mCPBA (35.5 g of 77% purity, 158 mmol) was added to a stirred solution of 1-[7-bromo-2-(ethoxymethyl)-1H-imidazo[4,5-c][1,5]naphthyridin-1-yl]-2-methylpropan-2-ol (15 g, 0.040 mol) in chloroform (400 mL), and the reaction was stirred at room temperature for 2.5 hours. Concentrated ammonium hydroxide (200 mL) was added, and then p-toluenesulfonyl chloride (18.9 g, 98.9 mmol) was added over a period of five minutes. The reaction mixture was stirred at room temperature for 2.5 hours, and an analysis by liquid chromatography/mass spectrometry (LC/MS) indicated the presence of starting material. Additional p-toluenesulfonyl chloride (11 g) was added, and the reaction mixture was stirred at room temperature for one hour. An analysis by LC/MS indicated the reaction was still incomplete. Additional ammonium hydroxide (100 mL) and p-toluenesulfonyl chloride (10 g) were added, and the mixture was stirred for 30 minutes at room temperature. The aqueous layer was separated and extracted with dichloromethane (2×300 mL). The combined organic fractions were dried over magnesium sulfate, filtered, and concentrated under reduced pressure. The residue (41.4 g) was purified by automated flash chromatography (FLASH 65I cartridge, eluting with ethyl acetate:methanol in a gradient from 97:3 to 85:15) to provide 5.96 g of 1-[4-amino-7-bromo-2-(ethoxymethyl)-1H-imidazo[4,5-c][1,5]naphthyridin-1-yl]-2-methylpropan-2-ol as a yellow solid.
