Synthesis, radiofluorination, and in vitro evaluation of pyrazolo[1,5-a]pyridine-based dopamine D4 receptor ligands: discovery of an inverse agonist radioligand for PET

J Med Chem. 2008 Mar 27;51(6):1800-10. doi: 10.1021/jm701375u. Epub 2008 Feb 29.


A series of fluoro-substituted analogs structurally derived from the aminomethyl-substituted pyrazolo[1,5- a]pyridine lead compounds 9 (FAUC 113) and 10 (FAUC 213) were synthesized and evaluated as high-affinity D 4 receptor (D 4R) ligands ( 3a- 3h, K i = 1.3-28 nM). The para-fluoroethoxy-substituted derivatives 3f and 3h revealed an outstanding D 4 subtype selectivity of more than 3 orders of magnitude over both congeners D 2 and D 3 combined with inverse agonism at D 4R. The corresponding (18)F-labeled radioligands revealed high serum stability in vitro and log P values of 2-3. In vitro rat brain autoradiography showed specific binding of [ (18)F]3h in distinct brain regions, including the gyrus dentate of the hippocampus, that were inhibited by both eticlopride (65-80%) and the selective D 4R antagonist 10 (78-93%). The observed binding pattern was mainly consistent with the known D 4R distribution in the rat brain. Thus, [(18)F]3h (FAUC F41) represents a potential radioligand for studying the D 4R in vivo by positron emission tomography (PET).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Brain / diagnostic imaging
  • Drug Design
  • Drug Evaluation, Preclinical
  • Female
  • Fluorine Radioisotopes / chemistry*
  • Humans
  • Isotope Labeling / methods
  • Ligands
  • Molecular Structure
  • Positron-Emission Tomography*
  • Pyrazoles* / chemical synthesis
  • Pyrazoles* / pharmacology
  • Pyridines* / chemical synthesis
  • Pyridines* / pharmacology
  • Radioligand Assay
  • Radiopharmaceuticals* / chemical synthesis
  • Radiopharmaceuticals* / pharmacology
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Dopamine D4 / drug effects*
  • Stereoisomerism


  • Fluorine Radioisotopes
  • Ligands
  • Pyrazoles
  • Pyridines
  • Radiopharmaceuticals
  • pyrazolo(3,4-b)pyridine
  • Receptors, Dopamine D4