At 0 °C, 73.7 mL of acetyl chloride (1.4 eq.) was slowly added dropwise to 250 mL of methanol. Maintaining 0 °C, the mixture was added dropwise to a 250 mL methanol suspension containing 100 g (751 mmol) of (R)-2-aminosuccinic acid. The reaction mixture was stirred at 0 °C for 3 h before gradually warming to room temperature and continuing to stir overnight. Five identical reaction vials were set up in parallel for the same operation. The mixtures from all six reaction flasks were combined and concentrated under reduced pressure. The concentrated residue was treated with methyl tert-butyl ether (MTBE) and the resulting precipitate was filtered and dried under reduced pressure to give (R)-2-amino-4-methoxy-4-oxobutanoic acid (600 g, 90% yield) as a white solid. The product was characterized by 1H NMR (400 MHz, deuterium oxide): δ 4.33 (t, J = 5.5 Hz, 1H), 3.81 (s, 1H), 3.72 (s, 3H), 3.10 (d, J = 4.9 Hz, 2H).
