An Efficient Route for the Synthesis of New Analogues of Polyaminocarboxylic Acid Incorporating O, N, and S Atoms

We have synthesised three rigid polycarboxylated hexadentate ligands that differ only in the nature of their heteroatom, either oxygen (1), nitrogen (2), or sulfur (3). These compounds were obtained in four or five steps from substituted orthoanilines after protection/deprotection sequences. An aromatic backbone was chosen to stiffen the structure of the ligands and, thus, facilitate complexation (preorganization concept). A preliminary chelation test revealed a marked selectivity of the nitrogen‐containing ligand for indium‐111. In accordance with the hard and soft acid and base (HSAB) theory, the choice of ligand should result in notable differences in behaviour during complexation and, thus, augment selectivity with regard to the metal. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)