[S:1]1[CH:5]=[CH:4][CH:3]=[C:2]1[CH2:6][CH:7]([C:9]([OH:11])=[O:10])[NH2:8].C(=O)([O-])[O-].[K+].[K+].[C:18](Cl)([O:20][CH2:21][C:22]1[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=1)=[O:19]>O.O1CCOCC1>[CH2:21]([O:20][C:18]([NH:8][CH:7]([C:9]([OH:11])=[O:10])[CH2:6][C:2]1[S:1][CH:5]=[CH:4][CH:3]=1)=[O:19])[C:22]1[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=1To a mixture of 3.0 g (16.9 mmol) of β-thienyl-D,L-alanine in 75 mL of water and 60 mL of dioxane, was added 5.6 g (40.6 mmol) of anhydrous potassium carbonate, followed by 2.85 mL (20 mmol) of carbobenzyloxychloride. The resulting mixture was stirred rapidly for approximately one hour. When the reaction was substantially complete, as indicated by thin layer chromatography (21/7/7/9, EtOAc/AcOH/CH3 CN/H2O), the reaction mixture was concentrated. The resultant layers were separated and the aqueous layer was washed with 75 mL of diethyl ether and then layered with 150 mL of methylene chloride. The resultant mixture was acidified with rapid stirring to pH=2.0 using 5N hydrochloric acid. The layers were then separated, and the organic layer was dried with sodium sulfate (Na2SO4), filtered and concentrated to provide 5.05 g of desired compound (98%).
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