Synthesis, biological evaluation and molecular docking study of some novel indole and pyridine based 1,3,4-oxadiazole derivatives as potential antitubercular agents

Biocatalytic synthesis of oxa(thia)diazole aryl thioethers

A novel approach for the synthesis of 1,3,4-oxa(thia)diazole aryl thioethers through a biocatalytic strategy has been introduced. By leveraging Myceliophthora thermophila laccase (Novozym 51003) as a catalyst, catechol undergoes oxidation to ortho-quinone, facilitating subsequent 1,4-thia-Michael addition reactions. The method offers efficiency and mild reaction conditions, demonstrating promise for sustainable synthesis pathways in organic chemistry. Using this approach, 13 new derivatives of 2,5-disubstituted-1,3,4-oxa(thia)diazole aryl thioethers, with a yield of 46-94%, were synthesized.

Unlocking InhA: Novel approaches to inhibit Mycobacterium tuberculosis

Multidrug-resistant tuberculosis continues to pose a health security risk and remains a public health emergency. Antimicrobial resistance result from treatment regimens that are both insufficient and incomplete leading to the emergence of multidrug-resistant tuberculosis, extensively drug-resistant tuberculosis and totally drug-resistant tuberculosis. The impact of tuberculosis on the people suffering from HIV (Human immunodeficiency virus infection) have resulted in the increased research efforts in designing and discovery of novel antitubercular drugs that may result in decreasing treatment duration, minimising the need for multiple drug intake, minimising cytotoxicity and enhancing the mechanism of action of drug. While many drugs are available to treat tuberculosis, a precise and timely cure is still absent. Consequently, further investigation is needed to identify more recent molecular equivalents that have the potential to swiftly remove this disease. Isoniazid (INH), a treatment for tuberculosis (TB), targets the enzyme InhA (mycobacterium enoyl acyl carrier protein reductase), the Mycobacterium tuberculosis enoyl-acyl carrier protein (ACP) reductase, most common INH resistance is circumvented by InhA inhibitors that do not require KatG (catalase-peroxidase) activation, as a result, researchers are trying to work in the area of development of InhA inhibitors which could help in eradicating the era of tuberculosis from the world.

Current Market Potential and Prospects of Copper-based Pyridine Derivatives: A Review

Nicotine, minodronic acid, nicotinamide (niacin), zolpidem, zolimidine, and other pyridine-based chemicals play vital roles in medicine and biology. Pyridinecontaining drugs are widely available on the market to treat a wide range of human ailments. As a result of these advances, pyridine research is continually expanding, and there are now higher expectations for how it may aid in the treatment of numerous ailments. This evaluation incorporates data acquired from sources, like PubMed, to provide a thorough summary of the approved drugs and bioactivity data for compounds containing pyridine. Most of the reactions discussed in this article will provide readers with a deeper understanding of various pyridine-related examples, which is necessary for the creation of copper catalysis-based synthetic processes that are more accessible, secure, environmentally friendly, and practical, and that also have higher accuracy and selectivity. This paper also discusses significant innovations in the multi-component copper-catalyzed synthesis of N-heterocycles (pyridine), with the aim of developing precise, cost-effective, and environmentally friendly oxygenation and oxidation synthetic methods for the future synthesis of additional novel pyridine base analogs. Therefore, the review article will serve as a novel platform for researchers investigating copperbased pyridine compounds.

Targeting polyketide synthase 13 for the treatment of tuberculosis

Tuberculosis (TB) is one of the most threatening diseases for humans, however, the drug treatment strategy for TB has been stagnant and inadequate, which could not meet current treatment needs. TB is caused by Mycobacterial tuberculosis, which has a unique cell wall that plays a crucial role in its growth, virulence, and drug resistance. Polyketide synthase 13 (Pks13) is an essential enzyme that catalyzes the biosynthesis of the cell wall and its critical role is only found in Mycobacteria. Therefore, Pks13 is a promising target for developing novel anti-TB drugs. In this review, we first introduced the mechanism of targeting Pks13 for TB treatment. Subsequently, we focused on summarizing the recent advance of Pks13 inhibitors, including the challenges encountered during their discovery and the rational design strategies employed to overcome these obstacles, which could be helpful for the development of novel Pks13 inhibitors in the future.

Design, synthesis, antimicrobial activity, DFT, and molecular docking studies of pyridine-pyrazole-based dihydro-1,3,4-oxadiazoles against various bacterial and fungal targets

Antimicrobial resistance which is increasing at an alarming rate is a severe public health issue worldwide. Hence, the development of novel antibiotics is an urgent need as microbes have developed resistance against available antibiotics. In search of novel antimicrobial agents, a convenient route for the preparation of substituted 3-(1-phenyl-3-(p-tolyl)-1H-pyrazol-4-yl)-1-(2-phenyl-5-(pyridin-3-yl)-1,3,4-oxadiazol-3(2H)-yl)prop-2-en-1-ones (6a-6o) has been adopted by using pyridine-3-carbohydrazide and various aromatic aldehydes. The newly synthesized compounds were characterized by using various spectral techniques, for example, IR, 1 H NMR, 13 C NMR, and mass spectroscopy. Synthesized hybrids were studied for in vitro antimicrobial potency against various bacterial and fungal strains. Antibacterial results revealed that compounds 6e, 6h, 6i, 6l, and 6m were found to be most active against bacterial strains as they showed minimum inhibitory concentration (MIC) value of 62.5 μg/mL while compounds 6d, 6e, and 6h showed MIC value of 200 μg/mL against Candida albicans. The quantum parameters that relate to the bioavailability of the compounds were computed, followed by docking with different bacterial and fungal targets like sortase A, dihydrofolate reductase, thymidylate kinase, gyrase B, sterol 14-alpha demethylase. The experimental and computational results are in good agreement.

In Silico Development of Novel Benzofuran-1,3,4-Oxadiazoles as Lead Inhibitors of M. tuberculosis Polyketide Synthase 13

Benzofuran and 1,3,4-oxadiazole are privileged and versatile heterocyclic pharmacophores which display a broad spectrum of biological and pharmacological therapeutic potential against a wide variety of diseases. This article reports in silico CADD (computer-aided drug design) and molecular hybridization approaches for the evaluation of the chemotherapeutic efficacy of 16 S-linked N-phenyl acetamide moiety containing benzofuran-1,3,4-oxadiazole scaffolds BF1-BF16. This virtual screening was carried out to discover and assess the chemotherapeutic efficacy of BF1-BF16 structural motifs as Mycobacterium tuberculosis polyketide synthase 13 (Mtb Pks13) enzyme inhibitors. The CADD study results revealed that the benzofuran clubbed oxadiazole derivatives BF3, BF4, and BF8 showed excellent and remarkably significant binding energies against the Mtb Pks13 enzyme comparable with the standard benzofuran-based TAM-16 inhibitor. The best binding affinity scores were displayed by 1,3,4-oxadiazoles-based benzofuran scaffolds BF3 (-14.23 kcal/mol), BF4 (-14.82 kcal/mol), and BF8 (-14.11 kcal/mol), in comparison to the binding affinity score of the standard reference TAM-16 drug (-14.61 kcal/mol). 2,5-Dimethoxy moiety-based bromobenzofuran-oxadiazole derivative BF4 demonstrated the highest binding affinity score amongst the screened compounds, and was higher than the reference Pks13 inhibitor TAM-16 drug. The bindings of these three leads BF3, BF4, and BF8 were further confirmed by the MM-PBSA investigations in which they also exhibited strong bindings with the Pks13 of Mtb. Moreover, the stability analysis of these benzofuran-1,3,4-oxadiazoles in the active sites of the Pks13 enzyme was achieved through molecular dynamic (MD) simulations at 250 ns virtual simulation time, which indicated that these three in silico predicted bio-potent benzofuran tethered oxadiazole molecules BF3, BF4, and BF8 demonstrated stability with the active site of the Pks13 enzyme.

Recent Advances in Pyridine Scaffold: Focus on Chemistry, Synthesis, and Antibacterial Activities

Multidrug-resistant (MDR) pathogens have created a fatal problem for human health and antimicrobial treatment. Among the currently available antibiotics, many are inactive against MDR pathogens. In this context, heterocyclic compounds/drugs play a vital role. Thus, it is very much essential to explore new research to combat the issue. Of the available nitrogen-bearing heterocyclic compounds/drugs, pyridine derivatives are of special interest due to their solubility. Encouragingly, some of the newly synthesized pyridine compounds/drugs are found to inhibit multidrug-resistant S. aureus (MRSA). Pyridine scaffold bearing poor basicity generally improves water solubility in pharmaceutically potential molecules and has led to the discovery of numerous broad-spectrum therapeutic agents. Keeping these in mind, we have reviewed the chemistry, recent synthetic techniques, and bacterial preventative activity of pyridine derivatives since 2015. This will facilitate the development of pyridine-based novel antibiotic/drug design in the near future as a versatile scaffold with limited side effects for the next-generation therapeutics.

Modular and Computational Access to Innocuous Multistep Metal-Free Synthesis of 1,3,4-Oxadiazoles as Enzyme Inhibitors

An array of 1,3,4-oxadiazole hybrids, 7a-s, structurally intriguing cores with potential in natural product synthesis and drug discovery, have been synthesized using innovative comparable conventional and microwave-assisted protocols. The synthesis was performed by the reaction of secondary amine-based acetamides, 6a-s, as the electrophile and piperidine-based oxadiazoles as the nucleophile, 3, under the metal-free reaction conditions. High yield in minimum time with highest purity was obtained by the microwave-irradiated method instead of the conventional one. The structural elucidations were made through infrared, 1H NMR, 13C NMR, and elemental analysis studies. The whole array of synthesized compounds, 7a-s, was evaluated for their potential against α-glucosidase and butyryl cholinesterase (BChE) enzymes. Natural bond orbital and structural optimizations were made by using the B3LYP method and the basis set of 6-311++G(d,p). Frontier molecular orbitals and molecular electrostatic potential were calculated at the same level of selected compounds as potential candidates against BChE and α-glucosidase enzymes utilizing the time-dependent density functional theory. Fifteen compounds out of 19 were observed to be active against α-glucosidase enzyme in comparison with acarbose as the reference standard and 7 against the BChE enzyme compared to eserine as the reference standard. The highest potential of compound 7j against BChE is well correlated by the higher binding interaction with target protein as -10.2, calculated by docking studies. The recruited compounds against both enzymes could be the best anti-enzymatic drugs and part of drugs discovery programs after further analysis.

Pyridine Derivatives as Potential Inhibitors for Coronavirus SARS-CoV-2: A Molecular Docking Study

Coronavirus SARS-CoV-2, a causative agent for the global epidemic disease COVID-19, which has a highest modality rate. Several initiatives have been undertaken to repurpose current antiviral medications and tested the classic pyridine derivatives (PyDev), which have showed substantial therapeutic potential against a variety of illnesses and also have several biological functions such as, antibacterial, antiviral, and anti-inflammatory. However, limited reports are available for the treatment of Coronavirus SARS-CoV-2 using PyDev. Hence, the possibilities of the best-described PyDev molecules of powerful Coronavirus SARS-CoV-2 inhibitors have been attempted in this investigation. This study primarily focused on blocking four key targets of Coronavirus SARS-CoV-2 proteins. Terpyridine has shown the greatest inhibitory potential (with a binding energy of −8.8 kcal/mol) against all four coronavirus targets. This study results would pave the potential lead medication for Coronavirus SARS-CoV-2 therapeutic strategies.

Synthesis, Biological Evaluation and Computational Studies of New Hydrazide Derivatives Containing 1,3,4-Oxadiazole as Antitubercular Agents

To extend our screening for novel antimycobacterial molecules, we have designed, synthesized, and biologically evaluated a library of 14 new hydrazide derivatives containing 1,3,4-oxadiazole core. A variety of mycobacterial strains, including some drug-resistant strains, were tested for antimycobacterial activity. Among the compounds tested, five showed high antimycobacterial activity (MIC values of 8 μg/mL) against M. tuberculosis H37Ra attenuated strain, and two derivatives were effective (MIC of 4 µg/mL) against pyrazinamide-resistant strains. Furthermore, the novel compounds were tested against the fungal C. albicans strain, showing no antimycotic activity, and thus demonstrating a good selectivity profile. Notably, they also exhibited low cytotoxicity against human SH-SY5Y cells. The molecular modeling carried out suggested a plausible mechanism of action towards the active site of the InhA enzyme, which confirmed our hypothesis. In conclusion, the active compounds were predicted in silico for ADME properties, and all proved to be potentially orally absorbed in humans.

1,3,4-oxadiazole derivatives as potential antimicrobial agents

Due to the emergence of drug-resistant microbial strains, different research groups are continuously developing novel drug molecules against already exploited and unexploited targets. 1,3,4-Oxadiazole derivatives exhibited noteworthy antimicrobial activities. The presence of 1,3,4-oxadiazole moiety in antimicrobial agents can modify their polarity and flexibility, which significantly improves biological activities due to various bonded and non-bonded interactions viz. hydrogen bond, steric, electrostatic, and hydrophobic with target sites. The present review elaborates the therapeutic targets and mode of interaction of 1,3,4-oxadiazoles as antimicrobial agents. 1,3,4-oxadiazole derivatives target enoyl reductase (InhA), 14α-demethylase in the mycobacterial cell; GlcN-6-P synthase, thymidylate synthase, peptide deformylase, RNA polymerase, dehydrosqualene synthase in bacterial strains; ergosterol biosynthesis pathway, P450-14α demethylase, protein-N-myristoyltransferase in fungal strains; FtsZ protein, interfere with purine and functional protein synthesis in plant bacteria. The present review also summarizes the effect of different moieties and functional groups on the antimicrobial activity of 1,3,4-oxadiazole derivatives.

Antibacterial and antibiofilm activities of thiazolidine-2,4-dione and 4-thioxo-thiazolidin-2-one derivatives against multidrug-resistant Staphylococcus aureus clinical isolates

AIMS

Antimicrobial resistance is one of the highest priorities in global public health with Staphylococcus aureus among the most important microorganisms due to its rapidly evolving antimicrobial resistance. Despite all the efforts of antimicrobial stewardship, research and development of new antimicrobials are still imperative. The thiazolidine ring is considered a privileged structure for the development of new antimicrobials. This study aimed to compare the antibacterial effects of two analog series of thiazolidine-2,4-dione and 4-thioxo-thiazolidin-2-one against multidrug-resistant Staphylococcus aureus clinical isolates.

METHODS AND RESULTS

The derivatives 1a, 2a, and 2b exhibited MIC between 1-32 μg.mL^-1 , with time-to-kill curves showing a bactericidal effect up to 24 h. In the antibiofilm assay, the most active derivatives were able to inhibit about 90% of biofilm formation. The 4-thioxo-thiazolidine-2-one derivatives were more active against planktonic cells, while the thiazolidine-2,4-dione derivatives were able to disrupt about 50% of the preformed biofilm. In the in vivo infection model using Caenorhabditis elegans as a host, the derivatives 1a, 2a, and 2b increased nematode survival with a concentration-dependent effect. Exposure of S. aureus to the derivatives 2a and 2b induced surface changes and decrease cell size. None of the derivatives was cytotoxic for human peripheral blood mononuclear cells (PBMC) but showed moderate cytotoxicity for L929 fibroblasts.

CONCLUSION

The 5-(3,4-dichlorobenzylidene)-4-thioxothiazolidin-2-one (2b) was the most active derivative against S. aureus and showed the higher selective indexes.

SIGNIFICANCE AND IMPACT OF STUDY

4-thioxo-thiazolidin-2-one are a promising scaffold for the research and development of new antimicrobial drugs against multidrug-resistant S. aureus.

Catalytic synthesis of new pyrazolo [3,4-b] pyridine via a cooperative vinylogous anomeric-based oxidation

In this study, a novel nano-magnetic metal-organic frameworks based on Fe3O4 namely Fe3O4@MIL-101(Cr)-N(CH2PO3)2 was synthesized and fully characterized. The prepared sample was used as catalyst in the synthesis of pyrazolo [3,4-b] pyridines as convenient medicine by condensation reaction of aldehydes, 5-(1H-Indol-3-yl)- 2H-pyrazol-3-ylamine and 3-(cyanoacetyl)indole via a CVABO. The products were obtained with high yields at 100 °C and under solvent-free conditions.

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.

Antitubercular activity assessment of fluorinated chalcones, 2-aminopyridine-3-carbonitrile and 2-amino-4H-pyran-3-carbonitrile derivatives: In vitro, molecular docking and in-silico drug likeliness studies

A series of newer previously synthesized fluorinated chalcones and their 2-amino-pyridine-3-carbonitrile and 2-amino-4H-pyran-3-carbonitrile derivatives were screened for their in vitro antitubercular activity and in silico methods. Compound 40 (MIC~ 8 μM) was the most potent among all 60 compounds, whose potency is comparable with broad spectrum antibiotics like ciprofloxacin and streptomycin and three times more potent than pyrazinamide. Additionally, compound 40 was also less selective and hence non-toxic towards the human live cell lines-LO2 in its MTT assay. Compounds 30, 27, 50, 41, 51, and 60 have exhibited streptomycin like activity (MIC~16–18 μM). Fluorinated chalcones, pyridine and pyran derivatives were found to occupy prime position in thymidylate kinase enzymatic pockets in molecular docking studies. The molecule 40 being most potent had shown a binding energy of -9.67 Kcal/mol, while docking against thymidylate kinase, which was compared with its in vitro MIC value (~8 μM). These findings suggest that 2-aminopyridine-3-carbonitrile and 2-amino-4H-pyran-3-carbonitrile derivatives are prospective lead molecules for the development of novel antitubercular drugs.

Oxadiazole: A highly versatile scaffold in drug discovery

As a pharmacologically important heterocycle, oxadiazole paved the way to combat the problem associated with the confluence of many commercially available drugs with different pharmacological profiles. The present review focuses on the potential applications of five-membered heterocyclic oxadiazole derivatives, especially 1,2,4-oxadiazole, 1,2,5-oxadiazole, and 1,3,4-oxadiazole, as therapeutic agents. Designing new hybrid molecules containing the oxadiazole moiety is a better solution for the development of new drug molecules. The designed molecules may accumulate a biological profile better than those of the drugs currently available on the market. The present review will guide the way for researchers in the field of medicinal chemistry to design new biologically active molecules based on the oxadiazole nucleus. Antitubercular, antimalarial, anti-inflammatory, anti-HIV, antibacterial, and anticancer activities of various oxadiazoles have been reviewed extensively here.

Biological activity of oxadiazole and thiadiazole derivatives

Abstract

The 5-membered oxadiazole and thiadiazole scaffolds are the most privileged and well-known heterocycles, being a common and essential feature of a variety of natural products and medicinal agents. These scaffolds take up the center position and are the core structural components of numerous drugs that belong to different categories. These include antimicrobial, anti-tubercular, anti-inflammatory, analgesic, antiepileptic, antiviral, and anticancer agents. In this review, we mostly talk about the isomers 1,2,4-oxadiazole and 1,3,4-thiadiazole because they have important pharmacological properties. This is partly because they are chemical and heat resistant, unlike other isomers, and they can be used as bio-isosteric replacements in drug design. We are reviewing the structural modifications of different oxadiazole and thiadiazole derivatives, more specifically, the anti-tubercular and anticancer pharmacological activities reported over the last 5 years, as we have undertaken this as a core area of research. This review article desires to do a thorough study and analysis of the recent progress made in the important biological isomers 1,2,4-oxadiazole and 1,3,4-thiadiazol. This will be a great place to start for future research.

Key points

• Five-membered heterocyclic compound chemistry and biological activity recent survey.

• Synthesis and pharmacological evolution of 1,2,4-oxadiazole and 1,3,4-thiadiazole are discussed in detail.

• The value and significance of heterocyclic compounds in the field of drug designing are highlighted.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-11969-0.

Synthesis, characterization, and in vitro antibacterial activity of some new pyridinone and pyrazole derivatives with some in silico ADME and molecular modeling study

A new series of pyridine-2-one and pyrazole derivatives were designed and synthesized based on cyanoacrylamide derivatives containing 2,4-dichlro aniline and 6-methyl 2-amino pyridine as an aryl group. Condensation of cyanoacrylamide derivatives 3a–d with different active methylene (malononitrile, ethyl cyanoacetate cyanoacetamide, and ethyl acetoacetate) in the presence of piperidine as basic catalyst afforded the corresponding pyridinone derivatives 4a–c, 5, 9, and 13. Furthermore, the reaction of cyanoacrylamide derivatives 3a–d with bi-nucleophile as hydrazine hydrate and thiosemicarbazide afforded the corresponding pyrazole derivatives 14a,b and 16. The newly designed derivatives were confirmed and established based on the elemental analysis and spectra data (IR, 1H NMR, 13C NMR, and mass). The in vitro antibacterial activity was evaluated against four bacterial strains with weak to good antibacterial activity. Moreover, the results indicated that the most active derivatives 3a, 4a, 4b, 9, and 16 might lead to antibacterial agents, especially against B. subtilis and P. vulgaris. The DFT calculations were performed to estimate its geometric structure and electronic properties. In addition, the most active pyridinone and pyrazole derivatives were further evaluated for in silico physicochemical, drug-likeness, and toxicity prediction. These derivatives obeyed all Lipinski’s and Veber’s rules without any violation and displayed non-immunotoxin, non-mutagenic, and non-cytotoxic. Molecular docking simulation was performed inside the active site of Topoisomerase IV (PDB:3FV5). It displayed binding energy ranging from -14.97 kcal/mol to -18.86 kcal/mol with hydrogen bonding and arene–cation interaction. Therefore, these derivatives were suggested to be good antibacterial agents via topoisomerase IV inhibitor.

Graphical abstract

Microwave-Assisted Synthesis of 2-Methyl-1H-indole-3-carboxylate Derivatives via Pd-Catalyzed Heterocyclization

Indole moiety is well-known as a superlative framework in many natural products and synthetic pharmaceuticals. Herein, we report an efficient procedure to synthesize a series of functionalized 2-methyl-1H-indole-3-carboxylate derivatives from commercially available anilines properly functionalized by different electron-withdrawing and -donating groups through a palladium-catalyzed intramolecular oxidative coupling. The conversion of a variety of enamines into the relevant indole was optimized by exposing the neat mixture of reactants to microwave irradiation, obtaining the desired products in excellent yields and high regioselectivity. The synthesized compounds were confirmed by 1H and 13C spectroscopic means as well as by high-resolution mass spectrometry.

Microwave-assisted organic synthesis, antimycobacterial activity, structure-activity relationship and molecular docking studies of some novel indole-oxadiazole hybrids

Multidrug-resistant tuberculosis (MDR-TB) is a severe threat to mankind because most drugs are ineffective in inhibiting tubercular strains. Due to the increase of MDR-TB, many first and second-line drugs are ineffective against tubercular strains. To combat the resistance of currently accessible drugs, structural changes must be made on a regular basis. Thus, in the search for new antimycobacterial drugs, a series of 1-(2-(1H-indol-3-yl)-5-phenyl-1,3,4-oxadiazol-3(2H)-yl)-3-phenylprop-2-en-1-ones (5a-o) have been developed, synthesized, characterized, and screened for antimycobacterial activity. The synthetic approach includes imine generation and cyclization using both conventional and microwave methods to create hybrid molecules with indole and oxadiazole motifs. The set of synthesized compounds have demonstrated some promising activity against tubercular strains of Mycobacterium tuberculosis (ATCC 25177) and M. bovis (ATCC 35734). Compound 5l inhibited M. bovis strain 100% in 10 µg/mL concentration, while compound 5m inhibited M. tuberculosis strain 90.4% in 30 µg/mL concentration. Molecular docking study against mycobacterial enoyl reductase (InhA) could provide well-clustered solutions to the binding modes and affinity for these molecules as compound 5l showed glide score of -12.275 and glide energy of -54.937 kcal/mol.

Chemistry of 2-Vinylindoles: Synthesis and Applications

As a class of compounds, 2-vinylindoles have demonstrated a wide range of biological properties. Due to the general interest in these synthons, new divergent protocols of chemical synthesis have been...

Exploration of electronic properties, radical scavenging activity and QSAR of oxadiazole derivatives by molecular docking and first-principles approaches

Eight new oxadiazole derivatives were designed then geometries for ground state were optimized through Density Functional Theory (DFT) at B3LYP/6-31G** level. Single electron transfer mechanism has been studied to understand the antioxidant ability of the oxadiazole derivatives. Then molecular electrostatic potential and quantitative structure–activity relationship (QSAR) was probed. Additionally, we shed light on different molecular descriptors, e.g., electrophilicity(ω), electronegativity(χ), electrophilicity indices(ωi), hardness(η), softness(S) and chemical potential(μ).The smaller value of ionization potential for 5a is showing that it might be efficient antioxidant candidate. The electrophilic reactive sites in 2a, 3a, 4a, 5a and 7a derivatives might be a good choice for reactivity that would be advantageous to improve the biological activity. The polar surface area of 3a, 4a and 5a derivatives was found < 60 A² which is enlightening that these drugs might be suitable as orally active and for brain penetration. First-principles calculations and molecular docking results revealed that 5a would lead to superior antioxidant activity.

Indole-fused spirochromenes as potential anti-tubercular agents: design, synthesis and in vitro evaluation

As part of an ongoing effort to develop new anti-tubercular agents, a series of novel indole-fused spirochromene hybrids (7a-l) were efficiently synthesized in excellent yields by the popular 'Fisher-Indole synthesis' approach. The structure elucidation of the target compounds was carried out by different spectral techniques including 1H-NMR, 13C-NMR, ESI Mass, and FTIR analysis. Additionally, the proposed structure of 7i was proved by single-crystal X-ray analysis. These compounds (7a-l) were screened for in vitro anti-tubercular activity against Mycobacterium tuberculosis H37Rv (ATCC 27294) strain. The results showed that most of the targets exhibited promising antimycobacterial activity with MICs of 1.56-6.25 μg/mL and weak cytotoxicity (19.93-32.16% at 50 μg/mL). Among them, compound 7l was found to be the most active compound (MIC of 1.56 μg/mL) with a good safety profile (32.16% at 50 μg/mL).

Conventional and Microwave-Assisted Synthesis, Antitubercular Activity, and Molecular Docking Studies of Pyrazole and Oxadiazole Hybrids

Microwave-assisted organic reaction enhancement (MORE) has become more important in synthetic organic chemistry for efficient resource utilization. In this study, we synthesized bioactive compounds using both traditional and microwave methods. Microwave-assisted synthesis takes less time and produces higher yields and quality than conventional approaches. We reported the synthesis of N'-(1-(2-(3-(4-chlorophenyl)-1-phenyl-1H-pyrazol-4-yl)-5-phenyl-1,3,4-oxadiazol-3(2H)-yl)ethylidene) substituted hydrazides (4a-t). We also tested them against two strains: M. tuberculosis H₃₇Ra and M. bovis BCG. Against M. tuberculosis H₃₇Ra, the compounds 4e, 4h, 4k, 4p, and 4s were the most effective. Compounds 4f, 4g, and 4s showed significant activity against M. bovis BCG. The structures of newly synthesized molecules were determined using spectral methods. Furthermore, molecular docking investigations into the active site of mycobacterial InhA yielded well-clustered solutions for these compounds' binding modalities producing a binding affinity in the range of -10.366 to -8.037. Theoretical results were in good accord with the observed experimental values. The docking score of compound 4e was -10.366, and the Glide energy was -66.459 kcal/mol.

The Expanding Role of Pyridine and Dihydropyridine Scaffolds in Drug Design

Pyridine-based ring systems are one of the most extensively used heterocycles in the field of drug design, primarily due to their profound effect on pharmacological activity, which has led to the discovery of numerous broad-spectrum therapeutic agents. In the US FDA database, there are 95 approved pharmaceuticals that stem from pyridine or dihydropyridine, including isoniazid and ethionamide (tuberculosis), delavirdine (HIV/AIDS), abiraterone acetate (prostate cancer), tacrine (Alzheimer's), ciclopirox (ringworm and athlete's foot), crizotinib (cancer), nifedipine (Raynaud's syndrome and premature birth), piroxicam (NSAID for arthritis), nilvadipine (hypertension), roflumilast (COPD), pyridostigmine (myasthenia gravis), and many more. Their remarkable therapeutic applications have encouraged researchers to prepare a larger number of biologically active compounds decorated with pyridine or dihydropyridine, expandeing the scope of finding a cure for other ailments. It is thus anticipated that myriad new pharmaceuticals containing the two heterocycles will be available in the forthcoming decade. This review examines the prospects of highly potent bioactive molecules to emphasize the advantages of using pyridine and dihydropyridine in drug design. We cover the most recent developments from 2010 to date, highlighting the ever-expanding role of both scaffolds in the field of medicinal chemistry and drug development.

Antimicrobial Activity of 1,3,4-Oxadiazole Derivatives

The worldwide development of antimicrobial resistance forces scientists to search for new compounds to which microbes would be sensitive. Many new structures contain the 1,3,4-oxadiazole ring, which have shown various antimicrobial activity, e.g., antibacterial, antitubercular, antifungal, antiprotozoal and antiviral. In many publications, the activity of new compounds exceeds the activity of already known antibiotics and other antimicrobial agents, so their potential as new drugs is very promising. The review of active antimicrobial 1,3,4-oxadiazole derivatives is based on the literature from 2015 to 2021.

1,3,4-Oxadiazole N-Mannich Bases: Synthesis, Antimicrobial, and Anti-Proliferative Activities

The reaction of 5-(3,4-dimethoxyphenyl)-1,3,4-oxadiazole-2(3H)-thione 3 with formaldehyde solution and primary aromatic amines or 1-substituted piperazines, in ethanol at room temperature yielded the corresponding N-Mannich bases 3-arylaminomethyl-5-(3,4-dimethoxyphenyl)-1,3,4-oxadiazole-2(3H)-thiones 4a-l or 3-[(4-substituted piperazin-1-yl)methyl]-5-(3,4-dimethoxyphenyl)-1,3,4-oxadiazole-2(3H)-thiones 5a-d, respectively. The in vitro inhibitory activity of compounds 4a-l and 5a-d was assessed against pathogenic Gram-positive, Gram-negative bacteria, and the yeast-like pathogenic fungus Candida albicans. The piperazinomethyl derivatives 5c and 5d displayed broad-spectrum antibacterial activities the minimal inhibitory concentration (MIC) 0.5-8 μg/mL) and compounds 4j, 4l, 5a, and 5b showed potent activity against the tested Gram-positive bacteria. In addition, the anti-proliferative activity of the compounds was evaluated against prostate cancer (PC3), human colorectal cancer (HCT-116), human hepatocellular carcinoma (HePG-2), human epithelioid carcinoma (HeLa), and human breast cancer (MCF7) cell lines. The optimum anti-proliferative activity was attained by compounds 4l, 5a, 5c, and 5d.

Tuberculosis: An Overview of the Immunogenic Response, Disease Progression, and Medicinal Chemistry Efforts in the Last Decade toward the Development of Potential Drugs for Extensively Drug-Resistant Tuberculosis Strains

Tuberculosis (TB) is a slow growing, potentially debilitating disease that has plagued humanity for centuries and has claimed numerous lives across the globe. Concerted efforts by researchers have culminated in the development of various strategies to combat this malady. This review aims to raise awareness of the rapidly increasing incidences of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis, highlighting the significant modifications that were introduced in the TB treatment regimen over the past decade. A description of the role of pathogen-host immune mechanisms together with strategies for prevention of the disease is discussed. The struggle to develop novel drug therapies has continued in an effort to reduce the treatment duration, improve patient compliance and outcomes, and circumvent TB resistance mechanisms. Herein, we give an overview of the extensive medicinal chemistry efforts made during the past decade toward the discovery of new chemotypes, which are potentially active against TB-resistant strains.

Contribution of N-heterocycles towards anti-tubercular drug discovery (2014-2019); predicted and reengineered molecular frameworks

Tuberculosis is an infectious disease caused by Mycobacterium tuberculosis, responsible for high death frequency every year all over the world. In this regard, efficient drug-design and discovery towards the prevention of M.tb H₃₇ R_v is of prime concern. Prevention of the infection may include vaccination, and the treatment comprises anti-TB drug regimen. However, the vaccine decreases the risk of tuberculosis infection only to some extent, while drug-resistance limits the efficacy of the existing anti-TB agents. Much improvement has to be achieved to overcome pitfalls such as side effects, high-toxicity, low bioavailability, pharmacokinetics and pharmacodynamics, and hence forth in clinical therapeutics. Amongst heterocyclic compounds, N-heterocycles played a pivotal role in drug-design and discovery. A wide range of microbial diseases are being treated by the N-heterocyclic drugs. The present review comprises description of anti-TB effects of the N-heterocycles such as indoles, triazoles, thiazoles, and pyrazoles. The potent anti-TB activity exerted by the derivatives of these heterocycles is evaluated critically alongside emphasizing structure-activity relationship. Besides, docking studies supporting anti-TB activity is supplemented. Alongside this, based on the potent heterocyclic molecules, the molecular frameworks are designed that would bring about enhanced M. tb H₃₇ R_v inhibitory potencies.

Structure-Activity Relationship Modeling and Experimental Validation of the Imidazolium and Pyridinium Based Ionic Liquids as Potential Antibacterials of MDR Acinetobacter Baumannii and Staphylococcus Aureus

Online Chemical Modeling Environment (OCHEM) was used for QSAR analysis of a set of ionic liquids (ILs) tested against multi-drug resistant (MDR) clinical isolate Acinetobacter baumannii and Staphylococcus aureus strains. The predictive accuracy of regression models has coefficient of determination q² = 0.66 - 0.79 with cross-validation and independent test sets. The models were used to screen a virtual chemical library of ILs, which was designed with targeted activity against MDR Acinetobacter baumannii and Staphylococcus aureus strains. Seven most promising ILs were selected, synthesized, and tested. Three ILs showed high activity against both these MDR clinical isolates.

Synthetic approaches to unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles and their MAO-B inhibitory activity. A review

Selective monoamine oxidase type B (MAO-B) inhibitors are currently used as coadjuvants for treating early motor symptoms of Parkinson's disease. Aiming at the elucidation of MAO-B inhibitors with 1,3,4-oxadiazole scaffolds, we make a comprehensive update on the new and old chemical methods employed for the synthesis of the unsymmetrical oxadiazole derivatives that lead to high yield compounds. We summarize a state of the selective MAO-B inhibitors with oxadiazole scaffold, describing the results, structures, structure-activity relationships (SARs) and medicinal chemistry strategies over the years. The analysis of the recent papers would facilitate tracking the increasing number of oxadiazole derivatives as new chemical spaces with MAO-B inhibitory potential designed to ensure the safe use of the compounds and elimination of the unwanted drug-drug interactions.

A brief review of the biological potential of indole derivatives

Background

Various bioactive aromatic compounds containing the indole nucleus showed clinical and biological applications. Indole scaffold has been found in many of the important synthetic drug molecules which gave a valuable idea for treatment and binds with high affinity to the multiple receptors helpful in developing new useful derivatives.

Main text

Indole derivatives possess various biological activities, i.e., antiviral, anti-inflammatory, anticancer, anti-HIV, antioxidant, antimicrobial, antitubercular, antidiabetic, antimalarial, anticholinesterase activities, etc. which created interest among researchers to synthesize a variety of indole derivatives.

Conclusion

From the literature, it is revealed that indole derivatives have diverse biological activities and also have an immeasurable potential to be explored for newer therapeutic possibilities.

Anti-tuberculosis activity and its structure-activity relationship (SAR) studies of oxadiazole derivatives: A key review

With the increasing number of cases of inactive and drug-resistance tuberculosis, there is an urgent need to develop new potent molecules set for fighting this brutal disease. Medicinal chemistry concerns the discovery, the development, the identification, and the interpretation of the mode of action of biologically active compounds at the molecular level. Molecules bearing oxadiazoles are one such class that could be considered to satisfy this need. Oxadiazole regioisomers have been investigated in drug discovery programs for their capacity to go about as powerful linkers and as pharmacophoric highlights. Oxadiazoles can go about as bioisosteric substitutions for the hydrazide moiety which can be found in first-line anti-TB drugs, and some have been likewise answered to cooperate with more current anti-TB targets. This present review summarizes the current innovations of oxadiazole-based derivatives with potential antituberculosis activity and bacteria discussing various aspects of structure-activity relationship (SAR).

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

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

Indole/isatin-containing hybrids as potential antibacterial agents

The emergence and worldwide spread of drug-resistant bacteria have already posed a serious threat to human life, creating the urgent need to develop potent and novel antibacterial drug candidates with high efficacy. Indole and isatin (indole-2,3-dione) present a wide structural and mechanistic diversity, so their derivatives possess various pharmacological properties and occupy a salient place in the development of new drugs. Indole/isatin-containing hybrids, which demonstrate a promising activity against a panel of clinically important Gram-positive and Gram-negative bacteria, are privileged scaffolds for the discovery of novel antibacterial candidates. This review, covering articles published between January 2015 and May 2020, focuses on the development and structure-activity relationship (SAR) of indole/isatin-containing hybrids with potential application for fighting bacterial infections, to facilitate further rational design of novel drug candidates.

Structural Basis for Inhibition of Enoyl-[Acyl Carrier Protein] Reductase (InhA) from Mycobacterium tuberculosis

Background::

The enzyme trans-enoyl-[acyl carrier protein] reductase (InhA) is a central protein for the development of antitubercular drugs. This enzyme is the target for the pro-drug isoniazid, which is catalyzed by the enzyme catalase-peroxidase (KatG) to become active.

Objective::

Our goal here is to review the studies on InhA, starting with general aspects and focusing on the recent structural studies, with emphasis on the crystallographic structures of complexes involving InhA and inhibitors.

Method::

We start with a literature review, and then we describe recent studies on InhA crystallographic structures. We use this structural information to depict protein-ligand interactions. We also analyze the structural basis for inhibition of InhA. Furthermore, we describe the application of computational methods to predict binding affinity based on the crystallographic position of the ligands.

Results::

Analysis of the structures in complex with inhibitors revealed the critical residues responsible for the specificity against InhA. Most of the intermolecular interactions involve the hydrophobic residues with two exceptions, the residues Ser 94 and Tyr 158. Examination of the interactions has shown that many of the key residues for inhibitor binding were found in mutations of the InhA gene in the isoniazid-resistant Mycobacterium tuberculosis. Computational prediction of the binding affinity for InhA has indicated a moderate uphill relationship with experimental values.

Conclusion::

Analysis of the structures involving InhA inhibitors shows that small modifications on these molecules could modulate their inhibition, which may be used to design novel antitubercular drugs specific for multidrug-resistant strains.

An insight into the medicinal perspective of synthetic analogs of indole: A review

Heterocycles occupy a salient place in chemistry due to their wide range of activity in the fields of drug design, photochemistry, agrochemicals, dyes, and so on. Amongst all, indole scaffold is considered as one of the most promising heterocycles found in natural and synthetic sources and has been shown to possess various biological activity, including anti-inflammatory, anti-HIV, antitubercular, antimalarial, anticonvulsant, antidiabetic, antihypertensive, analgesics, antidepressant, anticancer, antioxidant, antifungal, and antimicrobial, etc. All the reported indole molecules bind to multiple receptors with high affinity, thus expedite the research on the development of novel biologically active compounds through the various approach. In this review, we aimed to highlight synthetic and medicinal perspective on the development of indole-based analogs. In addition, structural activity relationship (SAR) study to correlate for their biological activity also discussed.

Oxadiazole scaffolds in anti-tuberculosis drug discovery

With the increasing number of cases of latent and drug resistant tuberculosis, there is an urgent need to develop new, potent molecules capable of combating this deadly disease. Molecules containing oxadiazoles are one such class that could be considered to fulfil this need. Oxadiazole regioisomers have been explored in drug discovery programs for their ability to act as effective linkers and also as pharmacophoric features. Oxadiazoles can act as bioisosteric replacements for the hydrazide moiety which can be found in first line anti-TB drugs, and some have been also reported to interact with newer anti-TB targets. In this context, the present review describes the potential of oxadiazoles as antituberculosis agents.

Synthesis and evaluation of some new 1,3,4-oxadiazoles bearing thiophene, thiazole, coumarin, pyridine and pyridazine derivatives as antiviral agents

In an attempt to produce heterocyclic compounds based on 1,3,4-oxadiazole derivatives with potential antiviral activity, synthesis of compound 1 [2-(5-thioxo-4,5-dihydro-1,3,4-oxadiazol-2-yl)acetonitrile] was performed through the reaction of cyanoacetic acid hydrazide with carbon disulfide in alcoholic potassium hydroxide. Compound 1 has an activating methylene group, so it was directed toward some specific reactions. Thus, aryldiazonium chlorides reacted with compound 1 affording hydrazono derivatives 2a-c. Also, aromatic aldehydes reacted with compound 1 to produce compounds 3a,b. Furthermore, cyclic ketones were subjected to the synthesis of fused thiophene derivatives 4a,b via reaction with compound 1 in the presence of elemental sulfur. In addition, 1,3,4-oxadiazole derivative 1, when reacted with isothiocyanates, salicylaldehyde or 1,3-dicarbonyl compounds, formed thiazole derivatives 5a,b, coumarin derivative 6 and alkenyl derivatives 7a,b resp. Compound 7b underwent cyclization to afford pyridine derivative 8. Arylhydrazono derivatives 9a,b were produced through the reaction of compound 7a with aryldiazonium chlorides. Products 9a,b underwent cyclization to produce pyridazine derivatives 10a,b. Finally, 1,3,4-oxadiazole derivative 1 was directed toward reaction with hydrazine derivatives, bromoacetophenone and ethylchloroacetate affording compounds 11a,b, 12 and 13, resp. Fused thiophene derivatives 14a,b were produced via reaction of compounds 4a,b with a mixture of malononitrile and ethylorthoformate. Antiviral activity of the synthesized products showed that 5-(4-amino-3-ethyl-2-thioxo-2,3-dihydrothiazol-5-yl)-1,3,4-oxadiazole-2(3H)-thione (5a) and 5-(4-amino-3-phenyl-2-thioxo-2,3-dihydrothiazol-5-yl)-1,3,4-oxadiazole-2(3H)-thione (5b) acted as the most active agents against Feline herpes virus, Feline corona virus, Herpes simplex virus-1 and Herpes simplex virus-2, whereas compound 2-(5-(2-phenylhydrazono)-4,5-dihydro-1,3,4-oxadiazol-2-yl)acetonitrile (11b) was the most effective against Vaccinia virus, Herpes simplex virus (TK-KOS-ACVr), Coxsackie virus B4 and Vesicular stomatitis virus.