0.72 g of 2',5'-dideoxy-5-ethyl-5'-methylaminouridine in 25 ml of dry pyridine was stirred at 0° C. and treated with a solution of (2-bromophenyl)acetyl chloride (prepared from 0.65 g of the acid by treatment with thionyl chloride in benzene under reflux) in 7 ml of benzene. The mixture was stirred at 0° C. for 0.5 hour and then stored at 4° C. overnight. The solvents were removed by evaporation and the residue was re-evaporated with toluene to give a gum which was subsequently triturated with diethyl ether to yield a solid. This solid was taken up in 5 ml of methylene chloride/methanol (9:1) and chromatographed on a column of silica gel using methylene chloride/methanol (9:1) for the elution. The fractions containing the product were combined and evaporated. The residue was re-evaporated with ethanol and recrystallized from methanol to give 0.18 g of 5'-[2-(2-bromophenyl)-N-methylacetamido]-2',5'-dideoxy-5-ethyluridine of melting point 182° -185° C.
