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Org Biomol Chem. 2011 Oct 7;9(19):6629-38. doi: 10.1039/c1ob05555k. Epub 2011 Aug 16.

Syntheses of mGluR5 PET radioligands through the radiofluorination of diaryliodonium tosylates.

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Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, Rm. B3 C346A, 10 Center Drive, Bethesda, MD 20892-1003, USA.


3-Fluoro-1-((thiazol-4-yl)ethynyl)benzenes constitute an important class of high-affinity metabotropic glutamate subtype 5 receptor (mGluR5) ligands, some of which have been labeled with fluorine-18 (t(1/2) = 109.7 min), to provide radioligands for molecular imaging of brain mGluR5 in living animal and human subjects with positron emission tomography (PET). Labeling in the 3-fluoro position of such ligands can be achieved through aromatic nucleophilic substitution of a halide leaving group with [(18)F]fluoride ion when a weakly activating m-nitrile group is present, but is generally very low yielding (<8%). Here we used a microfluidic reaction platform to show that greatly enhanced (up to 6-fold) radiochemical yields can be achieved from suitably synthesized diaryliodonium tosylate precursors. The presence of a m-nitrile or other activating group is not required. Similar conditions were adopted in a more conventional automated radiochemistry platform having a single-pot reactor, to produce mGluR5 radioligands with useful radioactivities for PET imaging.

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