(S)-3-(Boc-amino)-2-methylpropionic acid

168828-18-0

190897-47-3

The general procedure for the synthesis of (S)-3-((tert-butoxycarbonyl)amino)-2-methylpropanoic acid using tert-butyl (S)-2-(methoxycarbonyl)propylcarbamate as a raw material was as follows: firstly, 1.30 g (5.98 mmol) of (2S)-3-[(tert-butoxycarbonyl)amino]-2-methylpropanoic acid methyl ester was dissolved in 16 mL of tetrahydrofuran and 4 mL of distilled water in a mixed in the solvent. Subsequently, 0.75 g (18.0 mmol) of lithium hydroxide was added and the reaction was stirred at room temperature for 15 hours. Upon completion of the reaction, the solvent was removed by distillation under reduced pressure, ethyl acetate was added, the reaction solution was neutralized with 1N HCl, and the organic phase was dried with magnesium sulfate. After that, the solvent was removed by distillation and the residue was purified by column chromatography to give 1.05 g of the target compound in 87% yield. Next, the resulting compound was dissolved in 20 mL of diethyl ether and cooled to -30°C. At this temperature, 0.82 mL (5.90 mmol) of triethylamine and 0.78 mL (5.90 mmol) of isobutyl chloroformate were added sequentially. After stirring for 15 minutes, diazomethane dissolved in diethyl ether was slowly added (in excess). After continued stirring for 2 hours, acetic acid and ethyl acetate were added sequentially and the reaction solution was washed with sodium carbonate solution and water. The organic phase was dried and the residue was purified by column chromatography to give 0.31 g of (S)-3-((tert-butoxycarbonyl)amino)-2-methylpropanoic acid in 28% yield. The product was confirmed by 1H NMR (CDCl3): δ 5.35 (1H, s), 5.01 (1H, s), 3.28 (2H, t, J=6Hz), 2.71 (1H, m), 1.45 (9H, s), 1.15 (3H, d, J=6.8Hz). Mass spectral analysis showed m/e of 228 (M+1).