Synthesis of temporin L hydroxamate-based peptides and evaluation of their coordination properties with iron(iii )

Ferric iron is an essential nutrient for bacterial growth. Pathogenic bacteria synthesize iron-chelating entities known as siderophores to sequestrate ferric iron from host organisms in order to colonize and replicate. The development of antimicrobial peptides (AMPs) conjugated to iron chelators represents a promising strategy for reducing the iron availability, inducing bacterial death, and enhancing simultaneously the efficacy of AMPs. Here we designed, synthesized, and characterized three hydroxamate-based peptides Pep-cyc1, Pep-cyc2, and Pep-cyc3, derived from a cyclic temporin L peptide (Pep-cyc) developed previously by some of us. The Fe3+ complex formation of each ligand was characterized by UV-visible spectroscopy, mass spectrometry, and IR and NMR spectroscopies. In addition, the effect of Fe3+ on the stabilization of the alpha-helix conformation of hydroxamate-based peptides and the cotton effect were examined by CD spectroscopy. Moreover, the antimicrobial results obtained in vitro on some Gram-negative strains (K. pneumoniae and E. coli) showed the ability of each peptide to chelate efficaciously Fe3+ obtaining a reduction of MIC values in comparison to their parent peptide Pep-cyc. Our results demonstrated that siderophore conjugation could increase the efficacy and selectivity of AMPs used for the treatment of infectious diseases caused by Gram-negative pathogens.