To tert-butyl 4-(3-amino-6-(1,4-dioxaspiro[4.5]decan-8-yl)pyrazin-2-yl)-2-fluorobenzoate (14.34 g, 33.4 mmol) were added acetonitrile (250 mL), water (160 mL) and then 3 M aqueous solutionueous HCl (55.6 mL, 167 mmol). The reaction mixture was stirred at 25° C. for 30 min which was monitored by LCMS. The mixture was basified with 2 M NaOH aqueous solution under stirring to pH 9. Light yellow solid was precipitated out. Acetonitrile was removed under reduced pressure at room temperature. The solid was filtered and washed with water (2×30 mL), and dried under high vacuum overnight to afford tert-butyl 4-(3-amino-6-(4-oxocyclohexyl)pyrazin-2-yl)-2-fluorobenzoate (12 g, 31.1 mmol, 93%) as a light yellow solid. LCMS (m/z): 386.1 (MH+), 0.89 min; 1H NMR (400 MHz, ACETONITRILE-d3) δ ppm 8.05-7.89 (m, 2H) 7.73-7.51 (m, 2H), 5.14 (br. s., 2H), 3.30-3.08 (m, 1H), 2.64-2.48 (m, 2H), 2.40 (br. s., 2H), 2.30-2.17 (m, 2H), 2.12-1.99 (m, 2H), 1.96 (dt, J=4.99, 2.40 Hz, 4H), 1.61 (s, 9H).
