Synthesis of the Kinase Inhibitors Nintedanib, Hesperadin, and Their Analogues Using the Eschenmoser Coupling Reaction

A novel synthetic approach involving an Eschenmoser coupling reaction of substituted 3-bromooxindoles (H, 6-Cl, 6-COOMe, 5-NO₂) with two substituted thiobenzanilides in dimethylformamide or acetonitrile was used for the synthesis of eight kinase inhibitors including Nintedanib and Hesperadin in yields exceeding 76%. Starting compounds for the synthesis are also easily available in good yields. 3-Bromooxindoles were prepared either from corresponding isatins using a three-step synthesis in an average overall yield of 65% or by direct bromination of oxindoles (yield of 65-86%). Starting N-(4-piperidin-1-ylmethyl-phenyl)-thiobenzamide was prepared by thionation of the corresponding benzanilide in an 86% yield and N-methyl-N-(4-thiobenzoylaminophenyl)-2-(4-methylpiperazin-1-yl)acetamide was prepared by thioacylation of the corresponding aniline with methyl dithiobenzoate in an 86% yield.

Self-Immolative RAFT-Polymer End Group Modification

Reversible modifications of reversible addition-fragmentation chain transfer (RAFT)-polymerization derived end groups are usually limited to reductive degradable disulfide conjugates. However, self-immolative linkers can promote ligation and traceless release of primary and secondary amines as well as alcohols via carbonates or carbamates in β-position to disulfides. In this study, these two strategies are combined and the concept of self-immolative RAFT-polymer end group modifications is introduced: As model compounds, benzylamine, dibenzylamine, and benzyl alcohol are first attached as carbamates or carbonates to a symmetrical disulfide, and in a straightforward one-pot reaction these groups are reversibly attached to aminolyzed trithiocarbonate end groups of RAFT-polymerized poly(N,N-dimethylacrylamide). Quantitative end group modification is confirmed by ¹ H NMR spectroscopy, size exclusion chromatography, and mass spectrometry, while reversible release of attached compounds under physiological reductive conditions is successfully monitored by diffusion ordered NMR spectroscopy and thin layer chromatography. Additionally, this concept is further expanded to protein-reactive, self-immolative carbonate species that enable reversible bioconjugation of lysozyme and α-macrophage mannose receptor (MMR) nanobodies as model proteins. Altogether, self-immolative RAFT end group modifications can form the new basis for reversible introduction of various functionalities to polymer chain ends including protein bioconjugates and, thus, opening novel opportunities for stimuli-responsive polymer hybrids.

Nanoengineering with RAFT polymers: from nanocomposite design to applications

Reversible addition–fragmentation chain-transfer (RAFT) polymerization is a powerful tool for the precise formation of macromolecular building blocks that can be used for the construction of well-defined nanocomposites.

Poly(N-vinylpyrrolidone) Antimalaria Conjugates of Membrane-Disruptive Peptides

The concepts of polymer-peptide conjugation and self-assembly were applied to antimicrobial peptides (AMPs) in the development of a targeted antimalaria drug delivery construct. This study describes the synthesis of α-acetal, ω-xanthate heterotelechelic poly(N-vinylpyrrolidone) (PVP) via reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization, followed by postpolymerization deprotection to yield α-aldehyde, ω-thiol heterotelechelic PVP. A specific targeting peptide, GSRSKGT, for Plasmodium falciparum-infected erythrocytes was used to sparsely decorate the α-chain ends via reductive amination while cyclic decapeptides from the tyrocidine group were conjugated to the ω-chain end via thiol-ene Michael addition. The resultant constructs were self-assembled into micellar nanoaggregates whose sizes and morphologies were determined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The in vitro activity and selectivity of the conjugates were evaluated against intraerythrocytic P. falciparum parasites.

Stimuli-responsive polymeric nanomaterials for rheumatoid arthritis therapy

Rheumatoid arthritis (RA) is a long-term inflammatory disease derived from an autoimmune disorder of the synovial membrane. Current therapeutic strategies for RA mainly aim to hamper the macrophages' proliferation and reduce the production of pro-inflammatory cytokines. Therefore, the accumulation of therapeutic agents targeted at the inflammatory site should be a crucial therapeutic strategy. Nowadays, the nanocarrier system incorporated with stimuli-responsive property is being intensively studied, showing the potentially tremendous value of specific therapy. Stimuli-responsive (i.e., pH, temperature, light, redox, and enzyme) polymeric nanomaterials, as an important component of nanoparticulate carriers, have been intensively developed for various diseases treatment. A survey of the literature suggests that the use of targeted nanocarriers to deliver therapeutic agents (nanotherapeutics) in the treatment of inflammatory arthritis remains largely unexplored. The lack of suitable stimuli-sensitive polymeric nanomaterials is one of the limitations. Herein, we provide an overview of drug delivery systems prepared from commonly used stimuli-sensitive polymeric nanomaterials and some inorganic agents that have potential in the treatment of RA. The current situation and challenges are also discussed to stimulate a novel thinking about the development of nanomedicine.

Pyridyl disulfide-based thiol–disulfide exchange reaction: shaping the design of redox-responsive polymeric materials

This review provides an overview of synthetic approaches utilized to incorporate the thiol-reactive pyridyl-disulfide motif into various polymeric materials, and briefly highlights its utilization to obtain functional materials.

Aminolysis induced functionalization of (RAFT) polymer-dithioester with thiols and disulfides

Efficient exchange of the polymer-dithioester end group by aminolysis/functionalization with thiol or disulfide under ambient atmospheric conditions.

Fabrication of Polymer-Protein Hybrids

Rapid developments in organic chemistry and polymer chemistry promote the synthesis of polymer-protein hybrids with different structures and biofunctionalities. In this feature article, recent progress achieved in the synthesis of polymer-protein conjugates, protein-nanoparticle core-shell structures, and polymer-protein nanogels/hydrogels is briefly reviewed. The polymer-protein conjugates can be synthesized by the "grafting-to" or the "grafting-from" approach. In this article, different coupling reactions and polymerization methods used in the synthesis of bioconjugates are reviewed. Protein molecules can be immobilized on the surfaces of nanoparticles by covalent or noncovalent linkages. The specific interactions and chemical reactions employed in the synthesis of core-shell structures are discussed. Finally, a general introduction to the synthesis of environmentally responsive polymer-protein nanogels/hydrogels by chemical cross-linking reactions or molecular recognition is provided.

CuS-Based Theranostic Micelles for NIR-Controlled Combination Chemotherapy and Photothermal Therapy and Photoacoustic Imaging

Cancer remains a major threat to human health due to low therapeutic efficacies of currently available cancer treatment options. Nanotheranostics, capable of simultaneous therapy and diagnosis/monitoring of diseases, has attracted increasing amounts of attention, particularly for cancer treatment. In this study, CuS-based theranostic micelles capable of simultaneous combination chemotherapy and photothermal therapy (PTT), as well as photoacoustic imaging, were developed for targeted cancer therapy. The micelle was formed by a CuS nanoparticle (NP) functionalized by thermosensitive amphiphilic poly(acrylamide-acrylonitrile)-poly(ethylene glycol) block copolymers. CuS NPs under near-infrared (NIR) irradiation induced a significant temperature elevation, thereby enabling NIR-triggered PTT. Moreover, the hydrophobic core formed by poly(acrylamide-acrylonitrile) segments used for drug encapsulation exhibited an upper critical solution temperature (UCST; ∼38 °C), which underwent a hydrophobic-to-hydrophilic transition once the temperature rose above the UCST induced by NIR-irradiated CuS NPs, thereby triggering a rapid drug release and enabling NIR-controlled chemotherapy. The CuS-based micelles conjugated with GE11 peptides were tested in an epidermal growth factor receptor-overexpressing triple-negative breast cancer model. In both two-dimensional monolayer cell and three-dimensional multicellular tumor spheroid models, GE11-tagged CuS-based micelles under NIR irradiation, enabling the combination chemotherapy and PTT, exhibited the best therapeutic outcome due to a synergistic effect. These CuS-based micelles also displayed a good photoacoustic imaging ability under NIR illumination. Taken together, this multifunctional CuS-based micelle could be a promising nanoplatform for targeted cancer nanotheranostics.

Thiol-Reactive Star Polymers Display Enhanced Association with Distinct Human Blood Components

Directing nanoparticles to specific cell types using nonantibody-based methods is of increasing interest. Thiol-reactive nanoparticles can enhance the efficiency of cargo delivery into specific cells through interactions with cell-surface proteins. However, studies to date using this technique have been largely limited to immortalized cell lines or rodents, and the utility of this technology on primary human cells is unknown. Herein, we used RAFT polymerization to prepare pyridyl disulfide (PDS)-functionalized star polymers with a methoxy-poly(ethylene glycol) brush corona and a fluorescently labeled cross-linked core using an arm-first method. PDS star polymers were examined for their interaction with primary human blood components: six separate white blood cell subsets, as well as red blood cells and platelets. Compared with control star polymers, thiol-reactive nanoparticles displayed enhanced association with white blood cells at 37 °C, particularly the phagocytic monocyte, granulocyte, and dendritic cell subsets. Platelets associated with more PDS than control nanoparticles at both 37 °C and on ice, but they were not activated in the duration examined. Association with red blood cells was minor but still enhanced with PDS nanoparticles. Thiol-reactive nanoparticles represent a useful strategy to target primary human immune cell subsets for improved nanoparticle delivery.

Catalyst-Free Photoinduced End-Group Removal of Thiocarbonylthio Functionality

An initiator- and catalyst-free method for polymer end-group modification has been designed. Under long-wave ultraviolet irradiation, polymers with thiocarbonylthio end groups undergo photolytic cleavage to reveal an active macroradical capable of irreversible termination with a suitable hydrogen source. This straightforward method was successfully demonstrated by the removal of a range of end groups that commonly result from reversible addition-fragmentation chain transfer or photoiniferter polymerizations, including trithiocarbonate, dithiobenzoate, xanthate, and dithiocarbamate mediating agents. This strategy proved efficient for polymers derived from acrylamido, acrylic, methacrylic, styrenic, and vinylpyrrolidone monomers.

Polymers with acyl-protected perthiol chain termini as convenient building blocks for doubly responsive H2S-donating nanoparticles

H₂S-releasing polymers with an acyl-protected perthiol chain terminus were prepared using a simple, high yielding end-group modification process.

New biocompatible polymeric micelles designed for efficient intracellular uptake and delivery

New amphiphilic block copolymers are easily synthesised by post-polymerisation modifications of poly(glycidyl methacrylate) chain derivatives. The obtained material, upon dispersion in water, is capable of self-assembling into robust micelles. These nanoparticles, which are also characterised by adaptable stability, were loaded with different thiophene based fluorophores. The photoluminescent micelles were administered to cultured cells revealing a high and rapid internalisation of structurally different fluorescent molecules by the same internalisation pathway. Appropriate pairs of chromophores were selected and loaded into the micelles to induce Förster resonance energy transfer (FRET). The disappearing of the FRET phenomenon, after cell uptaking, demonstrated the intracellular release of the nanoparticle contents. The studied nanomaterial and the loaded chromophores have also shown to be biocompatible and non toxic towards the tested cells.

Transformation of RAFT Polymer End Groups into Nitric Oxide Donor Moieties: En Route to Biochemically Active Nanostructures

Polymers with a terminal S-nitrosothiol moiety were synthesized by modifying the thiocarbonylthio end group formed by reversible addition-fragmentation chain transfer polymerization. Specifically, benzodithioate-terminated poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) was first synthesized by polymerizing OEGMA in the presence of 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid. Sequential treatment with hydrazine hydrate and a stoichiometric amount of nitrous acid resulted in the formation of S-nitrosothiol-terminated polymers. A similar approach was applied to block copolymers of POEGMA incorporating a domain of poly[(N,N-diisopropylamino)ethyl methacrylate], thus, enabling the preparation of pH responsive nitric oxide (NO)-releasing micelles. The micelles possessed substantially modified S-nitrosothiol loss kinetics compared to the hydrophilic homopolymer analogue. Moreover, thiol-triggered degradation of the S-nitrosothiol was significantly slower when the S-nitrosothiol was embedded in a micellar structure. These results demonstrate that it is possible to incorporate nitric oxide donor moieties directly onto a polymer chain end, enabling simple synthesis of biochemically active nanostructures.

Brush macromolecules with thermo-sensitive coil backbones and pendant polypeptide side chains: synthesis, self-assembly and functionalization

Macromolecular brushes with thermo-sensitive coil backbones and pendant poly(γ-benzyl-l-glutamate) side chains were synthesized by reversible addition–fragmentation chain transfer and ring-opening polymerization. Functionalization and self-assembly of the macromolecules were investigated.

Stimuli-responsive polymeric nanoparticles for nanomedicine

Nature continues to be the ultimate in nanotechnology, where polymeric nanometer-scale architectures play a central role in biological systems. Inspired by the way nature forms functional supramolecular assemblies, researchers are trying to make nanostructures and to incorporate these into macrostructures as nature does. Recent advances and progress in nanoscience have demonstrated the great potential that nanomaterials have for applications in healthcare. In the realm of drug delivery, nanomaterials have been used in vivo to protect the drug entity in the systemic circulation, ensuring reproducible absorption of bioactive molecules that do not naturally penetrate biological barriers, restricting drug access to specific target sites. Several building blocks have been used in the formulation of nanoparticles. Thus, stability, drug release, and targeting can be tailored by surface modification. Herein the state of the art of stimuli-responsive polymeric nanoparticles are reviewed. Such systems are able to control drug release by reacting to naturally occurring or external applied stimuli. Special attention is paid to the design and nanoparticle formulation of these so-called smart drug-delivery systems. Future strategies for further developments of a promising controlled drug delivery responsive system are also outlined.

Fast conversion of terminal thiocarbonylthio groups of RAFT polymers to “clickable” thiol groups via versatile sodium azide

A facile and fast way of converting thiocarbonylthio end groups of RAFT polymers to thiol groups was demonstrated.

Stimuli responsive triblock copolymers by chain-growth polymerization from telechelic macroinitiators prepared via a step-growth polymerization

The synthesis of stimuli-responsive ABA tri-block copolymers using a step-growth polmerization followed by a chain-growth polymerization.

Synthesis of RAFT polymers as bivalent inhibitors of cholera toxin

We report a new strategy to develop low molecular weight (18–28 kDa) poly(N-acryloylmorpholine) (PNAM) polymers as bivalent inhibitors of cholera toxin (CT) using Reversible Addition–Fragmentation chain Transfer (RAFT) technology.

Zwitterionic guanidine-based oligomers mimicking cell-penetrating peptides as a nontoxic alternative to cationic polymers to enhance the cellular uptake of micelles

The aim of this work is to generate polymer micelles decorated with a synthetic version of cell-penetrating peptides, which are often rich in arginine with its positively charged guanidine group. A methacrylate-based monomer with guanidinium as functional groups was prepared using arginine (M-Arg) as a building block, resulting in a zwitterionic monomer. RAFT (reversible addition-fragmentation chain transfer) polymerization was employed to generate triblock copolymers with poly(methyl methacrylate)-block-poly(polyethylene glycol methyl ether methacrylate) as the first two blocks, which were subsequently chain extended with the guanidine-based monomer to generate micelles with guanidinium functional groups on the surface. To simulate the actual oligoarginine peptide, which only carries cationic charges, the carboxylate group of P(M-Arg) was methylated to convert the zwitterionic polymer into a cationic polymer P(Me-M-Arg). For comparison, micelles based on triblock copolymers with a third block with permanently cationic charges, poly(2-methacryolyloxy ethyl) trimethyl ammonium chloride (PTMA), was prepared. The hydrodynamic diameters of the micelles were approximately 30-40 nm based on DLS and TEM. A direct correlation between surface charge (zeta potential ζ) and cytotoxicity was observed. The micelles based on the zwitterionic P(M-Arg) were nontoxic (ζ = -10 mV at pH = 7), while the methylated version P(Me-M-Arg) with a high cationic charge (ζ = +35 mV at pH = 7) were observed to be toxic. The cellular uptake of the block copolymers by OVCAR-3 ovarian cancer cell lines was found to be relatively fast (about 35% in 3 min) reaching an equilibrium after approximately 30 min. Both micelles, with either P(M-Arg) or P(Me-M-Arg) on the surface, showed an enhanced uptake compared to micelles with P(PEGMEMA) as shell only. In fact, the percentage of uptake was similar, with the difference that cells incubated with micelles with P(M-Arg) (zwitterionic) stayed alive, while P(Me-M-Arg) (cationic) led to significant cell death.