[CH3:1][O:2][C:3](=[O:17])[C:4]1[CH:9]=[C:8]([N:10]2[CH2:14][CH2:13][CH2:12][C:11]2=[O:15])[CH:7]=[C:6]([NH2:16])[CH:5]=1.C(O[BH-](OC(=O)C)OC(=O)C)(=O)C.[Na+].[CH:32](=O)[CH2:33][CH3:34].CC(O)=O>C(Cl)Cl>[CH3:1][O:2][C:3](=[O:17])[C:4]1[CH:5]=[C:6]([NH:16][CH2:32][CH2:33][CH3:34])[CH:7]=[C:8]([N:10]2[CH2:14][CH2:13][CH2:12][C:11]2=[O:15])[CH:9]=1To a solution of 3-amino-5-(2-oxo-pyrrolidin-1-yl)-benzoic acid methyl ester (D4a) (500 mg, 2,14 mmol, 1 equiv) in (CH2Cl)2 (10 ml) was added sodium triacetoxyborohydride (640 mg, 3.02 mmol, 1.4 equiv), propionaldehyde (0.156 ml, 2.14 mmol, 1 equiv) and CH3COOH (0.125 ml, 2.18 mmol, 1.02 equiv) The resulting mixture was stirred at room temperature for 2 h, diluted with CH2Cl2 (20 ml), washed with saturated aqueous NaHCO3 solution (20 ml), dried over MgSO4 and concentrated in vacuo. Purification of the residue by flash chromatography on silica gel (iso-hexane/AcOEt: 3/2) gave 3-(2-oxo-pyrrolidin-1-yl)-5-propylamino-benzoic acid methyl ester (B35) (250 mg, 42%) as a colourless oil.
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