摘要:

Two derivatives of β-maltosyl-(1→4)-trehalose monodeoxygenated at positions 4 or 4′″ have been synthesized in [2+2] block syntheses. After the preparation of precursors with only one free hydroxyl group the deoxy function was introduced by a Barton-McCombie reaction. Thus, glycosylation of 2,3,6-tri-O-benzyl-α-D-glucopyranosyl 2,3,6-tri-O-benzyl-α-D-glucopyranoside (4) with octa-O-acetyl-β-maltose (3) gave tetrasaccharide5with only one free hydroxyl group at the 4-position. The 4′-position of an allyl maltoside was available selectively after removal of a 4′,6′-cyclic acetal and selective benzoylation of the 6′-position. Reduction of this derivative11afforded allylO-(2,3-di-O-acetyl-6-O-benzoyl-4-deoxy-α-D-glucopyranosyl)-(1→4)-2,3,6-tri-O-acetyl-β-D-glucopyranoside (14), which was deallylated, activated as an trichloroacetimidate, and coupled to 2,3-di-O-benzyl-4,6-O-benzylidene-α-D-glucopyranosyl 2′,3′,6′-tri-O-benzyl-α-D-glucopyranoside (20). Several compounds were fully characterized by1H NMR spectroscopy. Deprotection furnished the monodeoxygenated tetrasaccharides9and23.

ISSN:0732-8303    

DOI:10.1080/07328309608005691

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The clean one step synthesis of the amphiphilic α-, β-, and γ-cyclodextrins starting from per-(6-bromo-6-deoxy)-α-, -β-, and -γ-cyclodextrins is described. The role of the lipophilic tail is played by various aryl groups (phenyl,p-bromophenyl,p-O-butoxyphenyl,p-pentylphenyl, ando-,m-, andp-nitrophenyl) linked by a thioether bridge to the position C-6 of each glucopyranose unit. The yields of the S-alkylation reactions were very high (85-95%).

ISSN:0732-8303    

DOI:10.1080/07328309608005692

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Stereospecific synthesis of 1,2-anhydromanno-, lyxo-, gluco-, and xylofuranose perbenzyl ethers was successfully achievedviaintramolecularSN2 reaction of the corresponding C-1 alkoxide with C-2 bearing tosyloxy group. The key intermediates, furanose 2-sulfonates, were prepared from the corresponding 1,2-diols and tosyl chloride under phase transfer conditions in good yields. Condensation of the anhydro sugars with 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose orN-benzyloxycarbonyl L-serine methyl ester in the absence of catalyst gave 1,2-trans-linked glycofuranosides in high yield.

ISSN:0732-8303    

DOI:10.1080/07328309608005693

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The primary alcohol groups of ten polysaccharides, with widely different structures and water solubilities, were oxidized to carboxyl groups using 2,2,6,6-tetramethyl-1-piperidine oxoammonium ion (TEMPO) at pH 10.8 and 0°C. The yield and selectivity for the primary alcohol group were high for all ten of the polysaccharides. The oxidation greatly increased the water-solubility of the polysaccharides. Water-insoluble polysaccharides such as amylose, cellulose, and chitin became water-soluble to the extent of approximately 10% (w/v). The water-soluble polysaccharides had their degree of solubility doubled or tripled. The specific optical rotation, viscosity, and gelling properties with calcium ion were determined. The oxidized polysaccharides are new anionic polymers with unique structures that could have application as gums, gels, and films.

ISSN:0732-8303    

DOI:10.1080/07328309608005694

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The preparation of 9-O-glycosyloxime derivatives of erythromycin A (1) and tylosin (2) is reported. Access to this new class of macrolides was achieved from (E)-9-oxime of erythromycin A (3) and 9-oxime of tylosin 20-(1,3-dithiane) (4), by successful displacement of triflates of suitably protected carbohydrates.

ISSN:0732-8303    

DOI:10.1080/07328309608005695

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Glycosylation of an 8-unprotected sialyl fluoride16with 2β-chloro-3β-phenylthio-Neu5Ac2gave the desired α-disialate23. Subsequent glycosylation of a thiolactoside19with the disialyl fluoride23gave the tetrasaccharide28. Synthesis of GD31was realized by condensation of the tetrasaccharide28with azidosphingosine31, following our previously reported GM3synthesis procedure.

ISSN:0732-8303    

DOI:10.1080/07328309608005696

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Hydroxyl group deprotonation of the α and β anomers of methyl 3-O-benzyl-2,6-dideoxy-D-arabino-hexopyranoside (1and2) occurs readily in the gas phase to produce the corresponding anions3and4, respectively. Collisionally activated dissociation (CAD) of these anions causes fragmentation reactions that include ring opening, E2 elimination, and decarbonylation. Mechanisms for these reactions are proposed, and these mechanisms are supported by study of partially deuterated analogs of1and2.

ISSN:0732-8303    

DOI:10.1080/07328309608005697

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor