Direct glycosylation of protected O-tritylserine esters and oligopeptides

N-Fmoc-3-O-Tr-l-serine methyl and benzyl esters, as well as a tripeptide FmocAlaSer(Tr)GlyOBn were directly glycosylated by 3,4,6-tri-O-acetyl-1,2-O-(1-cyanoethylidene)-α-d-galactopyranose in the presence of TrClO4 in dichloromethane, yielding 32–57% of N-Fmoc-3-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-l-serine esters and the corresponding tripeptide.