5-(2-(3-Ethylureido)pyridin-4-yloxy)indole-1-carboxylic acid piperidin-4-ylamide (36 mg, 0.085 mmol, Example 181) was dissolved in tetrahydrofuran (2.0 ml) and methanol (1.0 ml); and a 37% aqueous formaldehyde solution (0.036 ml, 0.43 mmol) and acetic acid (0.0098 ml, 0.17 mmol) were added thereto. While stirring at room temperature, sodium triacetoxyborohydride (27 mg, 0.13 mmol) was added; and the reaction mixture was stirred for 30 minutes. The reaction mixture was partitioned between ethyl acetate and a saturated aqueous solution of sodium hydrogencarbonate; and the organic layer was washed with brine and dried over anhydrous sodium sulfate. The solvent was distilled off under reduced pressure; the obtained crystals were suspended in diethyl ether, filtered off, washed with diethyl ether, and dried to yield the title compound (25 mg, 0.057 mmol, 67%) as colorless crystals.
