Benzylamine (360 mg, 3.36 mmol, 3.0 eq) is added at room temperature to a stirred solution of {trans-4-[2-(3-chloro-6-methoxy-[1,5]naphthyridin-4-yl)-1-formyl-vinyl]-cyclohexyl}-carbamic acid tert-butyl ester (500 mg, 1.12 mmol, 1.0 eq) in ethanol (20 mL), followed by acetic acid (337 mg, 5.61 mmol, 5.0 eq) and sodium cyanoborohydride (352 mg, 5.61 mmol, 5.0 eq). After 2 hours stirring at room temperature, the reaction mixture is extracted with ethyl acetate (3×20 mL) and a saturated sodium hydrogen carbonate aqueous solution (20 mL). The combined organic layers are dried over sodium sulfate, filtered and concentrated to give a residue that is purified by column chromatography (silica gel, eluent: ethyl acetate:petroleum ether, 3:1 to 1:1, v/v) to afford {trans-4-[1-(benzylamino-methyl)-2-(3-chloro-6-methoxy-[1,5]naphthyridin-4-yl)-vinyl]-cyclohexyl}-carbamic acid tert-butyl ester as a light yellow solid (320 mg, 53% yield).
