Boron tribromide → N-[4-(4-amino-2-hydroxymethyl-1H-imidazo[4,5-c]quinolin-1-yl)butyl]methanesulfonamide

Boron tribromide (2.5 equivalents, 20 mL of 1 M solution in dichloromethane) was added dropwise to a cooled (ice bath) suspension of N-[4-(4-amino-2-ethoxymethyl-1H-imidazo[4,5-c]quinolin-1-yl)butyl]methanesulfonamide (3 g, 7.92 mmol) in dichloromethane (20 mL). The reaction mixture was allowed to slowly warm to ambient temperature and then stirred for 4 hours. Additional boron tribromide (2 mL) was added and the mixture was stirred for 3 hours. The reaction was quenched slowly with methanol (20 mL) and then concentrated under reduced pressure. The residue was combined with 6 M hydrochloric acid (50 mL), heated to 50° C., and stirred for 2 hours. The resulting solution was concentrated under reduced pressure to a slurry that cooled (ice bath) and then free-based with the addition of 7 M ammonia in methanol (40 mL). The mixture was concentrated under reduced pressure and the addition of 7 M ammonia in methanol (40 mL) was repeated 2 more times. The concentrated brown sludge like material was purified by prep HPLC (ISCO Combiflash Separation System, Biotage Si 40+M column, eluted with a gradient of methanol in dichloromethane with 1% ammonium hydroxide) to provide a light brown solid. The solid was triturated with hot acetonitrile, allowed to cool, isolated by filtration, washed with ether, and dried under vacuum to provide N-[4-(4-amino-2-hydroxymethyl-1H-imidazo[4,5-c]quinolin-1-yl)butyl]methanesulfonamide (0.1 g) as a fine beige solid, mp 216-219° C.; MS (ESI) m/z 364 (M+H)+; Anal. Calcd for C16H21N5O3S: C, 52.88; H, 5.82; N, 19.27. Found C, 52.62; H, 5.71; N, 19.02.