An amphipathic cyclic tetrapeptide scaffold containing halogenated β -amino acids with activity against multiresistant bacteria.

The present study describes the synthesis and biological studies of a small series of head-to-tail cyclic tetrapeptides of the general structure c(Lys-β -Xaa-Lys) containing one lipophilic β -amino acid and Lys, Gly, Ala, or Phe as the Xaa residue in the sequence. The peptides were investigated for antimicrobial activity against gram-positive and gram-negative reference strains and 30 multiresistant clinical isolates including strains with extended spectrum β-lactamase-carbapenemase (ESBL-CARBA) production. Toxicity was determined against human red blood cells. The most potent peptides showed high activity against the gram-positive clinical isolates with minimum inhibitory concentrations of 4-8 μg/mL and low haemolytic activity. The combination of high antimicrobial activity and low toxicity shows that these cyclic tetrapeptides containing lipophilic β -amino acids form a valuable scaffold for designing novel antimicrobial agents.