Synthesis of a New Diaminodithiol Bifunctional Chelator for Radiolabeling Biomolecules with Indium(III)

The synthesis of a new bifunctional ligand 1-(p-carboxybenzyl)-N,N′-bis-[1,1-dimethyl-1-(p-methoxybenzylthio)ethyl]-ethylenediamine-N,N′-diacetic acid, di-t-butyl ester (1, nbi6ss) is described. It consists of a carboxybenzyl group substituted on a carbon atom of the ethylenediamine moiety of a hexadentate ligand, which has been found to have a very high affinity for In(III). The gem-dimethylthiol groups and the carboxylic acid groups of the ligand were protected by groups that can be removed under mild conditions after conjugation to a peptide or protein.