Synthetic Polymers Active against <i>Clostridium difficile</i> Vegetative Cell Growth and Spore Outgrowth

Nylon-3 polymers (poly-β-peptides) have been investigated as synthetic mimics of host-defense peptides in recent years. These polymers are attractive because they are much easier to synthesize than are the peptides themselves, and the polymers resist proteolysis. Here we describe <i>in vitro</i> analysis of selected nylon-3 copolymers against <i>Clostridium difficile</i>, an important nosocomial pathogen that causes highly infectious diarrheal disease. The best polymers match the human host-defense peptide LL-37 in blocking vegetative cell growth and inhibiting spore outgrowth. The polymers and LL-37 were effective against both the epidemic 027 ribotype and the 012 ribotype. In contrast, neither vanco­mycin nor nisin inhibited outgrowth for the 012 ribotype. The best polymer was less hemolytic than LL-37. Overall, these findings suggest that nylon-3 copolymers may be useful for combatting <i>C. difficle</i>

Functionally Diverse Nylon-3 Copolymers from Readily Accessible β-Lactams

A new family of β-lactams is described that enables anionic ring-opening polymerization (AROP) to prepare nylon-3 materials bearing diverse appended functionality, including carboxylic acid, thiol, hydroxyl, and secondary amine groups. Nylon-3 copolymers generated with the new β-lactams are shown to display distinctive self-assembly behavior and biological properties

Interplay among Subunit Identity, Subunit Proportion, Chain Length, and Stereochemistry in the Activity Profile of Sequence-Random Peptide Mixtures

Fmoc-based solid-phase synthesis methodology was used to prepare peptide mixtures containing one type of hydrophobic residue and one type of cationic residue. Each mixture was random in terms of sequence but highly controlled in terms of length. Analysis of the antibacterial and hemolytic properties of these mixtures revealed that selective antibacterial activity can be achieved with heterochiral binary mixtures but not homochiral binary mixture, if the proper amino acid residues are used

Nylon‑3 Polymers Active against Drug-Resistant Candida albicans Biofilms

Candida albicans is the most common fungal pathogen in humans, and most diseases produced by C. albicans are associated with biofilms. We previously developed nylon-3 polymers with potent activity against planktonic C. albicans and excellent C. albicans versus mammalian cell selectivity. Here we show that these nylon-3 polymers have strong and selective activity against drug-resistant C. albicans in biofilms, as manifested by inhibition of biofilm formation and by killing of C. albicans in mature biofilms. The best nylon-3 polymer (poly-<b>βNM</b>) is superior to the antifungal drug fluconazole for all three strains examined. This polymer is slightly less effective than amphotericin B (AmpB) for two strains, but the polymer is superior against an AmpB-resistant strain

Evidence for Phenylalanine Zipper-Mediated Dimerization in the X‑ray Crystal Structure of a Magainin 2 Analogue

High-resolution structure elucidation has been challenging for the large group of host-defense peptides that form helices on or within membranes but do not manifest a strong folding propensity in aqueous solution. Here we report the crystal structure of an analogue of the widely studied host-defense peptide magainin 2. Magainin 2 (S8A, G13A, G18A) is a designed variant that displays enhanced antibacterial activity relative to the natural peptide. The crystal structure of magainin 2 (S8A, G13A, G18A), obtained for the racemic form, features a dimerization mode that has previously been proposed to play a role in the antibacterial activity of magainin 2 and related peptides

C-Terminal Functionalization of Nylon-3 Polymers: Effects of C-Terminal Groups on Antibacterial and Hemolytic Activities

Nylon-3 polymers contain β-amino-acid-derived subunits and can be viewed as higher homologues of poly­(α-amino acids). This structural relationship raises the possibility that nylon-3 polymers offer a platform for development of new materials with a variety of biological activities, a prospect that has recently begun to receive experimental support. Nylon-3 homo- and copolymers can be prepared via anionic ring-opening polymerization of β-lactams, and use of an <i>N</i>-acyl-β-lactam as coinitiator in the polymerization reaction allows placement of a specific functional group, borne by the <i>N</i>-acyl-β-lactam, at the N-terminus of each polymer chain. Controlling the unit at the C-termini of nylon-3 polymer chains, however, has been problematic. Here we describe a strategy for specifying C-terminal functionality that is based on the polymerization mechanism. After the anionic ring-opening polymerization is complete, we introduce a new β-lactam, approximately 1 equiv relative to the expected number of polymer chains. Because the polymer chains bear a reactive imide group at their C-termini, this new β-lactam should become attached at this position. If the terminating β-lactam bears a distinctive functional group, that functionality should be affixed to most or all C-termini in the reaction mixture. We use the new technique to compare the impact of N- and C-terminal placement of a critical hydrophobic fragment on the biological activity profile of nylon-3 copolymers. The synthetic advance described here should prove to be generally useful for tailoring the properties of nylon-3 materials

C-Terminal Functionalization of Nylon-3 Polymers: Effects of C-Terminal Groups on Antibacterial and Hemolytic Activities

Nylon-3 polymers contain β-amino-acid-derived subunits and can be viewed as higher homologues of poly­(α-amino acids). This structural relationship raises the possibility that nylon-3 polymers offer a platform for development of new materials with a variety of biological activities, a prospect that has recently begun to receive experimental support. Nylon-3 homo- and copolymers can be prepared via anionic ring-opening polymerization of β-lactams, and use of an <i>N</i>-acyl-β-lactam as coinitiator in the polymerization reaction allows placement of a specific functional group, borne by the <i>N</i>-acyl-β-lactam, at the N-terminus of each polymer chain. Controlling the unit at the C-termini of nylon-3 polymer chains, however, has been problematic. Here we describe a strategy for specifying C-terminal functionality that is based on the polymerization mechanism. After the anionic ring-opening polymerization is complete, we introduce a new β-lactam, approximately 1 equiv relative to the expected number of polymer chains. Because the polymer chains bear a reactive imide group at their C-termini, this new β-lactam should become attached at this position. If the terminating β-lactam bears a distinctive functional group, that functionality should be affixed to most or all C-termini in the reaction mixture. We use the new technique to compare the impact of N- and C-terminal placement of a critical hydrophobic fragment on the biological activity profile of nylon-3 copolymers. The synthetic advance described here should prove to be generally useful for tailoring the properties of nylon-3 materials

Nylon‑3 Polymers with Selective Antifungal Activity

Host-defense peptides inhibit bacterial growth but show little toxicity toward mammalian cells. A variety of synthetic polymers have been reported to mimic this antibacterial selectivity; however, achieving comparable selectivity for fungi is more difficult because these pathogens are eukaryotes. Here we report nylon-3 polymers based on a novel subunit that display potent antifungal activity (MIC = 3.1 μg/mL for Candida albicans) and favorable selectivity (IC₁₀ > 400 μg/mL for 3T3 fibroblast toxicity; HC₁₀ > 400 μg/mL for hemolysis)

Effects of Cyclic vs Acyclic Hydrophobic Subunits on the Chemical Structure and Biological Properties of Nylon‑3 Copolymers

Nylon-3 copolymers containing both hydrophobic and cationic subunits can mimic the activity profile of host-defense peptides, if subunit identity and proportion are carefully selected. These sequence- and stereo-random copolymers inhibit bacterial growth at relatively low concentrations, apparently via disruption of bacterial membranes, but they are relatively nondisruptive toward eukaryotic cell membranes (low hemolytic activity). In all previous examples, the hydrophobic subunits have contained cycloalkyl groups that incorporate the backbone Cα–Cβ bond. Here we have explored the effects of using analogous acyclic hydrophobic subunits. The results indicate that replacing cyclic with acyclic hydrophobic subunits has a modest influence on biological properties. This influence appears to arise from differences in subunit flexibility

Structure–Activity Relationships among Antifungal Nylon‑3 Polymers: Identification of Materials Active against Drug-Resistant Strains of <i>Candida albicans</i>

Fungal infections are a major challenge to human health that is heightened by pathogen resistance to current therapeutic agents. Previously, we were inspired by host-defense peptides to develop nylon-3 polymers (poly-β-peptides) that are toxic toward the fungal pathogen <i>Candida albicans</i> but exert little effect on mammalian cells. Based on subsequent analysis of structure–activity relationships among antifungal nylon-3 polymers, we have now identified readily prepared cationic homopolymers active against strains of <i>C. albicans</i> that are resistant to the antifungal drugs fluconazole and amphotericin B. These nylon-3 polymers are nonhemolytic. In addition, we have identified cationic–hydrophobic copolymers that are highly active against a second fungal pathogen, <i>Cryptococcus neoformans</i>, and moderately active against a third pathogen, <i>Aspergillus fumigatus</i>