Role of Protecting Groups in Synthesis and Self-Assembly of Glycopolymers

Carbohydrate-Based Macromolecular Biomaterials

Carbohydrates are the most abundant and one of the most important biomacromolecules in Nature. Except for energy-related compounds, carbohydrates can be roughly divided into two categories: Carbohydrates as matter and carbohydrates as information. As matter, carbohydrates are abundantly present in the extracellular matrix of animals and cell walls of various plants, bacteria, fungi, etc., serving as scaffolds. Some commonly found polysaccharides are featured as biocompatible materials with controllable rigidity and functionality, forming polymeric biomaterials which are widely used in drug delivery, tissue engineering, etc. As information, carbohydrates are usually referred to the glycans from glycoproteins, glycolipids, and proteoglycans, which bind to proteins or other carbohydrates, thereby meditating the cell-cell and cell-matrix interactions. These glycans could be simplified as synthetic glycopolymers, glycolipids, and glycoproteins, which could be afforded through polymerization, multistep synthesis, or a semisynthetic strategy. The information role of carbohydrates can be demonstrated not only as targeting reagents but also as immune antigens and adjuvants. The latter are also included in this review as they are always in a macromolecular formulation. In this review, we intend to provide a relatively comprehensive summary of carbohydrate-based macromolecular biomaterials since 2010 while emphasizing the fundamental understanding to guide the rational design of biomaterials. Carbohydrate-based macromolecules on the basis of their resources and chemical structures will be discussed, including naturally occurring polysaccharides, naturally derived synthetic polysaccharides, glycopolymers/glycodendrimers, supramolecular glycopolymers, and synthetic glycolipids/glycoproteins. Multiscale structure-function relationships in several major application areas, including delivery systems, tissue engineering, and immunology, will be detailed. We hope this review will provide valuable information for the development of carbohydrate-based macromolecular biomaterials and build a bridge between the carbohydrates as matter and the carbohydrates as information to promote new biomaterial design in the near future.

Exploring and Controlling the Polymorphism in Supramolecular Assemblies of Carbohydrates and Proteins

In biology, polymorphism is a well-known phenomenon by which a discrete biomacromolecule can adopt multiple specific conformations in response to its environment. This term can be extended to the ability of biomacromolecules to pack into different ordered patterns. Thus, exploration and control of the polymorphism of biomacromolecules via supramolecular methods have been key steps in achieving bioinspired structures, developing bioinspired functional materials, and exploring the mechanisms of these self-assembly processes, which are models for more complex biological systems. This task could be difficult for proteins and carbohydrates due to the complicated multiple noncovalent interactions of these two species which can hardly be manipulated.In this account, dealing with the structural polymorphisms from biomacromolecular assemblies, we will first briefly comment on the problems that carbohydrate/protein assemblies are facing, and then on the basis of our long-term research on carbohydrate self-assemblies, we will summarize the new strategies that we have developed in our laboratory in recent years to explore and control the polymorphism of carbohydrate/protein assemblies.Considering the inherent ability of carbohydrates to recognize lectin, we proposed the "inducing ligand" strategy to assemble natural proteins into various nanostructures with highly ordered packing patterns. The newly developed inducing ligand approach opened a new window for protein assembly where dual noncovalent interactions (i.e., carbohydrate-protein interactions and dimerization of rhodamine) instead of the traditionally used protein-protein interactions direct the assembly pattern of proteins. As a result, various polymorphisms of protein assemblies have been constructed by simply changing the ligand chemical structure and/or the rhodamine dimerization.Another concept that we proposed for glycopolymer self-assembly is DISA (i.e., deprotection-induced glycopolymer self-assembly). It is well known that protection-deprotection chemistry has been employed to construct complex oligosaccharide structures. However, its application in glycopolymer self-assembly has been overlooked. We initiated this new strategy with diblock copolymers. Such copolymers with a carbohydrate block having protected pendent groups exist as single chains in organic media. The self-assembly can be initiated by the deprotection of the pendent groups. The process was nicely controlled by introducing various protective groups with different deprotection rates. Later on, the DISA process has been proven practical in water and even in the cellular environment, which opens a new avenue for the development of polymeric glycomaterials.Finally, the resultant polymeric glyco-materials, as a new type of biomimetic materials, provide a nice platform for investigating the functions of glycocalyx. The glycocalyx-mimicking nanoparticles achieved unprecedent functions which exceed their carbohydrate precursors. Here, the reversion of tumor-associated macrophages induced by glycocalyx-mimicking nanoparticles will be discussed with potential applications in cancer immunotherapy, where such a reversion effect could be combined with other methods (e.g., tumor checkpoint blockade).

Poly(triazolyl methacrylate) glycopolymers as potential targeted unimolecular nanocarriers

Synthetic glycopolymers are increasingly investigated as multivalent ligands for a range of biological and biomedical applications. This study indicates that glycopolymers with a fine-tuned balance between hydrophilic sugar pendant units and relatively hydrophobic polymer backbones can act as single-chain targeted nanocarriers for low molecular weight hydrophobic molecules. Non-covalent complexes formed from poly(triazolyl methacrylate) glycopolymers and low molecular weight hydrophobic guest molecules were characterised through a range of analytical techniques - DLS, SLS, TDA, fluorescence spectroscopy, surface tension analysis - and molecular dynamics (MD) modelling simulations provided further information on the macromolecular characteristics of these single chain complexes. Finally, we show that these nanocarriers can be utilised to deliver a hydrophobic guest molecule, Nile red, to both soluble and surface-immobilised concanavalin A (Con A) and peanut agglutinin (PNA) model lectins with high specificity, showing the potential of non-covalent complexation with specific glycopolymers in targeted guest-molecule delivery.

Synthesis toward Bivalent Ligands for the Dopamine D2 and Metabotropic Glutamate 5 Receptors

In this study, we designed and synthesized heterobivalent ligands targeting heteromers consisting of the metabotropic glutamate 5 receptor (mGluR5) and the dopamine D₂ receptor (D₂R). Bivalent ligand 22a with a linker consisting of 20 atoms showed 4-fold increase in affinity for cells coexpressing D₂R and mGluR5 compared to cells solely expressing D₂R. Likewise, the affinity of 22a for mGluR5 increased 2-fold in the coexpressing cells. Additionally, 22a exhibited a 5-fold higher mGluR5 affinity than its monovalent precursor 21a in cells coexpressing D₂R and mGluR5. These results indicate that 22a is able to bridge binding sites on both receptors constituting the heterodimer. Likewise, cAMP assays revealed that 22a had a 4-fold higher potency in stable D₂R and mGluR5 coexpressing cell lines than 1. Furthermore, molecular modeling reveals that 22a is able to simultaneously bind both receptors by passing between the TM5-TM6 interface and establishing six protein-ligand H-bonds.

The effect of linker length on ConA and DC-SIGN binding of S-glucosyl functionalized poly(2-oxazoline)s

A series of poly(2-oxazoline) based glycopolymers with different linkers were prepared via thiol–ene click reaction and cationic ring opening reaction. The binding of these polymers to lectins were studied.