7536-58-5

24424-99-5

2177-63-1

7536-58-5

The general procedure for the synthesis of (S)-4-(benzyloxy)-2-((tert-butoxycarbonyl)amino)-4-oxobutanoic acid from di-tert-butyl dicarbonate and L-aspartic acid-4-benzyl ester is as follows: in a round-bottomed flask, L-aspartic acid-4-benzyl ester (79.7 g, 357 mmol), sodium bicarbonate (60 g, 714.2 mmol), water (700 mL), and tetrahydrofuran (550 mL). The reaction system was cooled to 0 °C, followed by the slow addition of di-tert-butyl dicarbonate (105 g, 481 mmol) to the reaction vial. After the dropwise addition, the reaction was kept at 0 °C for half an hour, then slowly warmed up to room temperature and continued stirring for 12 hours. After completion of the reaction, tetrahydrofuran was removed by distillation under reduced pressure. The aqueous phase was washed with ethyl acetate (20 mL), followed by adjusting the pH with 10% aqueous citric acid (10 mL) to 1. The aqueous phase was extracted with ethyl acetate (200 mL x 2) and the organic phases were combined. The organic phase was washed sequentially with saturated saline (100 mL × 2) and dried over anhydrous sodium sulfate. After filtration, the solvent was evaporated under reduced pressure to give a white solid product (104 g, 90% yield).