Coumarin-based silver complexes have excellent antimicrobial activity, but such complexes are typically insoluble in water and unstable under ambient light conditions. Herein, a water soluble coumarin-silver(I) complex is successfully prepared with the ability to eradicate preformed MRSA biofilms. A triphenylphosphine adduct of the complex lost all antimicrobial activity, though an improvement in solubility and light stability are noted.

Water-soluble photostable coumarin acetate complexes of silver(I) are successfully synthesized and characterized and found to have the ability to eradicate preformed MRSA biofilms. Substitution with short PEG chains at the 4-position of the coumarin ring allows the subsequent synthesis of water-soluble coumarin oxyacetate ligands which successfully allowed silver(I) complex formation. The new complexes are characterized by IR and NMR spectroscopy, microanalysis and high-resolution mass spectrometry where possible. Previous unPEGylated analogs has shown excellent antimicrobial activity against the pathogenic bacteria MRSA, Escherichia coli and Pseudomonas aeruginosa and that activity is maintained in the PEGylated complexes. However, the solubility of the un-PEGylated analogs is limited to DMSO, and those silver(I) complexes are unstable in ambient light conditions. Both issues are resolved with the new PEGylated complexes reported here and importantly the ability to eradicate preformed biofilms of MRSA is demonstrated. In addition, a triphenylphosphine adduct complex is also synthesized, but this complex has reduced activity compared to the simple PEGylated complex.