Transglucosidation of methyl and ethyl D-glucopyranosides by alcoholysis.
The transglucosidations of methyl 4-O-methyl-alpha- and -beta-D-glucopyranoside in ethanolic camphor-10-sulfonic acid, and of ethyl 4-O-methyl-alpha- and -beta-D-glucopyranoside in methanolic camphor-10-sulfonic acid, have been studied. Samples were removed at intervals and the proportions of the glucosides determined by GC of their acetates. The results show that the anomer with the inverted configuration predominates in the initially formed product (approximately 59-70%). This indicates that all the studied reactions proceed via the same mechanism, involving exocyclic C-O cleavage and formation of a glucopyranosylium ion, but that the eliminated alcohol exerts some steric hindrance, which favors the approach of the other alcohol from the opposite side.
Garegg
Per J
PJ
Arrhenius Laboratory, Department of Organic Chemistry, Stockholm University, S-106 91 Stockholm, Sweden.
Johansson
Karl-Jonas
KJ
Konradsson
Peter
P
Lindberg
Bengt
B
Trumpakaj
Zygmunt
Z
D002164:Camphor / Q000031:analogs & derivatives* / Q000737:chemistry; D002240:Carbohydrate Sequence; D000431:Ethanol / Q000737:chemistry*; D005960:Glucosides / Q000737:chemistry*; D006031:Glycosylation; D007700:Kinetics; D000432:Methanol / Q000737:chemistry*; D008745:Methylation; D008757:Methylglucosides / Q000737:chemistry*; D008969:Molecular Sequence Data
D005960:Glucosides; D008757:Methylglucosides; D000431:Ethanol; D002164:Camphor; C006881:10-camphorsulfonic acid; C108400:ethyl glucoside; D000432:Methanol