Incorporation of unprotected heterocyclic side chains into peptoid oligomers via solid-phase submonomer synthesis

Antimicrobial peptides as potential therapy for gastrointestinal cancers

Since conventional therapy faces limitations in the field of different cancers as well as gastrointestinal cancers, that decrease the survival rate of patients, there is an urgent need to find new effective therapeutic approaches without the adverse effects of the traditional agents. Antimicrobial peptides (AMPs) attract much attention and are well known for their role in innate immunity. These peptides, in addition to their antimicrobial activity, exhibit strong anticancer potential against various types of malignancy. AMPs specifically target tumor cells and have selective toxicity for these cells without affecting normal cells. Here we aim to comprehensively overview the current knowledge in the field of using AMPs as novel therapeutic agents for gastrointestinal cancer.

Late-Stage Chloride Displacements Enable Access to Peptoids with cis-Inducing Alkylammonium Side Chains

The synthesis of peptoids possessing multiple cis-inducing monomers with alkylammonium side chains is reported, where chloropropyl side chains are diversified on a solid support by late-stage SN2 displacements with amines. The conditions were optimized for a wide variety of primary, secondary, and tertiary alkyl amine nucleophiles. We also demonstrated that multiple chloride displacements could be achieved on sequences possessing trans-inducing N-aryl- and N-imino glycine monomers.

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.

Iterative Synthesis of Stereo- and Sequence-Defined Polymers via Acid-Orthogonal Deprotection Chemistry

Absolute control over polymer stereo- and sequence structure is highly challenging in polymer chemistry. Here, an acid-orthogonal deprotection strategy is proposed for the iterative synthesis of a family of unimolecular polymers starting with enantiopure serines, featuring precise sequence, stereoconfiguration and side-chain functionalities that cannot be achieved using traditional polymerization techniques. Acid-orthogonal deprotections proceed independently of one another by the selection of protecting groups that feature the respective acid-lability. Under p-toluenesulfonic acid, acidolysis of tert-butyloxycarbonyl can proceed exclusively, while low-dosage trifluoroacetic acid and low temperature only trigger the selective and quantitative cleavage of trityl. The pioneering use of this acid-orthogonal deprotection chemistry increases the compatibility with otherwise sensitive groups and opens up pathways to facilely introduce structural and functional diversity into stereo- and sequence-defined polymers, thus imparting their unique properties beyond natural biopolymers.

Bio-instructive materials on-demand - combinatorial chemistry of peptoids, foldamers, and beyond

Combinatorial chemistry allows for the rapid synthesis of large compound libraries for high throughput screenings in biology, medicinal chemistry, or materials science. Especially compounds from a highly modular design are interesting for the proper investigation of structure-to-activity relationships. Permutations of building blocks result in many similar but unique compounds. The influence of certain structural features on the entire structure can then be monitored and serve as a starting point for the rational design of potent molecules for various applications. Peptoids, a highly diverse class of bioinspired oligomers, suit perfectly for combinatorial chemistry. Their straightforward synthesis on a solid support using repetitive reaction steps ensures easy handling and high throughput. Applying this modular approach, peptoids are readily accessible, and their interchangeable side-chains allow for various structures. Thus, peptoids can easily be tuned in their solubility, their spatial structure, and, consequently, their applicability in various fields of research. Since their discovery, peptoids have been applied as antimicrobial agents, artificial membranes, molecular transporters, and much more. Studying their three-dimensional structure, various foldamers with fascinating, unique properties were discovered. This non-comprehensive review will state the most interesting discoveries made over the past years and arouse curiosity about what may come.

Submonomer synthesis of sequence defined peptoids with diverse side-chains

Peptoids are a diverse family of sequence-defined oligomers of N-substituted glycine monomers, that can be readily accessed by the solid-phase submonomer synthesis method. Due to the versatility and efficiency of this chemistry, and the easy access to hundreds of potential monomers, there is an enormous potential sequence space that can be explored. This has enabled researchers from many different fields to custom-design peptoid sequences tailored to a wide variety of problems in biomedicine, nanoscience and polymer science. Here we provide detailed protocols for the synthesis of peptoids, using optimized protocols that can be performed by non-chemists. The submonomer method is fully compatible with Fmoc-peptide synthesis conditions, so the method is readily automated on existing automated peptide synthesizers using protocols provided here. Although the submonomer synthesis for peptoids is well established, there are special considerations required in order to access many of the most useful and desirable sidechains. Here we provide methods to include most of the amino-acid-like side chains, some of the most important non-natural monomer classes, as well as the creation of peptoid conjugates and peptide-peptoid hybrids.

Submonomer synthesis of peptoids containing trans-inducing N-imino- and N-alkylamino-glycines

The use of hydrazones as a new type of submonomer in peptoid synthesis is described, giving access to peptoid monomers that are structure-inducing. A wide range of hydrazones were found to readily react with α-bromoamides in routine solid phase peptoid submonomer synthesis. Conditions to promote a one-pot cleavage of the peptoid from the resin and reduction to the corresponding N-alkylamino side chains were also identified, and both the N-imino- and N-alkylamino glycine residues were found to favor the trans-amide bond geometry by NMR, X-ray crystallography, and computational analyses.

Sequence-controlled and sequence-defined polypeptoids via the Ugi reaction: synthesis and sequence-driven properties

Ugi reaction offers opportunities to facilely access unprecedented sequence control and sequence-driven properties in polypeptoids.

Ugi Reaction of Amino Acids: From Facile Synthesis of Polypeptoids to Sequence-Defined Macromolecules

Polypeptoids have been prepared and researched for more than 20 years. However, the efficient generation of polypeptoids and sequence-defined polypeptoids faces many challenges and difficulties. The Ugi reaction of amino acids has recently been introduced into polypeptoid chemistry as a new and powerful method to furnish polypeptoids. In the following mini review, the recent progress on the application of the Ugi reaction of amino acids in polypeptoid science, including polypeptoid from sustainable furfural, sequence-defined polypeptoids, and more is summarized. Moreover, the future development of the Ugi reaction of amino acids in polypeptoid science is discussed.

Synthesis of Peptoids Containing Multiple Nhtrp and Ntrp Residues: A Comparative Study of Resin, Cleavage Conditions and Submonomer Protection

Peptoids hold status as peptide-mimetics with versatile biological applications due to their proteolytic stability and structural diversity. Among those that have been studied in different biological systems, are peptoids with dominant balanced hydrophobic and charge distribution along the backbone. Tryptophan is an important amino acid found in many biologically active peptides. Tryptophan-like side chains in peptoids allow H-bonding, which is absent from the parent backbone, due to the unique indole ring. Furthermore, the rigid hydrophobic core and flat aromatic system influence the positioning in the hydrocarbon core and allows accommodating tryptophan-like side chains into the interfacial regions of bacterial membranes and causing bacterial membrane damage. Incorporating multiple tryptophan-like side chains in peptoids can be tricky and there is a lack of suitable, synthetic routes established. In this paper, we investigate the synthesis of peptoids rich in Nhtrp and Ntrp residues using different resins, cleavage conditions, and unprotected as well as tert-butyloxycarbonyl-protected amines suitable for automated solid-phase submonomer peptoid synthesis protocols.

A convenient and efficient total solid-phase synthesis of DOTA-functionalized tumor-targeting peptides for PET imaging of cancer

Introduction

An efficient and cost-effective synthesis of the metal chelating agents that couple to tumor-targeting peptides is required to enhance the process of preclinical research toward the clinical translation of molecular imaging agents. DOTA is one of the most widely used macrocyclic ligands for the development of new metal-based imaging and therapeutic agents owing to its ability to form stable and inert complexes under physiological conditions. Although solid-phase synthesis compatible DOTA-tris-(t-Bu ester) is a commercial product, it is expensive and contain chemical impurities. There is a need to explore new and cost-effective methods for the preparation of metal chelating agents, i.e., DOTA, directly on solid support to facilitate rapid, cost-effective, and high purity preparation of DOTA-linked peptides for imaging and therapy. In the present study, we describe a facile synthetic strategy of DOTA preparation and its linkage to peptides directly on solid-phase support.

Methods

Bombesin (BN) peptides were functionalized with DOTA chelator prepared from cyclen precursor on solid-phase and from commercial DOTA-tris and radiolabeled with ⁶⁸Ga. In vitro BN/GRP receptor binding affinities of the corresponding radiolabeled peptides were determined by saturation binding assays on human breast MDA-MB-231, MCF7, T47D, and PC3 prostate cancer cells. Pharmacokinetics were studied in Balb/c mice and in vivo tumor targeting in MDA-MB-231 tumor-bearing nude mice.

Results

DOTA was prepared successfully from cyclen on solid-phase support, linked specifically to BN peptides and resultant DOTA-coupled peptides were radiolabeled efficiently with ⁶⁸Ga. The binding affinities of all the six BN peptides were comparable and in the low nanomolar range. All ⁶⁸Ga-labeled peptides showed high metabolic stability in plasma. These radiopeptides exhibited rapid pharmacokinetics in Balb/c mice with excretion mainly through the urinary system. In nude mice, MDA-MB-231 tumor uptake profiles were slightly different; the BN peptide with Ahx spacer and linked to DOTA through cyclen exhibited higher tumor uptake (2.32% ID/g at 1 h post-injection) than other radiolabeled BN peptides investigated in this study. The same leading BN peptide also displayed favorable pharmacokinetic profile in Balb/c mice. The PET images clearly visualized the MDA-MB-231 tumor.

Conclusions

DOTA prepared from cyclen on solid-phase support showed comparable potency and efficiency to DOTA-tris in both in vitro and in vivo evaluation. The synthetic methodology described here allows versatile, site-specific introduction of DOTA into peptides to facilitate the development of DOTA-linked molecular imaging and therapy agents for clinical translation.

A study of the cis–trans isomerization preference of N-alkylated peptides containing phosphorus in the side chain and backbone

The current work provides a study on the cis–trans isomerization behaviour of N-alkylated peptides decorated with phosphonate ester groups.

Solid-phase synthesis of biocompatible N-heterocyclic carbene–Pd catalysts using a sub-monomer approach

Biocompatible N-heterocyclic carbene (NHC) based Pd ligands were assembled and loaded with Pd via solid-phase synthesis.

Improved potency and reduced toxicity of the antifungal peptoid AEC5 through submonomer modification

As proteolytically stable peptidomimetics, peptoids could serve as antifungal agents to supplement a therapeutic field wrought with toxicity issues. We report the improvement of an antifungal peptoid, AEC5, through an iterative structure-activity relationship study. A sarcosine scan was used to first identify the most pharmacophorically important peptoid building blocks of AEC5, followed by sequential optimization of each building block. The optimized antifungal peptoid from this study, β-5, has improved potency towards Cryptococcus neoformans and decreased toxicity towards mammalian cells. For example, the selectivity ratio for C. neoformans over mammalian fibroblasts was improved from 8 for AEC5 to 37 for β-5.

Solid-Phase Synthesis of Azole-Comprising Peptidomimetics and Coordination of a Designed Analog to Zn2

Peptidomimetics that can coordinate transition metals have a variety of potential applications as catalysts, sensors, or materials. A new modular peptidomimetic scaffold, the “azole peptoid”, is introduced here. We report methods for the solid-phase synthesis of eleven examples of trimeric N-substituted oligoamides that include oxazole- or thiazole-functionalized backbones. The products prepared comprise a diversity of functionality, including a metal-coordinating terpyridine group. The modular synthetic approach enables ready preparation of analogs for specific applications. To highlight a potential use of this new synthetic scaffold, a trimeric azole peptoid functionalized with a terpyridine residue was prepared and studied. The characteristic 2:1 ligand:metal binding of this terpyridine-functionalized azole peptoid to Zn²⁺ in aqueous solution was observed. These studies introduce azole peptoids as a useful class of biomimetic molecules for further study and application.

Water soluble hydrophobic peptoids via a minor backbone modification

The incorporation of piperazine or homopiperazine within hydrophobic peptoid scaffolds leads to their water solubility while increasing their overall conformational order in water.

A modular platform to develop peptoid-based selective fluorescent metal sensors

Despite the reduction in industrial use of toxic heavy metals, there remain contaminated natural water sources across the world. Herein we present a modular platform for developing selective sensors for toxic metal ions using N-substituted glycine, or peptoid, oligomers coupled to a fluorophore. As a preliminary evaluation of this strategy, structures based on previously identified metal-binding peptoids were synthesized with terminal pyrene moieties. Both derivatives of this initial design demonstrated a turn-off response in the presence of various metal ions. A colorimetric screen was designed to identify a peptoid ligand that chelates Hg(ii). Multiple ligands were identified that were able to deplete Hg(ii) from a solution selectively in the presence of an excess of competing ions. The C-terminal fluoropeptoid derivatives demonstrated similar selectivity to their label-free counterparts. This strategy could be applied to develop sensors for many different metal ions of interest using a variety of fluorophores, leading to a panel of sensors for identifying various water source contaminants.

The Novel Property of Heptapeptide of Microcin C7 in Affecting the Cell Growth of Escherichia coli

Microcin C7 (McC), widely distributed in enterobacteria, is a promising antibiotic against antibiotic resistance [...].

Long, self-assembled molecular ladders by cooperative dynamic covalent reactions

The dynamic covalent self-assembly of peptoid-based oligomers bearing n complementary functional groups yields molecular ladders with n covalent rungs.

An Efficient Method for the Synthesis of Peptoids with Mixed Lysine-type/Arginine-type Monomers and Evaluation of Their Anti-leishmanial Activity

This protocol describes the manual solid-phase synthesis of linear peptoids that contain two differently functionalized cationic monomers. In this procedure amino functionalized 'lysine' and guanido functionalized 'arginine' peptoid monomers can be included within the same peptoid sequence. This procedure uses on-resin (N-(1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl) or Dde protection, orthogonal conditions to the Boc protection of lysine monomers. Subsequent deprotection allows an efficient on-resin guanidinylation reaction to form the arginine residues. The procedure is compatible with the commonly used submonomer method of peptoid synthesis, allowing simple peptoids to be made using common laboratory equipment and commercially available reagents. The representative synthesis, purification and characterization of two mixed peptoids is described. The evaluation of these compounds as potential anti-infectives in screening assays against Leishmania mexicana is also described. The protozoan parasite L. mexicana is a causative agent of cutaneous leishmaniasis, a neglected tropical disease that affects up to 12 million people worldwide.

Rapid identification of metal-binding peptoid oligomers by on-resin X-ray fluorescence screening

N-Substituted glycine peptoid oligomers have recently attracted attention for their metal binding capabilities. Due to their efficient synthesis on solid phase, peptoids are well suited for generation of compound libraries, followed by screening for molecular recognition and other diverse functional attributes. Ideally, peptoids could be simultaneously screened for binding to a number of metal species. Here, we demonstrate the use of bench-top X-ray fluorescence (XRF) instrumentation to screen rapidly, on solid support, a library of peptoid oligomers incorporating metal-binding functionalities. A subset of the peptoid sequences exhibited significant metal binding capabilities, including a peptoid pentamer and a nonamer that were shown to selectively bind nickel. The binding capabilities were validated by colorimetric assay and by depletion of Ni(2+) ion concentration from solution, establishing bench-top XRF as a rapid, practicable high-throughput screening technique for peptoid oligomers. This protocol will facilitate discovery of metallopeptoids with unique material properties.

A Peptoid-Based Fluorescent Sensor for Cyanide Detection

Peptoids, N-substituted glycine oligomers, are versatile peptidomimetics with diverse biomedical applications. However, strategies to the development of novel fluorescent peptoids as chemical sensors have not been extensively explored, yet. Here, we synthesized a novel peptoid-based fluorescent probe in which a coumarin moiety was incorporated via copper(I)-catalyzed azide-alkyne cycloaddition reaction. Fluorescence of the newly generated coumarin-peptoid was dramatically quenched upon coordination of the Cu(2+) ion, and the resulting peptoid-Cu(2+) complex exhibited significant Turn-ON fluorescence following the addition of CN(-). The rapid and reversible response, combined with cyanide selectivity of the synthesized peptoid, reflects a multistep photo-process and supports its utility as a new type of CN(-) sensor.

Peptidines: glycine-amidine-based oligomers for solution- and solid-phase synthesis

Efforts to emulate biological oligomers have given rise to a host of useful technologies, ranging from solid-phase peptide and nucleic acid synthesis to various peptidomimetic platforms. Herein we introduce a novel class of peptide-like oligomers called "peptidines" wherein each carbonyl O-atom within poly-N-alkyl glycine oligomers is replaced with a functionalized N-atom. Compared to peptoids or peptides, the presence of this amidine N-substituent in peptidines effectively doubles the number of diversification sites per monomeric unit, and can decrease their overall conformational flexibility. We have developed iterative solution- and solid-phase protocols for the straightforward assembly of peptidines containing diverse backbone and amidine substituents, derived from readily available primary and secondary amines. We have also performed crystallographic and computational studies, which demonstrate a strong preference for the trans (E) amidine geometry. Given their straightforward synthetic preparation and high functional group density, peptidines have the potential to serve as useful tools for library generation, peptide mimicry, and the identification of biologically active small molecules.

Versatile ruthenium complexes based on 2,2′-bipyridine modified peptoids

Helical peptoids bearing 2,2′-bipyridine form ruthenium complexes via intermolecular binding to linear peptoid strands or intramolecular binding to a cyclic scaffold.

Sequence Programmable Peptoid Polymers for Diverse Materials Applications

Polymer sequence programmability is required for the diverse structures and complex properties that are achieved by native biological polymers, but efforts towards controlling the sequence of synthetic polymers are, by comparison, still in their infancy. Traditional polymers provide robust and chemically diverse materials, but synthetic control over their monomer sequences is limited. The modular and step-wise synthesis of peptoid polymers, on the other hand, allows for precise control over the monomer sequences, affording opportunities for these chains to fold into well-defined nanostructures. Hundreds of different side chains have been incorporated into peptoid polymers using efficient reaction chemistry, allowing for a seemingly infinite variety of possible synthetically accessible polymer sequences. Combinatorial discovery techniques have allowed the identification of functional polymers within large libraries of peptoids, and newly developed theoretical modeling tools specifically adapted for peptoids enable the future design of polymers with desired functions. Work towards controlling the three-dimensional structure of peptoids, from the conformation of the amide bond to the formation of protein-like tertiary structure, has and will continue to enable the construction of tunable and innovative nanomaterials that bridge the gap between natural and synthetic polymers.

Development of Peptoid-Based Ligands for the Removal of Cadmium from Biological Media

To address the lack of current therapeutic strategies for cadmium poisoning, peptoid-based ligands are identified using combinatorial chemistry that can selectively coordinate cadmium in a complex biological sample matrix.

Cadmium poisoning poses a serious health concern due to cadmium's increasing industrial use, yet there is currently no recommended treatment. The selective coordination of cadmium in a biological environment—i.e. in the presence of serum ions, small molecules, and proteins—is a difficult task. To address this challenge, a combinatorial library of peptoid-based ligands has been evaluated to identify structures that selectively bind to cadmium in human serum with minimal chelation of essential metal ions. Eighteen unique ligands were identified in this screening procedure, and the binding affinity of each was measured using metal titrations monitored by UV-vis spectroscopy. To evaluate the significance of each chelating moiety, sequence rearrangements and substitutions were examined. Analysis of a metal–ligand complex by NMR spectroscopy highlighted the importance of particular residues. Depletion experiments were performed in serum mimetics and human serum with exogenously added cadmium. These depletion experiments were used to compare and demonstrate the ability of these peptoids to remove cadmium from blood-like mixtures. In one of these depletion experiments, the peptoid sequence was able to deplete the cadmium to a level comparable to the reported acute toxicity limit. Evaluation of the metal selectivity in buffered solution and in human serum was performed to verify minimal off-target binding. These studies highlight a screening platform for the identification of metal–ligands that are capable of binding in a complex environment. They additionally demonstrate the potential utility of biologically-compatible ligands for the treatment of heavy metal poisoning.

Facile solid-phase parallel synthesis of linear and cyclic peptoids for comparative studies of biological activity

A series of linear and cyclic peptoids, which were expected to possess better pharmacokinetic properties and biological activities for blocking the interaction between apolipoprotein E and amyloid-β, were designed and synthesized as possible therapeutic agents. Peptoids were easily synthesized on solid-phase by the submonomer strategy and polar side chain-containing amines were effectively introduced under the modified reaction conditions. For the synthesis of cyclic peptoids, β-alanine protected with the 2-phenylisopropyl group, which could be selectively removed by 2% TFA, was used as a primary amine to afford a complete peptoid unit. The macrolactamization between the carboxylic acid of β-alanine moiety and terminal amine of peptoids was successfully performed in the presence of the PyAOP coupling agent on solid-phase in all the cases, providing various sizes of cyclic peptoids. In particular, some cyclic peptoids prepared in this study are the largest in size among cyclic peptoids reported to date. The synthetic strategy which was adopted in this study can also provide a robust platform for solid-phase construction of cyclic peptoid libraries. Currently, synthetic peptoids have been used to test interesting biological activities including the ApoE/Aβ interaction inhibition, nontoxicity, the blood-brain barrier permeability, etc.

Learning from host-defense peptides: cationic, amphipathic peptoids with potent anticancer activity

Cationic, amphipathic host defense peptides represent a promising group of agents to be developed for anticancer applications. Poly-N-substituted glycines, or peptoids, are a class of biostable, peptidomimetic scaffold that can display a great diversity of side chains in highly tunable sequences via facile solid-phase synthesis. Herein, we present a library of anti-proliferative peptoids that mimics the cationic, amphipathic structural feature of the host defense peptides and explore the relationships between the structure, anticancer activity and selectivity of these peptoids. Several peptoids are found to be potent against a broad range of cancer cell lines at low-micromolar concentrations including cancer cells with multidrug resistance (MDR), causing cytotoxicity in a concentration-dependent manner. They can penetrate into cells, but their cytotoxicity primarily involves plasma membrane perturbations. Furthermore, peptoid 1, the most potent peptoid synthesized, significantly inhibited tumor growth in a human breast cancer xenotransplantation model without any noticeable acute adverse effects in mice. Taken together, our work provided important structural information for designing host defense peptides or their mimics for anticancer applications. Several cationic, amphipathic peptoids are very attractive for further development due to their high solubility, stability against protease degradation, their broad, potent cytotoxicity against cancer cells and their ability to overcome multidrug resistance.

Selective chromium(VI) ligands identified using combinatorial peptoid libraries

Hexavalent chromium [Cr(VI)] is a worldwide water contaminant that is currently without cost-effective and efficient remediation strategies. This is in part due to a lack of ligands that can bind it amid an excess of innocuous ions in aqueous solution. We present herein the design and application of a peptoid-based library of ligand candidates for toxic metal ions. A selective screening process was used to identify members of the library that can bind to Cr(VI) species at neutral pH and in the presence of a large excess of spectator ions. There were 11 sequences identified, and their affinities were compared using titrations monitored with UV-vis spectroscopy. To identify the interactions involved in coordination and specificity, we evaluated the effects of sequence substitutions and backbone variation in the highest affinity structure. Additional characterization of the complex formed between this sequence and Cr(VI) was performed using NMR spectroscopy. To evaluate the ability of the developed sequences to remediate contaminated solutions, the structures were synthesized on a solid-phase resin and incubated with environmental water samples that contained simulated levels of chromium contamination. The synthetic structures demonstrated the ability to reduce the amount of toxic chromium to levels within the range of the EPA contamination guidelines. In addition to providing some of the first selective ligands for Cr(VI), these studies highlight the promise of peptoid sequences as easily prepared components of environmental remediation materials.

Synthesis of libraries of peptidomimetic compounds containing a 2-oxopiperazine unit in the main chain

Peptoid libraries have been shown to be a useful source of protein-binding agents. However, simple linear peptoids lack conformational constraints, which may limit their binding affinity for proteins. Here we report facile chemistry for the assembly of 2-oxopiperazine rings into the main chain of peptoid-like oligomers, thus rigidifying the structure. This modified sub-monomer synthesis is suitable for the creation of high quality combinatorial libraries.

Decoding split and pool combinatorial libraries with electron-transfer dissociation tandem mass spectrometry

Screening of bead-based split and pool combinatorial chemistry libraries is a powerful approach to aid the discovery of new chemical compounds able to interact with, and modulate the activities of, protein targets of interest. Split and pool synthesis provides for large and well diversified chemical libraries, in this case comprised of oligomers generated from a well-defined starting set. At the end of the synthesis, each bead in the library displays many copies of a unique oligomer sequence. Because the sequence of the oligomer is not known at the time of screening, methods for decoding of the sequence of each screening "hit" are essential. Here we describe an electron-transfer dissociation (ETD) based tandem mass spectrometry approach for the decoding of mass-encoded split and pool libraries. We demonstrate that the newly described "chiral oligomers of pentenoic amides (COPAs)" yield non-sequence-specific product ions upon collisional activated dissociation; however, complete sequence information can be obtained with ETD. To aid in the decoding of libraries from MS and MS/MS data, we have incorporated (79)Br/(81)Br isotope "tags" to differentiate N- and C-terminal product ions. In addition, we have created "Hit-Find," a software program that allows users to generate libraries in silico. The user can then search all possible members of the chemical library for those that fall within a user-defined mass error.

Peptoid polymers: a highly designable bioinspired material

Bioinspired polymeric materials are attracting increasing attention due to significant advantages over their natural counterparts: the ability to precisely tune their structures over a broad range of chemical and physical properties, increased stability, and improved processability. Polypeptoids, a promising class of bioinspired polymer based on a N-substituted glycine backbone, have a number of unique properties that bridge the material gap between proteins and bulk polymers. Peptoids combine the sequence specificity of biopolymers with the simpler intra/intermolecular interactions and robustness of traditional synthetic polymers. They are highly designable because hundreds of chemically diverse side chains can be introduced from simple building blocks. Peptoid polymers can be prepared by two distinct synthetic techniques offering access to two material subclasses: (1) automated solid-phase synthesis which enables precision sequence control and near absolute monodispersity up to chain lengths of ~50 monomers, and (2) a classical polymerization approach which allows access to higher molecular weights and larger-scale yields, but with less control over length and sequence. This combination of facile synthetic approaches makes polypeptoids a highly tunable, rapid polymer prototyping platform to investigate new materials that are intermediate between proteins and bulk polymers, in both their structure and their properties. In this paper, we review the methods to synthesize peptoid polymers and their applications in biomedicine and nanoscience, as both sequence-specific materials and as bulk polymers.

Synthesis and screening of stereochemically diverse combinatorial libraries of peptide tertiary amides

Large combinatorial libraries of N-substituted peptides would be an attractive source of protein ligands, because these compounds are known to be conformationally constrained, whereas standard peptides or peptoids are conformationally mobile. Here, we report an efficient submonomer solid-phase synthetic route to these compounds and demonstrate that it can be used to create high quality libraries. A model screening experiment and analysis of the hits indicates that the rigidity afforded by the stereocenters is critical for high affinity binding.

Peptoids and polyamines going sweet: Modular synthesis of glycosylated peptoids and polyamines using click chemistry

Sugar moieties are present in a wide range of bioactive molecules. Thus, having versatile and fast methods for the decoration of biomimetic molecules with sugars is of fundamental importance. The glycosylation of peptoids and polyamines as examples of such biomimetic molecules is reported here. The method uses Cu-catalyzed azide alkyne cycloaddition to promote the reaction of azidosugars with either polyamines or peptoids. In addition, functionalized nucleic acids were attached to polyamines via the same route. Based on a modular solid-phase synthesis of peralkynylated peptoids with up to six alkyne groups, the latter were modified with azidosugar building blocks by using copper-catalyzed azide alkyne cycloadditions. In addition, the up-scaling of some particular azide-modified sugars is described.