Investigation into the ROMP copolymerization of peptide- and PEG-functionalized norbornene derivatives

Himic Anhydride: A Retro Diels-Alder Reaction for the Organic Laboratory and an Accompanying NMR Study

The thermal equilibration of himic anhydride [IUPAC (2-endo,3-endo)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid anhydride] to (2-exo,3-exo)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid anhydride and subsequent recrystallization of the exo-product can be performed as a standard undergraduate laboratory experiment requiring minimal equipment. The interpretation of the ¹H NMR spectra for these norbornene carboxylic anhydride molecules promotes an appreciation of constrained ring systems and factors that affect chemical shifts and coupling constants.

Electrochemical activation of polymer chains mediated with radical transfer reactions

This work demonstrates a general and effective approach to activate inert polymer chains for further reactions through electrochemically driven radical generation and radical transfer reactions. The generated radical-containing polymer chains show capacity for further polymer reactions and preparation of polymer hybrids.

Poly(peptide): Synthesis, Structure, and Function of Peptide-Polymer Amphiphiles and Protein-like Polymers

In this Account, we describe the organization of functional peptides as densely arrayed side chains on polymer scaffolds which we introduce as a new class of material called poly(peptide). We describe two general classes of poly(peptide): (1) Peptide-Polymer Amphiphiles (PPAs), which consist of block copolymers with a dense grouping of peptides arrayed as the side chains of the hydrophilic block and connected to a hydrophobic block that drives micelle assembly, and (2) Protein-like Polymers (PLPs), wherein peptide-brush polymers are composed from monomers, each containing a peptide side chain. Peptides organized in this manner imbue polymers or polymeric nanoparticles with a range of functional qualities inherent to their specific sequence. Therefore, polymers or nanoparticles otherwise lacking bioactivity or responsiveness to stimuli, once linked to a peptide of choice, can now bind proteins, enter cells and tissues, have controlled and switchable biodistribution patterns, and be enzyme substrates (e.g., for kinases, phosphatases, proteases). Indeed, where peptide substrates are incorporated, kinetically or thermodynamically driven morphological transitions can be enzymatically induced in the polymeric material. Synergistically, the polymer enforces changes in peptide activity and function by virtue of packing and constraining the peptide. The scaffold can protect peptides from proteolysis, change the pharmacokinetic profile of an intravenously injected peptide, increase the cellular uptake of an otherwise cell impermeable therapeutic peptide, or change peptide substrate activity entirely. Moreover, in addition to the sequence-controlled peptides (generated by solid phase synthesis), the polymer can carry its own sequence-dependent information, especially through living polymerization strategies allowing well-defined blocks and terminal labels (e.g., dyes, contrast agents, charged moieties). Hence, the two elements, peptide and polymer, cooperate to yield materials with unique function and properties quite apart from each alone. Herein, we describe the development of synthetic strategies for accessing these classes of biomolecule polymer conjugates. We discuss the utility of poly(peptide)-based materials in a range of biomedical applications, including imaging of diseased tissues (myocardial infarction and cancer), delivering small molecule drugs to tumors with high specificity, imparting cell permeability to otherwise impermeable peptides, protecting bioactive peptides from proteolysis in harsh conditions (e.g., stomach acid and whole blood), and transporting proteins into traditionally difficult-to-transfect cell types, including stem cells. Poly(peptide) materials offer new properties to both the constituent peptides and to the polymers, which can be tuned by the design of the oligopeptide sequence, degree of polymerization, peptide arrangement on the polymer backbone, and polymer backbone chemistry. These properties establish this approach as valuable for the development of peptides as medicines and materials in a range of settings.

Supramolecular behaviour and fluorescence of rhodamine-functionalised ROMP polymers

A ROMP platform leading to rhodamine B containing amphiphilic block copolymers, which self-assemble into micelles which are able to sequester molecular dyes and interact with them by energy transfer. The polymer micelles do not interact with DNA.

Modular Design of Poly(norbornenes) for Organelle-Specific Imaging in Tumor Cells

Through modular ROMP (ring-opening metathesis polymerization) directly from monomeric norbornenes of bioactive peptides, rhodamine B chromophore, and PEG solubilizer, we designed and synthesized a series of water-soluble poly(norbornenes) with organelle-specific imaging capability in tumor cells. For the selection of FxrFxK, TAT, and SV40 peptide sequences, these fluorescence probes exhibited different targeting specificity toward mitochondria, lysosome, and nucleolus, respectively, based on the same poly(norbornene) backbonds. More importantly, the ROMP strategy enables selective combination from various monomers and allows programmable biofunctionalization via peptide sequence permutations, which would greatly extend the biomedical applications such as imaging, diagnosis, and therapy for these synthetic polymers.

Switchable two-photon imaging of RGD-functionalized polynorbornenes with enhanced cellular uptake in living cells

Two-photon imaging polynorbornenes were fabricated directly from photochromic spiropyran, RGD peptides and hydrophilic PEG monomers via modular ROMP.

A modular designed copolymer with anti-thrombotic activity and imaging capability

Through a modular ROMP (ring-opening metathesis polymerization) strategy, a random copolymer with anti-thrombotic activity and imaging capability has been constructed from RGD, rhodamine B and PEG modified norbornene monomers. As we expected, these tri-component polynorbornenes exhibit significant enhancement in anti-thrombotic efficacy and bioavailability in vivo.

Poly(oligonucleotide)

Here we report the preparation of poly(oligonucleotide) brush polymers and amphiphilic brush copolymers from nucleic acid monomers via graft-through polymerization. We describe the polymerization of PNA-norbornyl monomers to yield poly-PNA (poly(peptide nucleic acid)) via ring-opening metathesis polymerization (ROMP) with the initiator, (IMesH2)(C5H5N)2(Cl)2RuCHPh.1 In addition, we present the preparation of poly-PNA nanoparticles from amphiphilic block copolymers and describe their hybridization to a complementary single-stranded DNA (ssDNA) oligonucleotide.

Synthesis and characterization of transferrin-targeted chemotherapeutic delivery systems prepared via RAFT copolymerization of high molecular weight PEG macromonomers

Reversible addition-fragmentation chain transfer (RAFT) polymerization was employed to prepare a nanoparticulate drug delivery system for chemotherapeutics. The nanoparticles contain a PEG "stealth" corona as well as reactive anhydride functionality designed for conjugating targeting proteins. The multifunctional carrier functionality was achieved by controlling the copolymerization of the hydrophobic monomer lauryl methacrylate (LMA), with a reactive anhydride functional methacrylate (TMA), and a large polyethyleneglycol methacrylate monomer (M_n~950 Da) (O950). RAFT polymerization kinetics of O950 were evaluated as a function of target degrees of polymerization (DP), initial chain transfer agent to initiator ratio ([CTA]_o/[I]_o), and solvent concentration. Excellent control over the polymerization was observed for target DPs of 25 and 50 at [CTA]_o/[I]_o ratio of 10 as evidenced by narrow and symmetric molecular weight distributions and the ability to prepare block copolymers. The TMA-functional copolymers were conjugated to the tumor targeting protein transferrin (Tf). The targeted copolymer was shown to encapsulate docetaxel at concentrations comparable to the commercial single vial formulation of docetaxel (Taxotere). In vitro cytotoxicity studies conducted in HeLa cells show that the Tf targeting enhances the cancer killing properties relative to the polymer encapsulated docetaxel formulation.

Polymerization of a peptide-based enzyme substrate

Polymers of norbornenyl-modified peptide-based enzyme substrates have been prepared via ring-opening metathesis polymerization (ROMP). Peptides displayed on water-soluble homopolymers retain the ability to be enzymatically processed by a disease-associated enzyme. In contrast, when the peptides are densely arrayed on a nanoparticle derived from a self-assembled amphiphilic block-copolymer, they function with reduced activity as enzymatic substrates.

Polymerization of Protecting-Group-Free Peptides via ROMP

A study was conducted to survey the tolerance of ring-opening metathesis polymerization (ROMP) with respect to amino acid (a.a) identity of pentapeptide-modified norbornene-based monomers. A library of norbornyl-pentapeptides were prepared with the general structure, norbornyl-GX2PLX5, where residue 'X' was changed at each of the two positions (2 or 5) alternately to consist of the natural amino acids F, A, V, R, S, K, N, T, M, Q, H, W, C, Y, E, Q, and D. Each peptide monomer, free of protecting groups, was mixed in turn under a standard set of polymerization conditions with the ROMP initiator (IMesH2)C5H5N)2(Cl)2Ru=CHPh. Two sets of polymerization reactions were performed, one with Monomer:Initiator (M:I) ratio of 20:1, and another with M:I of 200:1. For the nucleophilic amino acids cysteine and lysine, polymerization reactions were quantitatively compared to those of their protected analogues. Furthermore, we describe polymerization of macromonomers containing up to 30 a.a. to test for tolerance of ROMP to peptide molecular weight. These reactions were studied via SEC-MALS and NMR. Finally, with knowledge of sequence scope in hand, we prepared a set of enzyme-substrate containing brush polymers and studied them with respect to their bioactivity.

One-pot synthesis of brush-like polymers via integrated ring-opening metathesis polymerization and polymerization of amino acid N-carboxyanhydrides

We report here the integration of ring-opening metathesis polymerization (ROMP) and ring-opening polymerization of the amino acid N-carboxyanhydride (NCA) to allow facile synthesis of brush-like polymers containing polypeptide as the brush side chains. ROMP of N-trimethylsilyl norbornenes rendered the preparation of poly(norbornene)s bearing pendant N-TMS groups. With no need to purify the resulting polymers, such macromolecular initiators could subsequently initiate controlled NCA polymerizations. Brush-like poly(norbornene)s with grafted polypeptides or block copolypeptides were readily obtained with controlled molecular weights and narrow molecular weight distributions. Because numerous ROMP and NCA monomers are widely available, this novel polymerization technique will allow easy access to numerous brush-like hybrid macromolecules with unprecedented properties and broad applications.

Hydrophilic modifications of an amphiphilic polynorbornene and the effects on its hemolytic and antibacterial activity

Here we report the modification of an amphiphilic antibacterial polynorbornene, Poly3, via incorporation of hydrophilic, biocompatible groups. The sugar, zwitterionic, and polyethylene glycol based moieties were incorporated in varying ratios by copolymerization and postpolymerization techniques. Well-defined copolymers with molecular weights of 3 kDa and narrow polydispersity indices ranging from 1.08 to 1.15 were obtained. The effects of these modifications on the biological activity of these polymers were analyzed by determining their minimum inhibitory concentrations (MIC) and their hemolytic activities (HC50).

Peptide/protein-polymer conjugates: synthetic strategies and design concepts

This feature article provides a compilation of tools available for preparing well-defined peptide/protein-polymer conjugates, which are defined as hybrid constructs combining (i) a defined number of peptide/protein segments with uniform chain lengths and defined monomer sequences (primary structure) with (ii) a defined number of synthetic polymer chains. The first section describes methods for post-translational, or direct, introduction of chemoselective handles onto natural or synthetic peptides/proteins. Addressed topics include the residue- and/or site-specific modification of peptides/proteins at Arg, Asp, Cys, Gln, Glu, Gly, His, Lys, Met, Phe, Ser, Thr, Trp, Tyr and Val residues and methods for producing peptides/proteins containing non-canonical amino acids by peptide synthesis and protein engineering. In the second section, methods for introducing chemoselective groups onto the side-chain or chain-end of synthetic polymers produced by radical, anionic, cationic, metathesis and ring-opening polymerization are described. The final section discusses convergent and divergent strategies for covalently assembling polymers and peptides/proteins. An overview of the use of chemoselective reactions such as Heck, Sonogashira and Suzuki coupling, Diels-Alder cycloaddition, Click chemistry, Staudinger ligation, Michael's addition, reductive alkylation and oxime/hydrazone chemistry for the convergent synthesis of peptide/protein-polymer conjugates is given. Divergent approaches for preparing peptide/protein-polymer conjugates which are discussed include peptide synthesis from synthetic polymer supports, polymerization from peptide/protein macroinitiators or chain transfer agents and the polymerization of peptide side-chain monomers.