55750-61-3

6066-82-6

17686-36-1

55750-61-3

GENERAL STEPS: To a 500 mL three-necked flask was added N-maleimidoacetic acid (94 g, 0.6 mol) and 300 mL of methylene chloride, followed by oxalyl chloride (90 g, 0.72 mol). The reaction mixture was heated to reflux and a large amount of gas was observed to be released. After 2 hours of reaction, the solution became clarified. Subsequently, dichloromethane and excess oxalyl chloride were removed by concentration. 200 mL of dichloromethane was added to wash and remove the residual acid to give the crude product N-maleimidoacetyl chloride. The crude product was dissolved in 200 mL of dichloromethane. In another vessel, N-hydroxysuccinimide (69 g, 0.6 mol) and triethylamine (80.8 g, 0.8 mol) were dissolved in 300 mL of dichloromethane and the reaction temperature was controlled to be no more than 20° C. under the cooling of an ice water bath. A dichloromethane solution of the above N-maleimidoacetyl chloride was slowly added dropwise to this mixture and the dropwise process lasted for 2 hours. Upon completion of the reaction, the reaction solution was washed with 200 mL of water to remove the triethylamine hydrochloride, followed by 100 mL of 1N hydrochloric acid to remove excess triethylamine, and finally with 200 mL of saturated brine. The organic phase was dried and concentrated to dryness to give 137 g of white solid. Purification by recrystallization in a mixed solvent of ethyl acetate and petroleum ether resulted in 116 g of white solid with 98.7% HPLC purity and 76.7% yield.