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The pharmacological effect of the N-(beta-cyanoethyl) moiety is dependent on the opioid on which it is substituted. It caused a large increase in antinociceptive potency, in (--)-3-hydroxymorphinan and (--)-normetazocine, as compared with the N-methyl opioid. These cyanoethyl compounds do not substitute for morphine in morphine-dependent monkeys. This moiety also appears to greatly increase the ability of the opiate receptor to differentiate enantiomers. An ca. 100,000-fold difference in binding was noted between the epimeric N-(beta-cyanoethyl)-3-hydroxymorphinans and the normetazocines. The levo enantiomers have little acute toxicity and showed excellent therapeutic ratios. In contrast, the N-(beta-cyanoethyl) moiety on normorphine, norcodeine, and noroxymorphone did not appear to improve their pharmacological properties. Homologous N-cyanoalkyl opioids were less potent antinociceptives.

The receptor binding affinities of some diastereoisomeric prodine analgoues have been compared with their analgetic activities determined by the hot-plate test in mice. The close correlation found between these potencies indicates that the relative analgetic activities of the alpha/beta isomers are determined primarily by the appropriate association to the receptor sites.

Recently we reported the synthesis of the first enantiomeric pair of irreversible opioid ligands [(3S,4R)-(-)- and (3R,4S)-(+)-cis-4, SUPERFIT] and specific interaction of the latter with the delta receptor. Here we report another enantiomeric pair of irreversible opioid ligands, (+)-trans- and (-)-trans-3-methylfentanyl isothiocyanates [(3S,4S)-(+)-trans- and (3R,4R)-(-)-trans-4]. A single-crystal X-ray analysis of the 2,4,6-trinitrobenzenesulfonic acid salt of (+)-trans-3-methyl-N-phenyl-4-piperidinamine [(+)-trans-8] revealed it (and, therefore, 4) to have the trans configuration and the absolute configuration of (+)-trans-8 to be 3S,4S. The (+)-trans enantiomer of 4 was shown to be highly potent and about 10-fold more selective as an acylating agent than (-)-trans-4 for the higher affinity [3H]DADL (delta) binding site in rat brain membranes. In that assay, (+)-trans-4 and (+)-cis-4 were essentially equipotent as affinity ligands, and the levo enantiomers were considerably less potent. (+)-trans-4 was, thus, a potent, subtype-selective acylating agent for the delta opioid receptor in vitro. With membranes from NG108-15 neuroblastoma x glioma hybrid cells, containing only delta receptors, (+)-cis-4 was found to be a little more potent than (+)-trans-4. Similarly, (+)-cis-4 is the most effective inhibitor of adenylate cyclase in these membranes, (+)-trans-4 has weak activity, and the levo enantiomers are inactive. Only (+)-cis-4 was found to have antinociceptive activity in vivo.

Syntheses of affinity reagents for opiate receptors based on the fentanyl, endo-ethenotetrahydrooripavine, and etonitazene carbon-nitrogen skeletons are described. The isothiocyanate, bromoacetamido, and methylfumaramido alkylating functions were employed in these compounds, some of which had previously been shown to be mu specific (12, BIT) and delta specific (8, FIT and 19, FAO) in vitro. Antinociceptive activity of the title compounds was determined in the mouse hot-plate test, which revealed that certain compounds in each class showed morphine-like activity. The binding EC50 values against [3H]Dalamid for opiate receptors in NG108-15 (delta receptors) and rat brain membranes (mu + delta receptors) are also reported. With this type of experiment, it was possible to independently measure the apparent affinity of the etonitazene congeners 12-14 for the mu and delta receptors.

N-Allyl-, N-(cyclopropylmethyl)-, and N-propyl-endo-ethenotetrahydronororipavines (N-substituted 6,14-endo-etheno-4,5-epoxy-3-hydroxy-6-methoxymorphinans) were synthesized with potential acylating or alkylating moieties at the C-7 position (isothiocyanato, (bromoacetyl)amino, and (methoxyfumaroyl)amino) and examined in vivo for their narcotic agonist and antagonist activities and for their ability to interact with opioid receptors in vitro. The N-(cyclopropylmethyl)-substituted compounds were found to have the highest affinity for opioid receptors among these N-substituted compounds, although all of them were found to be reasonably potent narcotic antagonists in the mouse tail flick vs. morphine assay. Their in vivo potency ranged from 1/8 to 4 times that of nalorphine on intravenous injection in mice. Rat brain membrane binding studies indicated that the compounds interacted with opioid receptors with potencies that ranged from 0.5 times that of morphine (8c, 9c, and 10c) to 0.017 that of morphine (8b). Among the compounds studied here, only the previously reported isothiocyanato compound (10c) and (methoxyfumaroyl)amino compound (8c) interacted irreversibly and selectively with mu or delta opioid receptors, respectively, in assays using NG108-15 neuroblastoma-glioma hybrid cells and/or in a rat brain membrane preparation. Both 8c and 10c were found to interact irreversibly, to a limited extent, with kappa opioid sites in rat brain membranes in which the mu and delta opioid receptors were depleted by interaction with the mu-selective irreversible ligand BIT and the delta-selective irreversible ligand FIT. Neither compound showed irreversible actions in the electrically stimulated mouse vas deferens preparation.

The reaction of N-2,4,5-tribenzyloxyphenyl)ethyl methanesulfonate, prepared in a seven-step sequence, with normetazocine followed by hydrogenolysis of the benzyloxy-protecting groups, gave N-(2,4,5-trihydroxyphenethyl)normetazocine. This compound was prepared to study the effect of a narcotic analgesic containing a functional group which could be activated in situ to a moiety potentially capable of reacting irreversibly with the narcotic receptor. This 6-hydroxydopamin derivative of normetazocine did not prove to be a useful affinity label. Its low toxicity could indicate the necessity for the formation of an aminochrome system for the expression of toxicity by 6-hydroxydopamine.

The enantiomers of eseroline bind to opiate receptors of rat brain membranes with equal affinities and show opiate agonist properties as inhibitors of adenylate cyclase in vitro. However, only (-)-eseroline shows potent narcotic agonist activity in vivo, similar to that of morphine. Neither (-)-noreseroline, (+)-eseroline, nor the open dihydroseco analogue (-)-8 shows analgetic effects in vivo. The structure of rubreserine being a resonance hybrid of an o-quinone with its zwitterionic mesomer is confirmed by solid-state X-ray diffraction analysis.

Exorphins, peptides with opioid activity, have previously been isolated from pepsin hydrolysates of alpha-casein [Zioudrou, C., Streaty, R. A., & Klee, W. A. (1979) J. Biol. Chem. 254, 2446-2449]. Analysis of these peptides shows that they correspond to the sequences 90-96, Arg-Tyr-Leu-Gly-Tyr-Leu-Glu, and 90-95, Arg-Tyr-Leu-Gly-Tyr-Leu, of alpha-casein. These peptides, as well as two of their analogues Tyr-Leu-Gly-Tyr-Leu-Glu (91-96) and Tyr-Leu-Gly-Tyr-Leu (91-95), have now been synthesized and characterized. Their opioid activity was examined by three different bioassays: (a) displacement of D-2-alanyl[tyrosyl-3,5-3H]enkephalin-(5-L-methioninamide) and [3H]dihydromorphine from rat brain membranes; (b) naloxone-reversible inhibition of adenylate cyclase in homogenates of neuroblastoma x glioma hybrid cells; (c) naloxone-reversible inhibition of electrically stimulated contractions of the mouse vas deferens. The synthetic peptide of sequence 90-96 was the most potent opioid in all three bioassays and its potency was similar to that of the isolated alpha-casein exorphins. The synthetic peptides were totally resistant to hydrolysis by trypsin and homogenates of rat brain membranes, but were partially inactivated by chymotrypsin and subtilisin. The difference in opioid activity of alpha-casein exorphins may be related to differences in conformational flexibility observed by NMR spectroscopy.

Several 3-deoxy opioids and 3,6-dideoxydihydromorphine was synthesized to ascertain the effect of the phenolic hydroxyl group on antinociceptive potency and receptor binding affinity. Catalytic reduction of the 3-tetrazolyl ether derivatives of dihydromorphine provided the entry into the 3-deoxydihydro series. The prototype, 3-deoxymorphine, was prepared by lithium aluminum hydride reduction of 3-deoxy-N-carbethoxymorphinone, obtained via its 7-(phenylseleno) derivative. 3-Deoxydihydromorphinone and 3,6-dideoxydihydromorphine were found to be about as potent as, or more potent than, morphine in standard antiociceptive assays. Each of them, however, was less potent than the comparable 3-hydroxy analogue, and their binding affinity to the opiate receptor was substantially decreased. The epoxy ring in 3.6-dideoxydihydromorphine was found to increase the antinociceptive potency of the compound.

A homologous series of 3-alkyl-1,2,3,4,5,6-hexahydro-8-hydroxy-6-methyl-3-benzazocines (2) has been synthesized. Analgetic activity and binding constants for the opiate receptor for 2 and for an analogous series of benzomorphans (1 and 3) are reported. In 1, hot-plate analgesic activity is lost on increase of the N-alkyl chain length from ethyl through butyl (lc-e) and regained with amyl (lf) and hexyl (lg). Compounds lc-e show that antagonist properties and binding constants are similar throughout the series. With 2, where there has been loss of steric constraints through removal of the 2,6-methano bridge of 1 and 3, greatly diminished analgetic activity and receptor affinity and no antagonist properties were observed. Like 1, however, greatest agonist activity was shown by the N-methyl (2c), amyl (2g), hexyl (2h), and heptyl (2i) homologs and there is a parallel of in vitro binding strength and analgetic activity.

The first enantiomeric pair of irreversible opioid ligands [(+)- and (-)-4] were synthesized in greater than 99.6% optical purity as determined by HPLC analysis of diastereoisomeric derivatives of the intermediate 3-methyl-N-phenyl-4-piperidinamine enantiomers. Single-crystal X-ray analysis of the (R,R)-L-(+)-tartaric acid salt of (-)-9 revealed the absolute configuration to be 3S,4R. The absolute configuration of (-)-3 [cis-(-)-3-methylfentanyl] and (-)-4 derived from (-)-9 is thus 3S,4R and that of (+)-3 and (+)-4 is 3R,4S. The (+) enantiomer of 4 (SUPERFIT) was shown to be highly potent and specific for acylation of delta opioid receptors (to the exclusion of mu) in rat brain membranes like its achiral prototype FIT and was about 10 times as potent as the latter in this assay. The (+)-4 was about 5 times as potent as FIT in acylation of delta receptors in NG108-15 neuroblastoma X glioma hybrid cells and about 50 times as potent as its enantiomer. Both FIT and (+)-4 behaved as partial agonists in inhibition of delta receptor coupled adenylate cyclase in NG108-15 membranes and (+)-4 was 5-10 times more potent than FIT and about 100 times more potent than its enantiomer in this assay. Dibromination of amine 12, catalytic exchange of bromine with tritium gas, and reaction of the labeled amine with thiophosgene afforded [3H]-(+)-4 with a specific activity of 13 Ci/mmol. Previous experiments indicated (+)-4 acylates the same 58 000-dalton glycoprotein previously shown to be acylated by FIT but with less nonspecific labeling. In view of the high potency and specificity of (+)-4 and the availability of its enantiomer, it seems likely that these compounds will prove to be valuable tools for study of the opioid receptor complex.