Synthesis and antimicrobial activity against Pseudomonas aeruginosa of macrocyclic β-hairpin peptidomimetic antibiotics containing N-methylated amino acids

Abstract

Antimicrobial resistance among Gram-negative bacteria is a growing problem, fueled by the paucity of new antibiotics that target these microorganisms. One novel family of macrocyclic -hairpinshaped peptidomimetics was recently shown to act specifically against Pseudomonas spp. by a novel mechanism of action, targeting the outer membrane protein LptD, which mediates lipopolysaccharide transport to the cell surface during outer membrane biogenesis. Here we explore the mode of binding of one of these -hairpin peptidomimetics to LptD in Pseudomonas aeruginosa, by examining the effects on antimicrobial activity following N-methylation of individual peptide bonds. An N-methyl scan of the cyclic peptide revealed that residues on both sides of the -hairpin structure at a non-hydrogen bonding position likely mediate hydrogen-bonding interactions with the target LptD. Structural analyses by NMR spectroscopy further reinforce the conclusion that the folded -hairpin structure of the peptidomimetic is critical for binding to the target LptD. Finally, new NMe analogues with potent activity have been identified, which opens new avenues for optimization in this family of antimicrobial peptides.

Antimicrobial Agents That Inhibit the Outer Membrane Assembly Machines of Gram-Negative Bacteria

“…Additionally, these experiments revealed that several derivatives with N-methylation have more potent antimicrobial activity than LB-01. For example, a Dab4NMe analog of LB-01 displayed MICs of 0.005 and 0.009 μg/ml against P. aeuruginosa ATCC27853 and PAO1, respectively [71]. These results show that there is a novel avenue for optimization of peptidomimetics.…”

“…An alanine scan experiment to examine the critical residue for antimicrobial activity of each side chain in L27-11 showed that Trp2 and Trp8 residues located on the opposite face of each side chain are critical [70]. A novel modified derivative of L27-11, called LB-01, with MICs of 0.008 and 0.015 μg/ml against P. aeuruginosa ATCC27853 and PAO1, respectively, was developed [70,71]. An N-methyl scan experiment using N-methylation of each peptide bond showed that residues on both sides of LB-01 that do not participate in the intramolecular hydrogen bonding may play an important role in hydrogen-bonding interactions with LptD [71].…”

“…A novel modified derivative of L27-11, called LB-01, with MICs of 0.008 and 0.015 μg/ml against P. aeuruginosa ATCC27853 and PAO1, respectively, was developed [70,71]. An N-methyl scan experiment using N-methylation of each peptide bond showed that residues on both sides of LB-01 that do not participate in the intramolecular hydrogen bonding may play an important role in hydrogen-bonding interactions with LptD [71]. Additionally, these experiments revealed that several derivatives with N-methylation have more potent antimicrobial activity than LB-01.…”

“…The most successful case is Murepavadin, an L27-11-based peptidomimetic inhibitor of LptD, which has successfully completed phase-II clinical trials [72]. Because several additional optimization procedures of L27-11 have been suggested [70,71], there is the possibility of developing more potent antimicrobial agents.…”

Overcoming Intrinsic and Acquired Resistance Mechanisms Associated with the Cell Wall of Gram-Negative Bacteria

“…Beyond the biosynthetic pathway, the translocation of lipid A across the cytoplasmic membrane and transport of the LPS to the outer membrane mediated by the multi-protein Lpt complex are also attractive targets. Inhibition of this pathway was shown using a macrocyclic peptidomimetic compound (L27-11, Figure 1 ) that targets the LptD enzyme on the outer membrane [ 60 ], and displays antibacterial activity against P. aeruginosa [ 61 ]. Other macrocyclic peptides have also been used to target LptD in clinical trials.…”