摘要:

An analog (1) of GDP-fucose, where C-6 is derivatized with an eight-atom spacer terminating in a primary amino group, was chemically synthesized. This amino group in sugar nucleotide1can be acylated using anN-hydroxysuccinimide ester of biotin and it can be coupled to another molecule that also contains an amino group using squaric acid diethyl ester as the coupling reagent. In this way, biotin and a blood group A-active trisaccharide were linked to C-6 of fucose in GDP-fucose. Both complex sugar nucleotides thus prepared were active as donors for a human milk fucosyltransferase, which transferred the derivatized α-linked fucose residue to a glycoside ofN-acetyllactosamine, thus labeling this sequence with either biotin or the blood-group A trisaccharide. Compound1is proposed as a general and versatile reagent which should permit the addition of biological probes to the sugar chains of cell surface glycoproteins or glycolipids.

ISSN:0732-8303    

DOI:10.1080/07328309508005350

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A study of the selectivity of metal chelate-directed benzoylation of sucrose dianion, relative to unchelated sucrose anion, was conducted as part of a study on new synthetic approaches to the high-potency sweetener sucralose. Ionic complexes of sucrose with various metal ions were prepared in DMF and the resulting complexes reacted at low temperature with benzoic anhydride. Cobalt and manganese salts directed esterification mostly to the 3′-OH on the fructosyl portion. Unchelated sucrose anion and other metals favored esterification at the 2-OH of the glucosyl portion. Migration of the benzoate ester along the glucose portion was observed in the directionO-2 toO-6 at moderate temperature, but at higher temperature transannular migration was observed from the glucose to the fructose ring. Reaction mixtures were analyzed by HPLC and monobenzoates identified by retention times relative to standards. Six of eight possible monobenzoates of sucrose were isolated from mixtures and identified by their1H NMR spectra.

ISSN:0732-8303    

DOI:10.1080/07328309508005351

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

1,6-Anhydro-2-deoxy-3,4-di-O-benzyl-2-phthalimido-β-d- glucopyranose (5) was synthesized from 1,6-anhydro-β-d-mannopyranose (1) in five steps. Compound5was polymerized under cationic conditions and selectively yielded glucosamine oligomers (degree of polymerization 5-7). Copolymerization of5with 1,6-anhydro-2,3,4-tri-O-benzyl-β-d-glucopyranose indicated the low reactivity of5with the active cation derived from5. Deprotection of 2-deoxy-3,4-di-O-benzyl-2-phthalimido-(1→6)-β-d-glucopyranan (7) andN-acetylation gave 2-acetamido-2-deoxy-(1→6)-β-d-glucopyranan (9).

ISSN:0732-8303    

DOI:10.1080/07328309508005352

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A first total synthesis of a cholinergic neuron-specific ganglioside, GQ1bα (IV3Neu5Acα, III6Neu5Acα, II3Neu5Acα2-Gg4Cer) is described. Regio- and stereo-selective monosialylation of the hydroxyl group at C-6 of the GalNAc residue in 2-(trimethylsilyl)ethylO-(2-acetamido-2-deoxy-3,4-O-isopropylidene-β-d-galactopyranosyl)-(1→4)-O-(2,6-di-O-benzyl-β-dgalactopyranosyl)-(1→4)-O-2,3,6-tri-O-benzyl-β-dglucopyranoside (4) with methyl (phenyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-dglycero-dgalacto-2-nonulopyranosid) onate (5), and subsequent dimericsialylation of the hydroxyl group at C-3 of the Gal residue with methyl [phenyl 5-acetamido-8-O-(5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-dglycero-α-dgalacto-2-nonulopyranosylono-1′,9-lactone)-4, 7-di-O-acetyl-3,5-dideoxy-2-thio-dglycero-dgalacto-2-nonulopyranosid]onate (7), usingN-iodosuccinimide (NIS)-trifluoromethanesulfonic acid (TfOH) as a promoter, gave the desired hexasaccharide8containing α-glycosidically-linked mono- and dimeric sialic acids. This was transformed into the acceptor9by removal of the isopropylidene group. Condensation of methylO-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-dglycero-α-dgalacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-dgalactopyranoside (10) with9, using dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter, gave the desired octasaccharide derivative11in high yield. Compound11was converted into α-trichloroacetimidate14,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 (15), gave the β-glycoside16. Finally,16was transformed,viaselective reduction of the azido group, coupling with octadecanoic acid,O-deacylation, and hydrolysis of the methyl ester group, into the title ganglioside18in good yield.

ISSN:0732-8303    

DOI:10.1080/07328309508005353

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The first total synthesis of tumor-associated glycolipid antigen, sialyl dimeric Lex, is described. Regioselective glycosylation of the suitably protected Lewis X (Lex) pentasaccharide derivative6with phenyl 4-O-acetyl-6-O-benzyl-2-deoxy-3-O-(4-methoxy-benzyl)-2-phthalimido-1-thio-β-d-glucopyranoside (5) gave the hexasaccharide7, which was converted,viaremoval of the phthaloyl groups and selectiveN-acetylation, into the hexasaccharide acceptor9. Dimethyl(methylthio)sulfonium triflate (DMTST) promoted glycosylation of9with methylO-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glycero-α-d-galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-d-galactopyranoside (10) afforded regioselectively the expected octasaccharide11, which was converted into13viaO-acetylation and removal of the methoxybenzyl group. Fucosylation of13with the methyl thioglycoside14was performed by use ofN-iodosuccinimide (NIS)-trifluoromethanesulfonic acid(TfOH) as a promoter to give the desired nonasaccharide15. After replacing the benzyl groups of15by the acetyl groups, the 2-(trimethylsilyl)ethyl group at the reducing end was selectively transformed into the α-trichloroacetimidate18. Coupling of18with (2S, 3R, 4E)-2-azido-3-O-tert-butyldiphenylsilyl-4-octadecene-1,3-diol (19) gave the corresponding β-glycoside20, which was transformed,viaselective reduction of the azide group, coupling with octadecanoic acid,O-desilylation,O-deacylation, and hydrolysis of the methyl ester group, into the title ganglioside1in good yield.

ISSN:0732-8303    

DOI:10.1080/07328309508005354

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The stereospecific synthesis of methyl 3-O-benzoyl-6-O-(tert-butyldiphenylsilyl)-2-deoxy-α-d-erythro-hexopyranosid-4-ulose (5) - a Thromboxane B2(TXB2) precursor -starting from D-galactose is described. Facile and established methods including selective benzoylation, oxidation-elimination and a stereocontrolled hydrogenation (Pd/charcoal) were employed effectively.

ISSN:0732-8303    

DOI:10.1080/07328309508005355

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

TwelveN-acetyl orNH2-free D-glucosaminyl bolaamphiphiles have been synthesized by the intermediate ofN-allyloxycarbonyl-d-glucosaminyl precursors. Thus, glycosylation of α,ω-diols with 1,3,4,6-tetra-O-acetyl-2-allyloxycarbonylamino-2-deoxy-β-d-glucopyranose (1) gave the bis(glycosides)2a-hin good yields and without column chromatography. Alkaline treatment of these derivatives followed by acetylation gave the peracetylatedN-acetyl compounds3a-hwhich were further deprotected by the Zemplén deacetylation procedure to theN-acetyl-d-glucosaminyl bolaamphiphiles4a-h. The bis(glycosides)2c,d,gwere also transformed into theO-acetylated amino-free derivatives5c,d,gby chemospecific deprotection of theN-allyloxycarbonyl groups with palladium (0). Further deprotection of the ester functions led to the completely deprotected bolaamphiphiles7c,d,gwith high yields. Fully deprotected compounds7a,d,g,hwere also obtained from2a,d,g,hby alkaline treatment and purification by column chromatography. Surface tension measurements were realized for aqueous solutions containing the soluble bolaamphiphiles.

ISSN:0732-8303    

DOI:10.1080/07328309508005356

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Several ribofuranosyl derivatives bearing trichloroacetimidoyl or acetyl leaving groups in a Lewis acid promoted ribosylation reaction were prepared and used in an attempt to improve the yield and to avoid donor → acceptor transacetylation. Trichloroacetimidates were excellent donors affording disaccharides with very high yields under mild conditions. The corresponding 1-O-acetylated analogs could also be used with out transacetylation in the presence of boron trifluoride etherate.

ISSN:0732-8303    

DOI:10.1080/07328309508005357

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Ammonolysis of the epoxide rings of 2,3-anhydro-α-L-guluronic acid residues, generated in alkaline medium from 2-O-sulfated α-L-iduronic acid residues of heparin, quantitatively afforded 2-amino-2-deoxy-α-L-iduronic acid residues.N-sulfation of these residues by TMA·SO3complex led to a formal replacement of the original 2-O-sulfate groups of heparin withN-sulfates, without configurational changes. These modified uronic acid residues (no longer amenable to alkaline epoxidation) can be easilyN-desulfated. The presence of negative or positive charges at position 2 of the newly generated 2-amino-2-deoxy-α-L-iduronic acid residues influences thein vivoantithrombotic activity and haemorrhagic effects in different ways. A free amino group mainly decreases the haemorrhagic properties of heparin, while a negatively chargedN-sulfate group decreases the coagulation parameters.

ISSN:0732-8303    

DOI:10.1080/07328309508005358

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Upon sodium cyanoborohydride reduction followed by de-O-silylation, theO-methyloxime andN-benzylnitrone of 5′-TBDMS-3′-ketothymidine gave resolvable epimeric mixtures of 1-[2,3-dideoxy-3-(N-methoxyamino)-β-d-threo-and β-d-erythro-pentofuranosyl]thymine and 1-[3-(N-benzyl-N-hydroxyamino)-2,3-dideoxy-β-d-threo- and β-d-erythro-pentofuranosyl]thymine respectively. These compounds were inactive against HIV. On the other hand, 1-[2,3-dideoxy-3-(N-hydroxyamino)-5-O-TBDMS-β-d-threo-pentofuranosyl]thymine, upon treatment with acetone, then de-O-silylation, gave the bicyclonucleoside analogue15, slightly more active against HIVin vitrothan DDI.

ISSN:0732-8303    

DOI:10.1080/07328309508005359

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor