The general procedure for the synthesis of (R)-2-(methoxycarbonylamino)-3-methylbutanoic acid from D-valine and methyl chloroformate was as follows: sodium carbonate (276 mg, 2.6 mmol) was added to an aqueous sodium hydroxide solution (5 mL, 1 M, 5 mmol) containing D-valine (586 mg, 5.00 mmol), and the resultant solution was subsequently cooled in an ice water bath. . Methyl chloroformate (0.420 mL, 5.40 mmol) was slowly added dropwise with stirring. After completion of the dropwise addition, the ice water bath was removed and the reaction mixture was continued to be stirred at room temperature for 3.25 hours. After completion of the reaction, the reaction mixture was washed with ether (3 x 9 mL). The aqueous phase was again cooled in an ice water bath and acidified to pH 1-2 with concentrated hydrochloric acid and then extracted with dichloromethane (3 x 9 mL). The organic phases were combined, dried with anhydrous magnesium sulfate, filtered, and concentrated under reduced pressure to afford the target product (R)-2-(methoxycarbonylamino)-3-methylbutyric acid (760 mg, 87% yield) as a white solid. The product was characterized by 1H NMR (DMSO-d6, δ= 2.5 ppm, 300 MHz): 12.54 (s, 1H), 7.32 (d, 1H), 3.84 (t, 1H), 3.54 (s, 3H), 2.03 (m, 1H), 0.87 (d, 6H).
