Methanol → 4-[(1-Cyclohexylmethyl-5-hydroxy-2-oxo-3-phenyl-1,2-dihydro-[1,7]naphthyridine-6-carbonyl)-amino]-butyric acid

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A mixture of 4-[(1-cyclohexylmethyl-5-hydroxy-2-oxo-3-phenyl-1,2-dihydro-[1,7]naphthyridine-6-carbonyl)-amino]-butyric acid ethyl ester (39 mg, 0.079 mmol), 2 M NaOH (3 mL), MeOH (3 mL) and THF (3 mL) was stirred at r.t. for 16 h, then concentrated to approximately one-third of its original volume. 1 M HCl was added to acidify the mixture, and the resulting suspension was extracted with EtOAc. The organic layer was dried over MgSO4 and concentrated. The crude product was purified by silica gel chromatography (5-60% EtOAc/hexanes+1% AcOH). The product isolated was dissolved in saturated NaHCO3 and washed several times with ether. The aqueous layer was acidified to pH about 3 with 6 M HCl, and the resulting precipitate was isolated by filtration to give 18 mg of the title compound. MS: (+) m/z 464.41 (M+1).

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