Stereodirecting Effect of Cyclic Silyl Protecting Groups in Chemical Glycosylation

Total synthesis ofLentinus giganteusglycans with antitumor activitiesviastereoselective α-glycosylation and orthogonal one-pot glycosylation strategies

“…All α-Gal configurations of 5 were confirmed by the chemical shifts of anomeric carbon centers between 97.1 ppm and 97.8 ppm. Although 4,6-di- tert -butylsilyene (DTBS) directed galactosylation could also achieve highly selective α-galactosylation, 45 it usually needs five steps to achieve one sugar unit elongation for the synthesis of the heptasaccharide acceptor 5, including: (1) glycosylation; (2) deprotection of the 4,6-di- tert -butylsilyene protecting group; (3) selective protection of the C6–OH group; (4) protection of the resulting C4–OH group; and (5) deprotection of the C6–OH group for the next sugar elongation cycle. In contrast, the current RMRAA α-galactosylation only needs two steps (glycosylation and deprotection of the 6- O -Lev group) for elongation of one sugar unit, which significantly reduces the step counts.…”

Conformationally Constrained Glycosyl Donors as Tools to Control Glycosylation Outcomes

“…Finally, anomeric tethers, which have been used to exert stereocontrol over glycosylations by directing the nucleophilic attack, will also be reviewed (Section ). A number of excellent reviews have discussed efforts in this area prior to 2013 in addition to more recent reviews focusing specifically on the use of silyl protecting groups . As such, this current Perspective aims to focus on the most recent developments in the field and set them in context with the state-of-the-art glycosylation methods.…”