The general procedure for the synthesis of (2S,3R)-2-((tert-butoxycarbonyl)amino)-3-hydroxybutyric acid from L-threonine and di-tert-butyl dicarbonate was as follows:
1. To a methanol (5 mL) solution of L-threonine (400 mg, 3.36 mmol), a water (5 mL) solution of sodium bicarbonate (434 mg, 5.17 mmol) was added, followed by di-tert-butyl dicarbonate (1.07 g, 4.90 mmol).
2. The reaction mixture was stirred at room temperature for 3 days.
3. Upon completion of the reaction, the solvent was removed by vacuum distillation. 4.
4. The residue was diluted with water (20 mL) and washed with ether (2 x 20 mL).
5. The aqueous layer was acidified with saturated aqueous sodium bisulfite and then extracted with 2-methyltetrahydrofuran.
6. The organic layer was dried over anhydrous sodium sulfate and subsequently concentrated in vacuo to afford the title compound (2S,3R)-2-((tert-butoxycarbonyl)amino)-3-hydroxybutyric acid as a white solid (730 mg, 99% yield).
7. The product was characterized by 1H NMR (400 MHz, CDCl3) and LC-MS: 1H NMR δ 1.24 (d, 3H), 1.44 (s, 9H), 4.26 (d, 1H), 4.40 (d, 1H), 5.52 (d, 1H), 5.69 (br s, 1H); LCMS Rt = 1.68 min, MS m/z 218 [M + H]+.
