N‐Phenyl‐substituted carbene precursors and their silver complexes: synthesis, characterization and antimicrobial activities

Abstract

A series of unsymmetrically substituted N-heterocyclic carbene (NHC) precursors (1a-e) were synthesized from the reaction of N-phenylbenzimidazole with various alkyl halides. These compounds were used to synthesize NHC-silver(I) complexes (2a-e). The five new 1-phenyl-3-alkylbenzimidazolium salts (1a-e) and their NHC-silver complexes (2a-e) were characterized by the 1 H NMR, 13 C NMR and FT-IR spectroscopic methods and elemental analysis techniques. Also, the two NHC-silver complexes 2b and 2c were characterized by single-crystal X-ray crystallography, which confirmed the linear C-Ag-Cl arrangements. The antibacterial activities of the NHC precursor and NHC-silver complexes were tested against three Gram-positive bacterial strains (Bacillus subtilis, Listeria monocytogenes and Staphylococcus aureus) and three Gram-negative bacterial strains (Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa) using the microdilution broth method. The NHC-silver complexes showed higher antibacterial activity than the NHC precursors. In addition, silver complexes 2a-d showed high antibacterial activity against the Gram-positive bacteria L. monocytogenes and S. aureus compared to the standard, tetracycline.

Benzimidazolium-based novel silver N-heterocyclic carbene complexes: synthesis, characterisation and in vitro antimicrobial activity

“…The obtained Nalkylbenzimidazole was purified by crystallization. Subsequently, alkyl halide was added to the DMF solution of synthesised N-alkylbenzimidazole and it was stirred for 24 h at 80 C. Benzimidazolium salts were synthesised and purified by crystallisation in a mixture of ethyl alcohol-diethylether (2:1) 17,[22][23][24] . The Ag(I)-NHC complexes (2-6) were synthesised from N-propylphthalimide and N-methyldioxane substituted benzimidazolium salts (1) (2 mmol) and Ag 2 O (1 mmol) in 20 mL dry dichloromethane (Scheme 1).…”

“…Antimicrobial supplemented media was inoculated from the cell suspensions with sterile 10 mL inoculating loops. After inoculation, cultures were incubated at 35 C in static, aerobic conditions, for [16][17][18][19][20] …”

“…From investigations to date, many groups of researchers have synthesised and determined the biological activity of a broad range of Ag-NHC complexes [10][11][12] . Specifically, compounds derived from benzimidazole-based NHC ligands have shown promising antimicrobial activity 9,11,[13][14][15][16][17][18][19][20] and various studies have extended their research to anticancer activity 6,9,13,14 .…”

In vitro antimicrobial studies of new benzimidazolium salts and silver N-heterocyclic carbene complexes

“…Heterocyclic compounds such as benzimidazole, imidazole, triazole, benzodiazepine and indazole are very important for both pharmacological and industrial applications [1][2][3][4] . Different pharmacological and biological properties of many heteroaromatic compounds, which are stable, safe, and have biological activity, have been investigated for these two significant applications by different research groups [5][6][7][8][9][10][11][12] .…”

“…In particular, this nucleus is a constituent of vitamin-B12 17 . Benzimidazoles are regarded as a promising class of bioactive heterocyclic compounds, which have attracted considerable interest in medicinal chemistry because of their various range of biological activities including antiviral, anticancer 16,18,19 , antimicrobial 1,16,[18][19][20] , anti-inflammatory 16,19 , anthelmintic, antihistaminic, proton pump inhibitor, antioxidant, antihypertensive and anticoagulant activities 16 . The aim of this study was to investigate the in vitro antimicrobial activity of new synthesized benzimidazolium salts (1a-f) and Ag-NHC complexes (2a-g), which were formed in situ deprotonation with silver oxide of 1a-f.…”