[CH3:1][C:2]1[CH:10]=[CH:9][C:5]([C:6](Cl)=[O:7])=[CH:4][CH:3]=1.[CH3:11][C@H:12]1[C:16](=[O:17])[O:15][C:14](=[O:18])[NH:13]1>C(OCC)(=O)C.CN(C)C1C=CN=CC=1>[CH3:1][C:2]1[CH:10]=[CH:9][C:5]([C:6]([N:13]2[C@@H:12]([CH3:11])[C:16](=[O:17])[O:15][C:14]2=[O:18])=[O:7])=[CH:4][CH:3]=1p-Methylbenzoyl chloride (309 mg, 2.0 mmol) was dissolved in ethyl acetate (5 mL), followed by the addition of (S)-4-methyl-2,5-oxazolidinedione (L-alanine-NCA) (230 mg, 2.0 mmol) under ice cooling. Further, a solution of 4-dimethylaminopyridine (244 mg, 2.0 mmol) in ethyl acetate (10 mL) was added dropwise under ice cooling over 20 minutes. After the resulting mixture was stirred as was at 0° C. for 2 hours, a precipitated salt was filtered off, and the filtrate was concentrated under reduced pressure. The concentration residue was re-dissolved in a mixed solvent consisting of ethyl acetate (5 mL) and hexane (5 mL), and insoluble matter was filtered off. The filtrate was concentrated under reduced pressure to afford the title compound (152 mg, 33%) as a colorless clear syrup.
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