Synthesis and biological evaluation of 14-alkoxymorphinans. 17. Highly delta opioid receptor selective 14-alkoxy-substituted indolo- and benzofuromorphinans

Two-step synthesis of chiral fused tricyclic scaffolds from phenols via desymmetrization on nickel

Tricyclic furan derivatives with multiple chiral centers are ubiquitous in natural products. Construction of such tricyclic scaffolds in a stereocontrolled, step-economic, and atom-economic manner is a key challenge. Here we show a nickel-catalyzed highly enantioselective synthesis of hydronaphtho[1,8-bc]furans with five contiguous chiral centers via desymmetrization of alkynyl-cyclohexadienone by oxidative cyclization and following formal [4 + 2] cycloaddition processes. Alkynyl-cyclohexadienone was synthesized in one step from easily accessible phenols. This reaction represents excellent chemo-selectivity, regio-selectivity, diastereo-selectivity, and enantio-selectivity (single diastereomer, up to 99% ee). An extraordinary regioselectivity in the formal [4 + 2] cycloaddition step with enones revealed the diverse reactivity of the nickelacycle intermediate. Desymmetrization of alkynyl-cyclohexadienones via oxidative cyclization on nickel was supported by the isolation of a nickelacycle from a stoichiometric reaction. Enantioenriched tricyclic products contain various functional groups such as C=O and C=C. The synthetic utility of these products was demonstrated by derivatization of these functional groups.

Tricyclic furanic compounds with multiple chiral centers are found in a variety of natural products. Here, the authors show a highly enantioselective nickel-catalyzed procedure to access tricyclic oxygen-containing scaffolds with five contiguous chiral centers.

A one-pot multicomponent approach to a new series of morphine derivatives and their biological evaluation

Morphine derivatives displaying a mixed MOR/DOR biological characteristic were synthesized through a one-pot multicomponent approach.

Taming furfuryl cations for the synthesis of privileged structures and novel scaffolds

Furfuryl cations are generated via a highly efficient bismuth-catalyzed reaction of furfuryl alcohols. This systematic study provides insight on the reactivity profile of furfuryl cations towards nucleophilic substitution reactions. Novel C-C, C-N, C-O and C-S bond forming reactions of furfuryl cations have been developed, thus providing access to a diverse array of building blocks for further manipulations.

Opioid receptors and the discriminative stimulus effects of ethanol in squirrel monkeys: Mu and delta opioid receptor mechanisms

Mu and delta opioid receptors modulate the reinforcing effects of ethanol, however, their role in the subjective effects of ethanol is not well understood. This study evaluated the contribution of mu and delta opioid receptors to the subjective effects of ethanol using drug discrimination procedures. Monkeys were trained to discriminate ethanol from saline under a schedule of food delivery. In tests, ethanol engendered increases in drug-lever responding, reaching a maximum of >80%. The mu opioid receptor agonists fentanyl and buprenorphine and the delta opioid receptor agonists SNC 80 and SNC 162 did not substitute for the discriminative stimulus effects of ethanol. As pretreatments, the full agonists fentanyl and SNC 80 enhanced the effects of low doses of ethanol and fentanyl attenuated the effects of the ethanol training dose. Although the possibility of pharmacological antagonism of the effects of ethanol cannot be ruled out, a more likely alternative is that the diminished effects of ethanol were due to perceptual masking of the ethanol stimulus. In contrast, the partial agonists buprenorphine and SNC 162 did not alter ethanol's effects. Finally, the discriminative stimulus effects of ethanol were attenuated following administration of presumably mu-selective doses of the antagonist naltrexone, but not after administration of the delta opioid receptor antagonist naltrindole. The ability of naltrexone to block the discriminative stimulus effects of ethanol likely reflects its capacity to attenuate ethanol-induced increases in endogenous opioids, in particular beta-endorphin, because attenuation of the ethanol stimulus was not accompanied by significant suppression of response rate.

Synthesis of 14-alkoxymorphinan derivatives and their pharmacological actions

Among opioids, morphinans play an important role as therapeutically valuable drugs. They include pain relieving agents such as naturally occurring alkaloids (e.g. morphine, codeine), semisynthetic derivatives (e.g. oxycodone, oxymorphone, buprenorphine), and synthetic analogs (e.g. levorphanol). Currently used opioid analgesics also share a number of severe side effects, limiting their clinical usefulness. The antagonist morphinans, naloxone and naltrexone are used to treat opioid overdose, opioid dependence, and alcoholism. All these opioid drugs produce their biological actions through three receptor types, mu, delta, and kappa, belonging to the G-protein-coupled receptor family. Considerable effort has been put forward to understand the appropriate use of opioid analgesics, while medicinal chemistry and opioid pharmacology have been continuously engaged in the search for safer, more efficacious and nonaddicting opioid compounds, with the final goal to reduce complications and to improve patient compliance. Toward this goal, recent advances in chemistry, ligand-based structure activity relationships and pharmacology of 14-alkoxymorphinans are reviewed in this chapter. Current developments of different structural patterns of 14-alkoxymorphinans as research tools and their potential therapeutic opportunities are also summarized.

Non-peptidic delta-opioid receptor antagonists suppress mitogen-induced tryptophan degradation in peripheral blood mononuclear cells in vitro

Opioid receptors are expressed not only on neuroendocrine cells but also on immunocompetent cells such as lymphocytes, monocytes and macrophages. micro-Opioid receptor agonists were found to exert immunosuppressive effects, whereas delta-opioid receptor agonists have been shown to act as immunostimulants. delta-Opioid receptor agonists stimulate T and B cells and activate granulocytes and monocytes, conversely, immunostimulation can be blocked by the non-peptidic delta-opioid receptor antagonist (NTI). We investigated the impact of NTI and of the two structurally related compounds HS-378 and HS-459 on degradation of tryptophan and formation of neopterin in mitogen-stimulated human peripheral blood mononuclear cells (PBMC). Both these biochemical pathways were found to be suppressed by all three opioid receptor antagonists, HS-378 and HS-459 exhibiting slightly greater potency than NTI. The suppression of tryptophan degradation suggests that the tested delta-opioid antagonists are able to influence the serotonergic system via a non-opioid action.

Opioid receptor binding characteristics and structure-activity studies of novel tetrapeptides in the TIPP (Tyr-Tic-Phe-Phe) series

The development of the prototype synthetic delta-opioid receptor antagonist peptides TIPP [(H-Tyr-Tic-Phe- Phe-OH); Tic: tetrahydroisoquinoline-3-carboxylic acid] and TIPPpsi (H-Tyr-psiTic-Phe-Phe-OH) by Schiller and coworkers was followed by extensive structure-activity relationship studies, leading to the emergence of numerous analogs that are of pharmacological interest. Eight novel diastereomeric compounds in this peptide family were designed, prepared, and tested biologically to gain structure-activity relationship information. The new multisubstituted tetrapeptide analogs contain both a 2',6'-dimethyltyrosine residue at the N-terminus and beta-methyl-cyclohexylalanine at the third position as replacements for the original first tyrosine and the third phenylalanine, respectively. These derivatives wear either free acidic (-COOH) or amidated (-CONH2) C-terminal. The potency and delta- versus mu-opioid receptor selectivity were evaluated by in vitro radioreceptor-binding assays, while the intrinsic G-protein-activating efficacy of these analogs was tested in [35S]GTPgammaS-binding assays using rat brain membranes or Chinese hamster ovary cells stably expressing mu- or delta-opioid receptors. The analogs showed delta-antagonist selectivity with differences regarding their isomeric forms, and these analogs containing a C-terminal carboxamide group displayed a mixed mu-agonist/delta-antagonist profile, thus they are expected to be safer analgesics with a low propensity to produce tolerance and physical dependence. These results constitute further examples of the influence of beta-methyl substitution and C-terminal amidation on potency, selectivity, and signal transduction properties of TIPP-related peptides as well as they represent valuable pharmacological tools for opioid research.

Major effect of pyrrolic N-benzylation in norbinaltorphimine, the selective kappa-opioid receptor antagonist

Indolic N-benzylation of naltrindole reportedly extends the duration of delta-opioid receptor (DOR) antagonism. Similar modification of the kappa-opioid receptor (KOR) antagonist norBNI (1a) and its 17,17'-diNMe analogue (1d), a low potency mu-opioid receptor (MOR) partial agonist, was found to affect predominantly their MOR activity. When administered systemically in mouse antinociceptive assays, N-benzyl-norBNI (1b) had only MOR agonist activity of relatively short duration whereas on central administration it had only a KOR-antagonist action of extremely long duration.

Inverse agonism and neutral antagonism at wild-type and constitutively active mutant delta opioid receptors

The delta opioid receptor modulates nociceptive and emotional behaviors. This receptor has been shown to exhibit measurable spontaneous activity. Progress in understanding the biological relevance of this activity has been slow, partly due to limited characterization of compounds with intrinsic negative activity. Here, we have used constitutively active mutant (CAM) delta receptors in two different functional assays, guanosine 5'-O-(3-thio)triphosphate binding and a reporter gene assay, to test potential inverse agonism of 15 delta opioid compounds, originally described as antagonists. These include the classical antagonists naloxone, naltrindole, 7-benzylidene-naltrexone, and naltriben, a new set of naltrindole derivatives, H-Tyr-Tic-Phe-Phe-OH (TIPP) and H-Tyr-TicPsi[CH2N]Cha-Phe-OH [TICP(Psi)], as well as three 2',6'-dimethyltyrosine-1,2,3,4-tetrahydroquinoline-3-carboxylate (Dmt-Tic) peptides. A reference agonist, SNC 80 [(+)-4-[(alphaR)-alpha-((2S,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide], and inverse agonist, ICI 174864 (N,N-diallyl-Tyr-Aib-Aib-Phe-Leu), were also included. In a screen using wild-type and CAM M262T delta receptors, naltrindole (NTI) and close derivatives were mostly inactive, and TIPP behaved as an agonist, whereas Dmt-Tic-OH and N,N(CH3)2-Dmt-Tic-NH2 showed inverse agonism. The two latter compounds showed negative activity across 27 CAM receptors, suggesting that this activity was independent from the activation mechanism. These two compounds also exhibited nanomolar potencies in dose-response experiments performed on wild-type, M262T, Y308H, and C328R CAM receptors. TICP(Psi) exhibited strong inverse agonism at the Y308H receptor. We conclude that the stable N,N(CH3)2-Dmt-Tic-NH2 compound represents a useful tool to explore the spontaneous activity of delta receptors, and NTI and novel derivatives behave as neutral antagonists.

Effects of Substitution on the Pyrrole N Atom in Derivatives of Tetrahydronaltrindole, Tetrahydrooxymorphindole, and a Related 4,5-Epoxyphenylpyrrolomorphinan

The effect of substitution of the pyrrolo- and indolo-N atoms in tetrahydronaltrindole (TNTI), tetrahydrooxymorphindole (TOMI), and 17-cyclopropylmethyl-3,14-dihydroxy-4,5-epoxy-4'-phenyl-6,7:2',3'-pyrrolomorphinan (4) is reported. In opioid functional assays 4 were potent deltaopioid receptor (DOR) antagonists while the TNTI derivatives (7) were potent DOR antagonists or low-efficacy DOR partial agonists without substantial selectivity. The TOMI derivatives (8) were DOR agonists with significant selectivity. In vivo the DOR antagonist activity of 7d was confirmed, but the predominant agonist effect of 8d was shown to be mu opioid receptor mediated.

Effect of novel non-peptidic delta opioid receptor antagonists on human T and B cell activation

The effects of the antagonist naltrindole (NTI) on cells of the immune system have been largely studied although the mechanisms of action are still unclear. The aim of this study is to evaluate, in vitro, the immunomodulatory activity of four new delta-selective opioid compounds structurally related to naltrindole. The effects at different concentrations of these opioid antagonists on proliferative response were studied on normal human peripheral blood mononuclear cells (PBMC) stimulated with different stimuli: mitogens, the antigen PPD, the anti-CD3 monoclonal antibodies (mAb), the superantigen Staphylococcus aureus Cowan strain 1 (SAC) and alloantigens in the mixed lymphocyte cultures (MLR). The immunomodulatory capacity of these compounds was evaluated by determining the interleukin-2 (IL-2) release in mitogen activated PBMC. The present study shows that all the new delta opioid antagonists at 10(-5) M concentration are immunosuppressive. The inhibitory action is also evident at lower concentrations when anti-CD3 mAb and SAC were used as stimulators. In addition, the production of IL-2 was inhibited by the opioid treatment, but this might not be the only mechanism of action.

β-Phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids derived from them, including further products of oxidation. condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2002 to June 2003 is reviewed, with 568 references cited.

Endogenous opiates and behavior: 2002

This paper is the twenty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2002 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).