Design, synthesis and biological evaluation of cyclic peptidotriazoles derived from BPC194 as novel agents for plant protection

The search for novel antimicrobial agents to be used for plant protection has prompted us to design analogues incorporating non-natural amino acids. Herein, we designed and synthesized cyclic peptidotriazoles derived from the lead antimicrobial cyclic peptide c(Lys-Lys-Leu3-Lys-Lys5-Phe-Lys-Lys-Leu-Gln) (BPC194). In particular, Leu3 and Lys5 were replaced by a triazolyl alanine, a triazolyl norleucine or a triazolyl lysine. These peptides were screened for their antibacterial activity against Xanthomonas axonopodis pv. vesicatoria, Erwinia amylovora and Pseudomonas syringae pv. syringae, for their hemolysis and for their phytotoxicity. Results showed that the type of triazolyl amino acid and the substituent present at the triazole influenced the antibacterial and hemolytic activities. Moreover, the position of this residue was also crucial for the hemolysis. The lead compounds BPC548 and BPC550 exhibited high antibacterial activity (MIC of 3.1 to 25 μM), low hemolysis (19 and 26% at 375 μM, respectively) and low phytotoxicity. Therefore, these analogues could be used as new leads for the development of effective agents to control pathogenic bacteria responsible for plant diseases of economic importanceThis work was supported by the Spanish Ministerio de Economía y Competitividad (MINECO) [grant numbers AGL2009-13255-C02-02/AGR and AGL2012-39880-C02-02

Multivalent display of the antimicrobial peptides BP100 and BP143

Carbohydrates are considered as promising templates for the display of multiple copies of antimicrobial peptides. Herein, wedescribe the design and synthesis of chimeric structures containing two or four copies of the antimicrobial peptidesKKLFKKILKYL-NH2 (BP100) and KKLfKKILKYL-NH2 (BP143) attached to the carbohydrate template cyclodithioerythritol(cDTE) or α-D-galactopyranoside (Galp). The synthesis involved the preparation of the corresponding peptide aldehyde followedby coupling to an aminooxy-functionalized carbohydrate template. After purification, the multivalent display systems were obtainedin high purities (90–98%) and in good yields (42–64%). These compounds were tested against plant and human pathogenic bacteriaand screened for their cytotoxicity on eukaryotic cells. They showed lower MIC values than the parent peptides against the bacteriaanalyzed. In particular, the carbopeptides derived from cDTE and Galp, which contained two or four copies of BP100, respectively,were 2- to 8-fold more active than the monomeric peptide against the phytopathogenic bacteria. These results suggest thatpreassembling antimicrobial peptides to multimeric structures is not always associated with a significant improvement of theactivity. In contrast, the carbopeptides synthesized were active against human red blood cells pointing out that peptide preassemblyis critical for the hemolytic activity. Notably, peptide preassembly resulted in an enhanced bactericidal effec