GENERAL METHOD: O-Methyl-L-threonine (10 g, 75.11 mmol) was dissolved in a solvent mixture of THF (350 mL) and water (350 mL) and cooled to 0 °C. NaHCO3 (18.93 g, 225.32 mmol) and di-tert-butyl dicarbonate (Boc2O, 24.59 g, 112.66 mmol) were added sequentially, and the reaction mixture was gradually warmed to room temperature and stirred for 18 hours. Upon completion of the reaction, the pH was adjusted to 4 with aqueous KHSO4 to quench the reaction, followed by extraction with EtOAc (5 × 150 mL). The organic layers were combined, dried with Na2SO4 and concentrated under reduced pressure. The residue was ground with heptane to afford (2S,3R)-2-((tert-butoxycarbonyl)amino)-3-methoxybutyric acid as a white solid (16.50 g, 94% yield).1H NMR (400 MHz, CDCl3): δ 1.22 (d, 3H), 1.45 (s, 9H), 3.28 (s, 3H), 3.98 (br d, 1H). 4.38 (d, 1H), 5.28 (d, 1H), 10.40-10.60 (br s, 1H).
