Multi-step semi-synthesis, structural characterization and growth factor interaction study of regiochemically sulfated diabolican polysaccharides

Diabolican is an exopolysaccharide (EPS) produced by Vibrio diabolicus HE800, a mesophilic bacterium firstly isolated from a deep-sea hydrothermal field. Its glycosaminoglycan (GAG)-like structure, consisting of a tetrasaccharide repeating unit composed of two aminosugars (N-acetyl-glucosamine and N-acetyl-galactosamine) and two glucuronic acid units, suggested to subject it to regioselective sulfation processes, in order to obtain some sulfated derivatives potentially acting as GAG mimics. To this aim, a multi-step semi-synthetic approach, relying upon tailored sequence of regioselective protection, sulfation and deprotection steps, was employed in this work. The chemical structure of the obtained sulfated diabolican derivatives was characterized by a multi-technique analytic approach, in order to define both degree of sulfation (DS) and sulfation pattern within the polysaccharide repeating unit, above all. Finally, binding affinity for some growth factors relevant for biomedical applications was measured for both starting diabolican and sulfated derivatives thereof. Collected data suggested that sulfation pattern could be a key structural element for the selective interaction with signaling proteins not only in the case of native GAGs, as already known, but also for GAG-like structures obtained by regioselective sulfation of naturally unsulfated polysaccharides.

Towards the semi-synthesis of phosphorylated mimics of glycosaminoglycans: Screening of methods for the regioselective phosphorylation of chondroitin

Glycosaminoglycan (GAG) mimics carrying phosphate rather than sulfate anionic groups have been poorly investigated, in spite of their interesting perspectives. While some GAG-mimicking phosphorylated polymers have been reported, to the best of our knowledge no phosphorylated polysaccharides having the same backbone of natural sulfated GAGs have been accessed yet. To fill this gap, in this work two standard phosphorylation protocols and two recently reported procedures have been screened on a set of polysaccharide species composed by microbial sourced chondroitin and three partially protected, semi-synthetic derivatives thereof. A detailed structural characterization by 1H, 13C and 31P NMR spectroscopy revealed the higher versatility of the innovative, biomimetic reaction employing monopotassium salt of phosphoenolpyruvate (PEPK) with respect to standard phosphorylating agents (phosphoric acid or phosphorus oxychloride). Indeed, PEP-K and H3PO4 gave similar results in the regioselective phosphorylation of the primary hydroxyls of unprotected chondroitin, while only the former reacted on partially protected chondroitin derivatives in a controlled, regioselective fashion, affording chondroitin phosphate (CP) polysaccharides with different derivatization patterns. The reported results represent the first, key steps towards the systematic semi-synthesis of phosphorylated GAGs as a new class of GAG mimics and to the evaluation of their biological activities in comparison with native sulfated GAGs.

Glycosaminoglycans: What Remains To Be Deciphered?

Glycosaminoglycans (GAGs) are complex polysaccharides exhibiting a vast structural diversity and fulfilling various functions mediated by thousands of interactions in the extracellular matrix, at the cell surface, and within the cells where they have been detected in the nucleus. It is known that the chemical groups attached to GAGs and GAG conformations comprise "glycocodes" that are not yet fully deciphered. The molecular context also matters for GAG structures and functions, and the influence of the structure and functions of the proteoglycan core proteins on sulfated GAGs and vice versa warrants further investigation. The lack of dedicated bioinformatic tools for mining GAG data sets contributes to a partial characterization of the structural and functional landscape and interactions of GAGs. These pending issues will benefit from the development of new approaches reviewed here, namely (i) the synthesis of GAG oligosaccharides to build large and diverse GAG libraries, (ii) GAG analysis and sequencing by mass spectrometry (e.g., ion mobility-mass spectrometry), gas-phase infrared spectroscopy, recognition tunnelling nanopores, and molecular modeling to identify bioactive GAG sequences, biophysical methods to investigate binding interfaces, and to expand our knowledge and understanding of glycocodes governing GAG molecular recognition, and (iii) artificial intelligence for in-depth investigation of GAGomic data sets and their integration with proteomics.

Glycosaminoglycan Mimetic Precision Glycomacromolecules with Sequence-Defined Sulfation and Rigidity Patterns

Sulfated glycosaminoglycans (sGAGs) such as heparan sulfate (HS) are structurally diverse linear polysaccharides that are involved in many biological processes and have gained interest as antiviral compounds. Their recognition is driven by a complex orchestra of structural parameters that are still under intense investigation. One distinct characteristic is the incorporation of sulfation patterns including highly sulfated and non-sulfated sequences that provide variations in flexibility and conformation, which in turn impact the biological function of sGAGs. However, these distinct features have not yet been fully realized in the synthetic preparation of sGAG mimetics. Here, we present the synthesis of three groups of sulfated glycomacromolecules as sGAG mimetics: (i) globally sulfated glycooligomers, (ii) glycooligomers with sequence-defined sulfation patterns, and (iii) a globally sulfated glycooligomer-oligo-L-proline hybrid structure. The complete synthesis, including chemical sulfation, was conducted on solid support, enabled by the introduction of a commercially available photocleavable linker allowing for the preservation of sensitive sulfates during cleavage of the products. Structures were obtained in good purity and with high degrees of sulfation demonstrating the wide applicability of this methodology to prepare tailor-made sulfated glycomacromolecules and similar sGAG mimetics. Structures were tested for their anticoagulant properties showing activity similar to their natural HS counterpart and significantly lower than HP.

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.

Synthesis and Biopharmaceutical Applications of Sugar-Based Polymers: New Advances and Future Prospects

The rapid rise in research interest in carbohydrate-based polymers is undoubtedly due to the nontoxic nature of such materials in an in vivo environment and the versatile roles that the polymers can play in cellular functions. Such polymers have served as therapeutic tools for drug delivery, including antigens, proteins, and genes, as well as diagnostic devices. Our focus in the first half of this Review is on synthetic methods based on ring-opening polymerization and enzyme-catalyzed polymerization, along with controlled radical polymerization. In the second half of this Review, sugar-based polymers are discussed on the basis of their remarkable success in competitive receptor binding, as multifunctional nanocarriers of targeting inhibitors for cancer treatment, in genome-editing delivery, in immunotherapy based on endogenous antibody recruitment, and in treatment of respiratory diseases, including influenza A. Particular emphasis is put on the synthesis and biopharmaceutical applications of sugar-based polymers published in the most recent 5 years. A noticeable attribute of carbohydrate-based polymers is that the sugar-receptor interactions can be facilitated by the cooperative effect of multiple sugar units. Their diversified topology and structures will drive the development of new synthetic strategies and bring about important applications, including coronavirus-related drug therapy.

Vascular cell responses to silicone surfaces grafted with heparin-like polymers: surface chemical composition vs. topographic patterning

Heparin-like polymers are promising synthetic materials with biological functionalities, such as anticoagulant ability, growth factor binding to regulate cellular functions, and inflammation mediation, similar to heparin. The biocompatibility of heparin-like polymers with well-defined chemical structures has inspired many researchers to design heparin-like surfaces to explore their biological applications. The concept of the recombination of functional heparin structural units (sulfonate- and glyco-containing units) was proven to be successful in designing heparin-mimicking surfaces. However, besides surface structural units, topographic patterning is also an important contributor to the biological activity of the surfaces modified with heparin-like polymers. In this work, both surface structural units and topographic patterning were taken into account to investigate the vascular cell behaviors on the silicone surfaces. A facile method for the production of patterned bromine-containing polydimethylsiloxane surface (PDMS-Br) was developed from a one-step multicomponent thermocuring procedure and replica molding using a nanohole-arrayed silicon template. Different structural units of heparin-like polymers, i.e. homopolymer of sulfonate-containing sodium 4-vinylbenzenesulfonate (pSS), homopolymer of glyco-containing 2-(methacrylamido)glucopyranose (pMAG), and copolymers of MAG and SS (pSG), were then introduced on the flat and patterned PDMS-Br surface using visible light-induced graft polymerization. For the flat surfaces, compared with the PDMS-Br surface, pSS-grafted and pSG-grafted surfaces significantly increased cell densities of both human umbilical vein endothelial cells (HUVECs) and human umbilical vein smooth muscle cells (HUVSMCs), indicating that they are "vascular cell-friendly". In contrast, the pMAG-grafted surface showed decreased cell attachment of both HUVECs and HUVSMCs, indicating that the pMAG-grafted surface is "vascular cell-resistant". Moreover, surface topographic patterning enhanced the cell responses to the corresponding flat surfaces. That is to say, surface patterning can make the "vascular cell-friendly" surface still friendly, and the "vascular cell-resistant" surface much more resistant. The combination of surface structural units and topographic patterning shows promise in the preparation of new heparin-like surfaces with improved cell compatibility that is suitable for blood-compatible biomaterials.

Biomimetic synthesis of chondroitin sulfate-analogue hydrogels for regulating osteogenic and chondrogenic differentiation of bone marrow mesenchymal stem cells

As a typical representative of crucial glycosaminoglycans (GAGs), chondroitin sulfate (CS) with sulfonated polysaccharide in structures extensively exists in the extracellular matrix (ECM) and exhibits peculiar bioactivity on the regulation of cells behaviors and fates (e.g. proliferation and differentiation) in organisms. Nevertheless, some intrinsic disadvantages of natural CS mainly ascribe to the intricate structure and inhomogeneous composition (especially the uncontrollable sulfonate degrees), resulting in overt restrictions on its physiological functions and applications. Although recent bionic synthesis of artificial GAGs analogues at the molecular level have already provides an efficient strategy to reconstruct GAG for regulating the cellular behaviors and fates, it still remains great challenges to rationally design and synthesize GAGs analogues with special composition and structure for precisely mimicking ECM. Simultaneously, the relevant regulation process of GAG analogues on cell fate needs to be further studied as well. Herein, chondroitin sulfate-analogue (CS-analogue) hydrogels with diverse contents of saccharide and sulfonate units in the networks were fabricated through photo-polymerization and then characterized by Fourier transform infrared (FT-IR) spectroscopy, zeta potential and scanning electron microscope (SEM). Additionally, CS-analogue hydrogels with proper mechanical properties exhibited favorable swelling, degradation performance and prominent cytocompatibility. According to cell cultivation results, CS-analogue hydrogel with a certain proportion of saccharide and sulfonate units presented preferable promotion on the adhesion, spreading, proliferation and differentiation of bone marrow mesenchymal stem cells (BMSCs), shedding light on the significance of saccharide and sulfonate units in regulating cell behaviors. Furthermore, BMSCs cultivated with CS-analogue hydrogels under different culture conditions were also systematically investigated, revealing that with the help of cultivation environment CS-analogue hydrogels owned the remarkable capacity of directing either chondrogenic or osteogenic differentiation of BMSCs. Therefore, it is envisioned that versatile CS-analogue hydrogels would have promising application prospects in the biomedical and clinical fields.

Sulfonated RAFT Copolymers as Heparin Mimetics: Synthesis, Reactivity Ratios, and Anticoagulant Activity

The glycosaminoglycan heparin is a clinically important anticoagulant drug, primarily used to reduce the risk of blood clots (thrombosis) during surgery. Despite its importance in medicine and its continuous use over many decades, heparin suffers from several limitations associated with its heterogeneity and its extraction from animal tissues. In order to address these limitations, reversible addition-fragmentation chain transfer polymerization is utilized to prepare a library of heparin mimetic copolymers from the sulfonated monomers sodium 4-styrene sulfonate, potassium-3-sulfopropyl acrylate, potassium-3-sulfopropyl methacrylate, and sodium-2-acrylamido-2-methyl-1-propane sulfonate. Copolymers are prepared using combinations of two different monomers in various ratios. Monomer reactivity ratios are also determined for some representative monomer combinations, and all polymers are characterized by ¹ H NMR spectroscopy and gel permeation chromatography. The anticoagulant activities of the copolymers are determined by activated partial thromboplastin time and thrombin clotting time assays and structure-activity relationships are explored.

Chemoenzymatic Synthesis of Heparan Sulfate Mimetic Glycopolymers and Their Interactions with the Receptor for Advanced Glycation End-Product

Heparan sulfate (HS) is a sulfated polysaccharide presenting on the animal cell surface and in the extracellular matrix that plays a critical role in a range of different biological processes. The receptor for advanced glycation end-products (RAGE), as a major receptor linked to numerous diseases, can interact with HS to activate signaling of RAGE ligands in the disease process. We herein report a concise chemoenzymatic approach for the synthesis of HS-mimetic glycopolymers as RAGE antagonists. Glycopolymer with GlcA units was chemically synthesized and subsequently modified by enzymatic elongation and chemical sulfation. Six HS-mimetic glycopolymers with pendant sulfated di-, tri-, or tetrasaccharides were successfully prepared for evaluation of their interaction with RAGE. Upon evaluation, the HS-mimetic glycopolymer decorated with overall sulfated trisaccharides was determined to have the highest binding affinity with RAGE. These findings would promote the further exploration of HS-RAGE interactions and the development of RAGE antagonists.

Atom Transfer Radical Polymerization for Biorelated Hybrid Materials

Proteins, nucleic acids, lipid vesicles, and carbohydrates are the major classes of biomacromolecules that function to sustain life. Biology also uses post-translation modification to increase the diversity and functionality of these materials, which has inspired attaching various other types of polymers to biomacromolecules. These polymers can be naturally (carbohydrates and biomimetic polymers) or synthetically derived and have unique properties with tunable architectures. Polymers are either grafted-to or grown-from the biomacromolecule's surface, and characteristics including polymer molar mass, grafting density, and degree of branching can be controlled by changing reaction stoichiometries. The resultant conjugated products display a chimerism of properties such as polymer-induced enhancement in stability with maintained bioactivity, and while polymers are most often conjugated to proteins, they are starting to be attached to nucleic acids and lipid membranes (cells) as well. The fundamental studies with protein-polymer conjugates have improved our synthetic approaches, characterization techniques, and understanding of structure-function relationships that will lay the groundwork for creating new conjugated biomacromolecular products which could lead to breakthroughs in genetic and tissue engineering.

The First Synthesis of Periodic and Alternating Glycopolymers by RAFT Polymerization: A Novel Synthetic Pathway for Glycosaminoglycan Mimics

This study concerned the controlled synthesis of periodic glycopolymers by reversible addition-fragmentation chain transfer (RAFT) copolymerization. To this end, maltose- and lactose-substituted vinyl ethers (MalVE and LacVE, respectively) and maltose-substituted maleimide (MalMI) were newly synthesized. RAFT copolymerization of MalVE and ethyl maleimide (EtMI) (monomer feed ratio: MalVE:EtMI = 1:1) afforded periodic glycopolymers (poly(MalVE-co-EtMI)) consisting of major parts of alternating structure (-(MalVE-EtMI)n-) and a small part of consecutive sequences of EtMI (⁻EtMI-EtMI-). Occurrence of the latter sequences was caused by the homopolymerizability of maleimide under the present polymerization condition, and the formation of the consecutive sequences of EtMI was successfully suppressed by varying the monomer feed ratio. RAFT copolymerization of LacVE and EtMI was also found to proceed and similarly yielded periodic glycopolymers (poly(LacVE-co-EtMI)). Moreover, RAFT copolymerization of LacVE and MalMI (monomer feed ratio: LacVE:MalMI = 1:1) was performed to give copolymers (poly(LacVE-co-MalMI)) having composition ratio of LacVE/MalMI ≈ 36/64. The resultant periodic glycopolymers poly(MalVE-co-EtMI) and poly(LacVE-co-EtMI) were subjected to lectin binding assay using concanavalin A and peanut agglutinin, exhibiting the glycocluster effect. Moreover, these glycopolymers obtained from the copolymerization of VE and MI were found to be non-cytotoxic.

Chondroitin-analogue decorated magnetic nanoparticles via a click reaction for selective adsorption of low-density lipoprotein

Chondroitin-analogue polymers are synthesized to anchor on Fe₃O₄ nanoparticle surfaces to achieve efficient, selective and reusable adsorption of low-density lipoprotein.

Synthesis of chitosan-mimicking cationic glycopolymers by Cu(0)-LRP for efficient capture and killing of bacteria

A schematic representation of the preparation of cationic magnetic glyconanoparticles by Cu(0)-LRP to efficiently capture, kill and separate E. coli from water.