Selective benzylation of some D-galactopyranosides. Unusual relative reactivity of the hydroxyl group at C-4

Partial benzylation of methyl 2,3-di-O-benzyl-α-D-galactopyranoside gave methyl 2,3,6-tri-O-benzyl-α-D-galactopyranoside as the major product, whereas the isomeric 2,6-di-O-benzyl ether gave a mixture of products in which the ratio of methyl 2,4,6- to methyl 2,3,6-tri-O-benzyl-α-D-galactopyranoside was ≈4:1. The proportion of unreacted starting-material was low in both cases, whereas after a similar reaction of methyl 2,6-di-O-benzyl-β-D-galactopyranoside more than 50% of the dibenzyl ether was recovered unchanged. In this case also, considerably higher reactivity was exhibited by the hydroxyl group at C-4 than that at C-3. Acid hydrolysis of the methyl glycosides of the tribenzyl ethers afforded crystalline 2,4,6-tri-O-benzyl-α-D-galactose and syrupy 2,3,6-tri-O-benzyl-D-galactose. Structures of intermediates were established by acetylation, examination of their n.m.r. spectra, and conversion into the known 3-O and 4-O-methyl-D-galactose.     

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.     

An Escherichia coli antimicrobial effect of arabinoglucomannan from fruit of Bryonia lacinosa

Extraction of the pulp of ripe berries of Bryonia lacinosa with 1% aqueous acetic acid yielded a polysaccharide material, having d-glucose, d-mannose and l-arabinose in the molar ratio of. 5.00:3.01:4.00. Hydrolysis of the fully methylated polysaccharide furnished 2,3,4,6-tetra-O-methyl-d-glucose, 2,3-di-O-methyl-d-glucose, 2,3,6-tri-O-methyl-d-mannose, 2,3-di-O-methyl-d-mannose and 2,3,5,-tri-O-methyl-l-arabinose in 1:4:2:1:4 molar ratio. Partial hydrolysis of the polysaccharide furnished; mannobiose, epicellobiose, 6-O-β-l-arabinofuranosyl-d-glucose, 6-O-α-mannopyranosyl-d-mannose and epimaltose along with the component monosaccharides. On metaperiodate oxidation studies, 100 g of the polysaccharide liberated 0.055 mol of HCOOH consuming 0.7127 mol of periodate, indicating about 8.33% of the end groups. On the basis of the above results, a structure for the repeating unit of the polysaccharide has been proposed. The polysaccharide was tested for the microbial activity and was found to be active against Escherichia coli with a minimum dose of 6.25 mg/mL.     

Synthesis of a tetrasaccharide donor corresponding to the O-specific polysaccharide of Shigella dysenteriae type 1

O-(2,4-Di-O-chloroacetyl-α-l-rhamnopyranosyl)-(1 → 2)-O-(3,4,6-tri-O-benzoyl-α-d-galactopyranosyl)-(1 → 3)-O-(2-acetamido-4,6-di-O-acetyl-2-deoxy-α-d-glycopyranosyl)-(1 → 3)-2,4-di-O-benzoyl-α-l-rhamnopyranosyl trichloroacetimidate (1) was synthesized in a stepwise manner, using the following monosaccharide units: 2-(trimethylsilyl)ethyl 2,4-di-O-benzoyl-α-l-rhamnopyranoside, 2-azido-4,6-O-benzylidene-3-O-chloroacetyl-2-deoxy-β-d-glycopyranosyl chloride, methyl 3,4,6-tri-O-benzoyl-2-O-(4-methoxybenzyl)-1-thio-β-d-galactopyranoside, and 2,4-di-O-benzoyl-3-O-chloroacetyl-α-l-rhamnopyranosyl chloride. Compound 1 corresponds to a complete tetrasaccharide repeating unit of the O-specific polysaccharide of the lipopolysaccharide of Shigella dysenteriae type 1.     

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.     

The structure of lannea coromandelica gum

Lannea coromandelica trees exude a water-soluble gum polysaccharide containing galactose (70%), arabinose (11%), rhamnose (2%), and uronic acids (17%). 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-d-glucopyranosyluronic acid)-d-galactose. Linkage analysis of degraded gum A, 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 gum A was examined by methylation analysis, and was subjected to a Smith-degradation, giving degraded gum B, which was studied by linkage and methylation analysis. The O-methyl derivative of the whole gum was prepared by the Haworth and Purdie procedures and 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-, and 2,6- and 2,4-di-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 three successive Smith-degradations, giving Polysaccharides I–III which were examined by linkage and methylation analysis. The structural evidence obtained indicates that the gum molecules are very highly branched, based on a galactan framework consisting 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. The structure therefore appears to be very similar to that established recently for Lannea humilis gum.     

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.     

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.     

A synthesis of psi-cytidine

2-O-Benzoyl-3,6-di-O-benzyl-4-O-(chloroacetyl)-, 4-O-acetyl-2-O-benzoyl-3,6-di-O-benzyl-, and 2-O-benzoyl-3,4,6-tri-O-benzyl-α-d-galactopyranosyl chloride were converted into the corresponding 2,2,2-trifluoroethanesulfonates, and these were treated with allyl 2-O-benzoyl-3,6-di-O-benzyl-α-d-galactopyranoside, to give allyl 2-O-benzoyl-4-O-[2-O-benzoyl-3,6-di-O-benzyl-4-O-(chloroacetyl)-β-d-galactopyranosyl]-3,6-di-O-benzyl- α-d-galactopyranoside (26; 41% yield), allyl 4-O-(4-O-acetyl-2-O-benzoyl-3,6-di-O-benzyl-β-d-galactopyranosyl)-2-O-benzoyl-3,6-di-O-benzyl- α-d-galactopyranoside (27; 62% yield), and allyl 2-O-benzoyl-4-O-(2-O-benzoyl-3,4,6-tri-O-benzyl-β-d-galactopyranosyl)-3,6-di-O-benzyl-α-d-galactopyranoside (28; 65% yield). All disaccharides were free from their α anomers. Disaccharides 26 and 27 were found to be base-sensitive, and were de-esterified by KCN in aqueous ethanol, and debenzylated with H₂-Pd. Attempts to produce (1→4)-β-d-galactopyranosides from the coupling of a number of fully esterified d-galactopyranosyl sulfonates to allyl 2,3,6-tri-O-benzoyl-α-d-galactopyranoside were unsuccessful.     

Structure of the d-galacto-d-mannan isolated from the seeds of Melilotus indica All

A d-galacto-d-mannan ([α]_D +72.0 and d-galactose-to-d-mannose ratio 1:1.14) was isolated from the seeds of Melilotus indica All., syn. M. parviflora Desf. The ¹H- and ¹³C-n.m.r., and i.r. spectra indicated the presence of α-d-galactopyranosyl and β-d-mannopyranosyl residues. Methylation of the polysaccharide, followed by hydrolysis, afforded, 2,3,4,6-tetra-, 2,3,6-tri-, 2,3-di-, and 3,4-di-O-methyl-d-mannose, and 2,3,4,6-tetra- and 2,3,6-tri-O-methyl-d-galactose in the molar ratios of 1:2:22:6:27:3. Periodate oxidation of the polysaccharide, followed by reduction and hydrolysis, gave erythritol (1 mol) and glycerol (1.24 mol). Partial acid hydrolysis of the polysaccharide afforded O-β-d-mannopyranosyl-(1→2)-d-mannopyranose, O-β-d-mannopyranosyl-(1→4)-d-mannopyranose, O-α-d-galactopyranosyl-(1→6)-d-mannopyranose, O-α-d-galactopyranosyl-(1→4)-d-galactopyranose, and O-α-d-galactopyranosyl-(1→6)-O-β-d-mannopyranosyl-(1→4)-d-mannopyranose. A highly branched structure having a mannan backbone composed of 36% of (1→4)- and 10% of (1→2)-linked β-d-mannopyranosyl units is proposed for the galactomannan.     

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.     

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.     

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 4-O-β-D-mannopyranosyl-L-rhamnopyranose

The title disaccharide (16) has been synthesized in 50% overall yield by way of condensation of 4,6-di-O-acetyl-2,3-O-carbonyl-α-D-mannopyranosyl bromide 5 with methyl 2,3-O-isopropylidene-α-L-rhamnopyranoside (1) in chloroform solution, in the presence of silver oxide. The disaccharide was characterized as the crystalline isopropyl alcoholate of methyl 4-O-β-D-mannopyranosyl-α-L-rhamnopyranoside (11) and as 1,2,3-tri-O acetyl-4-O- (2,3,4,6-tetra-O-acetyl-β-D-mannopyranosyl)-α-L-rhamnopyranose (15). Methyl β-D-mannopyranoside isopropyl alcoholate 7 was readily obtained in 85% yield via the reaction of bromide 5 with methanol.Reduction of 2,3-di-O-methyl-L-rhamnose with sodium borohydride, followed by acetylation, may result in the formation of an appreciable proportion of a boric ester, namely 1,5-di-O-acetyl-4-deoxy-2,3-di-O-methyl-L-rhamnitol-4-yl dimethyl borate, depending on the procedure used.     

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.     

A complex polysaccharide from the seeds of anthocephalus indicus a. rich

The seeds of Anthocephalus indicus contain a water-soluble polysaccharide composed of D-xylose, D-mannose, and D-glucose in the molar ratios 1:3:5. Methylation analysis afforded 2,3,4-tri-O-methyl-D-xylose, 2,3,6,-tri-O-methyl-D-mannose, 2,3,6-tri-O-methyl-D-glucose, 2,3-di-O-methyl-D-glucose, and 2,3,4,6-tetra-O-methyl-D-glucose in the molar ratios 7:21:12:15:8. Periodate oxidation and methylation data indicated 22.5% and 21.9% of end groups, respectively. The above findings, together with the results of partial hydrolysis with acid, indicate the polysaccharide to consist of a linear chain of (1→4)-linked β-D-mannosyl and β-D-glucosyl residues to which α-D-xylosyl and β-D-glucosyl groups are attached by (1→6)-linkages.     

Synthesis of three oligosaccharides that form part of the complex type of carbohydrate moiety of glycoproteins

Silver trifluoromethanesulfonate-promoted condensation of 3,4,6-tri-O-acetyl-2-deoxy-phthalimido-β-d-glucopyranosyl bromide with benzyl 3,6-di-O-benzyl-α-d-mannopyranoside and benzyl 3,4-di-O-benzyl-α-d-mannopyranoside gave the protected 2,4- and 2,6-linked trisaccharides in yields of 54 and 32%, respectively. After exchanging the 2-deoxy-2-phthalimido groups for 2-acetamido-2-deoxy groups and de-blocking, the trisaccharides 2,4-di-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-d-mannose and 2,6-di-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-d-mannose were obtained. Similar condensation of 3,6-di-O-acetyl-2-deoxy-2-phthalimido-4-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-β-d-glucopyranosyl bromide with benzyl 3,4-di-O-benzyl-α-d-mannopyranoside gave a pentasaccharide derivative in 52% yield. After transformations analogous to those applied to the trisaccharides, 2,6-di-O-[β-d-galactopyranosyl-(1→4)-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)]-d-mannose was obtained.     

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.     

Structural investigation of oxalate-soluble rapeseed (Brassica campestris) polysaccharides. 3. An arabinan

An arabinan isolated from rapeseed was shown by sedimentation studies to be essentially homogeneous, and methylation analysis revealed a highly branched structure. Hydrolysis of the methylated polysaccharide yielded 2,3,5-tri-O-methyl-L-arabinose (11 mol.), 2,3-di-O-methyl-L-arabinose (7 mol.), 3-O-methyl-L-arabinose (trace), 2-O-methyl-L-arabinose (7 mol.), and L-arabinose (2 mol.). Periodate-oxidation data substantiate the methylation results. The general, structural features of the arabinan are discussed.     

Sulphated polysaccharides of the grateloupiaceae family : Part VII. Investigation of the acetolysis products of a partially desulphated sample of the polysaccharide of pachymenia carnosa

Investigation of the acetolysis products of a partially desulphated sample of the polysaccharide isolated from Pachymenia carnosa led to the isolation and characterization of the following oligosaccharides: 3-O-α-D-galactopyranosyl-D-galactose (1), 4-O-β-D-galactopyranosyl-D-galactose (2), 3-O-(2-O-methyl-α-D-galactopyranosyl)-D-galactose (3), a 4-O-galactopyranosyl-2-O-methylgalactose (4), 3-O-α-D-galactopyranosyl-6-O-methyl-D-galactose (5), 4-O-β-D-galactopyranosyl-2-O-methyl-D-galactose (6), 2-O-methyl-4-O-(6-O-methyl-β-D-galactopyranosyl)-D-galactose (14), O-β-D-galactopyranosyl-(1→4)-O-α-D-galactopyranosyl-(1→3)-D-galactose (8), O-α-D-galactopyranosyl-(1→3)-O-β-D-galactopyranosyl-(1→4)-D-galactose (9), O-β-D-galactopyranosyl-(1→4)-O-α-(2-O-methyl-D-galactopyranosyl)-(1→3)-D-galactose (11), O-α-(2-O-methyl-D-galactopyranosyl)-(1→3)-O-β-D-galactopyranosyl-(1→4)-D-galactose (12), O-α-D-galactopyranosyl-(1→3)-O-β-D-galactopyranosyl-(1→4)-2-O-methyl-D-galactose (13), O-α-(2-O-methyl-D-galactopyranosyl)-(1→3)-O-β-D-galactopyranosyl-(1→4)-2-O-methyl-D-galactose (16), and O-β-D-galactopyranosyl-(1→4)-O-α-D-galactopyranosyl-(1→3)-O-β-D-galactopyranosyl-(1→4)-D-galactose (10). In addition, evidence was obtained for the presence of 4-O-(6-O-methyl-β-D-galactopyranosyl)-D-galactose (7) and O-β-D-galactopyranosyl-(1→4)-O-α-D-galactopyranosyl-(1→3)-6-O-methyl-D-galactose (15).