[CH3:1][O:2][C:3](=[O:14])[C:4]1[CH:9]=[C:8]([O:10][CH2:11][CH3:12])[CH:7]=[C:6]([NH2:13])[CH:5]=1.CCN(CC)CC.[Cl:22][CH2:23][CH2:24][CH2:25][C:26](Cl)=[O:27]>C(Cl)Cl>[CH3:1][O:2][C:3](=[O:14])[C:4]1[CH:9]=[C:8]([O:10][CH2:11][CH3:12])[CH:7]=[C:6]([NH:13][C:26](=[O:27])[CH2:25][CH2:24][CH2:23][Cl:22])[CH:5]=13-Amino-5-ethoxy-benzoic acid methyl ester (D49) (4.0 g, 20.5 mmol, 1 equiv) was suspended in CH2Cl2 (40 ml) and treated at room temperature with NEt3 (2.32 g, 23 mmol, 1.1 equiv). The resulting solution was cooled to 0° C. and 4-chlorobutyryl chloride (3.1 g, 22 mmol, 1.1 equiv) was added dropwise. The resulting mixture was stirred at 0° C. for 3 h then allowed to warm to room temperature. The solution was washed with 2N aqueous HCl solution, dried over MgSO4 and concentrated in vacuo to give of 3-(4-chloro-butanoylamino)-5-ethoxy-benzoic acid methyl ester (D51) (7.0 g, 115%) as a brown oil.
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