Anticancer, antimicrobial and antiparasitical activities of copper(I) complexes based on N-heterocyclic carbene (NHC) ligands bearing aryl substituents

Synthesis of ferrocenyl benzimidazole derivatives as novel anti-Toxoplasma gondii agents

Toxoplasmosis, a disease caused by the apicomplexan parasite Toxoplasma gondii, affects up to one third of the global population. Although immunocompetent individuals rarely experience severe symptoms, those with immunodeficiencies may potentially face fatal disease. The frontline treatments are currently sulphadiazine and pyrimethamine, which suffer from adverse side effects, and lack efficiency in clearing parasite cysts from the muscles and brain of patients. To address the need for novel, more effective, and less toxic treatments, four new ferrocenyl benzimidazole complexes 15-18 were synthesised and evaluated against the ΔKu80:mNeonGreen strain of T. gondii. Complexes 15 and 17 were found to be active with EC50 values of 17.9 and 17.5 μM respectively, with comparable activity to pyrimethamine, which had an EC50 value of 13.8 μM, and less effective than sulphadiazine, which had an EC50 value of 2.56 μM. Additionally, the compounds were found to be relatively non-toxic against HEK 293T and PNT1A human cell lines. Further investigations found that the complexes act by generating reactive oxygen species (ROS) through the ferrocenyl moiety. These complexes show potential for the development of new treatments against Toxoplasmosis.

Biological Activities of Ruthenium NHC Complexes: An Update

Ruthenium N-heterocyclic carbene (NHC) complexes have unique physico-chemical properties as catalysts and a huge potential in medicinal chemistry and pharmacology, exhibiting a variety of notable biological activities. In this review, the most recent studies on ruthenium NHC complexes are summarized, focusing specifically on antimicrobial and antiproliferative activities. Ruthenium NHC complexes are generally active against Gram-positive bacteria, such as Bacillus subtilis, Staphylococcus aureus, Micrococcus luteus, Listeria monocytogenes and are seldom active against Gram-negative bacteria, including Salmonella typhimurium, Pseudomonas aeruginosa and Escherichia coli and fungal strains of Candida albicans. The antiproliferative activity was tested against cancer cell lines of human colon, breast, cervix, epidermis, liver and rat glioblastoma cell lines. Ruthenium NHC complexes generally demonstrated cytotoxicity higher than standard anticancer drugs. Further studies are needed to explore the mechanism of action of these interesting compounds.

Evaluation of Ruthenium(II) N-Heterocyclic Carbene Complexes as Enzymatic Inhibitory Agents with Antioxidant, Antimicrobial, Antiparasitical and Antiproliferative Activity

A series of [RuCl₂(p-cymene)(NHC)] complexes were obtained by reacting [RuCl₂(p-cymene)]2 with in situ generated Ag-N-heterocyclic carbene (NHC) complexes. The structure of the obtained complexes was determined by the appropriate spectroscopy and elemental analysis. In addition, we evaluated the biological activities of these compounds as antienzymatic, antioxidant, antibacterial, anticancer, and antiparasitic agents. The results revealed that complexes 3b and 3d were the most potent inhibitors against AchE with IC₅₀ values of 2.52 and 5.06 μM mL^-1. Additionally, 3d proved very good antimicrobial activity against all examined microorganisms with IZ (inhibition zone) over 25 mm and MIC (minimum inhibitory concentration) < 4 µM. Additionally, the ligand 2a and its corresponding ruthenium (II) complex 3a had good cytotoxic activity against both cancer cells HCT-116 and HepG-2, with IC₅₀ values of (7.76 and 11.76) and (4.12 and 9.21) μM mL^-1, respectively. Evaluation of the antiparasitic activity of these complexes against Leishmania major promastigotes and Toxoplasma gondii showed that ruthenium complexes were more potent than the free ligand, with an IC₅₀ values less than 1.5 μM mL^-1. However, 3d was found the best one with SI (selectivity index) values greater than 5 so it seems to be the best candidate for antileishmanial drug discovery program, and much future research are recommended for mode of action and in vivo evaluation. In general, Ru-NHC complexes are the most effective against L. major promastigotes.

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.

Reactivity of antitumor coinage metal-based N-heterocyclic carbene complexes with cysteine and selenocysteine protein sites

The reaction of the antitumor M(I)-bis-N-heterocyclic carbene (M(I)-NHC) complexes, M = Cu, Ag, and Au, with their potential protein binding sites, i.e. cysteine and selenocysteine, was investigated by means of density functional theory approaches. Capped cysteine and selenocysteine were employed to better model the corresponding residues environment within peptide structures. By assuming the neutral or deprotonated form of the side chains of these amino acids and by considering the possible assistance of an external proton donor such as an adjacent acidic residue or the acidic component of the surrounding buffer environment, we devised five possible routes leading to the binding of the investigated M(I)-NHC scaffolds to these protein sites, reflecting their different location in the protein structure and exposure to the bulk. The targeting of either cysteine or selenocysteine in their neutral forms is a kinetically unfavored process, expected to be quite slow if observable at all at physiological temperature. On the other hand, the reaction with the deprotonated forms is much more favored, even though an external proton source is required to assist the protonation of the leaving carbene. Our calculations also show that all coinage metals are characterized by a similar reactivity toward the binding of cysteine and selenocysteine sites, although the Au(I) complex has significantly higher reaction and activation free energies compared to Cu(I) and Ag(I).