Synthesis
General procedure for the synthesis of (S)-6-amino-2-((tert-butoxycarbonyl)amino)hexanoic acid methyl ester from (S)-6-(((benzyloxy)carbonyl)amino)-2-((tert-butoxycarbonyl)amino)hexanoic acid: intermediate 4 (839 mg, 2.1 mmol) was dissolved in methanol (15 mL). After addition of catalytic amount of Pd/C, the reaction was stirred under hydrogen atmosphere and room temperature for 40 min. The completion of the reaction was monitored by thin-layer chromatography (TLC, unfolding reagent ratio of ethyl acetate:hexane = 2:1). After completion of the reaction, the reaction solution was filtered through a diatomaceous earth pad. The filtrate was concentrated under reduced pressure to give Intermediate 5 (563 mg, quantitative yield) as a colorless oil, which can be used in subsequent reactions without further purification.
References
[1] Patent: US2015/80551, 2015, A1. Location in patent: Paragraph 0047
[2] Angewandte Chemie - International Edition, 2017, vol. 56, # 6, p. 1643 - 1647
[3] Angew. Chem., 2017, vol. 129, # 6, p. 1665 - 1669,5
[4] Tetrahedron, 1982, vol. 38, p. 697
[5] Chemistry - A European Journal, 2011, vol. 17, # 18, p. 5011 - 5018