[NH2:1][CH2:2][CH2:3][CH2:4][C:5]([OH:7])=[O:6].C1CCN2C(=NCCC2)CC1.[CH:19]1([N:25]=[C:26]=[O:27])[CH2:24][CH2:23][CH2:22][CH2:21][CH2:20]1.Cl>[OH-].[Na+]>[CH:19]1([NH:25][C:26](=[O:27])[NH:1][CH2:2][CH2:3][CH2:4][C:5]([OH:7])=[O:6])[CH2:24][CH2:23][CH2:22][CH2:21][CH2:20]1
To a cold solution of 4-aminobutyric acid (2.16 g, 21 mmol) and catalytic amount of DBU in 22 mL of 1.0 N NaOH, 2.5 g (20 mmol) of cyclohexyl isocyanate were added in one time. The mixture was strongly mixed at room temperature overnight. The reaction was then acidified with concentrated HCl. The formed white solid was collected by filtration. The mixture was purified by chromatography on a silica column (8×3 cm). Elution with a mixture 50:50:1 of hexane:ethyl acetate: acetic acid gave the pure targeted product. The resulting white crystal (3.46 g; yield: 76%) had a mp of 153.0-154.0° C. [M+H]+ 281.18
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