Phosgene-free synthesis of polypeptides: Useful synthesis for hydrophobic polypeptides through polycondensation of activated urethane derivatives of α-amino acids

Engineering Semicarbazide-Bearing Polypeptide Conjugates for Efficient Tumor Chemotherapy and Imaging of Tumor Metastasis

Polypeptide materials offer scalability, biocompatibility, and biodegradability, rendering them an ideal platform for biomedical applications. However, the preparation of polypeptides with specific functional groups, such as semicarbazide moieties, remains challenging. This work reports, for the first time, the straightforward synthesis of well-defined methoxy-terminated poly(ethylene glycol)-b-polypeptide hybrid block copolymers (HBCPs) containing semicarbazide moieties. This synthesis involves implementing the direct polymerization of environment-stable N-phenoxycarbonyl-functionalized α-amino acid (NPCA) precursors, thereby avoiding the handling of labile N-carboxyanhydride (NCA) monomers. The resulting HBCPs containing semicarbazide moieties enable facile functionalization with aldehyde/ketone derivatives, forming pH-cleavable semicarbazone linkages for tailored drug release. Particularly, the intracellular pH-triggered hydrolysis of semicarbazone moieties restores the initial semicarbazide residues, facilitating endo-lysosomal escape and thus improving therapeutic outcomes. Furthermore, the integration of the hypoxic probe (Ir(btpna)(bpy)2 ) into the pH-responsive nanomedicines allows sequential responses to acidic and hypoxic tumor microenvironments, enabling precise detection of metastatic tumors. The innovative approach for designing bespoke functional polypeptides holds promise for advanced drug delivery and precision therapeutics.

Syntheses of Polypeptides and Their Biomedical Application for Anti-Tumor Drug Delivery

Polypeptides have attracted considerable attention in recent decades due to their inherent biodegradability and biocompatibility. This mini-review focuses on various ways to synthesize polypeptides, as well as on their biomedical applications as anti-tumor drug carriers over the past five years. Various approaches to preparing polypeptides are summarized, including solid phase peptide synthesis, recombinant DNA techniques, and the polymerization of activated amino acid monomers. More details on the polymerization of specifically activated amino acid monomers, such as amino acid N-carboxyanhydrides (NCAs), amino acid N-thiocarboxyanhydrides (NTAs), and N-phenoxycarbonyl amino acids (NPCs), are introduced. Some stimuli-responsive polypeptide-based drug delivery systems that can undergo different transitions, including stability, surface, and size transition, to realize a better anti-tumor effect, are elaborated upon. Finally, the challenges and opportunities in this field are briefly discussed.

PiPo: random copolymers of C- with N-substituted glycines

This letter introduces a method to obtain PiPo by the copolymerization of N-phenyloxycarbonyl-amino acids initiated by primary amine. The obtained PiPo have adjustable solubility in water and organic solvents to assemble into nanoparticles.

One-Pot Synthesis of Oxidation-Sensitive Supramolecular Gels and Vesicles

Polypeptide-based nanoparticles offer unique advantages from a nanomedicine perspective such as biocompatibility, biodegradability, and stimuli-responsive properties to (patho)physiological conditions. Conventionally, self-assembled polypeptide nanostructures are prepared by first synthesizing their constituent amphiphilic polypeptides followed by postpolymerization self-assembly. Herein, we describe the one-pot synthesis of oxidation-sensitive supramolecular micelles and vesicles. This was achieved by polymerization-induced self-assembly (PISA) of the N-carboxyanhydride (NCA) precursor of methionine using poly(ethylene oxide) as a stabilizing and hydrophilic block in dimethyl sulfoxide (DMSO). By adjusting the hydrophobic block length and concentration, we obtained a range of morphologies from spherical to wormlike micelles, to vesicles. Remarkably, the secondary structure of polypeptides greatly influenced the final morphology of the assemblies. Surprisingly, wormlike micellar morphologies were obtained for a wide range of methionine block lengths and solid contents, with spherical micelles restricted to very short hydrophobic lengths. Wormlike micelles further assembled into oxidation-sensitive, self-standing gels in the reaction pot. Both vesicles and wormlike micelles obtained using this method demonstrated to degrade under controlled oxidant conditions, which would expand their biomedical applications such as in sustained drug release or as cellular scaffolds in tissue engineering.

Synthesis of Polypeptides with High-Fidelity Terminal Functionalities under NCA Monomer-Starved Conditions

Controlled polypeptide synthesis via α-amino acid N-carboxylic anhydride (NCA) polymerization using conventional primary amine initiators encounters two major obstacles: (i) normal amine mechanism (NAM) and activated monomer mechanism (AMM) coexist due to amine basicity and nucleophilicity and (ii) NCA is notoriously sensitive towards moisture and heat and unstable upon storage. We serendipitously discover that N-phenoxycarbonyl-functionalized α-amino acid (NPCA), a latent NCA precursor, could be polymerized solely based on NAM with high initiating efficiency by using primary amine hydrochloride as an initiator. The polymerization affords well-defined polypeptides with narrow polydispersity and high-fidelity terminal functionalities, as revealed by the clean set of MALDI-TOF MS patterns. We further demonstrate successful syntheses of random and block copolypeptides, even under open-vessel conditions. Overall, the integration of moisture-insensitive and air-tolerant NPCA precursors with stable primary amine hydrochloride initiators represents a general strategy for controlled synthesis of high-fidelity polypeptides with sophisticated functions.

Capsules from synthetic diblock-peptides as potential artificial oxygen carriers

The design of an encapsulation system consisting of a synthetic peptide which is fully biodegradable into non-toxic constituents. This system should be capable of encapsulating perfluorinated hydrocarbons and should be a promising basis for oxygen carriers to be used as artificial blood replacement. A diblock-peptide is synthesised following a phosgene-free method and characterised by ¹H-NMR. Subsequently, this diblock-peptide is self-assembled with perfluorodecalin (PFD) to form PFD-filled capsules as potential artificial oxygen carriers allowing for rapid oxygen uptake and release. The diblock-peptide Bu-PAsp₁₀-PPhe₁₀ is successfully synthesised and used to encapsulate PFD. The capsules have a spherical shape with an average diameter of 360 nm in stable aqueous dispersion. NMR measurements prove their physical capability for reversible uptake and release of oxygen. The resulting capsules are expected to be fully biodegradable and possibly could act as oxygen carriers for artificial blood replacement.

Designing peptide nanoparticles for efficient brain delivery

The targeted delivery of therapeutic compounds to the brain is arguably the most significant open problem in drug delivery today. Nanoparticles (NPs) based on peptides and designed using the emerging principles of molecular engineering show enormous promise in overcoming many of the barriers to brain delivery faced by NPs made of more traditional materials. However, shortcomings in our understanding of peptide self-assembly and blood-brain barrier (BBB) transport mechanisms pose significant obstacles to progress in this area. In this review, we discuss recent work in engineering peptide nanocarriers for the delivery of therapeutic compounds to the brain: from synthesis, to self-assembly, to in vivo studies, as well as discussing in detail the biological hurdles that a nanoparticle must overcome to reach the brain.

Well-Defined Construction of Functional Macromolecular Architectures Based on Polymerization of Amino Acid Urethanes

Polypeptide synthesis was accomplished using the urethane derivatives of amino acids as monomers, which can be easily prepared, purified, and stored at ambient temperature without the requirement for special precautions. The urethanes of amino acids are readily synthesized by the N-carbamoylation of onium salts of amino acids using diphenyl carbonate (DPC). The prepared urethanes are then efficiently cyclized to produce amino acid N-carboxyanhydrides (NCAs). Thereafter, in the presence of primary amines, the ring-opening polymerization (ROP) of NCAs is initiated using the amines, to yield polypeptides with controlled molecular weights. The polypeptides have propagating chains bearing reactive amino groups and initiating chain ends endowed with functional moieties that originate from the amines. Aiming to benefit from these interesting characteristics of the polypeptide synthesis using the urethanes of amino acids, various macromolecular architectures containing polypeptide components have been constructed and applied as biofunctional materials in highly efficient antifouling coatings against proteins and cells, as biosensors for specific molecules, and in targeted drug delivery.

How to define and study structural proteins as biopolymer materials

Structural proteins, including silk fibroins, play an important role in shaping the skeletons and structures of cells, tissues, and organisms. The amino acid sequences of structural proteins often show characteristic features, such as a repeating tandem motif, that are notably different from those of functional proteins such as enzymes and antibodies. In recent years, materials composed of or containing structural proteins have been studied and developed as biomedical, apparel, and structural materials. This review outlines the definition of structural proteins, methods for characterizing structural proteins as polymeric materials, and potential applications.

End‐to‐end image analysis pipeline for liquid‐phase electron microscopy

Liquid phase transmission electron microscopy allows the imaging of materials in liquid environments. The sample is encapsulated within electron‐beam transparent windows and hence protected by the ultrahigh vacuum necessary within the electron gun. Such an approach allows to study biological and soft materials in their natural environment and offers the possibility of accessing their dynamic nature. Yet, the electron beam scattering from the windows and solvent increases the image noise and blur. Herein, we propose a pipeline to both de‐noise and sharpen images obtained by liquid transmission electron microscopy. We develop the workflow in a way that it does not require any human interference, nor introduce artefacts, but actually unveils features of the imaged samples covered by the noise and the blur.

Insight into the synthesis of N-methylated polypeptides

The ring-opening polymerization of α-substituted N-methylated N-carboxy anhydrides is reported. The polymerization was tested using various amino acids and initiators, and was found to be limited by the steric demand of N-methylated compared to conventional amino acids.

PEG-Poly(1-Methyl-l-Tryptophan)-Based Polymeric Micelles as Enzymatically Activated Inhibitors of Indoleamine 2,3-Dioxygenase

Indoleamine 2,3-dioxygenase (IDO) is an immunomodulating enzyme that is overexpressed in many cancers with poor prognosis. IDO suppresses T cell immunity by catabolizing tryptophan into kynurenine (KYN), which induces apoptosis in T effector cells and enhances T regulatory cells, providing a powerful immunosuppressive mechanism in tumors. Thus, major efforts for developing IDO inhibitors have been undertaken. Among them, 1-Methyl-l-Tryptophan (MLT) and 1-Methyl-d-Tryptophan (MDT) effectively inhibit IDO in preclinical tumor models and the latter is under clinical evaluation. However, both MLT and MDT present poor pharmacokinetics, with the maximum serum concentration being below their 50% inhibitory concentration value. Herein, we have developed polymeric IDO inhibitors based on MLT, which can release active MLT after enzymatic degradation, toward establishing superior antitumor immunotherapies. These polymers were prepared by ring opening polymerization of an N-phenyl carbamate (NPC) derivative of MLT that was synthesized by carbamylation with diphenyl carbonate. By using ω-amino-poly(ethylene glycol) (PEG-NH2) as the macroinitiator, we prepared amphiphilic PEG-poly(MLT) block copolymers, which self-assembled into polymeric micelles in aqueous conditions. The PEG-poly(MLT) block copolymers could be readily degraded by chymotrypsin and the micelles were able to reduce the levels of KYN in activated macrophages. These results provide a strong rationale for pursuing MLT-based polymeric micelles as tumor-targeted prodrug systems.

One-step synthesis and regioselective polymerization of Nα,Nδ-bisphenoxycarbonyl-l-ornithine

N_α,N_δ-Bisphenoxycarbonyl-l-ornithine is synthesized by a one-step protection of l-ornithine, and it acts as a monomer for regioselective and controlled polymerization to yield poly(N_δ-phenoxycarbonyl-l-ornithine).

High-molecular-weight poly(Gly-Val-Gly-Val-Pro) synthesis through microwave irradiation

In this study, we synthesized a polypeptide from its pentapeptide unit using microwave irradiation. Effective methods for polypeptide synthesis from unit peptides have not been reported. Here, we used a key elastin peptide, H-GlyValGlyValPro-OH (GVGVP), as the monomer peptide. It is difficult to obtain poly(Gly-Val-Gly-Val-Pro) (poly(GVGVP)) from the pentapeptide unit of elastin, GVGVP, via polycondensation. Poly(GVGVP) prepared from genetically recombinant Escherichia coli is a well-known temperature-sensitive polypeptide, and this temperature sensitivity is known as the lower critical solution temperature. When microwave irradiation was performed in the presence of various additives, the pentapeptide (GVGVP) polycondensation reaction proceeded smoothly, resulting in a product with a high molecular weight in a relatively good yield. The reaction conditions, like microwave irradiation, coupling agents, and solvents, were optimized to increase the reaction efficiency. The product exhibited a molecular weight greater than Mr 7000. Further, the product could be synthesized on a gram scale. The synthesized polypeptide exhibited a temperature sensitivity that was similar to that of poly(GVGVP) prepared from genetically recombinant E. coli. Therefore, this technique offers a facile and quick approach to prepare polypeptides in large amounts. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

Synthesis and application of a novel poly-l-phenylalanine electroactive macromonomer as matrix for the biosensing of ‘Abused Drug’ model

The synthesis and biosensing application of a novel poly-l-phenylalanine-bearing electroactive macromonomer has been carried out.

Synthesis of polysarcosine from air and moisture stable N-phenoxycarbonyl-N-methylglycine assisted by tertiary amine base

Well-defined polysarcosines are synthesized from a stable urethane derivative ofN-methylglycine, avoiding the direct use of NCA.

Facile synthesis of polymethionine oxides through polycondensation of activated urethane derivative of α-amino acid and their application to antifouling polymer against proteins and cells

Polymethionine(oxide)s were readily synthesized through polycondensation with amines, accompanying the elimination of phenol and CO₂and used as antifouling polymer against biological matters.

Phosgene-free synthesis of polypeptides using activated urethane derivatives of α-amino acids: an efficient synthetic approach to hydrophilic polypeptides

Polypeptide synthesis has been successfully achieved through polycondensation of activated urethane derivatives with amines, accompanied by the elimination of phenol and CO₂.