MAIN GROUP AND TRANSITION METAL-BASED CHELATES FOR PET APPLICATIONS

Abstract

[AlCl3(BnMe2-tacn)] was radiolabelled by Cl/18F halide exchange reactions in the presence of 2.99 mol. equiv. of KF at pH 4 CH3CO2Na buffer solution with addition of 18F-target water, to give [Al18F19F2(BnMe2-tacn)] with RCY up to 24 %. The radio-product was purified through a simple SPE purification protocol in 99 % RCP and it shows excellent stability in 50 % EtOH/PBS solution for >3h.
[GaF3(BnMe2-tacn)] can be successfully 18F-radiolabelled using a precursor concentration as low as 27 nM through 18F/19F isotopic exchange reactions, using 18F-target water in a 75 % MeCN/H2O solution, in good RCYs (37 ± 5 %) within 10 minutes. The RCY of the reaction starting with a precursor concentration of 268 nM and 2.68 μM were 66 ± 4 % and 73 ± 4 %, respectively. [Ga18F19F2(BnMe2-tacn)] was purified through an SPE cartridge and formulated in 20 % EtOH/water solution showing a RCP of 99 % at t = 0 which decreases to 77-88 % after 2 h. The effect on the RCP of temperature, pH, addition of ascorbic acid, an excess of Cl− or OH− in solution were investigated.
The coordination chemistry of Group 13 metal fluorides towards O-donor ligands was developed. The MF3·3H2O (M = Al, Ga, In) were synthesised and the more readily soluble molecular species [MF3(OH2)2(DMSO)] (M = Al, Ga) were used as synthons for reactions with other ligands. The complexes were characterised by 1H, 19F{1H}, microanalysis and IR spectroscopy. The stability of [GaF3(OH2)2(dmso)] was tested to determine whether it could be used as a radiolabelling precursor.
The coordination chemistry of the Group 3, Sc(III), Y(III), and lanthanides, La(III) and Lu(III), trichlorides and trifluorides (Sc only) towards neutral N-donor ligands was developed. The complexes were characterised by 1H, 19F{1H} and 45Sc NMR spectroscopy, as appropriate, together with IR spectroscopy and microanalysis. The crystal structures of [ScCl3(terpy)], [MCl3(terpy)(OH2)] (M = Y, Lu), [YI3(Me3-tacn)]·MeCN, [{YI2(Me3-tacn)}2(μ-O)]·MeCN, [{La(terpy)(OH2)Cl2}2(μ-Cl)2], [ScF2Cl(Me3-tacn)] and [ScF2(Me3-tacn)(μ-F)SnMe3Cl] are reported. The first three examples of scandium fluoride complexes with neutral ligands are reported, [ScF3(BnMe2-tacn)], [ScF3(Me3-tacn)] and [ScF3(terpy)]. These complexes were obtained by halide exchange reactions using the trichloride analogues, by reaction with [Me4N]F or Me3SnF as the fluoride source.
The first row transition metal fluorides chemistry with terpy and Me3-tacn was explored in order to identify promising systems for 18F radiolabelling. The complexes [MF3(L)] (M = Cr, Mn, Fe, Co; L = Me3-tacn, terpy) were synthesised and fully characterised by UV-vis and IR spectroscopy, microanalysis, and, for the diamagnetic [CoF3(L)], using 1H, 19F{1H} and 59Co NMR spectroscopy. Single crystal X-ray analyses are reported for [MF3(Me3-tacn)] (M = Mn, Co). Stability tests on [MF3(Me3-tacn)] (M = Cr, Mn, Fe, Co) and [CrF3(terpy)] were performed and the Cl/19F halide exchange reactions using [CrCl3(Me3-tacn)] and [FeCl3(Me3-tacn)] were also carried out with added [Me4N]F. The halide exchange reactions allowed partial Cl/F exchange for the Cr(III) systems, and proved to be successful in forming [FeF3(Me3-tacn)] cleanly.

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Identifiers

ORCID for Francesco Matteo Monzittu: orcid.org/0000-0002-7080-3795

ORCID for Gillian Reid: orcid.org/0000-0001-5349-3468

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