A solution of 1,1-dimethylethyl (3S)-3-[2-(2-{[(4-bromo-2-fluorophenyl)amino]carbonyl}hydrazino)-2-oxoethyl]-1-pyrrolidinecarboxylate (3.59 mmol) in water (150 mL) was treated with potassium carbonate (17.96 mmol). The reaction was heated to reflux and was stirred overnight. A white solid had formed on the top of the aqueous solution. The reaction was allowed to cool to room temperature. Analysis by LCMS indicated complete consumption of the starting material and the mixture was concentrated to dryness in vacuo. The crude material was dissolved in dichloromethane (100 mL) and was treated with a solution of cyclopropanecarbonyl chloride (3.59 mmol) in dichloromethane (5 mL). After 30 min of stirring, LCMS analysis indicated that the intermediate amine had converted to a mixture of the desired product and a product that corresponded to bis-acylated product. The reaction solution was concentrated to dryness in vacuo and was dissolved in methanol (50 mL). The suspension was stirred at room temperature for 30 min. Analysis by LCMS indicated that the majority of the material now existed as a mixture of the desired product and the intermediate amine. Additional portions of cyclopropanecarbonyl chloride (3.59 mmol) were added to the reaction mixture twice (30 min apart). Analysis by LCMS indicated the complete conversion of the intermediate amine. The reaction mixture was diluted with water (100 mL) and acidified to pH˜4 using 1N aq HCl. The methanol was removed in vacuo, and the resulting aqueous phase was extracted with ethyl acetate. The combined organic phases were washed with saturated aq sodium bicarbonate, washed with brine, dried over MgSO4, filtered and concentrated in vacuo to dryness. The resulting solid was purified by flash chromatography (0-10% methanol/dichloromethane) to give the title compound as a white amorphous solid (850 mg, 58% yield). MS(ES)+ m/e 409/411 [M+H]+ (bromide isotope pattern).
