The Importance of Heterolepticity in Improving the Antibacterial Activity of Bismuth(III) Thiolates

Abstract

Five mixed thiolatobismuth(III) complexes [BiPh(5‐MMTD)2{4‐MMT(H)}] (1), [Bi(1‐MMTZ)2{(PYM)(PYM(H))2}] (2), [Bi(MBT)2(5‐MMTD)] (3), [Bi(4‐BrMTD)3{2‐MMI(H)}] (4) and [Bi(1‐MMTZ)2{1‐MMTZ(H)}(2‐MMI){2‐MMI(H)2}] (5) were synthesised from imidazole‐, thiazole‐, thiadiazole‐, triazole‐, tetrazole‐ and pyrimidine‐based heterocyclic thiones. Four of these complexes 1–4 were synthesized from BiPh3, while complex 5 was obtained from Bi[4‐(MeO)Ph]3. Complexes 1–5 were structurally characterised by XRD. Evaluation of the antibacterial properties against Mycobacterium smegmatis, Staphylococcus aureus, Methicillin‐resistant S. aureus (MRSA), Vancomycin‐resistant Enterococcus (VRE), Enterococcus faecalis and Escherichia coli showed that mixed thiolato complexes containing the anionic thiazole‐based ligands MBT and 4‐BrMTD are most effective. The mixed thiolato complexes [Bi(MBT)2(5‐MMTD)] (3) having thiazole‐ and thiadiazole‐ and [Bi(4‐BrMBT)3{2‐MMI(H)}] (4) containing thiazole‐ and imidazole‐based ligands proved to be more efficient, with low minimum inhibitory concentrations of 1.73 and 3.45 µm for 3 against VRE and E. faecalis, respectively, and 2.20 µm for 4 against M. smegmatis and E. faecalis. All complexes showed little or no toxicity towards mammalian COS‐7 cell lines at 20 µg mL–1.