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.     

Synthesis,biological activities,and docking study of novel chalcone‐pleuromutilin derivatives

The issue of antibiotic resistance is becoming progressively serious these days, and the feasible solution to address it is to develop and discover novel antibiotics. The diterpene natural pleuromutilin is a prominent candidate for its special mode of action by inhibiting protein synthesis. In this study, a series of novel pleuromutilin derivatives with chalcone moiety was designed and synthesized, and their antibacterial activities were assessed in vitro. As suggested from the results, most of compounds exhibited potent activities against two methicillin‐resistant Staphylococcus aureus (MRSA) ATCC 33591 and 43300. The further modification of the chalcone structure, aza‐cyclic derivatives were afforded and then assessed, and potent activities against the tested strains were reported. The preliminary docking studies were conducted to explore the interactions between target molecules and binding site.     

Synthesis and Biological Evaluation of 2‐Mercapto‐1,3‐benzothiazole Derivatives with Potential Antimicrobial Activity

The enhancement of bacterial resistance of pathogens to currently available antibiotics constitutes a serious public health threat. So, intensive efforts are underway worldwide to develop new antimicrobial agents. To identify compounds with a potent antimicrobial profile, we designed and synthesized low molecular weight 2‐mercaptobenzothiazole derivatives 2a – 2l and 3a – 3l . Both series were screened for in‐vitro antibacterial activity against the representative panel of Gram‐positive and Gram‐negative bacteria strains. The biological screening identified compounds 2e and 2l as the most active ones showing an interesting antibacterial activity with MIC values of 3.12 μg/mL against Staphylococcus aureus and 25 μg/mL against Escherichia coli, respectively. The replacement of the S‐H by the S‐Bn moiety resulted in considerable loss of the antibacterial action of the 3a – 3l series. The antibiotic action of compounds 2e and 2l was also investigated by testing their activity against some clinical isolates with different antimicrobial resistance profile. Moreover, the involvement of the NorA efflux pump in the antibacterial activity of our molecules was evaluated. Finally, in this paper, we also describe the cytotoxic activity of the most interesting compounds by MTS assay against HeLa and MRC‐5 cell lines.     

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.     

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 Biological Evaluation of Novel FtsZ‐targeted 3‐arylalkoxy‐2,6‐difluorobenzamides as Potential Antimicrobial Agents

Novel series of 3‐O‐arylalkylbenzamide and 3‐O‐arylalkyl‐2,6‐difluorobenzamide derivatives were synthesized and evaluated for their on‐target activity and antibacterial activity. The results indicated that the 3‐O‐arylalkyl‐2,6‐difluorobenzamide derivatives possessed much better on‐target activity and antibacterial activity than the 3‐O‐arylalkylbenzamide derivatives. Among them, 3‐O‐chlorobenzyl derivative 36 was the most effective in antibacterial activity (0.5, 4, and 8 μg/mL) against Bacillus subtilis ATCC9372, methicillin‐resistant Staphylococcus aureus ATCC29213, and penicillin‐resistant Staphylococcus aureus PR, while 3‐O‐methylbenzyl derivative 41 only exhibited the most potent activity (2 μg/mL) against Staphylococcus aureus ATCC25923.     

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 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.     

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 Antistaphylococcal Activity of N‐Substituted‐1H‐benzimidazole‐sulphonamides

A series of N‐substituted‐1H‐benzimidazole‐5(6)‐sulfonamides and 3‐(5,6‐dichloro‐1H‐benzimidazol‐2‐yl)‐N‐substituted benzensulfonamides were synthesized and evaluated for antibacterial activity against Staphylococcus aureus and methicillin‐resistant S. aureus (MRSA). Certain compounds inhibit bacterial growth with low MIC (μg/mL) values. The most active compounds 30 , 31 , and 32 have the lowest MIC values with 0.39 to 0.19 μg/mL. Among the compounds having sulfonamido moities, 16 , 23 , and 24 exhibited the strongest antibacterial activity with 1.56 μg/mL MIC values.     

6‐Substituted Indolo[1,2‐c]quinazolines as New Antimicrobial Agents

A series of 2‐o‐arylidineaminophenylindoles and their cyclic derivatives (indolo[1,2‐c]quinazolines) were synthesized. The reactions occurred under relatively mild conditions and afforded the desired product in good yields. Molecular structures of the synthesized compounds were confirmed by IR, ¹H‐NMR, ¹³C‐NMR, MS spectra, and elemental analyses. Furthermore, all the final products were screened for in‐vitro antibacterial activity against three Gram‐positive and three Gram‐negative bacteria and also tested for their inhibitory action against three strains of fungi. Compound IIc showed potent activity against all the bacterial (except S. typhimurium) and fungal strains. Especially, compounds IIi and IIj which have isoquinolyl and pyridyl substituents displayed potent antibacterial as well as antifungal activities compared to those of the respective standard drugs Ampicillin and Ketoconazole.     

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.     

Biofilm Eradication Kinetics of the Ultrashort Lipopeptide C12‐OOWW‐NH2 Utilizing a Modified MBEC Assay™

In this study, we report the antimicrobial planktonic and biofilm kill kinetics of ultrashort cationic lipopeptides previously demonstrated by our group to have a minimum biofilm eradication concentration (MBEC) in the microgram per mL (μg/mL) range against clinically relevant biofilm‐forming micro‐organisms. We compare the rate of kill for the most potent of these lipopeptides, dodecanoic (lauric) acid‐conjugated C₁₂‐Orn‐Orn‐Trp‐Trp‐NH₂ against the tetrapeptide amide H‐Orn‐Orn‐Trp‐Trp‐NH₂ motif and the amphibian peptide Maximin‐4 via a modification of the MBEC Assay^? for Physiology & Genetics (P&G). Improved antimicrobial activity is achieved upon N‐terminal lipidation of the tetrapeptide amide. Increased antimicrobial potency was demonstrated against both planktonic and biofilm forms of Gram‐positive micro‐organisms. We hypothesize rapid kill to be achieved by targeting of microbial membranes. Complete kill against established 24‐h Gram‐positive biofilms occurred within 4 h of exposure to C₁₂‐OOWW‐NH₂ at MBEC values [methicillin‐resistant Staphylococcus epidermidis (ATCC 35984): 15.63 μg/mL] close to the values for the planktonic minimum inhibitory concentration (MIC) [methicillin‐resistant Staphylococcus epidermidis (ATCC 35984): 1.95 μg/mL]. Such rapid kill, especially against sessile biofilm forms, is indicative of a reduction in the likelihood of resistant strains developing with the potential for quicker resolution of pathogenic infection. Ultrashort antimicrobial lipopeptides have high potential as antimicrobial therapy.     

Conformationally Constrained Analogs of N‐Substituted Piperazinylquinolones: Synthesis and Antibacterial Activity of N‐(2,3‐Dihydro‐4‐hydroxyimino‐4H‐1‐benzopyran‐3‐yl)‐piperazinylquinolones

A series of novel quinolone agents bearing a particular bulky and conformationally constrained bicyclic substituent (2,3‐dihydro‐4‐hydroxyimino‐4H‐1‐benzopyran‐3‐yl‐ moiety) on the piperazine ring of 7‐piperazinyl quinolones (norfloxacin, enoxacin, ciprofloxacin, and levofloxacin) were synthesized and evaluated against a panel of Gram‐positive and Gram‐negative bacteria. Among these derivatives, ciprofloxacin counterpart 9c , highly inhibited the tested Gram‐positive bacteria, superior to that of the reference drugs, and displayed antibacterial activity at non‐cytotoxic concentrations.     

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 Antibacterial Activity of Novel 4″‐O‐Carbamoyl Erythromycin‐A Derivatives

Novel 4″‐O‐carbamoyl erythromycin‐A derivatives were designed, synthesized, and evaluated for their in‐vitro antibacterial activities. All of the 4″‐O‐carbamoyl derivatives showed excellent activity against erythromycin‐susceptible Staphylococcus aureus ATCC25923, Streptococcus pyogenes, and Streptococcus pneumoniae ATCC49619. Most of the 4″‐O‐arylalkylcarbamoyl derivatives displayed potent activity against erythromycin‐resistant S. pneumoniae encoded by the mef gene and greatly improved activity against erythromycin‐resistant S. pneumoniae encoded by the erm gene or the erm and mef genes. In particular, the 4″‐O‐arylalkyl derivatives 4c–4e and 4g were found to possess the most potent activity against all the tested erythromycin‐susceptible strains, which were comparable to those of erythromycin, clarithromycin, or azithromycin. 4″‐O‐Arylalkyl derivatives 4e and 4g were the most effective against erythromycin‐resistant S. pneumoniae encoded by the mef gene (0.25 and 0.25 µg/mL). 4″‐O‐Arylalkyl derivatives 4a and 4b exhibited significantly improved activity against erythromycin‐resistant S. pneumoniae encoded by the erm gene. In contrast, the 4″‐O‐alkylcarbamoyl derivatives hardly showed improved activity against all the tested erythromycin‐resistant strains.     

Synthesis,Anti‐MRSA,and Anti‐VRE Activity of Hemin Conjugates with Amino Acids and Branched Peptides

The increasing prevalence of antibiotic‐resistant bacterial strains has necessitated the synthesis of novel antibacterial agents. It was previously shown that naturally occurring metalloporphyrin hemin possesses dark antibacterial activity against Gram‐positive bacteria. To improve hemin antibacterial activity, we synthesized a number of hemin conjugates with amino acids and branched peptides. Arginine‐containing hemin conjugates demonstrated high antibacterial activity against Gram‐positive bacteria including methicillin‐ and vancomycin‐resistant strains in vitro. Most of the synthesized conjugates showed low toxicity against human erythrocytes and leukocytes.     

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 .     

A Facile One‐Pot Synthesis of 2‐Arylamino‐5‐Aryloxylalkyl‐1,3,4‐Oxadiazoles and Their Urease Inhibition Studies

A one‐pot method for the synthesis of structural type urease inhibitors, 2‐amino‐1,3,4‐oxadiazoles, was developed. The structures of the compounds were established using spectroanalytical techniques and unambiguously confirmed by single‐crystal X‐ray analysis of compound 3o . The synthesized compounds were tested against jack beans urease, and most of the compounds ( 3c , 3g , 3j , 3k , 3n , 3r – 3v ) were found more active than the standard. The most potent compound ( 3u ) had an IC₅₀ value of 6.03 ± 0.02 μm as compared to the IC₅₀ value of the standard (thiourea; 22.0 ± 1.2 μm ). The prominent urease inhibition activity of these compounds may serve as an important finding in the development of less toxic and more potent antiulcer drugs. The compounds were also investigated against four bacterial strains, and some of the compounds ( 3g and 3r ) were found more potent than the standard drug (ciprofloxacin) against all the tested strains. The MIC value for compound 3g was 0.156 μmol/mL against the tested bacterial strains.     

Synthesis and Antibacterial Activity of a New Series of 3‐[3‐(Substituted Phenyl)‐1‐Isonicotinoyl‐1H‐Pyrazol‐5‐yl]‐2H‐Chromen‐2‐one Derivatives

A novel series of 3‐[3‐(substituted phenyl)‐1‐isonicotinoyl‐1H‐pyrazol‐5‐yl]‐2H‐chromen‐2‐one derivatives 4a – k have been synthesized by the reaction of 3‐[2,3‐dibromo‐3‐(substituted phenyl) propanoyl]‐2H‐chromen‐2‐one 3a – k and isonicotinic acid hydrazide in the presence of triethylamine in absolute ethanol, characterized by spectral data and screened for their in‐vitro antibacterial activity against Gram‐positive and Gram‐negative bacteria. Among the series, compounds 4e , 4i , and 4k displayed an encouraging antibacterial activity profile as compared to the reference drug ampicillin against tested bacterial strains.