[C:1]([O:5][C:6](=[O:13])[NH:7][CH2:8][C:9]([OH:12])([CH3:11])[CH3:10])([CH3:4])([CH3:3])[CH3:2].C(N(C(C)C)C(C)C)C.[C:23](OC(=O)C)(=[O:25])[CH3:24]>ClCCl.CN(C)C1C=CN=CC=1.C(OCC)(=O)C>[C:23]([O:12][C:9]([CH3:11])([CH3:10])[CH2:8][NH:7][C:6]([O:5][C:1]([CH3:4])([CH3:2])[CH3:3])=[O:13])(=[O:25])[CH3:24]
2-Hydroxy-2-methylpropylcarbamic acid tert-butylester (510 mg, 2.69 mmol) was dissolved in dichloromethane (7 ml). The solution was cooled to 0° C. Ethyldiisopropylamine (0.70 ml, 4.04 mmol), 4-dimethylaminopyridine (33 mg, 0.27 mmol), and acetic acid anhydride (0.33 ml, 3.50 mmol) were added successively. The reaction mixture was stirred for 16 h, while slowly warming up to room temperature. It was diluted with ethyl acetate (30 ml) and extracted with 1N hydrochloric acid (30 ml). The aqueous phase was extracted with ethyl acetate (2×20 ml). The combined organic layers were washed with saturated sodium hydrogen carbonate solution (50 ml) and dried over magnesium sulfate. The solvent was removed in vacuo. The crude product was purified by flash chromatography on silica (100 g), using ethyl acetate/heptane (1:2) as eluent, to give 550 mg of 2-(tert-butoxycarbonylamino)-1,1-dimethylethyl acetate.
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