摘要:

Sialyl Lewis X (SLex) analogs2aand2bwere synthesised, where theN-acetyl-D-glucose and the D-galactose units of SLex1were replaced with an alkyl and a heteroalkyl spacer. Sulphate ester6iwas also synthesised from alcohol6band chlorosulphonic acid. A novel promoter, silver mercaptoethanesulphonate, was used to synthesise α-sialosides2c. 7band7c.

ISSN:0732-8303    

DOI:10.1080/07328309608005661

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Three sialyl-Lexganglioside analogs containing carboxymethyl, sulfate, and phosphate groups in place of the sialic acid moiety, have been synthesized. Glycosylation of 2-(trimethylsilyl)ethylO-(2,3,4-tri-O-benzyl-α-L-fucopyranosyl)-(1→3)-O-(2-acetamido-6-O-benzyl-2-deoxy-β-d-glucopyranosyl) - (1→3) - 2, 4, 6-tri-O-benzyl-β-d-galactopyranoside (10) with methyl 2,4,6-tri-O-benzoyl-3-O-(methoxycarbonyl)methyl-1-thio-β-d-galactopyranoside (6) or methyl 2-O-benzoyl-4,6-O-benzylidene-3-O-levulinoyl-1-thio-β-d-galactopyranoside (9) using dimethyl-(methylthio)sulfonium triflate (DMTST) as a promoter, afforded the corresponding tetrasaccharide derivatives11and19. Compounds11and19were converted into the α-trichloroacetimidates14and23,viareductive removal of the benzyl and benzylidene 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 (15) or 2-(tetradecyl)hexadecan-1-ol (24), gave the lipophilic derivatives16and25. Compound16was transformed,viaselective reduction of the azido group, condensation with octadecanoic acid,O-deacylation, and hydrolysis of the methyl ester group, into the title compound18in good yield. Compound25was treated with hydrazine acetate to give compound26, which in turn was transformed,viasulfation or phosphorylation, andO-deacylation, into the target compounds28and31.

ISSN:0732-8303    

DOI:10.1080/07328309608005662

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The fractions of poly(methacrylamido D-glucose) with molecular weights 7< M·10-4< 550 have been studied in water by the methods of molecular hydrodynamics. Kuhn-Mark-Houwink equations were obtained. The hydrodynamic invariant and the sedimentation parameter were also calculated. The equilibrium rigidity and the hydrodynamic diameter of molecules modeling macromolecules in solution were evaluated on the basis of the theory of the wormlike necklace model with the effects of excluded volume taken into account at different values of the excluded-volume parameter. The effect of fraction polydispersity on the quantitative values of exponents in the equations of the Kuhn-Mark-Houwink type and the Kuhn segment length is discussed.

ISSN:0732-8303    

DOI:10.1080/07328309608005663

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

(2S,4S)-1-O-Benzyl-2,5-di-O-mesyl-4-O-methoxymethylpentan-1,2,4,5-tetrol, a versatile precursor for subsequent cyclisations with bivalent nucleophiles, was obtained in five steps from the easily accessible (3S,5S)-3-hydroxy-5-hydroxymethyldihydrofuran-2(3H)-one. Using diso-dium phosphide in DMSO or disodium selenide in acetone-water, (2R,4S)-2-benzyloxymethyl-4-O-methoxymethylphospholane and (2R,4S)-2-benzyloxymethyl-4-O-methoxymethylselenolane were prepared. The phospholane was oxidized by oxygen (hydrogen peroxide) to give the analogous cyclic phospholane oxide (phosphinic acid) which was then transformed with benzyl bromide and alkali carbonate into the 1-benzyl phospholane oxide (phosphinic acid benzyl ester). All heterocyclic compounds sythesized, formally resemblecarba-2,3-dideoxy-d-giycero-pentofuranose, the carbocyclic analog of 2-deoxy-α-d-ribofuranose.

ISSN:0732-8303    

DOI:10.1080/07328309608005664

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Starch, agarose, κ-carrageenan and porphyran were sulfated by sulfuric acid with dicyclohexylcarbodiimide as a condensation reagent. In all the cases, the sulfation at O-6 appeared to be predominant on the basis of results from methylation analyses. Although the reactivities of the other hydroxyl groups towards the present sulfation reaction were less than that at C-6, they varied depending on the position in the sugar residue of the polysaccharides. The sulfated agarose was further fractionated in terms of the difference in the solubility of its cetylpyridinium salt to KCl solution. The major fraction resembled the main polysaccharide of funoran (agarose 6-sulfate) on the basis of the behavior of its cetylpyridinium salt,13C NMR measurements and methylation analyses.

ISSN:0732-8303    

DOI:10.1080/07328309608005665

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The acylation of α-trinositol is very sensitive to reaction conditions. Competing condensation reactions may give pyrophosphates and cyclic phosphates. Treatment of atert-ammonium salt corresponding to α-trinositol with carboxylic acid anhydride and DMAP gives a good yield of the expected esters.

ISSN:0732-8303    

DOI:10.1080/07328309608005666

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

1,3-Dipolar cycloaddition of the acetylated 1,2-trans- and 1,2-cis-cellobiosyl, -lactosyl, -maltosyl, and -melibiosyl azides with various acetylenedicarboxylic acid esters gave the corresponding 1-N-glycobiosyl-1,2,3-triazoles (1a,b,c-8a,b,c) which have been used as glycosyl donors for the synthesis of oligosaccharides (15-17) and an anthracycline type antibiotic (18).

ISSN:0732-8303    

DOI:10.1080/07328309608005667

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Commercially availableN-Boc-4-O-benzyl-l-homoserine was treated with trifluoroacetic acid and the corresponding,N-deprotected derivative was submitted to deamination to give 4-O-benzyl-3-deoxy-l-glycero-tetronic acid (5). In another approach to 3-deoxy-l-glycero-tetronic acid protected at position 4, the carboxylic groups in L-malic acid were reduced, and the resulting triol was benzylidenated. Oxidation of the 2,4-O-benzylidene derivative formed with CrO3-pyridine complex in the presence oft-butyl alcohol gavet-butyl 2,4-O-benzylidene-3-deoxy-l-glycero-tetronate (13). The latter was saponified with aqueous sodium hydroxide to give, after Na+exchange for H+, 2,4-O-benzylidene-3-deoxy-l-glycero-tetronic acid (15). Opening of the acetal ring in13, followed by hydrolytic cleavage of thet-butyl ester function gave material indistinguishable from5obtained in the original way. When tested for their efficiency ofN-acylation of derivatives of D-perosamine, both acids5and15gave the corresponding tetronamido derivatives in high yields.

ISSN:0732-8303    

DOI:10.1080/07328309608005668

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Much attention has been focused on the stereoselective synthesis of glycosides and oligosaccharides, not only for the preparation of natural products,1but also for the homologation of sugars to serve as chiral templates for more complex synthetic targets.2Most current methods for the preparation of glycosides are based on the activation of a leaving group at the anomeric centre.3A wide range of (potential) leaving groups has been proposed. Some of them are stable in the absence of a suitable promoter and function as a temporary protecting group; others are very reactive.3The trifluoroacetoxyl group was found to be a good leaving group at the anomeric position andC, O, SandN-glycosides,4and oligosaccharides5were synthesized with high stereoselectivity in our laboratory using derivatives that contain this group. However the glycosyl trifluoroacetates were found to be too reactive, and new glycosyl donors containing the trichloroacetoxy leaving group were studied. We now report a stereoselective and mild method for the synthesis of α-mannosides and related oligosaccharides from benzylated mannopyranosyl trichloroacetate (1).

ISSN:0732-8303    

DOI:10.1080/07328309608005669

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Acid-catalysed opening of five- and six-membered cyclic orthoesters of hexopyranosides is well explored and often used in synthetic pathways.1-7Opening of a five-membered ring orthoacetate or benzoate (formed fromcis-vic-diols) gives the axial ester,1,2contrary to most other regioselective methods which give preferentially the equatorial ester, whereas opening of six-membered ring 4,6-orthoesters give a mixture of 4- and 6-esters, the ratio depending in part on the substituent at O-3 and on the amount of acyl migration during the reaction conditions.3,4Since chlorinated acetates (mono-, di- and tri-) are selectively removable in the presence of acetates and benzoates,8their introduction by means of the acidic opening of the corresponding orthoacetate could give a route to a flexible protecting group scheme with regioselective introduction of the selectively removable chloroacetate. This would open up a suitable way for synthesis of,inter alia, branched oligosaccharides. Therefore, mono-, di- and trichloroorthoacetates (both five- and six-membered) of different monosaccharide derivatives were synthesized and their acidic opening studied.

ISSN:0732-8303    

DOI:10.1080/07328309608005670

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor