[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[CH:17]=[C:16]([CH2:18][CH2:19][C:20]([O:22]C(C)(C)C)=[O:21])[CH:15]=[CH:14][N:13]=2)=[N:3]1.C(OC(C)C)(C)C>FC(F)(F)C(O)=O>[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[CH:17]=[C:16]([CH2:18][CH2:19][C:20]([OH:22])=[O:21])[CH:15]=[CH:14][N:13]=2)=[N:3]1tert-Butyl 3-[2-(4-oxo-4H-1,3-benzothiazin-2-yl)-4-pyridyl]propionate (0.45 g, 1.2 mmol) was dissolved in trifluoroacetic acid (3.0 ml), and the mixture was stirred at room temperature for 2.5 hrs. Isopropyl ether was added to the reaction mixture to precipitate crystals, which were collected by filtration and washed with ethanol-hexane to give the titled compound (0.32 g, 84%) as white crystals.
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