[OH:1][CH:2]([CH2:19][CH2:20][CH2:21][CH2:22][CH3:23])[CH2:3][CH2:4][CH2:5][N:6]([CH2:10][CH2:11][CH2:12][CH2:13][CH2:14][CH2:15][C:16]([OH:18])=[O:17])[C:7]([NH2:9])=[O:8].[C:24](OC(=O)C)(=[O:26])[CH3:25]>C(OCC)C>[C:24]([O:1][CH:2]([CH2:19][CH2:20][CH2:21][CH2:22][CH3:23])[CH2:3][CH2:4][CH2:5][N:6]([CH2:10][CH2:11][CH2:12][CH2:13][CH2:14][CH2:15][C:16]([OH:18])=[O:17])[C:7]([NH2:9])=[O:8])(=[O:26])[CH3:25]A mixture of 7-[1-(4hydroxynonyl)ureido]heptanoic acid (9.9 g., 0.03 mole) (Example 1, Step C) and acetic anhydride (6.1 g., 0.06 mole) is heated at 60° C. for 18 hours. The mixture is cooled and taken up in 80 ml. of ethyl ether. The solution is extracted with an ice-cold solution of 8 g. of sodium hydroxide in 150 ml. of water. The basis solution is separated and acidified with concentrated hydrochloric acid. The oil that separates is extracted into ether, washed with water and dried over sodium sulfate. The ether is evaporated and the residual oil is purified by chromatography on silica gel using 2% methanol in chloroform as the eluting solvent. Thus there is obtained 7-[1-(4-acetoxynonyl)ureido] heptanoic acid as a yellow oil.
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