Add triethylamine (0.04 mL, 0.32 mmol) followed by acetic anhydride (0.03 mL, 0.32 mmol) to a solution of 5-(R)-[2-(S)-amino-3-(3,5-difluorophenyl)-1-(S)-hydroxypropyl]-2-(S)-(2-cyclohexylethyl)-morpholine-4-carboxylic acid tert-butyl ester (138 mg, 0.29 mmol) in dry tetrahydrofuran (3 mL). Stir at room temperature for 10 min. Dilute with dichloromethane, wash with 0.1 N hydrochloric acid (30 mL), dry (sodium sulfate), filter, concentrate and purify (silica gel chromatography, eluting with 45:55 to 70:30 ethyl acetate:dichloromethane) to give the title compound (57 mg).
