The urgent need to combat antibiotic resistance and develop novel antimicrobial therapies has triggered studies on novel metal-based formulations. N-heterocyclic carbene (NHC) complexes coordinate transition metals to generate a broad range of anticancer and/or antimicrobial agents, with ongoing efforts being made to enhance the lipophilicity and drug stability. The lead silver(I) acetate complex, 1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene (NHC*) (SBC3), has previously demonstrated promising growth and biofilm-inhibiting properties. In this work, the responses of two structurally different bacteria to SBC3 using label-free quantitative proteomics were characterised. Multidrug-resistant Pseudomonas aeruginosa (Gram-negative) and Staphylococcus aureus (Gram-positive) are associated with cystic fibrosis lung colonisation and chronic wound infections, respectively. SBC3 increased the abundance of alginate biosynthesis, the secretion system and drug detoxification proteins in P. aeruginosa, whilst a variety of pathways, including anaerobic respiration, twitching motility and ABC transport, were decreased in abundance. This contrasted the affected pathways in S. aureus, where increased DNA replication/repair and cell redox homeostasis and decreased protein synthesis, lipoylation and glucose metabolism were observed. Increased abundance of cell wall/membrane proteins was indicative of the structural damage induced by SBC3 in both bacteria. These findings show the potential broad applications of SBC3 in treating Gram-positive and Gram-negative bacteria.

The antimicrobial properties of silver have been exploited for many centuries and continue to gain interest in the fight against antimicrobial drug resistance. The broad-spectrum activity and low toxicity of silver have led to its incorporation into a wide range of novel antimicrobial agents, including N-heterocyclic carbene (NHC) complexes. The antimicrobial activity and in vivo efficacy of the NHC silver(I) acetate complex SBC3, derived from 1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene (NHC*), has previously been demonstrated, although the mode(s) of action of SBC3 remains to be fully elucidated. Label-free quantitative (LFQ) proteomics was applied to analyse changes in protein abundance in the pathogenic yeast Candida parapsilosis in response to SBC3 treatment. Increased abundance of proteins associated with detoxification and drug efflux were indicative of a cell stress response whilst significant decreases in proteins required for protein and amino acid biosynthesis offer potential insight into the growth-inhibitory mechanisms of SBC3. Guided by the proteomic findings and the prolific biofilm and adherence capabilities of C. parapsilosis, our studies have shown the potential of SBC3 in reducing adherence to epithelial cells and biofilm formation and hence decrease fungal virulence.

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Since the advent of the armed-disarmed strategy, thioglycosides have become essential tools in one-pot oligosaccharide synthesis. The continuum of glycosyl donor reactivity has since been expanded to include so-called ‘superarmed’ thioglycoside donors whose reactivity relies on more than just the inductive effects of protecting groups. Here we report a new method for the synthesis of superarmed thioglycosides via the ring-opening of 1,2-orthoesters. This method ensures the necessary 1,2-trans stereochemistry, and importantly, makes use of trimethylsilyl thioethers as sulfur nucleophiles to avoid the use of unpleasant free thiols. Ten examples of ethyl and phenyl thioglycosides of mono- and disaccharides were synthesized from their orthoesters using tris(pentafluorophenyl)borane (BCF) as the Lewis acid promoter and were obtained in good yield and purity.