Dicyclohexylcarbodiimide → 4-Cyano-3-methylbenzoic acid

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4-Cyano-3-methyl-benzoic acid is synthesized based on the method described in patent EP1512687A1. To a solution of 2-pyridin-3-yl-1H-indole-5-carbonitrile (20 mg, 0.09 mmol), 4-dimethylaminopyridine (22 mg, 0.01 mmol) and 4-cyano-3-methyl-benzoic acid (29 mg, 0.18 mmol) at 0° C. in dichloromethane (2 mL) is added DCC (38 mg, 0.18 mmol). After stirring for 10 min the reaction is warmed to room temperature. A precipitate forms and stirring is continued for 16 h. The mixture is filtered and the filtrate is diluted with dichloromethane (10 mL), washed with water and a saturated sodium chloride solution. The combined organic extracts are dried over sodium sulfate, filtered, and concentrated. The resulting residue is purified by silica gel flash chromatography (ethyl acetate-heptane, 0:1 to 1:1) to furnish 1-(4-cyano-3-methyl-benzoyl)-2-pyridin-3-yl-1H-indole-5-carbonitrile. 1H NMR (400 MHz, CDCl3) δ ppm 2.47 (s, 3H), 6.91 (s, 1H), 7.14 (dd, J=8.0, 4.9 Hz, 1H), 7.43-7.48 (m, 2H), 7.49-7.54 (m, 2H), 7.61 (dd, J=8.7, 1.6 Hz, 1H), 7.93 (d, J=8.6 Hz, 1H), 8.03 (d, J=1.0 Hz, 1H), 8.44 (dd, J=4.8, 1.5 Hz, 1H), 8.55 (d, J=1.8 Hz, 1H). HRMS (ESI) m/z 363.1245 [(M+H)+: Calcd for C23H15N4O: 363.1246].

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