Diethylamine → 3-Amino-4-oxobutyric acid tert-butyl ester semicarbazone

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Reaction Steps

(3S) 3-(1-Fluorenylmethoxycarbonylamino)-4-oxobutyric acid tert-butyl ester semicarbazone (4; 226 mg, 0.5 mmol; prepared in a similar manner as the benzyloxycarbonly analog described in Graybill et al. Int. J. Protein Res., 44, pp. 173-82 (1994)) was dissolved in 10 ml of acetonitrile (20 ml) and diethylamine (2 ml) was added to the solution. The reaction was stirred for two hours, concentrated in vacuo, the resulting dissolved in acetonitrile and concentrated in vacuo again to give (3S) 3-amino-4-oxobutyric acid tert-butyl ester semicarbazone. A 5° C. solution of the semicarbazone and 3 (188 mg, 0.424 mmol) in methylene chloride/DMF (6 ml of 1:1) was treated with 1-hydroxybenzotriazole (HOBt; 57 mg, 0.424 mmol) and 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride (EDC; 115 mg, 0.6 mmol) and the reaction was stirred at room temperature for 16 hr. The reaction was diluted with ethyl acetate (100 ml) and washed with water, aqueous saturated NaHCO3 and aqueous saturated NaCl, dried over dried over anhydrous Na2SO4 and concentrated in vacuo. Chromatography (SiO2, 5% ammonium hydroxide/5% methanol/methylene chloride eluent) gave 250 mg of 5

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