ISSN:0732-8303    

DOI:10.1080/07328309608005698

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A branched hexasaccharide fragment of type Ia group B streptococcal polysaccharide, α-NeuAc(2→3)-β-D-Gal(1→4)-β-D-GlcNAc(1→3)-[β-D-Glc(1→4)]-β-D-Gal(1→4)-β-D-Glc-OMe (13), has been synthesized by chemical-enzymatic procedures. Chemical synthesis of a pentasaccharide, β-D-Gal(1→4)-β-D-GlcNAc(1→3)-[β-D-Glc(1→4)]-β-D-Gal(1→4)-β-D-Glc-OMe (12), was achieved from glycosyl donor, 4-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-3,6-di-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl trichloroacetimidate (9), and acceptor, methylO-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-(1→4)-O-(2,6-di-O-benzyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (6), by block condensation in 41% yield. Following enzymatic sialylation of12at the 3-O-position of its terminal galactopyranosyl residue using recombinant α-(2→3)-sialyltransferase and CMP-NeuAc afforded13in 59% yield.

ISSN:0732-8303    

DOI:10.1080/07328309608005699

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Synthesis of two isomeric tetrasaccharides, namely Neu5Acα(2→3)Galβ(1→3)[Fucα(1→4)GlcNAcβ (sLea) and Neu5Acα(2→3)Galβ(1→4)[Fucα(1→3)]GlcNAcβ (sLex) as 3-aminopropyl glycosides is described. Preparation of these compounds was performed by sialylation of selectively protected trisaccharides Leaand Lexwhich contain three unsubstituted OH groups at positions 2, 3 and 4 of Gal residue. Glycosylation of Lextrisaccharide with ethylthio sialoside under promotion by NIS and TfOH in acetonitrile was effective and regio- and stereoselective to give sLexderivative in 81% yield. In contrast, sialylation of the Lcaacceptor was accompanied by a variety of undesirable by-processes, namely.N-thioethylation of the GlcNAc residue, β-sialylation, and lactonisation. In order to improve the yield of sLcatetrasaccharide the glycosylation of Leaacceptor by sialyl donors of ethyl and phenyl thioglycoside (promoted by NIS-TfOH or NBS-Bu4NBr), xanthate (promotion by NIS-TfOH mixture or MeOTf) and phosphite (promoted by TMSOTf) types was also studied. Among the reactions investigated the glycosylation by phenyl thioglycoside sialoside promoted by NIS-TfOH gives the best yield (39%) of sLeatetrasaccharide product.

ISSN:0732-8303    

DOI:10.1080/07328309608005700

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A convenient, highly efficient, one-pot, three-step procedure has been developed for the synthesis of peracetylated glycal derivatives from various reducing sugars including D-glucose, D-galactose, L-rhamnose, L-arabinose, D-maltose, D-lactose, and maltotriose. This procedure involves peracetylation of the reducing sugars with acetic anhydride and HBr/acetic acid followed by the transformation of the anomeric acetates to the corresponding bromides with additional HBr/acetic acid and finally reductive elimination of the 1-bromo and 2-acetoxy groups with Zn/CuSO4·5H2O in acetic acid/water containing sodium acetate. The overall yields of purified peracetylated glycals from the corresponding sugars range from 50 - 98%.

ISSN:0732-8303    

DOI:10.1080/07328309608005701

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The methyl glycoside, (3-SO3Na)GlcNAcβ1→3Fucβ1→OMe, of a sulfated disaccharide that is involved in the species-specific reaggregation of dissociated cells ofMicrociona prolifera, was stereoselectively synthesized starting from L-fucose and 2-amino-2-deoxy-D-glucose.

ISSN:0732-8303    

DOI:10.1080/07328309608005702

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The readily available 2, 3-O-isopropylidene-D-erythrose has been stereoselectively transformed into L-ribono and D/L lyxonolactone derivatives via dihydroxylation, iodolactonisation and epoxidation. Also D-ribono-1,4-lactone was converted into L-lyxono-1,4-lactone. These lactones are considered as important starting materials for the synthesis of several chiral compounds. Our observations during these transformations are also presented.

ISSN:0732-8303    

DOI:10.1080/07328309608005703

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The conformation of two mannose-based amidines, theN-benzylmannoamidine and a pseudo (1→6) dimannoside, has been evaluated using semi-empirical AMI calculations and1H NMR studies. The most stable conformations of the mannoamidine ring correspond to the half-chair forms3H4and4H3. The conformations (Z) or (E) about the exocyclic C-N bond depend on the substituents and it was shown that, in solution, theN-benzylmannoamidine was (E)-configured whilst the pseudo (1→6) dimannoside was (Z)-configured. Using the grid-search approach, the potential energy maps of both mannoamidines were calculated as a function of the torsion angles which define the orientation of the amidine substituent. Three stable conformers were identified for theN-benzylmannoamidine and seven for the pseudo (1→6) dimannoside. Inter-glycosidic NOE have provided evidence for a preferred conformation of the pseudo (1→6) dimannoside in solution. The transition state structure of the α-phenylmannose hydrolysis was optimized using the AMI method and compared to theN-benzylmannoamidine. The developing oxocarbenium ion is well matched by the mannoamidine ring but the orientation of the phenyl group in the inhibitor differs significantly from the position of the leaving group in the transition state. The use of sugar type amidines as haptens to obtain catalytic antibodies is then discussed.

ISSN:0732-8303    

DOI:10.1080/07328309608005704

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

3-O-Sulfo glucuronyl paragloboside derivatives (pentasaccharides) have been synthesized. The important intermediate designed for a facile sulfation in the last step and effective, stereocontrolled glycosidation, methyl (4-O-acetyl-2-O-benzoyl-3-O-levulinoyl-α-D-glucopyranosyl trichloroacetimidate)uronate (8) was prepared from methyl [2-(trimethylsilyl)ethyl β-D-glucopyranosid]uronate (3)viaselective 4-O-acetylation, 2-O-benzoylation, 3-O-levulinoylation, removal of the 2-(trimethylsilyl)ethyl group and imidate formation. The glycosylation of8with 2-(trimethylsilyl)ethyl 2,4,6-tri-O-benzyl-β-D-galactopyranoside (9) using trimethylsilyl trifluoromethanesulfonate gave 2-(trimethylsilyl)ethylO-(methyl 4-O-acetyl-2-O-benzoyl-3-O-levulinoyl-β-D-glucopyranosyluronate)-(1→3)-2,4,6-tri-O-benzyl-β-D-galactopyranoside (10), which was transformedviaremoval of the benzyl group, benzoylation, removal of the 2-(trimethylsilyl)ethyl group and imidate formation into the disaccharide donor13. On the other hand, 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 (20) as the acceptor was prepared from 2-(trimethylsilyl)ethyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-D-glucopyranoside (14)via O-acetylation, removal of the 2-(trimethylsilyl)ethyl group, imidate formation, coupling with 2-(trimethylsilyl)ethylO-(2,4,6-tri-O-benzyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (18), removal of theO-acetyl andN-phthaloyl group followed byN-acetylation. Condensation of13with20using trimethylsilyl trifluoromethanesulfonate afforded the desired pentasaccharide21, which was transformed by removal of the benzyl group,O-acetylation, removal of the 2-(trimethylsilyl)ethyl group and imidate formation into the pentasaccharide donor24. Glycosylation of (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (25) with24gave the desired β-glycoside26, 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:10.1080/07328309608005705

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0732-8303    

DOI:10.1080/07328309608005706

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor