Radiosynthesis of N ‐[4‐(4‐fluorobenzyl)piperidin‐1‐yl]‐ N ′‐(2‐[ 11 C]oxo‐1,3‐dihydrobenzimidazol‐5‐yl)oxamide, a NR2B‐selective NMDA receptor antagonist

In order to perform in vivo imaging of the NR2B NMDA receptor system by positron emission tomography, a NR2B selective NMDA receptor antagonist has been labelled with carbon‐11 (half‐life: 20 min). N ‐[4‐(4‐fluorobenzyl)piperidin‐1‐yl]‐ N ′‐(2‐oxo‐1,3‐dihydrobenzimidazol‐5‐yl)oxamide has been described demonstrating high affinity and selectivity for the NR2B receptors (IC 50 of 5 nM in [ 3 H]Ro‐25,6981 binding assay). The labelling precursor and the reference compound were synthesized by coupling the 4‐(4‐fluorobenzyl)piperidine with the corresponding oxalamic acid. The reaction of [ 11 C]phosgene with phenylenediamine precursor led the formation of the [ 11 C]benzimidazolone ring present on the ligand. The labelling occurred in THF or acetonitrile and the decay corrected radiochemical yield was 30–40% from the produced [ 11 C]methane. HPLC purification and formulation led to 2.6–3.7 GBq (70–100 mCi) of radioligand within 30–35 min. The specific radioactivity was 72–127 GBq/µmol (2–3.4 Ci/µmol) at the end of synthesis. Copyright © 2009 John Wiley & Sons, Ltd.