Efficient Glycosylation Research Articles

Synthesis and Glycosylation of 2'-(Benzyloxycarbonyl)benzyl Glycosides as Glycosyl Donors

Department of Biology, Yonsei University, Seoul 120-749, KoreaReceived October 23, 2003Key Words : 2'-(Benzyloxycarbonyl)benzyl glycosides, Glycosylation, Glycosyl donorRecent advances in glycobiology have directed an increasedattention to efficient and stereoselective glycosylation ofoligosaccharides.

Glycosylation with glycosyl benzyl phthalates as a new type of glycosyl donor.

A glucopyranosyl benzyl phthalate, two mannopyranosyl benzyl phthalates, and a 2-deoxyglucopyranosyl benzyl phthalate, which were prepared from the corresponding 1-hydroxy sugars and benzyl hydrogen phthalate, were found to be efficient glycosyl donors in the glycosylations of various glycosyl acceptors using TMSOTf as a promoter.

Glycosylation affects the protein stability and cell surface expression of Kv1.4 but Not Kv1.1 potassium channels. A pore region determinant dictates the effect of glycosylation on trafficking.

Kv1.1 and Kv1.4 potassium channels are plasma membrane glycoproteins involved in action potential repolarization. We have shown previously that glycosylation affects the gating function of Kv1.1 and that a pore region determinant of Kv1.1 and Kv1.4 affects their cell surface trafficking negatively or positively, respectively. Here we investigated the role of N-glycosylation of Kv1.1 and Kv1.4 on their protein stability, cellular localization pattern, and trafficking to the cell surface. We found that preventing N-glycosylation of Kv1.4 decreased its protein stability, induced its high partial intracellular retention, and decreased its cell surface protein levels, whereas it had little or no effect on these parameters for Kv1.1. Exchanging a trafficking pore region determinant between Kv1.1 and Kv1.4 reversed these effects of glycosylation on these chimeric channels. Thus it appeared that the Kv1.4 pore region determinant and the sugar tree attached to the S1-S2 linker showed some type of dependence in promoting proper trafficking of the protein to the cell surface, and this dependence can be transferred to chimeric Kv1.1 proteins that contain the Kv1.4 pore. Understanding the different trafficking programs of Kv1 channels, and whether they are altered by glycosylation, will highlight the different posttranslational mechanisms available to cells to modify their cell surface ion channel levels and possibly their signaling characteristics.

An efficient, regioselective and fast enzymatic glycosylation for cyclodextrins

The introduction of a short spacer arm was necessary to obtain complete regioselectivity in the glycosylation of β-cyclodextrin (β-CD) mediated by glycosidases. Thus 6- N-(2-aminoethyl-α- d-galactopyranosyl)-6-deoxycyclomaltoheptaose was prepared in four steps from β-cyclodextrin with 30% overall yield using, in the key step, the transfer activity of green coffee bean α-galactosidase.

Catalytic and Stereoselective Glycosylation with Glucosyl Thioformimidates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Catalytic and Stereoselective Glycosylation with Glucosyl Thioformimidates

Abstract A novel and efficient glycosyl donor having a p-trifluoromethylbenzylthio-N-p-trifluoromethylphenylformimidate group at an anomeric position is easily prepared by the addition of anomeric hydroxy group of 2,3,4,6-tetra-O-benzyl-α,β-d-glucopyranose to p-trifluoromethylphenyl isothiocyanate, followed by treatment with p-trifluoromethylbenzyl bromide. Catalytic and stereoselective glycosylation of various glycosyl acceptors with the above glycosyl donor smoothly proceeds by using various protic and Lewis acid catalysts which interact with its nitrogen atom. Further, catalytic and highly 1,2-cis or 1,2-trans stereoselective and chemoselective glycosylation between two different “armed” and “disarmed” glycosyl p-trifluoromethylbenzylthio-N-p-trifluoromethylphenylformimidates is also performed effectively in the presence of a catalytic amount of trifluoromethanesulfonic acid (TfOH) at −78 °C in tBuOMe or EtCN, respectively. These glycosylations are applied to successful one-pot sequential syntheses of trisaccharides.

Trimellitic anhydride linker (TAL)—highly orthogonal conversions of primary amines employed in the parallel synthesis of labeled carbohydrate derivatives

Ṯrimellitic A̱nhydride Ḻinker (TAL) was introduced as an anchor in solid-phase synthesis allowing for immobilization of primary amines as phṮh AL imide derivatives. 1,2-Anhydro trimellitic acid chloride (trimellitic acid=1,2,4-benzene tricarboxylic acid) was coupled to methyl aminomethyl polystyrene at 0°C. Polymer-bound phthalimides were formed from primary amines by heating, preferably assisted by microwave irradiation, or via a condensation protocol at rt. In the latter case, the intermediary secondary amide was formed in the presence of 4- N, N-dimethylamino pyridine (DMAP), ring closure to the cyclic imide was effected smoothly in the presence of 1-(mesitylene-2-sulfonyl)-3-nitro-1 H-1,2,4-triazole (MSNT) as condensation agent. The linker was stable under a broad range of reaction conditions including strong acid, base, and oxidants, respectively. Efficient cleavage could be effected by treatment with 1% hydrazine or with ethylenediamine, respectively. Alternatively, products were released by a safety-catch procedure. Phthalimides were reduced with borohydrides, preferably with LiBH 4, and products were afforded in high purity and with excellent yields by treatment with dilute acid (5% trifluoroacetic acid (TFA)). Employment of the linker for the synthesis of labeled carbohydrates was demonstrated involving efficient solid-supported glycosylation.

Synthesis of Laminarin Oligosaccharide Derivatives Having d‐Arabinofuranosyl Side‐Chains

An efficient glycosylation strategy was applied in the synthesis of β‐d‐glucopyranosyl‐(1→3)‐[α‐d‐arabinopyranosyl‐(1→4)]‐β‐d‐glucopyranosyl‐(1→3)‐β‐d‐glucopyranosyl‐(1→3)‐[α‐d‐arabinopyranosyl‐(1→6)]‐d‐glucopyranose to secure β‐d‐(1→3) glycosidic bond formation between glucopyranosyl residues. The new strategy using a 4,6‐O‐benzylidenated acceptor avoided generation of the α major isomer in the attempted β‐d‐(1→3) glycosylation under standard glycosylation conditions. The hexasaccharide we prepared showed about 30% tumor growth inhibition towards S180 model study.

Efficient synthesis of glycosylated phenazine natural products and analogs with DISAL (methyl 3,5-dinitrosalicylate) glycosyl donors.

Inspired by the occurrence and function of phenazines in natural products, new glycosylated analogs were designed and synthesized. DISAL (methyl 3,5-dinitrosalicylate) glycosyl donors were used in an efficient and easily-handled glycosylation protocol compatible with combinatorial chemistry. Benzoylated D-glucose, D-galactose and L-quinovose DISAL glycosyl donors were synthesized in high yields and used under mild conditions to glycosylate methyl saphenate and 2-hydroxyphenazine. The glycosides were screened for biological activity and one compound showed inhibitory activity towards topoisomerase II.

Phenyl 2-Deoxy-2-iodo-1-thio-glycosides: New Glycosyl Donors for the Stereoselective Synthesis of 2-Deoxy-oligosaccharides

Phenyl 2-deoxy-2-iodo-1-thioglycosides, prepared from simple pentoses by olefination and iodine-induced cyclization, have proved to be efficient glycosyl donors for the stereoselective synthesis of 2-deoxy-2-iodo-oligosaccharides, which are precursors of 2-deoxy-oligosaccharides.

Catalytic and Stereoselective Glycosylation with a Novel and Efficient Disarmed Glycosyl Donor: Glycosyl p-Trifluoromethylbenzylthio-p-trifluoromethylphenyl Formimidate

Abstract A novel and efficient glycosyl donor having a p-trifluoro-methylbenzylthio-p-trifluoromethylphenyl formimidate function as a leaving group is easily prepared by the addition of anomeric hydroxyl group of 2,3,4,6-tetra-O-benzoyl-α,β-D-glucopyranose to p-trifluoromethylphenyl isothiocyanate, followed by treatment with p-trifluoromethylbenzyl bromide. Catalytic and stereoselective glycosylation using this glycosyl donor effectively proceeds by activating its nitorogen atom with various protic and Lewis acids.

ChemInform Abstract: A New, Efficient Glycosylation Method for Oligosaccharide Synthesis under Neutral Conditions: Preparation and Use of New DISAL Donors.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A new, efficient glycosylation method for oligosaccharide synthesis under neutral conditions: preparation and use of new DISAL donors.

Efficient, stereoselective glycosylation methods are required for the synthesis of complex oligosaccharides as tools in glycobiology. All glycosylation methods, which have found wide acceptance, rely on Lewis acid activation of glycosyl donors prior to glycosylation. Here, we present a new and efficient method for glycosylation under neutral or mildly basic conditions. Glycosides of methyl 2-hydroxy-3,5-dinitrobenzoate (DISAL) and its para regioisomer, methyl 4-hydroxy-3,5-dinitrobenzoate, were prepared by nucleophilic aromatic substitution. In a first demonstration of their potential as glycosyl donors, stereospecific glycosylation of methanol was achieved. In the glycosylation of more hindered alcohols, the beta-donor proved more reactive, and alpha-glucosides were predominantly formed. Glycosylation of protected monosaccharides, with free 6-OH or 3-OH, proceeded smoothly in 1-methyl-2-pyrrolidinone (NMP) at 40-60 degrees C in the absence of Lewis acids and bases in good to excellent yields. Glycosylation of 3-OH gave the alpha-linked disaccharide only.

Solid-phase glycosylation of peptide templates and on-bead MAS-NMR analysis: perspectives for glycopeptide libraries.

The efficient solid-phase glycosylation of amino acid side chains (serine (Ser), threonine (Thr), and tyrosine (Tyr)) in peptides was demonstrated with a variety of glycosyl trichloroacetimidate donors in high yields and purities. A novel photolabile linker, with no chiral centre, was introduced to facilitate analysis by both matrix-assisted laser desorption ionisation time of flight (MALDI-TOF) mass spectrometry and nanoprobe magic angle spinning (MAS) NMR spectroscopy. Product analysis by nanoprobe MAS NMR spectroscopy, LC-MS and MALDI-TOF mass spectrometry of the glycosylation reactions indicated that the reactivity order of the hydroxy side-chain functions of amino acids in peptides on the solid-phase was Tyr>Ser>Thr. The nearly quantitative glycosylation yields and the efficient on-bead product analysis by nanoprobe MAS NMR spectroscopy have made a truly solid-phase approach for the synthesis and analysis of glycopeptide libraries possible.

First Total Synthesis of the Re-Type Lipopolysaccharide.

Three sequential efficient glycosylation reactions starting from D-glucosamine were used in the first total synthesis of Escherichia coli Re lipopolysaccharide, which is one of the most simple lipopolysaccharides found on the surface of living bacteria.

6-O-sulfo de-N-acetylsialyl Lewis X as a novel high-affinity ligand for human L-selectin: total synthesis and structural characterization.

Total synthesis and structural characterization of a novel 6-O-sulfo de-N-acetylsialyl Lewis X, which was originally discovered as a minor by-product of the parent 6-O-sulfo N-acetylsialyl Lewis X, a high-affinity endogenous ligand for human L-selectin, are described. The total synthesis has been achieved by a highly efficient, regio- and alpha-stereoselective glycosylation of N-trifluoroacetylneuraminic acid, selective protections of the 3- and 6-hydroxyl groups of N-acetylglucosamine that undergo fucosylation and sulfation, and construction of the glycolipid structure containing a ceramide. The structure of 6-O-sulfo de-N-acetylsialyl Lewis X ganglioside was characterized by fast atom bombardment mass spectrometry (FAB-MS).

DISAL glycosyl donors for efficient glycosylations under acidic conditions: Application to solid-phase oligosaccharide synthesis

The use of DISAL (methyl dinitrosalicylate) glycosyl donors in efficient Lewis acid-promoted glycosylations is reported. N-Acetyl-D-glucosamine monosaccharide acceptors are successfully glycosylated at O-6 or O-4 using benzyl- and benzoyl-protected DISAL donors in CH2Cl2 or nitromethane in the presence of LiClO4. The resultant disaccharides are isolated in yields ranging from 35 to 93%. Other Lewis acids such as FeCl3, TMSOTf, or BF3·Et2O also prove efficient for glycosylation of the secondary alcohol cyclohexanol. However, for the synthesis of disaccharides, the mild activation by LiClO4 gives higher yields. This approach is extended to efficient solid-phase glycosylation of a D-glucosamine derivative anchored by the 2-amino group through a Backbone Amide Linker (BAL) to a polystyrene support.

αGal-conjugated anti-rhinovirus agents: chemo-enzymatic syntheses and testing of anti-Gal binding

The syntheses of αGal-conjugated anti-rhinovirus agents 1, 2 and 3 and their abilities to inhibit αGal binding of human anti-Gal antibody are described. An efficient enzymatic glycosylation using a novel fusion protein serves to provide the key αGal intermediate 7, which is elaborated to αGal amines 9, 12 and 14 with various tethers. The conjugates are then formed by amide coupling of these amines to heterocyclic acid 18 in the presence of 1,1′-carbonyldiimidazole (CDI), followed by deprotection of the αGal part. Conjugate 3 having a triethylene glycol linker displays the highest binding affinity to human anti-Gal antibody as tested by ELISA.

Novel enzymatic approach to the synthesis of flavonoid glycosides and their esters.

Flavonoids such as (+)catechin can be efficiently solubilised in supersaturated solutions prepared with donor glycosides, e.g., p-nitrophenyl glycosides, di- and higher oligosaccharides, and poly(ethylene glycol) dimethyl ether in sufficiently high concentration for their efficient enzymatic glycosylation. Under these conditions several glycosidases readily accept (+)catechin as substrate and the target glycosides were prepared in one step in up to 26% yields. The regioselectivity of the reaction depends on the enzyme and substrate combination used; three positions, 5, 7, and 4', in the flavonoid can be glycosylated. The resulting and similar flavonoid glycosides were further modified by regioselective acylation with vinyl esters of arylpropenoic acids using lipases as biocatalyst. The efficiency of acylation was found to diminish in the order of vinyl cinnamate > vinyl ferulate > vinyl coumarate. This work demonstrates the feasibility of assembling complex flavonoid glycoside esters in just two steps by sequential use of commercially available glycosidases and lipases.

Investigations into the Chemistry of Some 1,6-Epithio and 1,6-Episeleno ß-D-Glucopyranoses

Derivatives of 1,6-dideoxy-1,6-epithio-β-D-glucopyranose have been shown to undergo oxidation reactions to afford the corresponding sulfoxides and sulfones. The sulfoxides participate in Pummerer reactions to afford the corresponding α-acetoxy sulfides which were then oxidized further. None of the sulfoxides, sulfones or α-acetoxy sulfides prepared were particularly efficient glycosyl donors. Also presented are crystal structures of 1,6-dideoxy-1,6-epithio-β-D-glucopyranose S,S-dioxide and 1,6-dideoxy-1,6-episeleno-β-D-glucopyranose, interesting analogues of 1,6-anhydro-β-D-glucopyranose.