[NH2:1][C:2]1[CH:3]=[C:4]([CH:8]2[C:13]([C:14]([O:16][CH3:17])=[O:15])=[C:12]([CH3:18])[NH:11][C:10]([CH3:19])=[C:9]2[C:20]([O:22][CH3:23])=[O:21])[CH:5]=[CH:6][CH:7]=1.[Cl:24][CH2:25][CH2:26][CH2:27][C:28](Cl)=[O:29]>C1COCC1>[Cl:24][CH2:25][CH2:26][CH2:27][C:28]([NH:1][C:2]1[CH:3]=[C:4]([CH:8]2[C:9]([C:20]([O:22][CH3:23])=[O:21])=[C:10]([CH3:19])[NH:11][C:12]([CH3:18])=[C:13]2[C:14]([O:16][CH3:17])=[O:15])[CH:5]=[CH:6][CH:7]=1)=[O:29]4-(3-Aminophenyl)-1,4-dihydro-2,6-dimethyl-3,5-pyridinedicarboxylic acid, dimethyl ester (1.0 g, 3.16 mmol) was dissolved in THF (50 mL) and cooled to 0° C. 4-Chlorobutyryl chloride (0.446 g, 3.16 mmol) was dissolved in THF (10 mL) and added dropwise to the mixture over 5 min. The mixture was stirred at 0° C. for 0.5 h. and then at 23° C. for 1 h. The solvent was removed in vacuo and the concentrate chromatographed over silica gel (1:4 to 1:0 EtOAc:hexane gradient) to give the title compound (1.33 g, 100%) as a pale yellow foam.
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