Two ruthenium polypyridyl complexes functionalized with thiophen: synthesis and antibacterial activity against Staphylococcus aureus

Abstract

Two ruthenium polypyridyl complexes: [Ru(dmb)₂(ETPIP)](ClO₄)₂ (Ru(II)-1) and [Ru(phen)₂(ETPIP)](ClO₄)₂ (Ru(II)-2) (dmb = 4,4′-dimethyl-2,2′-bipyridine, phen = 1,10-phenanthroline, ETPIP = 2-(4-(thiophen-2-ylethynyl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline), have been synthesized and characterized. Their antimicrobial activities against S. aureus were assessed. Both the complexes Ru(II)-1, and Ru(II)-2 show meaningful activity against Staphylococcus aureus and the lead complex of this set, Ru(II)-2 (MIC = 0.025 mg mL⁻¹), was further tested against biofilms. Given the fact that S. aureus could easily develop resistance to common antimicrobials, we also investigated whether bacteria can easily develop resistance to Ru(II)-2. The result demonstrated that S. aureus did not easily develop resistance to the ruthenium complexes. In addition, the synergism between Ru(II)-2 and common antibiotics against S. aureus was also investigated using the checkerboard method. Interestingly, Ru(II)-2 could increase the susceptibility of S. aureus to the aminoglycoside antibiotic (kanamycin). Finally, a possible mechanism of the observed synergetic effects was investigated by real-time PCR. All in all, these results confirmed that ruthenium complexes have good antimicrobial activity against Staphylococcus aureus.