摘要:

Negative-ion, chemical-ionization mass spectra ofp-toluenesulfonates1-6, 2-naphtha-lenesulfonates7-10, andp-nitrobenzenesulfonate11show that these compounds readily form radical anions in the gas phase. Regardless of the structure of the carbohydrate portion of the molecule, tosylate radical anions fragment by cleavage of the sulfur-carbon bond. Changes in the sulfonic acid portion of the molecule open new reaction pathways. The radical anions derived from compounds7-10break carbon-oxygen and sulfur-oxygen bonds in addition to the sulfur-carbon bond cleavage observed forp-toluenesulfonates.

ISSN:0732-8303    

DOI:10.1080/07328309808007458

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

5-Azido-3-oxa-l-pentanol was prepared from 2-(2-chloroethoxy)ethanol and used as a spacer in the chemical synthesis of the trisaccharide β-D-Gal-(1→4)-[α-L-Fuc-(1→3)]-GlcNAc and the tetrasaccharide α-L-Fuc-α-(1→2)-β-D-Gal-(1→4)-[α-L-Fuc-(1→3)]-GlcNAc that represent the epitopes defining the human blood groups Lexand Ley. The classical 4-methoxybenzyl group and the remarably acid-stable 3-methoxybenzyl group were compared as temporary protective groups for position 3 at the glucosamine unit to circumvent the problems associated with the simultaneous presence of allyl and azido groups. The resulting oligosaccharides were coupled to proteins with high efficiency.

ISSN:0732-8303    

DOI:10.1080/07328309808007459

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Several oligosaccharides containing 3,6-branched-α-D-mannopyranosides were obtained by selective glycosylation of 5-azido-3-oxapentyl α-D-mannopyranoside with acetobromosugars. After deacetylation and reduction of the spacer azido group, the oligosaccharides were coupled with the activated hemisuccinate derivatives of cholesterol and 1,2-di-O-alkylglycerol. The neoglycolipids so obtained were characterized by NMR spectroscopy and will be used as liposome coating molecules for targeting entrapped antigens.

ISSN:0732-8303    

DOI:10.1080/07328309808007460

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Lithium diphenylcuprate treatment of methyl 2,3-anhydro-4,6-O-benzylidene-D-pyranosides in which the anomeric substituent and the three-membered rings arecisoriented furnished the expectedtrans-diaxial opening products. When the relationship between the anomeric group and the epoxide wastrans, the same experimental conditions led only to recovered starting material. Cyano cuprates of the type R2CuCNLi2added stereoselectively to carbohydrate ketones at C-2 and C-3 from the opposite side relative to the anomeric substituent.

ISSN:0732-8303    

DOI:10.1080/07328309808007461

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The structure of glucose oligomers obtained by sonochemical glucose polymerization in dodecanol under Fischer glycosylation conditions was investigated. Oligomers having a degree of polymerization up to 23 were observed, with a mean value higher for the sonocatalyzed reaction compared to classical heating, as revealed by mass spectroscopy using the MALDI-TOF technique. The presence of anhydro terminal units was also ascertained by this method. Glycosidic bond types and branching ratios were evaluated after chemical degradation of the oligomers.

ISSN:0732-8303    

DOI:10.1080/07328309808007462

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The synthesis of laminin hexasaccharide analogue di-O-[Gal-β-(1→4)-Glc-β]-(1→2)-(1→6)-man-α-(1→6)-man-α-Me derivative (1) was achieved with 1,2-anhydromannopyranose benzyl ether (3) as the key intermediate. Coupling of3with methyl 2,3,4-tri-O-benzyl-α-D-mannopyranoside (4) promoted by ZnCl2gave methyl 2,3,4-tri-O-benzyl-6-O-(3,4,6-tri-O-benzyl-α-D-mannopyranosyl)-α-D-mannopyranoside (2a). Selective 6-O-debenzylation of2bwith ZnCl2-Ac2O-HOAc followed by coupling with acetobromolactopyranose afforded1.

ISSN:0732-8303    

DOI:10.1080/07328309808007463

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The conformations of crystalline 6-C-(benzothiazol-2-yl)sulfonyl-6-deoxy-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose (1) andSR-6-deoxy-1,2:3,4-di-O-isopropylidene-6-C-(2-pyridyl)sulfinyl-α-D-galactopyranose (2) have been determined by X-ray diffraction. The crystal structure of1belongs to the monoclinic P21space group witha= 10.779(4),b= 10.431(6),c= 10.258(6) Å) and β =113.51(2)°C. The crystal structure of2belongs to the tetragonal space P41212 witha= 10.652(2) andc= 33.037(4) Å. The molecular features of these two compounds are compared with those of the related 6-S-(benzoxazol-2-yl)-1,2:3,4-di-O-isopropylidene-6-thio-α-D-galactopyranose (3).

ISSN:0732-8303    

DOI:10.1080/07328309808007464

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Several isomeric glycosyl glycerols were synthesized. Acetylated allyl glycosides of D-glucose and D-galactose were transformed into l-O-(glycopyranosyl)-rac-glycerols in a three step procedure via the corresponding 2,3-epoxypropyl glycosides and the peracetylated glycosyl glycerols. Tetra-O-benzyl-D-glucose was glycosylated with 1,3-di-O-benzylglycerol to give the α-aiomer preferentially. The 2-O-(tetra-O-acetyl-β-glycopyranosyl)-sn-glycerols and 2-O-(β-glycopyranosyl)-sn-glycerols of D-glucose, D-galactose andN-acetyl-D-glucosamine and the corresponding α-derivatives of D-mannose were synthesized by selective glycosylation methods from 1,3-di-O-benzylglycerol and 1,3-O-benzylideneglycerol, respectively, and activated sugar compounds followed by hydrogenolysis. After long chain acylation and selective deacetylation the 1,3-di-O-acyl-2-O-(β-glycopyranosyl)-sn-glycerols of D-glucose, D-galactose andN-acetyl-D-glucosamine and the corresponding α-derivative of D-mannose were synthesized.

ISSN:0732-8303    

DOI:10.1080/07328309808007465

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The potent immunostimulant and antitumor activity of trehalose 6,6′-dimycolates from mycobacteria has led to a great deal of interest in the synthesis of these glycolipids and their analogs.1J To circumvent the formation of 3,6-anhydro derivatives and other by-products resulting from partial protection strategies, many of the synthetic routes to symmetrical 6,6′-diesters (including dimycolates) of trehalose have utilized trehalose intermediates fully protected at the secondary hydroxyl position.2,3Recently, we described the synthesis of one such intermediate, 2,3,4,2′,3 ′,4′-hexakis-O-trimethylsilyl-aptrehalose (l), directly from trehalose dihydrate via a novel persilylatioddesilylation protocol.4Diol 1 and related derivatives have been employed in the preparation of trehalose 6,6′-diesters both by direct acylation methods3,5-8and by nucleophilic displacement of 6,6′-dideoxy derivatives possessing various leaving groups on the 6 and 6′-positions.7-12

ISSN:0732-8303    

DOI:10.1080/07328309808007466

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Considerable effort has been devoted to the development of new methods for α-selective sialylation due to the growing importance of the synthetic sialoglycoconjugates in glycobiology3. The synthesis of α-sialoside has been establised by chemical routes,4which often involve many steps and are complicated. The promising chemoenzymatic procedure through the use of sialyltransferases has already become a preparative technique.5However, laborious isolation and the pronounced acceptor specificity of the transferases limit their synthetic potential. Recently, a novel procedure for α-sialylation has been reported, which uses sialosides of synthetic substrate as donors and is catalyzed by sialidase in place of sialyltransferase. Thiem et a1.6have reported the enzymatic synthesis of α(2→6)-linked sialyl galactose, glucose, lactose and lactosamine in preference to the corresponding α(2→3)-linked derivatives employing sialidase fromvibrio cholerae, while Ajisaka et al.7have synthesized α(2→3)-linked sialyl lactose and lactosamine with sialidase from new castle disease virus.

ISSN:0732-8303    

DOI:10.1080/07328309808007467

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor