摘要:

A total synthesis of tumor-associated glycolipid antigen sialyl Lea, and a first total synthesis of glycononaosyl ceramide with a dimeric Leasequence are described. Regio-and stereoselective coupling of sialyl donor12with suitably protected Leatrisaccharide fluoride17was performed by orthogonal glycosylation to give the expected tetrasaccharide18in good yield. Glycosylation of its acetate19with lactose derivative8by use of Cp2HfCl2-AgOTf as a promoter, gave the desired hexasaccharide20. On the other hand, glycosylation between sialyl Leatetrasacchande donor34and Leapentasaccharide acceptor35under the agency of PhSeOTf afforded the desired nonasaccharide36. After replacement of the benzyl groups in20and36by acetyl groups, the anomeric acetate was transformed into the α-trichloroacetoimidates23, 39and the fluoride derivative40. The crucial couplings of23, 39and40with azidosphingosine derivative3or ceramide derivative4were executed to afford β-glycosides24and41. Compound24was converted to26viareduction of the azide group followed byN-acylation. The target gangliosides1and2were obtained from26and41, respectively, by selective cleavage of the methyl ester, conversion of theN-phthalimido group to theN-acetamido group, andO-deprotection.

ISSN:0732-8303    

DOI:10.1080/07328309808002343

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A stereocontrolled synthesis of Lexoligosaccharide derivatives using a facile one-pot, two-step glycosylation based on the “Armed-Disarmed” concept are described. The first coupling of phenylO-(2,6-di-O-benzoyl-3,4-O-isopropylidene-β-D-galacto-pyranosyl)-(1→4)-2,6-di-O-benzoyl-1-thio-β-D-glucopyranoside (2) with phenyl 2,3,4-tri-O-benzyl-1-thio-β-L-fucopyranoside (3) usingN-iodosuccinimide (NIS)-trifluoromethanesulfonic acid (TfOH) gave the trisaccharide (8) which was subjected to the second condensation without purification with several acceptors such as ethyl 2,4,6-tri-O-benzyl-β-D-galactopyranoside (4), ethyl 2,6-di-O-benzoyl-β-D-galactopyranoside (5), ethylO-(2,6-di-O-benzyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (6), and ethylO-(2,6-di-O-benzoyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (7), to afford the desired Lextetra- and pentasaccharides in good yields, respectively.

ISSN:0732-8303    

DOI:10.1080/07328309808002344

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A novel regioselectivity was observed in the silver salt promoted glycosylation of 2-(trimethylsilyl)ethyl 3′-O-benzyl-β-D-lactoside using acetobromogalactose as the glycosyl donor. The resulting trisaccharide, obtained in 67% yield, was shown to have the newly formed β-glycosidic linkage at theO-6 position of the lactoside. This was confirmed by synthesis of the authentic product by an alternate route. The novel regioselectivity observed is attributed to the presence of the axially disposed 4′-OH group in the lactoside acceptor.

ISSN:0732-8303    

DOI:10.1080/07328309808002345

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Treatment of per-O-acetylated mono- and di-saccharides with (alkyl/arylthio)tri-methylsilane and iodine at ambient temperature results in the formation of the corresponding 1,2-trans-1-thioglycosides in very high yield. In the case of higher boiling thiols such as ethanethiol, the reaction can be effectively carried out in the presence of the thiol itself instead of the silylated derivative, but the reaction is not stereospecific. Moreover, in the latter reactions a portion of the starting material remains unchanged even on prolonged reaction. With β-D-glucose pentaacetate (11) as the starting material, its epimerisation occurred during the reaction and therefore the recovered starting material was of α-D-configuration. In addition, the methyl disulphide-hexamethyldisilane system has been found to serve as an effective and cheaper alternative to the expensive (methylthio)-trimethylsilane.

ISSN:0732-8303    

DOI:10.1080/07328309808002346

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Regioselective protection ofN-acetyllactosamine with triphenylmethyl (trityl) and pivaloyl groups afforded the corresponding 3, 2′, 4′-tri- and 2′,4′-dihydroxyl derivatives in a few steps. respectively; these derivatives were used efficiently for the syntheses of the title compounds fromN-acetyllactosamine in 46% (7 steps) and 19% (8 steps) overall yields. respectively.

ISSN:0732-8303    

DOI:10.1080/07328309808002347

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Sulfo Lewisxanalog containing 1-deoxynojirimycin (13) has been efficiently synthesized. Glycosidation of ethyl 2,3,4-tri-O-benzyl-1-thio-β-D-fucopyranoside (5) withO-2,6-di-O-benzoyl-3,4-isopropylidene-β-D-galactopyranosyl)-(1→4)-2,6-di-O-benzoyl-N-benzyloxycarbonyl-1,5-dideoxy-1,5-imino-D-glucitol (4), prepared fromO-β-D-galactopyranosyl-(1→4)-1,5-dideoxy-1,5-imino-D-glucitol (1)via3 steps, and subsequent acid hydrolysis of the isopropylidene group gave the desired trisaccharide diol derivative (7) in good yield. Compound7was easily converted into 3′-O-sulfo Lewisxanalog (13)via6 steps in high yield.

ISSN:0732-8303    

DOI:10.1080/07328309808002348

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Thexyldimethylsilyl 4,6-O-benzylidene-2-deoxy-2-trichloroethoxycarbonylamino-β-D- glucopyranoside (4), having the 3-hydroxy group unprotected, is a versatile starting material for the synthesis of glucosamine containing oligosaccharides. Thus, reaction with galactosyl donor5or fucosyl donor6afforded the desired β(1-3)- and α(1-3)-linked disaccharides7and8, respectively, in high yields. Reductive opening of the benzylidene moieties in7and8gave access to the 4-hydroxy groups in9and10. Ensuing fucosylation of9or galactosylation of10led to Lewis A (Lea) and Lewis X (Lex) trisaccharide building blocks13and14, respectively. Their transformation into glycosyl donors19and20and subsequent reaction with 3b-O-unprotected lactose derivative23as acceptor furnished the Lea−and Lexpentasaccharide precursors24and25. Exchange of theN-trichloroethoxycarbonyl group for anN-acetyl group and removal of theO-benzyl andO-acetyl protective groups afforded the desired Lea−and Lex−pentasaccharides1and2.

ISSN:0732-8303    

DOI:10.1080/07328309808002349

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Glycosyl-N-allyl carbamates, obtained by reaction of anomerically unprotected saccharides with allyl isocyanate, can be activated by an electrophile-induced cyclisation and reacted with glycosyl acceptors to form the corresponding oligosaccharides By this method the mucin core 2 trisaccharide2has successfully been synthesized. Due to the mild glycosylation conditions even 1-O-acetyl protected glycosyl acceptors can be used. This was demonstrated in the synthesis of a 1,6-linked glucosyl trisaccharide whereby a reptitious glycosylation strategy could be applied.

ISSN:0732-8303    

DOI:10.1080/07328309808002350

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Boron trifluoride etherate-induced glucosylation of methanol, 1-propanol, 2-propanol, 2-bromoethanol, and 3-bromo-2-(bromomethyl)propan-1-ol, using 1,2,3,4,6-penta-O-acetyl-β-D-glucopyranose as donor, gave the corresponding β-glucopyranosides. The α-glucosides and 1,2,3,4,6-penta-O-acetyl-α-D-glucopyranose were formed as byproducts in varying amounts, according to GLC analysis. The propensity of the different glucopyranosides to anomerize was determined in separate experiments.

ISSN:0732-8303    

DOI:10.1080/07328309808002351

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Various glycals underwent smooth Lewis acid-catalysed allylic rearrangement reactions withO-nucleophiles to yield 2,3-unsaturated glycoside derivatives. In the hexose series predominantly α-D-, and in the pentose series β-D-anomers resulted. Among others Ω-cyano- as well as Ω-benzyloxycarbonylamino functionalised alcohols could be used successfully. With diols the corresponding 1,1′-bridged disaccharides could be obtained.

ISSN:0732-8303    

DOI:10.1080/07328309808002352

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor