摘要:

The synthesis of a branched trisaccharide, the repeating unit of the antigen O2 polymer containing L-rhamnose, D-mannose, and L-xylose, was achieved using orthoester formation - rearrangement strategy.

ISSN:0732-8303    

DOI:10.1080/07328309908543994

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The enzymatic synthesis of ß2-2' and ß2-1'-D- fructopyranosyl glycerol was carried out with levansucrase fromBacillus circulansorB.subtilis, using sucrose as fructosyl donor and glycerol. The specificity and efficiency of the enzyme was modified by controlling both the water and the total substrate concentrations. The products were purified by HPLC and analyzed by1H,13C NMR and GC-MS.

ISSN:0732-8303    

DOI:10.1080/07328309908543995

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Allylphosphonates can be prepared in high yields, under mild conditions and in a stereospecific way by the reaction of uloses or dialdohexoses with 1-bromo-2-propenyl phosphonate and the highly active zinc-silver/graphite surface compound.

ISSN:0732-8303    

DOI:10.1080/07328309908543996

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The reaction of D-glucal and its derivatives with the electrophilicN-F-fluorination reagents F-TEDA tetrafluoroborate and triflate was studied by means of19F NMR spectroscopy. In all cases mixtures of 2-deoxy-2-fluoro-D-gluco- and -D-mannopyranose derivatives were formed, the ratio of which was dependent on the nature of theO-protecting groups. Concerning the products arising from the direct addition of reagents across the double bond, the D-gluco-configured compounds (13-20) generally showed higher hydrolysis rates than their D-manno-counterparts (21-28). Product separation was only achieved when single anomers (e.g., 2,4-dinitrophenyl glycosides29e/37eand disaccharidic fluorides35d/43d) or per-O-acetates (e.g.29f/37f) were formed.

ISSN:0732-8303    

DOI:10.1080/07328309908543997

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Saccharidic benzothiazol-2-yl sulfones - readily obtained through regioselective Mitsunobu thiofunctionalization followed by standard S-oxidation - can easily undergo benzothiazol-2-yl group S → O transfer when submitted to the action of a hindered base under controlled conditions. Anipso-substitution process is the key-step of this novel intramolecular rearrangement of saccharidic sulfones.

ISSN:0732-8303    

DOI:10.1080/07328309908543998

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Dithioacetals of aldopentoses (D-arabinose, D-ribose, D-xylose, and D-lyxose), aldohexoses (D-glucose, D-mannose, D-galactose), and common oligosaccharides (cellobiose, lactose, gentibiose, melibiose, maltose, and maltotriose) were conveniently prepared by reacting the corresponding free sugars respectively with benzenethiol and/or 1,3-propanedithiol at room temperature in 90% trifluoroacetic acid in much better yields than by the conventional methods.

ISSN:0732-8303    

DOI:10.1080/07328309908543999

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Treated with salicylaldehyde or its 5-methoxy derivative, a series of blocked terminal(E)-nitroenoses underwent a condensation reaction leading in fair to good yields to blocked 2-glycosyl-3-nitro-2H-chromene derivatives. Treated with cyanide, the nitro derivatives afforded 4-cyano-2-glycosyl-2H-chromenesviaan addition-elimination reaction. These two types of chromenes bearing an electron-withdrawing group have been previously shown to have antiviral or cytotoxic properties related to their electrophilicity.

ISSN:0732-8303    

DOI:10.1080/07328309908544000

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Thioglycosides are very useful glycosyl donors for the synthesis of oligosaccharides.1Frequent use of these donors is due to their ease of preparation, stability and capability of reaction in the presence of a variety of promoters like iodonium dicollidine perchlorate,2N-iodosuccinimide–triflic acid (NIS-TfOH),3dimethyl-(methylthio)sulfonium triflate,4methyl triflate,5etc. to form glycosidic bonds. In addition, the armed - disarmed glycosylation strategy6was also successfully applied and it was claimed that 2-O-substituents play the greater role in activating or deactivating a donor molecule. Thus coupling of an ethyl thioglycoside donor having a 2-O-benzyl substituent with an ethyl thioglycoside acceptor having a 2-O-acyl protecting group, proceeds with high chemoselectivity to give the desired product in good yield.2,3There are also reports on the concept of active and latent thioglycosyl donors7caused by activation or deactivation of the anomeric center. The enhanced reactivities ofp-acetamidophenyl and ethyl thioglycoside in comparison top-nitrophenyl thioglycoside are also examples of anomeric activation and deactivation.8More recently, it was reported9that the bulky dicyclohexylmethyl thioglycoside donors are much less reactive than the ethyl thioglycosides and this strategy was applied to chemoselective glycosylation utilising donors and acceptors both having either 2-O-benzyl or 2-O-acyl substituents.

ISSN:0732-8303    

DOI:10.1080/07328309908544001

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor