Structural characterization and antibacterial activity against clinical isolates of Staphylococcus of N-phenylamide of monensin A and its 1:1 complexes with monovalent cations.

The ability of N-phenylamide of monensin A (M-AM1) to form complexes with Li(+), Na(+) and K(+) cations is studied by ESI MS, (1)H and (13)C NMR, FT-IR spectroscopy and PM5 semi-empirical methods. ESI mass spectrometry indicates that M-AM1 forms complexes with the Li(+), Na(+) and K(+) cations of exclusively 1:1 stoichiometry which are stable up to cv = 90 V, and the formation of the complex with the Na(+) cation is strongly favoured. In the ESI MS spectra measured at cv = 110 V the fragmentation of the respective complexes, involving several dehydration steps, is observed. The spectroscopic studies show that the structures of M-AM1 and its complexes with Li(+), Na(+) and K(+) cations are stabilized by intramolecular hydrogen bonds in which OH groups are always involved. The CO amide group is shown to be engaged in the complexation process of each cation. However, there is a complex with K(+) cation in whose structure this CO amide group does not participate to a significant extent. The in vitro biological tests of M-AM1 amide have proved its good activity towards some strains of methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA) and methicillin-resistant Staphylococcus epidermidis (MRSE).