C([O:4][C:5]([C:7]1[C:12]([CH2:13][N:14](S(C2C=CC=CC=2)(=O)=O)[CH2:15][C:16]([O:18][CH3:19])=[O:17])=[CH:11][CH:10]=[C:9]([CH3:29])[N:8]=1)=O)(C)C.C[O-].[Na+]>CO>[CH3:19][O:18][C:16]([C:15]1[C:5]([OH:4])=[C:7]2[C:12]([CH:11]=[CH:10][C:9]([CH3:29])=[N:8]2)=[CH:13][N:14]=1)=[O:17]To a stirred solution of crude 3-[(benzenesulfonyl(methoxycarbonylmethyl)amino)methyl]-6-methylpyridine-2-carboxylic acid isopropyl ester (from Step C) in MeOH (20 mL) at 0° C. was added a solution of NaOMe in MeOH (prepared from Na (200 mg) in MeOH (4 mL)) dropwise over 20 min. The resulting solution was left to stir at 0° C. for a further hour and concentrated. Ethyl acetate (50 mL) and ice-H2O (50 mL) were added. The layers were separated; the aqueous layer was extracted with ethyl acetate (2×), the pH adjusted to 6 (5 M HCl) and extracted with dichloromethane (20 mL×3). The extracts were combined, dried, and concentrated to give pure 8-hydroxy-2-methyl-[1,6]naphthyridine-7-carboxylic acid methyl ester as a cream solid (708 mg, 98% (2 steps)).—1H NMR (CDCl3): δ 8.87 (s, 1H), 8.26 (d, J=8.5, 1H), 7.62 (d, J=8.5, 1H), 5.40 (br, 1H), 4.13 (s, 3H), 2.91 (s, 3H).
読み込み中…
