摘要:

A carboxylate-containing pentasaccharide, methylO-(β-d-galactopyranosyl)-(1→4)-O-(β-d-glucopyranosyl)-(1→6)-O-{3-O-[(S)-1-carboxyethyl]-β-d-galactopyranosyl-(1→4)-O}-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-β-d-galactopyranoside (27) was synthesized by block condensation of suitably protected donors and acceptors. Phenyl 3-O-benzyl-4,6-di-O-chloroacetyl-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside (17) was condensed with methyl 2,4,6-tri-O-benzyl-β-d-galactopyranoside (4) to afford a disaccharide, methylO-(3-O-benzyl-4,6-di-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (18). Removal of chloroacetyl groups gave 4,6-diol, methyl 0-(3-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (19), in which the primary hydroxy group (6-OH) was then selectively chloroacetylated to give methylO-(3-O-benzyl-6-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (20). This acceptor was then coupled with 2,4,6-tri-O-acetyl-3-O-[(S)-1-(methoxycarbonyl)ethyl]-α-d-galactopyranosyl trichloroacetimidate (14) to afford a trisaccharide, methylO-{2,4,6-tri-O-acetyl-3-O-[(S)-l-(methoxycarbonyl)ethyl]-β-d-galactopyranosyl}-(1→4)-O-(3-O-benzyl-6-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (21). Removal of the 6-O-chloroacetyl group in21gave22, which was coupled with 4-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-2,3,6-tri-O-acetyl-α-d-glucopyranosyl trichloroacetimidate (23) to yield protected pentasaccharide24. Standard procedures were used to remove acetyl groups and the phthalimido group, followed byN-acetylation, and debenzylation to yield pentasaccharide27and a hydrazide by-product (28) in a 5:1 ratio, respectively. Compound27contains a complete repeating unit of the capsular polysaccharide of type III group BStreptococcusin which terminal sialic acid is replaced by an (S)-1-carboxyethyl group.

ISSN:0732-8303    

DOI:10.1080/07328309608005652

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

3-AminopropylO-(β-d-galactopyranosyl)-(1→4)-O-(β-d-glucopyranosyl)-(1→6)-O-{3-O-[(S)-1-carboxyethyl]-β-d-galactopyranosyl-(1→4)-O}-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-O-(β-d-galactopyranosyl)-(1→4)-β-d-glucopyranoside (18) was synthesized by block condensations from suitably protected acceptors and donors, namely 3-azidopropyl 4-O-(2,4,6-tri-O-acetyl-β-d-galactopyranosyl)-2,3,6-tri-O-acetyl-β-d-glucopyranoside (5), phenyl 3-O-benzyl-4,6-di-O-isopropylidene-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside (7), 2,4,6-tri-O-acetyl-3-O-[(S)-1-(methoxycarbonyl)ethyl]-α-d-galactopyranosyl trichloroacetimidate (11), and 4-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-2,3,6-tri-tri-O-acetyl-α-d-glucopyranosyl trichloroacetimidate (14). Compound18contains structural elements of type III group BStreptococcuscapsular polysaccharide in which terminal sialic acid is replaced by an (S)-1-carboxyethyl group, and has a short spacer for the conjugation with peptide or protein.

ISSN:0732-8303    

DOI:10.1080/07328309608005653

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

β-Glycosidations of peracetylated chitobiose with such alcohols as methyl, allyl, benzyl, isopropyl,tert-butyl alcohol and 1,2:3,4-O-diisopropylidene-1-O-α-D-galactoside were carried out in good yields by employing TMSOTf as a promoter. The reaction proceeded through the oxazoline intermidiate.

ISSN:0732-8303    

DOI:10.1080/07328309608005654

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Reaction of 2,3:4,5-di-O-isopropylidene-β-d-arabino--hexos-2-ulo-2,6-pyranose (1) with (methoxycarbonylmethylene)triphenylphosphorane in either dichloromethane or methanol gave methyl (E)-2,3-dideoxy-4,5:6,7-di-O-isopropylidene-β-d-arabino-oct-2-ene-4-ulo-4,8-pyranosonate (2) or a 1:2.3 mixture of2and its Z-isomer (3), respectively. Bishydroxylation of2with osmium tetraoxide gave a mixture of methyl 4,5:6,7-di-O-isopropylidene-β-d-glycero-d-galacto- (4) and -d-glycero-d-ido-oct-4-ulo-4,8-pyranosonate (5) which were carefully resolved by column chromatography. Compound4was transformed into its 2,3-di-O-methyl derivative (6) which was deacetonated to7and subsequently degraded to dimethyl 2,3-di-O-methyl-(+)-L-tartrate (8). On the other hand, acetonation of a mixture of4and5gave the corresponding tri-O-isopropylidene derivatives (9) and (10). Compounds4and5were reduced with LiAlH4to the related 4,5:6,7-di-O-isopropylidene-β-d-glycero-d-galacto- (11) and β-d-glycero-d-ido-oct-4-ulo-4,8-pyranose (12). Treatment of11and12with acetone/PTSA/CuSO4only produced the acetonation at the C-2,3 positions. Finally, compounds11and12were deacetonated to the corresponding D-glycero-d-galacto- (15) and D-glycero-d-ido-oct.-4-ulose (16).

ISSN:0732-8303    

DOI:10.1080/07328309608005655

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The oxidation oftrans-1,2-cyclohexanediol, methyl α-D-glucopyranoside and β-cyclodextrin has been studied, using a heterogeneous oxidation system in water at 50-75 °C. Molecular oxygen at 15–20 bar was used as the oxidant, in combination with a bismuth-rich ruthenium pyrochlore oxide as the catalyst. Both oxidative cleavage of the vicinal diols and oxidation of the primary hydroxyl groups occurred. HPLC and13C NMR were used to analyse the complex product mixtures. The oxidation method is successful for glycol cleavage in small carbohydrates but not for polysaccharides.

ISSN:0732-8303    

DOI:10.1080/07328309608005656

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Silica-alumina cracking catalysts and acid clays efficiently catalyze the 2-O-alkylation ofd-fructose with long chain alcohols. Under the conditions applied virtually no degradation of fructose is observed.l-Sorbose and the aldopentoses also undergo silica-alumina-catalyzed alkylation. The rate of conversion is related to the solubility of the monosaccharide and the stability of the intermediate oxocarbenium ion. Best results in fructose alkylation are obtained by applying a recirculation method with butyl fructoside as soluble intermediate.

ISSN:0732-8303    

DOI:10.1080/07328309608005657

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The isolation of a heparan sulfate derived tetrasaccharide containingN-acetylmannosamine is described. TheN-acetylmannosamine residue at the reducing terminus of heparin lyase derived tetrasaccharide is formed by base catalyzed C-2 epimerization ofN-acetylglucosamine. This C-2 epimerization takes place under very mild conditions suggesting that this residue may be formed in small amounts under physiologic conditions.

ISSN:0732-8303    

DOI:10.1080/07328309608005658

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The synthesis of 3-deoxy-1,2,O-isopropylidene-3-C-trifluoromethyl-α-D-ribofuranose is described. After a first approach from a commercial D-xylose derivative which was limited by an incomplete stereoselectivity, the synthesis of the title compound was performed from 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose by a reaction sequence where key steps: trifluoromethylation with CF3SiMe3and radical deoxygenation are highly stereoselective.

ISSN:0732-8303    

DOI:10.1080/07328309608005659

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Although the deprotection of amides by hydrazinolysis is a well established method in carbohydrate chemistry, this reaction is dependent upon the nearby substituents. In our facile synthesis of intermediate benzyl 2-amino-3-azido-4-O-p-methoxybenzyl-6-O-benzyl-2,3-dideoxy-α-d-glucopyranoside (3), we found that the use of trifluoroacetamides provided a more efficient protection strategy.

ISSN:0732-8303    

DOI:10.1080/07328309608005660

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor