Seeking potent anti-tubercular agents: Design, synthesis, anti-tubercular activity and docking study of various ((triazoles/indole)-piperazin-1-yl/1,4-diazepan-1-yl)benzo[d]isoxazole derivatives

Theoretical screening of N-[5'-methyl-3'-isoxasolyl]-N-[(E)-1-(-2-thiophene)] methylidene]amine and its isoxazole based derivatives as donor materials for bulk heterojunction organic solar cells: DFT and TD-DFT investigation

CONTEXT

In the present work, the influence of aromatic ring substitution on a series of small-donor organic molecules (A, B, C, D, and E) with isoxazole cores was investigated for photovoltaic applications in organic solar cells. Frontier molecular orbital analysis, chemical reactivity descriptors, dipole moment, and population analysis showed that all the organic materials have intramolecular charge transfer abilities capable of donating electrons to the acceptor material (PCBM). The required photovoltaic parameters such as Voc, FF, Jsc, LHE, and other associated optoelectronic parameters are reported. The results demonstrate that aromatic ring substitution influences charge transfer and power conversion efficiencies of solar cells. That is, an increase in the aromatic character of a material increases its charge transfer, and as a result, its photovoltaic properties are increased. Additionally, all the investigated derivatives are good charge transporters with suitable electron reorganization energies, which are beneficial for minimizing energy loss. Hence, these organic derivatives with isoxazole backbones are promising materials and may provide fresh insights into the design of new materials for organic solar cell applications.

METHOD

All calculations were performed using DFT and the ORCA 4.1.0 program package as the main tool for geometry optimization and frequency calculations. The Avogadro 1.2.1 visualization tool was used to prepare all input files executed by ORCA 4.1.0. The BP86, B3LYP, and wB97M series of functionals coupled with the def2/TZVP basis set were employed for geometry optimization. All energy-related calculations were carried out using the M06-2x functional. Multiwfn version 3.7 was used for aromaticity and population analysis. Excited state and UV-visible spectra were simulated using the TD-DFT method at the CAM-B3LYP-D3, wB97X-D3, and PBE0-D3 coupled with the ma-def2-TZVP basis set. Moreover, solvent effects were incorporated using the SMD scheme as incorporated in the ORCA software. Lastly, the RIJCOSX approximations were used to speed up calculations while maintaining accuracy.

A Comprehensive Examination of Heterocyclic Scaffold Chemistry for Antitubercular Activity

Tuberculosis is a communicable disease which affects humans particularly the lungs and is transmitted mainly through air. Despite two decades of intensive research aimed at understanding and combating tuberculosis, persistent biological uncertainties continue to hinder progress. Nowadays, heterocyclic compounds have proven themselves in effective treatment of tuberculosis because of their wide range of biological and pharmacological activities. Antituberculosis or antimycobacterial agents encompass a broad array of compounds utilized singly or in conjunction to combat Mycobacterium infections, spanning from tuberculosis to leprosy. Here, we summarize the synthesis of various heterocyclic compounds which includes the greener synthetic route as well as use of nano compounds as catalyst along with their anti TB activities.

Discovery of 1,2,3-triazole incorporated indole-piperazines as potent antitubercular agents: Design, synthesis, in vitro biological evaluation, molecular docking and ADME studies

In this report, a library consisting of three sets of indole-piperazine derivatives was designed through the molecular hybridization approach. In total, fifty new hybrid compounds (T1-T50) were synthesized and screened for antitubercular activity against Mycobacterium tuberculosis H37Rv strain (ATCC-27294). Five (T36, T43, T44, T48 and T49) among fifty compounds exhibited significant inhibitory potency with the MIC of 1.6 µg/mL, which is twofold more potent than the standard first-line TB drug Pyrazinamide and equipotent with Isoniazid. N-1,2,3-triazolyl indole-piperazine derivatives displayed improved inhibition activity as compared to the simple and N-benzyl indole-piperazine derivatives. In addition, the observed activity profile of indole-piperazines was similar to standard anti-TB drugs (isoniazid and pyrazinamide) against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa strains, demonstrating the compounds' selectivity towards the Mycobacterium tuberculosis H37Rv strain. All the active anti-TB compounds are proved to be non-toxic (with IC50 > 300 μg/mL) as verified through the toxicity evaluation against VERO cell lines. Additionally, molecular docking studies against two target enzymes (Inh A and CYP121) were performed to validate the activity profile of indole-piperazine derivatives. Further, in silico-ADME prediction and pharmacokinetic parameters indicated that these compounds have good oral bioavailability.

Synthesis, antimycobacterial screening, molecular docking, ADMET prediction and pharmacological evaluation on novel pyran-4-one bearing hydrazone, triazole and isoxazole moieties: Potential inhibitors of SARS CoV-2

The respiratory infection tuberculosis is caused by the bacteria Mycobacterium tuberculosis and its unrelenting spread caused millions of deaths around the world. Hence, it is needed to explore potential and less toxic anti-tubercular drugs. In the present work, we report the synthesis and antitubercular activity of four different (hydrazones 7-12, O-ethynyl oximes 19-24, triazoles 25-30, and isoxazoles 31-36) hybrids. Among these hybrids 9, 10, 33, and 34, displayed high antitubercular activity at 3.12 g/mL with >90% of inhibitions. The hybrids also showed good docking energies between -6.8 and -7.8 kcal/mol. Further, most active molecules were assayed for their DNA gyrase reduction ability towards M. tuberculosis and E.coli DNA gyrase by the DNA supercoiling and ATPase gyrase assay methods. All four hybrids showed good IC50 values comparable to that of the reference drug. In addition, the targets were also predicted as a potential binder for papain-like protease (SARS CoV-2 PLpro) by molecular docking and a good interaction result was observed. Besides, all targets were predicted for their absorption, distribution, metabolism, and excretion - toxicity (ADMET) profile and found a significant amount of ADMET and bioavailability.

An insight into the recent developments in anti-infective potential of indole and associated hybrids

Prevention, accurate diagnosis, and effective treatment of infections are the main challenges in the overall management of infectious diseases. The best example is the ongoing SARs-COV-2(COVID-19) pandemic; the entire world is extremely worried about at present. Interestingly, heterocyclic moieties provide an ideal scaffold on which suitable pharmacophores can be designed to construct novel drugs. Indoles are amongst the most essential class of heteroaromatics in medicinal chemistry, which are ubiquitous across natural sources. The aforesaid derivatives have become invaluable scaffolds because of their wide spectrum therapeutic applications. Therefore, many researchers are focused on the design and synthesis of indole and associated hybrids of biological relevance. Hence, in the present review, we concisely discuss the indole containing natural sources, marketed drugs, clinical candidates, and their biological activities like antibacterial, antifungal, anti-TB, antiviral, antimalarial, and anti-leishmanial activities. The structure-activity relationships study of indole derivatives is also presented for a better understanding of the identified structures. The literature data presented for the anti-infective agents herein covers largely for the last twelve years.

Design, Synthesis and Biological Evaluation of Novel Spiro-[chroman-2,4'-piperidin]-4-one Analogues as Anti-Tubercular Agents

A series of novel spiro-[chromane-2,4'-piperidine]-4(3 H )-one derivatives were designed, synthesized and structures were confirmed by analytical methods viz., 1 H NMR, 13 C NMR and Mass spectrometry. Synthesized derivatives were evaluated for their anti-mycobacterial activity against Mycobacterium tuberculosis ( Mtb ) H37Ra strain. Among all the evaluated compounds, PS08 exhibited significant inhibition with MIC value of 3.72 μM while MIC values of the remaining compounds ranged from 7.68 to 230.42 μM in comparison to the standard drug INH (MIC 0.09 μM). The two most active compounds however showed acute cytotoxicity towards the human MRC-5 lung fibroblast cell line. The in-silico ADMET profiles of the titled compounds were predicted and found within the prescribed limits of the Lipinski and Jorgenson rules. Molecular docking study of the significantly active compound ( PS08 ) was also carried out after performing validation in order to understand the putative binding position of the test ligand at the active site of selected target protein Mtb tyrosine phosphatase (PtpB).

Seeking heterocyclic scaffolds as antivirals against dengue virus

Dengue is one of the most typical viral infection categorized in the Neglected Tropical Diseases (NTDs). It is transmitted via the female Aedes aegypti mosquito to humans and majorly puts risk to the lives of more than half of the world. Recent advancements in medicinal chemistry have led to the design and development of numerous potential heterocyclic scaffolds as antiviral drug candidates for the inhibition of the dengue virus (DENV). Thus, in this review, we have discussed the significance of inhibitory and antiviral activities of nitrogen, oxygen, and mixed (nitrogen-sulfur and nitrogen-oxygen) heterocyclic scaffolds that are published in the last seven years (2016–2022). Furthermore, we have also discussed the probable mechanisms of action and the diverse structure-activity relationships (SARs) of the heterocyclic scaffolds. In addition, this review has elaborately outlined the mechanism of viral infection and the life cycle of DENV in the host cells. The wide set of heterocycles and their SARs will aid in the development of pharmaceuticals that will allow the researchers to synthesize the promising anti-dengue drug candidate in the future.

Emerging impact of triazoles as anti-tubercular agent

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

Discovery of potent antitubercular agents: Design, synthesis and biological evaluation of 4-(3-(4-substitutedpiperazin-1-yl)-quinoxalin-2-yl)-naphthalen-1-ol analogues

A series of twenty-five novel 4-(3-(4-substituted piperazin-1-yl)-quinoxalin-2-yl)-naphthalen-1-ol analogues were synthesized, characterized and screened for in vitro antitubercular activity against Mycobacterium tuberculosis H37Rv strain. These compounds exhibited minimum inhibitory concentration in the range of 1.56-50 μg/mL. Among these derivatives, compounds 5a, 5b, 5f, 5m, 5p, and 5r displayed moderate activity (MIC 6.25 μg/mL). Compounds 5c, 5d, 5g, 5l, and 5o showed significant antitubercular activity (MIC 3.125 μg/mL), while compounds 5h, 5n, and 5q exhibited potent antitubercular activity (MIC 1.56 μg/mL). In addition, MTT assay was performed on the active analogues of the series against mouse macrophage cells to assess the cytotoxic effect of the newly synthesized compounds, and a selectivity index of the compounds was established. Selectivity index values of the most active compounds (5h, 5n, and 5q) are >47, indicating the compounds' suitability for further potential drug development. A molecular docking study was performed to understand the putative binding mode and binding strength of the selected significantly active and weakly active compounds with the target enzyme mycobacterial topoisomerase II using moxifloxacin as standard. In-silico ADME prediction and bioavailability studies of the titled compounds obey Lipinski's rule of five and Jorgensen's rule of three. To further ascertain the structure of the compounds, a suitable single crystal for the compounds 5a, 6, and 7d was developed and studied.

A multi-targeting pre-clinical candidate against drug-resistant tuberculosis

FNDR-20081 [4-{4-[5-(4-Isopropyl-phenyl)- [1,2,4]oxadiazol-3-ylmethyl]-piperazin-1-yl}-7-pyridin-3-yl-quinoline] is a novel, first in class anti-tubercular pre-clinical candidate against sensitive and drug-resistant Mycobacterium tuberculosis (Mtb). In-vitro combination studies of FNDR-20081 with first- and second-line drugs exhibited no antagonism, suggesting its compatibility for developing new combination-regimens. FNDR-20081, which is non-toxic with no CYP3A4 liability, demonstrated exposure-dependent killing of replicating-Mtb, as well as the non-replicating-Mtb, and efficacy in a mouse model of infection. Whole genome sequencing (WGS) of FNDR-20081 resistant mutants revealed the identification of pleotropic targets: marR (Rv0678), a regulator of MmpL5, a transporter/efflux pump mechanism for drug resistance; and Rv3683, a putative metalloprotease potentially involved in peptidoglycan biosynthesis. In summary, FNDR-20081 is a promising first in class compound with the potential to form a new combination regimen for MDR-TB treatment.

Synthesis of alkynylated 1,2,4-oxadiazole/1,2,3-1H-triazole glycoconjugates: Discovering new compounds for use in chemotherapy against lung carcinoma and Mycobacterium tuberculosis

A total of forty-three compounds were synthesized, including thirty-two new ones. Among those compounds, seventeen were selected and tested on human tumor cell lines: PC-3 (prostate adenocarcinoma), HCT-116 (colorectal tumor), NCIH-460 (lung carcinoma), SKMEL-103 (melanoma) and AGP-01 (gastric tumor). Alkynylated 1,2,4-oxadiazoles 2m, 3g and 3k exhibited antiproliferative activities against NCIH-460 in culture. Alkynylated N-cyclohexyl-1,2,4-oxadiazoles 3a-m and bis-heterocycle glucoglycero-1,2,3-triazole-N-cyclohexyl-1,2,4-oxadiazole derivatives 5a-k and 6-11 were evaluated for their in vitro efficacy towards Mycobacterium tuberculosis (Mtb) H₃₇Ra and H₃₇Rv strains. In general, glycerosugars conjugated to 1,2,4-oxadiazole via a 1,2,3-triazole linkage (5a, 5e, 5j, 5k, and 7) showed in vitro inhibitory activity against Mtb (H₃₇Rv). The largest molecules bis-triazoles 10 and 11, proved inactive against TB. Probably, the absence of the N-cyclohexyl group in compound 8 and 1,2,4-oxadiazole nucleus in compound 9 were responsible for its low activity. Glucoglycero-triazole-oxadiazole derivatives 5e (10 μM) and 7 (23.9 μM) were the most promising antitubercular compounds, showing a better selective index than when tested against RAW 264.7 and HepG2 cells. Vero cell were used to investigate cytotoxicity of compounds 5a, 5h, 5j, 5k, and these compounds showed good cell viability. Further, in silico studies were performed for most active compounds (5e and 7) with potential drug targets, DprE1 and InhA of Mtb to understand possible interactions aided with molecular dynamic simulation (100ns).

Design, synthesis and biological evaluation of novel 1,2,3-triazole analogues of Imidazo-[1,2-a]-pyridine-3-carboxamide against Mycobacterium tuberculosis

Twenty-eight novel 1,2,3-triazole analogues of imidazo-[1,2-a]-pyridine-3-carboxamide were designed and synthesized based on hybridization approach. The structure of the final compounds are characterized using ¹HNMR, ¹³CNMR, LCMS and elemental analyses and are screened in vitro for anti-tubercular activity using low-oxygen recovery assay (LORA) non-replicating and using microplate alamar blue assay (MABA) against replicating M. tuberculosis. MIC was determined. From the obtained results, it was observed that, among (2,7-dimethylimidazo[1,2-a]pyridin-3-yl)(4-((1-subtituted phenyl-1H-1,2,3-triazol-4-yl)methyl)piperazin-1-yl)methanones and (6-chloro-2-methylimidazo[1,2-a]pyridin-3-yl)(4-((1-substituted phenyl-1H-1,2,3-triazol-4-yl)methyl)piperazin-1-yl)methanones, compounds with substitution at para position with electron electron releasing groups exhibited the best activity (< 34 μg/mL). Amidst, (2,7-dimethylimidazo[1,2-a]pyridin-3-yl)(4-(2-(4-alkyl/substituted aryl-1H-1,2,3-triazol-1-yl)ethyl)piperazin-1-yl)methanones and (6-chloro-2-methylimidazo[1,2-a]pyridin-3-yl)(4-(2-(4- alkyl/substituted aryl -1H-1,2,3-triazol-1-yl)ethyl)piperazin-1-yl)methanones, compounds with long alkyl chain or cyclo propyl group were most active (< 21 μg/mL) in MABA method against the tested strain of MTB. Compound 10b emerged to be the most active compound in MABA and LORA with MIC values 13.74 and 24.63 μg/mL respectively. In-silico ADMET parameters were also predicted for the significantly active compound. Finally, molecular docking study was carried out to predict the feasible binding pattern of the most active compound at the active site of enoyl acyl carrier protein reductase from Mycobacterium tuberculosis (PDB-4TZK) using Glide module of Schrodinger software.

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.

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.

Vitamin in the Crosshairs: Targeting Pantothenate and Coenzyme A Biosynthesis for New Antituberculosis Agents

Despite decades of dedicated research, there remains a dire need for new drugs against tuberculosis (TB). Current therapies are generations old and problematic. Resistance to these existing therapies results in an ever-increasing burden of patients with disease that is difficult or impossible to treat. Novel chemical entities with new mechanisms of action are therefore earnestly required. The biosynthesis of coenzyme A (CoA) has long been known to be essential in Mycobacterium tuberculosis (Mtb), the causative agent of TB. The pathway has been genetically validated by seminal studies in vitro and in vivo. In Mtb, the CoA biosynthetic pathway is comprised of nine enzymes: four to synthesize pantothenate (Pan) from l-aspartate and α-ketoisovalerate; five to synthesize CoA from Pan and pantetheine (PantSH). This review gathers literature reports on the structure/mechanism, inhibitors, and vulnerability of each enzyme in the CoA pathway. In addition to traditional inhibition of a single enzyme, the CoA pathway offers an antimetabolite strategy as a promising alternative. In this review, we provide our assessment of what appear to be the best targets, and, thus, which CoA pathway enzymes present the best opportunities for antitubercular drug discovery moving forward.

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.

Synthesis and biological evaluation of novel isoxazole derivatives from acridone

The present study was carried out in an attempt to synthesize a new class of potential antibacterial agents. In this context, novel isoxazoles were synthesized and evaluated for their potential antibacterial behavior against four pathogenic bacterial strains. The synthesized compounds exhibited moderate-to-good antibacterial activity against these strains. The highest antibacterial activity was observed against the Escherichia coli strains, particularly for compounds 4a and 4e with phenyl and para-nitrophenyl groups on the isoxazole-acridone skeleton; they showed promising minimum inhibitory concentration values of 16.88 and 19.01 μg/ml, respectively, compared with the standard drug chloramphenicol (22.41 µg/ml). The synthesized compounds were subjected to in silico docking studies to understand the mode of their interactions with the DNA topoisomerase complex (PDB ID: 3FV5) of E. coli. The molecular docking results showed that compounds 4a-l occupy the active site of DNA topoisomerase (PDB ID: 3FV5), stabilized via hydrogen bonding and hydrophobic interactions, which may be the reason behind their interesting in vitro antibacterial activity.

An appraisal of anti-mycobacterial activity with structure-activity relationship of piperazine and its analogues: A review

Piperazine, is privileged six membered nitrogen containing heterocyclic ring also known as 1,4-Diazacyclohexane. Consequently, piperazine is a versatile medicinally important scaffold and is an essential core in numerous marketed drugs with diverse pharmacological activities. In recent years several potent molecules containing piperazine as an essential subunit of the structural frame have been reported, especially against Mycobacterium tuberculosis (MTB). Remarkably, a good number of these reported molecules also displayed potential activity against multidrug-resistant (MDR), and extremely drug-resistant (XDR) strains of MTB. In this review, we have made a concerted effort to retrace anti-mycobacterial compounds for the past five decades (1971-2019) specifically where piperazine has been used as a vital building block. This review will benefit medicinal chemists as it elaborates on the design, rationale and structure-activity relationship (SAR) of the reported potent piperazine based anti-TB molecules, which in turn will assist them in addressing the gaps, exploiting the reported strategies and developing safer, selective, and cost-effective anti-mycobacterial agents.

Molecule Property Analyses of Active Compounds for Mycobacterium tuberculosis

Tuberculosis (TB) continues to claim the lives of around 1.7 million people per year. Most concerning are the reports of multidrug drug resistance. Paradoxically, this global health pandemic is demanding new therapies when resources and interest are waning. However, continued tuberculosis drug discovery is critical to address the global health need and burgeoning multidrug resistance. Many diverse classes of antitubercular compounds have been identified with activity in vitro and in vivo. Our analyses of over 100 active leads are representative of thousands of active compounds generated over the past decade, suggests that they come from few chemical classes or natural product sources. We are therefore repeatedly identifying compounds that are similar to those that preceded them. Our molecule-centered cheminformatics analyses point to the need to dramatically increase the diversity of chemical libraries tested and get outside of the historic Mtb property space if we are to generate novel improved antitubercular leads.

The Azoles in Pharmacochemistry: Perspectives on the Synthesis of New Compounds and Chemoinformatic Contributions

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Due to their versatile biological activity, Azoles are widely studied in pharmacochemistry. It is possible to use them in many applications and in studies aimed at discovering antiparasitic, antineoplastic, antiviral, antimicrobial compounds; and in the production of materials for treatment of varied pathologies. Based on their biological activity, our review presents several studies that involve this class of organic compounds. A bibliographic survey of this type can effectively contribute to pharmaceutical sciences, stimulating the discovery of new compounds, and structural improvements to biological profiles of interest. In this review, articles are discussed involving the synthesis of new compounds and chemoinformatic contributions. Current applications of azoles in both the pharmaceutical and agri-business sectors are well known, yet as this research highlights, azole compounds can also bring important contributions to the fight against many diseases. Among the heterocyclics, azoles are increasingly studied by research groups around the world for application against tuberculosis, HIV, fungal and bacterial infections; and against parasites such as leishmaniasis and trypanosomiasis. Our hope is that this work will help arouse the interest of research groups planning to develop new bioactives to fight against these and other diseases.

Opportunities and challenges of using five-membered ring compounds as promising antitubercular agents

Tuberculosis (TB), a chronic infectious disease, is one of the greatest risks to human beings and 10 million people were diagnosed with TB and 1.6 million died from this disease in 2017. In addition, with the emergence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB), the TB situation has become even worse, which has aggravated the mortality and spread of this disease. To overcome this problem, research into novel antituberculosis agents with enhanced activities against MDR-TB, reduced toxicity, and shortened duration of therapy is of great importance. Fortunately, many novel potential anti-TB drug candidates with five-membered rings, which are most likely to be effective against sensitive and resistant strains, have recently entered clinical trials. Different five-membered rings such as furans, pyranoses, thiazoles, pyrazolines, imidazoles, oxazolidinone, thiazolidins, isoxazoles, triazoles, oxadiazoles, thiadiazoles, and tetrazoles have been designed, prepared, and evaluated for their antimycobacterial activity against Mycobacterium tuberculosis. In this article, we highlight the recent advances made in the discovery of novel five-membered ring compounds and focus on their antitubercular activities, toxicity, structure-activity relationships, and mechanisms of action.

Seeking potent anti-tubercular agents: design and synthesis of substituted-N-(6-(4-(pyrazine-2-carbonyl)piperazine/homopiperazine-1-yl)pyridin-3-yl)benzamide derivatives as anti-tubercular agents

We herein report 27 pyrazinamide analogues as anti-tubercular agents, of which six exhibited excellent activity with IC₅₀ ≤ 2.18 μM and these were less toxic against HEK 293 cells.

Synthesis, crystal structures, antiproliferative activities and reverse docking studies of eight novel Schiff bases derived from benzil

Eight novel Schiff bases derived from benzil dihydrazone (BDH) or benzil monohydrazone (BMH) and four fused-ring carbonyl compounds (3-formylindole, FI; 3-acetylindole, AI; 3-formyl-1-methylindole, MFI; 1-formylnaphthalene, FN) were synthesized and characterized by elemental analysis, ESI-QTOF-MS, ¹H and ¹³C NMR spectroscopy, as well as single-crystal X-ray diffraction. They are (1Z,2Z)-1,2-bis{(E)-[(1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethane (BDHFI), C₃₂H₂₄N₆, (1Z,2Z)-1,2-bis{(E)-[1-(1H-indol-3-yl)ethylidene]hydrazinylidene}-1,2-diphenylethane (BDHAI), C₃₄H₂₈N₆, (1Z,2Z)-1,2-bis{(E)-[(1-methyl-1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethane (BMHMFI) acetonitrile hemisolvate, C₃₄H₂₈N₆·0.5CH₃CN, (1Z,2Z)-1,2-bis{(E)-[(naphthalen-1-yl)methylidene]hydrazinylidene}-1,2-diphenylethane (BDHFN), C₃₆H₂₆N₄, (Z)-2-{(E)-[(1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethanone (BMHFI), C₂₃H₁₇N₃O, (Z)-2-{(E)-[1-(1H-indol-3-yl)ethylidene]hydrazinylidene}-1,2-diphenylethanone (BMHAI), C₂₄H₁₉N₃O, (Z)-2-{(E)-[(1-methyl-1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethanone (BMHMFI), C₂₄H₁₉N₃O, and (Z)-2-{(E)-[(naphthalen-1-yl)methylidene]hydrazinylidene}-1,2-diphenylethanone (BMHFN) C₂₅H₁₈N₂O. Moreover, the in vitro cytotoxicity of the eight title compounds was evaluated against two tumour cell lines (A549 human lung cancer and 4T₁ mouse breast cancer) and two normal cell lines (MRC-5 normal lung cells and NIH 3T3 fibroblasts) by MTT assay. The results indicate that four (BDHMFI, BDHFN, BMHMFI and BMHFN) are inactive and the other four (BDHFI, BDHAI, BMHFI and BMHAI) show severe toxicities against human A549 and mouse 4T₁ cells, similar to the standard cisplatin. All the compounds exhibited weaker cytotoxicity against normal cells than cancer cells. The Swiss Target Prediction web server was applied for the prediction of protein targets. After analyzing the differences in frequency hits between these active and inactive Schiff bases, 18 probable targets were selected for reverse docking with the Surflex-dock function in SYBYL-X 2.0 software. Three target proteins, i.e. human ether-á-go-go-related (hERG) potassium channel, the inhibitor of apoptosis protein 3 and serine/threonine-protein kinase PIM1, were chosen as the targets. Finally, the ligand-based structure-activity relationships were analyzed based on the putative protein target (hERG) docking results, which will be used to design and synthesize novel hERG ion channel inhibitors.

Medicinal chemistry of indole derivatives: Current to future therapeutic prospectives

Indole is a versatile pharmacophore, a privileged scaffold and an outstanding heterocyclic compound with wide ranges of pharmacological activities due to different mechanisms of action. It is an superlative moiety in drug discovery with the sole property of resembling different structures of the protein. Plenty of research has been taking place in recent years to synthesize and explore the various therapeutic prospectives of this moiety. This review summarizes some of the recent effective chemical synthesis (2014-2018) for indole ring. This review also emphasized on the structure-activity relationship (SAR) to reveal the active pharmacophores of various indole analogues accountable for anticancer, anticonvulsant, antimicrobial, antitubercular, antimalarial, antiviral, antidiabetic and other miscellaneous activities which have been investigated in the last five years. The precise features with motives and framework of each research topic is introduced for helping the medicinal chemists to understand the perspective of the context in a better way. This review will definitely offer the platform for researchers to strategically design diverse novel indole derivatives having different promising pharmacological activities with reduced toxicity and side effects.

A Review Exploring Therapeutic Worth of 1,3,4-Oxadiazole Tailored Compounds

1,3,4-Oxadiazole, a five-membered aromatic ring can be seen in a number of synthetic molecules. The peculiar structural feature of 1,3,4-oxadiazole ring with pyridine type of nitrogen atom is beneficial for 1,3,4-oxadiazole derivatives to have effective binding with different enzymes and receptors in biological systems through numerous weak interactions, thereby eliciting an array of bioactivities. Research in the area of development of 1,3,4-oxadiazole-based derivatives has become an interesting topic for the scientists. A number of 1,3,4-oxadiazole based compounds with high therapeutic potency are being extensively used for the treatment of different ailments, contributing to enormous development value. This work provides a systematic and comprehensive review highlighting current developments of 1,3,4-oxadiazole based compounds in the entire range of medicinal chemistry such as anticancer, antifungal, antibacterial, antitubercular, anti-inflammatory, antineuropathic, antihypertensive, antihistaminic, antiparasitic, antiobesity, antiviral, and other medicinal agents. It is believed that this review will be of great help for new thoughts in the pursuit for rational designs for the development of more active and less toxic 1,3,4-oxadiazole based medicinal agents.

Synthesis and Screening of Pro-apoptotic and Angio-inhibitory Activity of Novel Benzisoxazole Derivatives both In Vitro and In Vivo

BACKGROUND

Triple Negative Breast Cancer (TNBC) tends to be more aggressive than other types of breast cancer. Resistance to chemotherapy is a major obstacle hence there is a significant need for new antineoplastic drugs with multi-target potency. Numerous Benzoisoxazole moieties have been found to possess a broad spectrum of pharmacological activities. In the present study, we have synthesized 9 novel derivatives of Benzisoxazole 7(a-i) and screened them for their biological potential.

METHODS

Chemical synthesis, Mass spectrometry (HRMS), cell proliferation and cytotoxicity assay, wound healing assay, flow cytometry and nuclear staining. Angio-inhibitory activity assessed by corneal micropocket assay and in vivo peritoneal angiogenesis assay.

RESULTS

The Benzisoxazole derivatives 7(a-i) were synthesized and screened for their biological potency by both in vitro and in vivo experimental models. Among the series, compound 3-(1-((3-(3(Benzyloxy)-4-methoxyphenyl)- 4,5-dihydroisoxazole-5-yl)methyl)piperidine-4-yl)6-fluorobenzo[d] isoxazole (7e) was found to be most promising, with an average IC50 value of 50.36 ± 1.7 µM in MTT assay and showed 81.3% cell death. The compound 7e also showed 60-70% inhibition on a recombinant Metastasis-Associated protein (MTA1) induced proliferation and cell migration in MDAMB-231 cells, which is known to play a major role in angiogenesis. The anti-tumour studies inferred the regression of tumour activity. This was due to inhibition of neovascularization and evoking apoptosis process as assessed by corneal vascularization, peritoneal angiogenesis and apoptotic hallmarks in 7e treated cells.

CONCLUSION

These findings not only show the biological efficacy of compound 7e but it is also an effective beginning to explore the mechanism of metastasis and cancer therapy strategy targeting MTA1. The observed biological activity makes compound 7e an attractive drug candidate.

Benzisoxazole: a privileged scaffold for medicinal chemistry

The benzisoxazole analogs represent one of the privileged structures in medicinal chemistry and there has been an increasing number of studies on benzisoxazole-containing compounds. The unique benzisoxazole scaffold also exhibits an impressive potential as antimicrobial, anticancer, anti-inflammatory, anti-glycation agents and so on. This review examines the state of the art in medicinal chemistry as it relates to the comprehensive and general summary of the different benzisoxazole analogs, their use as starting building blocks of multifarious architectures on scales sufficient to drive human drug trials. The number of reports describing benzisoxazole-containing highly active compounds leads to the expectation that this scaffold will further emerge as a potential candidate in the field of drug discovery.

Metal-Involving Synthesis and Reactions of Oximes

This review classifies and summarizes the past 10-15 years of advancements in the field of metal-involving (i.e., metal-mediated and metal-catalyzed) reactions of oximes. These reactions are diverse in nature and have been employed for syntheses of oxime-based metal complexes and cage-compounds, oxime functionalizations, and the preparation of new classes of organic species, in particular, a wide variety of heterocyclic systems spanning small 3-membered ring systems to macroheterocycles. This consideration gives a general outlook of reaction routes, mechanisms, and driving forces and underlines the potential of metal-involving conversions of oxime species for application in various fields of chemistry and draws attention to the emerging putative targets.

Triazole derivatives and their anti-tubercular activity

Tuberculosis (TB) remains one of the most widespread and leading deadliest diseases, threats one-third of the world's population. Although numerous efforts have been undertaken to develop new anti-TB agents, only a handful of compounds have entered human trials in the past 5 decades. Triazoles including 1,2,3-triazole and 1,2,4-triazole are one of the most important classes of nitrogen containing heterocycles that exhibited various biological activities. Triazole derivatives are regarded as a new class of effective anti-TB candidates owing to their potential anti-TB potency. Thus, molecules containing triazole moiety may show promising in vitro and in vivo anti-TB activities and might be able to prevent the drug resistant to certain extent. This review outlines the advances in the application of triazole-containing hybrids as anti-TB agents, and discusses the structure-activity relationship of these derivatives.

Advances in Drug Discovery of New Antitubercular Multidrug-Resistant Compounds

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

Synthesis of novel inhibitors of α-amylase based on the thiazolidine-4-one skeleton containing a pyrazole moiety and their configurational studies

Postprandial hyperglycemia can be controlled by delaying the absorption of glucose resulting from carbohydrate digestion. α-Amylase is the initiator of the hydrolysis of polysaccharides, and therefore developing α-amylase inhibitors can lead to development of new treatments for metabolic disorders like diabetes mellitus. In the present work, we set out to rationally develop α-amylase inhibitors based on the thiazolidine-4-one scaffold. The structures of all these newly synthesized hybrids were confirmed by spectroscopic analysis (IR, ¹H-NMR, MS). The appearance of two sets of signals for some protons in ¹H NMR revealed the existence of a mixture of 2E,5Z (37.1-42.0%) and 2Z,5Z isomers (58.4-62.8%), which was further supported by DFT studies. All the newly synthesized compounds have potential inhibitory properties as revealed through in vitro α-amylase inhibition activity. Compound 5a at 100 μg mL^-1 concentration showed a remarkable inhibition of 90.04%. In vitro α-amylase inhibition was further supported by docking studies of compound 5a against the active site of human pancreatic α-amylase (PDB ID: ; 2QV4). The docking studies revealed that the bonding interactions found between 5a and human pancreatic α-amylase are similar to those responsible for α-amylase inhibition by acarbose.

Identification and development of pyrazolo[4,3-c]pyridine carboxamides as Mycobacterium tuberculosis pantothenate synthetase inhibitors

A novel series of pyrazolo[4,3-c]pyridine carboxamides were synthesized and characterized. The compounds were evaluated for their antitubercular activity and pantothenate synthetase enzyme inhibition study.