摘要:

Synthesis of sialyl-Lewis x (15) and sialyl-Lewis a (17) epitope analogs containing the 2-acetamido derivative ofN-methyl-1-deoxynojirimycin has been achieved. A suitably protected 2-acetamido- 1-deoxynojirimycin derivative5, prepared from 1-deoxynojirimycinviathe epoxide intermediate3, was successively coupled with methyl- 1-thioglycosides of L-fucose (6) and β-sialyl-(2→3)-D-galactose (9). The resulting tetrasaccharides (10and13) were each converted, by reductiveN-methylation and deprotection, into the desired epitope analogs.

ISSN:0732-8303    

DOI:10.1080/07328309608005420

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Methyl β-D-arabinopyranoside (1), phenyl 1-thio-β-D-galactopyranoside (3), methyl β-L-fucopyranoside (7), methyl β-L-fucopyranoside (9), 1,6-anhydro-β-D-galactopyranoside (D-galactosan;11), and 1,6-anhydro-β-D-mannopyranoside (D-mannosan;14) were stereospecifically converted in moderate up to good yields into methyl 4-O-cyclohexylcarbamoyl-2,3-O-(2,2,2-trichloroethylidene)-β-D-lyxopyranoside (2), phenyl 4-(9-cyclohexyIcarbamoyl-6-O-formyl-2,3-O-(2,2,2-trichloroethylidene)-1-thio-β-D-gulopyranoside (4) / phenyl 4-O-cyclohexylcarbamoyl-2,3-O-(2,2,2-trichloroethylidene)-1-thio-β-D-gulopyraoside (5), methyl 4-O-cyclohexylcarbamoyl-2,3-O-(2,2,2-trichloroethylidene)-6-deoxy-α-L-gulopyranoside (8), methyl 2,3-O-(2,2,2-trichloroethylidene)-4-O-cyclohexylcarbamoyl-6-deoxy-β-L-gulopyranoside (10), 1,6-anhydro-4-O-cyclohexyl-carbamoyl-2,3-O-(2,2,2-trichloroethylidene)-β-D-gulopyranoside (12), and 1,6-anhydro-2-O-cyclohexylcarbamoyl-3,4-O-(2,2,2-trichloroethylidene)-β-D-altropyranoside (15), respectively, using a nonclassic pathway of chloral acetalisation with dicyclohexylcarbodiimide (DCC) as coagent. In the case of1,3, and9, chloral acetalisations yielded diastereomeric mixtures, e.g., the acetals2,4,5, and10consist ofendo-H/enxo-H dioxolane type acetals with preference of theendo-H form. In contrast to this, the compounds7,11, and14gave exclusively theendo-H diastereomers8,12, and15. Additionally, the structure of the anhydro compound15was confirmed by intramolecular glycosylation of the 2-O-cyclohexylcarbamoyl-3,4-O-(2,2,2-trichloroethylidene)-α-D-altropyranosyl fluoride (17). Finally, the 6-O-formyl-α-D-gulopyranoside4was alternatively deformylated by methanol/triethylamine giving5and methanol/sodium methoxide yielding phenyl 6-O-cyclohexylcarbamoyl-2,3-O-(2,2,2-trichloroethylidene)-1-thio-β-D-gulopyranoside (6). The carbamoyl protecting group of12was cleaved by refluxing with methanolic sodium methoxide solution giving 1,6-anhydro-2,3-O-(2,2,2-trichloroethylidene)-β-D-gulopyranoside (13).

ISSN:0732-8303    

DOI:10.1080/07328309608005421

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Photolysis of 1,2:3,4-di-O-isopropylidene-6-O-(p-tolylsulfonyl)-α-D-galactopyranose (5) in methanol under nitrogen in the presence of sodium hydroxide or diazabicyclo[2.2.2]octane (3, DABCO) produces toluene and 1,2:3,4-di-O-isopropylidene-α-D-gatactopyranose (6). Electron transfer from DABCO or hydroxide ion to singlet excited5to generate a radical anion is the first step in this reaction. The radical anion rapidly fragments to give thep-tolylsulfonyl radical (2) and deprotonated6, which accepts a proton from the solvent. Thep-tolylsulfonyl radical (2) then abstracts a hydrogen atom from the solvent to givep-toluenesulfinic acid, a compound that is converted to thep-toluenesulfinate anion (8) under the basic reaction conditions. Photolysis of8completes the reaction sequence by forming toluene.

ISSN:0732-8303    

DOI:10.1080/07328309608005422

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Model experiments using methyl α-d-galactopyranoside 6-sulfate have implied that the Carlson conditions (1 M sodium borohydride and 0.05 M sodium hydroxide at 45°C) for the release ofO-linked oligosaccharides from glycoproteins do not cause significant loss of sulfate ester groups. However the more vigorous conditions used to releaseN-linked oligosaccharides are more likely to cause considerable sulfate loss from a galactoside 6-sulfate as a result of 3,6-anhydride formation. Experiments with dextran sulfate suggested that sulfate loss due to oxirane formation was also not significant under the Carlson conditions. These results were supported by experiments with [35S]sulfate-labelled human rectal mucus glycoprotein.

ISSN:0732-8303    

DOI:10.1080/07328309608005423

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The synthesis ofN-(2-acetamido-4-O-[2-acetamido-4-O-{2-acetamido-2-deoxy-β-D-glucopyranosyl}-2-deoxy-β-D-glucopyranosyl]-2-deoxy-β-D-glucopyranosyl)-L-histidine amide (3),N-(2-acetamido-2-deoxy-β-D-glucopyranosyl)-(6S)-4,5,6,7-tetrahy-droimidazo[4,5-c]pyridine-6-carboxylic amide (4) andN-(2-acetamido-4-O-[2-acetamido-2-deoxy-β-D-glucopyranosyl]-2-deoxy-β-D-glucopyranosyl)-(6S)-4,5,6,7-tetrahydroimidazo[4,5-c]pyridine-6-carboxamide (5) is achievedviacoupling of the appropiate glycosylamines with Boc-protected L-histidine or with (6S)-4,5,6,7-tetrahydroimidazo[4,5-c]pyridine-6-carboxylic acid ((-)-spinacine), respectively, by means of EEDQ and subsequent deprotection.

ISSN:0732-8303    

DOI:10.1080/07328309608005424

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Debromination of 4,5-dibromopentanyl glycosides to (re)generaten-pentenyl glycosides has been accomplished using zinc, samarium(II) iodide, and sodium iodide, respectively. The choice of reagent is dependent upon the reactivity of the substrate, as well as the protecting groups thereon.

ISSN:0732-8303    

DOI:10.1080/07328309608005425

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Selective transformations of the free hydroxyl groups in 2,3,4,3′,4′-penta-O-benzyl-sucrose (1) were studied. Oxidation of1with the Swern reagent followed by reaction with Ph3P=CH-COOMe gave 2,3,4,3′,4′-penta-O-benzyl-1′,6,6′-tris-(E)(C-carbomethoxy-methylene)sucrose (2) in ca.40% as the single product. Reaction of1withp-nitrobenzoic acid under Mitsunobu conditions gave 6,6′-di-O-p-nitrobenzoyl-2,3,4,3′,4′-penta-O-benzylsucrose (3) which was easily converted into 2,3,4,3′,4′-penta-O-benzyl-1′-methoxy-methylsucrose (5). Reaction of1with one equivalent of pivaloyl chloride gave monoprotected 2,3,4,3′,4′-penta-O-benzyl-6′-O-pivaloylsucrose (6) [30% with triethylamine or 45% yield in the presence of (Bu3Sn)2O] together with a small amount of diprotected 2,3.4,3′,4′-penta-O-benzyl-6,6′-di-O-pivaloylsucrose (7).

ISSN:0732-8303    

DOI:10.1080/07328309608005426

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The effects of salts and other solutes on the degradation of highly pure sucrose in concentrated aqueous solutions (∼65°Brix or % dissolved solids) at 100°C were investigated. Polarimetry and ion chromatography with pulsed amperometric detection (ICIPAD) were used to quantify sucrose degradation. Pseudo-first order kinetic constants of initial degradation rates were calculated. Salt and solute effects were first considered with relation to their effect on water structure around the sucrose molecule. Na+, Mg2+and Ca2+, which act to enhance water structure, slightly increased initial degradation; the latter two ions significantly increased subsequent accelerated degradation. Highly charged, small cations, e.g., Al3+, significantly increased sucrose degradation through polarized hydrated ions/acidic pH effects. Larger cations, e.g., K+, which act to reduce water structure, significantly increased degradation. The Hofmeister (lyotropic) anion order was not followed for sucrose thermal degradation effects, which indicated that anion binding to hydrophobic sites on the sucrose molecule is not critical. Other possible mechanisms of salt-induced sucrose thermal degradation are discussed.

ISSN:0732-8303    

DOI:10.1080/07328309608005427

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The regioselectivity of benzylation of stannylene acetals oftrans-diols on pyranose rings is improved by performing the reaction in benzyl bromide, for instance, for methyl 4,6-O-benzylidene-2,3-O-dibutylstannylene-α-D-glucopyranoside, the ratio of 2-O-benzyl ether to 3-O-benzyl ether changed from 70:20 in DMF to 74:8 in benzyl bromide, then improved further to 84:2 if the dihexylstannylene acetal was used. Standard conditions for methylation of stannylene acetals are methyl iodide in DMF. Non-polar conditions give much improved regioselectivity, theO-2 toO-3 product ratio for the above dibutylstannylene acetal changed from 57:30 in DMF to 84:13 with methyl iodide in 1,1,2,2-tetrachloroethane or 90:8 with methyl triflate in chloroform. Examples of benzylation and methylation reactions on different dialkylstannylene acetals on three differenttrans-diols are included.

ISSN:0732-8303    

DOI:10.1080/07328309608005428

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Sinigrin (1), the most commonly known glucosinolate, is a naturally occurring thiosugar, widely distributed in the botanic family Cruciferae. Sinigrin was first isolated in 1839 from seeds of black mustard in the form of its potassium salt.1Commercially available sinigrin is obtained by extraction from horseradish.2So far a number of natural glucosinolates and their analogs have been synthesized.3-10The only synthesis of compound1, leading to a crystalline product on the miligram scale, has been reported by Benn and Ettlinger3(Scheme 1). Their procedure has been applied by Kjaer and Jensen4for the synthesis of the higher homologue of sinigrin (1), but no information of the overall yield has been provided.

ISSN:0732-8303    

DOI:10.1080/07328309608005429

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor