N1 '‐( p ‐[ 18 F]Fluorobenzyl)naltrindole ( p ‐[ 18 F]BNTI) as a potential PET imaging agent for DOP receptors

The N1 '‐( p ‐fluorobenzyl)naltrindole 5 has been synthesized by reaction of 3‐ O ‐benzyl NTI 3 with p ‐fluorobenzylbromide under phase transfer catalysis. The subsequent 3‐ O ‐benzyldeprotection of 4 in HBr/CH 3 COOH gave the target compound 5 in three steps from naltrindole 2 . p ‐FBNTI 5 is a novel delta opioid receptor antagonist ( K i =0.00312 nM) and antagonizes the delta opioid (DOP) agonist, DPDPE, with a K e =1.55 nM in the mouse vas deferens preparation. Using the same synthetic strategy the synthesis of p ‐[ 18 F]BNTI 10 was undertaken. The final yield was 4% and the specific activity varied in a range of 250–400 mCi/µmol. Copyright © 2006 John Wiley & Sons, Ltd.