NEW MATERIAL:A maleimide-substituted carboxylic acid ester of formula I (R is difunctional aliphatic, alicyclic, or araliphatic hydrocarbon residue, difunctional aromaticring-containing residue; Z is 0, sulfone).

EXAMPLE: p-(N-Maleimido)benzoic acid 4-morpholinyl ester.

USE: Efficient bonding reagent of sulfuhydryl-containing compound with an amino- containing compound. Useful for the immobilization of enzyme, enzyme immuno- assay, etc.

PROCESS: The compound I is prepared by reacting a compound II with a compound III in a solvent such as benzene, toluene, etc., in the presence of a dehydrating condensation agent such as carbodiimide, sulfuric acid, etc. The reaction temp. is -15 W +50°C when the condensing agent is carbodiimide, and room temp. -150°C when it is other compound.