Isomerization of 4-O-methyl-D-glucuronic acid in neutral,aqueous solution

Aqueous solutions of 4-O-methyl-D-glucuronic acid at pH 7 were heated at 100°, and the monocarboxylic acids formed by isomerization were separated by anion-exchange chromatography and further identified by gas-liquid chromatography-mass spectrometry. After 6 h, the following yields of acids were obtained: 3-O-methyl-D-lyxo-5-hexulosonic (47%), 3-O-methyl-L-ribo-5-hexulosonic (12%), 4-O-methyl-D-mannuronic (4%), and 3-O-methyl-L-ribo-4-hexulosonic (1%).     

Synthesis of methyl glycoside derivatives of tri- and penta-saccharides related to the antithrombin III-binding sequence of heparin, employing cellobiose as a key starting-material

Two key synthons for the title pentasaccharide derivative, methyl O-(methyl 2-O-benzoyl-3-O-benzyl-alpha-L-idopyranosyluronate)-(1----4)-6-O-acetyl- 2-azido - 3-O- benzyl-2-deoxy-beta-D-glucopyranoside and O-(methyl 2,3-di-O-benzyl-4-O- chloroacetyl-beta-D-glucopyranosyluronate)-(1----4)-3,6-di-O-acetyl-2-az ido-2- deoxy-alpha-D- glucopyranosyl bromide, were prepared from a common starting material, cellobiose. They were coupled to give a tetrasaccharide derivative that underwent O-dechloroacetylation to the corresponding glycosyl acceptor. Its condensation with the known 6-O-acetyl-2-azido-3,4-di-O-benzyl-2-deoxy-alpha-D-glucopyranosyl bromide afforded a 77% yield of suitably protected pentasaccharide, methyl O-(6-O- acetyl-2-azido-3,4-di-O-benzyl-2-deoxy-alpha-D-glucopyranosyl)-(1----4)- O- (methyl 2,3- di-O-benzyl-beta-D-glucopyranosyluronate)-(1----4)-O-(3,6-di-O-acetyl-2- azido-2 - deoxy-alpha-D-glucopyranosyl)-(1----4)-O-(methyl 2-O-benzoyl-3-O-benzyl-alpha-L- idopyranosyluronate)- (1----4)-6-O-acetyl-2-azido-3-O-benzyl-2-deoxy-beta-D-glucopyranoside. Sequential deprotection and sulfation gave the decasodium salt of methyl O-(2- deoxy-2-sulfamido-6-O-sulfo-alpha-D-glucopyranosyl)-(1----4)-O-(be ta-D- glucopyranosyl-uronic acid)-(1----4)-O-(2-deoxy-2-sulfamido-3,6-di-O-sulfo-alpha-D-gluco pyranosyl)- (1----4)-O-(2-O-sulfo-alpha-L-idopyranosyluronic acid)-(1----4)-2-deoxy-2- sulfamido-6-O- sulfo-beta-D-glucopyranoside (3). In a similar way, the trisaccharide derivative, the hexasodium salt of methyl O-(2-deoxy-2-sulfamido-6-O-sulfo-alpha-D- glucopyranosyl)- (1----4)-O-(beta-D-glucopyranosyluronic acid)-(1----4)-2-deoxy-2-sulfamido-3,6- di-O- sulfo-alpha-D-glucopyranoside (4) was synthesized from methyl O-(6-O-acetyl-2- azido- 3,4-di-O-benzyl-2-deoxy-alpha-D-glucopyranosyl)-(1----4)-O-(methyl 2,3-di-O- benzyl-beta- D-glucopyranosyluronate)-3,6-di-O-acetyl-2-azido-2-deoxy-alpha-D- glucopyranoside. The pentasaccharide 3 binds strongly to antithrombin III with an association constant almost equivalent to that of high-affinity heparin, but the trisaccharide 4 appears not to bind.     

Syntheses of the methyl glycosides of the repeating units of chondroitin 4- and 6-sulfate

3,4,6-Tri-O-acetyl-D-galactal was transformed into methyl 6-O-acetyl-2-azido-4-O-benzyl-2-deoxy-beta-D-galactopyranoside and its 4-O-acetyl-6-O-benzyl analogue, each of which was glycosylated with activated, O-acetylated derivatives of methyl D-glucopyranosyluronate. The resulting beta-(1----3)-linked disaccharide derivatives were each reductively N-acetylated, hydrogenolysed, O-sulfated, and saponified to afford the disodium salts of methyl 2-acetamido-2-deoxy-3-O-(beta-D-glucopyranosyluronic acid)-4-O-sulfo-beta-D-galactopyranoside and the 6-O-sulfo analogue. D-Galactal was also transformed into activated derivatives of 2-azido-3,6-di-O-benzyl-2-deoxy-D-galactopyranose and their 3,4-di-O-benzyl analogues with various substituents at O-4 and O-6. These glycosyl donors were condensed with 6-O-protected derivatives of methyl 2,3-di-O-benzyl-beta-D-glucopyranoside to give the beta-(1----4)-linked disaccharide derivatives, which were selectively deprotected, then oxidised at C-6 of the gluco unit, reductively N-acetylated, selectively deprotected, O-sulfated at C-4 or C-6 of the galacto unit, and hydrogenolysed to give the disodium salts of methyl 4-O-(2-acetamido-2-deoxy-4-O-sulfo-beta-D-galactopyranosyl)-beta-D- glucopyranosiduronic acid and the 6-O-sulfo analogue.     

Synthesis of the optically active 4-O-phosphono-D-glucosamine derivatives related to the nonreducing-sugar subunit of bacterial lipid A

The optically active lipid A-subunit homologs named GLA-46, GLA-47, GLA-59, and GLA-60 have been synthesized stepwise by successive acylation at N-2 and O-3 of benzyl 2-amino-2-deoxy-4,6-O-isopropylidene-beta-D-glucopyranoside with the 3-9O-(benzyloxy)methyl or 39O-tetradecanoyl derivative of optically active 3-hydroxytetradecanoic acid, and phosphorylation at O-4 of the D-glucosamine residue.     

An improved method for the syntheses of p-aminophenyl 1-thio-β-d-glycosides

The condensation of the appropriate acetylglycosyl bromides with p-amino-benzenethiol in the presence of sodium methoxide afforded p-aminophenyl 1-thio-β-d-glucopyranoside, 1-thio-β-d-galactopyranoside, 1-thio-β-d-xylopyranoside, and 2-acetamido-2-deoxy-1-thio-β-d-glucopyranoside. p-Aminophenyl 1-thio-β-d-glucopyranosiduronic acid was synthesized by condensation of methyl (2,3,4-tri-o-acetyl-β-d-glucopyranosyl bromide)uronate with p-aminobenzenethiol, followed by saponification with sodium hydroxide.     

Synthesis of furanose derivatives of 3-deoxy-D-erythro-2-hexulosonic acid and their 3-bromo and 3-deuterio analogs

Methanolysis of 2,4,6-tri-O-benzoyl-2,3-dibromo-3-deoxy-D-altrono-1,5-lactone gave methyl 3-bromo-3-deoxy-2,4,6-tri-O-benzoyl-alpha-D-ribo-hex-2-ulofuranosonat e (3) and the anomeric mixture of the analogous 4,6-di-O-benzoyl derivative, having HO-2 free. Compound 3 was subjected to debromination with tributyltin hydride and tributyltin deuteride in the presence of 2,2'-azo-bisisobutyronitrile affording, respectively, the corresponding derivatives of 3-deoxy-D-erythro-2-hexulosonic acid and its 3-deuterio analog. The structure of the products and intermediates was established by spectroscopic methods and chemical transformations.     

The synthesis of racemic purpurosamine B

Starting from methyl 4,6-dichloro-4,6-dideoxy-α-D-galactopyranoside (1), D-chalcose (4,6-dideoxy-3-O-methyl-D-xcylo-hexopyranose) (5) was prepared by dechlorination with tributyltin hydride, selective benzoylation with benzoyl cyanide at O-2, methylation at O-3, and acid hydrolysis. D-Chalcose (5) was obtained as well by direct methylation of 1 with diazomethane at O-3, reduction with tin hydride, and hydrolysis. Chalcosyl bromide prepared from 5 was not very suitable for β-glycoside synthesis under Koenigs-Knorr conditions, and better results were obtained with 2- O-acetyl-4,6-dichloro-4,6-dideoxy-3-O-methyl-α-D-galactopyranosyl bromide, which gave β-glycosides with methanol, cyclohexanol, benzyl alcohol, 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose, and methyl 2,3-di-O-benzyl-6-deoxy-α-D-glucopyranoside. After dechlorination with tributyltin hydride, the corresponding β-glycosides of D-chalcose were obtained in good yield.     

Synthesis and NMR properties of novel 5,6-dihydroborauracil derivatives

Novel boron compounds - 5,6-saturated borauracil derivatives (4-bromo-5,6-dihydroborauracil, 4-hydroxy-5,6-dihydroborauracil and 4-methoxy-5,6-dihydroborauracil) are presented along with other boron compounds obtained from N-vinylurea: N-substituted β-boronic amino acid - 2-{[(dihydroxyborano-amino)(dihydroxyboranooxy)methyl]-amino}ethylboronic acid and substituted methoxy-borane O-[(1-amino-1-N-vinylamino)methyl]dihydroxyboronate.     

Synthesis of a neoglycoconjugate containing a Chlamydophila psittaci-specific branched Kdo trisaccharide epitope

The branched Kdo trisaccharide sodium (3-deoxy-α-d-manno-oct-2-ulopyranosyl)onate-(2→8)-[sodium (3-deoxy-α-d-manno-oct-2-ulopyranosyl)onate-(2→4)]-sodium (allyl 3-deoxy-α-d-manno-oct-2-ulopyranosid)onate has been prepared utilizing the regioselective glycosylation of the C-7, C-8 diol entity of a Kdo monosaccharide acceptor with a Kdo bromide donor followed by the attachment of the third Kdo unit to O-4 of the disaccharide intermediate. Deacetylation and hydrolysis of the methyl ester groups furnished the trisaccharide allyl glycoside which was converted into the corresponding 3-(2-aminoethylthio)propyl glycoside. Subsequent covalent attachment to bovine serum albumin furnished a neoglycoconjugate serving as an antigen for the induction of Chlamydophila psittaci-specific monoclonal antibodies.     

Chemical structure of an acidic polysaccharide produced by serratia piscatorum

The acidic polysaccharide of Serratia piscatorum consists of L-rhamnopyranosyl, D-galactopyranosyl, and D-galactopyranosyluronic acid residues in the molar ratio of 2:1:1. Some of the D-galactopyranosyluronic acid residues are acetylated at O-2 or O-3, or both. Smith degradation and methylation analysis indicated that the L-rhamnopyranosyl, D-galactopyranosyl, and D-galactopyranosyluronic acid residues are substituted with glycosidic linkages at O-3, O-3, and O-4, respectively. Partial acid hydrolysis of the native polysaccharide gave four acidic oligosaccharides, each of which was isolated and characterized, suggesting the following tetrasaccharide repeating unit: →3)-L-Rhap-(1→4)-D-GalAp-(1→3)-L-Rhap-(1→3)-D-Galp-(1→.     

Synthesis of a peripheral trisaccharide sequence of lutropin, a pituitary glycoprotein hormone; use of chitobiose as a key starting material

A chitobiose derivative, methyl O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl)-(1--- -4)-3,6 - di-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranoside, was derived from the corresponding N-acetyl derivative and this was converted into the glycosyl bromide (5). Glycosidation reaction between 5 and methyl 3,4,6-tri-O-benzyl-alpha-D-mannopyranoside in the presence of silver trifluoromethanesulfonate gave a beta-D-linked trisaccharide derivative. Replacement of the N,N-phthaloyl group by acetyl groups resulted in a product that was converted into methyl O-(2-acetamido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranosyl)-(1----4)-O -(2- acetamido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranosyl)-(1----2)-3,4,6- tri-O- benzyl-alpha-D-mannopyranoside (11) by use of a few reaction steps. The 4(3)-hydroxyl group of 11 was methanesulfonylated, and the product subjected to SN2 replacement with acetate anion, to give the D-galactosamine-containing trisaccharide derivative (12). After basic hydrolysis of 12, the 4(3)-hydroxyl group was sulfated, and all benzyl groups were removed by hydrogenolysis, giving methyl O-(2-acetamido-2-deoxy-4-O-sulfo-beta-D-galactopyranosyl)-(1----4)-O-(2- acetamido-2-deoxy-beta-D-glucopyranosyl)-(1----2)-alpha-D-mannopyranosid e monosodium salt, the methyl alpha-glycoside derivative of the peripheral trisaccharide sequence of the pituitary glycoprotein hormone lutropin.     

Depolymerization of heparin with diazomethane. Structure of N,O-methylated,even-numbered oligosaccharides produced by β-eliminative cleavage of the 2-amino-2-deoxyglycosylic linkage

The long-period reaction of heparin with excess diazomethane at 20° resulted in cleavage at the β-position of the uronic acid carboxyl group to give a mixture of methyl α- and β-glycosides of N,O-methylated di-, tetra-, and hexa-saccharides having a 4,5-unsaturated uronic acid, nonreducing end-group. The major disaccharides obtained were methyl O-(4-deoxy-3-O-methyl-α-l-threo-hex-4-enopyranosyluronic acid 2-sulfate)-(1→4)-2-deoxy-3-O-methyl-2-(N-methylsulfoamino)-α- and -β-d-glucopyranoside. The reaction of heparin at 4° yielded a mixture of methylated, higher-molecular-weight oligosaccharides, which retained some affinity for antithrombin III-Sepharose.     

Synthèse du méthyl-2-acétamido-2-désoxy-β-D-glucofuranoside et de dérivés

Methyl 2-acetamido-2-deoxy-5,6-O-isopropylidene-β-D-glucofuranoside was prepared in excellent yield from methyl 2-benzamido-2-deoxy-5,6-O-isopropylidene-β-D-glucofuranoside by alkaline hydrolysis, followed by selective N-acetylation. Treatment with 60% acetic acid at room temperature gave syrupy methyl 2-acetamido-2-deoxy-β-D-glucofuranoside, characterized by a crystalline tri-O-p-nitrobenzoyl derivative. The same treatment, at 100° gave methyl 2-acetamido-2-deoxy-β-D-glucopyranoside. In an alternative procedure, the selective N-acetylation was performed after acetic acid hydrolysis of methyl 2-amino-2-deoxy-5,6-O-isopropylidene-β-D-glucofuranoside. Several derivatives of methyl 2-acetamido-2-deoxy-β-D-glucofuranoside were prepared and compared with the corresponding pyranosides. The furanoside structure was clearly demonstrated by mass spectrometry and periodate oxidation.     

Synthesis of 2,5-dideoxy-2-C-methyl-d-arabinose derivatives from methyl 2,3-anhydro-5-deoxy-α-d-ribofuranoside

Treatment of methyl 2,3-anhydro-5-deoxy-α-d-ribofuranoside with lithium dimethyl cuprate gave methyl 2,5-dideoxy-2-C-methyl-α-d-arabinofuranoside (54% yield) and methyl 3,5-dideoxy-3-C-methyl-α-d-xylofuranoside (10%). The former was converted into its 3-O-acetyl and 3-O-benzyl derivatives, which, upon acid hydrolysis, afforded 3-O-acetyl- and 3-O-benzyl-2,5-dideoxy-2-C-methyl-d-arabinofuranose in 60–75% overall yield. Treatment of the 3-O-benzyl compound with ethanethiol in the presence of trifluoromethanesulfonic acid afforded 3-O-benzyl-2,5-dideoxy-2-C-methyl-d-arabinose diethyl dithioacetal (20%) and ethyl 3-O-benzyl-2,5-dideoxy-2-C-methyl-1-thio-α-d-arabinoside (73%). The former, which was also available from the latter by equilibration in acidic ethanethiol, was acetylated at O-4 and the product converted into the corresponding dimethyl acetal (85% overall yield). This compound was, after debenzylation, hydrolyzed with acid, to provide 4-O-acetyl-2,5-dideoxy-2-C-methyl-d-arabinose in 70% overall yield.     

Synthetic receptor analogues: the conformation of methyl 4-O-alpha-D-galactopyranosyl-beta-D-galactopyranoside (methyl beta-D-galabioside) and related derivatives, determined by n.m.r. and computational methods

The conformations of galabiose and its methyl and ethyl beta-glycosides as well as the 3-deoxy, 3-O-methyl, 3-deoxy-3-C-methyl, 3-deoxy-3-C-ethyl, and 6-deoxy analogues were investigated by n.m.r. (1H, 13C, n.O.e.) and computational (HSEA) methods. A good correlation was found between the computational data and the n.m.r. data for aqueous solutions. The conformations in aqueous solution were similar, whereas crystalline galabiose or methyl beta-D-galabioside in solution in methyl sulfoxide adopted different conformations that showed intramolecular hydrogen bonds (O-5'. . . O-3 and O-2'. . . O-6, respectively).     

Structural studies of the antigenic polysaccharide of Eubacterium saburreum, strain S29

The antigenic polysaccharide produced by Eubacterium saburreum, strain S29, is composed of (1→6)-linked β-d-glycero-d-galacto-heptopyranosyl residues, all of which are substituted with 6-deoxy-α-d-altro-heptofuranosyl groups at O-2.     

Synthesis of di-, tri-, and tetra-saccharides corresponding to receptor structures recognised by Streptococcus pneumoniae

Syntheses are described for methyl 2-acetamido-2-deoxy-4-O-β-d-galactopyranosyl-α-d-glucopyranoside, methyl 2-acetamido-2-deoxy-4-O-β-d-galactopyranosyl-β-d-glucopyranoside, methyl 3-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl-β-d-galactopyranoside, methyl 3-O-(2-acetamido-2-deoxy-4-O-β-d-galactopyranosyl-β-d-glucopyranosyl)-β-d-galactopyranoside, and methyl 4-O-[3-O-(2-acetamido-2-deoxy-4-O-β-d-galactopyranosyl-β-d-glucopyranosyl)-β-d-galactopyranosyl]- β-d-glucopyranoside.     

Structural confirmation of dihydrocinnamic acids from Adiscanthus fusciflorus by 13C NMR

In the wood of Adiscanthus fusciflorus six known alkaloids 4-methoxy-2-quinolone, 1-methyl-4-methoxy-2-quinolone, dictamine, skimmianine, γ-fagarine and N-methylflindersine and two new dihydrocinnamic acids 3-[2′,6′-dimethoxy-6″,6″-dimethylpyrano(2″,3″:4′, 3′)phenyl]-propionic acid and its methyl ester were identified. The structures of the dihydrocinnamic acid derivatives were confirmed by ¹³C NMR.     

Nitrous acid deamination of methylated amino-oligosaccharide glycosides

G.l.c.-mass spectrometry has been used to characterize the products of N-deacetylation-nitrous acid deamination of per-O-methylated derivatives (8–11) of methyl 2-acetamido-2-deoxy-3-O-β-D-galactopyranosyl-α-D-glucopyranoside(1), methyl (2) and benzyl (3) 2-acetamido-2-deoxy-4-O-β-D-galactopyranosyl-β-D-glucopyranosides, and methyl 2-acetamido-2-deoxy-6-O-β-D-galactopyranosyl-α-D-glucopyranoside (4). 2,5-Anhydrohexoses have been converted into alditol trideuteriomethyl ethers, alditol acetates, and aldononitriles. The importance of side reactions that lead to the formation of 2-deoxy-2-C-formylpentofuranosides is discussed.     

Structure of an l-arabino-d-xylan from the bark of Cinnamomum zeylanicum

An arabinoxylan isolated from the bark of Cinnamomum zeylanicum was composed of l-arabinose and d-xylose in the molar ratio 1.6:1.0. Partial hydrolysis furnished oligosaccharides which were characterised as α-d-Xylp-(1→3)-d-Ara, β-dXylp-(1→4)-d-Xyl, β-d-Xylp-(1→4)-β-d-Xylp-(1→4)-d-Xyl, β-d-Xylp-(1→4)-β-d-Xylp-(1→4)-β-d-Xylp-Xylp-(1→4)-d-Xyl, xylopentaose, and xylohexaose. Mild acid hydrolysis of the arabinoxylan gave a degraded polysaccharide consisting of l-arabinose (8%) and d-xyolse (92%). Methylation analysis indicated the degraded polysaccharide to be a linear (1→4)-linked d-xlan in which some xylopyranosyl residues were substituted at O-2 or O-3 with l-arabinofuranosyl groups. These data together with the results of methylation analysis and periodate oxidation of the arabinoxylan suggested that it contained a (1→4)-linked β-d-xylan backbone in which each xylopyranosyl residue was substituted both at O-2 and O-3 with l-arabinofuranosyl, 3-O-α-d-xylopyranosyl-l-arabinofuranosyl, and 3-O-l-arabinofuranosyl-l-arabinofuranosyl groups.