Benzylidene Acetal Fragmentation Route to 6-Deoxy Sugars:  Direct Reductive Cleavage in the Presence of Ether Protecting Groups, Permitting the Efficient, Highly Stereocontrolled Synthesis of β-d-Rhamnosides from d-Mannosyl Glycosyl Donors. Total Synthesis of α-d-Gal-(1→3)-α-d-Rha-(1→3)- β-d-Rha-(1→4)-β-d-Glu-OMe, the Repeating Unit of the Antigenic Lipopolysaccharide from Escherichia hermannii ATCC 33650 and 33652

An approach to the stereocontrolled synthesis of beta-d-rhamnopyranosides is described in which 2,3-O-benzyl or related 4,6-O-[alpha-(2-(2-iodophenyl)ethylthiocarbonyl)benzylidene]-mannosyl thioglycosides are first used to introduce the beta-d-mannopyranoside linkage in high yield and stereoselectiv...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2004-07, Vol.126 (26), p.8232-8236
Main Authors: CRICH, David, YAO, Qingjia
Format: Article
Language:English
Subjects:
Benzylidene Compounds - chemistry
Carbohydrates with 4, 5, 6, ... C atoms, dissacharides and oligosaccharides
Carbohydrates. Nucleosides and nucleotides
Chemistry
Escherichia - chemistry
Exact sciences and technology
Glycosylation
Lipopolysaccharides - chemistry
Mannosides - chemistry
Molecular Structure
Oligosaccharides - chemical synthesis
Oligosaccharides - chemistry
Organic chemistry
Preparations and properties
Rhamnose - chemical synthesis
Rhamnose - chemistry
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Summary:An approach to the stereocontrolled synthesis of beta-d-rhamnopyranosides is described in which 2,3-O-benzyl or related 4,6-O-[alpha-(2-(2-iodophenyl)ethylthiocarbonyl)benzylidene]-mannosyl thioglycosides are first used to introduce the beta-d-mannopyranoside linkage in high yield and stereoselectivity. Following glycosylation, treatment with tributyltin hydride in toluene at reflux brings about reductive radical fragmentation directly to the 6-deoxy sugar in high yield. A variation of these donors bearing a carboxylated donor on O3 is a highly alpha-selective mannosyl and, after radical fragmentation, alpha-d-rhamnosyl donor. Using this stereoselective glycosylation/radical-fragmentation approach, a concise synthesis of the title tetrasaccharide is realized in which both the beta-d- and alpha-d-rhamnopyranosyl units are obtained in a single step by a double radical fragmentation of the modified benzylidene acetals.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja048070j