[C:1]([O:5][C:6]([NH:8][C@@H:9]([CH2:13][C:14]1[CH:19]=[C:18]([F:20])[CH:17]=[C:16]([F:21])[CH:15]=1)[C:10](O)=[O:11])=[O:7])([CH3:4])([CH3:3])[CH3:2].CN1CCOCC1.ClC(OCC(C)C)=O.[BH4-].[Na+]>COCCOC.O>[C:1]([O:5][C:6](=[O:7])[NH:8][C@H:9]([CH2:10][OH:11])[CH2:13][C:14]1[CH:19]=[C:18]([F:20])[CH:17]=[C:16]([F:21])[CH:15]=1)([CH3:2])([CH3:4])[CH3:3]
Dissolve commercially available 2-(S)-tert-butoxycarbonylamino-3-(3,5-difluorophenyl)propionic acid (5.995 g, 19.9 mmol) in ethylene glycol dimethyl ether (20 mL) and cool −20° C. Add 4-methylmorpholine (2.4 mL, 21.89 mmol) and stir 5 min, then add isobutyl chloroformate (2.9 mL, 21.89 mmol) dropwise and stir 5 min. Filter into −15° C. cooled flask with course frit, rinse with cold ethylene glycol dimethyl ether. Add sodium borohydride (1.129 g, 29.85 mmol) in water (9 mL) followed by water (500 mL), then warm to room temperature. Filter and dissolve solid in dichloromethane. Wash with saturated aqueous sodium chloride, dry (magnesium sulfate) and concentrate to give the title compound as a solid (4.57 g, 80%).
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