Antibacterial and antitubercular evaluation of dihydronaphthalenone‐indole hybrid analogs

A new series of indole appended dihydronaphthalenone hybrid analogs ( 5a–t ) have been synthesized through the Lewis acid catalyzed Michael addition of indoles to the arylidene/hetero arylidene ketones. All the synthesized derivatives are well characterized through the ¹H‐NMR, ¹³C‐NMR, HRMS spectroscopic techniques, compound 5r was further confirmed through single crystal X‐ray analysis and screened for antibacterial and antitubercular activities. Among the synthesized compounds, the minimum inhibition concentration of 5l (against Escherichia coli) and 5o & 5p (against E. coli & Staphylococcus aureus) was found to be as low as 3.12 μg/ml as compared to the standard antibacterial drug ciprofloxacin 2.5 μg/ml. In antitubercular activity, compounds 5o and 5p with minimum inhibition concentration 6.25 μg/ml were found to be comparable with that of the drugs Pyrazinamide 5 μg/ml and Streptomycin 5 μg/ml. Compounds 5i , 5j , 5m , 5n , 5q , and 5r also showed promising activity against group of organisms tested.     

4‐Substituted thieno[2,3‐d]pyrimidines as potent antibacterial agents: Rational design,microwave‐assisted synthesis,biological evaluation and molecular docking studies

In an attempt to discover a new class of antibacterial agents with improved efficacy and to overcome the drug‐resistant problems, some novel 4‐substituted thieno[2,3‐d]pyrimidines have been synthesized via microwave‐assisted methodology and evaluated for their in vitro antibacterial activity against various pathogenic bacterial strains. Compounds 12 b and 13 c showed the promising inhibitory potencies against Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa and Escherichia coli with MICs ranging from 2 to 10 μg/ml. Compound 13 c was also found to be highly potent against methicillin‐resistant S. aureus (MRSA) with MIC value of 4 μg/ml. Docking simulation studies have been performed to unravel the mode of action and association study indicate the binding of potent compounds with DHPS enzyme. In silico ADME studies suggest the drug‐like characteristics of the potent compounds.     

Synthesis and Antimicrobial Activity of the Hybrid Molecules between Sulfonamides and Active Antimicrobial Pleuromutilin Derivative

A series of novel hybrid molecules between sulfonamides and active antimicrobial 14‐o‐(3‐carboxy‐phenylsulfide)‐mutilin were synthesized, and their in vitro antibacterial activities were evaluated by the broth microdilution. Results indicated that these compounds displayed potent antimicrobial activities in vitro against various drug‐susceptible and drug‐resistant Gram‐positive bacteria such as Staphylococci and streptococci, including methicillin‐resistant Staphylococcus aureus, and mycoplasma. In particular, sulfapyridine analog ( 6c ) exhibited more potent inhibitory activity against Gram‐positive bacteria and mycoplasma, including Staphylococcus aureus (MIC = 0.016–0.063 μg/mL), methicillin‐resistant Staphylococcus aureus (MIC = 0.016 μg/mL), Streptococcus pneumoniae (MIC = 0.032–0.063 μg/mL), Mycoplasma gallisepticum (MIC = 0.004 μg/mL), with respect to other synthesized compounds and reference drugs sulfonamide (MIC = 8–128 μg/mL) and valnemulin (MIC = 0.004–0.5 μg/mL). Furthermore, comparison between MIC values of pleuromutilin‐sulfonamide hybrids 6a–f with pleuromutilin parent compound 3 revealed that these modifications at 14 position side chain of the pleuromutilin with benzene sulfonamide could greatly improve the antibacterial activity especially against Gram‐positives.     

Novel 3‐Substituted Ocotillol‐Type Triterpenoid Derivatives as Antibacterial Candidates

Plant‐derived triterpenoid saponins are involved in the plant defense system by targeting bacterial membranes. A series of ocotillol‐type triterpenoid derivatives were synthesized starting from PPD, one of the main components of Panax ginseng and their antibacterial activity against several representative bacteria were evaluated. Compounds 5 and 11 exhibited excellent antibacterial activity with MIC values of 1 μg/mL against Staphylococcus aureus and 8 μg/mL and 4 μg/mL against Bacillus subtilis, respectively. Furthermore, when compounds 5 and 11 were combined with two commercial antibiotics kanamycin and chloramphenicol, they showed strong synergistic activity at sub‐MIC levels against S. aureus USA300 and B. subtilis 168. Moreover, chloramphenicol turned from a bacteriostatic to a bactericidal agent when combined with compound 11 against B. subtilis 168.     

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 In Vitro Activity of Polyhalogenated 2‐phenylbenzimidazoles as a New Class of anti‐MRSA and Anti‐VRE Agents

A series of novel polyhalogenated 2‐phenylbenzimidazoles have been synthesized and evaluated for in vitro antistaphylococcal activity against drug‐resistant bacterial strains (methicillin‐resistant Staphylococcus aureus, and vancomycin‐resistant Enterococcus faecium. Certain compounds inhibit bacterial growth perfectly. 11 was active than vancomycin (0.78  μ g/mL) with the lowest MIC values with 0.19  μ g/mL against methicillin‐resistant Staphylococcus aureus, 8 and 35 exhibited best inhibitory activity against vancomycin‐resistant Enterococcus faecium (1.56  μ g/mL). The mechanism of action for this class of compounds appears to be different than clinically used antibiotics. These polyhalogenated benzimidazoles have potential for further investigation as a new class of potent anti‐methicillin‐resistant Staphylococcus aureus and anti‐vancomycin‐resistant Enterococcus faecium agents.     

Synthesis and Antimicrobial Activity of Some Novel 2‐[4‐(Substituted Piperazin‐/Piperidin‐1‐ylcarbonyl)phenyl]‐1H‐benzimidazole Derivatives

In this study, we report the synthesis and antimicrobial evaluation of several new 4‐(1H‐benzimidazol‐2‐yl)benzamides ( 11 – 30 ) and 5‐chloro‐1‐(p‐fluorobenzyl)‐2‐{4‐[(4‐methylpiperazin‐1‐yl)carbonyl]phenyl}‐1H‐benzimidazole ( 33 ). Compound 20 exhibited the best antibacterial activity with MIC value of 6.25 μg/mL against Staphylococcus aureus and methicillin‐resistant Staphylococcus aureus (MRSA). Significant antifungal activities were obtained with the compounds 13 , 14, 18 , 19, and 33 with MIC values of 3.12 μg/mL which are close to fluconazole.     

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 .     

Design and synthesis of 4′‐((5‐benzylidene‐2,4‐dioxothiazolidin‐3‐yl)methyl)biphenyl‐2‐carbonitrile analogs as bacterial peptide deformylase inhibitors

Herein, we report the synthesis and screening of 4′‐((5‐benzylidene‐2,4‐dioxothiazolidin‐3‐yl)methyl)biphenyl‐2‐carbonitrile analogs 11(a–j) as bacterial peptide deformylase (PDF) enzyme inhibitors. The compounds 11b (IC₅₀ value = 139.28 μm ), 11g (IC₅₀ value = 136.18 μm ), and 11h (IC₅₀ value = 131.65 μm ) had shown good PDF inhibition activity. The compounds 11b (MIC range = 103.36–167.26 μg/mL), 11g (MIC range = 93.75–145.67 μg/mL), and 11h (MIC range = 63.61–126.63 μg/mL) had also shown potent antibacterial activity when compared with standard ampicillin (MIC range = 100.00–250.00 μg/mL). Thus, the active derivatives were not only PDF inhibitors but also efficient antibacterial agents. To gain more insight on the binding mode of the compounds with PDF enzyme, the synthesized compounds 11(a–j) were docked against PDF enzyme of Escherichia coli and compounds exhibited good binding properties. The results suggest that this class of compounds has potential for development and use in future as antibacterial drugs.     

New fluoroquinolone compounds with endo‐nortropine derivatives at C‐7 position show antibacterial activity against fluoroquinolone‐resistant strains of Staphylococcus aureus

A series of new fluoroquinolone analogs ( 3 – 18) were prepared, in three steps, by substituting chloro esters and esters with cyclic amines on the C‐7 endo‐nortropine derivatives of difluoroquinolone acid. All the synthesized compounds displayed good MIC against the Staphylococcus aureus when initially screened for Escherichia coli, S. aureus, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa. The molecules were further evaluated for their antibacterial activity against fluoroquinolone‐resistant strains of S. aureus and for cytotoxic assay. Based on the results, five of the sixteen compounds displayed the potential to be developed further for treatment against fluoroquinolone‐resistant strains of S. aureus.     

Synthesis and antimicrobial activity of new 2‐piperazin‐1‐yl‐N‐1,3‐thiazol‐2‐ylacetamides of cyclopenta[c]pyridines and pyrano[3,4‐c]pyridines

In this study, we report the synthesis and antimicrobial activity of some new disubstituted piperazines. Thus, 3‐chlorocyclopenta[c]pyridines and 6‐chloropyrano[3,4‐c]pyridine 1 under mild reaction conditions with piperazine gave the 3(6)‐piperazine‐substituted cyclopenta[c]pyridines and pyrano[3,4‐c]pyridine 2 . Furthermore, the latter, by alkylation with 2‐chloro‐N‐1,3‐thiazol‐2‐ylacetamide, led to the formation of the target compounds. The evaluation of the antibacterial activity revealed that 3k was the most potent compound. The most sensitive bacterium was found to be Listeria monocytogenes, whereas Staphylococcus aureus was the most resistant one. Three compounds, 3d , 3g , and 3k , were tested also against the following resistant strains: methicillin‐resistant S. aureus (MRSA), Escherichia coli, and Pseudomonas aeruginosa. All three compounds appeared to be more potent than ampicillin against MRSA. Moreover, compound 3d showed a better activity than the reference drug ampicillin against P. aeruginosa, whereas 3g was more efficient against E. coli. The best antifungal activity was observed again for compound 3k . The most resistant fungi appeared to be Aspergillus fumigatus, whereas Trichoderma viride seemed the most sensitive one toward the compounds tested. Molecular docking studies on E. coli MurB, as well as on Candida albicans CYP51 and dihydrofolate reductase, were used for the prediction of the mechanisms of the antibacterial and antifungal activities, confirming the experimental results.     

Design,Synthesis, Antibacterial Evaluation and Docking Study of Novel 2‐Hydroxy‐3‐(nitroimidazolyl)‐propyl‐derived Quinolone

A novel series of 2‐hydroxy‐3‐(nitroimidazolyl)‐propyl‐derived quinolones 6a – o were synthesized and evaluated for their in vitro antibacterial activity. Most of the target compounds exhibited potent activity against Gram‐positive strains. Among them, moxifloxacin analog 6n displayed the most potent activity against Gram‐positive strains including S. epidermidis (MIC = 0.06 μg/mL), MSSE (MIC = 0.125 μg/mL), MRSE (MIC = 0.03 μg/mL), S. aureus (MIC = 0.125 μg/mL), MSSA (MIC = 0.125 μg/mL), (MIC = 2 μg/mL). Its activity against MRSA was eightfold more potent than reference drug gatifloxacin. Finally, docking study of the target compound 6n revealed that the binding model of quinolone nucleus was similar to that of gatifloxacin and the 2‐hydroxy‐3‐(nitroimidazolyl)‐propyl group formed two additional hydrogen bonds.     

Potent antibacterial activity of dihydydropyrimidine‐1,3,5‐triazines via inhibition of DNA gyrase and antifungal activity with favourable metabolic profile

The compounds were tested against panel of three Gram‐positive, viz. Staphylococcus aureus, Bacillus subtilis, Bacillus cereus and three Gram‐negative bacterial strains viz. Pseudomonas aeruginosa, Escherichia coli, and Proteus vulgaris where they showed significant to moderate antibacterial activity. The compound also showed considerable antibiofilm activity against S. aureus and B. subtilis. The most potent compounds 7l and 7m found bacteriostatic in time‐kill assay via inhibition of DNA gyrase enzyme and interacting with Glu58, Val130, Ile175 and Ile186 via numerous H‐bonds as revealed by docking. In S. aureus‐induced murine infection model, compound 7m showed dose‐dependent reduction of viability of bacteria with maximum activity in 25 mg/kg treated group. The antifungal activity against human fungal pathogens was also estimated, where these compounds showed considerable inhibitory activity as compared to standard. The metabolic liability of compound 7m was determined using RS‐Predictor and MetaPrint 2D React. The molecules were proved as effective antibacterial agent via inhibition of DNA gyrase as a mechanism together with significant antifungal activity.     

Synthesis and Antimicrobial Activity of 4‐Chloro‐3‐Nitrophenylthiourea Derivatives Targeting Bacterial Type II Topoisomerases

A series of novel 4‐chloro‐3‐nitrophenylthiourea derivatives were synthesized and evaluated for their antimicrobial, antibiofilm and tuberculostatic activities. Most of compounds exhibited high antibacterial activity against both standard and hospital strains (MIC values 0.5–2 μg/mL), as compared to Ciprofloxacin. Derivatives with 3,4‐dichlorophenyl ( 11 ) and 3‐chloro‐4‐methylphenyl ( 13 ) substituents were the most promising towards Gram‐positive pathogens. Both of them exhibited antibiofilm potency and effectively inhibited the formation of biofilms of methicillin‐resistant and standard strains of Staphylococcus epidermidis. Two N‐alkylthioureas ( 20, 21 ) showed twofold to fourfold increase in in vitro potency against isolates of Mycobacterium tuberculosis, as compared to Isoniazid. An action of 7, 10 , 11, 13, 20 and 21 against activity of topoisomerases isolated from Staphylococcus aureus was studied. Synthesized compounds were found as non‐genotoxic.     

Chromanyl–isoxazolidines as Antibacterial agents: Synthesis,Biological Evaluation,Quantitative Structure Activity Relationship,and Molecular Docking Studies

Regio‐ and stereoselective 1,3‐dipolar cycloadditions of C‐(chrom‐4‐one‐3‐yl)‐N‐phenylnitrones ( N ) with different mono‐substituted, disubstituted, and cyclic dipolarophiles were carried out to obtain substituted N‐phenyl‐3′‐(chrom‐4‐one‐3‐yl)‐isoxazolidines ( 1‐40 ). All the synthesized compounds were assayed for their in vitro antibacterial activity and display significant inhibitory potential; in particular, compound 32 exhibited good inhibitory activity against Salmonella typhymurium‐1 & Salmonella typhymurium‐2 with minimum inhibitory concentration value of 1.56 μ g/mL and also showed good potential against methicillin‐resistant Staphylococcus aureus with minimum inhibitory concentration 3.12 μ g/mL. Quantitative structure activity relationship investigations with stepwise multiple linear regression analysis and docking simulation studies have been performed for validation of the observed antibacterial potential of the investigated compounds for determination of the most important parameters regulating antibacterial activities.     

Design,synthesis, and structure–activity relationship studies of novel pleuromutilin derivatives having a piperazine ring

A series of novel pleuromutilin derivatives possessing piperazine moieties were synthesized under mild conditions. The in vitro antibacterial activities of these derivatives against Staphylococcus aureus and Escherichia coli were tested by the agar dilution method. Structure–activity relationship studies resulted in compounds 11b , 13b , and 14a with the most potent in vitro antibacterial activity among the series (minimal inhibitory concentration = 0.0625–0.125 μg/mL). The binding of compounds 11b , 13b , and 14a to the E. coli ribosome was investigated by molecular modeling, and it was found that there is a reasonable correlation between the binding free energy and the antibacterial activity.     

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.     

Discovery of the Highly Potent Fluoroquinolone‐Based Benzothiazolyl‐4‐thiazolidinone Hybrids as Antibacterials

A new series of fluoroquinolone‐based benzothiazolyl‐4‐thiazolidinone hybrids has been yielded via sulfated tungstate‐promoted highly accelerated N‐formylation at a piperazine residue of ciprofloxacin and norfloxacin entities. The formylated fluoroquinolone moieties were then coupled with substituted 2‐aminobenzothiazoles, which were generated from their respective para‐substituted amines to form corresponding Schiff base intermediates. The Schiff bases were then treated with thioglycolic acid to equip a new class of 4‐thiazolidinones to be analyzed for their antibacterial effects against two Gram‐positive (Staphylococcus aureus and Bacillus subtilis) and two Gram‐negative (Escherichia coli and Pseudomonas aeruginosa) bacterial strains and were found highly potent with lowest Minimum inhibitory concentrations (MIC), 1–2 μg/mL, that is, more potent than control drugs ciprofloxacin (3.12–6.25 μg/mL). Initial outcomes provided for these novel molecular systems will aid researchers to design and develop new antibacterial drugs. The structural assignments of the new products were done on the basis of FT‐IR, ¹H NMR and ¹³C NMR spectroscopy, and elemental analysis.     

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.     

Synthesis and Antibacterial Activity of a Series of α‐Substituted Acetylpiperazinyl Oxazolidinones

A series of oxazolidinone derivatives with α‐substituted acetylpiperazinyl groups were prepared. Their in vitro antibacterial activities were studied against Gram‐positive pathogens, including methicillin‐resistant Staphylococcus aureus, Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis. The compounds with chloroacetyl‐piperazinyl or dichloroacetyl‐piperazinyl group were found to have superior antibacterial activities to linezolid against most of tested Gram‐positive pathogens. The compounds with propionylpiperaziny or fluoroacetylpiperazinyl group were found to have comparable antibacterial activities with linezolid. However, the replacement of phenyl ring of the compounds with pyridine ring resulted in the significant loss of antibacterial activity.