Benzannulated Re(i)–NHC complexes: synthesis, photophysical properties and antimicrobial activity

Abstract

A series of novel Re(i)(CO)-NHC complexes bearing unsubstituted benzimidazol-2-ylidene ligands as well as a variety of bisimine ligands has been prepared and comprehensively characterised. The complexes were found to exhibit potent antimicrobial activity on Gram-positive bacterial strains in the low micromolar concentration range, rendering these compounds interesting lead structures for the development of novel metal-based antibiotic agents. Further, the complexes exhibit pronounced luminescence with large Stokes shifts in acetonitrile and water at ambient temperature. The photophysical properties including luminescence lifetimes and quantum yields are consistent with emission from MLCT (d(Re) → π*(bisimine)) states.

Properties and prospects for rhenium(i) tricarbonyl N-heterocyclic carbene complexes

“…In addition to their early study in cancer and Alzheimer's disease research, Re-NHC complexes have also recently been found by the Metzler-Nolte group to exhibit potent antimicrobial activity on Gram-positive bacterial strains. 56 By utilising an elegant templatebased approach, cationic complexes of the type shown in Figure 14 were prepared. The complexes were generally found to exhibit moderate to low micromolar activity against three Gram-positive bacterial strains: B. subtilis 168 DSM 402, S. aureus DSM 20231, and S. aureus ATCC43300.…”

Design, synthesis and in vivo evaluation of 3-arylcoumarin derivatives of rhenium(I) tricarbonyl complexes as potent antibacterial agents against methicillin-resistant Staphylococcus aureus (MRSA)

“…Some of these molecules demonstrated activity in the low micromolar or even nanomolar range with no cytotoxicity or hemolytic activity at much higher concentrations [20,24]. Interestingly, rhenium complexes, mostly explored for their anti-tumor properties, were recently shown to possess promising antibacterial potency [35][36][37][38][39][40][41]. In particular, Wenzel, Patra et al introduced a trimetallic complex comprised of a ferrocenyl (Fc), a cymantrene and a [(dpa)Re(CO)s] residue (dpa = N,N-bis(pyridine-2ylmethyl)prop-2-yn-1-amine) as the main biological active moiety of the construct [36,37].…”

“…MIC values of the compound against Gram-positive bacterial strains such as B. subtilis and S. aureus strains involving S. aureus ATCC 43300 (MRSA) were in the range of 1.4-21 µM [36]. Siegmund et al described a family of antimicrobial N-heterocyclic carbene (NHC) fac-Re(I)(CO) 3 complexes containing unsubstituted benzimidazol-2-ylidene and bisimine ligands with MIC values of the complexes between 0.7-2 µM against Gram-positive B. subtilits and S. aureus strains [39]. Recently, Frei et al reported the synthesis of three rhenium bisquinoline complexes and light-induced activity against drug-resistant S. aureus and E. coli strains, with an increase in antimicrobial activity between 4-to 16-fold under photo-irradiation than in the dark [40].…”

Bioactive Heterobimetallic Re(I)/Au(I) Complexes Containing Bidentate N-Heterocyclic Carbenes

“…Alternatively antimicrobial activity was also recently found for rhenium complexes containing monodentate NHC ligands. 9 Therefore, it can be postulated that the combination of an NHC-Re(I) derivative with a metallodrug would be an excellent approach to maximize the therapeutic potential of a trackable metallodrug. Additionally, further substitution of L, which to the best of our knowledge has been only reported as a halogen for these types of Re(I) bidentate N-heterocyclic carbene derivatives 10 for a neutral N-donor ligand, will deliver high-potential mitochondrial bioprobes, as (1) cationic species present a greater predisposition to permeate those cellular membranes and (2) the N-donor ligand could be easily used as a linker to build the theranostic agents.…”