[CH2:1]([O:8][C:9]([NH:11][C@@H:12]([CH:16]([CH3:18])[CH3:17])[C:13]([OH:15])=O)=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.Cl.[CH3:20][O:21]CN.CCN=C=NCCC[N:32]([CH3:34])C.Cl.CCN(C(C)C)C(C)C>C(Cl)Cl>[CH2:1]([O:8][C:9](=[O:10])[NH:11][C@H:12]([C:13](=[O:15])[N:32]([O:21][CH3:20])[CH3:34])[CH:16]([CH3:18])[CH3:17])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1To (S)-2-benzyloxycarbonylamino-3-methyl-butyric acid (7) (50.0 g, 199 mmol), N-methoxymethylamine hydrochloride (38.8 g, 398 mmol) and EDC.HCl (47.7 g, 249 mmol) in DCM (500 mL) was added DIPEA (87 mL, 497 mmol) and the reaction mixture stirred at ambient temperature for 20 h, after which time the reaction mixture was diluted with DCM (200 mL), washed with 1M HCl (aq) (3×200 mL), 1M NaOH (aq) (200 mL), sat. NaHCO3 (aq) (200 mL) and brine (300 mL). The organic layer was dried over MgSO4, filtered and the solvent removed under vacuum to give the desired compound as a colourless oil (51.2 g, 87%); (AnalpH2_MeOH—4 min) Rt 2.76 min; m/z 295 (MH)+.
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