The general procedure for the synthesis of N-Fmoc-N'-Boc-L-2,4-diaminobutyric acid from di-tert-butyl dicarbonate and Fmoc-L-2,4-diaminobutyric acid was as follows: 50 g (146.8 mmol) of Fmoc-L-2,4-diaminobutyric acid was suspended in 700 mL of a mixed solvent of acetone and water (1:1, v/v/v/v/v) at 0-10 °C. 38.4 g (176 mmol) of di-tert-butyl dicarbonate was slowly added. Subsequently, the pH of the reaction system was adjusted to 7.5-8 with 0.5 N NaOH solution.After 4 h of reaction, 56 g of N-fluorenylmethoxycarbonyl-N'-tert-butoxycarbonyl-L-2,4-diaminobutyric acid was obtained by the treatment in a yield of 86.62% and a purity of 99.4% by HPLC. The structure of the product was confirmed by IR and NMR spectra as detailed in Figures 3 and 4 in the literature.
[1] Patent: CN105348147, 2016, A. Location in patent: Paragraph 0020
[2] Bulletin of the Chemical Society of Japan, 2004, vol. 77, # 10, p. 1915 - 1924
[3] European Journal of Medicinal Chemistry, 1995, vol. 30, # 2, p. 115 - 122
