Efforts to generate antibacterial agents via mimicry of host-defense peptides have focused on discrete oligomers that can adopt a regular globally amphiphilic conformation in the presence of bacterial cell membranes and ultimately disrupt those membranes. Although considerable success has been achieved with this approach, application of the resulting molecules is hampered by the high cost associated with stepwise oligomer synthesis. We show that random poly-β-peptide copolymers, prepared by ring-opening polymerization of β-lactams, can be tuned to display good activity against a panel of four bacteria along with low lytic activity toward human red blood cells. These findings support a nonclassical design hypothesis for antibacterial agents.

Host-defense peptides are natural antibiotics produced by multicellular organisms to ward off bacterial infection. Since the discovery of these molecules in the 1980s, a great deal of effort has been devoted to elucidating their mechanisms of action and to developing analogues with improved properties for possible therapeutic use. The vast majority of this effort has focused on materials composed of a single type of molecule, most commonly a peptide with a specific sequence of alpha-amino acid residues. We have recently shown that sequence-random nylon-3 copolymers can mimic favorable properties of host-defense peptides, and here we document structure-activity relationships in this polymer family. Although the polymers are heterogeneous in terms of subunit order and stereochemistry, these materials display structure-activity relationships comparable to those that have been documented among host-defense peptides and analogous synthetic peptides. Previously such relationships have been interpreted in terms of a specific and regular folding pattern (usually an alpha-helix), but our findings show that these correlations between covalent structure and biological activity do not require the adoption of a specific or regular conformation. In some cases our observations suggest alternative interpretations of results obtained with discrete peptides.

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