Glycosylation Of Methyl Research Articles

Synthesis of a Gal-β-(1→4)-Gal disaccharide as a ligand for the fimbrial adhesin UcaD

The disaccharide Gal-β-(1→4)-Gal was recently identified as a ligand for the adhesin UcaD, a fimbrial protein used by Proteus mirabilis to adhere to exfoliated uroepithelial cells and colonise the urinary tract. To facilitate further studies, Gal-β-(1→4)-Gal was synthesised as the α-methyl glycoside via glycosylation of methyl 2,3,6-tri-O-benzoyl-α-d-galactopyranoside with 2,3,4,6-tetra-O-acetyl-d-galactopyranosyl trichloroacetimidate, followed by deprotection. The disaccharide was fully characterised by NMR spectroscopy. Earlier attempts to use a thiogalactoside as the glycosyl acceptor were hindered by intermolecular aglycone transfer side reactions.

Synthesis of a disaccharide fragment of rhamnogalacturonan II

A disaccharide portion of the A-side chain of the rhamnogalacturonan II oligosaccharide has been prepared. Glycosylation of methyl (methyl 3,4- O-isopropylidene-α- d-galactopyranosid)uronate with p-tolyl 2,3-di- O-acetyl-3- C-(benzyloxymethyl)-1-thio-α/β- d-erythrofuranoside was carried out using N-iodosuccinimide as promoter and silver trifluoromethanesulfonate as catalyst. Removal of the protecting groups gave the β- d-Api f-(1→2)-α- d-Gal pA-OMe disaccharide.

Synthetic α,β-(1→4)-Glucan Oligosaccharides as Models for Heparan Sulfate. Part II.

Abstract α,β-(1→4)-Glucan oligosaccharides were prepared as models for heparan sulfate with the simplifying assumptions that carboxyl-reduction and sulfation of heparan sulfate does not decrease the SMC antiproliferative activity and that N-sulfates in glucosamines can be replaced by O-sulfates. The target saccharides were synthesized using maltosyl building blocks. Glycosylation of methyl 2,3,6-tri-O-benzyl-α-D-glucopyranoside (1) with hepta-O-acetyl-α-maltosyl bromide (2) furnished trisaccharide 3 which was deprotected to α-D-Glc-(1→4)-β-D-Glc-(1→4)-α-D-Glc(1→OCH3) (5) or, alternatively, converted to the trisaccharide glycosyl acceptor (8) with one free hydroxyl function (4″-OH). Further silver triflate mediated glycosylation with glucosyl or maltosyl bromide followed by deblocking gave the tetrasaccharide β-D-Glc-(1→4)-α-D-Glc-(1→4)-β-D-Glc-(1→4)-α-D-Glc-(1→OCH3) (11) and the pentasaccharide [α-D-Glc-(1→4)-β-D-Glc-(1→4)]2-α-D-Glc-(1→OCH3) (14). The trisaccharides 3, 4, 6, and 8 as well as pentasaccharide 12 were fully characterized by 1H, 3, 8 and 12 also by 13C NMR spectroscopy. Assignments were possible using 1D TOCSY, in some cases supplemented by 2D T-ROESY, 1H,1H 2D COSY, and 1H-detected one-bond and multiple-bond 1H,13C 2D COSY experiments.

Synthetic α,β(1→4)-Glucan Oligosaccharides as Models for Heparan Sulfate

Abstract α,β-(1→4)-Glucans were devised as models for heparan sulfate with the simplifying assumptions that carboxyl-reduction and sulfation of heparan sulfate does not decrease the SMC antiproliferative activity and that N-sulfates in glucosamines can be replaced by O-sulfates. The target oligo-saccharides were synthesized using maltosyl building blocks. Glycosylation of methyl 2,3,6,2′,3′,6′-hexa-O-benzyl-β-maltoside (1) with hepta-O-acetyl-α-maltosyl bromide (2) furnished tetrasaccharide 3 which was deprotected to α-D-Glc-(1→4)-β-D-Glc-(1→4)-α-D-Glc-(1→4)-β-D-Glc-(1→OCH3) (5) or, alternatively, converted to the tetrasaccharide glycosyl acceptor (8) with one free hydroxyl function (4‴′-OH). Further glycosylation with glucosyl or maltosyl bromide followed by deblocking gave the pentasaccharide [β-D-Glc-(1→4)-α-D-Glc-(1→4)]2-β-D-Glc-(1→OCH3) (11) and hexasaccharide [α-D-Glc-(1→4)-β-D-Glc-(1→4)2-α-D-Glc-(1→4)-β-D-Glc-(1→OCH3) (14). The protected tetrasaccharide 3 and hexasaccharide 12 were fully characteri...

Modulation of antibody affinity by synthetic modifications of the most exposed pyranose residue of a trisaccharide epitope

When the Salmonella trisaccharide epitope, methyl 3- O-(3,6-dideoxy-α- d- xylo-hexopyranosyl)-2- O-(α- d-galactopyranosyl)-α- d-mannopyranoside 12 is bound by a monoclonal antibody Sel 55.4, the 3,6-dideoxy-α- d-hexose is completely buried, while the galactopyranosyl mannopyranosyl units lay across the protein surface. Crystallography of an antibody complexed with 12 also shows that the galactose residue is the most exposed saccharide. A simplified strategy to synthesize 12 and analogues modified at the galactose residue is described. Monosaccharide building blocks containing benzyl ether and ester protecting groups were used for efficient assembly of trisaccharides that can be deprotected by a single hydrogenolysis step, or occasionally preceded by a transesterification stage. Glycosylation of methyl 2- O-benzoyl-4,6-di- O-benzyl-α- d-mannopyranoside 4 by 2,4-di- O-benzyl-3,6-dideoxy- d- xylo-hexopyranosyl chloride 8 affords after transesterification the disaccharide acceptor 10. This disaccharide serves as a universal acceptor for glycosylation by glycosyl donors that lead, following facile deprotection, to the α- and β- d- galacto, α- and β- d- gluco, and 2-amino-2-deoxy-α- d- galactotrisaccharides 12, 14, 17, 18 and 21. Only a small change in binding energy Δ(Δ G) occurs when the α- d-galactopyranosyl residue of 12 is replaced by either an α- d-glucopyranosyl 17 or a 2-amino-2-deoxy α- d-galactopyranosyl unit 21. Whereas binding of the β- d-glucopyranose congener 18 was tolerated by the antibody, the β- d-galactopyranose analogue 14, showed a 250 fold loss of affinity. These relative activities of the trisaccharide congeners are correlated with a solved crystal structure for the antibody complex with 12.

Synthesis of a peptidyldimannosyl phosphate: fragment of the variant-specific surface glycoprotein membrane anchor from trypanosoma brucei

Condensation of protected β-benzyl-aspartate 4 with 2-amino-ethanol, subsequent deprotection of the amino function and coupling with N, N′-di-benzyloxycarbonyl-lysine ( 7) afforded the peptidyl alcohol 8. Glycosylation of methyl 3,4,6 tri- O-benzyl-α- d-mannopyranoside ( 11) by ethyl 2,6-di- O-benzoyl-3,4-di- O-benzyl-1-thio-α- d-mannopyranoside ( 14) gave, after debenzoylation and protection of the 2′-hydroxyl function, the suitably protected dimannoside 21. Phosphitylation of 21 with benzyloxy- bis-( N, N-diisopropylamino)phosphine ( 18) followed by the addition of 8 gave, after oxidation and subsequent hydrogenolysis of the benzyl groups, the title compound in a good yield.

Synthesis Of Isomaltose Analogues

ABSTRACT Preparation of the α-glucosides 11, 12, 13 and 14 were accomplished through glycosylation of racemic trans-1-hydroxy-2-(hydroxymethyl)cyclohexane using 2-thiopyridyl tetra-O-benzyl-glucoside as the glycosyl donor in acceptable overall yield for α-selectivity, but with poor regioselectivity. Glycosylation under thermodynamic control using tetrabenzyl glucopyranose acetate and trimethylsilyl triflate as the promotor gave similar results. The unprotected glucosides 12 and 13 were separated and characterized by NMR spectroscopy. Similarly methyl 4-deoxy-α-isomaltoside (5a) was prepared through halide catalyzed glycosylation of methyl 2,3-di-O-benzoyl-4-deoxy-α-D-glucopyranoside (15) in acceptable yield and the unprotected compound characterized by NMR spectroscopy. Compounds 5a, 12a, 13a and the mixture 11a and 14a were all tested as substrates for the enzyme glucoamylase from Aspergillus niger and proved to be very poor substrates for the enzymic hydrolysis.

Synthesis and conformational studies of carrabiose and its 4′-sulphate and 2,4′-disulphate

Methyl α-carrabioside ( 13), and its 4′-sulphate ( 19) and 2,4′-disulphate ( 20) have been synthesised via glycosylation of methyl 3,6-anhydro-2- O-benzyl-α- d-galactopyranoside with 2,3,6-tri- O-acetyl-4- O-benzyl-β- d-galactopyranosyl bromide and subsequent partial or complete debenzylation, sulphation, and deprotection of the resulting disaccharide derivatives. Conformational studies have been carried out on 13, 19, and 20 on the basis of 1D and 2D 1H-n.m.r. spectroscopy and molecular mechanics calculations.

Syntheses of trisaccharide CDE and tetrasaccharide BCDE fragments found in orthosomycins

1,5-Anhydro-3- O-benzyl-2,6-dideoxy-4- O-(3,4-di- O-benzyl-2,6-dideoxy-β- d- arabino-hexopyranosyl)- d- arabino-hex-1-enitol ( 17), which corresponds to the BC fragment of various orthosomycins, was prepared from phenyl 2,3-di- O-benzyl-6-deoxy-4- O-(3,4-di- O-benzyl-2,6-dideoxy-β- d- arabino-hexopyranosyl)-1-thio-β- d-glucopyranoside ( 16) by reductive lithiation. The synthesis of 16 involved a stereoselective coupling of phenyl 2,3-di- O-benzyl-6-deoxy-1-thio-β- d-glucopyranoside ( 9) and 1,2-di- O-acetyl-3,4-di- O-benzyl-6-deoxy-β- d-glucopyranose ( 14) followed by deoxygenation at C-2′. Glycosylation of methyl 2- O-benzyl-6-deoxy-4- O-methyl-β- d-galactopyranoside ( 25) with 3,4,6-tri- O-acetyl-2-deoxy-2-phthalimido-β- d-glucopyranosyl trichloroacetimidate, followed by deamination at C-2′, led stereospecifically to methyl 2- O-benzyl-6-deoxy-4- O-methyl-3- O-(3,4,6-tri- O-acetyl-2-deoxy-β- d- arabino-hexopyranosyl)-β- d-galactopyranoside ( 26). The 2-deoxy unit of 26 was then modified by consecutive axial introduction of a C-Me group at position 3′, protection of HO-3′, and deoxygenation at C-6′, in order to obtain methyl 3- O-(3- O-benzoyl-2,6-dideoxy-3- C-methyl-β- d- arabino-hexopyranosyl)-2- O-benzyl-6-deoxy-4- O-methyl-β- d- galactopyranoside ( 39), which corresponds to the DE fragment of orthosomycins. A glycosyloxyselenation-oxidation-elimination sequence was performed on 39 and either 1,5-anhydro-3,4-di- O-benzyl-2,6-dideoxy- d- arabino-hex-1-enitol ( 40) or 1,5-anhydro-3- O-benzyl-2,6-dideoxy-4- O-(3,4-di- O-benzyl-2,6-dideoxy-β- d- arabino-hexopyranosyl)- d- arabino- hex-1-enitol ( 17) to give the CDE tri- and BCDE tetrasaccharide fragments, respectively. Each fragment contained the spiro-ortholactone junction with an ( R) configuration at the anomeric carbon atom of the C-unit.

Synthesis of trisaccharides containing 3-deoxy- d- manno-2-octulosonic acid residues related to the KDO-region of enterobacterial lipopolysaccharides

Glycosylation of methyl (allyl 7,8- O-carbonyl-3-deoxy-α- d- manno-2-octulopyranosid)onate with an α-(2→4) linked per- O-acetylated KDO-disaccharide bromide derivative under Helferich conditions afforded a 2:1 mixture of the α- and β-linked trisaccharide derivatives in 50% yield. Removal of the protecting groups gave sodium O-[sodium (3-deoxy-α- d- manno-2-octulopyranosyl)onate]-(2→4)- O-[sodium (3-deoxy-α- and -β- d- manno-2-octulopyranosyl)onate]-(2→4)-sodium (allyl 3-deoxy-α- d- manno-2-octulopyranosid)onate. Radical copolymerization of the allyl glycosides afforded artificial antigens, suitable for defining antibody specificities directed against the KDO-region of enterobacterial lipopolysaccharides.

Block synthesis of two pentasaccharide determinants of the Brucella M antigen using thioglycoside methodologies

Two frame shifted pentasaccharides containing 4,6-dideoxy-4-formamido-D-mannose (4-deoxy-4-formamido-D-rhamnose) have been synthesized by application of a strategy utilizing S-ethyl disaccharide glycoside building blocks 16 and 25. The target molecules contain a single α1,3 linkage as either the first or last inter-residue linkage in an otherwise α1,2-linked homo-pentameric structure:[Formula: see text]and[Formula: see text]These structures represent possible biological repeating units of the Brucella M antigen and their synthesis is designed to facilitate the identification of the structural element that is polymerized to provide the intact polysaccharide antigen. The α1,2-linked tetrasaccharide component of each pentasaccharide was constructed by methyl triflate promoted activation of the α1,2-linked S-ethyl disaccharide glycoside 16. Glycosylation of methyl 4-azido-2-O-benzyl-4,6-dideoxy-α-D-mannopyranoside 3 by 16, followed by a second block extension, gave the pentasaccharide 22 with an α1,3 linkage at the reducing terminus. In analogous fashion the α1,3-linked S-ethyl derivative 25 was used in conjunction with methyl triflate to glycosylate the α1,2-linked trisaccharide 26, and provided the pentasaccharide 27 that possesses a 1,3 linkage at its non-reducing end. The synthesis of an α1,3-linked disaccharide and a trisaccharide are also reported. Keywords: Brucella M antigen, synthesis of frame shifted pentasaccharides, thioglycoside building units, 4,6-dideoxy-4-formamido-D-mannose, biological repeating unit.

Synthesis of a trisaccharide of 3-deoxy- d- manno-2-octulopyranosylonic acid (KDO) residues related to the genus-specific lipopolysaccharide epitope of chlamydia

The disaccharides, O-(sodium 3-deoxy-α- and -β- d- manno-2-octulopyranosylonate)-(2→8)-sodium (allyl 3-deoxy-α- d- manno-2-octulopyranosid)onate, were prepared via glycosylation of methyl (allyl 4,5,7-tri- O-acetyl-3-deoxy-α- d- manno-2- octulopyranosid)onate with methyl (4,5,7,8-tetra- O-acetyl-3-deoxy- d- manno-2- octulopyranosyl bromide)onate under Helferich and Koenigs-Knorr conditions, respectively. Based on g.l.c.-m.s. data of the α- and β-(2→8)-linked disaccharide derivatives, obtained after carbonyl- and carboxyl-group reduction, followed by methylation, the α-anomeric configuration was assigned to the terminal KDO-residue in the KDO-region of Chlamydial lipopolysaccharide. The trisaccharide O-(sodium 3-deoxy-α- d- manno-2-octulopyranosylonate)-(2→8)-(sodium 3-deoxy- α- d- manno-2-octulopyranosylonate)-(2→4)-sodium (allyl 3-deoxy-α- d- manno-2- octulopyranosid)onate was obtained via block synthesis using an α-(2→8)-linked disaccharide bromide derivative as the glycosyl donor. Copolymerization of the allyl glycosides with acrylamide gave water-soluble macromolecular antigens, suitable for defining epitope specificities of monoclonal antibodies directed against Chlamydial LPS.

Synthesis of polyacrylamide copolymers containing α-(2→4)-β-, β-(2→4)-β-, and β-(2→4)-α-linked O-(3-deoxy- d- manno-2-octulopyranosylonate)-(3-deoxy- d- manno-2-octulo-pyranosylono) (KDO) residues

Glycosylation of methyl (allyl 7,8-di- O- tert-butyldimethylsilyl-3-deoxy-β- d- manno-2-octulopyranosid)onate with methyl (4,5,7,8-tetra- O-acetyl-3-deoxy-α- d- manno-2-octulopyranosyl bromide)onate under Helferich conditions gave a 3:1 mixture of the corresponding α- and β-(2→4)-linked disaccharide derivatives in 58% yield. Separation and subsequent deprotection of the isomers afforded sodium O-[sodium (3-deoxy-α- and -β- d- manno-2-octulopyranosyl)onate]-(2→4)-(allyl 3-deoxy-β- d- manno-2-octulopyranosid)onate. Similarly, the glycoside sodium O-[sodium (3-deoxy-β- d- manno-2-octulopyranosyl)onate]-(2→4)-(allyl 3-deoxy-α- d- manno-2-octulopyranosid)onate was obtained by glycosylation of methyl (allyl 7,8- O-carbonyl-3-deoxy-α- d- manno-2-octulopyranosid)onate, followed by removal of the protecting groups. Radical copolymerization of the allyl glycosides with acrylamide afforded linear macromolecular antigens suitable for the determination of epitope-specificities of monoclonal antibodies directed against the KDO-region of enterobacterial lipopolysaccharides.

Synthetic Mucin Fragments: Methyl-3-O-(2-Acetamido-2-Deoxy-4-O- and 6-O-β-D-Galactopyranosyl-β-D-Glucopyranosyl)-β-D-Galactopyranoside and Methyl 3-O-(2-Acetamido-2-Deoxy-4-O- and 3-O-Methyl-β-D-Glucopyranosyl-3-D-Galactopyranoside

Abstract Glycosylation of methyl 3-O-(2-acetamido-3, 6-di-O-benzyl-2-deoxy-β-D-glucopyranosyl)-2,4,6-tri-O-benzyl-β-D-galactopyranoside (2) with 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl bromide (1), catalyzed by mercuric cyanide, afforded a trisaccharide derivative, which was not separated, but directly O-deacetylated to give methyl 3-O-(2-acetamido-3,6-di-O-benzyl-2-deoxy-4-O-β-D-galactopyranosyl-β-D-giucopyranosyl)-2,4,6-tri-O-benzyl-β-D-galactopyranoside (8). Hydrogenolysls of the benzyl groups of 8 then furnished the title trisaccharide (9). A similar pflyccsylation of methyl 3-O-(2-acetamido-3-O-acetyl-2-deoxy-β-D-glucopyranosyl)-2,4,6-tri-O-benzyl- β-D-galactopyranoside (obtained by acetylation of 4, followed by hydrolysis of the benzylidene acetal group) with bromide 1 gave a tribenzyl trisaccharide, which, on catalytic hydrogenolysls, furnished the isomeric trisaccharide (12). Methylation of 4 and 2 with methyl iodide-silver oxide in 1:1 dichloro-methane-N, N-dimethylformamide gave the 3-O- and 4-O-monomethyl ethers (13) and (15), respectively. Hydrogenolysis of the benzyl groups of 13 and 15 then provided the title monomethylated disaechartdes (15) and (16), respectively. The structures of trisacchacides 9 and 12, and disaccharides 14 and 16 were all established by 13C MMR spectroscopy.

Articial carbohydrate antigens: A block synthesis of a linear, tetrasaccharide repeating-unit of the Shigella flexneri varianty polysaccharide

Glycosylation of methyl 2,4-di- O-benzoyl-α- l-rhamnopyranoside with 2,3,4-tri- O-acetyl-α- l-rhamnopyranosyl bromide gave methyl 2,4-di- O-benzoyl-3- O-(2,3,4-tri- O-acetyl-α- l-rhamnopyranosyl)-α- l-rhamnopyranoside ( 4) in 93% yield. Conversion of 4 into the corresponding glycosyl bromide was accomplished with dibromomethyl methyl ether. Under Koenings-Knorr conditions, this bromide reacted with 8-(methoxycarbonyl)octyl 2- O-(2-acetamido-4,6- O-benzylidene-2-deoxy-β- d-glycopyranosyl)-3,4-di- O-benzyl-α- l- rhamnopyranoside, to provide the protected tetrasaccharide in 91% yield. Removal of blocking groups gave 8-(methoxycarbonyl)octyl O-α- l-rhamnopyranosyl-(1→3)-α- l-rhamnopyranosyl-(1→3)- O-2-acetamido-2-deoxy-β- d-glucopyranosyl-(1→2)- α- l-rhamnopyranoside. Together with previously synthesized tetrasaccharides of the Shigella flexneri Y O-antigen, this oligosaccharide has been used to study the conformation of O-antigens and to assist in the selection of S. flexneri, variant Y, specific monoclonal antibodies.