[NH2:1][C@@H:2]([CH2:8][CH:9]([CH3:11])[CH3:10])[CH:3]([OH:7])[C:4]([OH:6])=[O:5].C(N(CC)CC)C.[C:19]([O:23][C:24](ON=C(C1C=CC=CC=1)C#N)=[O:25])([CH3:22])([CH3:21])[CH3:20]>O.O1CCOCC1>[C:19]([O:23][C:24]([NH:1][C@@H:2]([CH2:8][CH:9]([CH3:11])[CH3:10])[CH:3]([OH:7])[C:4]([OH:6])=[O:5])=[O:25])([CH3:22])([CH3:21])[CH3:20]To a solution of 3.22 g of (2RS,3S)-3-amino-2-hydroxy-5-methylhexanoic acid and 3.08 ml of triethylamine in 30 ml of water was added a solution of 5.41 g of 2-(tert-butyloxycarbonyloxyimino)-2-phenylacetonitrile in 30 ml of dioxane, and the mixture was stirred for 16 hours at room temperature. To the reaction mixture was added 100 ml of water, and the mixture was extracted with ethyl acetate to remove neutral materials. The aqueous layer was acidified by the addition of an aqueous citric acid solution, and the acid solution was extracted with ethyl acetate. The ethyl acetate layer was washed with a saturated sodium chloride aqueous solution, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure to obtain 5.10 g of (2RS,3S)-3-tert-butyloxycarbonylamino-2-hydroxy-5-methylhexanoic acid as a pale yellow oil.
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