摘要:

A new procedure is described for oligosaccharide sequencing that combines HPLC purification, the sensitive technique of fluorescence detection, and partial polymer degradation by ionic hydrogenation with component determination by direct chemical ionization mass spectrometry (DCI-MS) and GC-MS. The methodology is demonstrated for a series of model compounds and is shown to provide linkage information as well as sugar sequence.

ISSN:0732-8303    

DOI:10.1080/07328308308058806

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The cyanomethylidenic sugars 1 -3 (α-D-erythroconfiguration) reacted with various phosphorus nucleophiles, gave branched-chain phosphorus-bearing sugar derivatives. The reactions were not discriminating towards the geometrical isomerism of the starting material. For reactions implying the formation of a phosphoryl group (P-OR →P=O) a hydroxyl group was necessary, either in the solvent or the C-5 position of the substrate. In the cases where the substrate was not hydroxylated at C-5, an exo attack leading to the D-xyloisomer took place when kinetic control was operating, whereas ″thermodynamic control led to the endo (D-ribo) isomer. A hydroxyl group at the C-5 position of the substrate directed the nucleophilic conjugate addition towards the exo face. When an asymmetric phosphorus atom was formed (cyclic compounds9and10), the epimers could be separated and their configuration established. The benzoylmethylidenic sugar12behaved somewhat differently because of the larger charge delocalization in the intermediate enolate than in its nitrogen analog. This enolate effected readily (presumably intramolecularly) the elimination reaction leading to phosphoryl formation. No hydroxyl group was necccessary. The relationship between the steric course of the reaction and its type of control which supposes that elimination occurs much slower than addition did not apply here.

ISSN:0732-8303    

DOI:10.1080/07328308308058807

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The 360 MHz1H NMR spectra of four closely related synthetic oligomannosides have been completely assigned. This was achieved by a combination of spin-tickling difference spectroscopy and spectral simulation. The compounds are: methyl 3-0-(α-D-mannopyranosyl)-α-D-mannopyranoside (II3), methyl 6-0-(α-D-mannopyranosyl) -α-D-mannopyranoside (II6), methyl 3,6-di-0-(α-D-mannopyranosyl) -α-D mannopyranoside (III) and methyl 3-0-(α-D-mannopyranosyl)-6-0-(3-0-α-D-manno-pyranosyl-α-D-mannopyranosyl)-α-D-mannopyranoside (IV). These oligomannosides are analogues of the high mannose structures occurring naturally in theN-linked glycopeptides of glycoproteins. A number of long range chemical shift perturbations were observed which are interpreted as being of methyl mannotrioside, methyl 3,6-di-0-(α-D-mannopyranosyl)-α-D-mannopyranoside (III); the related disaccharides, methyl 6-0-(α-D-mannopyranosyl)-α-D-mannopyranoside (II6) and methyl 3-0-(α-D-mannopyranosyl)-α-D-mannopyranoside (II3); and a tetrasaccharide, methyl 3-0

ISSN:0732-8303    

DOI:10.1080/07328308308058808

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The glycosylation reaction based upon anomeric free hydroxyl group activation by its transformation into an alkcxyiminium salt by the action of theN,N-dimethylformamide/phosgene complex has been extended to the pentofuranose series. The mechanism of this glycosylation is discussed. Nine glycosides have been prepared.

ISSN:0732-8303    

DOI:10.1080/07328308308058809

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Treatment of methyl 3,4-di-O-acyl-2,6-dideoxy-α-D-ribo-hexo-pyranoside1or2with trimethylsilyl halide leads to the formation of a complex mixture of α-D-ribo-hexopyranosyl halides3or5together with the educts1or2as well as their β-anomers8or9. The bromides3and5, suitable for glycosidations, are preferably obtained by reaction of the digitoxose acetate derivatives6and7, respectively, which in turn are prepared from1and2by mild acetolysis. Further reaction of the halides3to5with trimethylsilyl halides gives rise to a quantitative formation of the 2,3,6-trideoxy-4-0-acyl-3-halo-α-D -arabino-hexopyranosyl halides10to12. In another reaction sequence starting with the olivose triacetate20the formation of10via the halide13is demonstrated. Structural evidence for the halides10to12is given by1H NMR data as well as by analyses of their glycosides14to19. The results support a mechanistic interpretation for the formation of10to12via a 3,4-acetoxonium ion as the key intermediate obtained from3by an SNfi and from13and SN2i step. Final conversion into the terminal halodeoxy compounds10to12proceeds by and SN2 reaction with the halide ion.

ISSN:0732-8303    

DOI:10.1080/07328308308058810

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Intense interest in sugar components of anthracycline antibiotics and antitumor drugs generated a need for stereoselective methods of synthesis of 2-deoxy sugar glycosides. Although several efficient procedures leading to 2-deoxy-α-glycosides were elaborated, there is no satisfactory general procedure leading to the β-anomers. The methods described are not stereoselective and involve separation of anomeric intermediates of glycosides.

ISSN:0732-8303    

DOI:10.1080/07328308308058811

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0732-8303    

DOI:10.1080/07328308308058805

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor