Document Detail

The disarming effect of the 4,6-acetal group on glycoside reactivity: torsional or electronic?
MedLine Citation:
PMID:  15281809     Owner:  NLM     Status:  MEDLINE    
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.
Henrik Helligsø Jensen; Lars Ulrik Nordstrøm; Mikael Bols
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of the American Chemical Society     Volume:  126     ISSN:  0002-7863     ISO Abbreviation:  J. Am. Chem. Soc.     Publication Date:  2004 Aug 
Date Detail:
Created Date:  2004-07-29     Completed Date:  2004-11-01     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  7503056     Medline TA:  J Am Chem Soc     Country:  United States    
Other Details:
Languages:  eng     Pagination:  9205-13     Citation Subset:  IM    
Department of Chemistry, University of Aarhus, 8000 Aarhus C, Denmark.
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MeSH Terms
Acetals / chemistry*,  metabolism
Carbohydrate Conformation
Glycosides / chemical synthesis,  chemistry*,  metabolism
Oligosaccharides / chemistry,  metabolism
Pyrans / chemistry,  metabolism
Static Electricity
Structure-Activity Relationship
Torsion Abnormality
Reg. No./Substance:
0/Acetals; 0/Glycosides; 0/Oligosaccharides; 0/Pyrans

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