To a stirred solution of the crude 2-(2-carboxy-1-methylsulfanyl-propyl)-pyrrolidine-1-carboxylic acid tert-butyl ester (223 mg) obtained above in CH2Cl2 (3 ml) was added phenethylamine(0.18 ml, 1.41 mmol), WSCI monohydrochloride(203 mg, 1.06 mmol), HOBt monohydrate(162 mg, 1.06 mmol) and diisopropylethylamine(0.37 ml, 2.12 mmol) at room temperature. After being stirred at room temperature for 4.5 hr, the mixture was quenched with 1N HCl (20 ml), extracted with AcOEt, dried (MgSO4) and concentrated in vacuo to give a crude oil, which was purified by flash column chromatography (hexane:AcOEt=3:1) to give 2-(1-methylsulfanyl-2-phenethylcarbamoyl-propyl)-pyrrolidine-1-carboxylic acid tert-butyl ester as an oil(123 mg, 43%).
