The structure of Lannea humilis gum

Lannea humilis trees exude a water-soluble gum polysaccharide containing galactose (75%), arabinose (11%), rhamnose (2%), and uronic acids (12%). Three aldobiouronic acids are present (chromatographic analysis), namely 4-O-(α-D-galactopyranosyluronic acid)-D-galactose, 6-O-(β-D-glucopyranosyluronic acid)-D-galactose, and 6-O-(4-O-methyl-β-D-glucopyranosyluronic acid)-D-galactose. Linkage analysis of degraded gums A and B, obtained by controlled, acid hydrolysis, gave (chromatographic analysis) 3-O-β-L-arabinofuranosyl-L-arabinose, 3-O-β-L-arabinopyranosyl-L-arabinose, 3-O-α-D-galactopyranosyl-L-arabinose, 3-O-β-D-galactopyranosyl-D-galactose, and 6-O-β-D-galactopyranosyl-D-galactose. Degraded gums A and B were examined by methylation analysis, and the former was subjected to a Smith-degradation, giving degraded gum C, which was studied by linkage and methylation analysis. The O-methyl derivative of the whole gum was prepared (a) by the Haworth and Purdie procedures, and (b) by the sodium hydride-methyl iodide-methyl sulphoxide technique. Both products were examined, after methanolysis, by g.l.c.: 2,3,4-tri-O-methyl-L-rhamnose; 2,3,5- and 2,3,4-tri- and 2,5-di-O-methyl-L-arabinose; 2,3,4,6-tetra-, 2,3,6-, 2,4,6- and 2,3,4-tri-, 2,6- and 2,4-di-, and 2-O-methyl-D-galactose; 2,3,4-tri-O-methyl-D-glucuronic acid and 2,3,4-tri-O-methyl-D-galacturonic acid were identified. The whole gum was subjected to four successive Smith-degradations giving Polysaccharides I–IV, which were examined by linkage and methylation analysis. Polysaccharide IV is a branched galactan; the arabinose-containing sidechains in L. humilis gum therefore do not contain more than four residues, and only a few of that length occur. The evidence obtained indicates that the gum molecules are very highly branched. The galactan framework consists of short chains of β-(1→3)-linked D-galactose residues, branched and interspersed with β-(1→6)-linkages. To positions 3 and 6 of this framework are attached either single D-galactose end-groups or short side-chains of D-galactose or of L-arabinose residues, and three aldobiouronic acids. A possible structural fragment that shows these features is proposed.     

The structure of bael (Aegle marmelos) gum

Purified, bael-gum polysaccharide containsd-galactose (71%),l-arabinose (12.5%),l-rhamnose (6.5%), andd-galacturonic acid (7%). Hydrolysis of one mole of the fully methylated polysaccharide gave: (a) from the neutral part, 2,3,4-tri-O-methyl-l-rhamnose (2 moles), 2,3,5-tri-O-methyl-l-arabinose (4 moles), 2,3,4,6-tetra-O-methyl-d-galactose (8 moles), 3,4-di-O-methyl-l-rhamnose (2 moles), 2,5-di-O-methyl-l-arabinose (1 mole), 2,4,6-tri-O-methyl-d-galactose (10 moles), 2,3-di-O-methyl-l-arabinose (1 mole), 2,4-di-O-methyl-d-galactose (14 moles), and 2-O-methyl-d-galactose (2 moles); and (b) from the acidic part, 2,3,4-tri-O-methyl-d-galacturonic acid (1 mole), 2,4,6-tri-O-methyl-3-O-(2,3,4-tri-O-methyl-d-galactopyranosyluronic acid)-d-galactose (2.6 moles), and 2,4,6-tri-O-methyl-3-O-[2,4,6-tri-O-methyl-3-O-(2,3,4-tri-O-methyl-d-galactopyranosyluronic acid)-d-galactopyranosyl]-d-galactose (1 mole). Mild hydrolysis of the whole gum yielded oligosaccharides from which 3-O-β-d-galactopyranosyl-l-arabinose, 5-O-β-d-galactopyranosyl-l-arabinose, 3-O-β-d-galactopyranosyl-d-galactose, and 6-O-β-d-galactopyranosyl-d-galactose could be isolated and characterized. The results of methylation, periodate oxidation, Smith degradation, Barry degradation, and graded hydrolysis studies were employed for the elucidation of the structure of the whole gum.     

A new water-soluble polysaccharide from the seeds of Cassia multijuga

A polysaccharide consisting of D-galactose, D-mannose, and D-xylose in the molecular ratios 5:1:2 has been isolated from the defatted seeds of Cassia multijuga. Methylation analysis yielded 2,3-di-O-methyl-D-galactose (2 mol), 2,3,6-tri-O-methyl-D-galactose (4 mol), 2,3,4,6-tetra-O-methyl-D-galactose (4 mol), 2,3-di-O-methyl-D-mannose (2 mol), 2-O-methyl-D-xylose (1 mol), 2,3-di-O-methyl-D-xylose (2 mol), and 2,3,4-tri-O-methyl-D-xylose (1 mol). Periodate oxidation indicated 32.4% of end-groups and methylation indicated 31.2%. Partial hydrolysis with acid gave 6-O-α-D-galactosyl-D-galactose, 6-O-α-D-galactosyl-D-mannose, 4-O-β-D-galactosyl-D-xylose, and 3-O-β-D-xylosyl-D-xylose, together with monosaccharides. The polysaccharide is highly branched, consisting of galactosyl, mannosyl, and xylosyl residues in the main chain, with (1→4)-β linkages, and galactosyl and xylosyl end-groups.     

Synthesis of a series of fully methylated aldobiouronic acids,and β-elimination reactions of their synthetic precursors

Treatment of methyl 2,3,4-tri-O-acetyl-l-bromo-l-deoxy-α-d-glucopyranuronate severally with 2,4,6-, 2,3,6-, and 2,3,4-tri-O-methyl derivatives of methyl α-d-glucopyranoside and with methyl 4,6-O-benzylidene-3-O-methyl-α-d-glucopyranoside, in the presence of silver carbonate, afforded crystalline aldobiouronic acid derivatives in high yield. Deacetylation followed by methylation gave a series of fully methylated derivatives of laminaribiouronic, cellobiouronic, and gentiobiouronic acids, and the (1 → 2)-linked analogue. Methylation with methyl iodide and silver oxide in N,N-dimethylformamide was invariably accompanied by a small amount ofβ-elimination, with the formation of olefinic disaccharides which were also obtained by β-elimination reactions of the precursor acetates followed by methylation. Methyl 4,5-unsaturated 4-deoxyhexopyranosyluronate derivatives were the main products of the reaction, but these underwent further degradation with cleavage of the interglycosidic linkage and formation of 6-methoxycarbonyl-4-pyrone.     

Synthesis of phenyl 2-acetamido-2-deoxy-3-O-α-l-fucopyranosyl-β-d-glucopyranoside and related compounds

The reaction of phenyl 2-acetamido-2-deoxy-4,6- O-(p-methoxybenzylidene)-β-d-glucopyranoside with 2,3,4-tri-O-benzyl-α-l-fucopyranosyl bromide under halide ion-catalyzed conditions proceeded readily, to give phenyl 2-acetamido-2-deoxy-4,6-O-(p-methoxybenzylidene)-3-O-(2,3,4-tri-O-benzyl-α-l-fucopyranosyl)-β-d-glucopyranoside (8). Mild treatment of 8 with acid, followed by hydrogenolysis, provided the disaccharide phenyl 2-acetamido-2-deoxy-3-O-α-l-fucopyranosyl-β-d-glucopyranoside. Starting from 6-(trifluoroacetamido)hexyl 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-β-d-glucopyranoside, the synthesis of 6-(trifluoroacetamido)hexyl 2-acetamido-2-deoxy-3-O-β-l-fucopyranosyl-β-d-glucopyranoside has been accomplished by a similar reaction-sequence. On acetolysis, methyl 2-acetamido-2-deoxy-3-O-α-l-fucopyranosyl-α-d-glucopyranoside gave 2-methyl-[4,6-di-O-acetyl-1,2-dideoxy-3-O-(2,3,4-tri-O-acetyl-α-l-fucopyranosyl)-α-d-glucopyrano]-[2, 1-d]-2-oxazoline as the major product.     

Synthesis of 3- and 2′-fucosyl-lactose and 3,2′-difucosyl-lactose from partially benzylated lactose derivatives

O-β-d-Galactopyranosyl-(1→4)-O-[α-l-fucopyranosyl-(1→3)]-d-glucose has been synthesised by reaction of benzyl 2,6-di-O-benzyl-4-O-(2,3,4,6-tetra-O-benzyl-β-d-galactopyranosyl)-β-d-glucopyranoside with 2,3,4-tri-O-benzyl-α-l-fucopyranosyl bromide in the presence of mercuric bromide, followed by hydrogenolysis. Benzylation of benzyl 3′,4′-O-isopropylidene-β-lactoside, via tributylstannylation, in the presence of tetrabutylammonium bromide or N-methylimidazole, gave benzyl 2,6-di-O-benzyl-4-O-(6-O-benzyl-3,4-O-isopropylidene-β-d-galactopyranosyl)-β-d-glucopyranoside (6). α-Fucosylation of 6 in the presence of tetraethylammonium bromide provided either benzyl 2,6-di-O-benzyl-4-O-[6-O-benzyl-3,4-O-isopropylidene-2-O-(2,3,4-tri-O-benzyl-α-l-fucopyransoyl)-β-d- galactopyranosyl]-β-d-glucopyranoside (13, 73%) or a mixture of 13 (42%) and benzyl 2,6-di-O-benzyl-4-O-[6-O-benzyl-3,4,-O-isopropylidene-2-O-(2,3,4-tri-O-benzyl-α-l-fucopyranosyl)-β-d- galactopyranosyl-3-O-(2,3,4-tri-O-benzyl-α-l-fucopyranosyl)-β-d-glucopyranoside (16, 34%). α-Fucosylation of 13 in the presence of mercuric bromide and 2,6-di-tert-butyl-4-methylpyridine gave 16 (73%). Hydrogenolysis and acid hydrolysis of 13 and 16 afforded O-α-l-fucopyranosyl-(1→2)-O-β-d-galactopyranosyl-(1→4)-d-glucose and O-α-l-fucopyranosyl-(1→2)-O-β-d-galactopyranosyl-(1→4)-O-[α-l-fucopyranosyl-(1→3)]-d-glucose, respectively.     

Synthèse des 2-acé-tamido-2-désoxy-6-O-α-et β-D-xylopyranosyl-α-D-glucopyranose

2-Acetamido-2- deoxy-6-O-, -xylopyranosyl-O-D-glucopyranose has been synthesized in crystalline form by condensation of 2,3,4-tri-O-acetyl-α-D-xylopyranosyl chloride (1) with benzyl 2-acetamido-3,4-di-O-acetyl-2-deoxy-β-D-glucopyranoside (2), followed by O-deacetylation and catalytic hydrogenation. Condensation of 2 with 2,3,4-tri-O-chlorosulfonyl-β-D-xylopyranosyl chloride, followed by dechlorosulfonylation and acetylation, gave benzyl 2-acetamido-3,4-di-O-acetyl-2-deoxy-6-O-(2,3,4-tri-O-acetyl-α-D-xylopyranosyl)β-D-glucopyranoside in crystalline form. O-Deacetylation, followed by catalytic hydrogenation, gave 2-acetamido-2-deoxy-6-O-α-D-xylopyranosyl-α-D-glucopyranose in crystalline form.     

Synthesis of the tetrasaccharide repeating-unit of the O-specific polysaccharide from Salmonella senftenberg

The oligosaccharide β-d-Man-(1 → 4)-α-l-Rha (1 → 3)-d-Gal-(6 ← 1)-α-d-Glc, which is the repeating unit of the O-specific polysaccharide chain of the lipopolysaccharide from Salmonella senftenberg, was obtained by glycosylation of benzyl 2,4-di-O-benzyl-6-O-(2,3,4-tri-O-benzyl-6-O-p-nitrobenzoyl-α-d-glucopyranosyl)-β-d-galactopyranoside or benzyl 2-O-acetyl-6-O-(2,3,4-tri-O-benzyl-6-O-p-nitrobenzoyl-α-d-glucopyranosyl)-β-d-galactopyranoside with 3-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-β-d-mannopyranosyl)-β-l-rhamnopyranose 1,2-(methyl orthoacetate) followed by removal of protecting groups.     

Synthesis of methyl O-(3-deoxy-3-fluoro-β-d-galactopyranosyl)-(1→6)-β-d-galactopyranoside and methyl O-(3-deoxy-3-fluoro-β-d-galactopyranosyl)-(1→6)-O-β-d-galactopyranosyl-(1→6)-β-d-galactopyranoside

Condensation of 2,4,6-tri-O-acetyl-3-deoxy-3-fluoro-α-d-galactopyranosyl bromide (3) with methyl 2,3,4-tri-O-acetyl-β-d-galactopyranoside (4) gave a fully acetylated (1→6)-β-d-galactobiose fluorinated at the 3′-position which was deacetylated to give the title disaccharide. The corresponding trisaccharide was obtained by reaction of 4 with 2,3,4-tri-O-acetyl-6-O-chloroacetyl-α-d-galactopyranosyl bromide (5), dechloroacetylation of the formed methyl O-(2,3,4-tri-O-acetyl-6-O-chloroacetyl-β-d-galactopyranosyl)-(1→6)- 2,3,4-tri-O-acetyl-β-d-galactopyranoside to give methyl O-(2,3,4-tri-O-acetyl-β-d-galactopyranosyl)-(1→6)-2,3,4-tri-O-acetyl-β-d-galactopyranoside (14), condensation with 3, and deacetylation. Dechloroacetylation of methyl O-(2,3,4-tri-O-acetyl-6-O-chloroacetyl-β-d-galactopyranosyl)-(1→6)-O-(2,3,4-tri-O-acetyl- β-d-galactopyranosyl)-(1→6)-2,3,4-tri-O-acetyl-β-d-galactopyranoside, obtained by condensation of disaccharide 14 with bromide 5, was accompanied by extensive acetyl migration giving a mixture of products. These were deacetylated to give, crystalline for the first time, the methyl β-glycoside of (1→6)-β-d-galactotriose in high yield. The structures of the target compounds were confirmed by 500-MHz, 2D, ¹H- and conventional ¹³C- and ¹⁹F-n.m.r. spectroscopy.     

Purification and properties of an endo-(1 leads to 3)-beta-D-glucanase from malted barley

3,6-Anhydro-α-D-galactopyranose 1,2-(methyl orthoacetate) and its 4-acetate were synthesized from 2,3,4-tri-O-acetyl-6-O-tosyl-α-D-galactopyranosyl bromide. Condensation of the above-mentioned, acetylated ortho ester with 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose gave 6-O-(2,4-di-O-acetyl-3,6-anhydro-β-D-galactopyranosyl)-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose. The same disaccharide derivative was synthesised from 6-O-β-D-galactopyranosyl-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose by mono-O-tosylation followed by treatment with alkali and acetylation.     

Facile syntheses of methyl α-D-altropyranoside and its 3,4-and 4,6-O-isopropylidene derivatives

An L-arabino-D-glucurono-D-xylan isolated from the mature stalk of the reed Arundo donax contained the neutral sugars D-xylose, L-arabinose, and D-glucose in molar proportions 8.9:1:traces. 2-O-(4-O-Methyl-α-D-glucopyranosiduronic acid)-D-xylose was also present. The results of methylation analysis showing the presence of 2,3,4-tri-, 2,3-di-, 2-, and 3-O-methyl-D-xylose together with 2,3,5-tri-O-methyl-L-arabinose were determined by the gas-liquid chromatography-mass spectrometry technique and were in good agreement with those of the periodate oxidation. The D-xylan has an average degree of polymerization of about 80 and is essentially linear. The polysaccharide has structural features similar to those of polysaccharides isolated from other Gramineae.     

Synthesis of two purple-membrane glycolipids and the glycolipid sulfate O-(β-d-glucopyranosyl 3-sulfate)-(1→6)-O-α-d-mannopyranosyl-(1→2)-O-α-d-glucopyranosyl-(1→1)-2, 3-di-O-phytanyl-sn-glycerol

The two purple-membrane glycolipids O-β-d-glucopyranosyl- and O-β-d-galactopyranosyl-(1→6)-O-α-d-mannopyranosyl-(1→2)-O-α-d-glucopyranosyl-(1→1)-2, 3-di-O-phytanyl-sn-glycerol were prepared by coupling O-(2,3,4-tri-O-acetyl-α-d-mannopyranosyl)-(1→2)-O-(3,4,6-tri-O-acetyl-α-d-glucopyranosyl)-(1→1)-2, 3-di-O-phytanyl-sn-glycerol (9) with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide or 2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl bromide, respectively, followed by deacetylation. The glycolipid sulfate O-(β-d-glucopyranosyl 3-sulfate)-(1→6)-O-α-d-mannopyranosyl-(1→2)-O-α-d-glucopyranosyl-(1→1)-2,3-di-O-phytanyl-sn-glycerol was prepared by coupling of 9 with 2,4,6-tri-O-acetyl-3-O-trichloroethyloxycarbonyl-α-d-glucopyranosyl bromide in the presence of Hg(CN)₂/HgBr₂ followed by selective removal of the 3?-trichloroethyloxycarbonyl group, sulfation of HO-3?, and deacetylation. The suitably protected key-intermediate 9 could be prepared by two distinct approaches.     

Regioselective synthesis of a glycomimetic trisaccharide of Sialyl Lewis (sLe)

Sialyl Lewis (sLe^x) is the smallest naturally occurring carbohydrate ligand that binds to E-Selectin on the activated endothelium. We report here the total synthesis of acetic acid-sLe^x analog (12), for testing as a therapeutic agent. Methoxyethyl 4-O-(3,4-O-isopropylidene-β-d-galactopyranosyl)-β-d-glucopyranoside (3) was prepared starting from the methoxyethyl-β-d-lactoside (2), which was selectively benzoylated to give the methoxyethyl 2,6-di-O-benzoyl-4-O-(2,6-di-O-benzoyl-3,4-O-isopropylidene-β-d-galactopyranosyl)-β-d-glucopyranoside (4). Glycosylation of acceptor 4 with methyl 2,3,4-tri-O-benzyl-1-thio-β-l-fucopyranoside (5) in the presence of cupric bromide and tetrabutylammonium bromide afforded the corresponding methoxyethyl 2,6-di-O-benzyl-3-O-(2,3,4-tri-O-benzyl-α-l-fucopyranosyl)-4-O-(2,6-di-O-benzyl-3,4-O-isopropylidene-β-d-galactopyranosyl)-β-d-glucopyranoside (6). Selective removal of the 4″,6″-O-isopropylidene group from 6 gave the deprotected trisaccharide 7. The regioselective esterification of O-3″ of trisaccharide 8 (obtained from the dibutylstannylene derivative of 7) with benzyl-2-bromoacetate and tetrabutylammonium bromide afforded the 3″-O-carbobenzyloxymethyl trisaccharide derivative 9, which on saponification and hydrogenolysis with palladium-charcoal afforded the target trisaccharide 12 glycomimetic of Sialyl Lewis (sLe^x) trisaccharide omitting the sialic acid moiety.     

The structure of a dextran produced by Leuconostoc mesenteroides NRRL B-1397: the linkages and length of the branches

The structure of a dextran produced by Leuconostoc mesenteroides NRRL B-1397 has been investigated in relation to its immunological properties. The methylated dextran yielded on acid hydrolysis 2,3,4,6-tetra-, 2,3,4-tri-, 3,4,-di-, and 2,4-di-O-methyl-d-glucose, in the molar ratio of 1.0:3.1:0.7:0.2, together with a trace of 2,4,6-tri-O-methyl-dglucose, indicating that the branches occur mainly at O-2 and the remainder at O-3. A carboxyl-dextran, obtained by catalytic oxidation of the dextran to convert the terminal, non-reducing d-glucose residues d-glucuronic acid residues, was partially hydrolyzed with acid. Fractionation gave 2-O-(α-d-glucopyranosyluronic acid) d-glucose (major), 6-O-(α-d-glucopyranosyluronic acid)-d-glucose, and mixtures of aldotri-, aldotetra-, and aldopentaouronic acid that contain both (1 → 6)- and (1 → 2)-d-glucosidic linkages. It is concluded that the branches at O-2 are mainly single d-glucose units, whereas those occurring at O-3 may be longer than two glucose units, forming a highly branched structure having an average repeating- unit of 5 sugar residues.     

First synthesis of the immunodominant beta-galactofuranose-containing tetrasaccharide present in the cell wall of Aspergillus fumigatus

β-Galf-(1→5)-β-Galf-(1→6)-α-Manp-(1→6)-α-Manp, the immunodominant epitope in the cell-wall galactomannan of Aspergillus fumigatus, was synthesized for the first time as its allyl glycoside. The key disaccharide glycosyl donor, 2,3,5,6-tetra-O-benzoyl-β-d-galactofuranosyl-(1→5)-2-O-acetyl-3,6-di-O-benzoyl-β-d-galactofuranosyl trichloroacetimidate (10), was constructed by 5-O-glycosylation of 1,2-O-isopropylidene-3,6-di-O-benzoyl-α-d-galactofuranose (4) with 2,3,5,6-tetra-O-benzoyl-β-d-galactofuranosyl trichloroacetimidate (5), followed by 1,2-O-deacetonation, acetylation, selective 1-O-deacetylation, and trichloroacetimidation. The target tetrasaccharide 16 was obtained by the condensation of allyl 2,3,4-tri-O-benzoyl-α-d-mannopyranosyl-(1→6)-2,3,4-tri-O-benzoyl-α-d-mannopyranoside (14) as glycosyl acceptor with the disaccharide glycosyl donor 10, followed by deprotection.     

An approach to stereoselective preparation of 3-C-glycosylated d- and l-glucals

An approach to stereoselective synthesis of α- or β-3-C-glycosylated l- or d-1,2-glucals starting from the corresponding α- or β-glycopyranosylethanals is described. The key step of the approach is the stereoselective cycloaddition of chiral vinyl ethers derived from both enantiomers of mandelic acid. The preparation of 1,5-anhydro-4,6-di-O-benzyl-2,3-dideoxy-3-C-[(2,3,4,6-tetra-O-benzyl-β-d-glucopyranosyl)methyl]-l-arabino-hex-1-enitol, 1,5-anhydro-4,6-di-O-benzyl-2,3-dideoxy-3-C-[(2,3,4,6-tetra-O-benzyl-β-d-glucopyranosyl)methyl]-d-arabino-hex-1-enitol, and 1,5-anhydro-4,6-di-O-benzyl-2,3-dideoxy-3-C-[(2,3,4-tri-O-benzyl-α-l-fucopyranosyl)methyl]-d-arabino-hex-1-enitol serves as an example of this approach.     

Synthesis of glycosyl esters of oleanolic acid

The trisaccharide, O-(2,3,4-tri-O-benzoyl-β-L-rhamnopyranosyl)-(1→4)-O-(2,3,6-tri-O-benzoyl-β-D-glucopyranosyl)-(1→6)-1,2,3,4-tetra-O-acetyl-β-D-glucopyranose has been prepared by two different routes. Condensation of this trisaccharide with oleanolic acid afforded the corresponding 1,2-trans glycosyl ester. Some other glycosyl esters of oleanolic acid were also prepared by the same method.     

Synthetic mucin fragments. Methyl 6-O-(2-acetamido-2-deoxy-β-D-glycopyranosyl)-β-D-galactopyranoside,methyl 3,4-di-O-(2-acetamido-2-deoxy-β-D-glycopyranosyl)-β-D-galactopyranoside,and methyl O-(2-acetamido-2-deoxy-β-D-glucopyranosyl)-(1 å 3)-O-β-D-galactopyranosyl-(1 å 3)-O-(2-acetamido-2-deoxy-β- D-glucopyranosyl)-(1 å 3)-β-D-galactopyranoside

Condensation of methyl 2,6-di-O-benzyl-β-d-galactopyranoside with 2-methyl-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-d-glucopyrano)-[2,1,-d]-2-oxazoline (1) in 1,2-dichloroethane, in the presence of p-toluenesulfonic acid, afforded a trisaccharide derivative which, on deacetylation, gave methyl 3,4-di-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-2,6-di-O-benzyl-β-d- glactopyranoside (5). Hydrogenolysis of the benzyl groups of 5 furnished the title trisaccharide (6). A similar condensation of methyl 2,3-di-O-benzyl-β-d-galactopyranoside with 1 produced a partially-protected disacchraide derivative, which, on O-deacetylation followed by hydrogenolysis, gave methyl 6-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-β-d-glactopyranoside (10). Condensation of methyl 3-O-(2-acetamido-4,6-O-benzylidene-2-deoxy-β-d-glucopyranosyl)-2,4,6-tri-O-benzyl-β-d- galactopyranoside with 3-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-β-d-glucopyranosyl)-2,4,6-tri-O-acetyl-α-d-galactopyranosyl bromide in 1:1 benzene-nitromethane in the presence of powdered mercuric cyanide gave a fully-protected tetrasaccharide derivative, which was O-deacetylated and then subjected to catalytic hydrogenation to furnish methyl O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-O-β-d-galactopyranosyl-(1å3)-O-(2-acetamido-2-deoxy- β-d-glucopyranosyl)-(1å3)-β-d-galactopyranoside (15). The structures of 6, 10, and 15 were established by ¹³C-n.m.r. spectroscopy.     

Methylation analysis of carrageenans from the seaweed Iridaea undulosa

Two carrageenans from Iridaea undulosa, isolated by precipitation of the crude polysaccharide at O.70–1.05 M and 1.55–1.65 M KCl concentrations, were studied by methylation analysis. Acid hydrolysis of the methylated derivative of the less soluble carrageenan (molar ratio galactose: 3,6-anhydrogalactose: sulphate 1.00: 0.50: 1.20) yielded major amounts of 2,6-di-O-methylgalactose (51.3 mol %), 4,6-di-O-methylgalactose (25.6%) and 4-O-methylgalactose (51.3mol%), 4,6-di-O-methylgalactose (25.6%) and 4-O-methylgalactose (13.4%). Minor quantities of 3-O-methylgalactose (4.6%) and 6-O-methylgalactose (3.2%) were found together with traces of 2,3,6- and/or 2,4,6-tri-O-methylgalactose, 2-O-methylgalactose and galactose. Oxidative acid hydrolysis produced 3,6-anhydro-2-O-methylgalactonic acid and 3,6-anhydrogalactonic acid in a molar ratio 3.5-4.0:1.0. The methylated derivative of the more soluble carrageenan (molar ratio galactose:3,6-anhydrogalactose:sulphate 1.00:0.04:1.43) gave on acid hydrolysis, 2,3,4,6-tetra-O-methylgalactose (4.6%), 2,3,6-tri-O-methylgalactose (4.2%), 2,4,6-tri-O-methylgalactose (10.7%), 4,6-di-O-methylgalactose (24.1%), 3,6-di-0-methylgalactose (8.0%), 2,3-di-O- methylgalactose (3.4%), 2,4-di-O-methylgalactose (4.6%), 2,6-di-O-methylgalactose (4.2%), 3-O-methylgalactose (19.5%),4-O-methylgalactose (9.6%),6-O-methylgalactose(3.1%),galactose (3.4%)and traces of 2-O-methylgalactose.     

The stepwise synthesis of a methyl β-xylotetraoside related to branched xylans

3,4-Di-O-acetyl-2-O-benzyl-α-d-xylopyranosyl bromide (1) reacts with methyl 2,3-anhydro-α-d-ribopyranoside (2) to afford, in high yield, methyl 2,3-anhydro-4-O- (3,4-di-O-acetyl-2-O-benzyl-β-d-xylopyranosyl)-β-d-ribopyranoside (3). Deacetylation of 3 gave 4, which reacted with 2,3,4-tri-O-acetyl-α-d-xylopyranosyl bromide to give the branched tetrasaccharide derivative 5, which, in turn, was converted by a series or conventional reactions into methyl 4-O-[3,4-di-O-(β-d-xylopyranosyl)-β-d- xylopyranosyl]-β-d-xylopyranoside. The reaction of 1 with its hydrolysis product gave 3,4-di-O-acetyl-2-O-benzyl-α-d-xylopyranosyl 3,4-di-O-acetyl-2-O-benzyl-β-d-xylopyranoside, which was also isolated after the reaction of 1 with 2.