[C:1]([OH:8])(=[O:7])[CH2:2][CH2:3][CH2:4][C:5]#[CH:6].[CH3:9][C:10](O)([CH3:12])[CH3:11].C1(N=C=NC2CCCCC2)CCCCC1>CN(C)C1C=CN=CC=1.C(Cl)Cl>[C:1]([O:8][C:10]([CH3:12])([CH3:11])[CH3:9])(=[O:7])[CH2:2][CH2:3][CH2:4][C:5]#[CH:6]Hex-5-ynoic acid (Compound SP424) (8.0 g, 71.3 mmol), 2-methylpropan-2-ol (10.6 g, 143.0 mmol) and 4-(dimethylamino)pyridine (0.44 g, 3.60 mmol) were dissolved in DCM (17.5 ml), a solution of dicyclohexylcarbodiimide (16.2 g, 78.5 mmol) in DCM (17.5 ml) was added, and the mixture was stirred at room temperature overnight. The white solid in the reaction solution was removed by filtration, after which the filtrate was washed with a 0.5 M aqueous hydrochloric acid solution and a saturated aqueous sodium bicarbonate solution and dried over anhydrous magnesium sulfate. The residue obtained by filtration and concentration under reduced pressure was purified by column chromatography (hexane:ethyl acetate=100:0-90:10) to afford the title compound SP423 (6.73 g, 56.1%).
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