Anomeric stereocontrol is usually one of the major issues in the synthesis of complex carbohydrates, particularly those involving β-configured 2,6-dideoxyglycoside and D/L-rhamnoside moieties. Recently, Li’s group reported that 2-(diphenylphosphinoyl)acetyl is highly effective as a remote stereodirecting group in the direct synthesis of these challenging β-glycosides under mild conditions. A deoxy-trisaccharide as a mimic of the sugar chain of landomycin E was prepared stereospecifically in high yield. The synthetic potential was also highlighted in the synthesis of Citrobacter freundii O-antigens composed of a [→4)-α-D-Manp-(1→3)-β-D-Rhap(1→4)-β-D-Rhap(1→] repeating unit, wherein the convergent assembly up to a nonasaccharide was realized with a strongly βdirecting trisaccharide donor. Variable-temperature NMR studies indicate the presence of intermolecular H-bonding between the donor and the bulky acceptor as direct spectral evidence in support of the concept of hydrogen-bond-mediated aglycone delivery.
These results have been published on Angewandte Chemie International Edition.
https://onlinelibrary.wiley.com/doi/10.1002/anie.202206128
