Synthesis and antitubercular evaluation of novel dibenzo[ b , d ]thiophene tethered imidazo[1,2- a ]pyridine-3-carboxamides

Structure-activity relationship of 2-aminodibenzothiophene pharmacophore and the discovery of aminobenzothiophenes as potent inhibitors of Mycobacterium smegmatis

Tuberculosis (TB) is one of the deadliest infectious diseases worldwide and its current treatments have been complicated with the emergence of multi-drug resistant (MDR-TB) and extensively drug-resistant (XDR-TB) strains. Therefore, the discovery of new antitubercular agents is in need to overcome this problem. In our efforts to discover novel candidates for the treatment of tuberculosis, we describe in this work in vitro activityagainstM. smegmatis for a series of aminated benzo-fused heterocycles, particularly, dibenzothiophene to explore the structure-activity relationship of 2-aminodibenzothiophene 3aa. From these studies, three compounds 5-aminobenzothiophene 3ia, 6-aminobenzothiophene 3ma (MIC: 0.78 µg/mL) and 5-aminobenzofuran 3ja (MIC: 1.56 µg/mL) were identified as potent inhibitors of M. smegmatis with low cytotoxicity. These results suggested the significance of these compounds 3ia, 3ja and 3ma for the future development of candidate agents to treat tuberculosis.

Design, synthesis and anti-mycobacterial evaluation of imidazo[1,2-a]pyridine analogues

Based on the molecular hybridization strategy, thirty-four imidazo[1,2-a]pyridine amides (IPAs) and imidazo[1,2-a]pyridine sulfonamides (IPSs) were designed and synthesized. The structures of the target compounds were characterized using ¹H NMR, ¹³C NMR, LCMS, and elemental analyses. The synthesized compounds were evaluated in vitro for anti-tubercular activity using the microplate Alamar Blue assay against Mycobacterium tuberculosis H37Rv strain and the MIC was determined. The evaluated compounds exhibited MIC in the range 0.05-≤100 μg mL^-1. Among these derivatives, IPA-6 (MIC 0.05 μg mL^-1), IPA-9 (MIC 0.4 μg mL^-1), and IPS-1 (MIC 0.4 μg mL^-1) displayed excellent anti-TB activity, whereas compounds IPA-5, IPA-7 and IPS-16 showed good anti-TB activity (MIC 0.8-3.12 μg mL^-1). The most active compounds with MIC of <3.125 μg mL^-1 were screened against human embryonic kidney cells to check their cytotoxicity to normal cells. It was observed that these compounds were nontoxic (SI value ≥66). The ADMET characteristics of the final compounds were also predicted in silico. Further, using the Glide module of Schrodinger software, a molecular docking study of IPA-6 was carried out to estimate the binding pattern at the active site of enoyl acyl carrier protein reductase from Mycobacterium tuberculosis (PDB 4TZK). Finally, molecular dynamics simulations were performed for 100 ns to elucidate the stability, conformation, and intermolecular interactions of the co-crystal ligand and significantly active compound IPA-6 on the selected target protein. IPA-6, the most active compound, was found to be 125 times more potent than the standard drug ethambutol (MIC 6.25 μg mL^-1).

Current Pharmaceutical Aspects of Synthetic Quinoline Derivatives

Quinoline derivatives are considered broad-spectrum pharmacological compounds that exhibit a wide range of biological activities. Integration of quinoline moiety can improve its physical and chemical properties and also pharmacological behavior. Due to its wide range of pharmaceutical applications, it is a very popular compound to design new drugs for the treatment of multiple diseases like cancer, dengue fever, malaria, tuberculosis, fungal infections, AIDS, Alzheimer's disease and diabetes. In this review, our major focus is to pay attention to the biological activities of quinoline compounds in the treatment of these diseases such as anti-viral, anti-cancer, anti-malarial, antibacterial, anti-fungal, anti-tubercular and anti-diabetic.

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

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

One-Pot Synthesis of Aminated Benzo-Fused Heterocycles and N-Substituted Dibenzothiophenes via Copper-Catalyzed Ullmann Type Reaction

We report here a direct and effective method to synthesize a primary amine of several polycyclic aromatic compounds. This reaction has been achieved through copper (I)-catalyzed Ullmann C-N coupling. Furthermore, this strategy allows the synthesis of new N-substituted dibenzothiophene derivatives through the coupling of 2-bromodibenzothiophene with various ranges of primary and secondary amines. The use of inexpensive catalysts, aqueous ammonia as the convenient source of ammonia and ligand free, makes this protocol environmentally and economically favorable for the synthesis of these compounds.

Computational Study of Structural, Molecular Orbitals, Optical and Thermodynamic Parameters of Thiophene Sulfonamide Derivatives

Thiophene and sulfonamide derivatives serve as biologically active compounds, used for the manufacture of large numbers of new drugs. In this study, 11 selected derivatives of thiophene sulfonamide were computed for their geometric parameters, such as hyperpolarizability, chemical hardness (ƞ), electronic chemical potential (μ), electrophilicity index (ω), ionization potential (I), and electron affinity (A). In addition, FT-IR and UV-Vis spectra were also simulated through theoretical calculations. The geometrical parameters and vibrational frequencies with assignments of the vibrational spectra strongly resemble the experimentally calculated values. Besides, the frontier molecular orbitals were also determined for various intramolecular interactions that are responsible for the stability of the compounds. The isodensity surfaces of the frontier molecular orbitals (FMOs) are the same pattern in most of the compounds, but in some compounds are disturbed due to the presence of highly electronegative hetero-atoms. In this series of compounds, 3 shows the highest HOMO–LUMO energy gap and lowest hyperpolarizability, which leads to the most stable compound and less response to nonlinear optical (NLO), while 7 shows the lowest HOMO–LUMO energy gap and highest hyperpolarizability, which leads to a less stable compound and a high NLO response. All compounds have their extended three-dimensional p-electronic delocalization which plays an important role in studying NLO responses.

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.

Structural modification of zolpidem led to potent antimicrobial activity in imidazo[1,2-a]pyridine/pyrimidine-1,2,3-triazoles

New imidazo[1,2-a]pyridine/pyrimidine-1,2,3-triazoles (IPTs) designed by specific structural modifications of zolpidem exhibited superior antitubercular activity than the parent compound.

Synthesis of novel morpholine, thiomorpholine and N-substituted piperazine coupled 2-(thiophen-2-yl)dihydroquinolines as potent inhibitors of Mycobacterium tuberculosis

A series of novel morpholine, thiomorpholine and N-substituted piperazine coupled 2-(thiophen-2-yl)dihydroquinolines 7a-p was designed and synthesized from 2-acetyl thiophene in six step reaction sequence involving modified Bohlmann-Rahtz and Vilsmeier-Haack-Arnold reactions as key transformations. 2-(Thiophen-2-yl)dihydroquinoline was formylated and subsequently chlorinated using DMF-POCl₃. The resulting aldehyde was reduced to give an alcohol and then converted to bromide using PBr_3. Further coupling of bromide with morpholine, thiomorpholine and N-substituted piperazines resulted in the desired quinolines 7a-p in very good yields. All the new derivatives 7a-p were characterized by their NMR and mass spectral analysis. In vitro screening of new compounds for antimycobacterial activity against Mycobacterium tuberculosis H37Rv (MTB), resulted in two derivatives 7f and 7p as most potent antitubercular agents (MIC:1.56 μg/mL) with lower cytotoxicity profiles.

Computational Studies on Imidazo[1,2-a] Pyridine-3-Carboxamide Analogues as Antimycobacterial Agents: Common Pharmacophore Generation, Atom-based 3D-QSAR, Molecular dynamics Simulation, QikProp, Molecular Docking and Prime MMGBSA Approaches

Background:

IMB-1402, Q203 and ND09759 analogs were found to have strong efficiency against Multi-drug-resistant tuberculosis (MDR-TB)/Extensively drug-resistant tuberculosis (XDR-TB) strains.

Objectives:

To know the structural necessities for imidazo[1,2-a]pyridine-3-carboxamide analogues, we intended to develop the ligand-based pharmacophore, Quantitative structure–activity relationship models(3D-QSAR model). We also performed Molecular docking, molecular simulation and Prime/Molecular Mechanics Generalized Born Surface Area (Prime/MM-GBSA) studies.

Methods:

All the studies like Common pharmacophore hypothesis generation, Atom based 3D-QSAR study, Prime MMGBSA, Docking, Qikprop, and Molecular dynamics simulation were processed using various modules incorporated within the maestro software interface from Schrodinger, LLC, New York USA (release 2017).

Results:

The common pharmacophore hypothesis(CPH) generation resulted in a five-featured hypothesis HHPRR, containing 1 positive, 2 hydrophobic and 2 aromatic rings. An Atom-based 3D-QSAR model was predicted for twenty seven training sets (a correlation coefficient i.e.R2= 0.9181,Standard deviation i.e.SD =0.3305, variance ratio i.e. F = 85.9) and eleven test sets (cross-validation correlation coefficient i.e.Q2 =0.6745, Root Mean Square Error i.e. RMSE = 0.65, Pearson R = 0.8427, P=1.21E-12) compounds employing alignment based on CPH. The dataset of thirty-eight molecules was allowed for docking into the active site of pantothenate synthetase (PDBID-3IVX) that shows H-bonding (Hydrogen bonding) interactions with residues Gly158, Met195, Pro38 and additionally shows further Pi-cation interactions with a residue like Hie47. We also obtained good simulation results for1.2ns study.

Conclusion:

From the results, the generated 3D-QSAR model may be applicable for additional designing of various novel potent derivatives in the future.

Dibenzofuran, dibenzothiophene and N-methyl carbazole tethered 2-aminothiazoles and their cinnamamides as potent inhibitors of Mycobacterium tuberculosis

Herein described the design, synthesis and antitubercular evaluation of novel series of dibenzofuran, dibenzothiophene and N-methyl carbazole tethered 2-aminothiazoles and their cinnamamide analogs. One pot condensation of N-methyl carbazole, dibenzofuran and dibenzothiophene methyl ketones with thiourea in the presence of Iodine and CuO gave respective 2-aminothiazoles 4-6 in very good yields. Aminothiazoles were further coupled with substituted cinnamic acids using acid-amine coupling conditions to give desired cinnamamide analogs 8a-e, 9a-e and 10a-e. All the newly synthesized compounds were fully characterized by their NMR and mass spectral analysis. In vitro screening of new derivatives against Mycobacterium tuberculosis H37Rv (Mtb) resulted 8c, 10d and 10e (MIC: 0.78 µg/mL) and 2-aminothiazoles 5 and 6 (MIC: 1.56 µg/mL) as potent compounds with lower cytotoxicity profile.

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

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