N-PEG’ylation of chitosan via “click chemistry” reactions

Conjugation of CRAMP18-35 Peptide to Chitosan and Hydroxypropyl Chitosan via Copper-Catalyzed Azide-Alkyne Cycloaddition and Investigation of Antibacterial Activity

We developed a synthesis strategy involving a diazo transfer reaction and subsequent click reaction to conjugate a murine cathelicidin-related antimicrobial peptide (CRAMP18-35) to chitosan and hydroxypropyl chitosan (HPC), confirmed the structure, and investigated the antimicrobial activity. Chitosan azide and HPC-azide were prepared with a low degree of azidation by reacting the parent chitosan and HPC with imidazole sulfonyl azide hydrochloride. CRAMP18-35 carrying an N-terminal pentynoyl group was successfully grafted onto chitosan and HPC via copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The chitosan-peptide conjugates were characterized by IR spectroscopy and proton NMR to confirm the conversion of the azide to 1,2,3-triazole and to determine the degree of substitution (DS). The DS of the chitosan and HPC CRAMP18-35 conjugates was 0.20 and 0.13, respectively. The antibacterial activity of chitosan-peptide conjugates was evaluated for activity against two species of Gram-positive bacteria, Staphylococcus aureus (S. aureus) and Enterococcus faecalis (E. faecalis), and two species of Gram-negative bacteria, Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa). The antimicrobial peptide conjugates were selectively active against the Gram-negative bacteria and lacking activity against Gram-positive bacteria.

'Click' synthesized calcium-chitosan-triazole nanocomplex from CaC2 as an efficient drug carrier, antimicrobial and antioxidant polymer

A calcium-chitosan-triazole nanocomplex (Ca@CS-Tz) was synthesized via the robust copper catalyzed azide-alkyne cycloaddition using calcium carbide (CaC2) as an in-situ source of acetylene. The nanocomplex was characterized by various techniques and it was proved to be an efficient drug carrier with satisfactory antimicrobial and antioxidant properties. Quercetin loaded nanocomplex (encapsulation efficiency- 68.2 ± 1.0 %) was studied for targeted drug release and the drug release after 120 h was found to be 80.7 ± 0.8 % and 8.69 ± 0.5 % at pH 5.0 and 7.4 respectively. On biological evaluation, the nanocomplex showed enhanced antimicrobial activity against gram-negative bacteria Escherichia coli (E. coli), gram-positive bacteria Bacillus subtilis (B. subtilis) and a fungi Aspergillus niger (A. niger). Moreover, the synthesized Ca@CS-Tz nanocomplex also exhibited significant antioxidant property. Herein, the novel results corresponding to the antimicrobial effect on A. niger and drug delivery studies performed using our previously synthesized chitosan triazole (CS-triazole) derivative have also been reported. Finally, the results of the present study were compared to the results obtained to our previously reported derivative. The incorporation of calcium ions into CS-triazole can lead to the utilization of this complex in various other biomedical applications e.g. bone tissue engineering.

Eco-friendly and efficient modification of native hemicelluloses via click reactions

An atom-economic strategy is proposed to valorise the byproducts from an invasive bamboo with improved thermal stability for potential use in composites.

Organoselenium-chitosan derivative: Synthesis via "click" reaction, characterization and antioxidant activity

The derivatization of chitosan (CS) is widely exploited to endow this polysaccharide with enhanced physicochemical and biological properties. Beyond the synthetic route, the nature of the compounds used to functionalize the CS-derivatives exerts a pivotal role in their final properties. Making use of a simple "click" reaction, we synthesized for the first time an organoselenium-CS derivative through a 1,2,3-triazole formation. The product (CS-TSe) was characterized in detail by FTIR, NMR (¹H, ¹³C, and ⁷⁷Se) and UV-Vis techniques, and SEM microscopy. The antioxidant activity of CS-TSe was examined by ABTS⁺ and DPPH (free radical-scavenging) assays. Experimentally, it was demonstrated that CS-TSe has superior antioxidant activity compared with raw CS and "free" organoselenium compound, suggesting a benign and synergistic effect due to the derivatization. In short, the antioxidant property of CS-TSe combined with the other attractive properties of CS and selenium could be useful in the formulation of advanced materials for biomedical and packaging applications.

Chitotriazolan (poly(β(1-4)-2-(1H-1,2,3-triazol-1-yl)-2-deoxy-d-glucose)) derivatives: Synthesis, characterization, and evaluation of antibacterial activity

Here we describe the first synthesis of a new type of polysaccharides derived from chitosan. In these structures, the 2-amino group on the pyranose ring was quantitively replaced by an aromatic 1,2,3-triazole moiety. The 2-amino group of chitosan and di-TBDMS chitosan was converted into an azide by diazo transfer reaction. The chitosan azide and TBDMS-chitosan azide were poorly soluble but could be fully converted to triazoles by "copper-catalysed Huisgen cycloaddition" in DMF or DMSO. The reaction could be done with different alkynes but derivatives lacking cationic or anionic groups were poorly soluble or insoluble in tested aqueous and organic solvents. Derivatives with N,N-dimethylaminomethyl, N,N,N-trimethylammoniummethyl, sulfonmethyl, and phosphomethyl groups linked to the 4-position of the triazole moiety were soluble in water at neutral or basic conditions and could be analyzed by ¹H, ¹³C APT, COSY, and HSQC NMR. The quaternized cationic chitotriazolan's had high activity against S. aureus and E. coli, whereas the anionic chitotriazolan's lacked activity.

Chitosan Derivatives: Introducing New Functionalities with a Controlled Molecular Architecture for Innovative Materials

The functionalization of polymeric substances is of great interest for the development of innovative materials for advanced applications. For many decades, the functionalization of chitosan has been a convenient way to improve its properties with the aim of preparing new materials with specialized characteristics. In the present review, we summarize the latest methods for the modification and derivatization of chitin and chitosan under experimental conditions, which allow a control over the macromolecular architecture. This is because an understanding of the interdependence between chemical structure and properties is an important condition for proposing innovative materials. New advances in methods and strategies of functionalization such as the click chemistry approach, grafting onto copolymerization, coupling with cyclodextrins, and reactions in ionic liquids are discussed.

Electro-click construction of hybrid nanocapsule films with triggered delivery properties

Nanocapsule films composed of hollow PAA/IONPs hybridosomes were covalently assembled in one-pot by electro-click, enabling the encapsulation and triggered release of bodipy.

Poly(ethylene glycol) and Cyclodextrin-Grafted Chitosan: From Methodologies to Preparation and Potential Biotechnological Applications

Chitosan, a polyaminosaccharide obtained by alkaline deacetylation of chitin, possesses useful properties including biodegradability, biocompatibility, low toxicity, and good miscibility with other polymers. It is extensively used in many applications in biology, medicine, agriculture, environmental protection, and the food and pharmaceutical industries. The amino and hydroxyl groups present in the chitosan backbone provide positions for modifications that are influenced by factors such as the molecular weight, viscosity, and type of chitosan, as well as the reaction conditions. The modification of chitosan by chemical methods is of interest because the basic chitosan skeleton is not modified and the process results in new or improved properties of the material. Among the chitosan derivatives, cyclodextrin-grafted chitosan and poly(ethylene glycol)-grafted chitosan are excellent candidates for a range of biomedical, environmental decontamination, and industrial purposes. This work discusses modifications including chitosan with attached cyclodextrin and poly(ethylene glycol), and the main applications of these chitosan derivatives in the biomedical field.

pH Sensitive Hydrogels in Drug Delivery: Brief History, Properties, Swelling, and Release Mechanism, Material Selection and Applications

Improving the safety efficacy ratio of existing drugs is a current challenge to be addressed rather than the development of novel drugs which involve much expense and time. The efficacy of drugs is affected by a number of factors such as their low aqueous solubility, unequal absorption along the gastrointestinal (GI) tract, risk of degradation in the acidic milieu of the stomach, low permeation of the drugs in the upper GI tract, systematic side effects, etc. This review aims to enlighten readers on the role of pH sensitive hydrogels in drug delivery, their mechanism of action, swelling, and drug release as a function of pH change along the GI tract. The basis for the selection of materials, their structural features, physical and chemical properties, the presence of ionic pendant groups, and the influence of their pKa and pKb values on the ionization, consequent swelling, and targeted drug release are also highlighted.

Novel triazole-modified chitosan@nickel nanoparticles: efficient and recoverable catalysts for Suzuki reaction

The synthesis of triazole-modified chitosan@nickel catalyst through the click reaction of azide-functionalized chitosan with an alkynated imino-thiophene ligand for Suzuki–Miyaura coupling reactions.

Azide-rich peptides via an on-resin diazotransfer reaction

Azide-containing amino acids are valuable building blocks in peptide chemistry, because azides are robust partners in several bioorthogonal reactions. Replacing polar amino acids with apolar, azide-containing amino acids in solid-phase peptide synthesis can be tricky, especially when multiple azide residues are to be introduced in the amino acid sequence. We present a strategy for effectively incorporating multiple azide-containing residues site-specifically.

Injectable biopolymer based hydrogels for drug delivery applications

Biopolymer based pH-sensitive hydrogels were prepared using chitosan (CS) with polyethylene glycol (PEG) of different molecular weights in the presence of silane crosslinker. The incorporated components remain undissolved in different swelling media as they are connected by siloxane linkage which was confirmed by Fourier transform infrared spectroscopy. The swelling in water was enhanced by the addition of higher molecular weight PEG. The swelling behaviour of the hydrogels against pH showed high swelling in acidic and basic pH, whereas, low swelling was examined at pH 6 and 7. This characteristic pH responsive behaviour at neutral pH made them suitable for injectable controlled drug delivery. The controlled release analysis of Cefixime (CFX) (model drug) loaded CS/PEG hydrogel exhibited that the entire drug was released in 30 min in simulated gastric fluid (SGF) while in simulated intestinal fluid (SIF), 85% of drug was released in controlled manner within 80 min. This inferred that the developed hydrogels can be an attractive biomaterial for injectable drug delivery with physiological pH and other biomedical applications.

Regioselective Sequential Modification of Chitosan via Azide-Alkyne Click Reaction: Synthesis, Characterization, and Antimicrobial Activity of Chitosan Derivatives and Nanoparticles

Recently, the attention of researchers has been drawn toward the synthesis of chitosan derivatives and their nanoparticles with enhanced antimicrobial activities. In this study, chitosan derivatives with different azides and alkyne groups were synthesized using click chemistry, and these were further transformed into nanoparticles by using the ionotropic gelation method. A series of chitosan derivatives was successfully synthesized by regioselective modification of chitosan via an azide-alkyne click reaction. The amino moieties of chitosan were protected during derivatization by pthaloylation and subsequently unblocked at the end to restore their functionality. Nanoparticles of synthesized derivatives were fabricated by ionic gelation to form complexes of polyanionic penta-sodium tripolyphosphate (TPP) and cationic chitosan derivatives. Particle size analysis showed that nanoparticle size ranged from 181.03 ± 12.73 nm to 236.50 ± 14.32 nm and had narrow polydispersity index and positive surface charge. The derivatives and corresponding nanoparticles were evaluated in vitro for antibacterial and antifungal activities against three gram-positive and gram-negative bacteria and three fungal strains, respectively. The minimum inhibitory concentration (MIC) of all derivatives ranged from 31.3 to 250 µg/mL for bacteria and 188 to1500 µg/mL for fungi and was lower than that of native chitosan. The nanoparticles with MIC ranging from 1.56 to 25 µg/mLfor bacteria and 94 to 750 µg/mL for fungi exhibited higher activity than the chitosan derivatives. Chitosan O-(1-methylbenzene) triazolyl carbamate and chitosan O-(1-methyl phenyl sulfide) triazolyl carbamate were the most active against the tested bacterial and fungal strains. The hemolytic assay on erythrocytes and cell viability test on two different cell lines (Chinese hamster lung fibroblast cells V79 and Human hepatic cell line WRL68) demonstrated the safety; suggesting that these derivatives could be used in future medical applications. Chitosan derivatives with triazole functionality, synthesized by Huisgen 1,3-dipolar cycloaddition, and their nanoparticles showed significant enhancement in antibacterial and antifungal activities in comparison to those associated with native, non-altered chitosan.

Modification of arabinogalactan propargyl ethers by triazolyl functions

Polysaccharide arabinogalactan (AG) has been modified by triazolyl functions via the copper-catalyzed 1,3-dipolar addition of azides to propargyl ethers. A range of new AG triazolo derivatives bearing benzyl, 4-vinylbenzyl, 1-naphthylmethyl, (1-vinylimidazol-2-yl)methyl, (1-ethylimidazol-2-yl)methyl, (1-vinylbenzimidazol-2-yl)methyl, allyl, carboxymethyl (as Na-salt) substituents is prepared by "one-pot" approach from organic azides generated in situ and AG propargyl ethers. The latter (degree of substitution 2.0-2.2) are converted into 1,2,3-triazolo AGs in DMSO/water mixture in the presence of CuSO4·5H2O/sodium ascorbate/Et3N in 82-94% yields and with 60-100% conversion.

The Synthesis of the Locating Substitution Derivatives of Chitosan by Click Reaction at the 6-Position of Chitin

A novel method to prepare the macrocyclic compound locating substitution derivatives of chitosan was investigated, by using cyclodextrin as the model of macrocyclic compound. The method combines the advantages of activated 6-OH of chitin and high efficiency of click reaction. Chitin C6-OHp-toluenesulfonate (CTN-6-OTs) was generated and subsequently transferred to chitin C6-N3via nucleophilic substitution. Afterwards,β-cyclodextrin was immobilized at 6-OH of chitin via click reaction to afford CTN-6-CD. Ultimately, CTS-6-CD was obtained by removing the acetyl group of chitin unit. The structures and properties of these products were characterized by FTIR, TG, and XRD, respectively. It was found that CTN-6-CD synthesized at the optimum conditions has an immobilized loading of1.6126×10-4 mol/g and that of the corresponding CTS-6-CD, generated by removal of the acetyl group, was1.6891×10-4 mol/g.

Carbohydrate PEGylation, an approach to improve pharmacological potency

Conjugation with polyethylene glycol (PEG), known as PEGylation, has been widely used to improve the bioavailability of proteins and low molecular weight drugs. The covalent conjugation of PEG to the carbohydrate moiety of a protein has been mainly used to enhance the pharmacokinetic properties of the attached protein while yielding a more defined product. Thus, glycoPEGylation was successfully applied to the introduction of a PEGylated sialic acid to a preexisting or enzymatically linked glycan in a protein. Carbohydrates are now recognized as playing an important role in host–pathogen interactions in protozoal, bacterial and viral infections and are consequently candidates for chemotherapy. The short in vivo half-life of low molecular weight glycans hampered their use but methods for the covalent attachment of PEG have been less exploited. In this review, information on the preparation and application of PEG-carbohydrates, in particular multiarm PEGylation, is presented.

Antibacterial hydrogel coating by electrophoretic co-deposition of chitosan/alkynyl chitosan

Despite much effort has been paid to develop aseptic implant devices, the infection associated with medical implant still remains a significant problem. Here, we report a potential coating material derived from a natural biopolymer chitosan. Firstly, chitosan functionalized with alkynyl moiety (ACS) was prepared by reaction between chitosan and 3-bromopropyne. The structure of the alkynyl chitosan was characterized by FT-IR, (1)H NMR, XRD, TGA and element analysis. The minimum inhibitory concentration (MIC) of ACS with a degree of substitution (DS) of 0.40 was 0.03% against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Subsequently, the alkynyl chitosan was co-deposited with chitosan on stainless steel wire to fabricate a composite hydrogel. The composite hydrogel exhibited better antibacterial activities than pure chitosan hydrogel.

Effect of PEGylation on the toxicity and permeability enhancement of chitosan

The aim of the present work is to investigate if conditions can be devised where PEGylation of chitosan would reduce its toxicity toward the nasal mucosa while maintaining its ability to open the cellular tight junctions and, consequently, produce an enhancement of macromolecular permeability. A series of mPEG-g-chitosan copolymers with varying levels of mPEG substitution, mPEG molecular weight, and chitosan molecular weight were synthesized by grafting carboxylic acid-terminated mPEGs (Mw 1.9 and 5.0 × 10(3) g mol(-1)) to chitosans (Mw 28.9 and 82.0 × 10(3) g mol(-1)) using a NHS/EDC coupling system. The synthesized mPEG-g-chitosans were fully characterized using a number of techniques, including FT-IR, (1)H NMR, and SEC-MALLS and their physicochemical properties were analyzed by TGA and DSC. Thereafter, the conjugates were tested for their cytotoxicity and tight junction modulating property in a relevant cell model, a mucus producing Calu-3 monolayer. mPEG-g-chitosan conjugates exhibited reduced toxicity toward cells, as compared to unmodified chitosan counterparts. Furthermore, the conjugates demonstrated a dramatic effect on cell monolayer transepithelial electrical resistance (TEER) and enhancement of permeability of model macromolecules. TEER and permeability-enhancing effects, as measurable indicators of tight junction modulation, were found to be pH-dependent and were notably more pronounced than those exhibited by unmodified chitosans. This work therefore demonstrates that conditions can be contrived where PEGylation improves the toxicity profile of chitosan, while preserving its effect on epithelial tight junctions in the nose.