Synthesis, derivatization, and conformational scanning of peptides containing N-Aminoglycine.

N-alkylated glycine residues are the main constituent of peptoids and peptoid-peptide hybrids that are employed across the biomedical and materials sciences. While the impact of backbone N-alkylation on peptide conformation has been extensively studied, less is known about the effect of N-amination on the secondary structure propensity of glycine. Here, we describe a convenient protocol for the incorporation of N-aminoglycine into host peptides on solid support. Amide-to-hydrazide substitution also affords a nucleophilic handle for further derivatization of the backbone. To demonstrate the utility of late-stage hydrazide modification, we synthesized and evaluated the stability of polyproline II helix and ß-hairpin model systems harboring N-aminoglycine derivatives. The described procedures provide facile entry into peptidomimetic libraries for conformational scanning.

Design of Triazolium-Grafted Peptidomimetic Macrocycles with Facial Amphipathicity to Target Pathogenic Bacteria.

Access to 1,2,3-triazolium-grafted peptoid macrocycles was developed by macrocyclization and multivalent postmodification of linear peptoid oligomers carrying an alternance of benzylic and propargyl groups as side chains. X-ray analysis and NMR studies revealed a conformational preference for constrained hairpin-shaped structures leading to the facial amphipathic character of these macrocycles. A preliminary evaluation showed the antimicrobial activities of these new cationic amphipathic architectures.

Preferential HDAC6 inhibitors derived from HPOB exhibit synergistic antileukemia activity in combination with decitabine.

Histone deacetylase 6 (HDAC6) is an emerging drug target to treat oncological and non-oncological conditions. Since highly selective HDAC6 inhibitors display limited anticancer activity when used as single agent, they usually require combination therapies with other chemotherapeutics. In this work, we synthesized a mini library of analogues of the preferential HDAC6 inhibitor HPOB in only two steps via an Ugi four-component reaction as the key step. Biochemical HDAC inhibition and cell viability assays led to the identification of 1g (highest antileukemic activity) and 2b (highest HDAC6 inhibition) as hit compounds. In subsequent combination screens, both 1g and especially 2b showed synergy with DNA methyltransferase inhibitor decitabine in acute myeloid leukemia (AML). Our findings highlight the potential of combining HDAC6 inhibitors with DNA methyltransferase inhibitors as a strategy to improve AML treatment outcomes.

Rationally Designed Peptoid Inhibitors of Amyloid-ß Oligomerization.

While plaques comprised of fibrillar Aß aggregates are hallmarks of Alzheimer's disease, soluble Aß oligomers present higher neurotoxicity. Thus, one therapeutic approach is to prevent the formation of Aß oligomers and reduce their associated harmful effects. We have proposed a peptoid mimic of the Aß hydrophobic KLVFF core as an ideal candidate aggregation inhibitor due to its ability to evade proteolytic degradation via repositioning of the side chain from the α-carbon to the amide nitrogen. This peptoid, JPT1, utilizes chiral sidechains to achieve a helical structure, while C-terminal addition of two phenylalanine residues places aromatic groups on two sides of the helix with spacing designed to facilitate interaction with amyloid ß-sheet structure. We have previously shown that JPT1 modulates Aß fibril formation. Here, we demonstrate that JPT1 also modulates Aß oligomerization, and we explore the role of the charge on the linker between the KLVFF mimic and the extended aromatic residues. Additionally, we demonstrate that peptoid-induced changes in Aß oligomerization correlate with attenuation of oligomer-induced nuclear factor-κB activation in SH-SY5Y human neuroblastoma cells. These findings support the therapeutic potential of peptoids to target early stages of Aß aggregation and impact the associated Aß-induced cellular response.

Anti-Neuroinflammatory Effects of a Macrocyclic Peptide-Peptoid Hybrid in Lipopolysaccharide-Stimulated BV2 Microglial Cells.

Inflammation processes of the central nervous system (CNS) play a vital role in the pathogenesis of several neurological and psychiatric disorders like depression. These processes are characterized by the activation of glia cells, such as microglia. Clinical studies showed a decrease in symptoms associated with the mentioned diseases after the treatment with anti-inflammatory drugs. Therefore, the investigation of novel anti-inflammatory drugs could hold substantial potential in the treatment of disorders with a neuroinflammatory background. In this in vitro study, we report the anti-inflammatory effects of a novel hexacyclic peptide-peptoid hybrid in lipopolysaccharide (LPS)-stimulated BV2 microglial cells. The macrocyclic compound X15856 significantly suppressed Interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α), c-c motif chemokine ligand 2 (CCL2), CCL3, C-X-C motif chemokine ligand 2 (CXCL2), and CXCL10 expression and release in LPS-treated BV2 microglial cells. The anti-inflammatory effects of the compound are partially explained by the modulation of the phosphorylation of p38 mitogen-activated protein kinases (MAPK), p42/44 MAPK (ERK 1/2), protein kinase C (PKC), and the nuclear factor (NF)-κB, respectively. Due to its remarkable anti-inflammatory properties, this compound emerges as an encouraging option for additional research and potential utilization in disorders influenced by inflammation, such as depression.

Hierarchical Self-Assembly of Multidimensional Functional Materials from Sequence-Defined Peptoids.

Hierarchical self-assembly represents a powerful strategy for the fabrication of functional materials across various length scales. However, achieving precise formation of functional hierarchical assemblies remains a significant challenge and requires a profound understanding of molecular assembly interactions. In this study, we present a molecular-level understanding of the hierarchical assembly of sequence-defined peptoids into multidimensional functional materials, including twisted nanotube bundles serving as a highly efficient artificial light harvesting system. By employing synchrotron-based powder X-ray diffraction and analyzing single crystal structures of model compounds, we elucidated the molecular packing and mechanisms underlying the assembly of peptoids into multidimensional nanostructures. Our findings demonstrate that incorporating aromatic functional groups, such as tetraphenyl ethylene (TPE), at the termini of assembling peptoid sequences promotes the formation of twisted bundles of nanotubes and nanosheets, thus enabling the creation of a highly efficient artificial light harvesting system. This research exemplifies the potential of leveraging sequence-defined synthetic polymers to translate microscopic molecular structures into macroscopic assemblies. It holds promise for the development of functional materials with precisely controlled hierarchical structures and designed functions.

Assembly of short amphiphilic peptoids into nanohelices with controllable supramolecular chirality.

A long-standing challenge in bioinspired materials is to design and synthesize synthetic materials that mimic the sophisticated structures and functions of natural biomaterials, such as helical protein assemblies that are important in biological systems. Herein, we report the formation of a series of nanohelices from a type of well-developed protein-mimetics called peptoids. We demonstrate that nanohelix structures and supramolecular chirality can be well-controlled through the side-chain chemistry. Specifically, the ionic effects on peptoids from varying the polar side-chain groups result in the formation of either single helical fiber or hierarchically stacked helical bundles. We also demonstrate that the supramolecular chirality of assembled peptoid helices can be controlled by modifying assembling peptoids with a single chiral amino acid side chain. Computational simulations and theoretical modeling predict that minimizing exposure of hydrophobic domains within a twisted helical form presents the most thermodynamically favorable packing of these amphiphilic peptoids and suggests a key role for both polar and hydrophobic domains on nanohelix formation. Our findings establish a platform to design and synthesize chiral functional materials using sequence-defined synthetic polymers.

Dimeric peptoids as antibacterial agents.

Building upon our previous study on peptoid-based antibacterials which showed good activity against Gram-positive bacteria only, herein we report the synthesis of 34 dimeric peptoid compounds and the investigation of their activity against Gram-positive and Gram-negative pathogens. The newly designed peptoids feature a di-hydrophobic moiety incorporating phenyl, bromo-phenyl, and naphthyl groups, combined with variable lengths of cationic units such as amino and guanidine groups. The study also underscores the pivotal interplay between hydrophobicity and cationicity in optimizing efficacy against specific bacteria. The bromophenyl dimeric guanidinium peptoid compound 10j showed excellent activity against S. aureus 38 and E. coli K12 with MIC of 0.8 µg mL-1 and 6.2 µg mL-1, respectively. Further investigation into the mechanism of action revealed that the antibacterial effect might be attributed to the disruption of bacterial cell membranes, as suggested by tethered bilayer lipid membranes (tBLMs) and cytoplasmic membrane permeability studies. Notably, these promising antibacterial agents exhibited negligible toxicity against mammalian red blood cells. Additionally, the study explored the potential of 12 active compounds to disrupt established biofilms of S. aureus 38. The most effective biofilm disruptors were ethyl and octyl-naphthyl guanidinium peptoids (10c and 10 k). These compounds 10c and 10 k disrupted the established biofilms of S. aureus 38 with 51 % at 4x MIC (MIC = 17.6 µg mL-1 and 11.2 µg mL-1) and 56 %-58 % at 8x MIC (MIC = 35.2 µg mL-1 and 22.4 µg mL-1) respectively. Overall, this research contributes insights into the design principles of cationic dimeric peptoids and their antibacterial activity, with implications for the development of new antibacterial compounds.

Access to Advanced Functional Materials through Postmodification of Biomimetic Assemblies via Click Chemistry.

The design, synthesis, and fabrication of functional nanomaterials with specific properties remain a long-standing goal for many scientific fields. The self-assembly of sequence-defined biomimetic synthetic polymers presents a fundamental strategy to explore the chemical space beyond biological systems to create advanced nanomaterials. Moreover, subsequent chemical modification of existing nanostructures is a unique approach for accessing increasingly complex nanostructures and introducing functionalities. Of these modifications, covalent conjugation chemistries, such as the click reactions, have been the cornerstone for chemists and materials scientists. Herein, we highlight some recent advances that have successfully employed click chemistries for the postmodification of assembled one-dimensional (1D) and two-dimensional (2D) nanostructures to achieve applications in molecular recognition, mineralization, and optoelectronics. Specifically, biomimetic nanomaterials assembled from sequence-defined macromolecules such as peptides and peptoids are described.

Supramolecular Peptoid Structure Strengthens Complexation with Polyacrylic Acid Microgels.

We have studied the complexation between cationic antimicrobials and polyanionic microgels to create self-defensive surfaces that responsively resist bacterial colonization. An essential property is the stable sequestration of the loaded (complexed) antimicrobial within the microgel under a physiological ionic strength. Here, we assess the complexation strength between poly(acrylic acid) [PAA] microgels and a series of cationic peptoids that display supramolecular structures ranging from an oligomeric monomer to a tetramer. We follow changes in loaded microgel diameter with increasing [Na+] as a measure of the counterion doping level. Consistent with prior findings on colistin/PAA complexation, we find that a monomeric peptoid is fully released at ionic strengths well below physiological conditions, despite its +5 charge. In contrast, progressively higher degrees of peptoid supramolecular structure display progressively greater resistance to salting out, which we attribute to the greater entropic stability associated with the complexation of multimeric peptoid bundles.

Antiviral effect of peptoids on hepatitis B virus infection in cell culture.

Although antimicrobial peptides have been shown to inactivate viruses through disruption of their viral envelopes, clinical use of such peptides has been hampered by a number of factors, especially their enzymatically unstable structures. To overcome the shortcomings of antimicrobial peptides, peptoids (sequence-specific N-substituted glycine oligomers) mimicking antimicrobial peptides have been developed. We aimed to demonstrate the antiviral effects of antimicrobial peptoids against hepatitis B virus (HBV) in cell culture. The anti-HBV activity of antimicrobial peptoids was screened and evaluated in an infection system involving the HBV reporter virus and HepG2.2.15-derived HBV. By screening with the HBV reporter virus infection system, three (TM1, TM4, and TM19) of 12 peptoids were identified as reducing the infectivity of HBV, though they did not alter the production levels of HBs antigen in cell culture. These peptoids were not cytotoxic at the evaluated concentrations. Among these peptoids, TM19 was confirmed to reduce HBV infection most potently in a HepG2.2.15-derived HBV infection system that closely demonstrates authentic HBV infection. In cell culture, the most effective administration of TM19 was virus treatment at the infection step, but the reduction in HBV infectivity by pre-treatment or post-treatment of cells with TM19 was minimal. The disrupting effect of TM19 targeting infectious viral particles was clarified in iodixanol density gradient analysis. In conclusion, the peptoid TM19 was identified as a potent inhibitor of HBV. This peptoid prevents HBV infection by disrupting viral particles and is a candidate for a new class of anti-HBV reagents.

Synthesis and Structural Characterization of Macrocyclic α-ABpeptoids and Their DNA-Encoded Library.

The first synthesis of macrocyclic α-ABpeptoids with varying lengths is described. X-ray crystal structures reveal that cyclic trimer displays a chair-like conformation with a cct amide sequence and cyclic tetramer has a saddle-like structure with an uncommon cccc amide arrangement. The creation of a DNA-encoded combinatorial library of macrocyclic α-ABpeptoids is described.

Influence of Peptoid Sequence on the Mechanisms and Kinetics of 2D Assembly.

Two-dimensional (2D) materials have attracted intense interest due to their potential for applications in fields ranging from chemical sensing to catalysis, energy storage, and biomedicine. Recently, peptoids, a class of biomimetic sequence-defined polymers, have been found to self-assemble into 2D crystalline sheets that exhibit unusual properties, such as high chemical stability and the ability to self-repair. The structure of a peptoid is close to that of a peptide except that the side chains are appended to the amide nitrogen rather than the α carbon. In this study, we investigated the effect of peptoid sequence on the mechanism and kinetics of 2D assembly on mica surfaces using in situ AFM and time-resolved X-ray scattering. We explored three distinct peptoid sequences that are amphiphilic in nature with hydrophobic and hydrophilic blocks and are known to self-assemble into 2D sheets. The results show that their assembly on mica starts with deposition of aggregates that spread to establish 2D islands, which then grow by attachment of peptoids, either monomers or unresolvable small oligomers, following well-known laws of crystal step advancement. Extraction of the solubility and kinetic coefficient from the dependence of the growth rate on peptoid concentration reveals striking differences between the sequences. The sequence with the slowest growth rate in bulk and with the highest solubility shows almost no detachment; i.e., once a growth unit attaches to the island edge, there is almost no probability of detaching. Furthermore, a peptoid sequence with a hydrophobic tail conjugated to the final carboxyl residue in the hydrophilic block has enhanced hydrophobic interactions and exhibits rapid assembly both in the bulk and on mica. These assembly outcomes suggest that, while the π-π interactions between adjacent hydrophobic blocks play a major role in peptoid assembly, sequence details, particularly the location of charged groups, as well as interaction with the underlying substrate can significantly alter the thermodynamic stability and assembly kinetics.

Conformational Studies of ß-Azapeptoid Foldamers: A New Class of Peptidomimetics with Confined Dihedrals.

Controlling amide bond geometries and the secondary structures of ß-peptoids is a challenging task as they contain several rotatable single bonds in their backbone. Herein, we describe the synthesis and conformational properties of novel "ß-azapeptoids" with confined dihedrals. We discuss how the acylhydrazide sidechains in these molecules enforce trans amide geometries (ω ~180°) via steric and stereoelectronic effects. We also show that the Θ(Cα -Cß ) and Ψ(OC-Cα ) backbone torsions of ß-azapeptoids occupy a narrow range (170-180°) that can be rationalized by the staggered conformational preference of the backbone methylene carbons and a novel backbone nO →σ*Cß-N interaction discovered in this study. However, the ϕ (Cß -N) torsion remains freely rotatable and, depending on ϕ, the sidechains can be parallel, perpendicular, and anti-parallel relative to each other. In fact, we observed parallel and perpendicular relative orientations of sidechains in the crystal geometries of ß-azapeptoid dimers. We show that ϕ of ß-azapeptoids can be controlled by incorporating a bulky substituent at the backbone ß-carbon, which could provide complete control over all the backbone dihedrals. Finally, we show that the ϕ and Ψ dihedrals of ß-azapeptoids resemble that of a PPII helix and they retain PPII structure when incorporated in Host-guest proline peptides.

2-Pyridone Formation: An Efficient Method for the Solid-Phase Synthesis of Homodimers.

This study presents an efficient method for on-resin dimer generation through self-condensation of 3,3-dimethoxypropionic acid-modified molecules, resulting in 2-pyridones. The approach demonstrated remarkable versatility by producing homodimers of peptides, peptoids, and non-peptidic ligands. Its ease of application, broad utility, and mild reaction conditions not only hold significance for peptide and peptoid research but also offer potential for the on-resin development of a wide range of bivalent ligands.

Structural Element of Vitamin U-Mimicking Antibacterial Polypeptide with Ultrahigh Selectivity for Effectively Treating MRSA Infections.

Antimicrobial peptides (AMPs) exhibit mighty antibacterial properties without inducing drug resistance. Achieving much higher selectivity of AMPs towards bacteria and normal cells has always been a continuous goal to be pursued. Herein, a series of sulfonium-based polypeptides with different degrees of branching and polymerization were synthesized by mimicking the structure of vitamin U. The polypeptide, G2 -PM-1H+ , shows both potent antibacterial activity and the highest selectivity index of 16000 among the reported AMPs or peptoids (e.g., the known index of 9600 for recorded peptoid in "Angew. Chem. Int. Ed., 2020, 59, 6412."), which can be attributed to the high positive charge density of sulfonium and the regulation of hydrophobic chains in the structure. The antibacterial mechanisms of G2 -PM-1H+ are primarily ascribed to the interaction with the membrane, production of reactive oxygen species (ROS), and disfunction of ribosomes. Meanwhile, altering the degree of alkylation leads to selective antibacteria against either gram-positive or gram-negative bacteria in a mixed-bacteria model. Additionally, both in vitro and in vivo experiments demonstrated that G2 -PM-1H+ exhibited superior efficacy against methicillin-resistant Staphylococcus aureus (MRSA) compared to vancomycin. Together, these results show that G2 -PM-1H+ possesses high biocompatibility and is a potential pharmaceutical candidate in combating bacteria significantly threatening human health.

Peptoids: Smart and Emerging Candidates for the Diagnosis of Cancer, Neurological and Autoimmune Disorders.

Early detection of fatal and disabling diseases such as cancer, neurological and autoimmune dysfunctions is still desirable yet challenging to improve quality of life and longevity. Peptoids (N-substituted glycine oligomers) are a relatively new class of peptidomimetics, being highly versatile and capable of mimicking the architectures and the activities of the peptides but with a marked resistance to proteases and a propensity to cross the cellular membranes over the peptides themselves. For these properties, they have gained an ever greater interest in applications in bioengineering and biomedical fields. In particular, the present manuscript is to our knowledge the only review focused on peptoids for diagnostic applications and covers the last decade's literature regarding peptoids as tools for early diagnosis of pathologies with a great impact on human health and social behavior. The review indeed provides insights into the peptoid employment in targeted cancer imaging and blood-based screening of neurological and autoimmune diseases, and it aims to attract the scientific community's attention to continuing and sustaining the investigation of these peptidomimetics in the diagnosis field considering their promising peculiarities.

Cis-trans isomerization of peptoid residues in the collagen triple-helix.

Cis-peptide bonds are rare in proteins, and building blocks less favorable to the trans-conformer have been considered destabilizing. Although proline tolerates the cis-conformer modestly among all amino acids, for collagen, the most prevalent proline-abundant protein, all peptide bonds must be trans to form its hallmark triple-helix structure. Here, using host-guest collagen mimetic peptides (CMPs), we discover that surprisingly, even the cis-enforcing peptoid residues (N-substituted glycines) form stable triple-helices. Our interrogations establish that these peptoid residues entropically stabilize the triple-helix by pre-organizing individual peptides into a polyproline-II helix. Moreover, noting that the cis-demanding peptoid residues drastically reduce the folding rate, we design a CMP whose triple-helix formation can be controlled by peptoid cis-trans isomerization, enabling direct targeting of fibrotic remodeling in myocardial infarction in vivo. These findings elucidate the principles of peptoid cis-trans isomerization in protein folding and showcase the exploitation of cis-amide-favoring residues in building programmable and functional peptidomimetics.

Peptidomimetic Oligomers Targeting Membrane Phosphatidylserine Exhibit Broad Antiviral Activity.

The development of durable new antiviral therapies is challenging, as viruses can evolve rapidly to establish resistance and attenuate therapeutic efficacy. New compounds that selectively target conserved viral features are attractive therapeutic candidates, particularly for combating newly emergent viral threats. The innate immune system features a sustained capability to combat pathogens through production of antimicrobial peptides (AMPs); however, these AMPs have shortcomings that can preclude clinical use. The essential functional features of AMPs have been recapitulated by peptidomimetic oligomers, yielding effective antibacterial and antifungal agents. Here, we show that a family of AMP mimetics, called peptoids, exhibit direct antiviral activity against an array of enveloped viruses, including the key human pathogens Zika, Rift Valley fever, and chikungunya viruses. These data suggest that the activities of peptoids include engagement and disruption of viral membrane constituents. To investigate how these peptoids target lipid membranes, we used liposome leakage assays to measure membrane disruption. We found that liposomes containing phosphatidylserine (PS) were markedly sensitive to peptoid treatment; in contrast, liposomes formed exclusively with phosphatidylcholine (PC) showed no sensitivity. In addition, chikungunya virus containing elevated envelope PS was more susceptible to peptoid-mediated inactivation. These results indicate that peptoids mimicking the physicochemical characteristics of AMPs act through a membrane-specific mechanism, most likely through preferential interactions with PS. We provide the first evidence for the engagement of distinct viral envelope lipid constituents, establishing an avenue for specificity that may enable the development of a new family of therapeutics capable of averting the rapid development of resistance.

N-substituting perturbation on the interaction affinity and recognition specificity between rheumatic immune-related Abl SH3 domain and its peptoid ligands.

Abl is a nonreceptor tyrosine kinase involved in a variety of disease pathways such as rheumatic immune. Full-length Abl protein consists of a catalytic tyrosine kinase (TK) domain as well as two regulatory Src homology domains 2 and 3 (SH2 and SH3, respectively); the latter recognizes and binds to those natural proline-rich peptide segments containing a PxxP motif on the protein surface of its interacting partners. However, natural peptides cannot bind effectively to the modular domain in high affinity and strong selectivity due to their small size and broad specificity. Here, a synthetic proline-rich peptide p41 was used as template; its structural diversity was extended by combinationally replacing the Pro0 and Pro+3 residues with a number of N-substituted amino acids. Consequently, peptide affinity change upon the replacement was derived to create a systematic N-substituting perturbation profile, from which we identified several N-substitution combinations at the Pro0 and Pro+3 residues of p41 PxxP motif that may moderately or significantly improve the peptide binding potency to Abl; they represent potent peptoid binders of Abl SH3 domain, with affinity improved considerably relative to p41. More significantly, the designed potent peptoids were also found to exhibit a good SH3-selectivity for their cognate Abl over other noncognate nonreceptor tyrosine kinases, with S = 9.7-fold.