A solution of sodium hydroxide (500 mg, 12.5 mmol, 33.6 eq) in water (6 mL) is added at room temperature to a stirred solution of {trans-4-[1-(benzylamino-methyl)-2-(3-chloro-6-methoxy-[1,5]naphthyridin-4-yl)-vinyl]-cyclohexyl}-carbamic acid tert-butyl ester (200 mg, 0.37 mmol, 1.0 eq) in tetrahydrofuran (6 mL). After 16 hours stirring at 60° C., tetrahydrofuran is removed and the residue is extracted with ethyl acetate (3×10 mL). The combined organic layers are dried over sodium sulfate, filtered and concentrated to give the crude product that is purified by column chromatography (silica gel, eluent: petroleum ether:ethyl acetate, 5:1 to 3:1, v/v) to afford [trans-4-(1-benzyl-6-methoxy-1,2-dihydro-1,5,9-triaza-phenanthren-3-yl)-cyclohexyl]-carbamic acid tert-butyl ester as a light yellow solid (110 mg, 59% yield).
