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Toward Organometallic Tc-99m Imaging Agents: Synthesis of Water-Stable Tc-99-NHC Complexes


Benz, Michael; Spingler, Bernhard; Alberto, Roger; Braband, Henrik (2013). Toward Organometallic Tc-99m Imaging Agents: Synthesis of Water-Stable Tc-99-NHC Complexes. Journal of the American Chemical Society, 135(46):17566-17572.

Abstract

(TcO2)-Tc-99-O-V-NHC complexes containing monodentate and bidentate N-heterocyclic carbenes (NHCs) have been prepared by the reactions of TcO(glyc)(2)](-) (glyc = ethyleneglycolato) with 1,3-dimethylimidazoline-2-ylidene (L1), 1,1'-methylene-3,3'-dimethyl-4,4'-diimidazoline-2,2'-diylidene (L2), and 1,1'-methylene-3,3'-diethyl-4,4'-diimidazoline-2,2'-diylidene (L3) in THF. The resulting complexes were fully characterized and their stabilities investigated. While complexes with monodentate NHCs only are hydrolytically unstable, complexes containing bidentate NHCs are water-stable over a broad pH range. The high water stability allows interconversion of the {(TcO2)-Tc-99-O-V}(+) core into {(TcOCl)-Tc-99-O-V}(2+) with HCl as the H+ and Cl- source. An alternative procedure to obtain (TcO2)-Tc-99-O-V-NHC complexes is the in situ deprotonation of imidazolium salts, enabling the preparation of (TcO2)-Tc-99-O-V-NHC compounds without free NHCs, thus increasing the scope of NHC ligands drastically. The remarkable stability and pH-controllable reactivity of the new complexes underlines the potential of NHCs as stabilizing ligands for Tc-99 complexes and paves the way for the first Tc-99m-NHC complexes in the future.

Abstract

(TcO2)-Tc-99-O-V-NHC complexes containing monodentate and bidentate N-heterocyclic carbenes (NHCs) have been prepared by the reactions of TcO(glyc)(2)](-) (glyc = ethyleneglycolato) with 1,3-dimethylimidazoline-2-ylidene (L1), 1,1'-methylene-3,3'-dimethyl-4,4'-diimidazoline-2,2'-diylidene (L2), and 1,1'-methylene-3,3'-diethyl-4,4'-diimidazoline-2,2'-diylidene (L3) in THF. The resulting complexes were fully characterized and their stabilities investigated. While complexes with monodentate NHCs only are hydrolytically unstable, complexes containing bidentate NHCs are water-stable over a broad pH range. The high water stability allows interconversion of the {(TcO2)-Tc-99-O-V}(+) core into {(TcOCl)-Tc-99-O-V}(2+) with HCl as the H+ and Cl- source. An alternative procedure to obtain (TcO2)-Tc-99-O-V-NHC complexes is the in situ deprotonation of imidazolium salts, enabling the preparation of (TcO2)-Tc-99-O-V-NHC compounds without free NHCs, thus increasing the scope of NHC ligands drastically. The remarkable stability and pH-controllable reactivity of the new complexes underlines the potential of NHCs as stabilizing ligands for Tc-99 complexes and paves the way for the first Tc-99m-NHC complexes in the future.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:2013
Deposited On:13 Jan 2014 15:13
Last Modified:21 Nov 2017 17:03
Publisher:American Chemical Society
ISSN:0002-7863
Additional Information:This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of the American Chemical Society, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/ja409499u.
Publisher DOI:https://doi.org/10.1021/ja404499u
PubMed ID:24156612

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