Anhydrous pyridine (9.9 mL) was added to a solution of 5′-O-(4,4′-dimethoxitrityl)-5-methyluridine (6.9 g) and AgNO3 (2.51 g) in dry THF (123 mL) and stirred at room temperature for 20 min under an argon atmosphere. Followed by addition of tert-butyldimethylsilyl chloride (2.51 g) in dry THF (6 mL) and stirred at the same temperature for 2-3 h. The solids were filtered off and the filtrate was concentrated to a crude residue which was applied to a column of silica gel eluted with hexane-ethyl acetate (3:1) to give a pure title compound (7.04 g) as an amorphous solid.
