A stereocontrolled synthetic approach to glycopeptides corresponding to the carbohydrate-protein linkage region of cell-surface proteoglycans Original Research Article

The glycopeptides 1 (Gly{O-β-D-Xylp }-L-Ser-Gly-L-Glu) and 2 (Gly{O-[β-D-GlcpA-(1→3)-β-D-Galp-(1→3)-β-D-Galp]-(1→4)-β-D-Xylp}-L-Ser-Gly-L-Glu }-L-Ser-Gly-L-Glu)), carrying the core structure of serine-linked cell-surface proteoglycans were synthesized in a stereocontrolled manner. The carbohydrate key imidate xylosyl donors 3 and glycotetraosyl donors 4 and 5, as well as a tetrapeptide glycosyl acceptor 6, were coupled in the crucial glycosylation step. In these reactions, the application of either trimethylsilyl trifluoromethanesulfonate (TMSOTf) or borontrifluoride etherate (BF3-Et2O) as catalysts proved to be highly efficient. The serine linked glycopeptides 34, 36 and 37 thus obtained yielded target compounds 1 and 2 on complete deprotection.