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.
Chelating Carboxylic Acid Amides as Robust Relay Protecting Groups of Carboxylic Acids and their Cleavage under Mild Conditions
作者:Manuel C. Bröhmer、Stephan Mundinger、Stefan Bräse、Willi Bannwarth
DOI:10.1002/anie.201100271
日期:2011.6.27
Free choice: Carboxamides of bispicolylamine are alternative protectinggroups for carboxylic acids (see scheme). As a consequence of their straightforward applicability, their high chemical stability towards a broad range of conditions, and their selective cleavage undermildconditions to give either carboxylic acids or their methyl esters, this new protection method should find widespread application