Contribution of carbohydrate chemistry to assessment of the biological role of natural α-glucosides

Biotinylated Oligo-α-(1 → 4)-d-galactosamines and Their N-Acetylated Derivatives: α-Stereoselective Synthesis and Immunology Application

“…Several preliminary α-galactosylation experiments with donor 5 and aliphatic and monosaccharide acceptors showed that the optimal promoter system is Me 2 S 2 −MeOTf, which is more convenient than the previously used NIS−TMSOTf The glycosylation of acceptor 11 with donor 5, removal of the DTBS group, and 6′-O-benzoylation gave disaccharide glycosyl acceptor 13. Subjecting this compound to multiple cycles of these reactions under similar conditions afforded the tri-( 14), tetra- (15), penta-( 16), and hexasaccharide (17) glycosyl acceptors. Their structures, particularly the location of the Bz groups and free OH groups as well as the αconfiguration of the anomeric centers, were confirmed by a combination of 1D and 2D NMR spectra, and these data are summarized in the Supporting Information.…”

“…The di-( tert -butyl)­silylidene (DTBS) group was selected to protect O-4 and O-6 because of its steric hindrance, which disfavors the formation of undesirable β-glycosylation products . Despite the previous observation , of the good efficiency of 3-O-benzylated 2-azido-2-deoxygalactosyl donors, a 3-O-benzoyl group was applied in this work as a temporary protecting group on O-3 of the glycosyl donor 5 because 3-benzoates offer α-stereocontrol through remote anchimeric participation. ,− The synthesis of the designed donor 5 is shown in Scheme and is described in the Supporting Information.…”