Solid-phase Oligosaccharide Synthesis Research Articles

Accelerated Solid Phase Glycan Synthesis: ASGS.

Solid phase synthesis is the most dominant approach for the preparation of biological oligomers as it enables the introduction of monomers iteratively. Accelerated solid phase synthesis of biological oligomers is crucial for chemical biology, but its application to the synthesis of oligosaccharides is not trivial. Solid-phase oligosaccharide assembly is a slow process performed in a variety of conditions and temperatures, requires an inert gas atmosphere, and demands high excess of glycosyl donors. The process is done in special synthesizers and poor mixing of the solid support increases the risk of diffusion-independent hydrolysis of the activated donors. High shear stirring is a new way to accelerate solid phase synthesis. The efficient mixing ensures that reactive intermediates can diffuse faster to the solid support thereby increasing the kinetics of the reactions. We report here a stirring-based accelerated solid-phase oligosaccharide synthesis. We harnessed high shear mixing to perform diffusion-dependent glycosylation in a short reaction time. We minimized the use of glycosyl donors and the need to use an inert atmosphere. We showed that by tailoring the deprotection and glycosylation conditions to the same temperature, assembly steps are performed continuously, and full glycosylation cycles are completed in minutes.

Towards a Systematic Understanding of the Influence of Temperature on Glycosylation Reactions.

Glycosidic bond formation is a continual challenge for practitioners. Aiming to enhance the reproducibility and efficiency of oligosaccharide synthesis, we studied the relationship between glycosyl donor activation and reaction temperature. A novel semi‐automated assay revealed diverse responses of members of a panel of thioglycosides to activation at various temperatures. The patterns of protecting groups and the thiol aglycon combine to cause remarkable differences in temperature sensitivity among glycosyl donor building blocks. We introduce the concept of donor activation temperature to capture experimental insights, reasoning that glycosylations performed below this reference temperature evade deleterious side reactions. Activation temperatures enable a simplified temperature treatment and facilitate optimization of glycosyl donor usage. Isothermal glycosylation below the activation temperature halved the equivalents of building block required in comparison to the standard “ramp” regime used in solution‐ and solid‐phase oligosaccharide synthesis to‐date.

Liquid-Phase and Ultrahigh-Frequency-Acoustofluidics-Based Solid-Phase Synthesis of Biotin-Tagged 6′/3′-Sialyl-N-Acetylglucosamine by Sequential One-Pot Multienzyme System

6′/3′-Sialylated N-acetyllactosamine (6′/3′-SLN) is important for discrimination of the source (human or avian) of influenza virus strains. Biotinylated oligosaccharides have been widely used for analysis and quick detection. The development of efficient strategies to synthesize biotin-tagged 6′/3′-SLN have become necessary. Effective mixing is essential for enzymatic solid-phase oligosaccharide synthesis (SPOS). In the current study, newly developed technology ultrahigh-frequency-acoustofluidics (UHFA), which can provide a powerful source for efficient microfluidic mixing, solid-phase oligosaccharide synthesis and one-pot multienzyme (OPME) system, were used to develop a new strategy for oligosaccharide synthesis. Firstly, biotinylated N-acetylglucosamine was designed and chemically synthesized through traditional approaches. Secondly, biotinylated 6′- and 3′-sialyl-N-acetylglucosamines were prepared in solution through two sequential OPME modules in with a yield of ~95%. Thirdly, 6′-SLN was also prepared through UHFA-based enzymatic solid-phase synthesis on magnetic beads with a yield of 64.4%. The current strategy would be potentially used for synthesis of functional oligosaccharides.

The development of a dedicated polymer support for the solid-phase oligosaccharide synthesis.

Reported herein is the development of a novel polystyrene-based resin that we named PanzaGel. The resin was equipped with diethylene glycol-derived cross-linker with the dedicated application to polymer supported glycan synthesis in mind. After investigating its swelling properties and obtaining encouraging data for its chemical and thermal stability we accessed the amenability of PanzaGel to the HPLC-based platform for the automated synthesis. Comparable glycosylation results to those with traditional supports have been obtained in the synthesis of glycans up to pentasaccharide that was obtained in 30% overall yield. The automated synthesis set-up implemented a common analytical autosampler for delivering all reagents for all steps of the glycan synthesis and cleavage.

ChemInform Abstract: Principles of Modern Solid‐Phase Oligosaccharide Synthesis

AbstractReview: 82 refs.

Principles of modern solid-phase oligosaccharide synthesis

The past few decades have seen a renewed interest in the chemical synthesis of oligosaccharides, owing to increased recognition of their biological importance. Of the different approaches to oligosaccharides, solid-phase synthesis has emerged as a particularly attractive option, due in large part to its potential for automation. This perspective describes principles to consider when planning solid-phase oligosaccharide synthesis (SPOS), including recent achievements and areas where future work is necessary.

A Second-Generation Tandem Ring-Closing Metathesis Cleavable Linker for Solid-Phase Oligosaccharide Synthesis

A tandem ring-closing metathesis cleavable linker system for solid-phase oligosaccharide synthesis has been developed. The acid- and base-stable linker can be readily cleaved with Grubbs second-generation catalyst without the use of alkene additives to liberate the assembled oligosaccharides from the solid support. Application of the linker was shown in three solid-phase oligosaccharide synthesis campaigns. Two frame-shifted hyaluronic acid fragments were prepared, and we also report the synthesis of a trimeric β-1,3-glucan fragment, in which, next to the linker, our recently reported 4-azido-2,2-dimethylbutanoyl (AzDMB) protective group was applied.

Acylsulfonamide safety-catch linker: promise and limitations for solid-phase oligosaccharide synthesis.

Safety-catch linkers are useful for solid-phase oligosaccharide synthesis as they are orthogonal to many common protective groups. A new acylsulfonamide safety-catch linker was designed, synthesized and employed during glycosylations using an automated carbohydrate synthesizer. The analysis of the cleavage products revealed shortcomings for oligosaccharide synthesis.

Automated Solid-Phase Synthesis of Hyaluronan Oligosaccharides

Well-defined fragments of hyaluronic acid (HA) have been obtained through a fully automated solid-phase oligosaccharide synthesis. Disaccharide building blocks, featuring a disarmed glucuronic acid donor moiety and a di-tert-butylsilylidene-protected glucosamine part, were used in the rapid and efficient assembly of HA fragments up to the pentadecamer level, equipped with a conjugation-ready anomeric allyl function.

Chiral-auxiliary-mediated 1,2-cis-glycosylations for the solid-supported synthesis of a biologically important branched α-glucan

Solid phase oligosaccharide synthesis (SPOS) offers the promise to provide libraries of oligosaccharides for glycomics research. A major stumbling block to SPOS has been a lack of general methods to stereoselectively install 1,2-cis-glycosides, and intractable mixtures of compounds will be obtained if several of such glycosides need to be installed. We have prepared on-resin a biologically important glucoside containing multiple 1,2-cis-glycosidic linkages with complete anomeric control by using glycosyl donors having a participating (S)-(phenylthiomethyl)benzyl chiral auxiliary at C-2. A branching point could be installed by employing 9-fluorenylmethyloxycarbonyl (Fmoc) and allyloxycarbonyl (Alloc) as a versatile set of orthogonal protecting groups. The synthetic strategy made it possible for partial on-resin deprotection of the completed oligosaccharide thereby increasing the overall efficiency of the synthesis. The combination of classical and auxiliary mediated neighboring group participation for controlling anomeric selectivity is bringing the promise of routine automated solid supported oligosaccharides synthesis closer.

Comparative solution and solid-phase glycosylations toward a disaccharide library

A comparative study on solution-phase and solid-phase oligosaccharide synthesis was performed. A 16-member library containing all regioisomers of Glc–Glc, Glc–Gal, Gal–Glc, and Gal–Gal disaccharides was synthesized both in solution and on solid phase. The various reaction conditions for different approaches and corresponding yields are analyzed and discussed.

Application of Glycosyl Thioimidates in Solid-Phase Oligosaccharide Synthesis

Two stable classes of thioimidoyl derivatives, S-benzoxazolyl (SBox) and S-thiazolinyl (STaz) glycosides, were investigated as glycosyl donors for solid-phase oligosaccharide synthesis. It was demonstrated that these derivatives are suitable for both glycosyl acceptor-bound and glycosyl donor-bound strategies, commonly employed in resin-supported oligosaccharide synthesis.

Automated oligosaccharide synthesis

Peptides and oligonucleotides are prepared by automated synthesizers that can be operated by non-specialists. Carbohydrates have been hard to assemble, but the increasing awareness of the biological importance of this class of complex repeating biopolymers has prompted efforts to accelerate their synthesis. This tutorial review defines the state of the art of automated solid phase oligosaccharide synthesis and identifies areas in need of further innovation. Application of the automated synthesis method to prepare a malaria vaccine candidate is briefly highlighted.

Cap-and-Tag Solid Phase Oligosaccharide Synthesis

A new "cap-and-tag" strategy is applied to solid phase oligosaccharide synthesis. Acetyl-capping and fluorous-tagging allowed for the facile separation of the desired F-tagged oligosaccharide from the acetyl-capped deletion sequences using fluorous solid phase extraction. To illustrate this approach, a protected Glc-beta-(1-->6)-Man-alpha-(1-->6)-Glc-beta-1-->pentenyl trisaccharide was synthesized.

Automated Synthesis of the Tumor-Associated Carbohydrate Antigens Gb-3 and Globo-H: Incorporation of α-Galactosidic Linkages

The Globo series of tumor-associated antigens are glycosphingolipids implicated in several cancer types. These oligosaccharides contain an α-linked galactose. Reported are methods to efficiently install cis-galactosidic linkages by automated solid-phase oligosaccharide synthesis. The complex tumor-associated oligosaccharides Globo-H and Gb-3 were assembled in about 1 day using the new approach that extends the scope of automated oligosaccharide synthesis to structurally more challenging carbohydrates.

Optimization of microwave-assisted solid-phase oligosaccharides synthesis reaction and analysis of components and structure of synthetic product

Using phosphoric acid as the catalyst and glucose as substrate, microwave-assisted solid-phase oligosaccharide synthesis was studied. The parameters were optimized by orthogonal test design and statistical analysis method. Under the optimum reaction conditions, namely microwave power output of 1000 W, microwave irradiation time 9 min, adding 30% water to initiate reaction, adding 4% heteropoly acid A as the catalyst, the maximum yield ratio of product was 76.56%. The product was separated and characterized by using SephadexG-50 column, thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). The component and proportion of synthetic oligosaccharides included disaccharides 20.81%, trisaccharides 15.50%, tetrasaccharide 10.84%, pentasaccharides 7.79%, higher oligosaccharides 21.63%. Results suggest that microwave-assisted solid-phase organic synthesis reaction could be used for the production of oligosaccharides.

Solid‐Phase Oligosaccharide Synthesis of a Small Library of N‐Glycans

Solid-phase oligosaccharide synthesis is based on a hydroxymethylbenzyl benzoate spacer linker which is connected to the Merrifield resin (1 P). Glycosylation was performed with O-glycosyl trichloroacetimidates of glucosamine, mannose, and galactose permitting chain extension (2e, 5e), branching (4b, 7b, 8b), and chain termination (3t, 6t, 9t) with the use of O-benzyl, O-benzoyl, and N-dimethylmaleoyl as permanent and O-fluorenylmethoxycarbonyl (Fmoc) and O-phenoxyacetyl (PA) as temporary protecting groups. The steps required on solid phase are i) glycosylation under TMSOTf catalysis, ii) selective cleavage of the temporary protecting groups, Fmoc with NEt3 and PA with 0.5 equivalents of NaOMe in CH2Cl2/MeOH, and iii) product cleavage from the resin with 4.0 equivalents of NaOMe in CH2Cl2/MeOH and following O-acetylation for convenient product isolation. Thus a highly successful synthesis of a small library of seventeen N-glycan structures was made possible comprising the N-glycan pentasaccharide core structure 53 and two further chain extended hexa- and heptasaccharide N-glycans with a glucosamine or a lactosamine residue, respectively, which is attached to one of the mannose residues of the core structure (56 and 59).

Solid‐Phase Oligosaccharide Chemistry and Its Application to Library Synthesis

AbstractFor Abstract see ChemInform Abstract in Full Text.

Solid‐Phase Synthesis of Complex Oligosaccharides Using Azidoglucose as a Glycosyl Acceptor

AbstractThe solid phase synthesis of oligosaccharides 1−3 was performed on Merrifield resin. These syntheses are based on the hydroxymethylbenzyl benzoate spacer‐linker system and, for regioselective chain extension, the use of O‐glycosyl trichloroacetimidates as glycosyl donors containing temporary O‐Fmoc protection. The important lactosamine‐containing oligosaccharides 1−3 are accessible in excellent yields by using a 2‐azidoglucose residue as the glucosamine building block adjacent to the spacer‐linker system. Only standard amounts of the glycosyl donor are employed in this solid phase oligosaccharide synthesis and we did not have to resort to any capping procedures. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Solid-Phase Synthesis of α-Gal Epitopes: On-Resin Analysis of Solid-Phase Oligosaccharide Synthesis with 19F NMR Spectroscopy

A route for solid-phase synthesis of the alpha-Gal epitopes Gal(alpha1-3)Gal(beta1-4)Glc and Gal(alpha1-3)Gal(beta1-4)GlcNAc is described. These trisaccharide antigens are responsible for hyperacute rejection in xenotransplantation of porcine organs. Optimization of the solid-phase synthesis relied on use of fluorinated protective groups for the carbohydrate building blocks and use of a fluorinated linker. This allowed convenient on-resin analysis of the reactions with gel-phase (19)F NMR spectroscopy. Conditions were established which allowed reductive ring-opening of 4,6-O-benzylidene acetals to be performed on the solid phase with high regioselectivity to furnish the corresponding 6-O-benzyl ethers. It was found that glycosylations could be conveniently carried out by using thioglycosides as donors with N-iodosuccinimide and trifluoromethanesulfonic acid as the promoter system. With use of these conditions a challenging alpha-glycosidic linkage was successfully installed with complete stereoselectivity in the final glycosylation. It was also established that fluorinated benzoates, benzyl ethers, and benzylidene acetals display almost identical chemical properties as their nonfluorinated counterparts, a finding that is essential for future use of fluorinated protective groups in solid-phase oligosaccharide synthesis.