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At least 1,693 records · Page 94Linked to original sources
PubMed1994

The use of 2-deoxy-2-trichloroacetamido-D-glucopyranose derivatives in syntheses of oligosaccharides.

3,4,6-Tri-O-acetyl-2-deoxy-2-trichloroacetamido-alpha-D-glucopyran osyl trichloroacetimidate and its O-benzylated analogue were tested as glycosyl donors in the reaction with a set of sugar acceptors unsubstituted on O-3 and O-4, typically encountered in the synthesis of oligosaccharides. Glycosides were obtained in good to excellent yields with only a slight excess (1.1-1.2 equiv) of the donor, and with a high degree of 1,2-trans stereoselectivity. The corresponding 2-(trichloromethyl)oxazolinium ion was postulated to be the major reactive intermediate. The N-trichloroacetyl groups in the disaccharide products were easily transformed into N-acetyl under neutral conditions by reduction with tributylstannane.

Carbohydrate Conformation↗
PubMed1994

One-pot-synthesis of alpha-linked deoxy sugar trisaccharides.

Various alpha-linked 2,6-dideoxy-ribo-trisaccharides, models for part of the antibiotic kijanimicin, were synthesised by the N-iodosuccinimide method employing different pathways. The efficiency of a sequential synthesis suffered from side reactions of the axial HO-3, which are typical of digitoxosides. These problems did not arise in a straightforward polymerisation, performed as a one-pot-procedure. It afforded the trisaccharide directly from the monosaccharide precursor in 30% yield. A combination of the oligomerisation pathway and the sequential synthesis led to trisaccharides with different protecting group patterns. In these reactions different glycal and alcohol components were used and allowed to define the optimal partners in a sequential synthesis: the two components should ideally be of comparable reactivity.

Carbohydrate Conformation↗
PubMed1994

Convergent synthesis of an octasaccharide fragment of the O-specific polysaccharide of Shigella dysenteriae type 1.

A stereocontrolled, convergent synthesis is described of the linear octasaccharide methyl glycoside alpha-L-Rha p-(1-->2)-alpha-D-Gal p-(1-->3)-alpha-Glc p NAc-(1-->3)-al pha-L-Rha p-(1-->3)-alpha-L-Rha p-(1-->2)-alpha-D-Gal p-(1-->3) -alpha-D-Glc p NAc-(1-->3)-alpha-L-Rha p-OMe (11), which corresponds to two contiguous repeating units of the O-specific polysaccharide of Shigella dysenteriae type 1.

Carbohydrate Conformation↗
PubMed1994

Synthesis of a water-soluble serine-based neoglycolipid which can be covalently linked to solid phases.

N alpha-Fmoc-serine pentafluorophenyl ester was glycosylated with perbenzoylated lactosyl bromide. The resulting product was coupled to a resin functionalized with 6-aminohexanoic acid and then N alpha-acylated to give a serine-based analogue of lactosylceramide. The water-soluble neoglycolipid was covalently linked to microtiter plates via its carboxyl group and was recognized by a lactose-binding lectin in an ELISA.

Carbohydrate Conformation↗
PubMed1994

X-ray and conformational investigation of 6-deoxy-6-C-(1,5-di-O-acetyl-2,3-O- isopropylidene-beta-D-allo-pentofuranos-5-yl)-1,2:3,4-di-O-isopro pylidene-alpha-D-galactopyranose and 6-C-(benzyl 5-deoxy-2,3-O-isopropylidene-beta-D- ribofuranosid-5-yl)-1,2:3,4-di-O-isopropylidene-D-glycero-alpha-D-galac to-hexopyranose.

The structures of the title compounds (2b and 3) have been investigated in the solid state by X-ray methods. The crystals of 2b are monoclinic, space group P2(1), and of 3 orthorhombic, space group P2(1)2(1)2(1). The cell dimensions are: for 2b, a = 9.910(2), b = 11.745(1), c = 11.810(3) A, beta = 97.32(1) degrees; and for 3, a = 6.103(1), b = 15.954(1), c = 28.855(3) A. Both structures were solved by direct methods, and refined by a full-matrix, least-squares procedure giving for 2b, R = 0.0541 (unit weight), and for 3, R = 0.0451 (RW = 0.0445). The galactopyranose rings of 2b and 3 adopted a twist and a mixed twist-screw conformation, respectively. The absolute configuration at C-7 in 2b, as well as at C-6 in 3, was determined to be (R). Relatively strong intermolecular hydrogen bonds were observed in the crystal structure of 3.

Carbohydrate Conformation↗
PubMed1994

Synthesis of the methyl thioglycosides of 2-, 3-, and 4-deoxy-L-fucose.

Methyl thioglycoside derivatives of 2-, 3-, and 4-deoxy-L-fucopyranose have been prepared as glycosyl donors for the synthesis of sialyl Le(x) ganglioside analogues containing modified alpha-L-fucopyranose residues. Reductive dethioacylation of 2-(trimethylsilyl)ethyl 3,4-di-O-benzoyl-2-O-(phenoxy)thiocarbonyl-beta-L-fucopyranoside, prepared from L-fucose in eight steps, gave the 2-deoxy compound, which was transformed via selective removal of the 2-(trimethylsilyl)ethyl group, subsequent acetylation, and displacement of the 1-acetoxy group by a methylthio group, into methyl 3,4-di-O-benzoyl-2,6-dideoxy-1-thio- alpha,beta-L-lyxo-hexopyranoside (11). 2-(Trimethylsilyl)ethyl 2,4-di-O-benzoyl-3-O-(phenoxy)thiocarbonyl-beta- L-fucopyranoside, prepared from the unsubstituted glycoside in four steps, and 2-(trimethylsilyl)ethyl 2,3-di-O-benzoyl-4-O-(phenoxy)thiocarbonyl-beta-L-fucopyranoside, similarly prepared in two steps, were transformed via reduction of the (phenoxy)thiocarbonyloxy group, selective removal of the 2-(trimethylsilyl)ethyl group, O-acetylation, displacement of the 1-acetoxy group by a methylthio group as described for 11, and finally replacement of the benzoyl groups by benzyl groups, into the analogous, protected methyl 3- and 4-deoxy-1-thio-beta-L-fucopyranosides.

Carbohydrate Conformation↗
PubMed1994

Synthesis of deoxy-L-fucose-containing sialyl Lewis X ganglioside analogues.

Sialyl Lex ganglioside analogs containing 2-, 3-, and 4-deoxyfucose in the place of L-fucose have been synthesized. Glycosylation of 2-(trimethylsilyl)ethyl O-(2-acetamido-4,6-O-benzylidene-2-deoxy-beta-D-glucopyranosyl)-(1-->3)- 2,4,6-triO-benzyl-beta-D-galactopyranoside with the methyl 1-thioglycoside derivatives of the respective deoxyfucoses, using dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter, gave the corresponding three protected 2-(trimethylsilyl)ethyl dideoxy-alpha-L-heoxpyranosyl-(1-->3)- O-2(acetamido-2-deoxy-beta-glucopyranosyl)-(1-->3)-beta-D-galactop yranosides. These were transformed by reductive ring-opening of their benzylidene acetal groups into the glycosyl acceptors 6, 8, and 10. Dimethyl(methylthio)sulfonium triflate promoted glycosylation of 6, 8, and 10 with methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha- D-galacto-2-nonulopyranosylonate)-(2-->3)-2,4,6-tri-O-benzoyl-1-th io-beta-D-galactopyranoside afforded the desired pentasaccharides, which were converted via reductive removal of their benzyl groups, O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group, and reaction with trichloroacetonitrile, into the corresponding alpha-trichloroacetimidates 14, 18, and 22. Glycosylation of (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol with 14, 18, and 22 in the presence of boron trifluoride etherate afforded the expected beta-glycosides, which were transformed in good yields, via selective reduction of the azido group, coupling with octadecanoic acid, O-deacylation, and deesterification, into the target compounds.

Carbohydrate Conformation↗
PubMed1994

Synthesis of specifically monofluorinated ligands related to the O-polysaccharide of Shigella dysenteriae type 1.

The synthesis is reported of galactopyranose nucleophiles monofluorinated at positions 3, 4, or 6 and protected by 4,6-O-benzylidene, 3,6-di-O-benzyl, or 3,4-O-isopropylidene groups, respectively. The condensation of these nucleophiles with 2,3,4-tri-O-benzoyl-alpha-L-rhamnosyl bromide gave, after deprotection, the disaccharide analogues of methyl O-alpha-L-rhamnopyranosyl-(1-->2)-alpha-D-galactopyranoside, monofluorinated at position 3, 4, or 6 of the galactoside residue.

Carbohydrate Conformation↗
PubMed1994

Synthesis of tetrasaccharide analogues of the N-glycan substrate of beta-(1-->2)-N-acetylglucosaminyltransferase II using trisaccharide precursors and recombinant beta-(1-->2)-N-acetylglucosaminyltransferase I.

Recombinant rabbit UDP-GlcNAc: alpha-Man-(1-->3R) beta-(1-->2)-N-acetylglucosaminyl-transferase I (EC 2.4.1.101, GlcNAc-T I) produced in the Sf9 insect cell/baculovirus expression system has been used to convert compounds of the form 3-R-alpha-Man(1-->6)(alpha-Man(1-->3)) beta-Man-O-octyl to 3-R-alpha-Man(1-->6)(beta-GlcNAc(1-->2)alpha-Man(1-->3)) beta-Man-O-octyl where R is OH (14), O-methyl (17), O-pentyl (18), O-(4,4-azo)pentyl (19), O-(5-iodoacetamido)pentyl (20) and O-(5-amino)pentyl (21); 2-deoxy-alpha-Man(1-->6)(beta-GlcNAc(1-->2) alpha-Man(1-->3)) beta-Man-O-octyl (16), 4-O-methyl-alpha-Man(1-->6) (beta-GlcNAc(1-->2) alpha-Man(1-->3)) beta-Man-O-octyl (22), 6-O-methyl-alpha-Man(1-->6)(beta-GlcNAc(1-->2) alpha Man(1-->3)) beta-Man-O-octyl (23) and alpha-Man(1-->6)[beta-GlcNAc(1-->2)(4-O-methyl) alpha-Man(1-->3)] beta-Man-O-octyl (15) were also synthesized by this procedure. The yields ranged from 80 to 99%. Products were characterized by high resolution 1H and 13C nuclear magnetic resonance spectroscopy and fast atom bombardment mass spectrometry. Compounds 14, 15, 17, 22, and 23 are excellent substrates for UDP-GlcNAc: alpha-Man(1-->6R) beta-(1-->2)-N-acetylglucosaminyltransferase II and the other compounds are inhibitors of this enzyme.

Animals↗
PubMed1994

A chemoenzymatic synthesis of D-myo-inositol 1,4,5-trisphosphate.

Enzyme-catalyzed esterification of racemic 2,3-O-cyclohexylidene-myo-inositol (DL-1) proceeded exclusively in 1,4-dioxane to give optically pure L-1-O-acetyl-2,3-O-cyclohexylidene-myo-inositol (L-2) and D-2,3-O-cyclohexylidene-myo-inositol (D-1). A new practical route has been developed for the synthesis of D-myo-inositol 1,4,5-trisphosphate starting from D-1 via selective acylation of the 6-hydroxyl group.

Indicators and Reagents↗
PubMed1994

Synthesis of a glycopeptide with phytoalexin elicitor activity. I. Synthesis of a triglycosyl L-serine and a triglycosyl L-seryl-L-proline dipeptide.

A stereocontrolled synthesis of the model compound for the phytoalexin elicitor-active glycoprotein is described. Glycosylation of the disaccharide, 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl-(1-->6)-2,3,4-tri-O-acetyl- alpha- D-mannopyranosyl trichloroacetimidate, with N-(carbobenzoxy)-(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-(1-->3)-L- serine methyl ester or N-(carbobenzoxy)-(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-(1-->3)-L- seryl-L- proline methyl ester by use of AgOTf gave the desired trisaccharide-serine or trisaccharide-seryl-proline derivatives, which were transformed into beta-D-glucopyranosyl-(1-->6)-alpha-D-mannopyranosyl-(1-->6)-alpha-D- mannopyranosyl-(1-->3)-L-serine and triglycosyl-(1-->3)-L-seryl-L-proline via removal of the N-carbobenzoxy group, followed by deacylation.

Carbohydrate Conformation↗