L-homoserine (15 g, MW119.12, 0.126 mol) and NaHCO3 (22 g, MW84, 0.26 mol) were dissolved in water (600 mL). The solution was chilled in an ice bath, followed by addition of Fmoc-OSu (42.5 g, MW337.3, 0.126 mol) in acetone (400 mL). The mixture was stirred overnight. A mixture of ether/water (200 mL/200 mL) was added, and the solid was filtered off. The filtrate was separated and the aqueous phase was washed with ethyl twice (100 mL×2), followed by acidifying with 3N HClaq (about 100 mL) to pH3-4. The suspension was extracted with ether (200 mL×2). The combined organic phases were washed with brine once (100 mL) and dried over Na2SO4. After evaporation, white solid was obtained (weight: 38 g, yield: 88%).
