Conjugations with the recently developed [ 18 F]ethenesulfonyl fluoride ([ 18 F]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.
Effect of Rhenium(i) Complexation on Aza-Michael Additions to 5-Amino-1,10-Phenanthroline with [ 18 F]Ethenesulfonyl Fluoride towards PET Optical Tracer Development
Ciancaleoni G.;
2019-01-01
Abstract
Conjugations with the recently developed [ 18 F]ethenesulfonyl fluoride ([ 18 F]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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
