Discovery of Trp-His and His-Arg analogues as new structural classes of short antimicrobial peptides

Naturally occurring antimicrobial peptides contain a large number of amino acid residues, which limits their clinical applicability. In search of short antimicrobial peptides, which represent a possible alternative for lead structures to fight antibiotic resistant microbial infections, a series of synthetic peptide analogues based on Trp-His and His-Arg structural frameworks have been prepared and found to be active against several Gram-negative and Gram-positive bacterial strains as well as against a fungal strain with MIC values of the most potent structures in the range of 5-20 microg/mL ((IC(50) in the range of 1-5 microg/mL). The synthesized peptides showed no cytotoxic effect in an MTT assay up to the highest test concentration of 200 microg/mL. A combination of small size, presence of unnatural amino acids, high antimicrobial activity, and absence of cytotoxicity reveals the synthesized Trp-His and His-Arg analogues as promising candidates for novel antimicrobial therapeutics.