[C:1]([O:5][C:6](=[O:12])[NH:7][C@H:8]([CH3:11])[CH2:9][OH:10])([CH3:4])([CH3:3])[CH3:2].C(N(CC)C(C)C)(C)C.[CH3:22][S:23](Cl)(=[O:25])=[O:24].[Cl-].[NH4+]>ClCCl>[C:1]([O:5][C:6]([NH:7][C@H:8]([CH3:11])[CH2:9][O:10][S:23]([CH3:22])(=[O:25])=[O:24])=[O:12])([CH3:4])([CH3:2])[CH3:3]((R)-2-Hydroxy-1-methyl-ethyl)-carbamic acid tert-butyl ester (0.5 g, 2.85 mmol) was dissolved in dichloromethane (14 ml) and stirred in an ice bath. N,N-diisopropylethylamine (0.75 ml, 4.28 mmol) and then methanesulfonyl chloride (0.27 ml, 3.4 mmol) were slowly added and the reaction was warmed to room temperature over 16 h. Ammonium chloride solution was added to the reaction and it was extracted two times with ethyl acetate. The combined organics were washed with sodium chloride solution and dried over sodium sulfate. Evaporation gave 0.73 g of methanesulfonic acid (R)-2-tert-butoxycarbonylamino-propyl ester as a waxy white solid. 1H NMR (CDCl3) δ: 4.51-4.68 (m, 1H), 4.19-4.28 (m, 1H), 4.11-4.18 (m, 1H), 3.90-4.04 (m, 1H), 3.03 (s, 3H), 1.24 (d, J=6.8 Hz, 3H).
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