Conventional and microwave-assisted synthesis of new indole-tethered benzimidazole-based 1,2,3-triazoles and evaluation of their antimycobacterial, antioxidant and antimicrobial activities

Design, Synthesis and Biological Evaluation of Ethyl 5-(1-benzyl-1H-indol-5-yl) Isoxazole-3-Carboxylates as Antimycobacterial Agents

The continued prevalence of drug-resistant Mycobacterium tuberculosis (Mtb) strains, particularly against first-line antitubercular (anti-TB) drugs, presents an impending public health threat that necessitates the exploration and development of New Chemical Entities (NCEs). In search of new anti-TB leads, a library of ethyl 5-(1-benzyl-1H-indol-5-yl) isoxazole-3-carboxylates were generated through a strategy of scaffold hopping from the proven isoxazole-3-carboxylate-based anti-TB pharmacophore. We evaluated their antibacterial potential against a panel of pathogenic bacteria and Mtb H37Rv strains. The majority of the compounds exhibited notable in vitro efficacy against the H37Rv strains (MIC 0.25 to 16 μg/mL) and were not cytotoxic with a Selectivity Index (SI) >10. Compound 5e (3,4-dichlorobenzyl substituent) was found to be optimally active in the lot (MIC 0.25 μg/mL) and SI >200. It also displayed equipotent activity against drug-resistant Mtb (DR-Mtb) strains. In addition, it demonstrated concentration-dependent bactericidal activity in a time-kill kinetic assay similar to first-line anti-TB drugs besides exhibiting synergistic activity with Streptomycin. Moreover, it complies with the drug-likeness characteristic, making it a promising candidate for further exploration as a probable anti-TB lead.

Benzimidazole(s): synthons, bioactive lead structures, total synthesis, and the profiling of major bioactive categories

Benzimidazole, a fused bicyclic compound with benzene and pentacyclic 1,3-diazole moeities, has a simple aromatic heterocyclic structure. The moiety has become an indispensable anchor for the development of new pharmacologically active products, and has yielded several therapeutic agents with anticancer, antihypertensive, antimicrobial, antifungal and antiulcer effects. Benzimidazoles, as synthetically feasible and pharmacophoric synthons, have been relentlessly pursued for the preparation of new analogues and derivatives, and they have successfully developed into some of the most sought-after and vital pharmacophores for drug discovery. The use of varied substituents and differing patterns around the benzimidazole nucleus has provided a wide spectrum of biological activities. In addition, the benzimidazole moiety constitutes a building block for the production of several drugs, drug candidates, new chemical entities, and lead molecules. The importance of this nucleus for bioactivity, e.g., antibacterial, antitubercular, antidiabetic, anticancer, antifungal, anti-inflammatory, analgesic, antioxidant, antihistaminic, and antimalarial activity, has led us to take note and provide an overview of the synthetic development approaches for various benzimidazole derivatives together with their biological actions. This review is projected to further assist in the design and development of new benzimidazole-based compounds for new and optimized pharmacologically active products towards new drug-development strategies.

Development of 1,2,3-Triazolopyridazinone Derivatives as Potential Caspase 3 and Apoptosis Inducers: Design, Synthesis and Anticancer Activity Studies

Herein, the synthesis, anticancer activity and apoptotic pathways of 1,2,3-triazolopyridazinones compounds, which are similar to DNA bases not previously found in the literature have been investigated. To achieve this goal, it is designed the hybrid molecules combining triazole and pyridazinone/pyridazithione structures, bearing a lipophilic group (benzyl/phenyl) at the one position and benzene with electron withdrawing or donating groups at five positions, with high pharmacophoric properties on the same scaffold structure. The representative compounds in this series 5a, 5c, 6a and 8c exhibited higher anticancer activity than other compounds and cisplatin control against breast (MCF-7) and lung (A549) cell lines. These compounds were less toxic when tested against the noncancerous L929 cell line. In addition, the apoptotic effect mechanisms of these compounds were confirmed by AO/EB staining and caspase 3 activity results. These findings indicate that some derivatives of these compounds could be effective therapeutic agents for the treatment of cancer disease with an apoptosis-promoting.

Microwave-induced one-pot synthesis of 3-imidazolyl indole clubbed 1,2,3-triazole hybrids as antiproliferative agents and density functional theory study

Herein, we outline a highly efficient PEG-4000-mediated one-pot three-component reaction for the synthesis of 3-imidazolyl indole clubbed 1,2,3-triazole derivatives (5a-r) at up to 96% yield as antiproliferative agents. This three-component protocol offers the advantages of an environmentally benign reaction, excellent yield, quick response time, and operational simplicity triggered by the copper catalyst under microwave irradiation. All the synthesized compounds were tested for antiproliferative activity against six human solid tumor cell lines, that is, A549 and SW1573 (nonsmall cell lung), HBL100 and T-47D (breast), HeLa (cervix), and WiDr (colon). Among them, six compounds, 5g-j, 5m, and 5p, demonstrated effective antiproliferative action with GI50 values under 10 μM. Furthermore, density functional theory (DFT) calculations were performed for all the synthesized molecules through geometry optimizations, frontier molecular orbital approach, and molecular electrostatic potential (MESP). The theoretical DFT calculation was performed using the DFT/B3LYP/6-31+G (d,p) basis set. Moreover, the biological reactivity of all the representative synthesized molecules was compared with the theoretically calculated quantum chemical descriptors and MESP 3D plots. We also investigated the drug-likeness characteristic and absorption, distribution, metabolism, excretion, and toxicity (ADMET) prediction. In general, our approach enables environmentally friendly access to 3-imidazolyl indole clubbed 1,2,3-triazole derivatives as prospective antiproliferative agents.

A Review on Indole-triazole Molecular Hybrids as a Leading Edge in Drug Discovery: Current Landscape and Future Perspectives

Molecular hybridization is a rational design strategy used to create new ligands or prototypes by identifying and combining specific pharmacophoric subunits from the molecular structures of two or more known bioactive derivatives. Molecular hybridization is a valuable technique in drug discovery, enabling the modulation of unwanted side effects and the creation of potential dual-acting drugs that combine the effects of multiple therapeutic agents. Indole-triazole conjugates have emerged as promising candidates for new drug development. The indole and triazole moieties can be linked through various synthetic strategies, such as click chemistry or other coupling reactions, to generate a library of diverse compounds for biological screening. The achievable structural diversity with indole-triazole conjugates offers avenues to optimize their pharmacokinetic and pharmacodynamic attributes, amplifying their therapeutic efficacy. Researchers have extensively tailored both indole and triazole frameworks with diverse modifications to comprehend their impact on the drug's pharmacokinetic and pharmacodynamic characteristics. The current review article endeavours to explore and discuss various research strategies to design indoletriazole hybrids and elucidate their significance in a variety of pathological conditions. The insights provided herein are anticipated to be beneficial for the researchers and will likely encourage further exploration in this field.

Benzimidazole-Triazole Hybrids as Antimicrobial and Antiviral Agents: A Systematic Review

Bacterial infections have attracted the attention of researchers in recent decades, especially due to the special problems they have faced, such as their increasing diversity and resistance to antibiotic treatment. The emergence and development of the SARS-CoV-2 infection stimulated even more research to find new structures with antimicrobial and antiviral properties. Among the heterocyclic compounds with remarkable therapeutic properties, benzimidazoles, and triazoles stand out, possessing antimicrobial, antiviral, antitumor, anti-Alzheimer, anti-inflammatory, analgesic, antidiabetic, or anti-ulcer activities. In addition, the literature of the last decade reports benzimidazole-triazole hybrids with improved biological properties compared to the properties of simple mono-heterocyclic compounds. This review aims to provide an update on the synthesis methods of these hybrids, along with their antimicrobial and antiviral activities, as well as the structure-activity relationship reported in the literature. It was found that the presence of certain groups grafted onto the benzimidazole and/or triazole nuclei (-F, -Cl, -Br, -CF₃, -NO₂, -CN, -CHO, -OH, OCH₃, COOCH₃), as well as the presence of some heterocycles (pyridine, pyrimidine, thiazole, indole, isoxazole, thiadiazole, coumarin) increases the antimicrobial activity of benzimidazole-triazole hybrids. Also, the presence of the oxygen or sulfur atom in the bridge connecting the benzimidazole and triazole rings generally increases the antimicrobial activity of the hybrids. The literature mentions only benzimidazole-1,2,3-triazole hybrids with antiviral properties. Both for antimicrobial and antiviral hybrids, the presence of an additional triazole ring increases their biological activity, which is in agreement with the three-dimensional binding mode of compounds. This review summarizes the advances of benzimidazole triazole derivatives as potential antimicrobial and antiviral agents covering articles published from 2000 to 2023.

Synthesis, biological evaluation, and in silico studies of indole-tethered pyrazoline derivatives as anticancer agents targeting topoisomerase IIα

We herein report a new series of indole-tethered pyrazoline derivatives as potent anticancer agents. A total of 12 compounds were designed and synthesized by conventional as well as microwave-irradiated synthesis methods. The latter method results in a significant reduction in the duration of reaction along with improved yields. All synthesized derivatives (7a-7l) were evaluated for their cytotoxic activity against A431, HeLa, and MDAMB-231 cell lines. Compounds 7a and 7b were found most potent in the series and demonstrated an IC₅₀ value of 3.17 and 5.16 µM against the A431 cell line, respectively, compared to the standard drug doxorubicin. Compounds 7a and 7b significantly suppress colony formation, migration, and S phase cell cycle arrest of A431 cells. Furthermore, compound 7a regulated the expression of apoptotic proteins causing the downregulation of procaspase 3/9, antiapoptotic protein Bcl-xL, and upregulation of proapoptotic protein Bax in a dose-dependent manner. Topoisomerase enzyme inhibition assay confirmed that compounds 7a and 7b can significantly inhibit topoisomerase IIα. In vivo oral acute toxicity of compounds 7a and 7b revealed that both compounds are safe compared to doxorubicin; cardiomyopathy studies showed normal architecture of cardiomyocytes and myofibrils. In addition, molecular docking studies revealed the possible interaction of compounds 7a and 7b within the active binding site of the topoisomerase enzyme. The 100 ns molecular dynamic simulation of compounds 7a and 7b proved that both compounds validate all screening parameters.

Indole: A promising scaffold for the discovery and development of potential anti-tubercular agents

Indole-containing small molecules have been reported to have diverse pharmacological activities. The aromatic heterocyclic scaffold, which resembles various protein structures, has received attention from organic and medicinal chemists. Exploration of indole derivatives in drug discovery has rapidly yielded a vast array of biologically active compounds with broad therapeutic potential. Nature is the major source of indole scaffolds, but various classical and advanced synthesis methods for indoles have also been reported. One-pot synthesis is widely considered an efficient approach in synthetic organic chemistry and has been used to synthesize some indole compounds. The rapid emergence of drug-resistant tuberculosis is a major challenge to be addressed. Identifying novel targets and drug candidates for tuberculosis is therefore crucial. Researchers have extensively explored indole derivatives as potential anti-tubercular agents or drugs. Indole scaffolds containing the novel non-covalent (decaprenylphosphoryl-β-D-ribose2'-epimerase) DprE1 inhibitor 1,4-azaindole is currently in clinical trials to treat Mycobacterium tuberculosis. In addition, DG167 indazole sulfonamide with potent anti-tubercular activity is undergoing early-stage development in preclinical studies. Indole bearing cationic amphiphiles with high chemical diversity have been reported to depolarize and disrupt the mycobacterial membrane. Some indole-based compounds have potential inhibitory activities against distinct anti-tubercular targets, including the inhibition of cell wall synthesis, replication, transcription, and translation, as summarized in the graphical abstract. The success of computer-aided drug design in the fields of cancer and anti-viral drugs has accelerated in silico studies in antibacterial drug development. This review describes the sources of indole scaffolds, the potential for novel indole derivatives to serve as anti-tubercular agents, in silico findings, and proposed actions to facilitate the design of novel compounds with anti-tubercular activity.

A Comprehensive Account on Recent Progress in Pharmacological Activities of Benzimidazole Derivatives

Nowadays, nitrogenous heterocyclic molecules have attracted a great deal of interest among medicinal chemists. Among these potential heterocyclic drugs, benzimidazole scaffolds are considerably prevalent. Due to their isostructural pharmacophore of naturally occurring active biomolecules, benzimidazole derivatives have significant importance as chemotherapeutic agents in diverse clinical conditions. Researchers have synthesized plenty of benzimidazole derivatives in the last decades, amidst a large share of these compounds exerted excellent bioactivity against many ailments with outstanding bioavailability, safety, and stability profiles. In this comprehensive review, we have summarized the bioactivity of the benzimidazole derivatives reported in recent literature (2012-2021) with their available structure-activity relationship. Compounds bearing benzimidazole nucleus possess broad-spectrum pharmacological properties ranging from common antibacterial effects to the world's most virulent diseases. Several promising therapeutic candidates are undergoing human trials, and some of these are going to be approved for clinical use. However, notable challenges, such as drug resistance, costly and tedious synthetic methods, little structural information of receptors, lack of advanced software, and so on, are still viable to be overcome for further research.

Urea-thiazole/benzothiazole hybrids with a triazole linker: synthesis, antimicrobial potential, pharmacokinetic profile and in silico mechanistic studies

Some urea-thiazole/benzothiazole hybrids with a triazole linker were synthesized via Cu(I)-catalysed click reaction. After successfully analysed by various spectral techniques including FTIR, NMR and HRMS, antimicrobial screening of the synthesized hybrids along with their precursors was carried out against two Gram (+) bacteria (Staphylococcus aureus and Bacillus endophyticus), two Gram (-) bacteria (Escherichia coli and Pseudomonas fluorescens) and two fungi (Candida albicans and Rhizopus oryzae). All the synthesized compounds (4a-4l) displayed better biological response than the standard fluconazole against both of the tested fungi. Compounds 4h and 4j were found to be the most active compounds against R. oryzae and C. albicans, respectively. Molecular docking of hybrid 4j and its alkyne precursor 1b in the active site of C. albicans target sterol 14-α demethylase was also performed and was also supported by molecular dynamics studies. In silico ADME prediction of synthesized urea-thiazole/benzothiazole hybrids with a triazole linker and their alkyne precursors was also predicted.

Current Insights into the Chemistry and Antitubercular Potential of Benzimidazole and Imidazole Derivatives

Tuberculosis is a disease caused by Mycobacterium tuberculosis (Mtb), affecting millions of people worldwide. The emergence of drug resistance is a major problem in the successful treatment of tuberculosis. Due to the commencement of MDR-TB (multi-drug resistance) and XDR-TB (extensively drug resistance), there is a crucial need for the development of novel anti-tubercular agents with improved characteristics such as low toxicity, enhanced inhibitory activity and short duration of treatment. In this direction, various heterocyclic compounds have been synthesized and screened against Mycobacterium tuberculosis. Among them, benzimidazole and imidazole containing derivatives have been found to have potential anti-tubercular activity. The present review focuses on various imidazole and benzimidazole derivatives (from 2015-2019) with their structure-activity relationships in the treatment of tuberculosis.

Triazole based isatin derivatives as potential inhibitor of key cancer promoting kinases- insight from electronic structure, docking and molecular dynamics simulations

Computer Aided Drug Design approaches have been applied to predict potential inhibitors for two different kinases, namely, cyclin-dependent kinase 2 (CDK2) and Epidermal Growth Factor Receptor (EGFR) which are known to play crucial role in cancer growth. We have designed alkyl and aryl substituted isatin-triazole ligands and performed molecular docking to rank and predict possible binding pockets in CDK2 and EGFR kinases. Best-scoring ligands in the kinase-binding pocket were selected from the docking study and subjected to molecular dynamics simulation. Absolute binding affinities were estimated from the MD trajectories using the MM/PBSA approach. The results suggest that aryl substituted isatin-triazole ligands are better binder to the kinases relative to its alkyl analogue. Furthermore, aryl substituted isatin-triazole ligands prefer binding to EGFR kinases relative to CDK2. The ligand binding pockets of the kinases are primarily hydrophobic in nature. Ligand-kinase binding is favoured by electrostatic and Van der Waals interactions, later being the major contributor. Large estimated negative binding affinities (~ -10 to -25 kcal/mol) indicate that the ligands might inhibit the kinases. Physicochemical property analysis suggests that the proposed ligands could be orally bio-available.

Development of novel anti-infective and antioxidant azole hybrids using a wet and dry approach

Background: Considering emerging drug resistance in microbes, this work is focused on the synthesis of azole hybrids as novel antimicrobials. Materials & methods: The triazole derivatives were prepared using azide alkyne cycloaddition reaction. The antimicrobial potential of these compounds was evaluated by serial dilution method. Results: A series of azole hybrids containing benzimidazole-1,2,3-triazole skeleton was designed and synthesized via click reaction. Compound 4s showed notable antimicrobial activity against Staphylococcus aureus and Candida albicans (MIC 0.0165 μmol/ml), and 4q gives remarkable radical scavenging activity (IC₅₀ 0.0092 μmol/ml). The compounds 4a, 4k, 4o, 4s, 4x. 4m, 4n, 4s, 4t and 4x are commendable antibacterial and antifungal molecules, even better than established drugs. Molecular docking reveals that compound 4s binds with tyrosyl-tRNA synthetase residues through two H-bonds. Conclusion: Compounds 4s and 4k may be considered valuable lead compounds for further optimization as antimicrobial drugs.

Novel core-shell nanocomposite as an effective heterogeneous catalyst for the synthesis of benzimidazoles

Core-shell nanocomposites with a catalytic metal-organic framework (MOF) shell are more effective and stable than bare MOF. We have successfully designed an effective heterogeneous catalyst for the synthesis of benzimidazole by integrating acidic catalytic activity, and promoted the aerobic oxidation and magnetic recyclability of core-shell nanocomposite Fe₃O₄@SiO₂@UiO-66. The Fe₃O₄@SiO₂ core is encapsulated by the in situ-grown UiO-66 shell, and the UiO-66 shell retains the porous structure and crystallinity of UiO-66 with abundant exposed Lewis acid sites. It shows high catalytic ability for the synthesis of various benzimidazoles through the acid-catalyzed condensation and aerobic oxidation with in situ oxygen. The Fe₃O₄@SiO₂ core provides magnetic recyclability of Fe₃O₄@SiO₂@UiO-66, and maintains high catalytic ability and stability over six cycles.

Triazole-containing hybrids with anti-Mycobacterium tuberculosis potential - Part I: 1,2,3-Triazole

Tuberculosis regimens currently applied in clinical practice require months of multidrug therapy, which imposes a major challenge of patient compliance and drug resistance development. Moreover, because of the increasing emergence of hard-to-treat tuberculosis, this disease continues to be a significant threat to the human population. 1,2,3-triazole as a privileged structure has been widely used as an effective template for drug discovery, and 1,2,3-triazole-containing hybrids that can simultaneously act on dual or multiple targets in Mycobacterium tuberculosis have the potential to circumvent drug resistance, enhance efficacy, reduce side effects and improve pharmacokinetic as well as pharmacodynamic profiles. Thus, 1,2,3-triazole-containing hybrids are useful scaffolds for the development of antitubercular agents. This review aims to highlight recent advances of 1,2,3-triazole-containing hybrids with potential activity against various forms of M. tuberculosis, covering articles published between 2015 and 2020. The structure-activity relationship and the mechanism of action are also discussed to facilitate further rational design of more effective drug candidates.

Design and Synthesis of 2-(5-Phenylindol-3-yl)benzimidazole Derivatives with Antiproliferative Effects towards Triple-Negative Breast Cancer Cells by Activation of ROS-Mediated Mitochondria Dysfunction

Benzimidazole derivatives are widely studied because of their broad-spectrum biological activity, such as antitumor properties and excellent fluorescence performance. Herein, two types of 2-(5-phenylindol-3-yl)benzimidazole derivatives (1 a-1 h and 2 a-2 e) were rationally designed and synthesized. When these compounds were investigated in vitro anti-screening assays, we found that all of them possessed antitumor effect, in particular compound 1 b, which showed an outstanding antiproliferative effect on MDA-MB-231 cells (IC₅₀ ≈2.6 μm). A study of the drug action mechanisms in cells showed that the antitumor activity of the compounds is proportional to their lipophilicity and cellular uptake; the tested compounds all entered the lysosome of MDA-MB-231 cells and caused changes in the levels of reactive oxygen species (ROS), and then caused mitochondrial damage. Apparent differences in the ROS levels for each compound suggest that the lethality of these compounds towards MDA-MB-231 cells is closely related to the ROS levels. Taken together, this study not only provides a theoretical basis for 2-(5-phenylindol-3-yl)benzimidazole anticarcinogens but also offers new thinking on the rational design of next-generation antitumor benzimidazole derivatives.

Discovery of new potent dual sigma receptor/GluN2b ligands with antioxidant property as neuroprotective agents

Among several potential applications, sigma receptors (σRs) can be used as neuroprotective agents, antiamnesic, antipsychotics and against other neurodegenerative disorders. On the other hands, antagonists of the GluN2b-subunit-containing-N-methyl-D-aspartate (NMDA) receptors are of major interest for the same purpose, being this subunit expressed in specific areas of the central nervous system and responsible for the excitatory regulation of nerve cells. Under these premises, we have synthesized and biologically tested novel hybrid derivatives obtained from the combination of phenyloxadiazolone and dihydroquinolinone scaffolds with different amine moieties, peculiar of σ2R ligands. Most of the new ligands exhibited a pan-affinity towards both σR subtypes and high affinity against GluN2b subunit. The most promising compounds belong to the dihydroquinolinone series, with the best affinity profile for the cyclohexylpiperazine derivative 28. Investigation on their biological activity showed that the new compounds were able to protect SH-SY5Y cells against oxidative stress induced by hydrogen peroxide treatment. These results proved that our dual σR/GluN2b ligands have beneficial effects in a model of neuronal oxidative stress and can represent strong candidate pharmacotherapeutic agents for minimizing oxidative stress-induced neuronal injuries.

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.