The ribo-and arabinofuranosyl nucleosides of antitumor active 2-and 4-pyridones la and 2a were prepared by direct condensation of the silylated bases with either lO-acety~-2, 3, 5-tri- O-benzoyl-~-ribofuranose (4a) or 2, 3, 5-tri-O-benzyl-1-p-nitrobenzoyl-D-arabinofuranose (7) in the presence of trimethylsilyl triflate (Me, SiOTf). In the case of the arabinofuranosyl nucleosides, separation of the a and,/3 anomers was accomplished at the stage of 0- ...