Fluorinated N-Heterocyclic Carbene Silver(I) Complexes with High Cancer Cell Selectivity

This work presents the synthesis of five new functionalized (benz)imidazolium N-heterocyclic (NHC) ligands (L) and four new (benz)imidazole silver(I) NHC (Ag(I)-NHC) complexes of mononuclear [Ag(L)2](PF6) or binuclear [Ag2(L)2](PF6)2 type. The complexes have been fully characterized, including single crystal X-ray diffraction of three new structures. The complexes and their corresponding free NHC ligands have been screened against breast cancer and noncancerous cell lines, showing the mononuclear benzimidazole complex has the highest activity, while the binuclear benzimidazole complex has the highest cancer cell selectivity. The silver uptake was measured by ICP-MS and highlights a strong link between cytotoxicity and cellular uptake. DNA interaction studies, molecular docking, and evaluation of reactive oxygen species (ROS) have been conducted for the most promising complexes to identify modes of action. Overall, the binuclear benzimidazole complex is the most selective and promising candidate against the MDA-MD-231 (breast cancer) cell line and has potential to be developed for treatment of late-stage breast cancers.

Comprehensive Insights into Medicinal Research on Imidazole-Based Supramolecular Complexes

The electron-rich five-membered aromatic aza-heterocyclic imidazole, which contains two nitrogen atoms, is an important functional fragment widely present in a large number of biomolecules and medicinal drugs; its unique structure is beneficial to easily bind with various inorganic or organic ions and molecules through noncovalent interactions to form a variety of supramolecular complexes with broad medicinal potential, which is being paid an increasing amount of attention regarding more and more contributions to imidazole-based supramolecular complexes for possible medicinal application. This work gives systematical and comprehensive insights into medicinal research on imidazole-based supramolecular complexes, including anticancer, antibacterial, antifungal, antiparasitic, antidiabetic, antihypertensive, and anti-inflammatory aspects as well as ion receptors, imaging agents, and pathologic probes. The new trend of the foreseeable research in the near future toward imidazole-based supramolecular medicinal chemistry is also prospected. It is hoped that this work provides beneficial help for the rational design of imidazole-based drug molecules and supramolecular medicinal agents and more effective diagnostic agents and pathological probes.

Antibacterial silver and gold complexes of imidazole and 1,2,4-triazole derived N-heterocyclic carbenes

A series of gold(I) (4a-4h, 5a-5b) and silver(I) (3a-3h) complexes of 1,2,4-triazolylidene and imidazolylidene based N-heterocyclic carbene ligands were prepared and the antibacterial activities of these complexes have been evaluated. The complexes were characterised using ¹H-NMR, ¹³C-NMR, HRMS and in the cases of 3a, 3c, 4b and 5b by X-ray crystallography. The gold(I) complexes with phenyl substituents (4a-4d) were found to have potent antibacterial activity against Gram-positive bacteria, with the complexes of the 1,2,4-triazolylidene ligands being more active (4c, MIC = 4-8 μg mL^-1 against Enterococcus faecium and 2 μg mL^-1 against Staphylococcus aureus) than the analogous imidazolylidene complexes 4a and 4b (4a, MIC = 64 μg mL^-1 against E. faecium and 2-4 μg mL^-1 against S. aureus). Two of the silver(I) complexes have promising antibacterial activity against Acinetobacter baumannii (3f, MIC = 2-4 μg mL^-1 and 3g, MIC = 2 μg mL^-1). Silver(I) complex 3f and gold(I) complex 4c were tested against multi-drug resistant bacterial strains and high levels of antibacterial activity were observed. The potential for antibacterial resistance to develop against these metal containing complexes was investigated and significantly, no resistance was observed upon continuous treatment, whilst resistance was developed against the widely used broad-spectrum antibiotic ciprofloxacin in the same bacterial strains, under the conditions tested. The solution and gas phase stabilities of the complexes have been investigated using a combination of ¹H-NMR, HRMS and detailed computational mechanistic studies were undertaken to gain insights into the possible decomposition reactions for silver complexes in aqueous solution.

Cyanopropyl functionalized benzimidazolium salts and their silver N-heterocyclic carbene complexes: Synthesis, antimicrobial activity, and theoretical analysis

The reaction of N-substituted benzimidazole with 4-bromobutyronitrile gives the corresponding benzimidazolium salts as N-heterocyclic carbene (NHC) precursors. Silver(I) carbene complexes are synthesized by the reaction of the corresponding benzimidazolium salts with Ag₂ O in dichloromethane. These new NHC precursors and Ag-NHC complexes were characterized by spectroscopy techniques and also screened for their antibacterial activities against the standard bacterial strains Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, and Enterococcus faecalis, and the standard fungal strains Candida albicans and Candida glabrata, and promising results were achieved. The compounds were also analyzed by density functional theory (DFT)/time-dependent DFT and docking methods.

Synthesis, in vitro anticancer activities, and quantum chemical investigations on 1,3-bis-(2-methyl-2-propenyl)benzimidazolium chloride and its Ag(I) complex

1,3- Bis-(2-methyl-2-propenyl)benzimidazolium chloride and its Ag(I) complex are synthesized and the structures are elucidated using spectroscopies techniques. The molecular and crystal structures of the benzimidazolium salt are confirmed by X-ray crystallography. The molecular geometries of the benzimidazolium and its Ag(I) salt are analyzed using the B3LYP functional with the 6–311+G(d,p)/LANL2DZ basis set. The observed Fourier transform infrared and nuclear magnetic resonance isotropic shifts are compared with the calculated values. Besides, the quantum chemical identifiers, significant intramolecular interactions, and molecular electrostatic potential plots are used to show the tendency/site of the chemical reactivity behavior. The three-dimensional Hirshfeld surfaces and the associated two-dimensional fingerprint plots are applied to obtain an insight into the behavior of the interactions in the crystal. Both compounds are tested for their in vitro anticancer activities against DU-145 and MCF-7 cancer cells and L-929 non-cancer cells using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.

Synthesis, conformational analysis and antibacterial activity of Au(i)–Ag(i) and Au(i)–Hg(ii) heterobimetallic N-heterocyclic carbene complexes

A family heterobimetallic Au(i)–Ag(i) and Au(i)–Hg(ii) complexes of bis-N-heterocyclic carbene ligands been prepared and their antibacterial properties evaluated.

Recent Developments in the Medicinal Applications of Silver-NHC Complexes and Imidazolium Salts

Because of their great structural diversity and multitude of chemical properties, N-heterocyclic carbenes (NHCs) have been utilized in a variety of capacities. Most recently, NHCs have been utilized as carrier molecules for many transition metals in medicinal chemistry. Specifically, Ag(I)-NHCs have been investigated as potent antibacterial agents and chemotherapeutics and have shown great efficacy in both in vitro and in vivo studies. Ag(I)-NHC compounds have been shown to be effective against a wide range of both Gram-positive and Gram-negative bacterial strains. Many compounds have also shown great efficacy as antitumor agents demonstrating comparable or better antitumor activity than standard chemotherapeutics such as cisplatin and 5-fluorouracil. While these compounds have shown great promise, clinical use has remained an unattained goal. Current research has been focused upon synthesis of novel Ag(I)-NHC compounds and further investigations of their antibacterial and antitumor activity. This review will focus on recent advances of Ag(I)-NHCs in medicinal applications.

A comparative insight into the bioactivity of mono- and binuclear silver(I)-N-heterocyclic carbene complexes: synthesis, lipophilicity and substituent effect

Silver(I)-N-heterocyclic carbene (Ag(I)-NHC) complexes of mononuclear and binuclear species, synthesised by our group and others in recent years, offer a fascinating outlook on their bioactivity. These complexes advance a range of adaptable structural patterns, leading to intra-specific variation in anticancer and antimicrobial activities. This study therefore reviews the synthesis, structural analysis and bioactivity of Ag complexes derived from mononuclear-NHC complexes either with coordinating or non-coordinating anions and binuclear NHC complexes. Specifically, the effect of stability, chain lengths and lipophilicity on the biological activity of recently reported Ag(I)-NHC complexes is reviewed. These complexes can be further explored as novel antibacterial and anticancer drugs in the nearest future.

Unraveling the synthesis of homoleptic [Ag(N,N-diaryl-NHC)2]Y (Y = BF4, PF6) complexes by ball-milling

A user-friendly and general mechanochemical method was developed to access rarely described NHC (N-heterocyclic carbene) silver(i) complexes featuring N,N-diarylimidazol(idin)ene ligands and non-coordinating tetrafluoroborate or hexafluorophosphate counter anions.

Macrophage and colon tumor cells as targets for a binuclear silver(I) N-heterocyclic carbene complex, an anti-inflammatory and apoptosis mediator

Chronic inflammation intensifies the risk for malignant neoplasm, indicating that curbing inflammation could be a valid strategy to prevent or cure cancer. Cancer and inflammation are inter-related diseases and many anti-inflammatory agents are also used in chemotherapy. Earlier, we have reported a series of novel ligands and respective binuclear Ag(I)-NHC complexes (NHC=N-heterocyclic carbene) with potential anticancer activity. In the present study, a newly synthesized salt (II) and respective Ag(I)-NHC complex (III) of comparable molecular framework were prepared for a further detailed study. Preliminarily, II and III were screened against HCT-116 and PC-3 cells, wherein III showed better results than II. Both the compounds showed negligible toxicity against normal CCD-18Co cells. In FAM-FLICA caspase assay, III remarkably induced caspase-3/7 in HCT-116 cells most probably by tumor necrosis factor-alpha (TNF-α) independent intrinsic pathway and significantly inhibited in vitro synthesis of cytokines, interleukin-1 (IL-1) and TNF-α in human macrophages (U937 cells). In a cell-free system, both the compounds inhibited cyclooxygenase (COX) activities, with III being more selective towards COX-2. The results revealed that III has strong antiproliferative property selectively against colorectal tumor cells which could be attributed to its pro-apoptotic and anti-inflammatory abilities.

Preparation and structure of NHC Hg(ii) and Ag(i) macrometallocycles

A series of bis-azolium salts and their seven NHC metal (Hg(ii) and Ag(i)) complexes have been prepared and characterized.