[C:1]([O:5][C:6](=[O:17])[CH2:7][CH2:8][NH:9][C:10]([O:12][C:13]([CH3:16])([CH3:15])[CH3:14])=[O:11])([CH3:4])([CH3:3])[CH3:2].[CH:18]([N-]C(C)C)(C)[CH3:19].[Li+].C(Br)C.[Cl-].[NH4+]>O1CCCC1.CN(P(N(C)C)(N(C)C)=O)C>[C:1]([O:5][C:6](=[O:17])[CH:7]([CH2:18][CH3:19])[CH2:8][NH:9][C:10]([O:12][C:13]([CH3:16])([CH3:15])[CH3:14])=[O:11])([CH3:4])([CH3:3])[CH3:2]t-Butyloxycarbonyl-β-alanine t-butyl ester (2.26 g) was added dropwise to a solution of lithium diisopropylamide (LDA) (6.9 ml, 13.8 mmol) in tetrahydrofuran (10 ml) at -78° C. and hexamethylphosphoroamide (HMPA) (2 ml) was added thereto. The temperature of the reaction solution was elevated gradually to -20° C. over 1 hour and lowered again to -78° C. To the reaction solution, ethyl bromide (0.76 ml) was added dropwise. The temperature of the solution was elevated to 0° C. over 2 hours and the reaction was stopped by adding a saturated aqueous solution of ammonium chloride. After the solvent was distilled off, the residue was dissolved in ethyl acetate and washed sequentially with a 5% aqueous solution of sodium hydrogencarbonate, a 5% aqueous solution of citric acid and a saturated aqueous solution of NaCl 3 times each. The ethyl acetate layer was dried over anhydrous sodium sulfate and the solvent was then distilled off to yield an oil. The obtained oil was applied to a silica gel column (2.5×40 cm) and eluted with a mixed solution (hexane:ethyl acetate=40:1). The desired fractions were collected and the solvents were distilled off to yield an oil of N-t-butyloxycarbonyl-α-ethyl-β-alanine-t-butyl ester (0.98 g, 38.9%).
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