CPG-bound nucleosides (deoxyguanosine excepted) can be stereoselectively glycosylated in high yield at their 5'-hydroxyl by a "disarmed" trichloroacetimidate donor in the presence of stoichiometric amounts of TMSOTf (5 eq.) and in short reaction times. These results allowed the solid-phase synthesis of an oligonucleotide functionalized at both ends with sugar residues. (C) 1999 Elsevier Science Ltd. All rights reserved.