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Synthesis and NMR spectroscopic analysis of acylated pentasaccharide fragments of mycobacterial arabinogalactan.
MedLine Citation:
PMID:  20963246     Owner:  NLM     Status:  In-Data-Review    
Abstract/OtherAbstract:
The mycolyl-arabinogalactan (mAG) complex, a large glycolipid composed of arabinofuranose and galactofuranose monosaccharides and mycolic acid lipids, provides mycobacteria with substantial protection from their environment. It has been proposed that the presence of flexible furanose rings in the mAG facilitates the packing of the hydrophobic mycolic acids, forming a dense protective barrier of low permeability. In a previous article, we probed this "flexible scaffold hypothesis" through the synthesis and NMR analysis of di- and trisaccharide fragments of the mAG acylated with linear fatty acids. However, we saw few conformational changes due to the presence of the acyl chains. We proposed that branched pentasaccharide glycolipids 5-8 might exhibit larger changes due to the presence of more acyl chains, and studies with these compounds are described here. The carbohydrate portion of 5-8 was synthesized in a 1 + 2 + 2 manner. First, the monosaccharide diol was treated with an excess of appropriately protected thioglycoside donor to give a trisaccharide, which, following selective deprotection to a diol, was converted to the pentasaccharide in a one-pot glycosylation. The resulting differentially protected pentasaccharide 20 gave glycolipids 5-8 upon removal of the protecting groups at the primary positions, acylation, and hydrogenolysis. The conformations of 5-8 were probed using NMR spectroscopy, and chemical shift selective filtering 1D-TOCSY spectra allowed for the determination of all the ring coupling constants. It was found that the addition of four fatty acids to the parent pentasaccharide had little effect on the conformation of the compounds in solution.
Authors:
Chunjuan Liu; Michele R Richards; Todd L Lowary
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Publication Detail:
Type:  Journal Article     Date:  2010-10-21
Journal Detail:
Title:  Organic & biomolecular chemistry     Volume:  9     ISSN:  1477-0539     ISO Abbreviation:  Org. Biomol. Chem.     Publication Date:  2011 Jan 
Date Detail:
Created Date:  2010-12-14     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101154995     Medline TA:  Org Biomol Chem     Country:  England    
Other Details:
Languages:  eng     Pagination:  165-76     Citation Subset:  IM    
Affiliation:
Alberta Ingenuity Centre for Carbohydrate Science and Department of Chemistry, The University of Alberta, Gunning-Lemieux Chemistry Centre, Edmonton, Alberta, Canada. tlowary@ualberta.ca.
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