Side-chain cysteine-functionalized poly(2-oxazoline)s for multiple peptide conjugation by native chemical ligation

Protected amine-functional initiators for the synthesis of α-amine homo- and heterotelechelic poly(2-ethyl-2-oxazoline)s

Screening a series of protected amine cationic ring-opening polymerization initiators revealed the commercially available N-(3-bromopropyl)phthalimide as the most suitable to achieve defined polymers with high degree of amine functionalization.

Polyoxazolines with a Vicinally Double-Bioactivated Terminus for Biomacromolecular Affinity Assessment

Interactions between proteins and carbohydrates with larger biomacromolecules, e.g., lectins, are usually examined using self-assembled monolayers on target gold surfaces as a simplified model measuring setup. However, most of those measuring setups are either limited to a single substrate or do not allow for control over ligand distance and spacing. Here, we develop a synthetic strategy, consisting of a cascade of a thioesterification, native chemical ligation (NCL) and thiol-ene reaction, in order to create three-component polymer conjugates with a defined double bioactivation at the chain end. The target architecture is the vicinal attachment of two biomolecule residues to the α telechelic end point of a polymer and a thioether group at the ω chain end for fixating the conjugate to a gold sensor chip surface. As proof-of-principle studies for affinity measurements, we demonstrate the interaction between covalently bound mannose and ConA in surface acoustic wave (SAW) and surface plasmon resonance (SPR) experiments.

Drug–polymer conjugates with dynamic cloud point temperatures based on poly(2-oxazoline) copolymers

A shift in cloud point temperatures of poly(2-oxazoline)/ACE inhibitor polymer drug conjugates occurs on release of the drug.

Influence of charged groups on the cross-linking efficiency and release of guest molecules from thiol-ene cross-linked poly(2-oxazoline) hydrogels

We describe the preparation of hydrogels using highly functionalized poly(oxazoline) based polymeric precursors and cross-linking via UV mediated radical thiol-ene chemistry. Random copolymers were synthesized based on the combination of the more hydrophilic 2-methyl-2-oxazoline or the less hydrophilic monomer 2-ethyl-2-oxazoline with 2-(3-butenyl)-2-oxazoline. These copolymers were functionalized via a post-polymerization technique with thiol or cysteine functionality at the side chain. Hence, hydrogels were obtained, for which the thermo-responsive behavior, network density and correlated properties such as swelling and mechanics, as well as the possibility of electrostatic interaction, can be tuned. Cell culture tests demonstrated good cytocompatibility of the synthesized copolymers and hydrogels. A study with two low molecular weight substances, methylene blue and fluorescein sodium, was performed to investigate how the thermo-responsive behavior or the positive charge incorporated by cysteine could influence the interaction with the compounds. It was found that the interaction with the hydrogel network was strongly influenced by the chemical properties of the dye. A hydrophilic and positively charged hydrogel network was shown to be a promising candidate for the uptake and prolonged release of negatively charged low molecular weight substances.

Amidation of methyl ester side chain bearing poly(2-oxazoline)s with tyramine: a quest for a selective and quantitative approach

Three new amidation approaches are evaluated to incorporate tyramine on methyl ester functional poly(2-oxazolines).

A sequential native chemical ligation – thiol-Michael addition strategy for polymer–polymer ligation

Native Chemical Ligation (NCL) between cysteine-terminated polymers and functional thioesters has been employed to prepare functional (co)polymers. The retained thiol functionality at the NCL junction can be exploited for thiol-Michael addition.

Surface-Initiated Poly(oligo(2-alkyl-2-oxazoline)methacrylate) Brushes

Polymer brushes are particularly performant antifouling coatings, owing to their high grafting density that prevents unwanted biomacromolecules to diffuse through the coating and adhere to the underlying substrate. In addition to this structural feature, polymer brushes require a relatively high level of hydrophilicity and a globally neutral structure to display ultrahigh protein resistance. Poly(2-alkyl-2-oxaolines) are attractive building blocks for such coatings as they can display relatively high hydrophilicity, owing to their amide repeat units, but can also be side-chain and end-chain functionalized relatively readily. However, poly(2-alkyl-2-oxazolines) have not yet been introduced through a radical-mediated grafting from polymer brush structure that would confer the high level of grafting density that is the hallmark of highly protein resistant brushes. Here, we present the formation of a series of poly(oligo(2-alkyl-2-oxazoline)methacrylate) brushes generated via a grafting from approach, via atom transfer radical polymerization. We characterize the chemical structure of the resulting coatings via ellipsometry, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. We show that allyl end groups can be introduced as a side chain of these brushes to allow functionalization via thiol-ene chemistry. We demonstrate the excellent protein resistance of these coatings in single protein solutions as well as serum solutions at concentration typically used for cell culture. Finally, we demonstrate the feasibility of using these brushes for the micropatterning of cells and the generation of cell-based assays.

Unravelling the Excellent Chemical Stability and Bioavailability of Solvent Responsive Curcumin-Loaded 2-Ethyl-2-oxazoline-grad-2-(4-dodecyloxyphenyl)-2-oxazoline Copolymer Nanoparticles for Drug Delivery

A new gradient copolymer has been synthesized by the living cationic ring-opening polymerization of hydrophilic 2-ethyl-2-oxazoline with lipophilic 2-(4-dodecyloxyphenyl)-2-oxazoline (EtOx-grad-DPOx). The prepared copolymer is capable of assembling in water to yield polymeric nanoparticles that are successfully loaded with an anticancer agent, curcumin. Self-assembly of the copolymer was found to be tuned by the polarity as well as the hydrogen bonding ability of solvents. Solvent took distinctive role in the preparation of unloaded and curcumin-loaded nanoparticles. The stability of the nanoparticles was increased by curcumin loading promoted by curcumin-polymer interactions. Further, the chemical stability of curcumin in water is largely enhanced inside the polymeric nanoparticles. Curcumin-loaded (EtOx-grad-DPOx) copolymer nanoparticles showed excellent stability in the biological medium, low cytotoxicity, and concentration dependent uptake by U87 MG and HeLa cells, which indicate the possibility of their efficient application in drug delivery.

Enzymatic Synthesis of Amino Acids Endcapped Polycaprolactone: A Green Route Towards Functional Polyesters

ε-caprolactone (CL) has been enzymatically polymerized using α-amino acids based on sulfur (methionine and cysteine) as (co-)initiators and immobilized lipase B of Candida antarctica (CALB) as biocatalyst. In-depth characterizations allowed determining the corresponding involved mechanisms and the polymers thermal properties. Two synthetic strategies were tested, a first one with direct polymerization of CL with the native amino acids and a second one involving the use of an amino acid with protected functional groups. The first route showed that mainly polycaprolactone (PCL) homopolymer could be obtained and highlighted the lack of reactivity of the unmodified amino acids due to poor solubility and affinity with the lipase active site. The second strategy based on protected cysteine showed higher monomer conversion, with the amino acids acting as (co-)initiators, but their insertion along the PCL chains remained limited to chain endcapping. These results thus showed the possibility to synthesize enzymatically polycaprolactone-based chains bearing amino acids units. Such cysteine endcapped PCL materials could then find application in the biomedical field. Indeed, subsequent functionalization of these polyesters with drugs or bioactive molecules can be obtained, by derivatization of the amino acids, after removal of the protecting group.

Antifouling Manganese Oxide Nanoparticles: Synthesis, Characterization, and Applications for Enhanced MR Imaging of Tumors

Antifouling manganese oxide (Mn₃O₄) nanoparticles (NPs) were synthesized by solvothermal decomposition of tris(2,4-pentanedionato) manganese(III) in the presence of trisodium citrate, followed by surface modification with polyethylene glycol and l-cysteine. The as-prepared nanoparticles have a uniform size distribution, good colloidal stability and good cytocompatibility. The modification of l-cysteine rendered the particles with much longer blood circulation time (half-decay time of 28.4 h) than those without l-cysteine modification (18.5 h), and decreased macrophage cellular uptake. Thanks to desirable antifouling property and relatively high r₁ relaxivity (3.66 mM^-1 s^-1), the l-cysteine-modified Mn₃O₄ NPs can be used for enhanced tumor magnetic resonance imaging applications.

Maleimide-Functionalized Poly(2-Oxazoline)s and Their Conjugation to Elastin-Like Polypeptides

The design of drug delivery systems capable of efficiently delivering poorly soluble drugs to target sites still remains a major challenge. Such materials require several different functionalities; typically, these materials should be biodegradable and nontoxic, nonimmunogenic, responsive to their environment, and soluble in aqueous solution while retaining the ability to solubilize hydrophobic drugs. Here, a polypeptide-polymer hybrid of elastin-like polypeptides (ELPs) and poly(2-oxazoline)s (POx) is reported. This paper describes the chemical synthesis, physical characteristics, and drug loading potential of these novel hybrid macromolecules. A novel method is introduced for terminal functionalization of POx with protected maleimide moieties. Following recovery of the maleimide group via a retro Diels-Alder reaction, the consecutive Michael addition of thiol-functionalized ELPs yields the desired protein-polymer conjugate. These conjugates form nanoparticles in aqueous solution capable of solubilizing the anti-cancer drug paclitaxel with up to 8 wt% loading.

Single addition of an allylamine monomer enables access to end-functionalized RAFT polymers for native chemical ligation

A novel method for the introduction of a single protected amine-functional monomer at the chain end of RAFT polymers has been developed to enable native chemical ligation with peptide thioesters.

Supercritical carbon dioxide design strategies: from drug carriers to soft killers

The integrated use of supercritical carbon dioxide (scCO(2)) and micro- and nanotechnologies has enabled new sustainable strategies for the manufacturing of new medications. 'Green' scCO(2)-based methodologies are well suited to improve either the synthesis or materials processing leading to the assembly of three-dimensional multifunctional constructs. By using scCO(2) either as C1 feedstock or as solvent, simple, economic, efficient and clean routes can be designed to synthesize materials with unique properties such as polyurea dendrimers and oxazoline-based polymers/oligomers. These new biocompatible, biodegradable and water-soluble polymeric materials can be engineered into multifunctional constructs with antimicrobial activity, targeting moieties, labelling units and/or efficiently loaded with therapeutics. This mini-review highlights the particular features exhibited by these materials resulting directly from the followed supercritical routes.