Dissolve 1.05 g (0.008 mol) of L-isoleucine solid in a 10% sodium carbonate solution, stirring until the L-isoleucine solid is fully dissolved. At 20–30 °C, add dropwise a solution of 2.10 g (0.008 mol) of di-9-fluorenemethyloxycarbonyl chloride dissolved in toluene (2–205 mL). Add 3 drops of...
Addition was carried out over 0–60 minutes, followed by stirring at 20–30°C for 1–8 hours. The mixture was then diluted with 30–200 mL of water and extracted with 80 mL of n-butyl acetate to remove excess 9-fluorenemethyloxycarbonyl chloride. The resulting aqueous phase was acidified with concentrated hydrochloric acid to pH 0.5–3.5, and then extracted with 80 mL of n-butyl acetate. The resulting oil phase was washed with water to remove hydrochloric acid, concentrated to remove the n-butyl acetate solvent, and white crystals precipitated. The crystals were filtered and dried to obtain 2.48 g of Fmoc-Ile-OH, with a yield of 87.9% and a melting point of 145–146°C.
