摘要:

AnomericO-alkylation of mannopyranoses with various protecting groups was investigated using mannose derivatives and 2,3-O-isopropylidene-l-O-trifluoro-methanesulfonyl-D-glycerol (1) as alkylating agent. Generally, in polar solvents higher α/β ratios were obtained than in nonpolar solvents. Sterically demanding protecting groups at the 6-O-position and polar solvents led to higher yields. Reactivity differences were explained by different complex formation. Based on these results mannopyranosyl-α(1-4) glucopyranosides26and27were synthesized using mannose derivatives5and6having a 6-O-(p-methoxyphenyl)diphenylmethyl group and galactosyl trifluoromethane-sulfonate24or nonafluorobutanesulfonate (nonaflate)25, respectively, as alkylating agents.

ISSN:0732-8303    

DOI:10.1080/07328309508005384

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Both anomers of methyl 3-acetamido-3,6-dideoxy-l-galactopyranoside and of methyl 3-acetamido-3,6-dideoxy-l-gulopyranoside have been prepared by conversion of easily accessible derivatives of methyl 6-deoxy-(α and β)-l-galactopyranosides into 3-uloses and reduction of the correspondingO-methyloximes. The1H and13C NMR data of the four 3-acetamido methyl glycosides have been given.

ISSN:0732-8303    

DOI:10.1080/07328309508005385

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Stereoselective synthesis of a butenolide sugar derivative was possible by reaction of the appropriate sugar epoxide with the dilithium salt of phenylselenoacetic acid, followed by oxidation of the α-phenylselenobutanolide obtained with hydrogen peroxide in the presence of catalytic amounts of acetic acid. On the other hand, synthesis of an exocyclic α,β-unsaturated lactone was accomplished by Reformatsky reaction on the appropriate sugar carbonyl groups with ethyl bromomethylacrylate and activated zinc, leading to the introduction of this ring at position 2 or 4 of a furanose ring. Nuclear Overhauser effect studies led to the unambiguous determination of the configuration of the new chiral centre formed by the Reformatsky reaction. The fungicidal efficacy of some unsaturated lactone sugar derivatives is given.

ISSN:0732-8303    

DOI:10.1080/07328309508005386

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A series of three oligosaccharides, α-d-Glc-(1→4)-β-d-GlcA-1ωe, β-d-GlcA-(1→4)-α-d-Glc-(1→4)-β-d-GlcA-lωe and α-d-Glc-(1→4)-β-d-GlcA-(1→4)-α-d-Glc-(1→4)-β-d-GlcA-1ωe was prepared by a short synthetic route, using maltose and glucuronic acid derivatives as starting materials. The oligosaccharides contain glucose residues instead of glucosamines, and have a less complicated structure than the corresponding unsulphated structures found in native heparin and heparan sulphate. This simplification in structure has diminished the number of synthetic steps and raised the total yield compared to the preparation of the corresponding heparin/heparan sulphate structures which have been found to bind acidic and basic FGF.

ISSN:0732-8303    

DOI:10.1080/07328309508005387

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A first total synthesis of a β-series ganglioside GQ1β (IV3Neu5Acα2, III6Neu5Acα2-Gg4Cer) is described. Regio- and stereoselective dimeric sialylation of the hydroxyl group at C-6 of the GalNAc residue in 2-(trimethylsilyl)ethylO-(2-acetamido-2-deoxy-3-O-levulinyl-β-d-galactopyranosyl)-(1→4)-O-(2,3,6-tri-O-benzyl-β-d-galactopyranosyl)-(1→4)-O-2,3,6-tri-O-benzyl-β-d-glucopyranoside (3) with methyl [phenyl 5-acetamido-8-O-(5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glycero-α-d-galacto-2-nonulopyranosylono-1′,9-lactone)-4,7-di-O-acetyl-3,5-dideoxy-2-thio-d-glycero-d-galacto-2-nonulopyranosid]onate (4) usingN-iodosuccinimide (NIS)-trifluoromethanesulfonic acid (TfOH) as a promoter gave the desired pentasaccharide5containing α-glycosidically-linked dimeric sialic acids. This was transformed into the acceptor6by removal of the levulinyl group. Condensation of methylO-[methyl 5-acetamido-8-O-(5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glycero-α-d-galacto-2-nonulopyranosylono-1′,9-lactone)-4,7-di-O-acetyl-3,5-dideoxy-d-glycero-d-galacto-2-nonulopyranosylonate]-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-d-galactopyranoside (7) with6, using dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter, gave the desired octasaccharide derivative8in high yield. Compound8was converted into α-trichloroacetimidate11,viareductive removal of the benzyl groups,O-acetylation, removal of the 2-(trimethylsilyl)ethyl group, and treatment with trichloroacetonitrile, which, on coupling with (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (12), gave the β-glycoside13. Finally,13was transformed,viaselective reduction of the azido group, coupling with octadecanoic acid,O-deacylation, and hydrolysis of the methyl ester group, into the title ganglioside15in good yield.

ISSN:0732-8303    

DOI:10.1080/07328309508005388

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Upon reaction with sodium nitrite, the corresponding triflate2of known 1,3,4,6-tetra-O-pivaloyl-β-d-fructofuranosyl 2,3,6-tri-O-pivaloyl-α-d-glucopyranoside (1), afforded thegalacto-sucrose3in high yield. This compound was converted into 4-deoxy-4-fluorosucrose derivative4by treatment with DAST. The reaction of triflate6, derived from3, with lithium azide afforded 4-azido-4-deoxysucrose derivative7which was transformed into 4-amino-4-deoxysucrose9. SN2 Displacement of the triflate of compound6with thioacetate ion provided the expected 4-S-acetyl-4-thiosucrose derivative10in excellent yield. Deacetylation of10afforded a mixture of 4-thiosucrose11and 4-thiosucrose disulfide12.

ISSN:0732-8303    

DOI:10.1080/07328309508005389

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Reaction of 4-arylthiosemicarbazides (1) with 2,3,4,5-tetra-O-acetylgalactaroyl dichloride (2) gave the corresponding 2,3,4,5-tetra-O-acetylgalactaroyl-bis(4-aryl-thiosemicarbazides (3). The latter compounds underwent dehydrative cyclization by heating with phosphoryl chloride to give 1,2,3,4-tetra-O-acetyl-1,4-bis(5-arylamino-1,3,4-thiadiazol-2-yl)galacto-tetritols (4) which afforded, upon de-O-acetylation withmethanolic ammonia, the corresponding 1,4-bis(5-arylamino-1,3,4-thiadiazol-2-yl)-galacto-tetritols (5). Compounds3were also cyclodehydrated, in a different way, with concomitant de-O-acetylation upon treatment with ethanolic sodium ethoxide to give 1,4-bis(4-aryl-5-thioxo-1,2,4-triazol-3-yl)galacto-tetritols (6). Acetylation of6with acetic anhydride in the presence of pyridine afforded 1,2,3,4-tetra-O-acetyl-1,4-bis(1-acetyl-4-aryl-5-thioxo-1,2,4-triazol-3yl)galacto-tetritols (7). Compounds3a, 3band6a-cshowed no antibacterial activity againstBacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, orStaphylococcus aureusand showed weak to moderate antifungal activity againstAspergillus terreusandCandida albicans.

ISSN:0732-8303    

DOI:10.1080/07328309508005390

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Starting from methyl 4,6-O-benzylidene-2-deoxy-α-D-ribo-hexopyranoside-3-ulose1and proceeding through its corresponding tosyl-epoxide derivative2, various branched-chain sugars (3-8) were prepared by nucleophilic and reductive ring openings. The presence of the sulfonylated oxirane group was found to be compatible with chemical transformations of the benzylidene acetal group (9-11), allowing facile access to the 6-deoxyhexoses (12-13).

ISSN:0732-8303    

DOI:10.1080/07328309508005391

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The structure of one of the major products resulting from the treatment of diethyl galactarate (2) with an excess ofp-toluenesulfonyl chloride in pyridine has been shown to be diethyl 2,5-ditosyloxyhexa-2,4-diendioate (5) rather than hex-3-enoate1proposed earlier. The corresponding dimesyloxy derivative6was also prepared in a similar manner. Some additional aspects of the reactions, including some mechanistic proposals, are presented.

ISSN:0732-8303    

DOI:10.1080/07328309508005392

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In synthetic pathways to complex carbohydrates such as oligosaccharides or nucleotide sugars the activated sugar 1-phosphates serve as important starting molecules. In this study the enzymatic synthesis of α-glucose-1-phosphate (Glc-1-P) has been investigated using a new bacterial α-glucan phosphorylase fromCorynebacterium callunae. The major factors governing the rate of reaction and the attainable degree of substrate conversion have been identified and, accordingly, for optimizing the yield and limiting reaction time for the enzymatic process several points must be considered: (i) the pH-dependent equilibrium of reaction, (ii) product inhibition of the phosphorylase and (iii) enzymatic cleavage of α-1,6 glycosidic linkages present in α-1,4-glucans such as starch or maltodextrins by pullulanases to improve their phosphorolytic conversion. Results obtained in continuous experiments with the phosphorylase retained in an ultrafiltration membrane reactor confirmed the complete operational stability of the enzyme for several days at 30 °C. Since no more than approximately 18 % of the inorganic phosphate can be converted into Glc-1-P an efficient procedure for phosphate and product recovery will be particularly important.

ISSN:0732-8303    

DOI:10.1080/07328309508005393

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor