摘要:

Glycosides are widely occurring natural compounds. Among them, ergot alkaloids, therapeutically potent substances,1have been isolated only as mono-2-4and oligofructosides.4,5The formation of these metabolic by-products in saprophytic cultures of some Claviceps strains grown in sucrose media is catalysed by invertase present in fungal mycelia.3The other O-glycosides of ergot alkaloids, obtained either synthetically6using peracetylated glycosyl bromides and Ag2CO3as catalyst, or enzymatically7-12have a β-configuration at the sugar anomeric centre. Preparation of some ergot alkaloid α-glycosides needed to complete our studies regarding their potential immunomodulatory and antiviral activities is the subject of this paper.

ISSN:0732-8303    

DOI:10.1080/07328309808007468

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Caryophyllose 1 is a novel twelve carbon 4-C-branched monosaccharide and a component of the polysaccharide chains found in the lypopolysaccharide fraction fromPseudormnas caryophyllibacterium.1Its absolute stereochemistry was elucidated2by applying the exciton chiral coupling method to two fragments obtained by NaIO4, oxidation of the polysaccharide chain. The absolute configuration of a chiral secondary alcohol can be defined by Mosher's method.3It analyzes the signs of the differences between the chemical shifts of the protons vicinal to the chiral Center in the (S)- and (R)-α-methoxy-α-trifluoromethylphenylacetate (MPTA) esters obtained from the compound. However, the Mosher ester methodology failed to give completely reliable results when applied to the bisisopropylidene derivative 2 of caryophyllose. In fact, whereas ΔδH(δR-δS) was positive for 3′-H and negative for 5′-H, indicating R configuration for the 4′ chiral centre, it was positive for 1-H but of opposite sign for the two protons at C-3 (negative for 3eqand positive for 3ax), failing to indicate the configuration at C-2. This result, however, was in line with Mosher's warning3about circumspection in applying his correlation to molecules which “contain additional chiral centres, possess heteroatoms, or show unusual conformational restraints”. It also prompted us to an investigation of applicability of Mosher arguments to sugar MPTA esters, in view of our interest in carbohydrate structure elucidation.

ISSN:0732-8303    

DOI:10.1080/07328309808007469

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The ability to couple carbohydrate entities to produce glycosides or higher oligomers is an important goal of synthetic organic chemistry.1For the past several decades, methods to construct glycosidic linkages have improved as a result of the development of glycosidation procedures.2However, owing to their structural complexity, synthesis of oligosaccharides is still a laborious task compared with the synthesis of oligopeptides and oligonucleotides. Many additional sugar derivatives which can improve and simplifjr synthetic procedures of oligosaccharides are needed.

ISSN:0732-8303    

DOI:10.1080/07328309808007470

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0732-8303    

DOI:10.1080/07328309808007471

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0732-8303    

DOI:10.1080/07328309808007472

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor