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 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 chromatography using a Biotage Horizon™ High-Performance Flash Chromatography instrument (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.
