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PubMed1992

Efficient and stereoselective synthesis of methyl 3-O-(3,6-anhydro-beta-D-galactopyranosyl)-alpha-D-galactopyranoside and methyl 3,6-anhydro-4-O-beta-D-galactopyranosyl-alpha-D-galactopyranoside.

Methyl 3-O-(3,6-anhydro-beta-D-galactopyranosyl)-alpha-D-galactopyranoside (3) and methyl 3,6-anhydro-4-O-beta-D-galactopyranosyl-alpha-D-galactopyranoside (4) have been synthesised stereoselectively using three coupling procedures. Acceptable yields were achieved using acetylated derivatives as donors and trimethylsilyl triflate as the catalyst. Intramolecular tosylate displacement to form 3,6-anhydro rings proceeded in methanolic sodium methoxide.

Carbohydrate Conformation↗
PubMed1992

Papulacandins and chaetiacandin: a stereoselective route to their basic skeleton by a palladium-mediated arylation of 4,6-O-benzylidene-3-O-tert- butyldimethylsilyl-l-tributyl-stannyl-D-glucal.

Palladium(0)-catalysed coupling of 1,5-anhydro-4,6-O-benzylidene-3-O-tert- butyldimethylsilyl-2-deoxy-1-tributylstannyl-D-arabino-hex-1-eni tol (7) with 3,5-dibenzyloxy-2-bromobenzyl alcohol gave 1,1(2)-anhydro-4,6-O-benzylidene-3-O-tert-butyldimethylsilyl-2-deoxy-1-( 4,6- dibenzyloxy-2-hydroxymethyl-phenyl)-alpha-D-arabino-hexopyranos e (13). The same reaction buffered by sodium carbonate provided 1,5-anhydro-4,6- O-benzylidene-3-O-tert-butyldimethylsilyl-2-deoxy-1-(4,6-dibenzyloxy+ ++-2- hydroxymethyl-phenyl)-D-arabino-hex-1-enitol (11). Stereoselective oxidative spiroacetalisation of 11 provided 1,1(2)- anhydro-4,6-O-benzylidene-3-O-tert-butyldimethylsilyl-1-(4,6-dibenzyl oxy-2- hydroxymethyl-phenyl)-alpha-D-glucopyranose (15), the basic tricyclic structure of papulacandins. In a model study, 15 was converted in three steps into 1,1(2)-anhydro-1-(4,6-dihydroxy-2-hydroxymethylphenyl)-3-O- octadecanoyl-alpha-D-glucopyranose (24), a structural analogue of papulacandin D. Moreover, stereoselective hydroboration-oxidation of 11 furnished 2-(4,6-O-benzylidene-3-O-tert-butyldimethylsilyl-beta-D- glucopyranosyl)-3,5-dibenzyloxy-1-hydroxymethylbenzene (26), the structural skeleton of the chaetiacandin 3.

Aminoglycosides↗
PubMed1992

The structure of mytilan, a bioglycan-immunomodulator isolated from the mussel Crenomytilus grayanus.

Mytilan, isolated from the mantle of the mussel Crenomytilus grayanus and which possesses high immunomodulating activity, is a non-covalently linked complex of a polysaccharide (95%) and protein (5%) with lectin activities. Chromatography of mytilan on agarose separated the polysaccharide and protein constituents. The protein appeared to have the lectin properties. Methylation analysis, Smith degradation, digestion with alpha-amylase, and 13C-n.m.r. spectroscopy showed the polysaccharide to be a glycogen-like alpha-D-glucan.

Adjuvants, Immunologic↗
PubMed1992

C-glycosyl compounds bind to receptors on the surface of Escherichia coli and can target proteins to the organism.

A series of C-mannopyranosyl derivatives have been synthesized and their inhibitory activity towards the receptor-mediated adhesion of E. coli to yeast cells has been tested. Total inhibition of yeast-cell agglutination by C-glycosyl derivatives 4 and 9 is achieved at a concentration approximately one order of magnitude lower than that of methyl alpha-D-mannopyranoside, indicating that the binding affinity to the receptor is related to the hydrophobicity of the carbon-linked side chain. A biotin-linked C-glycosyl derivative of mannose (compound 9) has been synthesized and used to target avidin and streptavidin to the bacterial cell surface. Of the C-glycosyl derivatives tested in our study, the conjugate of compound 9 with avidin had the highest avidity for the bacterial receptors, inhibiting agglutination at a concentration three orders of magnitude lower than methyl alpha-D-mannopyranoside. The use of such bifunctional compounds as the mannose-biotin conjugate 9 is a general strategy to target molecules to pathogenic organisms via their cell-surface carbohydrate receptors and to change the antigenicity of the bacterial cell surface.

Bacterial Adhesion↗
PubMed1992

Synthesis and collagenase inhibition of new glycosides of aranciamycinone: the aglycon of the naturally occurring antibiotic aranciamycin.

Glycosides of aranciamycinone were prepared by glycosylation with sugar acetates and trimethylsilyl triflate in dichloromethane. Glycosides of the following sugars were prepared: alpha-L-rhamnopyranose, beta-D-glucopyranose, beta-D-ribopyranose, beta-D-xylopyranose, alpha-L-fucopyranose, 2-azido-2,6-dideoxy-alpha-L-mannopyranose, 2,6-dideoxy-alpha-L-arabino-hexopyranose, 3,6-dideoxy-alpha-L-arabino-hexopyranose, and 4,6-dideoxy-alpha-L-lyxo-hexopyranose. The new glycosides were tested for inhibition of Clostridium histolyticum collagenase and Yoshida Sarcoma tumor cells.

Animals↗
PubMed1992

Synthesis and preliminary characterisation of new esters of the bacterial polysaccharide gellan.

Under the appropriate experimental conditions, ethyl, propyl, and methylprednisolon-21-yl esters of gellan can be obtained without significant degradation. At low degrees of esterification (de), depending on the ester moiety, the products are water-soluble, which allows the influence of hydrophilicity and charge density on their ability to assume an ordered conformation in dilute aqueous solution to be studied. With high de, the products were soluble only in organic solvents (e.g., methyl sulphoxide) with good film-forming capacity. The methylprednisolon-21-yl esters have been characterised in a preliminary manner in terms of drug-release kinetics.

Alcohols↗
PubMed1992

Solution conformation and properties of the galactoglucan from Rhizobium meliloti strain YE-2(S1).

The physicochemical solution properties of the galactoglucan excreted by Rhizobium meliloti strain YE-2(S1) have been investigated by capillary viscometry, potentiometric titration, isothermal mixing microcalorimetry, and circular dichroism. Potentiometric and chiro-optical data, as a function of the degree of ionisation, indicate the absence of a co-operative conformational transition. Solution properties, as a function of ionic strength and temperature, suggest that the galactoglucan adopts a disordered conformation characterised by moderate flexibility. Polyelectrolyte theory is used to fit the enthalpy of dilution data with a suitable linear charge-density parameter. Conformational calculations and chain modelling, using molecular mechanics, give an unperturbed characteristic ratio, (C infinity) of 20, which was smaller than that estimated from intrinsic-viscosity and molecular-weight data for an expanded-coil chain model.

Calorimetry↗
PubMed1992

The structure of a glycerol teichoic acid-like O-specific polysaccharide of Hafnia alvei 1205.

The O-specific polysaccharide of Hafnia alvei 1205 contained D-glucose, D-galactose, 2-acetamido-2-deoxy-D-glucose, 4-acetamido-4,6-dideoxy-D-glucose (Qui4NAc), glycerol, phosphate, and O-acetyl groups. On the basis of 1D and 2D shift-correlated homonuclear and 13C-1H heteronuclear NMR spectroscopy, methylation analysis, Smith degradation, and dephosphorylation with hydrofluoric acid, it was concluded that the O-antigen was a partially O-acetylated teichoic acid-like polysaccharide having the following structure: [formula: see text]

Carbohydrate Conformation↗
PubMed1992

Syntheses of branched-chain sugars with push-pull functionality.

The reaction of methyl 4,6-O-benzylidene-3(2)-deoxy-alpha-D-erythro- hexopyranosid-2(3)-ulose with carbon disulfide, alkyl iodide, and sodium hydride gave methyl 4,6-O-benzylidene-3(2)-[bis(alkylthio)methylene]-3(2)-deoxy-alpha-D- erythro-hexopyranosid-2(3)-uloses. Methyl 4,6-O-benzylidene-2-[bis(methylthio)-methylene]-2-deoxy-alpha-D- erythro-hexopyranosid-3-ulose (5) reacted with aromatic amines to give, in a rearrangement process, N-aryl-2-aryliminomethyl-4,6-O-benzylidene-2-deoxy- alpha-D-erythro-hex-1-enopy-ranosylamin-3-uloses. The reaction of 5 with hydrazine hydrate afforded 5-methylthio-(methyl 4,6-O-benzylidene-2,3-dideoxy-alpha-D-erythro-hexopyranosido)[3,2- c]pyrazole.

Carbohydrate Conformation↗
PubMed1993

Synthesis of allyl O-[sodium(alpha-D-glycero-D-talo-2- octulopyranosyl)onate]-(2-->6)-2-acetamido-2-deoxy-beta-D-glucopyranosi de, a core constituent of the lipopolysaccharide from Acinetobacter calcoaceticus NCTC 10305.

Reaction of methyl 2,6-anhydro-2,3-dideoxy-D-manno-2-octenoate 1 with 3-chloroperoxybenzoic acid gave the 2,3-anhydro derivative 2, which was converted into the per-O-acetylated anomeric methyl glycosides of D-glycero-D-galacto-2-octulopyranosylonic acid in good yield. Subsequent inversion of the configuration at C-3 and deprotection afforded sodium (methyl beta-D-glycero-D-talo-2-octulopyranosid)onate. Alternatively, 2 was transformed into methyl (alpha-D-glycero-D-talo-2- octulopyranosyl bromide(onate derivatives. Reaction with methanol or allyl 2-acetamido-2-deoxy- 3,4-O-(1,1,3,3-tetraisopropyldisiloxan-1,3-diyl)-beta-D-g lycopyranoside, promoted by silver triflate, gave good yields of the corresponding orthoester derivatives. Me3Si triflate-catalyzed orthoester rearrangement and removal of the protecting groups afforded sodium O-(methyl alpha-D-glycero- D-talo-2-octulopyranosid)onate and the disacchanide, allyl O-[sodium(alpha-D-glycero-D-talo-2- octulopyranosyl)onate]-(2-->6)-2-acetamido-2-deoxy-beta-D-gl ucopyranoside in high yield.

Acinetobacter calcoaceticus↗
PubMed1993

Glycosylation by sugar 1,2-O-(1-cyanobenzylidene) derivatives: influence of glycosyl-donor structure and promoter.

3,4,6-Tri-O-acetyl-1,2-O-(1-cyanobenzylidene)-alpha-D-galactopy ranoses with differently substituted aromatic nuclei have been synthesised and used as glycosyl donors in reactions with the acceptors methyl 2,3,4-tri-O-acetyl-6-O-trityl-beta-D-galactopyranoside (11) and methyl 2,4,6-tri-O-acetyl-3-O-trityl-beta-D-galactopyranoside (12). The glycosylation of 11 gave only beta products. The effeciency and stereoselectivity of the glycosylations of 12 depend on the nature of the substituent in the aromatic ring. The stereoselectivity for the formation of 1,2-trans-glycosidic bonds was the highest with the p-methoxy-benzylidene derivative with triphenylmethylium triflate as the promoter.

Benzylidene Compounds↗