| The disarming effect of the 4,6-acetal group on glycoside reactivity: torsional or electronic? | |
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MedLine Citation:
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PMID: 15281809 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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An evaluation of whether the well-known deactivating effect of a 4,6-acetal protection group on glycosyl transfer is caused by torsional or an electronic effect from fixation of the 6-OH in the tg conformation was made. Two conformationally locked probe molecules, 2,4-dinitrophenyl 4,8-anhydro-7-deoxy-2,3,6-tri-O-methyl-beta-D-glycero-D-gluco-octopyranoside (18R) and the L-glycero-D-gluco isomer (18S), were prepared, and their rate of hydrolysis was compared to that of the flexible 2,4-dinitrophenyl 2,3,4,6-tetra-O-methyl-beta-D-glucopyranoside (21) and the locked 2,4-dinitrophenyl 4,6-O-methylidene-2,3-di-O-methyl-beta-D-glucopyranoside (26). The rate of hydrolysis at pH 6.5 was 21 > 18R > 18S > 26, which showed that the deactivating effect of the 4,6-methylene group is partially torsional and partially electronic. A comparison of the rate of acidic hydrolysis of the corresponding methyl alpha-glycosides likewise showed that the probe molecules 17S and 17R hydrolyzed significantly slower than methyl tetra-O-methyl-glucoside 19, confirming a deactivating effect of locking the saccharide in the (4)C(1) conformation. The experiments showed that the hydroxymethyl rotamers deactivate the rate of glycoside hydrolysis in the order tg >> gt > gg. |
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Authors:
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Henrik Helligsø Jensen; Lars Ulrik Nordstrøm; Mikael Bols |
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Publication Detail:
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Type: Journal Article; Research Support, Non-U.S. Gov't |
Journal Detail:
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Title: Journal of the American Chemical Society Volume: 126 ISSN: 0002-7863 ISO Abbreviation: J. Am. Chem. Soc. Publication Date: 2004 Aug |
Date Detail:
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Created Date: 2004-07-29 Completed Date: 2004-11-01 Revised Date: 2008-11-21 |
Medline Journal Info:
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Nlm Unique ID: 7503056 Medline TA: J Am Chem Soc Country: United States |
Other Details:
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Languages: eng Pagination: 9205-13 Citation Subset: IM |
Affiliation:
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Department of Chemistry, University of Aarhus, 8000 Aarhus C, Denmark. |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Acetals
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chemistry*,
metabolism Carbohydrate Conformation Glycosides / chemical synthesis, chemistry*, metabolism Hydrolysis Kinetics Oligosaccharides / chemistry, metabolism Pyrans / chemistry, metabolism Static Electricity Structure-Activity Relationship Torsion Abnormality |
| Chemical | |
Reg. No./Substance:
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0/Acetals; 0/Glycosides; 0/Oligosaccharides; 0/Pyrans |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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