An enantiomerically pure siderophore type ligand for the diastereoselective 1 : 1 complexation of lanthanide(III) ions

A facile synthesis of a highly preorganized tripodal enterobactine-type ligand 1a-H(3) consisting of a chiral C(3)-symmetric macrocyclic peptide and three tridentate 2-amido-8-hydroxyquinoline coordinating units is presented. Complex formation with various metal ions (Al(3+), Ga(3+), Fe(3+), La(3+) and Eu(3+)) was investigated by spectrophotometric methods. Only in the case of La(3+) and Eu(3+) were well defined 1 : 1 complexes formed. On the basis of CD spectroscopy and DFT calculations the configuration at the metal centre of the La(3+) complex was determined to show Λ helicity. The coordination compounds [(1a)Ln] presented should be prototypes for further lanthanide(III) complexes with an enterobactine analogue binding situation.