[NH2:1][C@@H:2]([C:7]([CH3:10])([CH3:9])[CH3:8])[CH2:3][C:4]([OH:6])=[O:5].[C:11]([Cl:14])(=O)C>CO>[Cl-:14].[CH3:11][O:5][C:4](=[O:6])[CH2:3][C@@H:2]([NH3+:1])[C:7]([CH3:10])([CH3:9])[CH3:8](R)-3-amino-4,4-dimethylpentanoic acid, 2a, was dissolved in methanol (1.4 L). The solution was cooled in an ice bath and acetyl chloride (67.0 mL, 947.0 mmol) was added dropwise (maintaining the temperature below 10° C.). The reaction mixture was heated to 65° C. and stirred at that temperature for 3 h. The reaction mixture was cooled to room temperature and then flushed with toluene to remove volatiles. The crude material was used without further purification: 1H NMR (400 MHz, MeOH-d4) δ 3.75 (s, 3H), 3.41 (t, 1H), 2.88 (dd, 1H), 2.64-2.46 (m, 1H), 1.04 (s, 9H).
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