Synthesis
General procedure for the synthesis of BOC-L-pyroglutamic acid ethyl ester from di-tert-butyl dicarbonate and D-pyroglutamic acid ethyl ester: D-pyroglutamic acid ethyl ester (5.1 g, 32.6 mmol) was dissolved in dichloromethane (70 ml), and triethylamine (4.55 ml, 32.6 mmol), di-tert-butyl dicarbonate (14.2 g, 65.2 mmol) and 4- ( dimethylamino)pyridine (3.98 g, 32.6 mmol). The reaction mixture was stirred at room temperature for 1.5 h. The progress of the reaction was monitored by thin layer chromatography (TLC) to confirm that the reaction was complete. After completion of the reaction, the reaction solution was washed twice with water and then with brine, the organic phase was dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The crude product was purified by column chromatography (eluent ratio of 1:1 ethyl acetate/petroleum ether) to afford ethyl Boc-D-pyroglutamate as a light yellow viscous oil (7.98 g, 95% yield), which solidified to a solid after standing.
References
[1] Patent: WO2007/36730, 2007, A1. Location in patent: Page/Page column 120
[2] Bioorganic and Medicinal Chemistry, 2014, vol. 22, # 4, p. 1383 - 1393
[3] Patent: EP1847536, 2007, A1. Location in patent: Page/Page column 28
[4] Patent: US2009/48213, 2009, A1. Location in patent: Page/Page column 70-71
[5] Patent: US2011/34469, 2011, A1. Location in patent: Page/Page column 124
