Synthesis of 7-arylmorphinans. Probing the "address" requirements for selectivity at opioid delta receptors

Through arylation of 6-keto opiates with diaryliodonium iodide, a series of 7-aryl opiates (3-8) have been prepared in an effort to investigate the effect of conformational mobility of the delta "address" moiety on opioid agonist and antagonist potencies. Evaluation of the ligands in the mouse vas deferens and guinea pig ileum preparations revealed that they were less potent and less selective than the conformationally constrained ligands, naltrindole (1, NTI) and 7-(spiroindanyl)oxymorphone (2, SIOM), at delta opioid receptors. It is concluded that the coplanarity of the address moiety with the C ring of the morphinan structure enhances delta antagonist potency and selectivity.

Pyrrolomorphinans as delta opioid receptor antagonists. The role of steric hindrance in conferring selectivity

A series of 2',3'-disubstituted pyrrolomorphinans (5a-i) were synthesized to determine the role of steric hindrance at mu and kappa receptors in promoting delta opioid receptor antagonist selectivity. In smooth muscle preparations, five members of the series (5a-c,e,f) possessed Ke values in the range 2-15 nM and were delta selective. Since the unsubstituted analogue 4 possessed delta antagonist potency of similar magnitude, but was not delta selective, it is suggested that the 2',3'-substitution confers delta selectivity by hindering the interaction of the pharmacophore at mu and kappa receptors, while not affecting delta receptors.

Syntheses of novel pyridazinomorphinans by inverse electron demand cycloaddition and their binding to mu and kappa receptors

A number of novel pyridazinomorphinans have been synthesized by the inverse electron demand Diels-Alder reaction of various 3,6-disubstituted 1,2,4,5-tetrazines with enamines derived from dihydrocodeinone and with codeinone. Reduction of some of the pyridazinomorphinans did not furnish the expected pyrroloepoxymorphinans; in all cases investigated reductive cleavage of the epoxybridge was observed to yield dihydropyridazino- or pyrrolomorphinans. The structures of all new compounds were assigned by the spectral data, that of the cycloadduct of codeinone was additionally verified by X-ray crystallography. Compounds 5a, 8, 11a and 16 have been evaluated for their affinity at mu and kappa opioid receptors in radioligand binding assays. Their ability to inhibit [3H]DAMGO binding at mu and [3H]U 69.593 binding at kappa receptors, respectively as compared to codeine has been found to be lower.

New nepenthone and thevinone derivatives

The diastereoselective reaction of thevinone (2a) and nepenthone (2c) and their dihydro derivatives (2b and d) with Grignard reagents afforded new N-substituted (20S)- and (20R)-phenyl-6,14-ethenomorphinan derivatives (6a-y). The Grignard reaction of the N-substituted-N-demethyl derivatives 4a-f and 4m-r with methylmagnesium iodide resulted in the (20R)-phenyl tertiary alcohols 5a-f and 5m-r, respectively, but the conversion of 4g-1 and that of the N-substituted-dihydrothevinone derivatives with phenylmagnesium bromide afforded the (20S)-phenyl derivatives 5g-l and 5s-y, respectively. The N-cyclopropylmethyl-, N-beta-phenylethyl-, and N-propyl derivatives were prepared by the 3-O-demethylation of compounds 5. For the synthesis of the N-allyl-, N-dimethylallyl-, and N-propargyl compounds 2a-d were reacted with the corresponding Grignard reagent, and treatment of the products with cyanogen bromide gave the cyanamides 8a-d. These latter compounds were transformed into 10a, b,d, whose alkylation led to the target derivatives 6d-f, j-l, p-r, and w-y. The biochemical investigation of these substances showed that the affinities to the delta-opioid receptors were high, but the selectivity was low. In two cases (6c and 11d) a mu-opioid receptor specificity was observed.

Synthesis and biological evaluation of 14-alkoxymorphinans. 11. 3-Hydroxycyprodime and analogues: opioid antagonist profile in comparison to cyprodime

A series of 3-hydroxy-substituted analogues (3-7) of the mu selective opioid antagonist cyprodime has been synthesized in order to evaluate the role of a hydroxy group at C-3 concerning mu opioid antagonist selectivity. Compounds 3-7 were tested in bioassays (electrical stimulated mouse vas deferens preparation and myenteric-plexus longitudinal muscle preparation of the guinea pig ileum) and opioid receptor binding assays. Antagonism of mu receptor-mediated responses induced by the mu selective agonist DAMGO afforded equilibrium dissociation constants in the mouse vas deferens preparation (Ke values) for compounds 3-7 which agreed closely with their affinities as determined by opioid receptor binding assays (Ki values). At kappa and delta receptors differences were apparent. Although the compounds had high affinity for both kappa and delta receptors in opioid receptor binding, they were very poor at antagonizing agonist responses mediated by kappa and particularly delta agonists in the mouse vas deferens preparation. None of the compounds tested showed agonist potency in the mouse vas deferens preparation or the myenteric-plexus longitudinal muscle preparation of the guinea pig ileum.

Probes for narcotic receptor-mediated phenomena. 20. Alteration of opioid receptor subtype selectivity of the 5-(3-hydroxyphenyl)morphans by application of the message-address concept: preparation of delta-opioid receptor ligands

Derivatives of racemic and optically active 5-(3-hydroxyphenyl)-2-methylmorphan (5-(3-hydroxyphenyl)-2-methyl-2-azabicyclo[3.3.1]nonane, 1) were synthesized containing additional aromatic moieties, as an application of the message-address concept targeted at producing delta-opioid receptor selective ligands. In vitro radioreceptor binding studies in rat brain revealed that both of the parent enantiomers, (-)- and (+)-1, had a high affinity for the mu-opioid receptor (21 nM), a slight affinity for kappa 1-opioid receptors (approximately 800-900 nM), and less than 1000 nM affinity for the delta-opioid receptor (mu/delta IC50 ratio of < 0.02 for both). A derivative of (-)-1 containing an indole moiety fused at the C6-C7 position of the phenylmorphan nucleus, (-)-11, displayed a > 180-fold increase in affinity for the delta-opioid receptor with an IC50 value of 6 nM. The parent compound (-)-1 had only 26% agonist activity at 30 microM in the mouse vas deferens (delta) bioassay, whereas compound (-)-11 had an IC50 of 393 nM in this preparation, indicating the importance of the indole moiety in imparting delta-opioid agonist activity to the phenylmorphan (-)-11. A structure-activity relationship (SAR) study of N-alkyl derivatives of the racemic nor 11 indicated similarities between the interaction of various derivatives with the mu- and delta- but not the kappa 1-opioid receptor. As studies on the molecular basis of the interaction of opioid ligands with their respective receptors continue to gain momentum, the SAR data described herein for the synthetic phenylmorphans will prove useful for further studies.

Agonist and antagonist opioid activity of axial and equatorial conformations of S-methyl- and S-allyl-morphinans

Resolved axial (beta) and equatorial (alpha) forms of S-methyl (beta-sulforphanol, alpha-sulforphanol) and S-allyl (beta-sulfallorphan, alpha-sulfallorphan) morphinans were tested for their ability to depress the electrically evoked contractions of the guinea pig ileum and of the mouse vas deferens, to compete with the binding of prototype ligands selective for mu-, delta-, and kappa-opioid receptors in membrane preparations of rat brain and guinea pig cerebellum and to produce analgesia in a rat thermal pain assay. beta-Sulforphanol was more potent than alpha-sulforphanol in the guinea pig ileum (relative potencies of 93% and 29% respectively, as compared with levorphanol). beta-Sulfallorphan and alpha-sulfallorphan were both inactive in the guinea pig ileum assay. In the mouse vas deferens preparation, beta-sulforphanol and alpha-sulforphanol had relative potencies of 2.1% and 1.2% as compared with levorphanol, respectively, while the S-allyl derivatives were inactive. All morphinan derivatives displayed marked binding selectivity for mu-opioid receptors but alpha-sulfallorphan also showed significant binding potency on delta-opioid receptors (12% as compared to levorphanol). The compounds were also tested for their ability to antagonize the biological activity of morphine. In the guinea pig ileum, alpha-sulfallorphan potently inhibited morphine with a Ke value of 41.7 nM. alpha-Sulforphanol also antagonized morphine but with a smaller potency (Ke = 350 nM). In the mouse vas deferens, no antagonist activity against morphine was observed with any morphinan derivative tested at 1 microM. In the rat thermal pain assay, beta-sulforphanol (intracisternally, i.c.) was more potent than alpha-sulforphanol in producing analgesia while the other morphinan derivatives were inactive.(ABSTRACT TRUNCATED AT 250 WORDS)

Conformational analysis of the opioid phenylmorphan and its 9 alpha-methyl analogue in solution using high-resolution nuclear magnetic resonance spectroscopy

The solution conformations of the opioid phenylmorphan (5-m-hydroxyphenyl-2-methylmorphan) and its 9 alpha-methyl analogue were studied using one- and two-dimensional high resolution NMR techniques. The NMR spectra were analyzed by interpreting the phase-sensitive 2-D COSY and double quantum filtered COSY spectra, 1H-1H vicinal coupling constants, and nuclear Overhauser effects in the phase-sensitive 2-D NOESY spectra. The results show that, for both compounds, a chair-chair conformation of the cyclohexane and piperidine rings is exclusively preferred with some distortion of the rings from perfectly staggered chairs. For phenylmorphans, the phenyl ring is oriented to fit into the cleft formed by the cyclohexane and piperidine rings. Thus, for the (+)-enantiomer, the phenyl group assumes the same orientation with regard to the piperidine ring as morphine consistent with the morphine-like properties of the compound. For the 9 alpha-methyl analogue, the plane of the phenyl ring essentially bisects the piperidine ring to which it is attached and is outside of the required range of opioid agonists. This is consistent with the atypical properties of the two enantiomers. The NMR results are compared to the conformations of (-)-phenylmorphan and the (+)-9 alpha-methyl analogue in the crystal state and to the results of molecular mechanics (MM2) studies.

O3-(2-carbomethoxyallyl) ethers of opioid ligands derived from oxymorphone, naltrexone, etorphine, diprenorphine, norbinaltorphimine, and naltrindole. Unexpected O3-dealkylation in the opioid radioligand displacement assay

O3-(2-Carbomethoxyallyl) ether derivatives of some phenolic 4,5-epoxymorphinan opioid ligands have been prepared in a simple one-step procedure, and their behavior in the radioligand receptor assay was compared to their phenolic precursors. These O3-ether ligands appeared to show significant affinity for opioid receptors, about 2-fold less than the parent phenols, and their receptor selectivities were similar. However, on close examination of the stability of a representative ether 2b in the radioligand displacement assay, considerable O3-dealkylation was observed. The dealkylation process occurred even after denaturation of the proteins of the membrane preparation, and it occurred in the presence of model nucleophiles imidazole and thiophenol. Thus, what apparently was unusual activity is explained by O3-dealkylation to the parent phenol (e.g., 2a). Saturated ether analog 2c was not dealkylated under the conditions of the radioligand displacement assay and was a very weak opioid ligand. We conclude that the conversion of the O3(2-carbomethoxyallyl) ether electrophilic ligands to their parent phenols accounts for their activity in the opioid radioligand displacement assay.

Opioid agonist and antagonist activities of morphindoles related to naltrindole

A series of naltrindole-related ligands (4-10) with an N-methyl,N-phenethyl,N-cinnamyl, or an unsubstituted basic nitrogen were synthesized and tested for opioid agonist and antagonist activity in smooth muscle preparations and in mice. The nor compounds (4 and 6) and the phenethyl derivatives (5 and 8) displayed full agonist activity (IC50 = 85-179 nM) in the mouse vas deferens preparation (MVD) while the other members of the series exhibited partial agonist or weak antagonist activity. In the guinea pig ileum preparation (GPI), all compounds except 8 were partial agonists. The ligands that were evaluated in mice were found to produce antinociception that was not selectively mediated via delta opioid receptors. However, two of these ligands (4 and 5) appeared to be delta-selective opioid receptor antagonists at subthreshold doses for antinociception. The finding that all of the compounds bind selectively to delta opioid receptors in guinea pig brain membranes together with the in vitro pharmacology and in vivo antagonist studies suggests that the lack of delta agonist selectivity in vivo may be due to a number of factors, including a basic difference between the delta receptor system in the MVD and in the mouse brain. Further, it is suggested that the constellation of message and address components in the morphindole nucleus may tend to stabilize delta receptors in the brain in antagonist state.

A pseudoreceptor docking study of 4,5-alpha-epoxymorphinans with a range of dielectric constants

Thirteen 4,5-epoxymorphinan mu agonists with established analgesic action were docked into an Asp-Lys-His-Phe pseudoreceptor complex under a range of distance-dependent dielectric conditions. The number of compounds with potential energies of the docked complexes that agreed in rank order with corresponding analgesic potencies was determined for each condition. Two dielectric conditions, n-decane (1.991) and ethanol (24.3), enabled the greatest number of compounds to relate to their pseudoreceptors with each having 9 and 8 successes respectively. Both of these conditions demonstrated unique influences on the types of structures that were successfully docked. For example, the morphine stereoisomer alpha-isomorphine, the geometric isomer B/C trans-morphine, and the 8-position-substituted gamma-isomorphine were successes in the n-decane condition, whereas the ethanol condition produced the substituted codeine derivatives dihydrocodeinone and dihydroxycodeinone. These findings emphasize the importance of dielectric influence when developing force-field modeled quantitative structure-activity relationships for a closely related homologous series.

Molecular structure of opiate alkaloids. IV. Structure of two thioniamorphinans

(I) S(equatorial)-Allyl-3-hydroxy-17-thioniamorphinan perchlorate, C19H25OS+.C1O4-, Mr = 400.91, monoclinic, P2(1)/n, a = 9.4171 (8), b = 10.7425 (10), c = 19.096 (2) A, beta = 95.666 (7) degrees, V = 1922.4 (3) A3, Z = 4, Dx = 1.385 Mg m-3, lambda (Mo K alpha) = 0.70930 A, mu = 0.33 mm-1, F(000) = 847.92, room temperature, final R = 0.052 for 1742 observed reflections. (II) S(axial)-Allyl-3-hydroxy-17-thioniamorphinan perchlorate, C19H25OS+.C1O4-, Mr = 400.91, monoclinic, P2(1), a = 8.4554 (10), b = 11.658 (3), c = 9.5831 (21) A, beta = 95.620 (10) degrees, V = 940.1 (3) A 3, Z = 2, Dx = 1.416 Mg m-3, lambda (Mo K alpha) = 0.70930 A, mu = 0.33 mm-1, F(000) = 423.96, room temperature, final R = 0.054 for 1015 observed reflections. The molecular structures of (I) and (II) are differentiated only by the orientation of the S-allyl substituent: the S-allyl group is equatorial in (I) and axial in (II). It has been shown that the activities as potent and selective blockers of kappa opioid receptors (kappa 2 subtype) are to be attributed to the alpha-thiamorphinan isomer (I). The inactive compound (II) is the beta-isomer. The fused ring systems are almost identical in the two molecules.

A Free-Wilson/Fujita-Ban analysis and prediction of the analgesic potency of some 3-hydroxy- and 3-methoxy-N-alkylmorphinan-6-one opioids

Herein we describe a Free-Wilson/Fujita-Ban QSAR (quantitative structure-activity relationship) analysis of the analgesic potency of over 50 semisynthetic opioid narcotics. The 3-hydroxy- and 3-methoxy-N-alkylmorphinan-6-ones of B/C-cis and -trans stereochemistry include compounds exhibiting structural variation at five positions [N-methyl (C17), oxygen at C3, C4-C5 oxygen bridge, alkyl substituents at C7 and C8]. The pharmacological parameter correlated was the analgesic potency (-log ED50) exhibited on abdominal contractions produced by acetylcholine injection in mice. A satisfactory correlation was obtained only by assuming interdependent contributions of the substituents on C17 and O(C3), with which it was possible to explain 75% of the variance. Phenolic compounds (3-OH) behave somewhat differently from the methyl ethers (3-OCH3), and in both series the substituents on C8 have a size-dependent negative contribution, implying steric hindrance at their contact point on the receptor. With use of this correlation the potency of five further members of the series was predicted. Subsequent testing fully confirmed the validity of the correlation since the measured potencies were, within experimental error, equal to those calculated. In a further refinement, phenolic compounds were considered separately from the ethers, and it was found that the contribution of the substituents on C17, C7, and C8 remained similar in sign and magnitude but not that of the furan oxygen. This analysis allows us to conclude that if both phenolic and nonphenolic members of this series act on the same receptor they must bind at different subsites or in alternate modes, supporting an earlier proposal in the literature.

Conformational search in enkephalin analogues containing a disulfide bond

A systematic conformational search has been performed for the 14-membered ring in model compounds for disulfide-containing enkephalin analogues. The model compounds examined are [formula: see text], and the corresponding compounds with L-amino acids at the C-terminus. About 100 starting conformations were generated for each compound with the RNGCFM program and energy minimized with the AMBER program. Between 21 and 38 conformers within 3 kcal/mole of the apparent global minimum were found for each compound. There appeared to be fewer possible conformations of the disulfide-containing side chain than of the main chain. [formula: see text], whose parent compound is selective for opioid delta receptors, was found to prefer conformers with a positive dihedral angle of the disulfide bond, which is consistent with the previous proposal that delta-receptor selectivity may be associated with this conformational preference. Additional calculations were performed on the complete structure of [formula: see text] (DPDPE) with various possible conformations of the tyrosine and phenylalanine side chains. Conformational free energies and entropies were computed for these conformers from the molecular vibrations obtained from a normal mode analysis. As was found previously, conformers with low energies tended to have lower entropies, which resulted in a narrowing of the free energy differences between conformers. A conformer is identified that has the lowest energy hitherto found for DPDPE. It is suggested that DPDPE may be a useful compound for evaluating conformational search strategies because of its relatively small size and the number of conformers that have already been identified. Conformational energy calculations are also reported for naltrindole using the MM2(87) program. Naltrindole, which incorporates two aromatic 6-membered rings in a rigid structure, is a highly selective and potent opioid delta-receptor antagonist and may be an important clue regarding the biologically active conformer of DPDPE. Various conformers of DPDPE have been superimposed quantitatively onto the structure of naltrindole using the SUPER program and those conformers of DPDPE that are the best fit to naltrindole are reported.