RADIOIODINATED PIPERAZINYL]-3-HYDROXYBENZYL]-N,N-DIETHYLBENZAMIDE - APOTENTIAL LIGAND FOR IN-VITRO AND IN-VIVO INVESTIGATIONS OF DELTA-OPIOID RECEPTORS())

(+)-4-(alpha R)-alpha-[(2S, l)-2,5-dimethyl-1-piperazinyl]-3-hydroxybe nzyl]-N, N-diethylbenzamide ((1) under bar), a novel radioiodinated de rivative of the selective delta-opioid antagonist (+)-BW373U86, was sy nthesized and evaluated in vitro for binding to opioid receptor subtyp es. This new compound was found to have high affinity (Ki = 0.57 +/- 0 .10 nM) and good selectivity for delta (delta) opioid receptors over m u (mu) (Ki mu/delta = 13.6) and kappa (kappa) (Ki kappa/delta = 175) r eceptors. The corresponding I-123 and I-125 derivatives were prepared by oxidative radioiododestannylation from a trans-vinyltributyltin pre cursor. The radiochemical yield was 72-78% EOS (74.3 +/- 2.6%, n = 3) for I-125-(1) under bar and 40-62% EOS (53.9 +/- 9.8%, n = 3) for I-12 3-(1) under bar. The specific activities were 200-300 mCi/mu mol and > 5,000 mCi/mu mol for the I-125 and I-123-labeled tracers, respectively .