A cloudy solution of 4-(4-amino-6,7,8,9-tetrahydro-1H-imidazo[4,5-c]quinolin-1-yl)butan-1-ol (1.0 g, 3.8 mmol), triphenylphosphine (1.49 g, 5.7 mmol) and N-hydroxyphthalimide (0.93 g, 5.7 mmol) in tetrahydrofuran (50 mL) was cooled to approximately 0° C.; then diisopropyl azodicarboxylate (1.33 mL, 6.8 mmol) was added dropwise. The reaction was allowed to warm to ambient temperature and was stirred for 5 hours. The solvent was removed under reduced pressure, and the resulting solid was purified by chromatography on silica gel (gradient elution with 0-10% methanol in dichloromethane with a small amount of concentrated ammonium hydroxide added) to provide 600 mg of 2-[4-(4amino-6,7,8,9-tetrahydro-1H-imidazo[4,5-c]quinolin-1-yl)butoxy]-1H-isoindole-1,3(2H)-dione as a yellow solid.
