Isoniazid Linked to Sulfonate Esters via Hydrazone Functionality: Design, Synthesis, and Evaluation of Antitubercular Activity.

Isoniazid (INH) is one of the key molecules employed in the treatment of tuberculosis (TB), the most deadly infectious disease worldwide. However, the efficacy of this cornerstone drug has seriously decreased due to emerging INH-resistant strains of Mycobacterium tuberculosis (Mtb). In the present study, we aimed to chemically tailor INH to overcome this resistance. We obtained thirteen novel compounds by linking INH to in-house synthesized sulfonate esters via a hydrazone bridge (SIH1-SIH13). Following structural characterization by FTIR, 1H NMR, 13C NMR, and HRMS, all compounds were screened for their antitubercular activity against Mtb H37Rv strain and INH-resistant clinical isolates carrying katG and inhA mutations. Additionally, the cytotoxic effects of SIH1-SIH13 were assessed on three different healthy host cell lines; HEK293, IMR-90, and BEAS-2B. Based on the obtained data, the synthesized compounds appeared as attractive antimycobacterial drug candidates with low cytotoxicity. Moreover, the stability of the hydrazone moiety in the chemical structure of the final compounds was confirmed by using UV/Vis spectroscopy in both aqueous medium and DMSO. Subsequently, the compounds were tested for their inhibitory activities against enoyl acyl carrier protein reductase (InhA), the primary target enzyme of INH. Although most of the synthesized compounds are hosted by the InhA binding pocket, SIH1-SIH13 do not primarily show their antitubercular activities by direct InhA inhibition. Finally, in silico determination of important physicochemical parameters of the molecules showed that SIH1-SIH13 adhered to Lipinski's rule of five. Overall, our study revealed a new strategy for modifying INH to cope with the emerging drug-resistant strains of Mtb.

Urea derivatives carrying a thiophenylthiazole moiety: Design, synthesis, and evaluation of antitubercular and InhA inhibitory activities.

The recent emergence of drug-resistant strains of Mycobacterium tuberculosis (Mtb) has complicated and significantly slowed efforts to eradicate and/or reduce the worldwide incidence of life-threatening acute and chronic cases of tuberculosis. To overcome this setback, researchers have increased the intensity of their work to identify new small-molecule compounds that are expected to remain efficacious antimicrobials against Mtb. Here, we describe our effort to apply the principles of molecular hybridization to synthesize 16 compounds carrying thiophene and thiazole rings beside the core urea functionality (TTU1-TTU16). Following extensive structural characterization, the obtained compounds were initially evaluated for their antimycobacterial activity against Mtb H37Rv. Subsequently, three derivatives standing out with their anti-Mtb activity profiles and low cytotoxicity (TTU5, TTU6, and TTU12) were tested on isoniazid-resistant clinical isolates carrying katG and inhA mutations. Additionally, due to their pharmacophore similarities to the well-known InhA inhibitors, the molecules were screened for their enoyl acyl carrier protein reductase (InhA) inhibitory potentials. Molecular docking studies were performed to support the experimental enzyme inhibition data. Finally, drug-likeness of the selected compounds was established by theoretical calculations of physicochemical descriptors.

Design and characterisation of piperazine-benzofuran integrated dinitrobenzenesulfonamide as Mycobacterium tuberculosis H37Rv strain inhibitors.

Molecular hybridisation of four bioactive fragments piperazine, substituted-benzofuran, amino acids, and 2,4-dinitrobenzenesulfonamide as single molecular architecture was designed. A series of new hybrids were synthesised and subjected to evaluation for their inhibitory activity against Mycobacterium tuberculosis (Mtb) H37Rv. 4d-f and 4o found to exhibit MIC as 1.56 µg/mL, equally active as ethambutol whereas 4a, 4c, 4j displayed MIC 0.78 µg/mL were superior to ethambutol. Tested compounds demonstrated an excellent safety profile with very low toxicity, good selectivity index, and antioxidant properties. All the newly synthesised compounds were thoroughly characterised by analytical methods. The result was further supported by molecular modelling studies on the crystal structure of Mycobacterium tuberculosis enoyl reductase.

Synthesis and Biological Evaluation of Novel Benzhydrylpiperazine-Coupled Nitrobenzenesulfonamide Hybrids.

A series of novel benzhydryl piperazine-coupled nitrobenzenesulfonamide hybrids were synthesized with good to excellent yields. They were tested for in vitro inhibition of mycobacterial activity against the Mycobacterium tuberculosis H37Rv strain, in vitro cytotoxicity MTT (RAW 264.7cells) assay, nutrient starvation (H37Rv strain), and ability to block Cav3.2 T-type calcium channels. Novel hybrids did not inhibit T-type calcium channels, whereas they showed excellent antituberculosis (TB) activity and low cytotoxicity with a selectivity index of >30. A direct impact of the amino acid linker was not observed. Studied hybrids exhibited good inhibition activities, and the 2,4-dinitrobenzenesulfonamide group emerged as a promising scaffold for further drug design by hybridization approaches for anti-TB therapy.

Design and Synthesis of "Chloropicolinate Amides and Urea Derivatives" as Novel Inhibitors for Mycobacterium tuberculosis.

A series of 30 novel diamino phenyl chloropicolinate fettered carboxamides, urea, and thiourea derivatives were synthesized by coupling of methyl 4-amino-6-(2-aminophenyl)-3-chloropyridine-2-carboxylate with different acid chlorides, urea, and thiourea moieties, respectively. All of these compounds were characterized by 1H and 13C nuclear magnetic resonance spectroscopy, CHN analysis, and high-resolution mass spectra for confirmation of the structures. Two compounds were also characterized by single-crystal X-ray diffraction analysis to confirm the structures obtained by spectral analysis. All these 30 compounds were tested for their in vitro antimycobacterial activity using the microplate alamar blue assay method against Mycobacterium tuberculosis. Five compounds have shown good minimum inhibitory concentration (MIC) values with low cytotoxicity when compared with the reference drugs. Moreover, some of the compounds have high MIC values compared with isoniazid, rifampicin, and so forth and also had shown good reign in the spread of bacteria by the nutrient starvation model. These antimycobacterial activity results have shown a good correlation with molecular docking model analysis with the inhibitors MurB by exhibiting strong interactions. Some of these compounds could be promising candidates against M. tuberculosis for future preclinical agent drug development.

Design and synthesis of purine connected piperazine derivatives as novel inhibitors of Mycobacterium tuberculosis.

A series of novel purine linked piperazine derivatives were synthesized to identify new, potent inhibitors of Mycobacterium tuberculosis. The compounds were designed to target MurB disrupting the biosynthesis of the peptidoglycan and exert antiproliferative effects. The first series of purine-2,6-dione linked piperazine derivatives were synthesized using an advanced intermediate 1-(3,4-difluorobenzyl)-7-(but-2-ynyl)-3-methyl-8-(piperazin-1-yl)-1H-purine-2,6(3H,7H)-dione hydrochloride (6) which was coupled with varied carboxylic acid chloride derivatives. Following this piperazine linked derivatives were also synthesized from 6 using diverse isocyanate partners. The anti-mycobacterial activity of the analogues was tested againstMycobacterium tuberculosis H37Rv which revealed a cluster of six analogues (11, 24,27, 32, 33 and34), possessed promising activity. In comparison, a set of these new compounds possessed greater potencies relative to current drugs used in the clinic such as Ethambutol. These results were also correlated with computational molecular docking analysis, providing models for strong interactions of the inhibitors with MurB providing a template for the future development of preclinical agents against Mycobacterium tuberculosis.

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.

1,3-Disubstituted urea derivatives: Synthesis, antimicrobial activity evaluation and in silico studies.

The development of new antimicrobial compounds is in high demand to overcome the emerging drug resistance against infectious microbial pathogens. In the present study, we carried out the extensive antimicrobial screening of disubstituted urea derivatives. In addition to the classical synthesis of urea compounds by the reaction of amines and isocyanates, we also applied a new route including bromination, oxidation and azidination reactions, respectively, to convert 2-amino-3-methylpyridine to 1,3-disubstituted urea derivatives using various amines. The evaluation of antimicrobial activities against various bacterial strains, Candida albicans as well as Mycobacterium tuberculosis resulted in the discovery of new active molecules. Among them, two compounds, which have the lowest MIC values on Pseudomonas aeruginosa, were further evaluated for their inhibition capacities of biofilm formation. In order to evaluate their potential mechanism of biofilm inhibition, these two compounds were docked into the active site of LasR, which is the transcriptional regulator of bacterial signaling mechanism known as quorum sensing. Finally, the theoretical parameters of the bioactive molecules were calculated to establish their drug-likeness properties.

Design, synthesis and biological evaluation of novel Pseudomonas aeruginosa DNA gyrase B inhibitors.

In the present study, we attempted to develop a novel class of compounds active against Pseudomonas aeruginosa (Pa) by exploring the pharmaceutically well exploited enzyme targets. Since, lack of Pa gyrase B crystal structures, Thermus thermophilus gyrase B in complex with novobiocin (1KIJ) was used as template to generate model structure by performing homology modeling. Further the best model was validated and used for high-throughput virtual screening, docking and dynamics simulations using the in-house database for identification of Pa DNA gyrase B inhibitors. This study led to an identification of three lead molecules with IC50 values in range of 6.25-15.6 µM against Pa gyrase supercoiling assay. Lead-1 optimization and expansion resulted in 15 compounds. Among the synthesized compounds six compounds were shown good enzyme inhibition than Lead-1 (IC50 6.25 µM). Compound 13 emerged as the most potential compound exhibiting inhibition of Pa gyrase supercoiling with an IC50 of 2.2 µM; and in-vitro Pa activity with MIC of 8 µg/mL in presence of efflux pump inhibitor; hence could be further developed as novel inhibitor for Pa gyrase B.

Design and synthesis of thiourea-based derivatives as Mycobacterium tuberculosis growth and enoyl acyl carrier protein reductase (InhA) inhibitors.

Tuberculosis remains the most deadly infectious disease worldwide due to the emergence of drug-resistant strains of Mycobacterium tuberculosis. Hence, there is a great need for more efficient treatment regimens. Herein, we carried out rational molecular modifications on the chemical structure of the urea-based co-crystallized ligand of enoyl acyl carrier protein reductase (InhA) (PDB code: 5OIL). Although this compound fulfills all structural requirements to interact with InhA, it does not inhibit the enzyme effectively. With the aim of improving the inhibition value, we synthesized thiourea-based derivatives by one-pot reaction of the amines with corresponding isothiocyanates. After the structural characterization using 1H NMR, 13C NMR, FTIR and HRMS, the obtained compounds were initially tested for their abilities to inhibit Mycobacterium tuberculosis growth. The results revealed that some compounds exhibited promising antitubercular activity, MIC values at 0.78 and 1.56 µg/mL, combined with low cytotoxicity. Moreover, the most active compounds were tested against latent as well as dormant forms of the bacteria utilizing nutrient starvation model and Mycobacterium tuberculosis infected macrophage assay. Enzyme inhibition assay against enoyl-acyl carrier protein reductase identified InhA as the important target of some compounds. Molecular docking studies were performed to correlate InhA inhibition data with in silico results. Finally, theoretical calculations were established to predict the physicochemical properties of the most active compounds.

Benzimidazoquinazolines as new potent anti-TB chemotypes: Design, synthesis, and biological evaluation.

In search for new molecular entities as anti-TB agents, the benzimidazoquinazoline polyheterocyclic scaffold has been designed adopting the scaffold hopping strategy. Thirty-two compounds have been synthesized through an improved tandem decarboxylative nucleophilic addition cyclocondensation reaction of o-phenylenediamine with isatoic anhydride followed by further cyclocondensation of the intermediately formed 2-(o-aminoaryl)benzimidazole with trialkyl orthoformate/acetate. The resultant benzimidazoquinazolines were evaluated in vitro for anti-TB activity against M. tuberculosis H37Rv (ATCC27294 strain). Fourteen compounds exhibiting MIC values in the range of 0.4-6.25 µg/mL were subjected to cell viability test against RAW 264.7 cell lines and were found to be non-toxic (<30% inhibition at 50 µg/mL). The active compounds were further evaluated against INH resistant Mtb strains. The most active compound 6x [MIC (H37Rv) of 0.4 µg/mL] and the compound 6d [MIC (H37Rv) of 0.78 µg/mL] were also found to be active against INH resistant Mtb strain with MIC values of 12.5 and 0.78 µg/mL, respectively.

Design and development of ((4-methoxyphenyl)carbamoyl) (5-(5-nitrothiophen-2-yl)-1,3,4-thiadiazol-2-yl)amide analogues as Mycobacterium tuberculosis ketol-acid reductoisomerase inhibitors.

Based on our previous finding that the titled compound possesses anti-tuberculosis activity, a series of novel ((4-methoxyphenyl)carbamoyl) (5-(5-nitrothiophen-2-yl)-1,3,4-thiadiazol-2-yl)amide analogues have been synthesized. Amongst the 22 compounds synthesized and tested, 5b, 5c and 6c showed potent inhibitory activity with Ki values of 2.02, 5.48 and 4.72 µM for their target, Mycobacterium tuberculosis (Mt) ketol-acid reductoisomerase (KARI). In addition, these compounds have excellent in vitro activity against Mt H37Rv with MIC values as low as 1 µM. The mode of binding for these compounds to Mt KARI was investigated through molecular docking and dynamics simulations. Furthermore, these compounds were evaluated for their activity in Mt infected macrophages, and showed inhibitory activities with up to a 1.9-fold reduction in growth (at 10 µM concentration). They also inhibited Mt growth in a nutrient starved model by up to 2.5-fold. In addition, these compounds exhibited low toxicity against HEK 293T cell lines. Thus, these compounds are promising Mt KARI inhibitors that can be further optimized into anti-tuberculosis agents.

Synthesis and efficacy of pyrvinium-inspired analogs against tuberculosis and malaria pathogens.

Herein, we report the synthesis and evaluation of pyrvinium-based antimalarial and antitubercular compounds. Pyrvinium is an FDA approved drug for the treatment of pinworm infection, and it has been reported to have antiparasitic and antimicrobial activities. Pyrvinium contains quinoline core coupled with pyrrole. We replaced the pyrrole with various aryl or heteroaryl substituents to generate pyrvinium analogs. The profiling of these compounds against malaria parasite P. falciparum 3D7 revealed analogs with better antimalarial activity than pyrvinium pamoate. Compound 14 and 16 showed IC50 of 23 nM and 60 nM against P. falciparum 3D7, respectively. These compounds were also effective against drug-resistant malaria parasite P. falciparum Dd2 with IC50 of 53 nM and 97 nM, respectively. The cytotoxicity against CHO-K1, HEK and NRK-49F cells revealed better selectivity index for these new analogs compared to pyrvinium. Additionally, this series of compounds showed activity against M. tuberculosis H37Rv; particularly compounds 10, 13, 14 and 16 showed equipotent antitubercular activity to that of pyrvinium pamoate. The compounds 14 and 16 should be taken forward as leads for further optimization.

Synthesis, in vitro, and in vivo (Zebra fish) antitubercular activity of 7,8-dihydroquinolin-5(6H)-ylidenehydrazinecarbothioamides.

We, herein, describe the synthesis of a series of novel aryl tethered 7,8-dihydroquinolin-5(6H)-ylidenehydrazinecarbothioamides 4a-v, which showed in vitro and in vivo antimycobacterial activity against Mycobacterium tuberculosis (Mtb) H37Rv. The intermediates dihydro-6H-quinolin-5-ones 3a-v were synthesized from ß-enaminones, reacting with cyclochexane-1,3-dione/5,5-dimethylcyclohexane-1,3-dione and ammonium acetate using a modified Bohlmann-Rahtz reaction conditions. They were further reacted with thiosemicarbazide to give the respective hydrazine carbothioamides 4a-v. All the new analogues 4a-v, were characterized by their NMR and mass spectral data analysis. Among the twenty-two compounds screened for in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Rv (ATCC27294), two compounds, 4e and 4j, exhibited the highest inhibition with an MIC of 0.39 µg/mL. Compounds 4a, 4g, and 4k were found to inhibit Mtb at an MIC of 0.78 µg/mL. Hydrazinecarbothioamides 4a-k, exhibited enhanced activity than dihydroquinolinones 3a-k. The observed increase in potency provides a clear evidence that hydrazinecarbothioamide is a potential pharmacophore, collectively imparting synergistic effect in enhancing antitubercular activity of the dihydroquinolinone core. The in vivo (Zebra fish) antimycobacterial screening of the in vitro active molecules led to the identification of a hit compound, 4j, with significant activity in the Mtb nutrient starvation model (2.2-fold reduction). Docking studies of 4j showed a hydrogen bond with the P156 residue of the protein.

Discovery of hydrazone containing thiadiazoles as Mycobacterium tuberculosis growth and enoyl acyl carrier protein reductase (InhA) inhibitors.

Tuberculosis, caused by Mycobacterium tuberculosis, is a serious infectious disease and remains a global health problem. There is an increasing need for the discovery of novel therapeutic agents for its treatment due to the emerging multi-drug resistance. Herein, we present the rational design and the synthesis of eighteen new thiadiazolylhidrazones (TDHs) which were synthesized by intramolecular oxidative N-S bond formation reaction of 2-benzylidene-N-(phenylcarbamothioyl)hydrazine-1-carboximidamide derivatives by phenyliodine(III) bis(trifluoroacetate) (PIFA) under mild conditions. The compounds were characterized by various spectral techniques including FTIR, 1H NMR, 13C NMR and HRMS. Furthermore, the proposed structure of TDH12 was resolved by single-crystal X-ray analysis. The compounds were evaluated for their in vitro antitubercular activity against M. tuberculosis H37Rv. Among them, some compounds exhibited remarkable antimycobacterial activity, MIC = 0.78-6.25 µg/mL, with low cytotoxicity. Additionally, the most active compounds were screened for their biological activities against M. tuberculosis in the nutrient starvation model. Enzyme inhibition assays and molecular docking studies revealed enoyl acyl carrier protein reductase (InhA) as the possible target enzyme of the compounds to show their antitubercular activities.

Novel benzimidazole-acrylonitrile hybrids and their derivatives: Design, synthesis and antimycobacterial activity.

This paper reports the synthesis and evaluation of some benzimidazole-acrylonitrile hybrid derivatives for their in vitro antimycobacterial activities against Mycobacterium tuberculosis H37Rv. Among the derivatives studied, 3b was found to be the most active compound with MIC of 0.78 µg/mL against M. tuberculosis. This is a quite good activity compared with ethambutol (MIC = 1.56 µg/mL). Moreover, 3b showed 2.8 log fold reduction in bacterial count of dormant forms of mycobacterium which is more potent than first line drugs isoniazid, ciprofloxacin, rifampicin and moxifloxacin. Having activities against both active and dormant forms of M. tuberculosis,3b may be a useful candidate for the development of new drugs to treat tuberculosis.

Regio- and diastereoselective synthesis of spiropyrroloquinoxaline grafted indole heterocyclic hybrids and evaluation of their anti-Mycobacterium tuberculosis activity.

An efficient and eco compatible approach for the regio- and stereoselective synthesis of structurally diverse novel hybrid heterocycles comprising spiropyrrolidine, indenoquinoxaline and indole structural units in excellent yields, has been achieved through a one-pot multicomponent process involving 1,3-dipolar cycloaddition as a key step. The 1,3-dipolar component is the azomethine ylide generated in situ from indenoquinoxaline and l-tryptophan and reacts with various substituted ß-nitrostyrenes affording the spiroheterocyclic hybrids. The ring system thus created possesses two C-C and three C-N bonds and four adjacent stereogenic carbons, one of which is quaternary and the reaction proceeded with full diastereomeric control. All the synthesized compounds were assayed for their in vitro activity against Mycobacterium tuberculosis H37Rv using MABA assay. Interestingly, the compound bearing a 2-fluoro substituent on the aryl ring displayed an equipotent activity (MIC 1.56 µg mL-1) to ethambutol against Mycobacterium tuberculosis H37Rv.

5-Chloro-2-thiophenyl-1,2,3-triazolylmethyldihydroquinolines as dual inhibitors of Mycobacterium tuberculosis and influenza virus: Synthesis and evaluation.

This study describes synthesis and evaluation of novel 5-Chloro-2-thiophenyl-1,2,3-triazolylmethyldihydroquinolines 7a-o as dual inhibitors of Mycobacterium tuberculosis and influenza virus. Huisgen's [3+2] dipolar cycloaddition of 6-(azidomethyl)-5-chloro-2-(thiophen-2-yl)-7,8-dihydroquinoline 5 with various alkynes 6a-o using sodium ascorbate and copper sulphate gave new dihydroquinoline-1,2,3-triazoles 7a-o in good to excellent yields. The new compounds were evaluated for in vitro antimycobacterial against M. tuberculosis H37Rv (Mtb) and antiviral activity against influenza virus A/Puerto Rico/8/34 (H1N1). Among the fifteen new analogs, compounds 7a (MIC: 3.12 µg/mL), 7j and 7k (MIC: 6.25 µg/mL) were identified as potent antitubercular agents. The virus-inhibiting activity of all the fifteen compounds was found to be moderate, and among them the compound 7l, bearing thiophene moiety appeared the most active with good selectivity index (IC50 = 19.5 µg/mL; SI = 15). The results presented here will help developing newer dual inhibitors of tuberculosis and influenza virus.

Synthesis and biological evaluation of 2,4,5-trisubstituted thiazoles as antituberculosis agents effective against drug-resistant tuberculosis.

The dormant and resistant form of Mycobacterium tuberculosis presents a challenge in developing new anti-tubercular drugs. Herein, we report the synthesis and evaluation of trisubstituted thiazoles as antituberculosis agents. The SAR study has identified a requirement of hydrophobic substituent at C2, ester functionality at C4, and various groups with hydrogen bond acceptor character at C5 of thiazole scaffold. This has led to the identification of 13h and 13p as lead compounds. These compounds inhibited the dormant Mycobacterium tuberculosis H37Ra strain and M. tuberculosis H37Rv selectively. Importantly, 13h and 13p were non-toxic to CHO cells. The 13p showed activity against multidrug-resistant tuberculosis isolates.

Ultrasonication-ionic liquid synergy for the synthesis of new potent anti-tuberculosis 1,2,4-triazol-1-yl-pyrazole based spirooxindolopyrrolizidines.

The aim of the study is to design and synthesis of a new series of potent anti-TB 1,2,4-triazol-1-yl-pyrazole based spirooxindolopyrrolizidines with their safety profile. A synergetic effect of ultrasonication and ionic liquid was shown successfully as a green methodology for the synthesis of title compounds 6a-t. These derivatives were obtained in shorter reaction time with good yields and well characterized by various spectroscopic methods, single-crystal X-ray diffraction (6f). The in vitro anti-tuberculosis activity for newly-synthesized derivatives has been screened against Mycobacterium tuberculosis. Among all, six compounds 6e, 6k, 6l, 6n, 6q and 6r exhibited equal potent activity compared to standard drug ethambutol (MIC: 1.56 µg/mL) and another compound 6h exhibited outstanding activity (MIC: 0.78 µg/mL) than the standard drug ethambutol. Cytotoxic nature of the anti-TB active compounds was evaluated against RAW 264.7 cells. The 6h, 6e, 6k, 6l, 6n, 6q and 6r exhibited lower toxicity which could be promising hits for anti-tuberculosis.