To a solution of {1-[4-(7,8-diamino-4-oxo-2-phenyl-4H-chromen-3-yl)-phenyl]-cyclobutyl}-carbamic acid tert-butyl ester (80 mg, 0.16 mmol) in CH3CN (8 mL) was added trimethylorthoacetate (25 μL, 0.20 mmol) and iodine (4 mg, 0.016 mmol) and the reaction mixture was stirred at RT for 2.5 hours. Further trimethylorthoacetate (50 μL, 0.40 mmol) and iodine (24 mg, 0.096 mmol) were added and the reaction stirred for 1 hour. The reaction was quenched with aqueous Na2S2O3, diluted with ethyl acetate and the phases separated. The organic extracts were washed with brine, dried (NaSO4), filtered and the solvents were removed in vacuo. The resulting residue was subjected to flash chromatography (SiO2, ethyl acetate) to give the title compound as a brown solid (35 mg, 42%). LCMS (Method G): RT=3.18 min, [M+H]+=522.
