3'-(Trityl)amino-5'-O-(tert-butyldimethylsilyl)-2',3'-dideoxyuridine, 2du. Crude 1du (33.2 g, 90.3 mmol) was dissolved in 2:1 EtOH/CH2Cl2 (300 mL) and reduced via hydrogenation (60 psi H2) in the presence of 10% Pd/C (3.0 g) for 18 h. Subsequent removal of the catalyst via filtration and evaporation of solvent in vacuo, afforded quantitative yield (30.4 g, 89.8 mmol) of the corresponding 3'-amine which was taken on directly to the next reaction. The 5'-O-(tert-butyldimethylsilyl)-3'-amino-2',3'-dideoxyuridine (30.4 g, 89.8 mmol) was azeotroped from pyridine (2×300 mL), and dissolved in a mixture of CH2Cl2 (600 mL) and anhydrous pyridine (70 mL). To this solution was added triethylamine (25.0 mL, 179.6 mmol) and trityl chloride (35.0 g, 125.7 mmol), and the reaction mixture was stirred for 2 h at ambient temperature. Solvents were removed in vacuo, and the crude product was purified on silica (1-5% MeOH/CH2Cl2) to afford 85% yield (44.3 g, 75.9 mmol) of 3'-(Trityl)amino-5'-O-(tert-butyldimethylsilyl)-2',3'-dideoxyuridine, 2du.
