Candidate PET radioligands for cannabinoid CB1 receptors: [18F]AM5144 and related pyrazole compounds.

Introduction: The mammalian brain contains abundant G protein-coupled cannabinoid CB(1) receptors that respond to Delta(9)-tetrahydrocannabinol, the active ingredient of cannabis. The availability of a positron emission tomography (PET) radioligand would facilitate studies of the addictive and medicinal properties of compounds that bind to this receptor. Among the known classes of ligands for CB(1) receptors, the pyrazoles are attractive targets for radiopharmaceutical development because they are antagonists and are generally less lipophilic than the other classes.