Co(II) and Fe(II) triazole-appended 4,10-diaza-15-crown-5-ether Macrocyclic complexes for CEST MRI applications

[Display omitted] •Synthetic methods such as “click chemistry” are useful for ligand functionalization.•Co(II) and Fe(II) complexes are effective paramagnetic shift agents.•A neutral Co(II) complex with triazole group effectively shifts water protons.•17O NMR studies are consistent with rapidly exch...

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Bibliographic Details
Published in:Inorganica Chimica Acta 2020-09, Vol.509, p.119649, Article 119649
Main Authors: Snyder, Eric M., Chowdhury, Md Saiful I., Morrow, Janet R.
Format: Article
Language:English
Subjects:
Alkynes
Carboxylic acids
Chemical synthesis
Co(II) and Fe(II) coordination complexes
Cobalt
Contrast agents
Coordination compounds
Cycloaddition
Iron
Ligands
Magnetic properties
paraCEST agents
Transition metals
Triazoles
Water proton shift agents
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Summary:[Display omitted] •Synthetic methods such as “click chemistry” are useful for ligand functionalization.•Co(II) and Fe(II) complexes are effective paramagnetic shift agents.•A neutral Co(II) complex with triazole group effectively shifts water protons.•17O NMR studies are consistent with rapidly exchanging innersphere waters. Transition metal ion complexes have several advantages as MRI contrast agents including low cost, biological relevance, rich coordination chemistry, tunable magnetic properties, and the potential for smart agents that are responsive to temperature, pH, and redox environment. Here we present triazole-appended azamacrocyclic ligands for Co(II) and Fe(II) complexes towards paraCEST and lipoCEST applications. The triazole pendants are synthesized using ‘click’ chemistry, in particular the azide-alkyne Huisgen cycloaddition reaction. The versatility and specificity of these reactions are particularly useful in synthesizing a variety of analogs and derivatives of triazole-containing ligands. The triazole-NH proton in our Co(II) complex is unsuitable for paraCEST applications at biological pH, but the carboxylic acid derivative produced exceptionally large paramagnetically shifted bulk water 1H resonances which are important towards the development of lipoCEST agents.
ISSN:0020-1693
1873-3255
DOI:10.1016/j.ica.2020.119649