Aspiring
to develop a positron emission tomography (PET) imaging
agent for the GluN2B subunits of the N-methyl-d-aspartate receptor (NMDAR), a key therapeutic target for drug
development toward several neurological disorders, we synthesized
a series of 2,3,4,5-tetrahydro-1H-3-benzazepine and
6,7,8,9-tetrahydro-5H-benzo[7]annulen-7-amine analogues.
After in vitro testing via competition binding assay and autoradiography,
[18F]PF-NB1 emerged as the best performing tracer with
respect to specificity and selectivity over σ1 and σ2
receptors and was thus selected for further in vivo evaluation. Copper-mediated
radiofluorination was accomplished in good radiochemical yields and
high molar activities. Extensive in vivo characterization was performed
in Wistar rats comprising PET imaging, biodistribution, receptor occupancy,
and metabolites studies. [18F]PF-NB1 binding was selective
to GluN2B-rich forebrain regions and was specifically blocked by the
GluN2B antagonist, CP-101,606, in a dose-dependent manner with no
brain radiometabolites. [18F]PF-NB1 is a promising fluorine-18
PET tracer for imaging the GluN2B subunits of the NMDAR and has utility
for receptor occupancy studies.