Development of acridine derivatives as selective Mycobacterium tuberculosis DNA gyrase inhibitors

In this study we have designed p-phenylene diamine linked acridine derivative from our earlier reported quinoline–aminopiperidine hybrid MTB DNA gyrase inhibitors with aiming more potency and less cardiotoxicity. We synthesized thirty six compounds using four step synthesis from 2-chloro benzoic acid. Among them compound 4-chloro-N-(4-((2-methylacridin-9-yl)amino)phenyl)benzenesulphonamide (6) was found to be more potent with MTB DNA gyrase super coiling IC₅₀ of 5.21 ± 0.51 μM; MTB MIC of 6.59 μM and no zHERG cardiotoxicity at 30 μM and 11.78% inhibition at 50 μM against mouse macrophage cell line RAW 264.7.     

Design,synthesis and biological evaluation of imidazo[2,1-b]thiazole and benzo[d]imidazo[2,1-b]thiazole derivatives as Mycobacterium tuberculosis pantothenate synthetase inhibitors

In the present study, we have designed imidazo[2,1-b]thiazole and benzo[d]imidazo[2,1-b]thiazole derivatives from earlier reported imidazo[1,2-a]pyridine based Mycobacterium tuberculosis (MTB) pantothenate synthetase (PS) inhibitors. We synthesized thirty compounds and they were evaluated for MTB PS inhibition study, in vitro anti-TB activities against replicative and non-replicative MTB, in vivo activity using Mycobacterium marinum infected Zebra fish and cytotoxicity against RAW 264.7 cell line. Among them compound 2-methyl-N′-(4-phenoxybenzoyl)benzo[d]imidazo[2,1-b]thiazole-3-carbohydrazide (5bc) emerged as potent compound active against MTB PS with IC₅₀ of 0.53 ± 0.13 μM, MIC of 3.53 μM, 2.1 log reduction against nutrient starved MTB, with 33% cytotoxicity at 50 μM. It also showed 1.5 log reduction of M. marinum load in Zebra fish at 10 mg/kg.     

Development of benzo[d]oxazol-2(3H)-ones derivatives as novel inhibitors of Mycobacterium tuberculosis InhA

A series of twenty seven substituted 2-(2-oxobenzo[d]oxazol-3(2H)-yl)acetamide derivatives were designed based on our earlier reported Mycobacterium tuberculosis (MTB) enoyl-acyl carrier protein reductase (InhA) lead. Compounds were evaluated for MTB InhA inhibition study, in vitro activity against drug-sensitive and -resistant MTB strains, and cytotoxicity against RAW 264.7 cell line. Among the compounds tested, 2-(6-nitro-2-oxobenzo[d]oxazol-3(2H)-yl)-N-(5-nitrothiazol-2-yl)acetamide (30) was found to be the most promising compound with IC₅₀ of 5.12 ± 0.44 μM against MTB InhA, inhibited drug sensitive MTB with MIC 17.11 μM and was non-cytotoxic at 100 μM. The interaction with protein and enhancement of protein stability in complex with compound 30 was further confirmed biophysically by differential scanning fluorimetry.     

Design,synthesis, biological evaluation of substituted benzofurans as DNA gyraseB inhibitors of Mycobacterium tuberculosis

DNA gyrase of Mycobacterium tuberculosis (MTB) is a type II topoisomerase and is a well-established and validated target for the development of novel therapeutics. By adapting the medium throughput screening approach, we present the discovery and optimization of ethyl 5-(piperazin-1-yl) benzofuran-2-carboxylate series of mycobacterial DNA gyraseB inhibitors, selected from Birla Institute of Technology and Science (BITS) database chemical library of about 3000 molecules. These compounds were tested for their biological activity; the compound 22 emerged as the most active potent lead with an IC₅₀ of 3.2 ± 0.15 μM against Mycobacterium smegmatis DNA gyraseB enzyme and 0.81 ± 0.24 μM in MTB supercoiling activity. Subsequently, the binding of the most active compound to the DNA gyraseB enzyme and its thermal stability was further characterized using differential scanning fluorimetry method.     

Design of novel quinoline-aminopiperidine derivatives as Mycobacterium tuberculosis (MTB) GyrB inhibitors: an in silico study

Tuberculosis (TB) is an infectious disease that causes a number of deaths, and the development of new, safer and more adequate TB inhibitors/drugs has become a necessity as well as a great challenge. Mycobacterial DNA gyrase B subunit has been identified to be one of the potentially underexploited drug targets in the field of anti-tubercular drug discovery. To design the novel and potent Mycobacterium tuberculosis (MTB) inhibitors, we performed molecular modeling studies that combined the 3D-QSAR, molecular docking, molecular dynamics (MD) simulations, and binding free energy calculations. Forty eight quinoline-aminopiperidine inhibitors which act on DNA gyrase B subunit were used for constructing 3D-QSAR models. The results showed that the best CoMFA model had the high performance with q²?=?0.643, r²?=?0.947, while the best CoMSIA model yielded q²?=?0.536, r²?=?0.948. The contour map was in good agreement with the docking and MD simulations which strongly demonstrated that the molecular modeling was reliable. Based on this information, several potential compounds were designed and their inhibitory activities were also verified by the accomplished models and ADME/T predictions. We hope that our research could bring new ideas to facilitate the development of novel inhibitors with higher inhibitory activity for TB.

Communicated by Ramaswamy H. Sarma     

Synthesis and biological evaluation of benzo[d]isothiazole, benzothiazole and thiazole Schiff bases

Three new series of benzo[d]isothiazole, benzothiazole and thiazole Schiff bases were synthesized and tested in vitro with the aim of identifying novel lead compounds active against emergent and re-emergent human and cattle infectious diseases (AIDS, hepatitis B and C, tuberculosis, bovine viral diarrhoea) or against drug-resistant cancers (leukaemia, carcinoma, melanoma, MDR tumors) for which no definitive cure or efficacious vaccine is available at present. In particular, these compounds were evaluated in vitro against representatives of different virus classes, such as a HIV-1 (Retrovirus), a HBV (Hepadnavirus) and the single-stranded RNA(+) viruses Yellow fever virus (YFV) and Bovine viral diarrhoea virus (BVDV), both belonging to Flaviviridae. Title compounds were also tested against representatives of Gram-positive and Gram-negative bacteria (Staphylococcus aureus, Salmonella spp.), various atypic mycobacterial strains (Mycobacterium fortuitum and Mycobacterium smegmatis), yeast (Candida albicans) and mould (Aspergillus fumigatus). None of the compounds showed antiviral or antimicrobial activity. The benzo[d]isothiazole compounds showed a marked cytotoxicity (CC(50)=4-9 microM) against the human CD4(+) lymphocytes (MT-4) that were used to support HIV-1 growth. For this reason, the most cytotoxic compounds of this series were evaluated for their antiproliferative activity against a panel of human cell lines derived from haematological and solid tumors. The results highlighted that all the benzo[d]isothiazole derivatives inhibited the growth of leukaemia cell lines, whereas only one of the above mentioned compounds (1e) showed antiproliferative activity against two solid tumor-derived cell lines.     

Identification and development of 2-methylimidazo[1,2-a]pyridine-3-carboxamides as Mycobacterium tuberculosis pantothenate synthetase inhibitors

In the present study, we used crystal structure of mycobacterial pantothenate synthetase (PS) bound with 2-(2-(benzofuran-2-ylsulfonylcarbamoyl)-5-methoxy-1H-indol-1-yl) acetic acid inhibitor for virtual screening of antitubercular compound database to identify new scaffolds. One of the identified lead was modified synthetically to obtain thirty novel analogues. These synthesized compounds were evaluated for Mycobacterium tuberculosis (MTB) PS inhibition study, in vitro antimycobacterial activities and cytotoxicity against RAW 264.7 cell line. Among the compounds tested, N′-(1-naphthoyl)-2-methylimidazo[1,2-a]pyridine-3-carbohydrazide (5b) was found to be the most active compound with IC₅₀ of 1.90 ± 0.12 μM against MTB PS, MIC of 4.53 μM against MTB with no cytotoxicity at 50 μM. The binding affinity of the most potent inhibitor 5b was further confirmed biophysically through differential scanning fluorimetry.     

Design,synthesis, biological evaluation and molecular docking studies of novel benzofuran–pyrazole derivatives as anticancer agents

This study deals with design and synthesis of novel benzofuran–pyrazole hybrids as anticancer agents. Eight compounds were chosen by National Cancer Institute (NCI), USA to evaluate their in vitro antiproliferative activity at 10⁻⁵ M in full NCI 60 cell panel. The preliminary screening of the tested compounds showed promising broad-spectrum anticancer activity. Compound 4c was further assayed for five dose molar ranges in full NCI 60 cell panel and exhibited remarkable growth inhibitory activity pattern against Leukemia CCRF-CEM, MOLT-4, Lung Cancer HOP-92, Colon Cancer HCC-2998, CNS Cancer SNB-75, Melanoma SK-MEL-2, Ovarian Cancer IGROV1, Renal Cancer 786-0, RXF 393, Breast Cancer HS 578T and T-47D (GI₅₀: 1.00–2.71 μM). Moreover, enzyme assays were carried out to investigate the possible antiproliferative mechanism of action of compound 4c. The results revealed that compound 4c has good c-Src inhibitory activity at 10 μM. In addition, molecular docking studies showed that 4c could bind to the ATP Src pocket sites. Fulfilling the Lipinskiís rule of five in addition to its ADME profile and the biological results, all strongly suggest that 4c is a promising Src kinase inhibitor.     

Development of novel tetrahydrothieno[2,3-c]pyridine-3-carboxamide based Mycobacterium tuberculosis pantothenate synthetase inhibitors: Molecular hybridization from known antimycobacterial leads

Twenty six 2,6-disubstituted 4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3-carboxamide derivatives were designed by molecular hybridization approach using and synthesized from piperidin-4-one by five step synthesis. Compounds were evaluated for Mycobacterium tuberculosis (MTB) pantothenate synthetase (PS) inhibition study, in vitro activities against MTB, cytotoxicity against RAW 264.7 cell line. Among the compounds, 6-(4-nitrophenylsulfonyl)-2-(5-nitrothiophene-2-carboxamido)-4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3-carboxamide (11) was found to be the most active compound with IC₅₀ of 5.87 ± 0.12 μM against MTB PS, inhibited MTB with MIC of 9.28 μM and it was non-cytotoxic at 50 μM. The binding affinity of the most potent inhibitor 11 was further confirmed biophysically through differential scanning fluorimetry.     

Design,synthesis and biological evaluation of benzofuran appended benzothiazepine derivatives as inhibitors of butyrylcholinesterase and antimicrobial agents

A series of bezofuran appended 1,5-benzothiazepine compounds 7a–v was designed, synthesized and evaluated as cholinesterase inhibitors. The biological assay experiments showed that most of the compounds displayed a clearly selective inhibition for butyrylcholinesterase (BChE), while a weak or no effect towards acetylcholinesterase (AChE) was detected. All analogs exhibited varied BChE inhibitory activity with IC₅₀ value ranging between 1.0?±?0.01 and 72?±?2.8?μM when compared with the standard donepezil (IC₅₀, 2.63?±?0.28?μM). Among the synthesized derivatives, compounds 7l, 7m and 7k exhibited the highest BChE inhibition with IC₅₀ values of 1.0, 1.0 and 1.8?μM, respectively. The results from a Lineweaver-Burk plot indicated a mixed-type inhibition for compound 7l with BChE. In addition, docking studies confirmed the results obtained through in vitro experiments and showed that most potent compounds bind to both the catalytic anionic site (CAS) and peripheral anionic site (PAS) of BChE active site. The synthesized compounds were also evaluated for their in vitro antibacterial and antifungal activities. The results indicated that the compounds possessed a broad spectrum of activity against the tested microorganisms and showed high activity against both gram positive and gram negative bacteria and fungi.     

Synthesis and biological evaluation of benzo[d]imidazole derivatives as potential anti-cancer agents

We herein report the synthesis, biological activity and structure-activity relationship of derivatives of 5,6-dichloro-1-β-D-ribofuranosylbenzimidazole and benzo[d]imidazole. A lead compound 6o demonstrates potent anti-proliferative activity and the ability to induce cancer cell apoptosis.     

Chemical synthesis and in silico molecular modeling of novel pyrrolyl benzohydrazide derivatives: Their biological evaluation against enoyl ACP reductase (InhA) and Mycobacterium tuberculosis

In efforts to develop new antitubercular agents, we report here the synthesis of a series of novel pyrrole hydrazine derivatives. The molecules were evaluated against inhibitors of InhA, which is one of the key enzymes involved in type II fatty acid biosynthetic pathway of the mycobacterial cell wall as well as inhibitors of Mycobacterium tuberculosis H37Rv. The binding mode of compounds at the active site of enoyl-ACP reductase was explored using the surflex-docking method. The model suggests one or two H-bonding interactions between the compounds and the InhA enzyme. Some compounds exhibited good activities against InhA in addition to promising activities against M. tuberculosis.     

Design,synthesis and biological evaluation of 4,5-dibromo-N-(thiazol-2-yl)-1H-pyrrole-2-carboxamide derivatives as novel DNA gyrase inhibitors

Development of novel DNA gyrase B inhibitors is an important field of antibacterial drug discovery whose aim is to introduce a more effective representative of this mechanistic class into the clinic. In the present study, two new series of Escherichia coli DNA gyrase inhibitors bearing the 4,5-dibromopyrrolamide moiety have been designed and synthesized. 4,5,6,7-Tetrahydrobenzo[1,2-d]thiazole-2,6-diamine derivatives inhibited E. coli DNA gyrase in the submicromolar to low micromolar range (IC₅₀ values between 0.891 and 10.4 μM). Their “ring-opened” analogues, based on the 2-(2-aminothiazol-4-yl)acetic acid scaffold, displayed weaker DNA gyrase inhibition with IC₅₀ values between 15.9 and 169 μM. Molecular docking experiments were conducted to study the binding modes of inhibitors.     

Gatifloxacin derivatives: synthesis, antimycobacterial activities, and inhibition of Mycobacterium tuberculosis DNA gyrase

Sixteen 7-substituted gatifloxacin derivatives were synthesized and evaluated for antimycobacterial activity in vitro and in vivo against Mycobacterium tuberculosis H37Rv (MTB) and multi-drug resistant M. tuberculosis (MDR-TB), and also tested for the ability to inhibit the supercoiling activity of DNA gyrase from M. tuberculosis. Among the synthesized compounds, 1-cyclopropyl-6-fluoro-8-methoxy-7-[[[N4-[1'-(5-isatinyl-beta-semicarbazo)]methyl]3-methyl]N1-piperazinyl]-4-oxo-1,4-dihydro-3-quinoline carboxylic acid (3d) was found to be the most active compound in vitro with an MIC of 0.0125 microg/mL against MTB and MTR-TB. In the in vivo animal model 3d decreased the bacterial load in lung and spleen tissues with 3.62- and 3.76-log10 protections, respectively. Compound 3d was also found to be equally active as gatifloxacin in the inhibition of the supercoiling activity of wild-type M. tuberculosis DNA gyrase with an IC50 of 3.0 microg/mL. The results demonstrate the potential and importance of developing new quinolone derivatives against mycobacterial infections.     

Synthesis of benzo[d]imidazo[2,1-b]thiazole-chalcone conjugates as microtubule targeting and apoptosis inducing agents

A series of benzo[d]imidazo[2,1-b]thiazole-chalcone conjugates (5a-aa) were designed, synthesized and evaluated for their cytotoxic potency against a panel of human cancer cell lines like lung (A-549), breast (MDA MB-231), prostrate (DU-145) and colon cancer (HT-29). Preliminary results revealed that some of these conjugates like 5d and 5u exhibited significant antiproliferative effect against human breast cancer (MDA MB-231) with IC₅₀ values of 1.3 and 1.2 µM respectively. To investigate the mechanistic aspects underlying the activity, the detailed biological studies of these promising conjugates (5d and 5u) were carried out on the MDA MB-231 cancer cells. Flow cytometric analysis revealed that these conjugates induce cell-cycle arrest in the G2/M phase. The tubulin polymerization assay suggests that these conjugates effectively inhibit microtubule assembly. In addition, morphological changes, reactive oxygen species (ROS) detection by 2′, 7′–dichlorofluorescin diacetate (DCFDA) and annexin V–FITC/PI assays indicate that 5d and 5u induces apoptosis. Furthermore, in silico computational studies, including molecular docking studies have been carried out to rationalise the binding modes of these conjugates with the tubulin protein.     

Stereospecific effects of benzo[d]isothiazolyloxypropanolamine derivatives at beta-adrenoceptors: synthesis, chiral resolution, and biological activity in vitro

We performed the asymmetric synthesis of four enantiopure benzo[d] isothiazo-3-or 5-yloxypropanolamine derivatives, previously described as competitive antagonists at beta-adrenoceptors. The chemical characterization of each enantiomer was accomplished by (1)H NMR and HPLC/DAD/CD. The direct chromatographic separation of the enantiomers via chiral HPLC was investigated. The best resolutions were achieved using cellulose tris (3,5-dimethylphenyl carbamate) (Chiralcel OD-H) and amylose tris (3,5-dimethylphenyl carbamate) (Chiralpak AD). The enantiomers obtained had enantiomeric purities suitable for biological assays. Tested in isolated rat cardiac and intestinal tissues to evaluate their effects at beta(1)- and beta(3)-adrenoceptors, the (S)-enantiomers revealed a higher degree of antagonism than (R)-enantiomers at both subtypes, even though their activity was greater at the cardiac beta(1)-subtype. The potent and cardiospecific antagonistic effect exerted by the compounds tested suggests that the benzisothiazole moiety could be an interesting scaffold for discovering new chiral beta-blocking drugs.     

Design,synthesis and antibacterial properties of pyrimido[4,5-b]indol-8-amine inhibitors of DNA gyrase

According to the World Health Organization (WHO), approximately 1.7 million deaths per year are caused by tuberculosis infections. Furthermore, it has been predicted that, by 2050, antibacterial resistance will be the cause of approximately 10 million deaths annually if the issue is not tackled. As a result, novel approaches to treating broad-spectrum bacterial infections are of vital importance. During the course of our wider efforts to discover unique methods of targeting multidrug-resistant (MDR) pathogens, we identified a novel series of amide-linked pyrimido[4,5-b]indol-8-amine inhibitors of bacterial type II topoisomerases. Compounds from the series were highly potent against gram-positive bacteria and mycobacteria, with excellent potency being retained against a panel of relevant Mycobacterium tuberculosis drug-resistant clinical isolates.     

Discovery of furan and dihydrofuran-fused tricyclic benzo[d]imidazole derivatives as potent and orally efficacious microsomal prostaglandin E synthase-1 (mPGES-1) inhibitors: Part-1

This letter describes the synthesis and biological evaluation of furan and dihydrofuran-fused tricyclic benzo[d]imidazole derivatives as novel mPGES-1 inhibitors, capable of inhibiting an increased PGE₂ production in the disease state. Structure-activity optimization afforded many potent mPGES-1 inhibitors having <50?nM potencies in the A549 cellular assay and adequate metabolic stability in liver microsomes. Lead compounds 8l and 8m demonstrated reasonable in vitro pharmacology and pharmacokinetic properties over other compounds. In particular, 8m revealed satisfactory oral pharmacokinetics and bioavailability in multiple species like rat, guinea pig, dog and cynomolgus monkey. In addition, the representative compound 8m showed in vivo efficacy by inhibiting LPS-induced thermal hyperalgesia with an ED₅₀ of 14.3?mg/kg in guinea pig.     

Design,synthesis, and analysis of antiproliferative and apoptosis-inducing activities of nitrile derivatives containing a benzofuran scaffold: EGFR inhibition assay and molecular modelling study

New cyanobenzofurans derivatives 2–12 were synthesised, and their antiproliferative activity was examined compared to doxorubicin and Afatinib (IC₅₀ = 4.17–8.87 and 5.5–11.2 µM, respectively). Compounds 2 and 8 exhibited broad-spectrum activity against HePG2 (IC₅₀ = 16.08–23.67 µM), HCT-116 (IC₅₀ = 8.81–13.85 µM), and MCF-7 (IC₅₀ = 8.36–17.28 µM) cell lines. Compounds 2, 3, 8, 10, and 11 were tested as EGFR-TK inhibitors to demonstrate their possible anti-tumour mechanism compared to gefitinib (IC₅₀ = 0.90 µM). Compounds 2, 3, 10, and 11 displayed significant EGFR TK inhibitory activity with IC₅₀ of 0.81–1.12 µM. Compounds 3 and 11 induced apoptosis at the Pre-G phase and cell cycle arrest at the G2/M phase. They also increased the level of caspase-3 by 5.7- and 7.3-fold, respectively. The molecular docking analysis of compounds 2, 3, 10, and 11 indicated that they could bind to the active site of EGFR TK.     

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 against Mycobacterium tuberculosis H37Rv which revealed a cluster of six analogues (11, 24, 27, 32, 33 and 34), 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.