Synthesis and Antimicrobial Evaluation of 1,4-Naphthoquinone Derivatives as Potential Antibacterial Agents

1,4-Naphthoquinones are an important class of compounds present in a number of natural products. In this study, a new series of 1,4-naphthoquinone derivatives were synthesized. All the synthesized compounds were tested for in vitro antimicrobial activity. In this present investigation, two Gram-positive and five Gram-negative bacterial strains and one pathogenic yeast strain were used to determine the antibacterial activity. Naphthoquinones tested for its antibacterial potencies, among seven of them displayed better antimicrobial activity against Staphylococcus aureus (S. aureus; 30–70 μg/mL). Some of the tested compounds showed moderate to low antimicrobial activity against Pseudomonas aeruginosa (P. aeruginosa) and Salmonella bongori (S. bongori; 70–150 μg/mL). In addition, most active compounds against S. aureus were evaluated for toxicity to human blood cells using a hemolysis assay. For better understanding, reactive oxygen species (ROS) generation, time-kill kinetic study, and apoptosis, necrosis responses were investigated for three representative compounds.     

One‐pot Synthesis of Novel Spirooxindoles as Antibacterial and Antioxidant Agents

The regioselective spiroindoline derivatives were afforded via multi‐componant reaction. Its process was one of the green chemistry (simplicity, mild conditions, and atomic economy). The electron repelling and attracting groups affected on reactivity of the azomethine ylides (increase E_HOMO value). All compound structures were confirmed by spectroscopic data and elemental analysis. The antibacterial and antioxidant activities for these synthesized compounds could be investigated; the highly antioxidant activity was observed with compounds, which proved to possess high HOMO values, and the highly antibacterial activity was observed against S . aureus , B . cereus , S . marcesens , and P . mirabilis , which proved to possess low HOMO values.     

Green and Efficient Synthesis of 4‐Heteryl‐Quinolines and Their Antibacterial Evaluations

A green and efficient synthesis of 4‐heteryl‐quinolines ( 9a , 9b , 9c , 9d ), ( 10a , 10b , 10c , 10d ) and ( 11a , 11b , 11c , 11d ) has been described using PEG‐600 as a green solvent. Initially, 4‐chloro‐2‐methylquinolines ( 5a , 5b , 5c , 5d ) on reaction with aromatic heterocyclic thiols ( 6 ), ( 7 ), and ( 8 ) using PEG‐600 at 100°C for 30–40 min resulted in ( 9 ), ( 10 ), and ( 11 ) in good yields. Alternatively, ( 9 ), ( 10 ), and ( 11 ) could also be prepared in dimethylformamide using K2CO3 as base and tetrabutylammonium bromide as phase transfer catalyst at 100°C for 1–2 h. All the compounds were synthesized and characterized by IR, NMR, mass spectroscopy, and 13C NMR analysis. All synthesized compounds were screened for their antibacterial activity against clinical strains that include Gram‐positive (Bacillus subtilis MTCC 121, staphylococcus aureus MLS‐16 MTCC 2940, Micrococcus lutes MTCC 2470, and Staphylococcus aureus MTCC 96) and Gram‐negative bacteria (Candida albicans MTCC 3017, Klebsiella planticola MTCC 530, Escherichia coli MTCC 739, and Pseudomonas aeruginosa MTCC 2453). The results revealed that compounds ( 9a , 9d , 10a , 10c , 11b , and 11d ) exhibited significant antibacterial activity almost equal to the standard drug, that is, Ciprofloxacin.     

Utility of Bis‐Hydrazonoyl Chlorides as Precursors for Synthesis of New Functionalized Bis‐Thiadiazoles as Potent Antimicrobial Agents

N′,N″‐([1,1’‐Biphenyl]‐4,4′‐diyl)bis(2‐oxopropanehydrazonoyl chloride) is considered to be the key intermediate for the synthesis of a variety bis‐1,3,4‐thiadiazole derivatives in one step methodology with good yields by reaction of with a series of hydrazinecarbodithioate derivatives 2a–e , 6a , b , and 8a–e . The assigned structures for all the newly synthesized compounds were confirmed on the basis of elemental analyses and spectral data (infrared, NMR, and mass), and the mechanisms of their formation were also discussed. Moreover, the antimicrobial activity for twelve selected products was screened, and the results obtained exploring the high potency of some of the tested compounds compared with the employed standard bactericides and fungicides. In addition, the minimum inhibitory concentration of the tested compounds was determined, and the results obtained exploring the high potency of three of the tested compounds against all the tested microorganisms.     

Synthesis of Some Novel Furan‐tagged Thienopyrimidine Derivatives as Antibacterial Agents

Cyclization of 2‐furan‐2‐yl‐4‐mercapto‐6‐methylpyrimidine‐5‐carbonitrile 1 with ethyl chloroacetate gave o‐aminoester thienopyrimidine derivative 3 , which was reacted with a variety of reagents to give a series of novel thienopyrimidines including tetrazolyl thienopyrimidine, pyrrolylthienopyrimidine, pyrimidothienotriazine, and thienodipyrimidines. Some of the synthesized compounds were tested for their antibacterial activities against Gram‐positive and Gram‐negative bacteria.     

Synthesis of New 2,4‐Diaryl‐6‐methyl‐5‐nitropyrimidines as Antibacterial and Antioxidant Agents

A new series of 2,4‐diaryl‐6‐methyl‐5‐nitropyrimidines ( 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i ) were synthesized in good yields by Suzuki–Miyaura coupling of 2,4‐dichloro‐6‐methyl‐5‐nitropyrimidine ( 3 ) with various aryl boronic esters ( 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i ) in the presence of 1,1′‐ bis(diphenylphosphino)ferrocene dichloropalladium(II) (Pd(dppf)₂Cl₂). Further, antibacterial and antioxidant properties were screened for the title compounds 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i . Most of the compounds possessed significant activity against Gram‐positive bacteria Staphylococcus aureus and Bacillus subtilis and Gram‐negative bacteria Escherichia coli and Klebsiella pneumoniae. The antioxidant activity of the title compounds showed significant antioxidant activity when compared with vitamin C.     

Synthesis,Characterization, and Pharmacological Evaluation of Some New Pteridine‐Based Heterocycles as Antimicrobial Agents

Considering pteridine as a worthy structure for improving probes of magnificent therapeutic potentials, some new pteridine conjugates were synthesized by aminomethylation of benzopteridinethione with a variety of primary aromatic amines and formaldehyde solution (37%) through the Mannich reaction. The proposed mechanism of formation of the synthesized compounds was discussed, and the structure of the newly synthesized compounds was elucidated on the basis of their IR, ¹H NMR, ¹³C NMR, mass spectral, and elemental analyses. Furthermore, some selected compounds were evaluated in vitro for their antimicrobial activities; the preliminary data stated that the majority of the tested compounds exhibited significant antimicrobial activity. Analogues 22 , 23 , 20 , 19 , 24 , and 15 were found to be the most potent against all the tested microorganisms.     

Synthesis of Some New Ciprofloxacin Hybrids as Potential Antimicrobial Agents

A new series of ciprofloxacin hybrid compounds as new type of antimicrobial agents were synthesized and evaluated for antibacterial activity against Gram‐positive and Gram‐negative bacteria.     

Ultrasound‐assisted Synthesis of Novel Pyrazole and Pyrimidine Derivatives as Antimicrobial Agents

Herein, we report a convenient and facile methodology for the synthesis of new series of pyrazole and pyrimidine derivatives 2a – f and 3a – f under ultrasound irradiation. Pyrazole and pyrimidine derivatives have been synthesized in better yields and shorter reaction times compared with the conventional method. The chemical structures of all the synthesized compounds were elucidated by their IR, ¹H NMR, ¹³C NMR, MS, and elemental analysis. Further, the target compounds were screened for their antimicrobial activity against four bacteria (Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa) and two fungi (Candida albicans, Aspergillus niger). In particular, compounds 2a , 2d , 2e , 3a , 3e , and 3f exhibited potent antimicrobial activity.     

Synthesis and Application of Some New Thienopyrimidine Derivatives as Antimicrobial Agents

The paper describes the synthesis of new ring system 5-phenylthieno[2,3-d]pyrimidine-4(3H)one (2). Chlorination of (2) with PCl₅, POCl₃ gave the corresponding 4-chloro derivative (4). Several derivatives of the latter compound have been synthesised and tested for antimicrobial activity.     

1,3‐Benzothiazoles as Antimicrobial Agents

Starting from 2‐amino‐1,3‐mercaptobenzothiazoles recently reported ( 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h ), a series of the corresponding 2‐mercapto‐1,3‐benzothiazole isosters ( 2a , 2b , 2c , 2d , 2e , 2f , 2g , 2h ) were screened for their in vitro antibacterial and antifungal activities. Results underline that the presence of the mercapto moiety at the 2‐position of the heterocyclic nucleus is crucial for activity against bacteria. The biological screening against Candida spp. identified commercial 2f as the most promising compound as antifungal against Candida albicans and tropicalis. Molecular modeling studies supported these results. Then, to enlarge structure‐activity relationship (SAR) studies on series 1 , newly synthesized compounds ( 1k , 1l , 1m , 1n , 1o , 1p ) were reported. All the compounds belonging to this series and bearing a bulky substituent at the 6‐position of the aryl moiety showed high antifungal activity.     

Synthesis of New 1, 10‐Phenanthroline Analogs as Potent Antimicrobial Agents Using Montmorillonite K‐10 as Catalyst

A series of new 1, 10‐phenanthroline derivatives are synthesized by the four‐component domino reactions of 8‐hydroxy quinoline, aromatic aldehydes, methyl/ethyl acetoacetate and ammonium acetate in the presence of zeolite (montmorillonite K‐10) using both conventional and microwave methods. Most of the new compounds possessed moderate to significant anti‐bacterial and anti‐fungal activities.     

Synthesis of Some New Fluorine Containing Thiadiazolotriazinones as Potential Antibacterial Agents

2,4-dichloro-5-fluorophenyl, 4-fluoro-3-(Phenoxy)phenyl, 4-fluorophen-yl groups are known pharmacophores and can be used in the synthesis of new biologically active molecules. Therefore, 4-amino-6-arylmethyl-3-mercapto-1,2,4-triazin5(4H)-ones 1 are condensed with 3-phenoxy-4-fluoro-benzoic acid, 2,4-dichloro-5-fluorobenzoic acid, and 4-fluorobenzoic acid 2 to give 7-substituted-3-arylmethyl-4H-1,3,4-thiadiazolo[2,3-c]-1,2,4-triazin-4-ones 3 . Phosphorous oxychloride was used as cyclizing agent. All the newly synthesized compounds 3a-l was screened for their antibacterial activities. Most of them showed promising activity in the range of 10 w g/mL concentrations.     

Design and Synthesis of Diverse Pyrrole‐2‐carboxamide Derivatives as a Potent Antibacterial Agents

A series of pyrrole–2–carboxamide derivatives ( 4a–j ) were synthesized and evaluated for theirantibacterial activity. Among the tested compounds, the most effective were 4a, 4b, 4c, 4d, 4e, 4g and 4h with MIC value in the range of 1.05–12.01 μg/mL against Gram–positive and Gramnegativebacterial strains. Further, the synthesized compounds have been screened for their invitro antifungal activity. In the present study, design and expeditious synthesis of novel 1–(4–chlorobenzyl)–N–(4–methoxybenzyl)–1H–pyrrole–2–carboxamide hybrid molecules as promising antibacterial agents.     

New Thiophene Derivatives as Antimicrobial Agents

Phenacylbromide derivatives constitute a multilateral group of precursors for the synthesis of numerous heterocycles of organic compounds. Briefly, 5‐(2‐bromo‐acetyl)‐substituted‐thiophene derivative has been used as a synthon for synthesis of new thiophene‐containing compounds through the reaction with nucleophilic nitrogen compounds and thioamides. The suggested structures of the newly synthesized thiophene compounds were confirmed and assured with different spectroscopic tools and with CHN elemental analysis. Additionally, the antimicrobial activity of these thiophene compounds was recorded to investigate their potency against various types of bacteria and fungi. Results showed that these compounds exhibit significant inhibitory activity against the growth of tested bacterial and fungal strains and that some derivatives were more potent than the employed reference drugs.     

Nucleosides: Synthesis of Some New Naphthimidazole Ribonucleosides as Potential Antibacterial Agents

Reaction of 2-trifluoromethyl- or 2-cyanonaphth[2,3-d] imidazole (1 or 2) with 1-O-acetyl-2,3,5-tri-O- benzoyl-β-D-ribofuranose (3), using the triflate or fusion method afforded 2-trifluoromethyl-1-(2,3,5-tri- O-benzoyl-α-D- or -β-D-ribofuranosyl)naphth[2,3-d]imidazole (4 or 6) and 2-cyano-1-(2,3,5-tri-O-benzoyl-α-D- or β-D-ribofuranosyl)naphth[2,3,-d] imidazole (5 or 7), respectively. The products 4 and 5 or 6 and 7 were separated by chromatography on silica gel. Treatment of the blocked nucleosides 4-7 with methanolic NH₃ at 0 °C furnished the deblocked nucleosides 8-11 respectively. Treatment of 10 with 5% NH₃ (aq) at 60 °C gave 11. Structural elucidation is based on elemental analysis, UV, FAB-MS and ¹H NMR spectra. Compounds 4-11 were subjected to antibacteial testing. Compounds 5, 7 and 10 have significant activity against Staphylococous aureus (gram positive) and Esherichia coli (gram negative) bacteria, whereas the other tested compounds showed no significant activity.     

Ultrasound‐Mediated Synthesis of Novel 1,2,3‐Triazole‐Based Pyrazole and Pyrimidine Derivatives as Antimicrobial Agents

In the development of novel antimicrobial agents, we synthesized novel 1,2,3‐triazole‐based pyrazole and pyrimidine derivatives 6 ( a–f ) and 7 ( a–f ) by ultrasound‐assisted method. The synthesized compounds were characterized by IR, ¹H NMR, ¹³C NMR, MS, and elemental analysis. All compounds were assessed in vitro for their efficacy as antimicrobial agents against four bacteria (Staphylococcus aureus , Bacillus subtilis , Escherichia coli , and Pseudomonas aeruginosa ) and two fungi (Candida albicans and Aspergillus niger ). In particular, compounds 6a , 6e , 7a , 7c , and 7e exhibited highly potent antimicrobial activity.     

One‐Pot Synthesis of New Thiadiazolyl‐Pyridines as Anticancer and Antioxidant Agents

The reaction of one equivalents of 5‐acetylthiadiazole with one equivalent of aldehyde in acetic acid and ammonium acetate yielded thiadiazolyl‐pyridine derivatives in a multicomponent reactions. The structures of all the new compounds were elucidated on the basis of elemental analysis and spectral data. The anticancer activities of the synthesized compounds were screened for their activity against human lung carcinoma (A549) and human hepatocellular carcinoma cell lines (HepG2) comparable with cisplatin, and the results showed that most of such compounds exhibit considerable activities. The order of activity against A549 cell line was 4c , 4e , 4a , 6d , 8d , 11 , 12 , 4b , 4f , and 4d . However, compound 4e exhibited the highest activity against HepG2, followed by 4a , 4c , 6d , 8d , 11 , 12 , 4f , 4d , and 4b . On the other hand, compounds 11 , 12 , and 4b showed the highest 2,2‐diphenyl‐1‐picrylhydrazyl free radical scavenging activities. Conclusively, the results of the current study approved the cytotoxic and antioxidant capabilities of the synthesized compounds.