[S:1]1[CH:5]=[CH:4][CH:3]=[C:2]1[C:6](=[NH:30])[NH:7][C:8]1[CH:9]=[CH:10][C:11]2[N:16]([CH:17]3[CH2:21][CH2:20][N:19](C(OC(C)(C)C)=O)[CH2:18]3)[CH2:15][CH2:14][S:13][C:12]=2[CH:29]=1.Cl>CO>[NH:19]1[CH2:20][CH2:21][CH:17]([N:16]2[CH2:15][CH2:14][S:13][C:12]3[CH:29]=[C:8]([NH:7][C:6]([C:2]4[S:1][CH:5]=[CH:4][CH:3]=4)=[NH:30])[CH:9]=[CH:10][C:11]2=3)[CH2:18]1A solution of tert-butyl 3-(7-(thiophene-2-carboximidamido)-2H-benzo[b][1,4]thiazin-4(3H)-yl)pyrrolidine-1-carboxylate (0.24 g, 0.554 mmol) in MeOH (5 mL) was treated with 1N HCl solution (9.98 mL, 9.98 mmol) at room temperature. The resulting mixture was refluxed for 30 minutes and brought to room temperature. The mixture was filtered and quenched with 1N NaOH (10 mL). The mixture was diluted with water (50 mL) and extracted with CH2Cl2 (2×50 mL). The organic phase was washed with brine (50 mL) and dried (Na2SO4). The crude material was subject to flash chromatography on silica gel (5-20% 2M NH3MeOH/CH2Cl2). The collected fractions gave compound 30 as yellow foam (0.15 g, 79%). 1H NMR (DMSO-d6) δ 7.69 (d, J=3.0 Hz, 1H), 7.56 (dd, J=0.9, 4.9 Hz, 1H), 7.07 (dd, J=3.9, 4.9 Hz, 1H), 6.79 (d, J=9.0 Hz, 1H), 6.52-6.49 (m, 2H), 6.31 (brs, 2H), 4.26-4.17 (m, 1H), 3.42-3.22 (m, 2H), 3.10-2.90 (m, 4H), 2.83-2.69 (m, 2H), 2.07-1.96 (m, 1H), 1.68-1.57 (m, 1H); ESI-MS (m/z, %): 347, 345 (MH+, 72), 278, 276 (100).
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