7-{2-[3-(2-Carboxy-ethyl)-benzo[b]thiophen-6-yloxy]-ethyl}-3,4-dihydro-2H-[1,8]naphthyridine-1-carboxylic acid tert-butyl ester → 3-{6-[2-(5,6,7,8-Tetrahydro-[1,8]naphthyridin-2-yl)-ethoxy]-benzo[b]thiophen-3-yl}-propionic acid

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7-{2-[3-(2-Carboxy-ethyl)-benzo[b]thiophen-6-yloxy]-ethyl}-3,4-dihydro-2H-[1,8]naphthyridine-1-carboxylic acid tert-butyl ester (168 mg, 0.35 mmol) was dissolved in THF (10 ml). Hydrogen chloride gas was bubbled through the solution until the starting material disappears by TLC. Then the solvent was evaporated under vacuum and the crude was chromatographied over silica gel using 5% methanol/ methylene chloride as solvent to yield 32 mg (24%) of 3-{6-[2-(5,6,7,8-Tetrahydro-[1,8]naphthyridin-2-yl)-ethoxy]-benzo[b]thiophen-3-yl}-propionic acid. NMR 1H Cl3CD δ: 7.55 (d, 1H, J=8.7 Hz), 7.25 (m, 2H), 6.93 (s, 1H), 6.88 (dd, 1H, J=2.1, 8.7 Hz), 6.43 (d, 1H, J=7.2 Hz), 4.24 (t, 2H, J=6.1 Hz), 3.45 (m, 2H), 3.10 (m, 4H), 2.71 (m, 4H), 1.88 (m, 2H). Mass Spectrum (LCMS, ESI) calculate for C21H23N2O3S 383.14 (M+H) found: 383.3.

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