, or affect the structural integrity of FtsZ by inducing its degradation. The impressive antimicrobial activities and resistance-breaking properties of certain compounds validate the inhibition of bacterial cell division as a promising strategy for antibiotic intervention.

Benzodioxane-Benzamides as Antibacterial Agents: Computational and SAR Studies to Evaluate the Influence of the 7-Substitution in FtsZ Interaction

FtsZ is a crucial prokaryotic protein involved in bacterial cell replication. It recently arose as a promising target in the search for antimicrobial agents able to fight antimicrobial resistance. In this work, going on with our structure-activity relationship (SAR) study, we developed variously 7-substituted 1,4-benzodioxane compounds, linked to the 2,6-difluorobenzamide by a methylenoxy bridge. Compounds exhibit promising antibacterial activities not only against multidrug-resistant Staphylococcus aureus, but also on mutated Escherichia coli strains, thus enlarging their spectrum of action toward Gram-negative bacteria as well. Computational studies elucidated, through a validated FtsZ binding protocol, the structural features of new promising derivatives as FtsZ inhibitors.

FtsZ inhibitors as a new genera of antibacterial agents

The continuous emergence and rapid spread of a multidrug-resistant strain of bacterial pathogens have demanded the discovery and development of new antibacterial agents. A highly conserved prokaryotic cell division protein FtsZ is considered as a promising target by inhibiting bacterial cytokinesis. Inhibition of FtsZ assembly restrains the cell-division complex known as divisome, which results in filamentation, leading to lysis of the cell. This review focuses on details relating to the structure, function, and influence of FtsZ in bacterial cytokinesis. It also summarizes on the recent perspective of the known natural and synthetic inhibitors directly acting on FtsZ protein, with prominent antibacterial activities. A series of benzamides, trisubstituted benzimidazoles, isoquinolene, guanine nucleotides, zantrins, carbonylpyridine, 4 and 5-Substituted 1-phenyl naphthalenes, sulindac, vanillin analogues were studied here and recognized as FtsZ inhibitors that act either by disturbing FtsZ polymerization and/or GTPase activity. Doxorubicin, from a U.S. FDA, approved drug library displayed strong interaction with FtsZ. Several of the molecules discussed, include the prodrugs of benzamide based compound PC190723 (TXA-709 and TXA707). These molecules have exhibited the most prominent antibacterial activity against several strains of Staphylococcus aureus with minimal toxicity and good pharmacokinetics properties. The evidence of research reports and patent documentations on FtsZ protein has disclosed distinct support in the field of antibacterial drug discovery. The pressing need and interest shall facilitate the discovery of novel clinical molecules targeting FtsZ in the upcoming days.

Novel T9 loop conformation of filamenting temperature-sensitive mutant Z from Mycobacterium tuberculosis

As of 2017, tuberculosis had infected 1.7 billion people (23% of the population of the world) and caused ten million deaths. Mycobacterium tuberculosis (Mtb) is quickly evolving, and new strains are classified as multidrug resistant. Thus, the identification of novel druggable targets is essential to combat the proliferation of these drug-resistant strains. Filamenting temperature-sensitive mutant Z (FtsZ) is a key protein involved in cytokinesis, an important process for Mtb proliferation and viability. FtsZ is required for bacterial cell division because it polymerizes into a structure called the Z-ring, which recruits accessory division proteins to the septum. Here, the crystal structure of the MtbFtsZ protein has been determined to 3.46 Å resolution and is described as a dimer of trimers, with an inter-subunit interface between protomers AB and DE. In this work, a novel conformation of MtbFtsZ is revealed involving the T9 loop and the nucleotide-binding pocket of protomers BC and EF.

3D QSAR-based design and liquid phase combinatorial synthesis of 1,2-disubstituted benzimidazole-5-carboxylic acid and 3-substituted-5H-benzimidazo[1,2-d][1,4]benzodiazepin-6(7H)-one derivatives as anti-mycobacterial agents

Tuberculosis (TB) is one of the world's deadliest infectious diseases, caused by Mycobacterium tuberculosis (Mtb). In the present study, a 3D QSAR study was performed for the design of novel substituted benzimidazole derivatives as anti-mycobacterial agents. The anti-tubercular activity of the designed compounds was predicted using the generated 3D QSAR models. The designed compounds which showed better activity were synthesized as 1,2-disubstituted benzimidazole-5-carboxylic acid derivatives (series 1) and 3-substituted-5H-benzimidazo[1,2-d][1,4]benzodiazepin-6(7H)-one derivatives (series 2) using the liquid phase combinatorial approach using a soluble polymer assisted support (PEG5000). The compounds were characterized by ¹H-NMR, ¹³C-NMR, FTIR and mass spectrometry. HPLC analysis was carried out to evaluate the purity of the compounds. We observed that the synthesised compounds inhibited the growth of intracellular M. tuberculosis H₃₇Rv in a bactericidal manner. The most active compound 16 displayed an MIC value of 0.0975 μM against the Mtb H₃₇Rv strain in liquid cultures. The lead compound was also able to inhibit the growth of intracellular mycobacteria in THP-1 macrophages.

Unpacking the Pathogen Box-An Open Source Tool for Fighting Neglected Tropical Disease

The Pathogen Box is a 400-strong collection of drug-like compounds, selected for their potential against several of the world's most important neglected tropical diseases, including trypanosomiasis, leishmaniasis, cryptosporidiosis, toxoplasmosis, filariasis, schistosomiasis, dengue virus and trichuriasis, in addition to malaria and tuberculosis. This library represents an ensemble of numerous successful drug discovery programmes from around the globe, aimed at providing a powerful resource to stimulate open source drug discovery for diseases threatening the most vulnerable communities in the world. This review seeks to provide an in-depth analysis of the literature pertaining to the compounds in the Pathogen Box, including structure-activity relationship highlights, mechanisms of action, related compounds with reported activity against different diseases, and, where appropriate, discussion on the known and putative targets of compounds, thereby providing context and increasing the accessibility of the Pathogen Box to the drug discovery community.

Molecular dynamics analysis of the effects of GTP, GDP and benzimidazole derivative on structural dynamics of a cell division protein FtsZ from Mycobacterium tuberculosis

The prevailing multi-drug resistance in Mycobacterium tuberculosis continues to remain one of the main challenges to combat tuberculosis. Hence, it becomes imperative to focus on novel drug targets. Filamenting temperature-sensitive mutant Z (FtsZ) is an essential cell division protein, a eukaryotic tubulin homologue and a promising drug target. During cytokinesis, FtsZ polymerises in the presence of GTP to form Z-ring and recruits other proteins at this site that eventually lead to the formation of daughter cells. Benzimidazoles were experimentally shown to inhibit Mtb-FtsZ, with one of the benzimidazole derivatives, M1, being reported to have the minimum inhibitory concentration (MIC) value of 3.13 µg/mL. In the present study, mechanism of destabilisation of FtsZ in the presence of M1 was computationally investigated in the presence of its substrate GTP/GDP employing molecular dynamics (MD) simulation analysis, principal component analysis (PCA), molecular mechanics combined with the generalised Born and surface area continuum salvation (MM-GBSA) and density functional theory (DFT). From the analyses, it is proposed that binding of M1 in the inter-domain cleft induces structural changes in the GTP-binding region that affect GTP binding, thus switching the preference of this protein towards depolymerised state and eventually inhibiting the cell division. Hence, this study provides mechanistic insights into the design of novel benzimidazole inhibitors against Mtb-FtsZ. Communicated by Ramaswamy H. Sarma.

Synthesis, screening and docking analysis of novel benzimidazolium compounds as potent anti microbial agents targeting FtsZ protein

The dominance of multi drug resistance in the clinically significant bacteria led to urgency in the development of new antibiotics with novel mechanism of action. Among the biochemical targets explored for selective toxicity, molecular mechanisms involving cell division remained focal point for novel antimicrobial drug discovery. For this purpose we have performed in-silico studies of FtsZ protein and obtained benzimidazolium compounds as potential hits. These molecules obtained in the dock results were synthesized via reacting benzimidazoles with appropriate benzyl halides. The structures of the synthesized compounds were confirmed by their ¹H NMR, ¹³C NMR, IR and mass spectral data. These were evaluated for anti-microbial activity. Among the tested compounds B14, B15 and B20 have shown highest activity (MIC 5 μg/mL) against Staphylococcus aureus, Macrococcus caseolyticus, Escherichia coli and Pseudomonas aeruginosa. . Microscopic examination of drug-treated cultures of Staphylococcus aureus and Pseudomonas aeruginosa showed rod-shaped filamentous growth of the dividing cells, which is a characteristic feature of FtsZ inhibition.

A novel synthesis of 2-arylbenzimidazoles in molecular sieves-MeOH system and their antitubercular activity

Arylbenzimidazoles have been synthesized as antimycobacterial agents. An efficient synthesis has been developed for 2-arylbenzimidazoles from o-phenylenediamines and aromatic aldehydes in molecular sieves-methanol system. The methodology is straightforward to get 2-arylbenzimidazoles (3a-3z) in excellent yields with high chemoselectivity over 2-aryl-1-benzylbenzimidazoles (4a-4z). All these benzimidazole analogues were evaluated against M. tuberculosis in BACTEC radiometric assay. The compounds 4y and 4z exhibited potential antitubercular activity against M. tuberculosis H₃₇R_V, MIC at 16 µM and 24 µM respectively. The best compound of the series i.e. compound 4y was well tolerated by Swiss-albino mice in acute oral toxicity. Compound 4y possessing a diarylbenzimidazole core, can further be optimized for better activity.

Recent advances of imidazole-containing derivatives as anti-tubercular agents

Tuberculosis still remains one of the most common, communicable, and leading deadliest diseases known to mankind throughout the world. Drug-resistance in Mycobacterium tuberculosis which threatens to worsen the global tuberculosis epidemic has caused great concern in recent years. To overcome the resistance, the development of new drugs with novel mechanisms of actions is of great importance. Imidazole-containing derivatives endow with various biological properties, and some of them demonstrated excellent anti-tubercular activity. As the most emblematic example, 4-nitroimidazole delamanid has already received approval for treatment of multidrug-resistant tuberculosis infected patients. Thus, imidazole-containing derivatives have caused great interests in discovery of new anti-tubercular agents. Numerous of imidazole-containing derivatives were synthesized and screened for their in vitro and in vivo anti-mycobacterial activities against both drug-sensitive and drug-resistant Mycobacterium tuberculosis pathogens. This review aims to outline the recent advances of imidazole-containing derivatives as anti-tubercular agents, and summarize the structure-activity relationship of these derivatives. The enriched structure-activity relationship may pave the way for the further rational development of imidazole-containing derivatives as anti-tubercular agents.

New Application of Neomycin B-Bisbenzimidazole Hybrids as Antifungal Agents

Alkylated aminoglycosides and bisbenzimidazoles have previously been shown to individually display antifungal activity. Herein, we explore for the first time the antifungal activity (in liquid cultures and in biofilms) of ten alkylated aminoglycosides covalently linked to either mono- or bisbenzimidazoles. We also investigate their toxicity against mammalian cells, their hemolytic activity, and their potential mechanism(s) of action (inhibition of fungal ergosterol biosynthetic pathway and/or reactive oxygen species (ROS) production). Overall, many of our hybrids exhibited broad-spectrum antifungal activity. We also found them to be less cytotoxic to mammalian cells and less hemolytic than the FDA-approved antifungal agents amphotericin B and voriconazole, respectively. Finally, we show with our best derivative (8) that the mechanism of action of our compounds is not the inhibition of ergosterol biosynthesis, but that it involves ROS production in yeast cells.

Strategic incorporation of fluorine in the drug discovery of new-generation antitubercular agents targeting bacterial cell division protein FtsZ

This article presents an account of our research on the discovery and development of new-generation fluorine-containing antibacterial agents against drug-resistant tuberculosis, targeting FtsZ. FtsZ is an essential protein for bacterial cell division and a highly promising therapeutic target for antibacterial drug discovery. Through design, synthesis and semi-HTP screening of libraries of novel benzimidazoles, followed by SAR studies, we identified highly potent lead compounds. However, these lead compounds were found to lack sufficient metabolic and plasma stabilities. Accordingly, we have performed extensive study on the strategic incorporation of fluorine into lead compounds to improve pharmacological properties. This study has led to the development of highly efficacious fluorine-containing benzimidazoles as potential drug candidates. We have also performed computational docking analysis of these novel FtsZ inhibitors to identify their putative binding site. Based on the structural data and docking analysis, a plausible mode-of-action for this novel class of FtsZ inhibitors is proposed.

Design and Synthesis of Some Novel Fluorobenzimidazoles Substituted with Structural Motifs Present in Physiologically Active Natural Products for Antitubercular Activity

Keeping in view the drawbacks associated with research on anti-TB drugs based on plant extracts and the non-availability of fluorinated natural products with antitubercular activity has prompted us to make an effort towards the synthesis and characterization of a novel series of fifteen substituted fluorobenzimidazoles. The newly synthesized compounds were characterized by I.R, ¹H-NMR, ¹³C-NMR, Mass, and elemental analysis. The synthesized compounds 4(a-f) and 5(b-j) have been evaluated for their in-vitro antimycobacterial activity against H37Rv strain (ATCC 27294) by MABA method. Incorporation of methylenedioxyphenyl moiety at 2- and 6-position of the benzimidazole ring furnished compounds 4d and 5i with antitubercular activity comparable or more potent than the naturally occurring compounds with reported antitubercular activity. Among the fifteen tested compounds, 4d and 5i emerged as promising hits characterized by MIC lower than that determined for sesamin against the pathogenic H37Rv strain. Antitubercular activity results indicate that these compounds may be suitable for further lead optimization. The cytotoxic effect of these active compounds on THP-1 cell line was assessed by MTT assay and the results suggest that these two molecules are potential candidates for further development as antitubercular agents.

Recent advances in the discovery and development of antibacterial agents targeting the cell-division protein FtsZ

With the emergence of multidrug-resistant bacterial strains, there is a dire need for new drug targets for antibacterial drug discovery and development. Filamentous temperature sensitive protein Z (FtsZ), is a GTP-dependent prokaryotic cell division protein, sharing less than 10% sequence identity with the eukaryotic cell division protein, tubulin. FtsZ forms a dynamic Z-ring in the middle of the cell, leading to septation and subsequent cell division. Inhibition of the Z-ring blocks cell division, thus making FtsZ a highly attractive target. Various groups have been working on natural products and synthetic small molecules as inhibitors of FtsZ. This review summarizes the recent advances in the development of FtsZ inhibitors, focusing on those in the last 5years, but also includes significant findings in previous years.

Drug resistance mechanisms and novel drug targets for tuberculosis therapy

Drug-resistant tuberculosis (TB) poses a significant challenge to the successful treatment and control of TB worldwide. Resistance to anti-TB drugs has existed since the beginning of the chemotherapy era. New insights into the resistant mechanisms of anti-TB drugs have been provided. Better understanding of drug resistance mechanisms helps in the development of new tools for the rapid diagnosis of drug-resistant TB. There is also a pressing need in the development of new drugs with novel targets to improve the current treatment of TB and to prevent the emergence of drug resistance in Mycobacterium tuberculosis. This review summarizes the anti-TB drug resistance mechanisms, furnishes some possible novel drug targets in the development of new agents for TB therapy and discusses the usefulness using known targets to develop new anti-TB drugs. Whole genome sequencing is currently an advanced technology to uncover drug resistance mechanisms in M. tuberculosis. However, further research is required to unravel the significance of some newly discovered gene mutations in their contribution to drug resistance.

FtsZ inhibition and redox modulation with one chemical scaffold: Potential use of dihydroquinolines against mycobacteria

The dual effect of FtsZ inhibition and oxidative stress by a group of 1,2-dihydroquinolines that culminate in bactericidal effect on mycobacterium strains is demonstrated. They inhibited the non-pathogenic Mycobacterium smegmatis mc(2) 155 with MIC as low as 0.9 μg/mL and induced filamentation. Detailed studies revealed their ability to inhibit polymerization and GTPase activity of MtbFtsZ (Mycobacterial filamentous temperature sensitive Z) with an IC50 value of ∼40 μM. In addition to such target specific effects, these compounds exerted a global cellular effect by causing redox-imbalance that was evident from overproduction of ROS in treated cells. Such multi-targeting effect with one chemical scaffold has considerable significance in this era of emerging drug resistance and could offer promise in the development of new therapeutic agents against tuberculosis.

Synthesis and investigation of novel benzimidazole derivatives as antifungal agents

The rise and emergence of resistance to antifungal drugs by diverse pathogenic fungal strains have resulted in an increase in demand for new antifungal agents. Various heterocyclic scaffolds with different mechanisms of action against fungi have been investigated in the past. Herein, we report the synthesis and antifungal activities of 18 alkylated mono-, bis-, and trisbenzimidazole derivatives, their toxicities against mammalian cells, as well as their ability to induce reactive oxygen species (ROS) in yeast cells. Many of our bisbenzimidazole compounds exhibited moderate to excellent antifungal activities against all tested fungal strains, with MIC values ranging from 15.6 to 0.975μg/mL. The fungal activity profiles of our bisbenzimidazoles were found to be dependent on alkyl chain length. Our most potent compounds were found to display equal or superior antifungal activity when compared to the currently used agents amphotericin B, fluconazole, itraconazole, posaconazole, and voriconazole against many of the strains tested.

Identification of agents targeting FtsZ assembly

Filamenting temperature-sensitive mutant Z (FtsZ), an essential cell division protein in bacteria, has recently emerged as an important and exploitable antibacterial target. Cytokinesis in bacteria is regulated by the assembly dynamics of this protein, which is ubiquitously present in eubacteria. The perturbation of FtsZ assembly has been found to have a deleterious effect on the cytokinetic machinery and, in turn, upon cell survival. FtsZ is highly conserved among prokaryotes, offering the possibility of broad-spectrum antibacterial agents, while its limited sequence homology with tubulin (an essential protein in eukaryotic mitosis) offers the possibility of selective toxicity. This review aims to summarize current knowledge regarding the mechanism of action of FtsZ, and to highlight existing attempts toward the development of clinically useful inhibitors.

Synthesis of cycloalkyl substituted purine nucleosides via a metal-free radical route

An efficient route to synthesize cycloalkyl substituted purine nucleosides was developed. This metal-free C-H activation was accomplished by a tBuOOtBu initiated radical reaction. By adjusting the amount of tBuOOtBu and reaction time, the selective synthesis of C6-monocycloalkyl or C6,C8-dicycloalkyl substituted purine nucleosides could be realized. Furthermore, uracil and related nucleosides were also suitable substrates, giving the C5-cyclohexyl substituted uracil derivatives in good yields with excellent regioselectivities.