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Ligands from the naltrexamine series have consistently demonstrated agonist activity at kappa opioid receptors (KOR), with varying activity at the mu opioid receptor (MOR). Various 6 beta-cinnamoylamino derivatives were made with the aim of generating ligands with a KOR agonist/MOR partial agonist profile, as ligands with this activity may be of interest as treatment agents for cocaine abuse. The ligands all displayed the desired high affinity, nonselective binding in vitro and in the functional assays were high efficacy KOR agonists with some partial agonist activity at MOR. Two of the new ligands (12a, 12b) have been evaluated in vivo, with 12a acting as a KOR agonist and therefore somewhat similar to the previously evaluated analogues 3-6, while 12b displayed predominant MOR agonist activity.

Both of the enantiomers of 5-(3-hydroxyphenyl)-N-phenylethylmorphan with C9alpha-methyl, C9-methylene, C9-keto, and C9alpha- and C9beta-hydroxy substituents were synthesized and pharmacologically evaluated. Three of the 10 compounds, (1R,5R,9S)-(-)-9-hydroxy-5-(3-hydroxyphenyl-2-phenylethyl-2-azabicyclo[3.3.1]nonane ((1R,5R,9S)-(-)-10), (1R,5S)-(+)-5-(3-hydroxyphenyl)-9-methylene-2-phenethyl-2-azabicyclo[3.3.1]nonane ((1R,5S)-(+)-14), and (1R,5S,9R)-(-)-5-(3-hydroxyphenyl)-9-methyl-2-phenethyl-2-azabicyclo[3.3.1]nonane ((1R,5S,9R)-(+)-15) had subnanomolar affinity at mu-opioid receptors (Ki = 0.19, 0.19, and 0.63 nM, respectively). The (1R,5S)-(+)-14 was found to be a mu-opioid agonist and a mu-, delta-, and kappa-antagonist in [35S]GTP-gamma-S assays and was approximately 50 times more potent than morphine in a number of acute and subchronic pain assays, including thermal and visceral models of nociception. The (1R,5R,9S)-(-)-10 compound with a C9-hydroxy substituent axially oriented to the piperidine ring (C9beta-hydroxy) was a mu-agonist about 500 times more potent than morphine. In the single-dose suppression assay, it was greater than 1000 times more potent than morphine. It is the most potent known phenylmorphan antinociceptive. The molecular structures of these compounds were energy minimized with density functional theory at the B3LYP/6-31G* level and then overlaid onto (1R,5R,9S)-(-)-10 using the heavy atoms in the morphan moiety as a common docking point. Based on modeling, the spatial arrangement of the protonated nitrogen atom and the 9beta-OH substituent in (1R,5R,9S)-(-)-10 may facilitate the alignment of a putative water chain enabling proton transfer to a nearby proton acceptor group in the mu-opioid receptor.

The synthesis, biological, and pharmacological evaluation of novel derivatives of cyprodime are described. Their binding affinities at mu, delta, and kappa opioid receptors were evaluated using receptor binding assay. It was observed that the affinity of these compounds was sensitive to the character and length of the substituent in position 4. Further prolongation of the 4-alkoxy group of cyprodime (1) and its 4-butoxy analogue 2 is detrimental for the mu opioid receptor affinity. Introduction of an arylalkoxy group at C-4 does not increase mu affinity in the case of benzyloxy, while a phenylpropoxy group reduces mu affinity. The delta and kappa affinities were also reduced compared to the reference compounds. A significant increase in the affinity at the mu opioid receptors was achieved by introducing a 14-phenylpropoxy group. Increases in the affinity at delta and kappa receptors were also observed. These findings provide further evidence that the nature of the substituent at position 14 has a major impact on the abilities of morphinans to interact with opioid receptors. In the [(35)S]GTPgammaS binding assay, all tested compounds were partial agonists at mu and delta receptors. Compounds 8 and 17 showed antagonism at kappa receptors, while compound 7 exhibited some partial agonist activity at this receptor. The novel derivatives of cyprodime containing a 14-phenylpropoxy group acted as potent antinociceptives. When tested in vivo, compounds 7, 8, and 17 were considerably more potent than morphine, with phenol 7 showing the highest antinociceptive potency (21-fold in the hot plate test, 38-fold in the tail flick test, and 300-fold in the paraphenylquinone writhing test) in mice. Introduction of a 14-phenylpropoxy substituent leads to a profound alteration in the pharmacological profile of this class of compounds.

The synthesis, biological, and pharmacological evaluations of 14beta-O-phenylpropyl-substituted morphinan-6-ones are described. The most striking finding of this study was that all of the compounds from the novel series of differently N-substituted 14beta-O-phenylpropylmorphinans acted as powerful opioid agonists. Even with N-substituents such as cyclopropylmethyl and allyl, which are usually associated with distinct antagonist properties, only agonists were obtained. Compared to morphine, the N-cyclopropylmethyl derivative 15 showed considerably increased potency in the in vivo assays in mice (600-fold in the tail-flick assay, 60-fold in the paraphenylquinone writhing test, and 400-fold in the hot-plate assay). Remarkably, most of the new ligands were nonselective and exhibited binding affinities in the subnanomolar range at opioid receptors (mu, kappa, delta), with the N-propyl derivative 19 displaying the highest affinity for the mu-receptor (K(i) = 0.09 nM).