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 CO amide group is engaged in the complexation process of each cation. However with the K⁺ cation we also found a structure in which this CO 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).