Chitosan-Oxanorbornadiene: A Convenient Chitosan Derivative for Click Chemistry without Metal Catalyst Problem

Trimesic acid-functionalized chitosan: A novel and efficient multifunctional organocatalyst for green synthesis of polyhydroquinolines and acridinediones under mild conditions

Trimesic acid-functionalized chitosan (Cs/ECH-TMA) material was prepared through a simple procedure by using inexpensive and commercially available chitosan (Cs), epichlorohydrin (ECH) linker and trimesic acid (TMA). The obtained bio-based Cs/ECH-TMA material was characterized using energy-dispersive X-ray (EDX) and Fourier-transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analysis. The Cs/ECH-TMA material was successfully used, as a multifunctional heterogeneous and sustainable catalyst, for efficient and expeditious synthesis of medicinally important polyhydroquinoline (PHQ) and polyhydroacridinedione (PHA) scaffolds through the Hantzsch condensation in a one-pot reaction. Indeed, the heterogeneous Cs/ECH-TMA material can be considered as a synergistic multifunctional organocatalyst due to the presence of a large number of acidic active sites in its structure as well as hydrophilicity. Both PHQs and PHAs were synthesized in the presence of biodegradable heterogeneous Cs/ECH-TMA catalytic system from their corresponding substrates in EtOH under reflux conditions and high to quantitative yields. The Cs/ECH-TMA catalyst is recyclable and can be reused at least four times without significant loss of its catalytic activity.

Covalently Crosslinked Hydrogels via Step-Growth Reactions: Crosslinking Chemistries, Polymers, and Clinical Impact

Hydrogels are an important class of biomaterials with the unique property of high-water content in a crosslinked polymer network. In particular, chemically crosslinked hydrogels have made a great clinical impact in past years because of their desirable mechanical properties and tunability of structural and chemical properties. Various polymers and step-growth crosslinking chemistries are harnessed for fabricating such covalently crosslinked hydrogels for translational research. However, selecting appropriate crosslinking chemistries and polymers for the intended clinical application is time-consuming and challenging. It requires the integration of polymer chemistry knowledge with thoughtful crosslinking reaction design. This task becomes even more challenging when other factors such as the biological mechanisms of the pathology, practical administration routes, and regulatory requirements add additional constraints. In this review, key features of crosslinking chemistries and polymers commonly used for preparing translatable hydrogels are outlined and their performance in biological systems is summarized. The examples of effective polymer/crosslinking chemistry combinations that have yielded clinically approved hydrogel products are specifically highlighted. These hydrogel design parameters in the context of the regulatory process and clinical translation barriers, providing a guideline for the rational selection of polymer/crosslinking chemistry combinations to construct hydrogels with high translational potential are further considered.

Glycosylated cellulose derivatives with regioselective distributions of pendant glucose moieties

Inspired by the presence of diverse carbohydrates on the surface of biological systems, we present herein a method for the synthesis of sugar-bearing polymers derived from renewable cellulose. In this paper, novel glycosylated cellulose derivatives were successfully synthesized containing a series of subsequent reactions: (1) synthesis of cellulose derivatives with pendant hydroxyl groups via nucleophilic substitution; (2) further sequential reactions containing a novel TEMPO/[bis(acetoxy)iodo]benzene (BAIB)-mediated oxidation of pendant hydroxyl groups, Schiff base formation and reduction in one-pot reaction; and (3) thiol-ene click reaction as an efficient tool to generate cellulose derivatives with pendant glucosyl groups. Furthermore, the glucosyl groups were only linked with the C6 position of anhydroglucose units (AGUs) of cellulose. Moreover, the glycosylated cellulose derivatives could be reversibly cross-linked by 1,4-phenylenediboronic acid at pH 10 and dissociated into single polymer chains by using glucose, which allow such glycolated cellulose derivatives to be interesting responsive materials.

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.

Cytocompatible in situ forming chitosan/hyaluronan hydrogels via a metal-free click chemistry for soft tissue engineering

Injectable hydrogels are important cell scaffolding materials for tissue engineering and regenerative medicine. Here, we report a new class of biocompatible and biodegradable polysaccharide hydrogels derived from chitosan and hyaluronan via a metal-free click chemistry, without the addition of copper catalyst. For the metal-free click reaction, chitosan and hyaluronan were modified with oxanorbornadiene (OB) and 11-azido-3,6,9-trioxaundecan-1-amine (AA), respectively. The gelation is attributed to the triazole ring formation between OB and azido groups of polysaccharide derivatives. The molecular structures were verified by FT-IR spectroscopy and elemental analysis, giving substitution degrees of 58% and 47% for chitosan-OB and hyaluronan-AA, respectively. The in vitro gelation, morphologies, equilibrium swelling, compressive modulus and degradation of the composite hydrogels were examined. The potential of the metal-free hydrogel as a cell scaffold was demonstrated by encapsulation of human adipose-derived stem cells (ASCs) within the gel matrix in vitro. Cell culture showed that this metal-free hydrogel could support survival and proliferation of ASCs. A preliminary in vivo study demonstrated the usefulness of the hydrogel as an injectable scaffold for adipose tissue engineering. These characteristics provide a potential opportunity to use the metal-free click chemistry in preparation of biocompatible hydrogels for soft tissue engineering applications.

Rapid hybridization of chitosan-gold-antibodies via metal-free click in water-based systems: a model approach for naked-eye detectable antigen sensors

A surface plasmon resonance (SPR) expression after hybridization of chitosan-gold nanoparticle-antibody (CS-AuNPs-Ab) based on: i) metal-free click chemistry, and, ii) in water system as an approach for a rapid antigen sensing, is proposed. The chitosan-hydroxybenzyl triazole complex enables us to carry out the conjugation of mPEG and trifluoromethylated oxanorbornadiene (OND) in water. CS-mPEG-OND further allows metal-free click to hybridize chitosan (CS) with azido-modified gold nanoparticles (azido-AuNPs) in aqueous solution at room temperature. The CS-mPEG-OND conjugated with LipL32 antibody (Ab) not only effectively binds with LipL32 antigen (Ag) but also performs the cycloaddition with azido-AuNPs to display a change in color within 2 min. The phenomenon leads to a simple and efficient naked-eye antigen detection technique.