摘要:

The glycosylation of sugar primary-secondary ditrityl ethers with glycosylating agents of different kinds occurs regioselectively at the secondary trityloxy group to give good yields of 6-O-trityl ethers of 1-2-, 1-3-, and 1-4-linked disaccharides.

ISSN:0732-8303    

DOI:10.1080/07328309608006496

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The direct coupling of 3-n-alkyl catechols to the acetate or trichloroacetimidate derivatives of β-D- or α-D-glycosides (glucose, galactose, xylose, mannose and maltose) catalyzed by BF3Ot2has been studied. β-Glycosides with an equatorial acetate group at position 2 formed exclusively β adducts with yields of 60–80%. α-Glycosides with an equatorial acetate group at position 2 formed β adducts, while β-glycosides with an axial acetate group formed α adducts when activated as trichloroacetimidates, with yields of 70–85%. This was applied to the coupling of 3-n-alkylcatechols of increasing chain length (up to C15) to sugar derivatives. The coupling position of glycosides on the catechol was determined either by differential NOE experiments and by the regioselective synthesis of 1-(O-β-D-glucopyranosyl)-3-pentadecylcatechol, a water soluble analogue of the poison ivy skin allergen.1H NMR of acetylated and deprotected compounds were investigated and the conformational preferences of the C6side chain determined using molecular modeling.

ISSN:0732-8303    

DOI:10.1080/07328309608006497

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Two interconvertible enediol group-containing reductones were produced nonenzymatically from L-xylosone in citrate-phosphate buffer (pH 6.0). These compounds were oxidized by ascorbate oxidase (E.C. 1.10.3.3.) and had ability to reduce 2.6-dichloroindophenol. GLC-MS analysis of trimethylsilylated L-xylosone indicates that it exists in several tautomeric forms including the enediol group-containing reductones which are L-glycero-2-pentenopyranose and L-glycero-2-pentenofuranose. The production rates of both reductones from L-xylosone were proportional to pH within a pH range 4 to 7, and above that pH range further degradation of the reductones occurred.

ISSN:0732-8303    

DOI:10.1080/07328309608006498

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The quinoxaline derivatives formed between dehydro-D-erythroascorbic acid (2) ando-phenylenediamine (3) were separated by preparative HPLC and their structures were analyzed by HPLC-MS, UV-vis spectrophotometry and1H NMR spectroscopy. The reaction of2with an excess amount of3in 5% aqm-phosphoric acid gave three different products, depending on the concentration of2: below 0.1 mM of2, only 3-(D-glycero-1,2-dihydroxyethyl)quinoxaline-2-carboxylic γ-lactone (4) was produced, between 0.1 to 5 mM of2, another product, 2,2′-anhydro-[2-hydroxy-3-(D-glycero-2,3-dihydroxypropanal-1-yl)quinoxaline] (5) was formed as well as4, and over 10 mM of2, the third product, 2,1′-anhydro-[2-hydroxy-4-(D-glycero-1,2-dihydroxyethyl)-1,5-benzodiazepin-3-one] (6) was formed as well as4and5, with an overall production yield over 95%. Quinoxaline6was slowly converted to4via5. Based on these results, it was concluded that all three products retain the lactone ring moiety of2, and the most stable product is4. Compounds5and6were produced with higher concentration of2, but they were unstable and slowly converted to4in aqueous solution. A possible mechanism for this conversion was proposed.

ISSN:0732-8303    

DOI:10.1080/07328309608006499

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Efficient syntheses of tumor-associated Lea, sialyl Leaand their deaminated analogs are described. The suitably protected D-glucosamine (4) or D-glucose (5) derivative was successively coupled with the methyl-1-thioglycosides (glycosyl donors) of D-galactose (6) and L-fucose (11) in high yields by usingN-iodosuccinimide/trifluoromethanesulfonic acid (NIS/TfOH) as the glycosyl promoter. The resulting trisaccharides (12and13) were each converted, by deprotections, to the Leadeterminant (17) and its deaminated analog (18), and by further glycosylation with the phenyl-2-thioglycoside ofN-acetylneuraminic acid (25), to the sialyl-Leadeterminant (30) and its deaminated analog (31), respectively.

ISSN:0732-8303    

DOI:10.1080/07328309608006500

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

3-O-Sulfo glucuronyl neolactohexanosyl ceramide derivatives (heptasaccharides) have been synthesized. Condensation of 2-(trimethylsilyl)ethyl 2,4,6-tri-O-benzyl-β-D-galactopyranoside (2) with 4-O-acetyl-3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl trichloroacetimidate (1) gave the desired β-glycoside3, which was converted into 2-(trimethylsilyl)ethylO-(2-acetamido-3,6-di-O-benzyl-2-deoxy-β-D-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-D-galactopyranoside (4)viaremoval of theO-acetyl andN-phthaloyl groups, followed byN-acetylation. Glycosylation of4withO-(methyl 4-O-acetyl-2-O-benzoyl-3-O-levulinoyl-β-D-glucopyranosyluronate)-(1→3)-2,4,6-tri-O-benzoyl-α-D-galactopyranosyl trichloroacetimidate (5) using trimethylsilyl trifluoromethanesulfonate gave the target tetrasaccharide6, which was transformedviaremoval of the benzyl group,O-benzoylation, removal of the 2-(trimethylsilyl)ethyl group and imidate formation into the tetrasaccharide donor9. Glycosylation of 2-(trimethylsilyl)ethylO-(2-acetamido-3,6-di-O-benzyl-2-deoxy-β-D-glucopyranosyl)-(1→3)-O-(2,4,6-tri-O-benzyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (10) with the imidate donor9using trimethylsilyl trifluoromethanesulfonate gave the desired heptasaccharide11, which was transformed into the heptasaccharide imidate donor14. Glycosylation of (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (15) with14gave β-glycoside16, which was transformed into the four target compounds,viareduction of the azido group, coupling with octadecanoic acid or tetracosanoic acid, selective removal of the levulinoyl group,O-sulfation, hydrolysis of the methyl ester group andO-deacylation.

ISSN:0732-8303    

DOI:10.1080/07328309608006501

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Glycosylations and deacetylations of 2-O-acetyl ofO-peracetylated β-D-glucopyranose were realized in one step by reactions with 4.0 equivalents of alcohols and 1.5 equivalents of trifluoroborane etherate. Thus, various β-D-glucopyranosides with a free hydroxyl group on C-2 were conveniently prepared and applied for synthesis of Glcl → 2 linked disaccharides.

ISSN:0732-8303    

DOI:10.1080/07328309608006502

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In a quadrupole mass spectrometer, under chemical ionization conditions with acetone as the reagent gas, 1,2:5,6-di-O-isopropylidene-β-D-glucofuranose and 1,2:5,6-di-O-isopropylidene-β-D-allofuranose form M+1, M+43, and M+59 ions in the gas phase. In addition, the allo isomer produces M+41 ions. These ions and the corresponding ions derived from isotopomers in which the isopropylidene groups were differentiated by deuterium substitution were separately subjected to collisionally activated dissociation conditions. The different reactivities of these ions were attributed to the ability of the allo structure to hydrogen bond internally and the different sizes of the electrophilic groups which formed adducts with the neutral protected sugar molecules.

ISSN:0732-8303    

DOI:10.1080/07328309608006503

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The 2-aminoethyl glycoside ofO-α-L-fucopyranosyl-(1→2)-O-β-D-galactopyranosyl-(1→3)-[O-α-L-fucopyranosyl-(1→4)]-2-acetamido-2-deoxy-β-D-glucopyranose (Lewis B tetrasaccharide) was synthesized on a large scale and acryloylated with acryloyl chloride. The obtained oligosaccharide 2-acrylamidoethyl glycoside was then copolymerized with acrylamide to form a water-soluble, high molecular weight polymer, suitable for use in adhesion inhibition studies withHelicobacter pylori. Also synthesized were the corresponding derivatives ofO-α-L-fucopyranosyl-(1→2)-O-β-D-galactopyranosyl-(1→3)-2-acetamido-2-deoxy-β-D-glucopyranose andO-β-L-fucopyranosyl-(1→2)-β-D-galactopyranose.

ISSN:0732-8303    

DOI:10.1080/07328309608006504

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Oligosaccharides containing thioglycosidic linkages are resistant to enzyme-catalysed hydrolysis and therefore interesting material for studies of carbohydrate hydrolases. Some of these were shown to be competitive inhibitors for several glycanases such as α-amylase,1cellobiohydrolase I and II,2and for α-l-fucosidase,3a glycosidase. Thio-oligosaccharides have also been used to prepare column material for affinity chromatography to isolate carbohydrate hydrolases. In contrast, affinity material containing normalO-glycosidic bonds was hydrolysed and led to column deterioration. By employing this approach, affinity materials containing 1,4-dithiocellobiose and 1,4,4′-trithiocellotriose could be used successfully to separate the cellobiohydrolases ofTrichoderma reesei.2

ISSN:0732-8303    

DOI:10.1080/07328309608006505

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor