A solution of tert-butyl 4-(3-amino-6-(4-oxocyclohexyl)pyrazin-2-yl)-2-fluorobenzoate (9 g, 23.35 mmol) in methanol (125 mL) and THF (125 mL) was cooled down to −78° C., and then NaBH4 (2.297 g, 60.7 mmol) was added portion wise. The reaction mixture was then stirred at −78° C. for 40 min, and LCMS indicated the reaction was completed. Some over-reduction product was observed. The ratio of trans to cis was about 8:1. 100 mL of sat. NH4Cl was added slowly at −78° C., and then the mixture was warmed up gradually to room temperature. The reaction mixture was quenched by sat. NaHCO3, and extracted by EtOAc (2×200 mL). The organic layers were combined, dried over Na2SO4, filtered off, concentrated and dried under high vacuum to provide tert-butyl 4-(3-amino-6-(4-hydroxycyclohexyl)pyrazin-2-yl)-2-fluorobenzoate (8.9 g, 22.97 mmol, 98%), which was used in next step without further purification. LCMS (m/z): 388.2 (MH+), 0.86 min.
