Design,Synthesis, and Biological Evaluation of 1,4‐dihydropyridine Derivatives as Potent Antitubercular Agents

A series of novel 1,4‐dihydropyridine‐3,5‐dicarbamoyl derivatives bearing an imidazole nucleus at C‐4 position were synthesized in excellent yields via multicomponent Hantzsch reaction. The newly synthesized compounds were characterized by IR, ¹H NMR, ¹³C NMR, and mass spectroscopy. The synthesized compounds 3a‐p were screened for antitubercular activity. Among all the screened compounds, compounds 3j and 3m showed most prominent activity against Mycobacterium tuberculosis with minimum inhibitory concentration of 0.02 μg/mL and SI > 500, making it more potent than first‐line antitubercular drug isoniazid. In addition, these compounds displayed relatively low cytotoxicity.     

Design,synthesis, and in vitro antituberculosis activity of benzo[6,7]cyclohepta[1,2‐b]pyridine‐1,3,4‐oxadiazole derivatives

A new antitubercular agents, benzo[6,7]cyclohepta[1,2‐b]pyridine‐1,3,4‐ oxadiazole hybrids ( 6a–o ), have been designed and synthesized involving oxidative cyclization of hydrazones by use of di(acetoxy)iodobenzene, characterized by IR,¹H NMR,¹³C NMR, and HRMS, and further confirmed by X‐ray analysis. All the newly synthesized compounds 4a–o evaluated for their in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Rv (ATCC27294). Among the compounds tested, the compounds 4o (MIC: 1.56  μg/ml) and 4l, 4m (MIC: 3.125  μg/ml) are promising lead analogues and have shown lower cytotoxicity.     

Synthesis and Antitubercular Activity of 2‐(substituted phenyl/benzyl‐amino)‐6‐(4‐chlorophenyl)‐5‐(methoxycarbonyl)‐4‐methyl‐3,6‐dihydropyrimidin‐1‐ium Chlorides

A series of 2‐(substituted phenyl/benzyl‐amino)‐6‐(4‐chlorophenyl)‐5‐(methoxycarbonyl)‐4‐methyl‐3,6‐dihydropyrimidin‐1‐ium chlorides 7–13 and 15 was synthesized in their hydrochloride salt form. The title compounds were characterized by FT‐IR, NMR (¹H and ¹³C) and elemental analysis. They were evaluated for their in vitro antitubercular activity against Mycobacterium tuberculosis H37Rv, multidrug resistance tuberculosis and extensively drug resistance tuberculosis by agar diffusion method and tested for the cytotoxic action on peripheral blood mononuclear cells by MTT assay. Among all the tested compounds in the series, compounds 7 and 11 emerged as promising antitubercular agents at 16 μg/mL against multidrug resistance tuberculosis and over 64 μg/mL against extensively drug resistance tuberculosis. The conformational features and supramolecular assembly of the promising compounds 7 and 11 were determined by single crystal X‐ray study.     

Synthesis and Antitubercular Screening of [(2‐Chloroquinolin‐3‐yl)methyl] Thiocarbamide Derivatives

A series of 1‐(substituted‐phenyl)‐1‐[(2‐chloroquinolin‐3‐yl)methyl]thiocarbamide and 1‐(substituted‐phenyl)‐1‐[(2‐chloroquinolin‐3‐yl)methyl]methylthiocarbamide derivatives was synthesized as antitubercular agent. The structure of quinolinyl amines and their thiocarbamide derivatives were established on the basis of IR, ¹H and ¹³C‐NMR and mass spectral data. All the compounds were tested in vitro for antimycobacterial activity against Mycobacterium tuberculosis (ATCC‐25177) in Lowenstein‐Jensen medium by well diffusion method and MIC by twofold serial dilution method. Results of the antitubercular screening revealed that compounds showed moderate to good antitubercular activity. Compound having two halogens in the phenyl rings viz. 3g , 3h , 4g, and 4h exhibited MIC of 50 μg/mL. The computational parameters relevant to absorption and permeation of target compounds were also calculated and found to be well correlated with antitubercular activity.     

Design,synthesis and biological evaluation of novel quinoline‐based carboxylic hydrazides as anti‐tubercular agents

In this study, seventeen novel quinoline‐based carboxylic hydrazides were designed as potential anti‐tubercular agents using molecular hybridization approach and evaluated in‐silico for drug‐likeness behavior. The compounds were synthesized, purified, and characterized using spectral techniques (like FTIR, ¹H NMR, and Mass). The in‐vitro anti‐tubercular activity (against Mycobacterium tuberculosisH37Ra) and cytotoxicity against human lung fibroblast cells were studied. Among the tested hydrazides, four compounds ( 6h , 6j , 6l, and 6m ) exhibited significant anti‐tubercular activity with MIC values below 20 μg/mL. The two most potent compounds of the series, 6j and 6m exhibited MIC values 7.70 and 7.13 μg/mL, respectively, against M. tuberculosis with selectivity index >26. Structure–activity relationship studies were performed for the tested compounds in order to explore the effect of substitution pattern on the anti‐tubercular activity of the synthesized compounds.     

Design,synthesis, and evaluation of novel diphenyl ether derivatives against drug‐susceptible and drug‐resistant strains of Mycobacterium tuberculosis

In our efforts to develop druggable diphenyl ethers as potential antitubercular agents, a series of novel diphenyl ether derivatives ( 5a – f , 6a – f ) were designed and synthesized. The representative compounds showed promising in vitro activity against drug‐susceptible, isoniazid‐resistant, and multidrug‐resistant strains of Mycobacterium tuberculosis with MIC values of 1.56 μg/ml ( 6b ), 6.25 μg/ml ( 6a–d ), and 3.125 μg/ml ( 6b–c ), respectively. All the synthesized compounds exhibited satisfactory safety profile (CC₅₀ > 300 μg/ml) against Vero and HepG2 cells. Reverse phase HPLC method was used to probe the physicochemical properties of the synthesized compounds. This series of compounds demonstrated comparatively low logP values. pKa values of representative compounds indicated that they were weak acids. Additionally, in vitro human liver microsomal stability assay confirmed that the synthesized compounds possessed acceptable stability under study conditions. The present study thus establishes compound 6b as the most promising antitubercular agent with acceptable drug‐likeness.     

Synthesis and biological evaluation of 1,2,4‐triazole‐3‐thione and 1,3,4‐oxadiazole‐2‐thione as antimycobacterial agents

Resistance among dormant mycobacteria leading to multidrug‐resistant and extremely drug‐resistant tuberculosis is one of the major threats. Hence, a series of 1,2,4‐triazole‐3‐thione and 1,3,4‐oxadiazole‐2‐thione derivatives ( 4a–5c ) have been synthesized and screened for their antitubercular activity against Mycobacterium tuberculosis H37Ra (H37Ra). The triazolethiones 4b and 4v showed high antitubercular activity (both MIC and IC₅₀) against the dormant H37Ra by in vitro and ex vivo. They were shown to have more specificity toward mycobacteria than other Gram‐negative and Gram‐positive pathogenic bacteria. The cytotoxicity was almost insignificant up to 100 μg/ml against THP‐1, A549, and PANC‐1 human cancer cell lines, and solubility was high in aqueous solution, indicating the potential of developing these compounds further as novel therapeutics against tuberculosis infection.     

Synthesis,biological evaluation,and molecular docking studies of novel 3‐aryl‐5‐(alkyl‐thio)‐1H‐1,2,4‐triazoles derivatives targeting Mycobacterium tuberculosis

A small library of new 3‐aryl‐5‐(alkyl‐thio)‐1H‐1,2,4‐triazoles was synthesized and screened for the antimycobacterial potency against Mycobacterium tuberculosis H₃₇Ra strain and Mycobacterium bovis BCG both in active and dormant stage. Among the synthesized library, 25 compounds exhibited promising anti‐TB activity in the range of IC₅₀0.03–5.88 μg/ml for dormant stage and 20 compounds in the range of 0.03–6.96 μg/ml for active stage. Their lower toxicity (>100 μg/ml) and higher selectivity (SI = >10) against all cancer cell lines screened make them interesting compounds with potential antimycobacterial effects. Furthermore, to rationalize the observed biological activity data and to establish a structural basis for inhibition of M. tuberculosis, the molecular docking study was carried out against a potential target MTB CYP121 which revealed a significant correlation between the binding score and biological activity for these compounds. Cytotoxicity and in vivo pharmacokinetic studies suggested that 1,2,4‐triazole analogues have an acceptable safety index, in vivo stability and bio‐availability.     

Design,Synthesis, and Antimycobacterial Activity of Novel Theophylline‐7‐Acetic Acid Derivatives With Amino Acid Moieties

The theophylline‐7‐acetic acid (7‐TAA) scaffold is a promising novel lead compound for antimycobacterial activity. Here, we derive a model for antitubercular activity prediction based on 14 7‐TAA derivatives with amino acid moieties and their methyl esters. The model is applied to a combinatorial library, consisting of 40 amino acid and methyl ester derivatives of 7‐TAA. The best three predicted compounds are synthesized and tested against Mycobacterium tuberculosis H37Rv. All of them are stable, non‐toxic against human cells and show antimycobacterial activity in the nanomolar range being 60 times more active than ethambutol.     

Synthesis and mycobacterial evaluation of 5‐substituted‐6‐acetyl‐2‐amino‐7‐methyl‐5,8‐dihydropyrido‐[2,3‐d]pyrimidin‐4(3H)‐one derivatives

5‐Substituted‐6‐acetyl‐2‐amino‐7‐methyl‐5,8‐dihydropyrido[2,3‐d]pyrimidin‐4(3H)‐one derivatives were synthesized and evaluated against Mycobacterium tuberculosis H37Rv, Mycobacterium aurum, Escherichia coli, and Staphylococcus aureus as well as a human monocyte‐derived macrophage (THP‐1), and murine macrophage (RAW 264.7) cell lines to assess their antibacterial and cytotoxic potential, respectively. The compounds showed activity in the range of 1.95–125 µg/ml against M. tuberculosis but showed no activity against M. aurum, E. coli, and S. aureus, indicating selectivity towards slow‐growing mycobacterial pathogens. The compounds exhibited very low to no cytotoxicity up to 500 µg/ml concentration against eukaryotic cell lines. The most potent molecule, 2l , showed a minimum inhibitory concentration of 1.95 µg/ml against M. tuberculosis H37Rv and a selectivity index of >250 against both the eukaryotic cell lines. Furthermore, 2l showed moderate inhibition of whole‐cell mycobacterial drug‐efflux pumps when compared to verapamil, a known potent inhibitor of efflux pumps. Thus, derivative 2l was identified as an antituberculosis hit molecule, which could be used to yield more potent lead molecules.     

5‐Arylaminouracil Derivatives: New Inhibitors of Mycobacterium tuberculosis

Three series of 5‐arylaminouracil derivatives, including 5‐(phenylamino)uracils, 1‐(4′‐hydroxy‐2′‐cyclopenten‐1′‐yl)‐5‐(phenylamino)uracils, and 1,3‐di‐(4′‐hydroxy‐2′‐cyclopenten‐1′‐yl)‐5‐(phenylamino)uracils, were synthesized and screened for potential antimicrobial activity. Most of compounds had a negative effect on the growth of the Mycobacterium tuberculosis H37Rv strain, with 100% inhibition observed at concentrations between 5 and 40 μg/mL. Of those, 1‐(4′‐hydroxy‐2′‐cyclopenten‐1′‐yl)‐3‐(4?‐hydroxy‐2?‐cyclopenten‐1?‐yl)‐5‐(4″‐butyloxyphenylamino)uracil proved to be the most active among tested compounds against the M. tuberculosis multidrug‐resistant strain MS‐115 (MIC₉₀ 5 μg/mL). In addition, the thymidylate kinase of M. tuberculosis was evaluated as a possible enzymatic target.     

Dual‐protected amino acid derivatives as new antitubercular agents

Tuberculosis is an infectious disease with high incidence and growing drug‐resistant rates. In an attempt to develop new antitubercular agents, 35 compounds were synthesized, most of them bearing a carbamate and enantiopure amino acid moiety. These compounds had their activity evaluated toward a Mycobacterium tuberculosis strain (ATCC 27294) and cytotoxicity against fibroblast MRC‐5 cells (ATCC CCL‐171). Three of the prepared derivatives presented a good antimicrobial inhibition and two of them a moderate cytotoxicity. The lipophilicity seems to play a vital role in the cell growth activity, with best results for the derivatives with a higher logP.     

Synthesis and Antimicrobial Evaluation of 6‐Alkylamino‐N‐phenylpyrazine‐2‐carboxamides

This work presents synthesis and antimicrobial evaluation of nineteen 6‐alkylamino‐N–phenylpyrazine‐2‐carboxamides. Antimycobacterial activity was determined against Mycobacterium tuberculosis H37Rv, M. kansasii and two strains of M. avium. Generally, the antimycobacterial activity increased with prolongation of simple alkyl chain and culminated in compounds with heptylamino substitution ( 3e , 4e ) with MIC = 5–10 μm against M. tuberculosis H37Rv. On the contrary, derivatives with modified alkyl chain (containing e.g. terminal methoxy or hydroxy group) as well as phenylalkylamino derivatives were mainly inactive. The most active compounds (with hexyl to octylamino substitution) were evaluated for their in vitro activity against drug‐resistant strains of M. tuberculosis and possessed activity comparable to that of the reference drug isoniazid. None of the tested compounds were active against M. avium. Some derivatives exhibited activity against Gram‐positive bacteria including methicillin‐resistant Staphylococcus aureus (best MIC = 7.8 μm ), while Gram‐negative strains as well as tested fungal strains were completely unsusceptible. Active compounds were tested for in vitro toxicity on various cell lines and in most cases were non‐toxic up to 100 μm .     

Synthesis and Comparative Study of Anti‐Mycobacterium Activity of a Novel Series of Fluoronitrobenzothiazolopyrazoline Regioisomers

In an attempt to find a new and a safer drug for tuberculosis, we have synthesized a series of fluoronitrobenzothiazolopyrazolines for antitubercular activity. The series comprises three subclasses: fluorobenzothiazolopyrazolines ( 11a–f ), fluoronitrobenzothiazolopyrazoline, nitro group at 5^th position ( 12a–f ) and 4^th position ( 13a–f ). All compounds were screened for their in‐vitro antitubercular activity against Mycobacterium tuberculosis H37Rv strain by using Middlebrook 7H‐9 broth. An introduction of ? NO₂ group at 5^th position of benzothiazole ring ( 12a–f ) increased the antitubercular activity whereas introduction of ? NO₂ group at 4^th position ( 13a–f ) was found to decrease the activity remarkably. Two compounds from each series showing good antitubercular activity were tested for cytotoxicity on THP‐1 cell lines and they showed low cytotoxicity.     

N‐Benzylsalicylthioamides: Highly Active Potential Antituberculotics

A gseries of 29 new derivatives of N‐benzylsalicylthioamides was synthesized and the compounds were tested for in‐vitro antimycobacterial activity against Mycobacterium tuberculosis, Mycobacterium kansasii, and Mycobacterium avium. The activity was analyzed by quantitative structure‐activity relationship (QSAR). Activity increased with increasing lipophilicity and electron donating effect of the substituents in the acyl moiety and decreased with the electrophilic superdelocalizability of the molecules. The most active compounds are more active than isoniazid (INH) and are active against INH‐resistant potential pathogenic strains of mycobacterium.     

2‐Aryl‐3‐(1H‐Azol‐1‐yl)‐1H‐Indole Derivatives: A New Class of Antimycobacterial Compounds – Conventional Heating in Comparison with MW‐Assisted Synthesis

2‐Aryl‐3‐(1H‐imidazol‐1‐yl and 1H‐1,2,4‐triazol‐1‐yl)‐1H‐indole derivatives were synthesized and tested for their in‐vitro antifungal and antimycobacterial activities. These indole derivatives were devoid of antifungal activity against the tested strains of Candida spp. Yet, they exhibited an interesting antitubercular activity against Mycobacterium tuberculosis reference strain H₃₇Rv.     

Synthesis and antimicrobial and anticancer activity of new of imidazo[2,1-<Emphasis Type="Italic">b</Emphasis>][1,3,4]thiadiazoles

A series of new 3-aryl-4-(6′-aryl-imidazo[2,1-b][1,3,4]thiadiazol-2′-yl-phenylsydnones (16 – 27) were synthesized. The structures of the synthesized compounds were confirmed by the IR, ¹H NMR, and mass spectroscopy techniques and elemental analysis. All the newly synthesized compounds were evaluated for their anticancer activity against cervical cancer cell line (Hela) and antimicrobial activity, in particular, antitubercular activity against Mycobacterium tuberculosis (H₃₇Rv).     

Synthesis and in‐vitro Antimycobacterial Evaluation of 1‐(Cyclopropyl/2,4‐difluorophenyl/tert‐butyl)‐1,4‐dihydro‐ 8‐methyl‐6‐nitro‐4‐oxo‐7‐(substituted secondary amino)quinoline‐3‐carboxylic acids

Fifty one newer 1‐(cyclopropyl/2,4‐difluorophenyl/tert‐butyl)‐1,4‐dihydro‐8‐methyl‐6‐nitro‐4‐oxo‐7‐(substituted secondary amino)quinoline‐3‐carboxylic acids were synthesized from 1,3‐dichloro‐2‐methylbenzene and evaluated for in‐vitro antimycobacterial activities against Mycobacterium tuberculosis H37Rv (MTB), multi‐drug resistant Mycobacterium tuberculosis (MDR‐TB), and Mycobacterium smegmatis (MC²). Among the synthesized compounds, 1‐cyclopropyl‐1,4‐dihydro‐7‐(3,4‐dihydro‐6,7‐dimethoxyisoquinolin‐2(1H)‐yl)‐8‐methyl‐6‐nitro‐4‐oxoquinoline‐3‐carboxylic acid 9p was found to be the most active compound in vitro with a MIC value of 0.39 μM against MTB. Against MDR‐TB, compound 7‐(2‐carboxy‐5,6‐dihydroimidazo[1,2‐a]pyrazin‐7(8H)‐yl)‐1‐cyclopropyl‐1,4‐dihydro‐8‐methyl‐6‐nitro‐4‐oxoquinoline‐3‐carboxylic acid 9n was found to be the most active with a MIC value of 0.09 μM.     

Design and synthesis of 9H‐fluorenone based 1,2,3‐triazole analogues as Mycobacterium tuberculosis InhA inhibitors

We prepared fifty various 9H‐fluorenone based 1,2,3‐triazole analogues varied with NH, –S–, and –SO₂– groups using click chemistry. The target compounds were characterized by routine analytical techniques, ¹H, ¹³CNMR, mass, elemental, single‐crystal XRD ( 8a ) and screened for in vitro antitubercular activity against Mycobacterium tuberculosis (MTB) H37Rv strain and two “wild” strains Spec. 210 and Spec. 192 and MIC₅₀ was determined. Further, the compounds were evaluated for MTB InhA inhibition study as well. The final analogues exhibited minimum inhibitory concentration (MIC) ranging from 52.35 to >295 μm . Among the –NH– analogues, one compound 5p (MIC 58.34 μm ), among –S– containing analogues four compounds 8e (MIC 66.94 μm ), 8f (MIC 74.20 μm ), 8g (MIC 57.55 μm ), and 8q (MIC 56.11 μm ), among –SO₂– containing compounds one compound 10p (MIC 52.35 μm ) showed less than MTB MIC 74.20 μm : Compound 4‐(((9H‐fluoren‐9‐yl)sulfonyl)methyl)‐1‐(3,4,5‐trimethoxyphenyl)‐1H‐1,2,3‐triazole ( 10p ) was found to be the most active compound with 73% InhA inhibition at 50 μm ; it inhibited MTB with MIC 52.35 μm . Further, 10f and 10p were docked to crystal structure of InhA to know binding interaction pattern. Most active compounds were found to be non‐cytotoxic against HEK 293 cell lines at 50 μm .     

Bioassay‐Guided Isolation and Structural Modification of the Anti‐TB Resorcinols from Ardisia gigantifolia

Tuberculosis (TB) is a highly contagious disease mainly caused by Mycobacterium tuberculosis H₃₇R_V. Antitubercular (anti‐TB) bioassay‐guided isolation of the CHCl₃ extract of the leaves and stems of the medicinal plant Ardisia gigantifolia led to the isolation of two anti‐TB 5‐alkylresorcinols, 5‐(8Z‐heptadecenyl) resorcinol ( 1 ) and 5‐(8Z‐pentadecenyl) resorcinol ( 2 ). We further synthesized 15 derivatives based on these two natural products. These compounds (natural and synthetic) were evaluated for their anti‐TB activity against Mycobacterium tuberculosis H₃₇R_V. Resorcinols 1 and 2 exhibited anti‐TB activity with MIC values at 34.4 and 79.2 μm in MABA assay, respectively, and 91.7 and 168.3 μm in LORA assay, respectively. Among these derivatives, compound 8 was found to show improved anti‐TB activity than its synthetic precursor ( 2 ) with MIC values at 42.0 μm in MABA assay and 100.2 μm in LORA assay. The active compounds should be regarded as new hits for further study as a novel class of anti‐TB agents. The distinct structure–activity correlations of the parent compound were elucidated based on these derivatives.