The general procedure for the synthesis of (S)-4-((tert-butoxycarbonyl)amino)-5-methoxy-5-oxopentanoic acid from methyl (S)-5-benzyl-2-((tert-butoxycarbonyl)amino)pentanedioate was as follows: methyl (S)-5-benzyl-2-((tert-butoxycarbonyl)amino)pentanedioate (4.95 g, 14.09 mmol) was dissolved in 50 mL of a round bottom flask of methanol (20 mL) and 10% palladium/carbon catalyst was added under nitrogen protection. Subsequently, the reaction vessel was purged three times with nitrogen and hydrogen alternately. The reaction mixture was stirred for 6 hours under hydrogen atmosphere and atmospheric pressure. Upon completion of the reaction, the catalyst was removed by filtration and the filtrate was concentrated to afford the target compound (S)-4-((tert-butoxycarbonyl)amino)-5-methoxy-5-oxopentanoic acid as a colorless gelatinous liquid (3.5 g, 96% yield). The specific optical rotation of the product [α]21D = +7 (c 0.1, CHCl3). Nuclear magnetic resonance hydrogen spectrum (1H NMR, CDCl3, 400 MHz) δ: 1.4 (s, 9H), 1.87-1.96 (m, 1H), 2.12-2.15 (m, 1H), 2.35-2.49 (m, 2H), 3.71 (s, 3H), 4.31-4.33 (d, 1H, J = 4.64 Hz), 5.24- 5.27 (d, 1H, J = 8.16 Hz), 10.19 (s, 1H). Nuclear magnetic resonance carbon spectrum (13C NMR, CDCl3, 100 MHz) δ: 27.5, 28.2, 30.0, 52.4, 52.8, 80.2, 155.5, 172.8, 177.7. infrared spectrum (IR, KBr) νmax: 3346, 2979, 1719, 1520, 1439, 1394, 1369. 1216, 1167, 1057, 1029, 879, 853, 816, 780, 596, 463 cm-1.
