[O:1]=[C:2]1[C:7]2[CH:8]=[CH:9][CH:10]=[CH:11][C:6]=2[S:5][C:4]([C:12]2[N:17]=[CH:16][CH:15]=[C:14]([CH2:18][CH2:19][C:20]([OH:22])=O)[CH:13]=2)=[N:3]1.ClC(OCC(C)C)=O.C([N:33](CC)CC)C.[NH4+]>C1COCC1>[O:1]=[C:2]1[C:7]2[CH:8]=[CH:9][CH:10]=[CH:11][C:6]=2[S:5][C:4]([C:12]2[N:17]=[CH:16][CH:15]=[C:14]([CH2:18][CH2:19][C:20]([NH2:33])=[O:22])[CH:13]=2)=[N:3]13-[6-(4-Oxo-4H-1,3-benzothiazin-2-yl)-4-pyridyl]propionic acid (0.31 g, 1.00 mmol), isobutyl chloroformate (0.22 ml, 1.50 mmol) and triethylamine (0.22 ml, 1.50 mmol) were dissolved in THF (10 ml), and the mixture was stirred under ice cooling condition for 1 hr. 25% aqueous ammonium solution was added to the mixture, and the mixture was stirred under ice cooling condition for 0.5 hr. The obtained precipitates were recrystallized from ethanol to give the titled compound (0.15 g, 49%) as white crystals.
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