[Br:1][C:2]1[NH:10][C:9]2[C:8](=[O:11])[N:7]([CH2:12][CH2:13][CH2:14][OH:15])[C:6](=[O:16])[N:5]([CH3:17])[C:4]=2[N:3]=1.I[CH2:19][CH3:20].C(=O)([O-])[O-].[K+].[K+]>CN(C=O)C>[Br:1][C:2]1[N:10]([CH2:19][CH3:20])[C:9]2[C:8](=[O:11])[N:7]([CH2:12][CH2:13][CH2:14][OH:15])[C:6](=[O:16])[N:5]([CH3:17])[C:4]=2[N:3]=1To a solution of 8-bromo-1-(3-hydroxypropyl)-3-methyl-1H-purine-2,6(3H,7H)-dione (0.4 g, 1.32 mmol, product of intermediate 16 step 2) in DMF (10 mL) was added iodoethane (0.25 g, 1.58 mmol) and potassium carbonate (0.27 g, 1.98 mmol). The reaction was heated at 50° C. for 2 h. The mixture was cooled and partitioned between ethyl acetate and water. The combined organic layer was dried over sodium sulfate, filtered and concentrated to give 8-bromo-7-ethyl-1-(3-hydroxypropyl)-3-methyl-1H-purine-2,6(3H,7H)-dione (0.4 g, 91.7% yield) as white solid. LCMS retention time 1.674 min; LCMS MH+ 331.
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