Polypeptoids and Peptoid-Peptide Hybrids by Transition Metal Catalysis

Clickable Polyprolines from Azido-proline N-Carboxyanhydride

Polyproline is a material of great interest in biomedicine due to its helical scaffold of structural importance in collagen and mucins and its ability to gel and to change conformations in response to temperature. Appending of function-modulating chemical groups to such a material is desirable to diversify potential applications. Here, we describe the synthesis of high-molecular-weight homo, block, and statistical polymers of azide-functionalized proline. The azide groups served as moieties for highly efficient click-grafting, as stabilizers of the polyproline PPII helix, and as modulators of thermoresponsiveness. Saccharides and ethylene glycol were utilized to explore small-molecule grafting, and glutamate polymers were utilized to form polyelectrolyte bottlebrush architectures. Secondary structure effects of both the azide and click modifications, as well as lower critical solution temperature behavior, were characterized. The polyazidoprolines and click products were well tolerated by live human cells and are expected to find use in diverse biomedical applications.

Biocompatible cationic polypeptoids with antibacterial selectivity depending on hydrophobic carbon chain length

The overuse of antibiotics has triggered a new infection crisis and natural antimicrobial peptides (AMPs) have been extensively studied as an alternative to fight microorganisms. Polypeptoids, or polypeptide-biomimetics, offer similar properties to polypeptides and a highly tunable structure that has been synthesized by various methods such as ring opening polymerization (ROP) using N-carboxyanhydride monomers. Simultaneous high antibacterial activity and biocompatibility of a structure by efficient synthesis is desired in the application of those materials. Herein, a series of cationic polypeptoids (PNBs) with variable side chain lengths was obtained by introducing positive charges to the main chain in one step and preserving the backbone structure, namely polypeptoids (PNBM, PNBE, PNBB) with different end groups (methyl (M), ethyl (E), butyl (B)). To address the issue of infection in interventional biomedical implants, we report cost-effective modified polyurethane (PU) films (PU-PNBM, PU-PNBE, PU-PNBB) as physical-biological synergistic antibacterial surfaces that overcome problems such as steric hindrance and the solubility of the materials. Antibacterial selectivity was achieved by regulating the different side chain lengths. When methyl and ethyl were used as hydrophobic side chains, they can only selectively kill Gram-positive Staphylococcus aureus. PNBB, the most hydrophobic and with a butyl side chain can kill both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus and inhibit the growth of bacterial biofilms. Effective in both solution and modified substrate, its biocompatibility is not compromised while the antibacterial properties are substantially improved. Furthermore, PU-PNBB films demonstrated their potential in vivo antimicrobial efficiency in a model of S. aureus infection established on mouse skin. The synthesis route and the surface modification strategies are convenient, providing a solution to the problem of poor biocompatibility in antimicrobial surface applications and a strategy for the use of peptide polymers for targeted therapy after specific infections in the biomedical field.

A hybrid approach for coarse-graining helical peptoids: Solvation, secondary structure, and assembly

Protein mimics such as peptoids form self-assembled nanostructures whose shape and function are governed by the side chain chemistry and secondary structure. Experiments have shown that a peptoid sequence with a helical secondary structure assembles into microspheres that are stable under various conditions. The conformation and organization of the peptoids within the assemblies remains unknown and is elucidated in this study via a hybrid, bottom-up coarse-graining approach. The resultant coarse-grained (CG) model preserves the chemical and structural details that are critical for capturing the secondary structure of the peptoid. The CG model accurately captures the overall conformation and solvation of the peptoids in an aqueous solution. Furthermore, the model resolves the assembly of multiple peptoids into a hemispherical aggregate that is in qualitative agreement with the corresponding results from experiments. The mildly hydrophilic peptoid residues are placed along the curved interface of the aggregate. The composition of the residues on the exterior of the aggregate is determined by two conformations adopted by the peptoid chains. Hence, the CG model simultaneously captures sequence-specific features and the assembly of a large number of peptoids. This multiscale, multiresolution coarse-graining approach could help in predicting the organization and packing of other tunable oligomeric sequences of relevance to biomedicine and electronics.

Principles of glycocalyx engineering with hydrophobic-anchored synthetic mucins

The cellular glycocalyx is involved in diverse biological phenomena in health and disease. Yet, molecular level studies have been challenged by a lack of tools to precisely manipulate this heterogeneous structure. Engineering of the cell surface using insertion of hydrophobic-terminal materials has emerged as a simple and efficient method with great promise for glycocalyx studies. However, there is a dearth of information about how the structure of the material affects membrane insertion efficiency and resulting density, the residence time of the material, or what types of cells can be utilized. Here, we examine a panel of synthetic mucin structures terminated in highly efficient cholesterylamide membrane anchors for their ability to engineer the glycocalyx of five different cell lines. We examined surface density, residence time and half-life, cytotoxicity, and the ability be passed to daughter cells. We report that this method is robust for a variety of polymeric structures, long-lasting, and well-tolerated by a variety of cell lines.

A Field Guide to Optimizing Peptoid Synthesis

N-Substituted glycines (peptoids) are a class of peptidomimetic molecules used as materials for health, environmental, and drug delivery applications. Automated solid-phase synthesis is the most widely used approach for preparing polypeptoids, with a range of published protocols and modifications for selected synthetic targets. Simultaneously, emerging solution-phase syntheses are being leveraged to overcome limitations in solid-phase synthesis and access high-molecular weight polypeptoids. This Perspective aims to outline strategies for the optimization of both solid- and solution-phase synthesis, provide technical considerations for robotic synthesizers, and offer an outlook on advances in synthetic methodologies. The solid-phase synthesis sections explore steps for protocol optimization, accessing complex side chains, and adaptation to robotic synthesizers; the sections on solution-phase synthesis cover the selection of initiators, side chain compatibility, and strategies for controlling polymerization efficiency and scale. This text acts as a "field guide" for researchers aiming to leverage the flexibility and adaptability of peptoids in their research.

Advance in Hybrid Peptides Synthesis

Hybrid peptides with heterogeneous backbone are a class of peptide mimics with adjustable proteolytic stability obtained from incorporating unnatural amino acid residues into peptide backbone. α/β-peptides and peptide/peptoid hybrids are two types of hybrid peptides that are widely studied for diverse applications, and several synthetic methods have been developed. In this mini review, the advance in hybrid peptide synthesis is summarized, including solution-phase method, solid-phase method, and novel polymerization method. Conventional solution-phase method and solid-phase method generally result in oligomers with defined sequences, while polymerization methods have advantages in preparing peptide hybrid polymers with high molecular weight with simple operation and low cost. In addition, the future development of polymerization method to realize the control of the peptide hybrid polymer sequence is discussed.

Exploring the potential of polypeptide–polypeptoide hybrid nanogels for mucosal delivery

By chain extension of polysarcosine with phenylalanine and cystine, nanogels are formed. The nanogels facilitate the transport of dyes across an artificial mucus coated membrane and their release by reductive bond cleavage.