Pentafluoropropionyl (PFP) and trifluoroacetyl (TFA) esters were demonstrated to be useful in facile oligosaccharide synthesis. These were well compatible with glycosylation conditions and removable by treatment with pyridine-EtOH, with complete preservation of acetyl groups. Analytically pure products were obtained quantitatively, simply by evaporating the reaction mixtures. Using O-PFP and O-TFA carrying glycosyl halides, trisaccharide (Manalpha1-->2Manalpha1-->2Man) and tetrasaccharide (Glcalpha1-->3Manalpha1-->2Manalpha1-->2Man) portions of monoglucosylated high-mannose type dodecasaccharide (Glc(1)Man(9)GlcNAc(2)), a putative ligand for the ER chaperon, calnexin and calreticulin, were synthesized.