[NH2:1][C@H:2]([C:13]([OH:15])=[O:14])[CH2:3][CH2:4][CH2:5][C:6]([O:8][C:9]([CH3:12])([CH3:11])[CH3:10])=[O:7].[OH-].[Na+].[CH2:18]([S:25](Cl)(=[O:27])=[O:26])[C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1>O1CCOCC1>[CH2:18]([S:25]([NH:1][C@H:2]([C:13]([OH:15])=[O:14])[CH2:3][CH2:4][CH2:5][C:6]([O:8][C:9]([CH3:10])([CH3:11])[CH3:12])=[O:7])(=[O:27])=[O:26])[C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1To a stirred solution of 0.5 g of H-Aad(OtBu)-OH in 4.4 mL of aqueous 1 N sodium hydroxide was added 0.42 g of benzylsulfonylchloride in 2 mL of dioxane. After 16 hours at room temperature, additional 1.4 mL of aqueous 2 N sodium hydroxide, 0.5 mL of dioxane and 0.09 g of benzylsulfonylchloride were added and the reaction mixture stirred for an additional day. The dioxane was removed, water was added, the mixture made acid (pH 3) using hydrochloric acid and extracted twice with diethyl ether. The combined ether layers were dried over sodium sulfate and concentrated to give 235 mg of BzlSO2-Aad(OtBu)-OH.
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