Chemoselective glycosylations using sulfonium triflate activator systems

A novel chemoselective glycosylation sequence is described that employs the recently developed BSP/Tf2O and DPS/Tf2O reagent systems to activate thioglycosides. In the first glycosylation event a relatively armed thioglycoside is activated with the BSP/Tf2O activator system and condensed with an acceptor thioglycoside to yield the thiodisaccharide, which is activated with the more potent DPS/Tf2O activator in the next glycosylation event. Quenching of (N-piperidino)phenyl(S-thiophenyl)sulfide triflate, which is formed upon activation of the first thioglycoside, with triethyl phosphite is crucial for a productive glycosylation. (C) 2003 Elsevier Ltd. All rights reserved.