mCPBA (4.8 g of 75%, 22 mmol) was added over a period of several minutes to a solution of ethyl 3-(2-ethyl-1H-imidazo[4,5-c]quinolin-1-yl)-2,2-dimethylpropanoate (3.6 g, 11 mmol) in dichloromethane (100 mL), which had been cooled to approximately 0° C. The reaction mixture was stirred cold for ten minutes and then for three hours at ambient temperature. The reaction mixture was then washed twice with a mixture of saturated aqueous sodium bicarbonate (34 mL) and 25% aqueous sodium hydroxide (1 mL), dried over potassium carbonate, filtered, and then cooled to 0° C. Trichloroacetyl isocyanate (1.7 mL, 14 mmol) was added, and the reaction was stirred cold for 15 minutes, warmed to ambient temperature, and stirred for one hour. The solvent was removed under reduced pressure, and the residue was dissolved in methanol (50 mL). Sodium methoxide (6.5 mL of a 25% solution in methanol, 30 mmol) was added to the resulting solution, and the reaction was stirred at ambient temperature overnight and cooled to approximately 0° C. for 30 minutes. A precipitate formed and was isolated by filtration to provide 1.2 g of methyl 3-(4-amino-2-ethyl-1H-imidazo[4,5-c]quinolin-1-yl)-2,2-dimethylpropanoate.
