C[O:2][C:3](=O)[C@@H:4]([CH2:15][CH:16]([CH3:18])[CH3:17])[NH:5][P@@:6]([CH3:14])([C:8]1[CH:13]=[CH:12][CH:11]=[CH:10][CH:9]=1)=[O:7].[NH2:20][O:21][K].Cl>>[OH:21][NH:20][C:3](=[O:2])[C@H:4]([NH:5][P@@:6]([CH3:14])([C:8]1[CH:13]=[CH:12][CH:11]=[CH:10][CH:9]=1)=[O:7])[CH2:15][CH:16]([CH3:18])[CH3:17]N-((R)-Methylphenylphosphinyl)-D-leucine methyl ester (60 mg, 0.21 mmol) is treated with a solution of NH2OK (0.57 mL, 1.76M in methanol) prepared as described in Fieser and Fieser, Vol. 1, p. 478. The reaction is stirred for 7 hours at which time TLC indicates completion. The reaction mixture is neutralized with 1M aqueous HCl and the volatiles are removed. The residue is purified by silica gel flash chromatography (95:5 ethyl acetate:ethanol) to give N-hydroxy-2(R)-[[(R)-methylphenylphosphinyl]amino]-4-methylpentanamide as a colorless solid: MS-IS m/z 285 [M+H]+.
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