Beta-Alanine → 3-[(1-Cyclohexylmethyl-5-hydroxy-2-oxo-3-phenyl-8-pyridin-3-yl-1,2-dihydro-[1,7]naphthyridine-6-carbonyl)-amino]-propionic acid

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A mixture of 1-cyclohexylmethyl-5-hydroxy-2-oxo-3-phenyl-8-pyridin-3-yl-1,2-dihydro-[1,7]naphthyridine-6-carboxylic acid methyl ester (41 mg, 0.087 mmol), β-alanine (623 mg, 7.0 mmol) and NaOMe solution (10 mL, 5.2 mmol, 0.5 M in MeOH) was refluxed for 16 h. After the mixture was cooled to r.t., the solvent was evaporated in vacuo. The residue was partitioned between EtOAc and water. 1 M HCl was added with vigorous stirring until pH was about 3-4. The aqueous layer was extracted with additional EtOAc, and the organic layers were combined, dried over MgSO4 and concentrated. The residue was dissolved in saturated NaHCO3 and washed several times with ether. The aqueous layer was acidified to pH about 3-4, and the resulting precipitate was isolated by filtration. The crude solid was purified by silica gel chromatography (5-90% 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 3-4, and the resulting precipitate was isolated by filtration to give 10 mg of the title compound as a white solid. MS: (+) m/z 527.45 (M+1).

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