The chelator Bn2DT3A was used to produce a novel 68Ga complex for positron emission tomography (PET). Unusually, this system is stabilized by a coordinated hydroxide in aqueous solutions above pH 5, which confers sufficient stability for it to be used for PET. Bn2DT3A complexes Ga3+ in a hexadentate manner, forming a mer-mer complex with log K([Ga(Bn2DT3A)]) = 18.25. Above pH 5, the hydroxide ion coordinates the Ga3+ ion following dissociation of a coordinated amine. Bn2DT3A radiolabeling displayed a pH-dependent speciation, with [68Ga][Ga(Bn2DT3A)(OH)]- being formed above pH 5 and efficiently radiolabeled at pH 7.4. Surprisingly, [68Ga][Ga(Bn2DT3A)(OH)]- was found to show an increased stability in vitro (for over 2 h in fetal bovine serum) compared to [68Ga][Ga(Bn2DT3A)]. The biodistribution of [68Ga][Ga(Bn2DT3A)(OH)]- in healthy rats showed rapid clearance and excretion via the kidneys, with no uptake seen in the lungs or bones.

Chemistry University of Hull Cottingham Road Hull HU6 7RX U K

Department of Biomedical Sciences University of Hull Cottingham Road Hull HU6 7RX U K

Department of Imaging Chemistry and Biology School of Biomedical Engineering and Imaging Sciences King's College London London SE1 7EH U K

Department of Inorganic Chemistry Faculty of Science Charles University Hlavova 2030 Prague 2 Czech Republic

E A Milne Centre for Astrophysics Department of Physics and Mathematics University of Hull Cottingham Road Hull HU6 7RX U K

Positron Emission Tomography Research Center University of Hull Cottingham Road Hull HU6 7RX U K

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