摘要:

Glucosides of unsaturated alcohols, bearing different functional groups on the carbohydrate units, underwent catalytic metathesis reaction affording neutral bolaforms in good yields. Tungsten aryloxo-complexes (1and2), due to large steric hindrance, were found to be superior catalysts for this process.

ISSN:0732-8303    

DOI:10.1080/07328309608005433

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The trisaccharide α-L-Rha-(1-2)-α-L-Rha-(1-2)-α-L-Rha with a dioxolane-type spacer was obtained by using the trichloroacetimidate method in all of the glycosidation steps. After deprotection, the trisaccharide was coupled to BSA or KLH by reductive amination of the spacer aldehyde group.

ISSN:0732-8303    

DOI:10.1080/07328309608005434

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Three sialyl-Lexepitope analogs, which carry fucose and α-sialyl-(2→3)-galactose residues atO-2 andO-3,O-3 andO-2, andO-4 andO-6 positions of 1-deoxy-D-glucose backbone, respectively, have been synthesized. Glycosylation of 1,5-anhydro-4,6-O-benzylidene-D-glucitol (1) or 1,5-anhydro-6-O-benzoyl-2,3-di-O-benzyl-d-glucitol (4) prepared from 1,5-anhydro-d-glucitol, with methyl 2,3,4-tri-O-benzyl-1-thio-β-L-fucopyranoside (5) using dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter, afforded the corresponding fucosyl 1,5-anhydro-d-glucitol derivatives7, 8and9. Glycosylation of7, 8or10derived from9, with methylO-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glyceroα-d-galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-d-galactopyranoside (11) in the presence of DMTST gave the expected tetrasaccharide derivatives12, 16and20. Hydrolysis of the benzylidene group in12and16gave compounds13and17. Finally13, 17and20were transformed, by reductive removal of the benzyl groups,O-deacylation and subsequent hydrolysis of the methyl ester, into the sialyl-Lexepitope analogs15, 19and22, respectively.

ISSN:0732-8303    

DOI:10.1080/07328309608005435

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The first, total synthesis of sialyl globopentaosyl ceramide (V3Neu5AcGb5Cer) and its positional isomer (V6Neu5AcGb5Cer) are described. α-Selective glycosylation of 2-(trimethylsilyl)ethylO-(2,3,6-tri-O-benzyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (7) with the suitably protected galactose donor, methyl 3-O-acetyl-2-O-benzyl-4,6-O-benzylidene-l-thio-β-D-galactopyranoside gave the desired trisaccharide, which was transformed into the trisaccharide acceptor, by removal of theO-acetyl group. Glycosylation of this acceptor with methyl 3-O-acetyl-4,6-O-benzylidene-2-deoxy-2-phthalimido-l-thio-β-D-galactopyranoside gave the globotetraose derivative, which was transformed into the acceptor12by removal of the phthaloyl andO-acetyl groups followed byN-acetylation. DMTST promoted coupling of this acceptor with 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-l-thio-β-D-galactopyranoside afforded the desired sialyl globopentaoside derivative in good yield, which was transformed, by removal of the benzyl and benzylidene groups followed byO-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group and subsequent imidate formation, into the final glycosyl donor17. Condensation of this imidate derivative with (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (18) gave the β-glycoside, which on channeling through selective reduction of the azido group, coupling of the amino group with octadecanoic acid,O-deacylation and saponification of the methyl ester group, gave the title compound, sialyl globopentaosyl ceramide. The positional isomer was also obtained by coupling of the globotetraose acceptor with methylO-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→6)-2,4-di-O-benzoyl-3-O-benzyl-1-thio-β-D-galactopyranoside, followed by essentially the same procedure employed for the synthesis of sialyl globopentaosyl ceramide.

ISSN:0732-8303    

DOI:10.1080/07328309608005436

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Stereocontrolled synthesis of α and β linked seleno-disaccharides is achieved by reaction of a diglycosyl-diselenide with a deoxyhalo sugar derivative under reducing conditions.

ISSN:0732-8303    

DOI:10.1080/07328309608005437

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

2-Azido-3,4,6-tri-O-benzyl-2-deoxy-d-galacto, gluco and mannopyranoses (1, 2, 3) were oxidized with DMSO in the presence of acetic anhydride. From1and2the corresponding lactone derivatives were obtained in good yield (89-92%), whereas from3, glucono-1,5-lactone was obtained (92%) after complete epimerization at C-2. 2-N-Acetylamino-3,4,6-tri-O-benzyl-2-deoxy-d-galacto, gluco and mannopyranoses (7, 8, 9) were obtained from the corresponding 2-azido phenylselenoglycopyranosides (13, 14, 15) by reduction,N-acetylation and hydrolysis catalyzed by mercury trifluoroacetate. Oxidation of7and8by tetra-n-propylammonium tetra-oxoruthenate (VII) in the presence of 4-methylmorpholine-N-oxide afforded the corresponding lactones in good yield (90%) and high purity. Epimerization at C-2 occurred during oxidation of9and perbenzylatedd-glucono-1,5-lactone (11) was obtained (90%).

ISSN:0732-8303    

DOI:10.1080/07328309608005438

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

α,β-(1→4)-Glucan oligosaccharides were prepared as models for heparan sulfate with the simplifying assumptions that carboxyl-reduction and sulfation of heparan sulfate does not decrease the SMC antiproliferative activity and thatN-sulfates in glucosamines can be replaced byO-sulfates. The target saccharides were synthesized using maltosyl building blocks. Glycosylation of methyl 2,3,6-tri-O-benzyl-α-D-glucopyranoside (1) with hepta-O-acetyl-α-maltosyl bromide (2) furnished trisaccharide3which was deprotected to α-D-Glc-(1→4)-β-D-Glc-(1→4)-α-D-Glc(1→OCH3) (5) or, alternatively, converted to the trisaccharide glycosyl acceptor (8) with one free hydroxyl function (4″-OH). Further silver triflate mediated glycosylation with glucosyl or maltosyl bromide followed by deblocking gave the tetrasaccharide β-D-Glc-(1→4)-α-D-Glc-(1→4)-β-D-Glc-(1→4)-α-D-Glc-(1→OCH3) (11) and the pentasaccharide [α-D-Glc-(1→4)-β-D-Glc-(1→4)]2-α-D-Glc-(1→OCH3) (14). The trisaccharides3, 4, 6, and8as well as pentasaccharide12were fully characterized by1H,3, 8and12also by13C NMR spectroscopy. Assignments were possible using 1D TOCSY, in some cases supplemented by 2D T-ROESY,1H,1H 2D COSY, and1H-detected one-bond and multiple-bond1H,13C 2D COSY experiments.

ISSN:0732-8303    

DOI:10.1080/07328309608005439

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A picomole determination of the absolute configurations of amino deoxy sugars was demonstrated through the derivatization at the anomeric carbon with a fluorescent chiral reagent, (S)-(+)-TBMB carboxylic acic, followed by the HPLC separations of the derived diastereomeric isomers. A new chemical procedure was developed to convert amino deoxy sugars into per-NH,O-acetylated glycosyl chlorides prior to derivatization with the reagent.

ISSN:0732-8303    

DOI:10.1080/07328309608005440

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

This paper reports a simple method for the preparation of isopropylidene carbohydrates using clay as a catalyst. Treatment of various monosaccharides and/or ribonucleosides with acetone in the presence of clay such as a montmorillonite K 10 (K 10) under mild reaction conditions gave isopropylidene carbohydrates (1–7) in good yields.

ISSN:0732-8303    

DOI:10.1080/07328309608005441

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Reaction of 2-O-unprotected 1-O-silyl-protected D-glucose and D-galactose derivatives5a-dwith benzyl bromide in the presence of sodium hydride as the base afforded 1-O-benzyl 2-O-silyl derivatives6aα/β -6dα/β. Thus, prior to anomericO-benzylation,trans-1,2-silyl group migration takes place. Ensuing removal of the 2-O-silyl group furnishes 2-O-unprotected compounds8aα/β -8dα/β, which are useful building blocks. More prone to 1-O-silyl group migration is mannose as shown for derivatives of 4,6-O-benzylidene-D-mannose9.Cis-1,2- andcis-2,3-silyl group migrations affording compounds15and13were already observed on deacetylation of the thexyldimethylsilyl 2,3-di-O-acetyl derivative12β under Zemplén conditions.

ISSN:0732-8303    

DOI:10.1080/07328309608005442

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor