General procedure for the synthesis of N-Boc-DL-2-aminobutyric acid from di-tert-butyl dicarbonate and DL-2-aminobutyric acid: 10 g (96.97 mmol, 1.0 eq.) of DL-2-aminobutyric acid was dissolved in 65 mL of methanol to which 97 mL of sodium hydroxide (NaOH) solution was added. Subsequently, 25.4 g (116.37 mmol, 1.2 eq.) of di-tert-butyl dicarbonate (Boc2O) was slowly added at 0 °C. The reaction mixture was stirred at room temperature for 48 h. After completion of the reaction, it was concentrated under reduced pressure. The concentrated reaction mixture was adjusted pH to 2-3 with 1N HCl and then extracted with ethyl acetate. The organic layer was separated, dried over anhydrous sodium sulfate (Na2SO4), filtered and concentrated under reduced pressure. The residue was purified by column chromatography (SiO2, eluent gradient: hexane/ethyl acetate, 10:1 to hexane/ethyl acetate, 3:1) to afford 18.5 g of N-Boc-DL-2-aminobutyric acid (2-((tert-butoxycarbonyl)amino)butyric acid) as a colorless oil (91.02 mmol, 94% yield).1H NMR (300 MHz, CDCl3) δ 6.24 (s, 1H), 5.00-5.03 (d, 1H).
