Selective delta-opioid receptor ligands: Potential PET ligands based on naltrindole

Two series of delta -selective ligands related to the prototypic delta -ant agonist naltrindole have been prepared and evaluated in opioid binding assa ys with the aim of developing new PET ligands for the delta -opioid recepto r. One compound (5d) had significantly here selectivity than naltrindole, b ut with substantially reduced binding affinity. For those compounds retaini ng similar affinity to naltrindole. those having ethyl and fluoroethyl subs tituents afforded the highest levels of selectivity. However, none of the c ompounds combined the high level of affinity and selectivity ideally suited to the development of an imaging agent. (C) 2001 Elsevier Science Ltd. All rights reserved.