C[O:2][C:3](=[O:24])[C:4]1[C:9]([N+:10]([O-:12])=[O:11])=[CH:8][CH:7]=[CH:6][C:5]=1[NH:13][CH2:14][CH2:15][NH:16][C:17]([O:19][C:20]([CH3:23])([CH3:22])[CH3:21])=[O:18].[OH-].[Li+]>C1COCC1.O.C(OCC)(=O)C>[C:20]([O:19][C:17]([NH:16][CH2:15][CH2:14][NH:13][C:5]1[CH:6]=[CH:7][CH:8]=[C:9]([N+:10]([O-:12])=[O:11])[C:4]=1[C:3]([OH:24])=[O:2])=[O:18])([CH3:23])([CH3:21])[CH3:22]To a solution of 2-(2-tert-butoxycarbonylaminoethylamino)-6-nitro-benzoic acid methylester (0.26 g, 0.00077 mol) in THF-water (3:1, 20 mL) under nitrogen was added lithium hydroxide (0.14 g, 0.00326 mol) as a solid in one portion. The reaction mixture was heated at 50° C. for 5 h then cooled to room temperature overnight. The mixture was diluted with ethyl acetate (10 mL) and washed with 10% aqueous HCl, water, and brine. The organic phase was dried over magnesium sulfate, filtered and concentrated in vacuo to a yellow oil which was purified by ISCO chromatography on silica gel using 15-50% ethyl acetate-hexane to give product as a pale yellow oil 2-(2-tert-butoxycarbonylaminoethylamino)-6-nitro-benzoic acid (0.24 g, 96%). 1H NMR (400 MHz, CDCl3) δ 11.8 (s, 1H), 7.57 (t, 1H, J=7.8 Hz), 7.05 (d, 1H, J=7.8 Hz), 6.81 (d, 1H, J=7.8 Hz), 6.73 (s, 1H), 4.5 (s, 1H), 3.47 (m, 2H), 3.19 (m, 2H), 1.47 (s, 9H); MS (m/e) 326 (M+1).
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