Maleimide derivatives are of high interest as substrates in biological applications. Due to its Michael-accepting ability the maleimido group is able to react with nucleophilic groups, eg thiol groups in biomolecules. I Therefore substrates containing terminal maleimido functionality can undergo covalent coupling to cysteine residues of enzymes or other proteins? Bifunctional derivatives with a maleimido group attached to one end and a ...