Conformation analysis of modified tetrasaccharide sequences of the N-glycoprotein type--problem of the alpha-(1 to 6)-glycosidic bond

The conformational analysis of the recently synthesized tetrasaccharides alpha-D-Manp (1----3)-[alpha-D-Manp-(1----6)]-4-deoxy-beta-D-lyx-hexp+ ++-(1----4)-D-GlcNAc (2) and alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Talp -(1----4)-D-GlcNAc (3) will be described. The preferred solution conformation of 2 and 3 is a gt-conformation, which is nearly identical with the preferred conformation of the naturally occurring tetrasaccharide alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Manp -(1----4)-D-GlcNAc (1). The main structural feature is the backfolding of the alpha-(1----6)-linked D-Man to the reducing D-GlcNAc unit. Conformational analysis of the tetrasaccharides alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Manp -(1----4)-1,6- anhydro-beta-D-GlcNAc (4), alpha-D-Manp-(1----3)-alpha-D-Manp-(1----6)]-4-deoxy-beta-D- lyx-hexp-(1----4)- 1,6-anhydro-beta-D-GlcNAc (5), and alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Talp -(1----4)- 1,6-anhydro-beta-D-GlcNAc (6) gave additional proof for this backfolding. The substitution of the reducing unit leads to a smaller amount of gt- and a greater amount of gg-conformers. The method used for conformational analysis of 2-6 is a combination of n.m.r.-experiments and HSEA-calculations with the program GESA. Concerning the application of new 2D-techniques, the COLOC-experiment turned out to be extremely useful in sequencing oligosaccharides.     

The structure of the asparagine-linked sugar chains of bovine brain ribonuclease

The asparagine-linked sugar chains of bovine brain ribonuclease were quantitatively released as oligosaccharides from the polypeptide backbone by hydrazinolysis. After N-acetylation, they were converted into radioactively-labeled oligosaccharides by NaB3H4 reduction. The radioactive oligosaccharide mixture was fractionated by ion-exchange chromatography, and the acidic oligosaccharides were converted into neutral oligosaccharides by sialidase digestion. The neutral oligosaccharides were then fractionated by Bio-Gel P-4 column chromatography. Structural studies of each oligosaccharide by sequential exoglycosidase digestion in combination with methylation analysis revealed that bovine brain ribonuclease showed extensive heterogeneity. It contains bi- and tri-antennary, complex-type oligosaccharides having alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Manp -(1----4)-beta-D- GlcpNAc-(1----4)-[alpha-L-Fucp-(1----6)]-D-GlcNAc as their common core. Four different outside oligosaccharide chains, i.e., beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----, alpha-Neu5Ac-(2----6)-beta-D- Galp-(1----4)-beta-D-GlcpNAc-(1----, alpha-Neu5Ac-(2----3)-beta-D-Galp-(1----4)- beta-D-GlcpNAc-(1----, and alpha-D-Galp-(1----3)-beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----, were found. The preferential distribution of the alpha-D-Galp-(1----3)-beta-D-Galp-(1----4)-beta-D-GlcpNAc group on the alpha-D-Manp-(1----6) arm is a characteristic feature of the sugar chains of this enzyme.     

Synthesis of alpha-D-Manp-(1----3)-[beta-D-GlcpNAc-(1----4)]-[alpha-D-Manp+ ++-(1----6)] - beta-D-Manp-(1----4)-beta-D-GlcpNAc-(1----4)-[alpha-L-Fucp- (1----6)]-D- GlcpNAc, a core glycoheptaose of a "bisected" complex-type glycan of glycoproteins

A synthesis of alpha-D-Manp-(1----3)-[beta-D-GlcpNAc-(1----4)]-[alpha-D-Manp++ +-(1----6)]- beta-D-Manp-(1----4)-beta-D-GlcpNAc-(1----4)-[alpha-L-Fucp-( 1----6)]-D- GlcpNAc was achieved by employing benzyl O-(3,4,6-tri-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl)-(1--- -4)-O- (2-O-benzyl-beta-D-mannopyranosyl)-(1----4)-O-(3,6-di-O-benzyl-2-deoxy-2 - phthalimido-beta-D-glucopyranosyl)-(1----4)-3-O-benzyl-2-deoxy-6-O-p- methoxyphenyl-2-phthalimido-beta-D-glucopyranoside as a key glycosyl acceptor. Highly stereoselective mannosylation was performed by taking advantage of the 2-O-acetyl group in the mannosyl donors. The alpha-L-fucopyranosyl residue was also stereoselectively introduced by copper(II)-mediated activation of methyl 2,3,4-tri-O-benzyl-1-thio-beta-L-fucopyranoside.     

Synthesis of phosphorylated trimannosides corresponding to end groups of the high-mannose chains of lysosomal enzymes

Glycosylation of suitably protected 8-methoxycarbonyloctyl alpha-D-manno-pyranosides with 2-O-acetyl-3,4,6-tri-O-benzyl-alpha-D-mannopyranosyl chloride provided alpha-D-Manp-(1----2)-alpha-D-Man, alpha-D-Manp-(1----3)-alpha-D-Man and alpha-D-Manp-(1----6)-alpha-D-Man derivatives from which the 2'-hydroxyl group was liberated by O-deacetylation. Addition of the terminal D-mannose 6-phosphate residues was achieved by reaction with the readily accessible 2,3,4-tri-O-acetyl-6-O-diphenoxyphosphoryl-alpha-D-mannopyranosyl bromide under standard glycosylation conditions. Conventional deprotection provided the terminal 6"-phosphate of alpha-D-Manp-(1----2)-alpha-D-Manp-(1----2)-alpha-D-Man, alpha-D-Manp-(1----2)-alpha-D-Manp-(1----3)-alpha-D-Man, and alpha-D-Manp-(1----2)-alpha-D-Manp-(1----6)-alpha-D-Man which are present as end groups on the high-mannose oligosaccharide chains of lysosomal enzymes.     

Structural determination of D-mannans of pathogenic yeasts Candida stellatoidea type I strains: TIMM 0310 and ATCC 11006 compared to IFO 1397

The structures of the cell-wall D-mannans of pathogenic yeasts of Candida stellatoidea Type I strains, IFO 1397, TIMM 0310, and ATCC 11006, were investigated by mild acid and, alkaline hydrolysis, by digestion with the Arthrobacter GJM-1 strain exo-alpha-D-mannosidase, and by acetolysis. The modified D-mannans and their degradation products were studied by 1H- and 13C-n.m.r. analyses. D-Manno-oligosaccharides released by acid treatment from the parent D-mannans were identified as the homologous beta-(1----2)-linked D-manno-oligosaccharides from biose to hexaose, whereas those obtained by alkaline degradation were the homologous alpha-(1----2)-linked D-mannobiose and D-mannotriose. The acid- and alkali-modified D-mannans lacking 1H-n.m.r. signals above 4.900 p.p.m. [corresponding to beta-(1----2)-linked D-mannopyranose units] were acetolyzed with 10:10:1 (v/v) Ac2O-AcOH-H2SO4, and the resultant D-manno-oligosaccharides were also analyzed. It was found that the longest branches of these D-mannans, corresponding to hexaosyl residues, had the following structures: alpha-D-Manp-(1----3)-alpha-D-Manp-(1----2)-alpha-D-Manp+ ++-(1----2)-alpha-D-Manp- (1----2)-alpha-D-Manp-(1----2)-D-Man and alpha-D-Manp-(1----2)-alpha-D-Manp-(1----3)-alpha-D-Manp+ ++-(1----2)-alpha-D-Manp- (1----2)-alpha-D-Manp-(1----2)-D-Man. These results indicate that the D-mannans of C. stellatoidea Type I strains possess structures in common with the D-mannans of Candida albicans serotype B strain (see ref. 4) containing phosphate-bound beta-(1----2)-linked oligo-D-mannosyl residues.     

Synthesis of four structural elements of xylose-containing carbohydrate chains from N-glycoproteins

The synthesis of the oligosaccharides beta-D-Xylp-(1----2)-beta-D-Manp-OMe (12), beta-D-Xylp-(1----2)-[alpha-D-Manp-(1----6)]-beta-D-Manp+ ++-OMe (17), beta-D-Xylp-(1----2)-[alpha-D-Manp-(1----3)]-beta-D-Manp+ ++-OMe (21), and beta-D-Xylp-(1----2)-[alpha-D-Manp-(1----3)] [alpha-D-Manp-(1----6)]-beta-D-Manp-OMe (25) is described. Methyl 3-O-benzyl-4,6-O-isopropylidene-beta-D-mannopyranoside (6) was prepared from the corresponding glucoepimer (4) by oxidation, followed by stereoselective reduction. Condensation of 6 with 2,3,4-tri-O-acetyl-alpha-D-xylopyranosyl bromide in the presence of mercuric cyanide gave a 1:9 mixture of methyl 3-O-benzyl-4,6-O-isopropylidene-2-O-(2,3,4- tri-O-acetyl-alpha- (7a) and -beta-D-xylopyranosyl)-beta-D-mannopyranoside (7), and then 7 was converted into the acetylated disaccharide-glycoside 11. Regioselective mannosylation, with 2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl bromide, at position 6 of deisopropylidenated 7 (8), using mercuric bromide as a promoter, afforded the trisaccharide-glycoside derivative 13, which was transformed into the acetylated trisaccharide-glycoside 16. The disaccharide derivative 10, obtained from 8, and the trisaccharide derivative 15, obtained from 13, were glycosylated at position 3 with O-(2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl)trichloroacetimidate (19), using trimethylsilyl triflate as a promoter, giving rise to acetylated tri- (20) and tetra-saccharide (24) derivatives, respectively. O-Deacetylation of 11, 16, 20, and 24 gave 12, 17, 21, and 25, respectively.     

Combined chemical-enzymic synthesis of deoxygenated oligosaccharide analogs: transfer of deoxygenated D-GlcpNAc residues from their UDP-GlcpNAc derivatives using N-acetylglucosaminyltransferase I

The 3'-, 4'-, and 6'-deoxy analogs of UDP-GlcpNAc have been synthesized chemically and found to act as donor-substrates for N-acetylglucosaminyltransferase-I (GnT-I) from human milk. Incubation of UDP-GlcpNAc and these deoxy analogs with GnT-I in the presence of alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Manp -O(CH2)8COOMe gave beta-D-GlcpNAc-(1----2)-alpha-D-Manp-(1----3)-[alpha-D-Manp- (1----6)]- beta-D-Manp-O(CH2)8COOMe (6), and the deoxy analogs 12-14 where HO-3, HO-4, and HO-6, respectively, of the beta-D-GlcNAc residue were replaced by hydrogen. The tetrasaccharide glycosides 6 and 12-14 were characterized by 1H-n.m.r. spectroscopy and evaluated as acceptors for GnT-II, the next enzyme in the pathway of biosynthesis of Asn-linked oligosaccharides. Deoxygenation of the 3-position of the beta-D-GlcNAc residue of 6 completely abolished its acceptor activity, whereas removal of HO-4 or HO-6 caused only modest decreases in activity.     

Primary structure of four human milk octa-, nona-, and undeca-saccharides established by 1H- and 13C-nuclear magnetic resonance spectroscopy.

The structures of two octasaccharides, one nonasaccharide, and one undecasaccharide, isolated from human milk, have been investigated by 1H- and 13C-nuclear magnetic resonance spectroscopy. The structures of these oligosaccharides are: beta-D-Galp-(1----4)-[alpha-L-Fucp- (1----3)]-beta-D-GlcpNAc-(1----3)-beta-D-Galp-(1----4)-[alpha-L-Fucp+ ++- (1----3)]-beta-D-GlcpNAc-(1----3)-beta-D-Galp-(1----4)-D-Glc; beta-D-GALp-(1----3)-[alpha-L-Fucp-(1----4)]-beta-D-GlcpNAc-(1---- 3)-beta-D - Galp-(1----4)-[alpha-L-Fucp-(1----3)]-beta-D-GlcpNAc-(1----3)-beta -D-Galp- (1----4)-D-Glc; beta-D-Galp-(1----4)-[alpha-L-Fucp-(1----3)]-beta-D-GlcpNAc-(1---- 6)-(alpha - L-Fucp-(1----2)-beta-D-Gal-(1----3)-[alpha-L-Fucp-(1----4)]- beta-D-GlcpNAc- (1----3))-beta-D-Galp-(1----4)-D-Glc; and alpha-L-Fucp-(1----2)-beta-D-Galp-(1----3)-beta-D-GlcpNAc-(1----3) -beta-D- Galp-(1----4)-[alpha-L-Fucp-(1----3)]-beta-D-GlcpNAc-(1----6)-[alp ha-L- Fucp-(1----2)-beta-D-Galp-(1----3)-beta-D-GlcpNAc-(1----3)]-beta-D -Galp- (1----4)-D-Glc. The two octasaccharides have been previously isolated from human milk as a mixture, and in a pure form from new-born feces, but the n.m.r. data were not provided. These two octasaccharides display the di-Lewis X and the composite Lewis A-Lewis X antigenic determinant, previously described as neo-antigens of adenocarcinoma cell lines.     

The carbohydrate units of asialo-ovomucoid: structural features

The structural features of a heterogeneous glycopeptide fraction from asialo-ovomucoid have been investigated by methylation analysis of the fraction and of products obtained at each stage of its sequential degradation with exo-glycosidases. All glycopeptides in the fraction had a common core-structure beta-D-GlcpNAc-(1 leads to 4)-[beta-D-GlcpNAc-(1 leads to 2)]-alpha-D-Manp-(1 leads to 3)-[beta-D-GlcpNAc-(1 leads to 4)]-[beta-D-GlcpNAc-(1 leads to 2)-alpha-D-Manp-(1 leads to 6)]-beta-D-Manp-(1 leads to 4)-beta-D-GlcpNAc-(1 leads to 4)-beta-D-GlcpNAc leads to Asn. Heterogeneity in the fraction arose from variation in the amount of terminal galactose attached via a hexosaminyl residue to the alpha-D-Manp-(1 leads to 3) residue, and from limited variation in the number of terminal hexosaminyl groups attached to the alpha-D-Manp-(1 leads to 6) residue. One glycopeptide in the fraction contained the unusual feature of two different, triply-substituted mannosyl residues. Other structural features of the glycopeptide are discussed.     

Biosynthesis of dolichyl pentasaccharide diphosphate in calf pancreas microsomes

Incubation of synthetic dolichyl pyrophosphate tetrasaccharide and GDP-[14C]mannose with calf pancreas microsomes gave three lipid-linked oligosaccharides, which could be extracted with chloroform/methanol (2:1) and separated on silica gel plates. The fastest migrating product was characterized as dolichyl pyrophosphate pentasaccharide based on gel filtration and high pressure liquid chromatography. The formation of the pentasaccharide-lipid was greatly stimulated by addition of synthetic tetrasaccharide-lipid and required the presence of Triton X-100. Dolichyl phosphate mannose could not replace GDP-mannose as a sugar donor. The structure of the pentasaccharide was determined by degradation with endo-beta-N-acetylglucosaminidase D, acetolysis, alpha-D-mannosidase, and concanavalin A-Sepharose chromatography, showing that the following reaction was taking place: alpha-D-Manp-(1 leads to 3)-beta-D-Manp-(1 leads to 4)-beta-D-GlcpNAc-(1 leads to 4)-alpha-D-GlcpNAcPPDol + GDPMan leads to GDP + alpha-D-Manp-(1 leads to 3)-[alpha-D-Manp-(1 leads to 6)]-beta-D-Manp-(1 leads to 4)-beta-D-GlcpNAc-(1 leads to 4)-alpha-D-GlcpNAcPPDol. The mannosyltransferase was partially characterized.     

Cross-reactive polysaccharides from Trypanosoma cruzi and fungi (especially Dactylium dendroides)

Cross-reactivity between fungal and Trypanosoma cruzi polysaccharides, owing to common residues of beta-D-galactofuranose, beta-D-galactopyranose, and alpha-D-mannopyranose, was demonstrated by using rabbit immune sera against T. cruzi epimastigotes and sera from patients with Chagas' disease. Several chagasic (Ch) sera precipitated partly purified galactomannans from Aspergillus fumigatus and from T. cruzi epimastigotes and also the galactoglucomannan from Dactylium dendroides. Reaction of one Ch serum with T. cruzi galactomannan (GM) was completely inhibited by synthetic beta-D-Galf-(1----3)-Me alpha-D-Manp, and that of another Ch serum with a purified D. dendroides galactoglucomannan (GGM) was partly inhibited by (1----6)-linked (81%) or by (1----3)-linked (33%) beta-D-Galf-Me alpha-D-Manp. The beta-D-Galf-(1----3)-alpha-D-Manp epitope was present in both T. cruzi and D. dendroides polysaccharides. Rabbit anti-T. cruzi antisera precipitated A. fumigatus GM, T. cruzi antigenic extracts containing the lipopeptidophosphoglycan (LPPG), T. cruzi alkali-extracted GM, a synthetic GM, and D. dendroides GGM. Weak reactivities were obtained for a Torulopsis lactis-condensi GM containing beta-D-Galp terminal residues and for baker's yeast mannan with alpha-D-Manp-(1----3)-alpha-D-Manp-(1----2)-alpha-D-Manp+ ++-(1----2) side chains. An anti-LPPG rabbit serum precipitated D. dendroides GGM--a reaction inhibited (82%) by beta-D-Galf-(1----3)-Me alpha-D-Manp and. less efficiently, by a (1----5)-linked beta-D-Galf-tetrasaccharide. Sera from mice immunized with D. dendroides whole cells reacted with CL-strain trypomastigotes as shown by indirect immunofluorescence, by a Staphylococcus adherence test, but were not lytic. Mice immunized with D. dendroides were not protected against a challenge with virulent T. cruzi trypomastigotes.     

Synthesis of a mannose nonasaccharide existing in the exopolysaccharide of Cryphonectria parasitica

alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->6)[alpha-D-Manp-(1-->3)-alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->2)]-alpha-D-Manp-(1-->6)-[alpha-D-Manp-(1-->2)]-alpha-D-Manp, existing in the exopolysaccharide of Cryphonectria parasitica was synthesized as its allyl glycoside in a regio- and stereoselective manner.     

Combined chemical-enzymic synthesis of a dideoxypentasaccharide for use in a study of the specificity of N-acetyl-glucosaminyltransferase-III.

The biantennary oligosaccharide glycoside beta-D-GlcpNAc-(1----2)-alpha-D- Manp-(1----3)- [beta-D-GlcpNAc-(1----2)-alpha-D-Manp-(1----6)]-beta-D-Manp- OR is a potential substrate for N-acetylglucosaminyltransferases (GlcNAcTs) III-V. The dideoxypentasaccharide glycoside beta-D-GlcpNAc-(1----2)-4- deoxy-alpha-D-lyxo-Hexp-(1----3)- [beta-DGlcpNAc-(1----2)-6-deoxy-alpha-D-Manp-(1----6)] beta-D-Manp-O(CH2)7CH3 (5), where the hydroxyl groups that would be acted on by GlcNAcTs IV and V have been removed, was prepared as a possible specific acceptor for GlcNAcT-III. The strategy involved the chemical synthesis of beta-D-GlcpNAc-(1----2)-4-deoxy-alpha-D-lyxo-Hexp-(1----3)-] 6- deoxy-alpha-D-Manp-(1----6)]-beta-D-Manp-O)CH2)7CH3 and then addition of the last GlcpNAc residue using partially purified GlcNAcT-II from rabbit liver. Preliminary results, using detergent extracts from rat kidney, indicate that 5 is an acceptor for a GlcNAcT whose identity remains to be established.     

Structural studies of the Escherichia coli O78 O-antigen polysaccharide

The structure of the O-antigen polysaccharide from Escherichia coli O78 has been investigated; methylation analysis, partial solvolysis with liquid hydrogen fluoride, and 2D-n.m.r. spectroscopy were the principal methods used. It is concluded that the polysaccharide is composed of tetrasaccharide repeating-units having the following structure.----3)-beta-D-GlcpNAc-(1----4)-beta-D-GlcpNAc- (1----4)-beta-D-Manp-(1----4)-alpha-D-Manp-(1----     

Lipoarabinomannan of Mycobacterium tuberculosis. Capping with mannosyl residues in some strains.

Previously we had demonstrated that the termini of the arabinan component of mycobacterial cell wall arabinogalactan, the site of mycolic acid location, consists mostly of clusters of a pentaarabinofuranoside, [beta-D-Araf-(1----2)-alpha-D-Araf-(1----]2----(3 and 5)-alpha-D-Araf. Subsequently, the same arrangement was shown to dominate the non-reducing ends of lipoarabinomannan (LAM), a key component in the interaction of mycobacteria with host cell. Accordingly, we had proposed that mycobacteria universally elaborate the same Araf-containing motifs in two settings for different pathophysiological purposes. However, we now report that the termini of LAM from the virulent, Erdman, strain of Mycobacterium tuberculosis, unlike those from the attenuated H37Ra strain, are extensively capped with mannosyl (Manp) residues, either a single alpha-D-Manp, a dimannoside (alpha-D-Manp-(1----2)-alpha-D-Manp), or a trimannoside (alpha-D-Manp-(1----2)-alpha-D-Manp-(1----2)-alpha-D-Manp ). The use of monoclonal antibodies demonstrates a clear difference in the antigenicity of the basic and mannose-capped LAM. The possibility that these structures are a factor in the virulence of some strains of M. tuberculosis and represent an example of carbohydrate mimicry in mycobacterial infections is discussed.     

Elongation of both branches of biantennary backbones of oligo-(N-acetyllactosamino)glycans by human serum (1----3)-N-acetyl-beta-D- glucosaminyltransferase.

Partial reactions catalyzed by a (1----3)-N-acetyl-beta-D- glucosaminyltransferase (EC2.4.1.149), known to be present in human serum, were studied by use of biantennary "backbone" saccharides of oligo-N-acetyllactosamine-type as acceptors. Incubation of the radiolabeled blood-group I-active hexasaccharide, beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----3)-[beta-D-Galp- (1----4)-beta-D-GlcpNAc-(1----6)]-beta-D-Galp-(1----4)-D-GlcNAc (1) and UDP-GlcNAc with serum gave first a transient 1:1 mixture of two isomeric heptasaccharides, beta-D-GlcpNAc-(1----3)-beta-D-Galp-(1----4)-beta-D- GlcpNAc-(1----3)-[beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----6)]-beta-D- Galp-(1----4)-D-GlcNAc (2) and beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----3)-[beta-D-GlcpNAc-(1----3)- beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----6)]-beta-D-Galp-(1----4)-D-Glc NAc (3), showing that both branches of 1 react equally well. The two heptasaccharides reacted further in the incubation mixture to form the radiolabeled octasaccharide, beta-D-GlcpNAc-(1----3)-beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----3)-[be ta-D- GlcpNAc-(1----3)-beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----6)]-beta-D-Ga lp- (1----4)-D-GlcNAc (4); during this second reaction, the composition of the heptasaccharide mixture remained unchanged, indicating that 2 and 3 reacted at approximately equal rates. The heptasaccharides 2 and 3 could not be separated from each other, but they could be detected, identified, and quantitatively determined by stepwise enzymic degradations. Partial (1----3)-N-acetyl-beta-D-glucosaminylation reactions, carried out with another acceptor, the branched pentasaccharide, beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----3)-[beta-D-Galp-(1----4)-beta- D- GlcpNAc-(1----6)]-beta-D-Gal (11), revealed that it reacted also equally well at both branches.(ABSTRACT TRUNCATED AT 400 WORDS)     

An unusual glucomannan from Tornabenia intricata.

Mannose-containing polysaccharides of 18 lichen species were prepared via successive alkaline extraction, precipitation with Fehling solution and fractional precipitation with Cetavlon. Products from Fehling and Cetavlon precipitation, the latter at pH 8.5 in the presence of borax, were structurally similar, except with those of Usnea sp., U. meridionalis, Parmotrema araucaria and Evernia prunastri, which were mixtures and initially provided precipitates at pH 7 due to the presence of carboxyl groups. With one exception, glucosyl units were detected in all preparations, but possibly arose from glucan contaminants of the galactomannans. Tornabenia intricata, however, did not contain galactose, and a glucomannan was isolated. It consisted of two components with M(r)s of ca 0.85 x 10(5) and ca 1.1 x 10(5) and whose 13C NMR spectra were identical. The overall preparation contained a (1-->6)-linked alpha-D-Manp main-chain substituted at 0-2 mainly with side chains of alpha-D-Manp with smaller amounts of alpha-D-Glcp, alpha-D-Glcp-(1-->2)-[alpha-D-Manp-(1-->4)]-alpha-D-Manp, and possibly alpha-D-Manp-(1-->2)-[alpha-D-Manp-(1-->4)]-alpha-D-Manp+ ++.     

Facile synthesis of the heptasaccharide repeating unit of O-deacetylated GXM of C. neoformans serotype B

A heptasaccharide, beta-D-Xylp-(1-->2)-alpha-D-Manp-(1-->3)-[beta-D-Xylp-(1-->2)]-alpha-D-Manp-(1-->3)-[beta-D-GlcpA-(1-->2)][beta-D-Xylp-(1-->4)]-alpha-D-Manp, the repeating unit of the exopolysaccharide from Cryptococcus neoformans serovar B, was synthesized as its methyl glycoside. Thus 2,3,4-tri-O-benzoyl-beta-D-xylopyranosyl-(1-->2)-3,4,6-tri-O-benzoyl-alpha-d-mannopyranosyl trichloroacetimidate (7) and allyl 2,3,4-tri-O-benzoyl-beta-D-xylopyranosyl-(1-->2)-4,6-di-O-benzoyl-alpha-D-mannopyranoside (8), readily obtained from the corresponding monosaccharide derivatives via simple transformation, were coupled to give a (1-->3)-linked tetrasaccharide 9. Deallylation of 9 followed by trichloroacetimidate formation produced the tetrasaccharide donor 11. Condensation of methyl 2,3,4-tri-O-benzoyl-beta-d-xylopyranosyl-(1-->4)-2-O-acetyl-6-O-benzoyl-alpha-D-mannopyranoside (18) with 11 followed by selective deacetylation yielded hexasaccharide acceptor 20. Coupling of 20 with methyl 2,3,4-tri-O-acetyl-alpha-D-glucopyranosyluronate bromide (21) and subsequent deprotection furnished the target heptaoside. A hexasaccharide fragment, alpha-D-Manp-(1-->3)-[beta-D-Xylp-(1-->2)]-alpha-D-Manp-(1-->3)-[beta-D-GlcpA-(1-->2)][beta-D-Xylp-(1-->4)]-alpha-D-Manp, was also similarly synthesized as its methyl glycoside.     

Facile syntheses of the hexasaccharide repeating unit of the exopolysaccharide from Cryptococcus neoformans serovar A

Two hexasaccharides, beta-D-Xylp-(1-->2)-alpha-D-Manp-(1-->3)-[beta-D-Xylp-(1-->2)-]alpha-D-Manp-(1-->3)-[beta-D-GlcpA-(1-->2)-]alpha-D-Manp and beta-D-GlcpA-(1-->2)-alpha-D-Manp-(1-->3)-[beta-D-Xylp-(1-->2)-]alpha-D-Manp-(1-->3)-[beta-D-Xylp-(1-->2)-]alpha-D-Manp, the repeating unit of the exopolysaccharide from Cryptococcus neoformans serovar A, were synthesized as their methyl glycosides in a regio- and stereoselective manner.     

Efficient synthesis of a 3,6-branched mannose hepta- and octasaccharide

Alpha-D-Manp-(1-->3)-[alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->6)]-alpha-D-Manp-(1-->3)-[alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->6)]-D-Manp and alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->3)-[alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->6)]-alpha-D-Manp-(1-->3)-[alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->6)]-D-Manp, were synthesized as their methyl glycosides in a regio- and stereoselective way.