A series of oligopyridine ligands were derived from amino acid amides in which amide oxygen and ternary nitrogen atoms were combined with pyridine moieties. 1H NMR and circular dichroism spectroscopic characterizations revealed that they formed stable Zn2+ complexes in neutral aqueous solutions and caused Zn2+ deficiency in the hepatic stellate cell systems. Since collagen synthesis was effectively promoted in the cells, the present oligopyridine derivatives worked as biocompatible ligands for Zn2+ complexation and cell activation.
The amino acid derived tertiary amide ligand tert-butoxycarbonyl-(S)-alanine-N,N-bis(picolyl)amide (Boc-(S)-Ala-bpa, 1) has been synthesized as a model for metal-coordinating peptide frameworks. Its reactions with copper(II) and cadmium(II) salts have been studied. Binding of Cu2+ results in amide bond cleavage and formation of [(bpa)(solvent) Cu](2+) complexes. In contrast, the stable, eight-coordinate complex [(Boc-(S)-Ala-bpa)Cd(NO3)(2)] (5) has been isolated and characterized by X-ray crystallography. An unusual tertiary amide nitrogen coordination is observed in 5 this gives rise to significantly reduced cis-trans isomerization barriers. Possible implications for metal-induced conformational changes in proteins are discussed.