A CONVENIENT NEW PATHWAY FOR STEREOSPECIFIC EPIMERIZATION OF MONOSACCHARIDE MOIETIES IN DISACCHARIDES

摘要

The disaccharides benzyl 4,6-O-benzylidene-2-O-alpha-D-mannopyranosyl-beta-D-glucopyranoside (2), 6-O-beta-D-galactopyranosyl-1,2:3,4-di-O-isopropylidene-alpha-D-galactopyr anose (4), and phenyl 4-O-beta-D-galactopyranosyl-1-thio-beta-D-glucopyranoside (7) were selectively acetalated with chloral-dicyclohexylcarbodiimide in a nonclassical pathway. During acetalation, the D-mannopyranosyl moiety of the disaccharide 2 and the unprotected beta-D-galactopyranosyl moieties of 4 and 7 were epimerized at their 3-positions, generating D-altro- and D-gulo-pyranosyl moieties, respectively. [References: 17]