[CH:1](O)=[O:2].C(OC(=O)C)(=O)C.[CH:11]1([CH2:16][C@H:17]([CH2:21][NH:22][O:23][CH2:24][C:25]2[CH:30]=[CH:29][CH:28]=[CH:27][CH:26]=2)[C:18]([OH:20])=[O:19])[CH2:15][CH2:14][CH2:13][CH2:12]1>C(Cl)Cl>[CH:11]1([CH2:16][C@H:17]([CH2:21][N:22]([CH:1]=[O:2])[O:23][CH2:24][C:25]2[CH:30]=[CH:29][CH:28]=[CH:27][CH:26]=2)[C:18]([OH:20])=[O:19])[CH2:12][CH2:13][CH2:14][CH2:15]1Under a nitrogen atmosphere, formic acid (192 mL, 5 mol) was dissolved in CH2Cl2 (450 mL) and cooled to 0° C. Acetic anhydride (73 mL, 0.77 mol) was then added, and the reaction mixture was stirred for 45 min. After this time, a solution of (2R)-3-cyclopentyl-2-({[(phenylmethyl)oxy]amino}methyl)propanoic acid (22.85 g crude material, assumed 77.1 mmol) in CH2Cl2 (450 mL) was added, and the resulting mixture was stirred for 1.5 h at 0° C. The volatiles were then removed, the crude residue was dissolved in EtOAc (500 mL), and the mixture was washed with brine (4×100 mL). The organics were dried (MgSO4) and concentrated to provide (2R)-3-cyclopentyl-2-({formyl[(phenylmethyl)oxy]amino}methyl)propanoic acid (23.5 g, 100%) as a thick syrup. LCMS: (M+H)+: 306.1.
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