Methanol → 3-[(1-Benzyl-5-hydroxy-2-oxo-3-phenyl-8-thiazol-2-yl-1,2-dihydro-[1,7]naphthyridine-6-carbonyl)-amino]-propionic acid

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A mixture of 3-[(1-benzyl-5-hydroxy-2-oxo-3-phenyl-8-thiazol-2-yl-1,2-dihydro-[1,7]naphthyridine-6-carbonyl)-amino]-propionic acid methyl ester (28 mg, 0.052 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 until pH was about 3-4, 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 3-4 with 6 M HCl, and the resulting precipitate was isolated by filtration to give 11 mg of the title compound. MS: (+) m/z 527.33 (M+1).

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