CI.[C:3]([O:7][C:8]([NH:10][CH2:11][CH2:12][CH2:13][CH:14]([OH:18])[C:15]([OH:17])=[O:16])=[O:9])([CH3:6])([CH3:5])[CH3:4].[C:19]([O-])(O)=O.[Na+].O>CN(C=O)C>[CH3:19][O:16][C:15](=[O:17])[CH:14]([OH:18])[CH2:13][CH2:12][CH2:11][NH:10][C:8]([O:7][C:3]([CH3:6])([CH3:4])[CH3:5])=[O:9]A solution of methyl iodide (11.5 mL, 0.189 mol) in DMF (50 mL) was added dropwise during 15 min. to a mixture of 5-tert-butoxycarbonylamino-2-hydroxy-pentanoic acid (22.0 g, 94.4 mmol) and NaHCO3 (11.8 g, 141 mmol) in DMF (150 mL). After stirring over night, water was added and the mixture was extracted with ethyl acetate. The pooled organic phases were washed with water and brine, dried and concentrated under reduced pressure. The crude product was purified using chromatography (heptane/ethyl acetate, 1:1) to give 5-tert-butoxycarbonylamino-2-hydroxy-pentanoic acid methyl ester 9.9 g, 42.5%).
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