To a stirred solution of 1-[(4-methylphenyl)sulfonyl]-4H-imidazo[1,5,4-de]quinoxaline-2,5(1H,6H)-dione from Step D (1.16 g, 3.38 mmol) in DMF (40 mL) was added potassium carbonate (467 mg, 3.38 mmol) and the resulting mixture was stirred at ambient temperature for 10 min. Iodomethane (480 mg, 3.38 mmol) was added dropwise and the reaction mixture was stirred for 18 h, then poured into H2O (50 mL). The resulting precipitate was isolated by filtration, washed with H2O, and dried in vacuo to give the title compound. MS: m/z=358 (M+1).
