At room temperature, O-benzyl-L-serine (25.0 g, 128 mmol) was dissolved in a mixed solvent of water (200 mL) and dioxane (100 mL) and sodium carbonate (7.46 g, 70 mmol) was added. Subsequently, a solution of dibenzyl dicarbonate (36.1 g, 126 mmol) in dioxane (100 mL) was slowly added dropwise and the reaction mixture was stirred at room temperature for 18 hours. Upon completion of the reaction, the dioxane was removed by vacuum evaporation and the remaining aqueous phase was extracted with ether. The organic phases were combined, dried over anhydrous sodium sulfate and concentrated under vacuum to give the crude product N-benzyloxycarbonyl-O-benzyl-L-serine (39.57 g, 95% yield) as a white solid, which was finally purified by washing with hexane.
