Convenient synthesis of maleimido-derivatized lanthanide(III) chelates and their use in mercapto group conjugation

Simple synthesis of luminescent europium(III) and terbium(III) chelates tethered to a maleimido function (7, 8) is described. The method is based on the following: (i) synthesis of protected ligands tethered to a maleimido function and their purification on silica gel; (ii) deprotection by acidolysis; (iii) conversion of the deprotected ligands to the corresponding lanthanide(III) chelates by passing them through a column of strong cation exchange resin loaded with the appropriate lanthanide(III) ions. According to this procedure, large quantities of mercapto-selective biomolecule-labeling reactants of high purity can be prepared.