[NH2:1][C@:2]([CH3:14])([CH2:5][CH2:6][C:7]1[N:8]([CH2:12][CH3:13])[CH:9]=[CH:10][CH:11]=1)[CH2:3][OH:4].[C:15](OC(OC(C)(C)C)=O)(OC(C)(C)C)=[O:16].C(N(CC)CC)C.O>ClCCl.CN(C)C1C=CN=CC=1>[CH3:14][C@@:2]1([CH2:5][CH2:6][C:7]2[N:8]([CH2:12][CH3:13])[CH:9]=[CH:10][CH:11]=2)[CH2:3][O:4][C:15](=[O:16])[NH:1]1
Subsequently, to a suspension of (2R)-2-amino-2-methyl-4-(1-ethylpyrrol-2-yl)butan-1-ol ½ D-(−)tartrate (55.5 mg, 0.16 mmol) in dichloromethane (1.6 ml) were added successively di-t-butyl dicarbonate (0.17 g, 0.78 mmol), triethylamine (0.22 ml, 1.58 mmol) and 4-dimethylaminopyridine (3.0 mg, 0.025 mmol) with stirring, and the resulting mixture was stirred at room temperature for 20minutes. After stirring, water was added to the reaction mixture, and the resulting mixture was concentrated in vacuo. The residue obtained was purified by chromatography on a silica gel column using a mixed solvent of hexane and ethylacetate (1:1) as the eluent to afford (4R)-4-methyl-4-[2-(1-ethylpyrrol-2-yl)ethyl]-1,3-oxazolidin-2-one (18.0 mg, yield: 58%).
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