[Br:1][C:2]1[N:10]([CH2:11]C2C=CC(Cl)=CC=2)[C:9]2[C:8](=[O:19])[NH:7][C:6](=[O:20])[N:5]([CH3:21])[C:4]=2[N:3]=1.C(=O)([O-])[O-].[K+].[K+].[CH3:28][Si:29]([CH3:36])([CH3:35])[CH2:30][CH2:31][O:32]CCl>CN(C=O)C>[Br:1][C:2]1[N:10]([CH2:11][O:32][CH2:31][CH2:30][Si:29]([CH3:36])([CH3:35])[CH3:28])[C:9]2[C:8](=[O:19])[NH:7][C:6](=[O:20])[N:5]([CH3:21])[C:4]=2[N:3]=1To a solution of 8-bromo-3-methyl-1H-purine-2,6(3H,7H)-dione (3.5 g, 14.3 mmol, intermediate 8 step 1) in DMF (30 mL) was added potassium carbonate (3.9 g, 28.6 mmol). Then 2-(trimethylsilyl)ethoxymethyl chloride (2.37 g, 14.3 mmol) was added dropwise 0° C., it was stirred room temperature for 3 h. The mixture was partitioned between ethyl acetate and water. The organic layers were combined, dried over sodium sulfate, filtered and concentrated to give a crude product which was washed with ethanol and dried in vacuo to give 8-bromo-3-methyl-7-((2-(trimethylsilyl)ethoxy)methyl)-1H-purine-2,6(3H,7H)-dione (4.0 g, 74.9%) as a white solid. LCMS retention time 1.458 min, LCMS MH+ 377.
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