期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 126, 期 26, 页码 8232-8236出版社
AMER CHEMICAL SOC
DOI: 10.1021/ja048070j
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资金
- NIGMS NIH HHS [GM 57335] Funding Source: Medline
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 O(3) 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.
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