Transglucosidation of methyl and ethyl D-glucofuranosides by alcoholysis

The acid catalyzed ethanolysis of methyl 5-O-methyl-alpha- and -beta -D-glu cofuranoside and the analogous methanolysis of ethyl 5-O-methyl-alpha- and -beta -D-glucofuranoside have been investigated. For all four reactions, th e primarily formed transglycosylation product was a single glycoside that h ad the opposite anomeric configuration to the starting material. This stron gly indicates that a D-glucose methyl ethyl acetal is first formed and is t hen ring closed by a nucleophilic attack by HO-4, giving either the startin g material or a transglycosylation product with the opposite anomeric confi guration. Low percentages of the methyl ethyl acetals and of dimethyl aceta ls were also observed in the reaction product during the methanolysis react ions. (C) 2001 Elsevier Science Ltd. All rights reserved.