Isomerism of [Cu-64-NOTA-Bn]-Labeled Radiotracers: Separation of Two Complex Isomers and Determination of Their Interconversion Energy Barrier Using Ion Pair Chromatography

Joern Schlesinger, Johan Rajander, Janne A. Ihalainen, Dinesh Ramesh, Patrik Christoffer Eklund, Veronica Fagerholm, Pirjo Nuutila, Olof Solin

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    The model complex [Cu-64((S)-p-NH2-Bn-NOTA)](-) ([Cu-64]1) was used to study the isomerism of [Cu-64-NOTA-Bn]-labeled radiotracers. Two complex isomers [Cu-64]1a and [Cu-64]1b, which were formed at a ratio of 1:9 during the complexation of [Cu-64]Cu2+ with (S)-p-NH2-Bn-NOTA, were separated using ion pair chromatography. To study the interconversion, the nonradioactive complex isomers Cu1a and Cu1b were separated and thermally treated at 90 degrees C in both ammonium acetate solution and deionized water. A faster interconversion rate was observed for both isomers with lower concentrations of ammonium ions. At the end of reaction, the thermodynamic Cu1a to Cu1b equilibrium ratio was 6:94. The particular energy barriers of the interconversion for Cu1a and Cu1b were 130 kJ mol(-1) and 140 kJ mol(-1). Spectrophotometric measurements with Cu1a and Cu1b revealed two isomers adopting different geometrical configurations.
    Original languageUndefined/Unknown
    Pages (from-to)4260–4271
    Number of pages12
    JournalInorganic Chemistry
    Issue number10
    Publication statusPublished - 2011
    MoE publication typeA1 Journal article-refereed

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