Direct N-substituted N-thiocarboxyanhydride polymerization towards polypeptoids bearing unprotected carboxyl groups

A Review on the Synthesis of Polypeptoids

Polyeptoids are a promising class of polypeptide mimetic biopolymers based on N-substituted glycine backbones. Because of the high designability of their side chains, polypeptoids have a wide range of applications in surface antifouling, biosensing, drug delivery, and stimuli-responsive materials. To better control the structures and properties of polypeptoids, it is necessary to understand different methods for polypeptoid synthesis. This review paper summarized and discussed the main synthesis methods of polypeptoids: the solid-phase submonomer synthesis method, ring-opening polymerization method and Ugi reaction method.

Research Progress in Polypeptoids Prepared by Controlled Ring-Opening Polymerizations

Polypeptoids, structural mimics of polypeptides, have attracted considerable attention due to their biocompatibility, proteolytic stability, thermal processability, good solubility, synthetic accessibility, and structural diversity. Polypeptoids have emerged as an interesting material in both polymer science and biological field. This review primarily discusses the research progress of polypeptoids prepared by controlled ring-opening polymerizations in the past decade, including synthetic strategies of monomers, polymerizations by different initiators, postfunctionalization, fundamental properties, crystallization-driven self-assembly, and potential biological applications.

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.

Biodegradable Polysarcosine with Inserted Alanine Residues: Synthesis and Enzymolysis

Polysarcosine (PSar), a water-soluble polypeptoid, is gifted with biodegradability via the random ring-opening copolymerization of sarcosine- and alanine-N-thiocarboxyanhydrides catalyzed by acetic acid in controlled manners. Kinetic investigation reveals the copolymerization behavior of the two monomers. The random copolymers, named PaS, with high molecular weights between 5.3 and 43.6 kg/mol and tunable Ala molar fractions varying from 6 to 43% can be degraded by porcine pancreatic elastase within 50 days under mild conditions (pH = 8.0 at 37 °C). Both the biodegradation rate and water solubility of PaS depend on the content of Ala residues. PaS with Ala fractions below 43% are soluble in water, while the one with 43% Ala self-assembles in water into nanoparticles. Moreover, PaS are noncytotoxic at the concentration of 5 mg/mL. The biodegradability and biocompatibility endow the Ala-containing PSar with the potential to replace poly(ethylene glycol) as a protective shield in drug-delivery.

An Inspection into Multifarious Ways to Synthesize Poly(Amino Acid)s

Poly(α-amino acid)s (PAAs) attract growing attention due to their essential role in the application as biomaterials. To synthesize PAAs with desired structures and properties, scientists have developed various synthetic techniques with respective advantages. Here, different approaches to preparing PAAs are inspected. Basic features and recent progresses of these methods are summarized, including polymerizations of amino acid N-carboxyanhydrides (NCAs), amino acid N-thiocarboxyanhydrides (NTAs), and N-phenoxycarbonyl amino acids (NPCs), as well as other synthetic routes. NCA is the most classical monomer to prepare PAAs with high molecular weights (MWs). NTA polymerizations are promising alternative pathways to produce PAAs, which can tolerate nucleophiles including alcohols, mercaptans, carboxyl acids, and water. By various techniques including choosing appropriate solvents or using organic acids as promoters, NTAs polymerize to produce polypeptoids and polypeptides with narrow dispersities and designed MWs up to 55.0 and 57.0 kg mol^-1 , respectively. NPC polymerizations are phosgene-free ways to synthesize polypeptides and polypeptoids. For the future prospects, detail investigations into polymerization mechanisms of NTA and NPC are expected. The synthesis of PAAs with designed topologies and assembly structures is another intriguing topic. The advantages and unsettled problems in various synthetic ways are discussed for readers to choose appropriate approaches for PAAs.

Understanding Acid-Promoted Polymerization of the N-Substituted Glycine N-Thiocarboxyanhydride in Polar Solvents

Polymerization of N-substituted glycine N-thiocarboxyanhydrides (NNTAs) is a promising pathway to prepare functional polypeptoids benefiting from their tolerance to nucleophilic impurities. However, controlled NNTA polymerization is hard to achieve in amide polar solvents, including N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N-methyl pyrrolidone (NMP), the only aprotic solvents for many biomacromolecules and polypeptoids. In the present work, we successfully achieve controlled NNTA polymerization in amide polar solvents by adding acetic acid as a promoter. The promotion is applied to the polymerization of sarcosine NTA, N-ethyl glycine NTA, and N-butyl glycine NTA. DMAc, DMF, and NMP are suitable solvents to prepare polypeptoids with designable molecular weights and low dispersities (1.06-1.21). The polysarcosines with high molecular weights are prepared up to 35.2 kg/mol. A kinetic investigation quantitatively reveals that the presence of acetic acid not only accelerates the polymerization, but also suppresses H₂S-catalyzed decomposition of NNTAs by decreasing the concentration of H₂S dissolved in polar solvents. Benzoic acid is also able to promote the polymerization, while trifluoroacetic acid, phosphoric acid, and phenol are not appropriate promoters. The moderate acidity of acids is essential. l-Methionine, l-tryptophan, and l-phenylalanine, which are dissolved in DMF, initiate the controlled polymerization of sarcosine-NTA in the presence of acetic acid and introduce functional end groups to polysarcosines quantitatively. In DMAc, hydrophilic vancomycin is grafted by poly(N-butyl glycine). The amphiphilic product dissolves in dichloromethane and stabilizes water-in-oil emulsion.

Controlled ring-opening polymerization of N-(3-tert-butoxy-3-oxopropyl) glycine derived N-carboxyanhydrides towards well-defined peptoid-based polyacids

Polypeptoids bearing carboxylic acid groups on the N-substituent are useful building blocks for the construction of peptidomimetic supramolecular assemblies with stimuli-responsive properties.