{2-[(1-Benzyl-5-hydroxy-2-oxo-3-phenyl-1,2-dihydro-[1,7]naphthyridine-6-carbonyl)-amino]ethyl}-carbamic acid tert-butyl ester (25 mg, 0.049 mmol) was dissolved in CH2Cl2 (2 mL). Trifluoroacetic acid (1 mL) was added, and the mixture was stirred for 2 h. Solvent and excess TFA was removed by evaporation, and to the residue were added CH2Cl2 (3 mL), triethylamine (0.068 mL, 0.49 mmol), and ethyl isocyanate (17 mg, 0.24 mmol). The resulting mixture was stirred overnight. EtOAc (50 mL) and 0.1 M HCl (20 mL) were added, and the aqueous layer was extracted with additional EtOAc. The organic layers were combined, dried over MgSO4 and concentrated. The crude product was purified by silica gel chromatography (0-8% MeOH/CH2Cl2) to give 17 mg of the title compound as a pale yellow solid. MS: (+) m/z 486.39 (M+1).
