An investigation of construction of chondroitin sulfate E (CS-E) repeating unit

Advances and challenges in biotechnological production of chondroitin sulfate and its oligosaccharides

Chondroitin sulfate (CS) is a member of glycosaminoglycans (GAGs) and has critical physiological functions. CS is widely applied in medical and clinical fields. Currently, the supply of CS relies on traditional animal tissue extraction methods. From the perspective of medical applications, the biggest drawback of animal-derived CS is its uncontrollable molecular weight and sulfonated patterns, which are key factors affecting CS activities. The advances of cell-free enzyme catalyzed systems and de novo biosynthesis strategies have paved the way to rationally regulate CS sulfonated pattern and molecular weight. In this review, we first present a general overview of biosynthesized CS and its oligosaccharides. Then, the advances in chondroitin biosynthesis, 3'-phosphoadenosine-5'-phosphosulfate (PAPS) synthesis and regeneration, and CS biosynthesis catalyzed by sulfotransferases are discussed. Moreover, the progress of mining and expression of chondroitin depolymerizing enzymes for preparation of CS oligosaccharides is also summarized. Finally, we analyze and discuss the challenges faced in synthesizing CS and its oligosaccharides using microbial and enzymatic methods. In summary, the biotechnological production of CS and its oligosaccharides is a promising method in addressing the drawbacks associated with animal-derived CS and enabling the production of CS oligosaccharides with defined structures.

β-Glycosylations with 2-Deoxy-2-(2,4-dinitrobenzenesulfonyl)-amino-glucosyl/galactosyl Selenoglycosides: Assembly of Partially N-Acetylated β-(1 → 6)-Oligoglucosaminosides

An efficient protocol has been established for β-glycosylations with 2-deoxy-2-(2,4-dinitrobenzenesulfonyl)amino (2dDNsNH)-glucopyranosyl/galactopyranosyl selenoglycosides using PhSeCl/AgOTf as an activating system. The reaction features highly β-selective glycosylation with a wide range of alcohol acceptors that are either sterically hindered or poorly nucleophilic. Thioglycoside- and selenoglycoside-based alcohols prove to be viable nucleophiles, opening up new opportunities for one-pot construction of oligosaccharides. The power of this approach is highlighted by the efficient assembly of tri-, hexa-, and nonasaccharides composed of β-(1 → 6)-glucosaminosyl residues based on one-pot preparation of a triglucosaminosyl thioglycoside with DNs, phthaloyl, and 2,2,2-trichloroethoxycarbonyl as the protecting groups of amino groups. These glycans are potential antigens for developing glycoconjugate vaccines against microbial infections.

Total synthesis of chondroitin sulfate E oligosaccharides and biological study

A total synthesis approach of CS-E oligosaccharides was established and a series of derivatives were synthesized. These oligosaccharides were evaluated for a glycosaminoglycan (GAG)-binding protein interaction against cytokines, midkine, and pleiotrophin, by surface-plasmon resonance (SPR) assay. The binding epitopes of oligosaccharides to midkine were mapped using a saturation transfer difference (STD) NMR technique. The groups on the reducing end contributed to binding affinity, and should not be ignored in biological assays. These findings contribute to the structure and activity relationship research and a foundation of understanding that will underpin potential future optimization of this class of oligosaccharides as pharmaceutical agents.

Synthesis of the Aeromonas veronii strain Bs8 disaccharide repeating unit

Presented herein is the synthesis of the Aeromonas veronii disaccharide repeating unit which has been achieved in 11 steps starting from d-fucose and d-galactosamine.

4-(tert-Butyldiphenylsilyloxy)-2,2-dimethylbutanoyl: An Easily Removable Pivaloyl-Type Protecting Group with High Orthogonality

Protecting groups play multiple and vital roles during the synthesis of carbohydrates and other natural products. We herein report the installation and orthogonal cleavage, under mild conditions, of a 4-(tert-butyldiphenylsilyloxy)-2,2-dimethylbutanoyl (BDMB) group as a sterically hindered pivaloyl-type hydroxy protecting group. The compatibility of this substituent with the removal of other protecting groups is also investigated. Due to its advantageous properties, BDMB is anticipated to function as a valuable agent for masking hydroxy groups.

Synthesis of structurally defined chondroitin sulfate: Paving the way to the structure-activity relationship studies

Chondroitin sulfate (CS) is one of the major and widespread glycosaminoglycans, a family of structurally complex, linear, anionic hetero-co-polysaccharides. CS plays a vital role in various normal physiological and pathological processes, thus, showing varieties of biological activities, such as anti-oxidation, anti-atherosclerosis, anti-thrombosis, and insignificant immunogenicity. However, the heterogeneity of the naturally occurring CS potentially leads to function unspecific and limits further structure-activity relationship studies. Therefore, the synthesis of CS with well-defined and uniform chain lengths is of major interest for the development of reliable drugs. In this review, we examine the remarkable progress that has been made in the chemical, enzymatic and chemoenzymatic synthesis of CS and its derivatives, providing a broad spectrum of options to access CS of well controlled chain lengths.

The synthesis and biological evaluation of chondroitin sulfate E glycodendrimers

Aim: Chondroitin sulfate (CS) is a class of highly sulfated polysaccharides that possess many important biological functions. The heterogeneity of CS limits pharmacological research and leads to ambiguous mechanisms. Thus, glycomimetics are demanded as replacement of natural polysaccharides to explore important biological processes. Results & methodology: Here the preparation of CS glycodendrimers is reported as well as their use as CS mimetics to regulate the NF-κB pathway. Multivalent presentation of sugar epitopes on appropriate dendrimer scaffolds increased the suppression of the NF-κB pathway. The interaction between CS-E molecules and TNF-α was examined by nuclear magnetic resonance technology. Conclusion: Overall, the glycodendrimer reported here may be potentially employed as molecular tool to investigate the biological functions of CS.

Unexpected loss of stereoselectivity in glycosylation reactions during the synthesis of chondroitin sulfate oligosaccharides

Here, we present an exploratory study on the fluorous-assisted synthesis of chondroitin sulfate (CS) oligosaccharides. Following this approach, a CS tetrasaccharide was prepared. However, in contrast to our previous results, a significant loss of β-selectivity was observed in [2 + 2] glycosylations involving N-trifluoroacetyl-protected D-galactosamine donors and D-glucuronic acid (GlcA) acceptors. These results, together with those obtained from experiments employing model monosaccharide building blocks, highlight the impact of the glycosyl acceptor structure on the stereoselectivity of glycosylation reactions. Our study provides useful data about the substitution pattern of GlcA units for the efficient synthesis of CS oligomers.

Synthesis of trisaccharide repeating unit of fucosylated chondroitin sulfate

A synthesis of repeating unit of trisaccharide, complete stereoselectivity of glycosylation and flexible synthetic strategy.

Synthesis of the tetrasaccharide repeating unit of the cryoprotectant capsular polysaccharide from Colwellia psychrerythraea 34H

Synthesis of the threonine-decorated tetrasaccharide repeating unit of a cryoprotectant polysaccharide with a glycosaminoglycan-like structure.

Total Synthesis of Zwitterionic Tetrasaccharide Repeating Unit from Bacteroides fragilis ATCC 25285/NCTC 9343 Capsular Polysaccharide PS A1 with Alternating Charges on Adjacent Monosaccharides

The tetrasaccharide repeating unit of zwitterionic polysaccharide A1 (PS A1) from Bacteroides fragilis ATCC 25285/NCTC 9343 has been synthesized using a linear glycosylation approach. One key step includes an α(1,4)-stereoselective [2 + 1] glycosylation of a 2,4,6-trideoxy-2-acetamido-4-amino-d-Gal p (AAT) donor with a poorly reactive axial C4-OH disaccharide acceptor. Mild acid-mediated deacetylation and a challenging [3 + 1] glycosylation are also highlighted. The strategy is inclusive of a single-pot, three-step deprotection affording PS A1 with alternating charges on adjacent monosaccharide units.

Synthesis of Azide-Modified Chondroitin Sulfate Precursors: Substrates for "Click"- Conjugation with Fluorescent Labels and Oligonucleotides

Azidopropyl-modified precursors of chondroitin sulfate (CS) tetrasaccharides have been synthesized, which, after facile conversion to final CS structures, may be conjugated with alkyne-modified target compounds by a one-pot “click”-ligation. RP HPLC was used for the monitoring of the key reaction steps (protecting group manipulation and sulfation) and purification of the CS precursors (as partially protected form, bearing the O-Lev, O-benzoyl, and N-trichloroacetyl groups and methyl esters). Subsequent treatments with aqueous NaOH, concentrated ammonia, and acetic anhydride (i.e., global deprotection and acetylation of the galactosamine units) converted the precursors to final CS structures. The azidopropyl group was exposed to a strain-promoted azide–alkyne cycloaddition (SPAAC) with a dibenzylcyclooctyne-modified carboxyrhodamine dye to give labeled CSs. Conjugation with a 5′-cyclooctyne-modified oligonucleotide was additionally carried out to show the applicability of the precursors for the synthesis of biomolecular hybrids.

An Approach to Synthesize Chondroitin Sulfate-E (CS-E) Oligosaccharide Precursors

An approach was developed to synthesize chondroitin sulfate-E (CS-E) oligosaccharides by adopting a postglycosylation-transformation strategy: different from all of the traditional approaches, the characteristic groups of CS-E were introduced following the assembly of the oligosaccharides. The adjusted strategy rendered an easy chain elongation strategy. All of the elongation steps generated high yields with excellent glycosylation outcomes. An orthogonally protected disaccharide was used as the building block to provide flexibility for the group transformation and derivatization at the N-2 position of the GalNAc residue and the O-1,5 positions of the GlcA residue, thereby providing ready access for the further examination of the structure-activity relationship (SAR) of CS-E molecules.