[C:1]([O:5][C:6]([N:8]([CH2:10][C:11]([OH:13])=O)[CH3:9])=[O:7])([CH3:4])([CH3:3])[CH3:2].CCN(CC)CC.ClC(OCC(C)C)=O.Cl.[CH2:30]([O:32][C:33](=[O:37])[CH2:34][NH:35][CH3:36])[CH3:31]>C(Cl)Cl>[CH2:30]([O:32][C:33](=[O:37])[CH2:34][N:35]([C:11](=[O:13])[CH2:10][N:8]([C:6]([O:5][C:1]([CH3:2])([CH3:3])[CH3:4])=[O:7])[CH3:9])[CH3:36])[CH3:31]
To a stirred solution of (tert-butoxycarbonyl-methyl-amino)-acetic acid (37 g, 0.2 mol) and Et3N (60.6 g, 0.6 mol) in CH2Cl2 (300 mL) was added isobutyl chloroformate (27.3 g, 0.2 mmol) dropwise at −20° C. under argon. After stirring for 0.5 h, methylamino-acetic acid ethyl ester hydrochloride (30.5 g, 129 mmol) was added dropwise at −20° C. The mixture was allowed to warm to room temperature (c.a. 1 h) and quenched with water (500 mL). The organic layer was separated, washed with 10% citric acid solution, dried over Na2SO4, filtered and concentrated. The residue was purified by column chromatography (petroleum ether/EtOAc 1:1) to give {[2-(tert-butoxycarbonyl-methyl-amino)-acetyl]-methyl-amino}-acetic acid ethyl ester (12.5 g, 22
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