General procedure for the synthesis of 3-((tert-butoxycarbonyl)amino)glutaric acid from β-glutamic acid and di-tert-butyl dicarbonate: β-glutamic acid (1.01 g, 6.8 mmol) was dissolved in a mixed solvent of tetrahydrofuran (30 mL) and water (15 mL). Subsequently, di-tert-butyl dicarbonate (2.98 g, 13.6 mmol) and 10% aqueous sodium hydroxide (8.3 mL) were added and the reaction mixture was stirred at room temperature for 5 days. Upon completion of the reaction, the solvent was removed by evaporation and the residue was redissolved in water (30 mL) and the pH was adjusted to 2 with 1 M potassium bisulfate solution. the aqueous phase was extracted with ethyl acetate (2 x 60 mL), the organic layers were combined, dried with anhydrous sodium sulfate, filtered and concentrated to afford 1.5 g (90% yield) of 3-((tert-butoxycarbonyl)amino)glutaric acid as a white crystal. The product was confirmed by NMR hydrogen spectroscopy (MeOD): δ 1.43 (s, 9H), 2.55 (d, 4H), 4.25 (quin, 1H). HPLC-MS (Method B) showed: m/z 148 ([M+1-Boc]+).
