Synthesis and simple 18F-labeling of 3-fluoro-5-(2-(2-(fluoromethyl)thiazol-4-yl)ethynyl)benzonitrile as a high affinity radioligand for imaging monkey brain metabotropic glutamate subtype-5 receptors with positron emission tomography

J Med Chem. 2007 Jul 12;50(14):3256-66. doi: 10.1021/jm0701268. Epub 2007 Jun 16.

Abstract

2-fluoromethyl analogs of (3-[(2-methyl-1,3-thiazol-4yl)ethynyl]pyridine) were synthesized as potential ligands for metabotropic glutamate subtype-5 receptors (mGluR5s). One of these, namely, 3-fluoro-5-(2-(2-(fluoromethyl)thiazol-4-yl)ethynyl)benzonitrile (3), was found to have exceptionally high affinity (IC50 = 36 pM) and potency in a phosphoinositol hydrolysis assay (IC50 = 0.714 pM) for mGluR5. Compound 3 was labeled with fluorine-18 (t1/2 = 109.7 min) in high radiochemical yield (87%) by treatment of its synthesized bromomethyl analog (17) with [18F]fluoride ion and its radioligand behavior was assessed with positron emission tomography (PET). Following intravenous injection of [18F]3 into rhesus monkey, radioactivity was avidly taken up into brain with high uptake in mGluR5 receptor-rich regions such as striata. [18F]3 was stable in monkey plasma and human whole blood in vitro and in monkey and human brain homogenates. In monkey in vivo, a single polar radiometabolite of [18F]3 appeared rapidly in plasma. [18F]3 merits further evaluation as a PET radioligand for mGluR5 in human subjects.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, N.I.H., Intramural

MeSH terms

  • Animals
  • Brain / diagnostic imaging*
  • Brain / metabolism
  • Chromatography, High Pressure Liquid
  • Humans
  • Macaca mulatta
  • Nitriles / metabolism*
  • Positron-Emission Tomography
  • Radioligand Assay
  • Rats
  • Receptor, Metabotropic Glutamate 5
  • Receptors, Metabotropic Glutamate / metabolism*
  • Thiazoles / metabolism*

Substances

  • 3-fluoro-5-(2-(2-(fluoromethyl)thiazol-4-yl)ethynyl)benzonitrile
  • GRM5 protein, human
  • Grm5 protein, rat
  • Nitriles
  • Receptor, Metabotropic Glutamate 5
  • Receptors, Metabotropic Glutamate
  • Thiazoles