A THF (5 mL) solution of acetic anhydride was added to a cloudy mixture of Fmoc-DAP-H (1) (980 mg, 3.0 mmol) and pyridine (483 L, 6.0 mmol) in THF (15 mL) at room temperature and with stirring.After 4 hr, the LCMS showed a clarified, light-yellow solution that was fully reacted. The reaction was evaporated under reduced pressure. The residue was dissolved in EtOAc (150 mL), washed with 0.1 M NaHSO4 (50 mL), water (50 mL), and saturated saline (50 mL), dried over Na2SO4, filtered, and concentrated under reduced pressure to give 1.1 g of white solid crude product. The crude product was purified by preparative HPLC to afford 0.99 g (90% yield) of 3-(acetylamino)-N-[fluorenylmethoxycarbonyl]-L-alanine.
