A straightforward synthesis of a C3‐symmetric imidazole‐containing macrocyclic peptide with three hydroxyquinoline side arms is presented. Complex formation with various metal ions (Al3+, Ga3+, Fe3+, La3+ and Y3+) was investigated by spectrophotometric methods. CD spectroscopy revealed a highly diastereoselective binding of these ions at room temperature. In the case of Al3+, Ga3+ and La3+ complexes, Job plot analyses gave evidence of pure 1:1 stoichiometry. Ab initio calculations for the Al3+ and Ga3+ complexes showed that the Λ isomers are considerably stabilized relative to the Δ isomers. Furthermore, the calculated CD spectra for the Al3+ complexes confirm the formation of the Λ isomers in solution. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
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Ziegler et al. (2009) studied this question.