Syntheses, structural and antimicrobial studies of a new N-allylamide of monensin A and its complexes with monovalent metal cations

A new N-allylamide of monensin A (M-AM2) was synthesized and its capacity to form complexes with Li+, Na+ and K+ cations was studied by ESI MS, 1H and 13C NMR, FTIR spectroscopy and PM5 semi-empirical methods. ESI mass spectrometry indicates that M-AM2 forms complexes with Li+, Na+ and K+ of exclusively 1:1 stoichiometry which are stable up to cv=70 V, and the formation of 1:1 complexes between M-AM2 and Na+ cations is strongly favoured. Above cv=90 V we observe fragmentation of the respective complexes involving several dehydration steps. The spectroscopic studies show that the structures of the M-AM2 and its complexes with Li+, Na+ and K+ cations are stabilized by intramolecular hydrogen bonds in which the OH groups are always involved. The data also demonstrate that the Cdouble bond; length as m-dashO amide group is engaged in the complexation process of each cation. However with the K+ cation we also found a structure in which this Cdouble bond; length as m-dashO amide group does not participate in the complexation to a significant extent. The in vitro biological tests of M-AM2 amide show its good activity towards some strains of Gram-positive bacteria (Giz 13–19 mm; MIC 25–100 μg/ml).