To benzyl chloroformate (17.06 mL, 119 mmol) was added slowly and dropwise (S)-2-aminobutyric acid (11.2 g, 109 mmol) solution of tetrahydrofuran (THF, 200 mL) and 2M aqueous sodium carbonate (65.2 mL, 130 mmol) at 0 °C. After dropwise addition, the reaction mixture was stirred at room temperature for 16 hours. After completion of the reaction, the aqueous layer was separated by extraction with H2O/tert-butyl methyl ether (TBME). The aqueous layer was acidified to pH=2 with 2M HCl aqueous solution and subsequently extracted with ethyl acetate (EtOAc). The organic layers were combined, dried with anhydrous sodium sulfate (Na2SO4), filtered and the filtrate was concentrated to afford (S)-2-(benzyloxycarbonylamino)butyric acid (22.8 g, 77% yield) as a colorless oil. The product could be used in the subsequent reaction without further purification.LC-MS analysis: [M-H] 236.2; retention time (Rt) 0.76 min (LCMS method 1).
[1] Chemical and Pharmaceutical Bulletin, 1994, vol. 42, # 9, p. 1927 - 1930
[2] Patent: US2014/135330, 2014, A1. Location in patent: Paragraph 0230
[3] Journal of the American Chemical Society, 1964, vol. 86, p. 4991 - 4999
[4] Bulletin of the Academy of Sciences of the USSR, Division of Chemical Science (English Translation), 1964, p. 635 - 640
[5] Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, 1964, # 4, p. 685 - 692
