Browsing by Author "Ciancaleoni, G"

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    Effect of rhenium(i) complexation on aza-Michael additions to 5-amino-1,10-phenanthroline with [18F]ethenesulfonyl fluoride towards PET optical tracer development
    (CSIRO Publishing, 2019-01-14) Klenner, MA; Pascali, G; Zhang, B; Ciancaleoni, G; Massi, M; Fraser, BH
    Conjugations with the recently developed [18F]ethenesulfonyl fluoride ([18F]ESF) were performed on 5-amino-1,10-phenanthroline, in its free form and coordinated to a rhenium(i) tricarbonyl complex, as a means of radiosynthesizing dual-modal optical and positron emission tomography (PET) tracers. The Michael-donating ability of the aromatic amine was noticeably perturbed on coordination with the rhenium(i) centre, resulting in decreased radiochemical yields from 34 %, in the case of the free ligand, to 1 %. We attribute the decreased nucleophilicity of the amine to metal deactivation from the electron-withdrawing feature of the rhenium(i) tricarbonyl centre, based on spectroscopic and computational evidence, thus highlighting this effect as a crucial parameter in designing late-stage metal coordination methods employing related aza-Michael additions. Photophysical analyses were also performed on the ESF-conjugated rhenium(i) complex, exhibiting a longer decay lifetime from the triplet metal-to-ligand charge transfer excited state when compared with the non-conjugated analogue. © CSIRO 1996-2021
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    Rhenium(i) complexation–dissociation strategy for synthesising fluorine-18 labelled pyridine bidentate radiotracers
    (Royal Society of Chemistry, 2020-02-28) Klenner, MA; Zhang, B; Ciancaleoni, G; Howard, JK; Maynard-Casely, HE; Clegg, JK; Massi, M; Fraser, BH; Pascali, G
    A novel fluorine-18 method employing rhenium(I) mediation is described herein. The method was found to afford moderate to high radiochemical yields of labelled rhenium(I) complexes. Subsequent thermal dissociation of the complexes enabled the radiosynthesis of fluorine-18 labelled pyridine bidentate structures which could not be radiofluorinated hitherto. This rhenium(I) complexation–dissociation strategy was further applied to the radiosynthesis of [18F]CABS13, an Alzheimer's disease imaging agent, alongside other 2,2′-bipyridine, 1,10-phenanthroline and 8-hydroxyquinoline labelled radiotracers. Computational modelling of the reaction mechanism suggests that the efficiency of rhenium(I) activation may be attributed to both an electron withdrawal effect by the metal center and the formation of an acyl fluoride intermediate which anchors the fluoride subsequent to nucleophilic addition. © The Royal Society of Chemistry 2020 - Open Access