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The synthesis of six novel N-heterocyclic carbene silver(I) acetate complexes, three symmetrical and three non-symmetrical, were achieved using 4,5-diphenylimidazole to produce intermediate imidazolium salts and then obtain the corresponding silver(I) complexes through complexation with silver acetate via the Youngs' method. In vitro biological testing, using the Kirby-Bauer disk diffusion method, was conducted against Methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli, with a NHC-silver(I) acetate compound, SBC3, and Tetracycline as standards. Silver(I) acetate complex 7 resulted in a 4 mm clearance against MRSA, showing the highest antibiotic activity of the novel derivatives. Crystallographic data revealed similar bond lengths and angles to previously reported NHC-silver(I) acetate complexes, with complex 8 showing interesting g 2-coordination between the silver atom and acetate oxygens. 109 Ag NMR studies were conducted, highlighting the effects of the substituents of the imidazole ring on the silver atom shown by the corresponding shifts in the 109 Ag NMR spectra. The incorporation of isopropyl groups to several of the novel complexes resulted in larger upfield 109 Ag NMR shift values compared to all other substituents.

Antibiotic resistance is a growing problem for public health and associated with increasing economic costs and mortality rates. Silver and silver‐related compounds have been used for centuries due to their antimicrobial properties. In this work, we show that 1,3‐dibenzyl‐4,5‐diphenyl‐imidazol‐2‐ylidene silver(I) acetate/NHC*‐Ag‐OAc (SBC3) is a reversible, high affinity inhibitor of E. coli thioredoxin reductase (TrxR; Ki=10.8±1.2 nM). Minimal inhibition concentration (MIC) tests with different E. coli and P. aeruginosa strains demonstrated that SBC3 can efficiently inhibit bacterial cell growth, especially in combination with established antibiotics like gentamicin. Our results show that SBC3 is a promising antibiotic drug candidate targeting bacterial TrxR.

N-Heterocyclic silver carbene compounds have been extensively studied and shown to be active agents against a host of pathogenic bacteria and fungi. By incorporating hypothesised virulence targeting substituents into NHC-silver systems via salt metathesis, an atom efficient complexation process can used to develop new complexes to target the passive and active systems of a microbial cell. The incorporation of fatty acids and an FtsZ inhibitor have been achieved, and creation of both the intermediate salt and subsequent silver complex has been streamlined into a continuous flow process. Biological evaluation was conducted with in vitro toxicology assays showing these novel complexes had excellent inhibition against Gram-negative strains E. coli, P. aeruginosa and K. pneumonia; further studies also confirmed the ability to inhibit biofilm formation in Methicillin-resistant S. aureus and C. Parapsilosis. In vivo testing using a murine thigh infection model showed promising inhibition of MRSA for the lead compound SBC3, which is derived from 1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene(NHC*).