Peracylated 1-(2′-azido--L-arabino-/β-D-ribofuranosyl)thymine has been chemoenzymatically synthesized and subjected to deacylation studies in the presence of CAL-B (Candida antarctica lipase-B immobilized on polyacrylate) in acetonitrile. It is observed that CAL-B mediates highly selective deacylation of the ester function involving C-5′ hydroxyl group of the nucleosides leading to the formation of 1-(2′-azido-3′-O-acyl--L-arabino / β-D-ribofuranosyl)thymine in very high yields, which are otherwise very difficult to prepare by classical chemical methods. The 3′-O-acylated azido-nucleosides may be used as key precursors for the preparation of 5′-O-2′-N-linked oligonucleotides of biological importance.