Beta-Alanine → 3-[(3-Benzo[1,2,5]oxadiazol-5-yl-1-benzyl-5-hydroxy-2-oxo-1,2-dihydro-[1,7]naphthyridine-6-carbonyl)-amino]-propionic acid

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A mixture of 3-benzo[1,2,5]oxadiazol-5-yl-1-benzyl-5-hydroxy-2-oxo-1,2-dihydro-[1,7]naphthyridine-6-carboxylic acid methyl ester (33 mg, 0.077 mmol), β-alanine (687 mg, 7.7 mmol) and NaOMe solution (12 mL, 6.2 mmol, 0.5 M in MeOH) was refluxed for 16 h. After stirring the mixture for another 24 h at 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 organic layer was washed with brine, dried over MgSO4 and concentrated. The crude solid was dissolved in saturated NaHCO3 and washed several times with ether. The aqueous layer was acidified to pH about 2 with 6 M HCl, and the resulting precipitate was isolated by filtration to give 23 mg of the title compound as a brown solid. MS: (+) m/z 486.26 (M+1).

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