[CH3:1][O:2][C@H:3]([CH3:9])[C@@H:4]([C:6]([OH:8])=[O:7])[NH2:5].[OH-].[Na+].Cl[C:13]([O:15][CH3:16])=[O:14].Cl>O>[CH3:1][O:2][C@H:3]([CH3:9])[C@H:4]([NH:5][C:13]([O:15][CH3:16])=[O:14])[C:6]([OH:8])=[O:7]To a mixture of O-methyl-L-threonine (3.0 g, 22.55 mmol), NaOH (0.902 g, 22.55 mmol) in H2O (15 mL) was added ClCO2Me (1.74 mL, 22.55 mmol) dropwise at 0° C. The mixture was allowed to stir for 12 h and acidified to pH 1 using 1N HCl. The aqueous phase was extracted with EtOAc and (2×250 mL) and 10% MeOH in CH2Cl2 (250 mL) and the combined organic phases were concentrated under in vacuo to afford a colorless oil (4.18 g, 97%) which was of sufficient purity for use in subsequent steps. 1H NMR (400 MHz, CDCl3) δ 4.19 (s, 1H), 3.92-3.97 (m, 1H), 3.66 (s, 3H), 1.17 (d, J=7.7 Hz, 3H). LC-MS: Anal. Calcd. for C7H13NO5: 191; found: 190 (M−H)−.
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