Synthesis
General procedure for the synthesis of Boc-L-glutamic acid 1-tert-butyl ester from (S)-1-tert-butyl 5-methyl 2-((tert-butoxycarbonyl)amino)pentanedioate: crude N-Boc-glutamic acid 1-tert-butyl ester (5-methyl ester from the previous step, 30.4 g, 95.8 mmol) was dissolved in THF (300 mL), 1N LiOH was added aqueous solution (144 mL). The reaction mixture was stirred at room temperature for 40 min and the progress of the reaction was monitored by TLC to confirm complete consumption of the feedstock. Upon completion of the reaction, THF was removed using a rotary evaporator.The remaining aqueous phase was extracted with ethyl acetate (3 × 100 mL) and subsequently acidified with solid citric acid to pH 4. The acidified aqueous phase was again extracted with ethyl acetate (3 × 100 mL). All the ethyl acetate extracts were combined, washed with saturated brine (2×50 mL), dried over anhydrous magnesium sulfate, filtered and concentrated to give the target product Boc-L-glutamic acid-1-tert-butyl ester as a colorless oil. Yield: 25 g (92% yield, calculated based on Boc-Glu(OMe)-OH). The structure of the product was confirmed by 1H NMR (300 MHz, CDCl3) and 13C NMR (75 MHz, CDCl3).
References
[1] Bioorganic and Medicinal Chemistry Letters, 2007, vol. 17, # 13, p. 3793 - 3797
[2] Journal of Organic Chemistry, 2005, vol. 70, # 22, p. 8730 - 8733
[3] Russian Chemical Bulletin, 2010, vol. 59, # 1, p. 110 - 115
[4] Journal of the American Chemical Society, 1993, vol. 115, # 15, p. 6646 - 6651
[5] Tetrahedron Letters, 2003, vol. 44, # 28, p. 5251 - 5253
