80307-12-6

6066-82-6

116965-29-8

80307-12-6

General procedure for the synthesis of 4-maleimidobutanoic acid-N-hydroxysuccinimide ester from N-hydroxysuccinimide and 4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)butyryl chloride: N-maleimidobutanoic acid (99 g, 0.54 mol) and acetonitrile (300 ml) were placed in a 500 ml three-necked flask and thionyl chloride was slowly added ( 93.6 g, 0.82 mol). The reaction mixture was heated to reflux during which a large amount of gas release was observed. After the reaction was refluxed for 4 h, the mixture became clarified and acetonitrile and excess thionyl chloride were subsequently removed by concentration. 200 ml of acetonitrile was added to remove the residual acid to give the crude product N-maleimidobutyryl chloride. The crude product was dissolved in 200 ml of acetonitrile and added dropwise to 300 ml of acetonitrile solution containing N-hydroxysuccinimide (69 g, 0.6 mol) and tri-n-butylamine (148 g, 0.8 mol), during which the temperature was controlled to be no more than 20 °C using an ice water bath. The titration process lasted for 2 hours and after completion the reaction was continued at room temperature. Upon completion of the reaction, the acetonitrile was removed by concentration and the residue was dissolved in 400 ml of dichloromethane and washed sequentially with 200 ml of dichloromethane, 100 ml of 1N hydrochloric acid and 200 ml of saturated brine solution to remove the tri-n-butylamine hydrochloride and an excess of tri-n-butylamine. After drying, 139 g of white solid was obtained, which was recrystallized by mixed solvent of ethyl acetate and petroleum ether to give a final white solid of 104.2 g. The HPLC purity was 98.9% and the yield was 69.1%.