Challenges in chelating positron emitting copper isotopes: tailored synthesis of unsymmetric chelators to form ultra stable complexes

Abstract

The synthesis of chelators that form high stability complexes with copper(II) isotopes and do not suffer from transchelation in vivo has been a goal for many chemists. Such chelators will facilitate the exploitation of the ⁶⁴Cu isotope (t_1/2 = 12.7 h, β⁺ (19%); β⁻ (39%); EC (41%)) for positron emission tomography imaging studies, which has a longer half life relative to the more commonly used ¹⁸F (t_1/2 = 109.8 min) and ¹¹C (t_1/2 = 20.4 min) isotopes. One option is the CBTE2A chelator, which has been championed by Weisman, Wong and Anderson, and, more recently, alternate bifunctional chelator (BFC) versions have been synthesised. Improved synthetic methods are required for unsymmetric derivatisation of these chelators to allow more selective biomolecule attachment. This work investigates synthetic routes to form new unsymmetric chelating ligands via stepwise reaction of the bisaminal precursor, determines their X-ray structures and demonstrates cold copper(II) isotope complex formation.