To a solution of tert-butyl 4-(3-amino-6-(4-oxocyclohexyl)pyrazin-2-yl)-2-fluorobenzoate (3 g, 7.78 mmol) in acetonitrile (130 mL) was added Boc2O (6.33 mL, 27.2 mmol) and DMAP (0.048 g, 0.389 mmol). The reaction mixture was stirred overnight at room temperature. After volatile materials were removed on rotavap under reduced pressure, the crude product was purified by flash chromatography eluting with 0-50% of EtOAc/heptane to provide imidodicarbonic acid, 4-(3-((tert-butoxycarbonyl)amino)-6-(4-oxocyclohexyl)pyrazin-2-yl)-2-fluorobenzoate, 1,3-bis(1,1-dimethylethyl) ester (4.34 g, 7.41 mmol, 95%). LCMS (m/z): 586.5 (MH+), 1.24 min; 1H NMR (500 MHz, CHLOROFORM-d) δ ppm 8.52-8.41 (m, 1H), 7.97 (t, J=7.7 Hz, 1H), 7.61-7.44 (m, 2H), 3.46-3.30 (m, 1H), 2.68-2.52 (m, 4H), 2.38 (dd, J=3.0, 13.7 Hz, 2H), 2.28-2.10 (m, 2H), 1.69-1.61 (m, 9H), 1.42-1.29 (m, 18H).
