Synthesis, characterization and antimicrobial activity of a series of substituted coumarin-3-carboxylatosilver(I) complexes

A series of new coumarin-derived carboxylate ligands and their silver(I) complexes have been synthesized, characterized and screened for their in vitro antibacterial activity against a range of Gram-positive and Gram-negative bacteria as well as for their antifungal activity against a clinical isolate of Candida albicans. The ligands were synthesised by either acid or base hydrolysis of their corresponding esters, which in turn were synthesised via the Knoevenegal reaction. The reaction of silver(I) nitrate with the coumarin carboxylate ligands in either aqueous or aqueous/ethanol solutions allowed the isolation of a series of novel Ag(I) carboxylate complexes. Whilst none of the ligands showed any antimicrobial activity, a number of the Ag(I) complexes exhibited potent activity. In particular, Ag(I) complexes of hydroxy-substituted coumarin carboxylates demonstrated potent activity against the clinically important methicillin-resistant Staphylococcus aureus (MRSA) bacterium (MIC80 = 0.63 μM).