[C:1]([O:5][C:6]([N:8]1[C:17]2[C:12](=[CH:13][CH:14]=[C:15]([CH2:18][C:19](OCC)=[O:20])[N:16]=2)[CH2:11][CH2:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].[BH4-].[Li+].[Cl-].[NH4+]>O1CCCC1>[C:1]([O:5][C:6]([N:8]1[C:17]2[C:12](=[CH:13][CH:14]=[C:15]([CH2:18][CH2:19][OH:20])[N:16]=2)[CH2:11][CH2:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2]7-Ethoxycarbonylmethyl-3,4-dihydro-2H-[1,8]naphthyridine-1-carboxylic acid tert-butyl ester (synthetic methodology described in WO 00/33838) (6.11 g, 19.0 mmol) was dissolved in tetrahydrofuran (40 ml) at room temperature. The solution was place under argon. Lithium borohydride [2M in tetrahydrofuran](22.8 mmol, 11.43 mL) was carefully added and the reaction was refluxed overnight (16 h). The mixture was poured into a solution of saturated ammonium chloride and extracted with ethyl acetate. The organic layer was dried over Na2SO4, filtered, and evaporated under vacuum to give a crude mixture, which was purified via column chromatography to give 7-(2-hydroxy-ethyl)-3,4-dihydro-2H-[1,8]naphthyridine-1-carboxylic acid tert-butyl ester (49% yield). 1H NMR (Cl3CD), δ: 7.30 (d, 1H, J=7.6 Hz), 7.76 (d, 1H, J=7.6 Hz), 3.98 (m, 2H), 3.78 (m, 2H), 2.92 (m, 2H), 2.71 (m, 2H), 1.92 (m, 2H), 1.54 (s, 9H).
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