136083-57-3

56-84-8

102774-86-7

136083-57-3

1. 3.03 g (22.8 mmol, 1.2 equiv) L-aspartic acid was dissolved in 54 mL (68.8 mmol, 3.6 equiv) of 13.5% (m/v) aqueous sodium carbonate in a 250 mL dry round bottom flask. 2. The reaction medium was cooled in an ice bath at 0°C, followed by the addition of 6.41 g (19.0 mmol, 1 equiv) of N-(9-fluorenylmethoxycarbonyloxy)succinimide (N-Fmoc) solution dissolved in 44 mL of DMF. 3. The reaction mixture was stirred vigorously (precipitate formed in the reaction medium) and stirring was continued for 1 hour at ambient temperature. 4. The reaction mixture was diluted with 665 mL of water and extracted sequentially with ether (1 x 80 mL) and ethyl acetate (2 x 60 mL). 5. The aqueous phase was cooled in an ice bath and acidified with concentrated hydrochloric acid (6 N) to pH 2, at which point the product precipitated as an oil. 6. The aqueous phase containing the precipitated product was extracted with ethyl acetate (6 x 60 mL). 7. The organic phases were combined and washed sequentially with saturated aqueous sodium chloride solution (3 x 35 mL) and water (2 x 35 mL), followed by drying with sodium sulfate. 8. Concentrate the organic phase to a small volume in a rotary evaporator (35°C). 9. recrystallize Fmoc-D-aspartic acid by addition of about 10 times the volume of petroleum ether (stirring vigorously). 10. The mixture was allowed to stand at 4°C for 2 hours to facilitate separation, after which the precipitate was collected by filtration and dried in a vacuum oven for 24 hours. 11. 6.22 g (17.5 mmol) of Fmoc-D-aspartic acid was obtained as a fine white powder in 92% yield. 12. 12. Product characterization: empirical formula C19H17NO6, molecular weight 355.35 g/mol, melting point 181°C. TLC analysis (Rf = 0.8, eluent: 60% AcOH/BuOH 4/6 v/v). ESI-MS+: m/z 378.1 [M + Na]+ (calculated value C17H17NO6Na: 378.1). 1H-NMR and 13C NMR. NMR and 13C NMR data are consistent with the structure.