In an inert atmosphere, a solution of 4-(methoxycarbonyl)-3,5-dimethylbenzoic acid (2.08 g, 10 mmol), diphenylphosphoryl azide (2.8 g, 10.17 mmol) and diisopropylethylamine (1.92 mL, 11 mmol) in benzene (25 mL) is stirred at room temperature for 1 h, then the reaction temperature is slowly raised to 75° C. The reaction is held at that temperature until the evolution of gas (CO2) is no longer evident and the reaction solution containing 3,5-dimethyl-4-(methoxycarbonyl)phenylisocyanate is cooled to 40° C. Another portion of diisopropylethylamine (1.92 mL, 11 mmol) is added, followed by 1H-indole-4-methanamine hydrochloride salt (Example 68; 2.95 g, 11 mmol) and the solution is stirred and heated at reflux under argon overnight. The reaction mixture is cooled, diluted with benzene (50 mL) and washed in turn with 1N hydrochloric acid (50 mL) and dilute brine. The aqueous layers are re-extracted with benzene and the combined extracts are dried (MgSO4) and evaporated under reduced pressure. The product is purified if necessary by crystallization or by chromatography over silica gel using increasing concentrations of ethyl acetate in hexane to furnish the urea, 4-[[(1H-indol-4-yl)methylamino]carbonyl]amino-2,6-dimethylbenzoic acid, methyl ester.
