N-(Trifluoromethyl)benzyl substituted N-Normetazocines and N-Norketobemidones Original Research Article

To further investigate the unusual profile of N-benzyl substituted opioids, N-trifluoromethylbenzyl normetazocines and norketobemidones were prepared. The introduction of trifluoromethyl substituents on the benzyl group of the (−)-metazocines reduced affinity at all three receptors, with the greatest loss at kappa receptors. Surprisingly, some of the (+)-normetazocines actually possessed higher affinity than the corresponding (−)-isomers. In the ketobemidone series, the effects were different—the 4-trifluoromethyl substituted ketobemidone actually possessed 3-fold higher mu affinity than the unsubstituted parent to give a ligand with good mu affinity. In functional in vitro assays, this compound was a weak antagonists, but in apparent contradiction it was inactive in in vivo assays.