A 200 mL flask was charged with 2.25 g 3-nitrobenzoic acid (13.46 mmol, 1.0 equiv), 3.59 g 2-aminobenzimidazole (26.92 mmol, 2.0 equiv), 5.63 g O-benzotriazol-1-yl-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HBTU, 14.81 mmol, 1.10 equiv), and 1-hydroxybenzotriazole hydrate (HOBT, 14.13 mmol, 1.05 equiv). The flask was then charged with 40 mL DMF, stirring was initiated (magnetic stirrer) and 1.71 mL N-methylmorpholine (NMM, 15.48 mmol, 1.15 equiv) was added in one portion to the suspension. After 6 h, the suspension was diluted with 200 mL of a 10% citric acid solution. After stirring an additional 30 min, the suspension was filtered and the resulting solid was washed (2×H2O, then 2×sat. NaHCO3). The solid was then triturated with EtOAc (30 mL), filtered, and dried under reduced pressure to give 3.16 g of the product as a tan solid (11.2 mmol). 1H NMR (DMSO-d6, 400 MHz) δ 12.60 (broad s, 2H), 8.96 (t, J=2.1 Hz, 1H), 8.55 (d, J=7.8 Hz, 1H), 8.38 (m, 1H), 7.78 (t, J=7.9 Hz, 1H), 7.43 (dd, J=3.2, 5.9 Hz, 2H), 7.18 (dd, J=3.2, 5.9 Hz, 2H); MS: ESI(−) m/z 281.1 (M−H).
