Abstract
Nonsymmetrically substituted N-heterocyclic carbene (NHC) precursors 1a–d and 3a–d were synthesised by first reacting 1H-(benz)imidazole with p-cyanobenzyl bromide to give 4-(1H-imidazole-1-ylmethyl)benzonitrile (1) and 4-(1H-benzimidazole-1-ylmethyl)benzonitrile (3) and afterwards introducing benzyl bromide, 1-(bromomethyl)-4-methylbenzene, 1-(bromomethyl)-4-methoxybenzene, and methyl 4-(bromomethyl)benzoate. The NHC-silver(I) acetate complexes (1-benzyl-3-(4-cyanobenzyl)-2,3-dihydro-1H-imidazole-2-ylidene) silver(I) acetate (2a), (1-(4-cyanobenzyl)-3-(4-methylbenzyl)-2,3-dihydro-1H-imidazole-2-ylidene) silver(I) acetate (2b), (1-(4-cyanobenzyl)-3-[4-(methoxycarbonyl)benzyl]-2,3-dihydro-1H-imidazole-2-ylidene) silver(I) acetate (2c), (1-benzyl-3-(4-cyanobenzyl)-2,3-dihydro-1H-benzimidazole-2-ylidene) silver(I) acetate (4a), (1-(4-cyanobenzyl)-3-(4-methylbenzyl)-2,3-dihydro-1H-benzimidazole-2-ylidene) silver(I) acetate (4b), (1-(4-cyanobenzyl)-3-(4-methoxybenzyl)-2,3-dihydro-1H-benzimidazole-2-ylidene) silver(I) acetate (4c), and (1-(4-cyanobenzyl)-3-[4-(methoxycarbonyl)benzyl]-2,3-dihydro-1H-benzimidazole-2-ylidene) silver(I) acetate (4d) were yielded by reacting these NHC precursors with silver(I) acetate. The silver(I) acetate complex 4b was characterised by single crystal X-ray diffraction. Preliminary in vitro antibacterial studies against the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Escherichia coli, using the Kirby-Bauer disc diffusion method, were carried out on the seven NHC-silver(I) acetate complexes 2a–c and 4a–d. Also the IC50 values of these seven complexes were determined by an MTT-based assay against the human renal cancer cell line Caki-1. The complexes 2a–c and 4a–c revealed the following IC50 values, respectively, 25 (±1), 15 (±2), 5.4 (±0.8), 16 (±2), 7.1 (±1), 20 (±4), and 14 (±1) μM.
Highlights
N-Heterocyclic carbenes (NHCs) are versatile ligands in silver complexes exhibiting antimicrobial activity, in particular for the possible treatment of pulmonary infections accompanying cystic fibrosis (CF) and chronic lung infections [1,2,3] and maybe in the treatment of cancer [4]
Youngs’ research group have reported antimicrobial activity of NHC-silver complexes derived from 1H-imidazole, 4,5dichloro-1H-imidazole and xanthines against a panel of highly resistant pathogens recovered from the respiratory tract of cystic fibrosis (CF) patients [1, 3, 5]
Another important contribution by the Ghosh research group led to the synthesis and antimicrobial evaluation of NHC-silver complexes derived from 1-benzyl-3-tert-butylimidazole [6]
Summary
N-Heterocyclic carbenes (NHCs) are versatile ligands in silver complexes exhibiting antimicrobial activity, in particular for the possible treatment of pulmonary infections accompanying cystic fibrosis (CF) and chronic lung infections [1,2,3] and maybe in the treatment of cancer [4]. Youngs’ research group have reported antimicrobial activity of NHC-silver complexes derived from 1H-imidazole, 4,5dichloro-1H-imidazole and xanthines against a panel of highly resistant pathogens recovered from the respiratory tract of cystic fibrosis (CF) patients [1, 3, 5]. Another important contribution by the Ghosh research group led to the synthesis and antimicrobial evaluation of NHC-silver complexes derived from 1-benzyl-3-tert-butylimidazole [6]. Youngs and coworkers have reported anticancer activity of NHC-silver complexes derived from 4,5-dichloro-1Himidazole against the human cancer cell lines OVCAR-3 (ovarian), MB157 (breast), and HeLa (cervical) [4]. We have reported the anticancer (CAKI-1, renal) and antibacterial (E. coli, S. aureus) activity of benzyl-substituted N-heterocyclic carbene-silver [12,13,14,15,16,17] and carbene-gold complexes [18, 19]
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