The general Fmoc-protected amino acids synthesis step is to add the amino acids to a mixed solution of water and sodium bicarbonate with stirring and cool the resulting solution to 5 °C, then slowly add Fmoc-OSu or Fmoc-Cl. After the resulting mixture is kept at 0 °C for 1 hour, and then heat to room temperature for one night. Then water is added and the aqueous layer is extracted twice with EtOAc. The organic layer is back extracted with saturated sodium bicarbonate solution twice. The combined aqueous layer is acidified to pH 1 with 10% hydrochloric acid and then extracted with EtOAc for 3 times. The combined organic layers are dried (sodium sulfate) and concentrated in vacuo and the resulting residue could be purified by flash chromatography (SiO).