C([O:3][C:4]([C:6]1[C:14]2[CH2:13][CH2:12][N:11]([C:15]([O:17][C:18]([CH3:21])([CH3:20])[CH3:19])=[O:16])[CH2:10][C:9]=2[S:8][C:7]=1[NH2:22])=O)C.C(O)(=O)C.[CH:27](N)=[NH:28]>CN(C=O)C>[C:18]([O:17][C:15]([N:11]1[CH2:10][C:9]2[S:8][C:7]3[N:22]=[CH:27][NH:28][C:4](=[O:3])[C:6]=3[C:14]=2[CH2:13][CH2:12]1)=[O:16])([CH3:21])([CH3:20])[CH3:19]To a 2-Amino-4,7-dihydro-5H-thieno[2,3-c]pyridine-3,6-dicarboxylic acid 6-tert-butyl ester 3-ethyl ester (5.0 g, 15 mmol) in DMF (50 mL) solution was added formamidine acetate (2.39 g, 23 mmol, 1.5 equiv). The mixture was heated at 100° C. in an oil bath for overnight. The reaction mixture was cooled to rt and then concentrated in vacuo. Ethyl acetate (50 mL) was added to the reaction solid mixture and stirred at rt for 2 h. The mixture was then filtered, rinsed with ethyl acetate (25 mL). The solid was placed in a vacuum oven and dried for overnight to yield a white solid (4.17 g, 90.6%). 1H NMR (CD3OD-d4) δ 8.05 (s, 1H), 4.57 (s, 2H), 3.61 (t, 2H), 2.92 (t, 2H), 1.42 (s, 9H); LCMS RT=2.78 min, [M+H]+=308.0.
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