Preliminary pharmacological evaluation of enantiomeric morphinans

Applications of palladium-catalyzed C-N cross-coupling reactions in pharmaceutical compounds

C-N cross-coupling bond formation reactions have become valuable approaches to synthesizing anilines and their derivatives, known as important chemical compounds. Recent developments in this field have focused on versatile catalysts, simple operation methods, and green reaction conditions. This review article presents an overview of C-N cross-coupling reactions in pharmaceutical compound synthesis reports. Selected examples of N-arylation reactions of various nitrogen-based compounds and aryl halides are defined for preparing pharmaceutical molecules.

Opioid toxicity: histamine, hypersensitivity, and MRGPRX2

Insights into the pathophysiology of many non-immune-mediated drug reactions referred to as toxicities, sensitivities, intolerances, or pseudoallergies have resulted from research identifying the mastocyte-related G-protein-coupled receptor (GPCR) member X2 (MRGPRX2), a human mast cell receptor mediating adverse reactions without the involvement of antibody priming. Opioid-induced degranulation of mast cells, particularly morphine, provoking release of histamine and other preformed mediators and causing hemodynamic and cutaneous changes seen as flushing, headache and wheal and flare reactions in the skin, is an example of results of MRGPRX2 activation. Opioids including morphine, codeine, dextromethorphan and metazocine as well as endogenous prodynorphin opioid peptides activate MRGPRX2 at concentrations causing mast cell degranulation. Unlike the canonical opioid receptors, MRGPRX2 shows stereochemical recognition preference for dextro rather than levo opioid enantiomers. Opioid analgesic drugs (OADs) display a range of histamine-releasing potencies from the strong releaser morphine to doubtful releasers like hydromorphone and the non-releaser fentanyl. Whether there is a correlation between histamine release by individual OADs, MRGPRX2 activation, and presence or absence of adverse cutaneous effects is not known. To investigate the question, ongoing research with recently pursued methodologies and strategies employing basophil and mast cell tests resulting from MRGPRX2 insights should help to elucidate whether or not an opioid's histamine-releasing potency, and its property of provoking an adverse reaction, are each a reflection of its activation of MRGPRX2.

The potential interplay between Opioid and the Toll-Like Receptor 4 (TLR-4)

CONTEXT

Opioids are available for the management of severe and chronic pain. However, long-term use of high-dose opioids could lead to physiologic tolerance, hyperalgesia, gastrointestinal immobility, addiction, respiratory depression, tumor progression, and inhibition of the immune system. It seems some of these adverse effects of opioids might be induced by TLR-4 signaling.

OBJECTIVE

The review aims to investigate the potential interplay between opioids and TLR-4 in CNS, gastrointestinal, cancer, and immune system.

METHODS

The search of PubMed, Embase, Scopus, web of sciences, and Google scholar was performed for all relevant studies published. From a total of 513 papers obtained at the initial database search, publications including in silico, in vitro, and in vivo studies were selected for the review.

RESULTS

A comprehensive review of studies indicated that using opioids for the reduction of pain might induce adverse effects such as analgesic tolerance, hyperalgesia, cancer progression, and suppression of the immune system. Some studies have indicated these effects may be due to a change in the level of expression and signaling pathway of TLR-4. The generalizability of the results was limited due to the inconsistency of findings.

CONCLUSIONS

More studies are needed to clarify TLR-4-mediated opioid effects on the biology or stages of the disease as well as the role of different types of opioids, appropriate dosage, and exposure in various contexts. Designing the drug candidate and doing many formulation studies for different diseases and various stages of disease could be associated with effective treatment and pain management.

The High Affinity Dopamine D2 Receptor Agonist MCL-536: A New Tool for Studying Dopaminergic Contribution to Neurological Disorders

The dopamine D₂ receptor exists in two different states, D₂^high and D_2low; the former is the functional form of the D₂ receptor and associates with intracellular G-proteins. The D₂ agonist [³H]MCL-536 has high affinity for the D₂ receptor (K_d 0.8 nM) and potently displaces the binding of (R-(-)-N-n-propylnorapomorphine (NPA; K_i 0.16 nM) and raclopride (K_i 0.9 nM) in competition binding assays. Here, we further characterize [³H]MCL-536. [³H]MCL-536 was metabolically stable, with about 75% of the compound remaining intact after 1 h incubation with human liver microsomes. Blood-brain barrier penetration in rats was good, attaining at 15 min a % injected dose per gram of wet tissue (%ID/g) of 0.28 in males versus 0.42 in females in the striatum. Specific uptake ratios ([%ID/g striatum]/[%ID/g cerebellum]) were stable in males during the first 60 min and in females up to 15-30 min. The D₂-rich striatum exhibited the highest uptake and slowest washout compared to D₂-poor cortex or cerebellum. In peripheral organs, uptake peaked at 15 min but declined to baseline at 60 min, indicating good clearance from the body. In vitro autoradiography on transaxial and coronal brain sections showed specific binding of [³H]MCL-536, which was abolished by preincubation with D₂/D₃ ligands sulpiride, NPA, and raclopride and in the presence of the stable GTP analogue guanylylimidodiphosphate. In amphetamine-sensitized animals, striatal binding was higher than in controls, indicating specificity for the D₂^high receptor state. [³H]MCL-536's unique properties make it a valuable tool for research on neurological disorders involving the dopaminergic system like Parkinson's disease or schizophrenia.

The present and future synthetic strategies of structural modifications of sinomenine

This review summarizes the modifications of sinomenine, a hot compound derived from herbal plants, which possesses diverse biological activities and low cytotoxicity.

Biaryl Monophosphine Ligands in Palladium-Catalyzed C-N Coupling: An Updated User's Guide

Over the past three decades, Pd-catalyzed cross-coupling reactions have become a mainstay of organic synthesis. In particular, catalysts derived from biaryl monophosphines have shown wide utility in forming C-N bonds under mild reaction conditions. This work summarizes a variety of C-N cross-coupling reactions using biaryl monophosphines as supporting ligands, with the goal of directing synthetic chemists towards the ligands and conditions best suited for a particular coupling.

Equipotent enantiomers of cyclic opioid peptides at μ opioid receptor

Head-to-tail cyclized analogues of the μ opioid receptor (MOR) agonist tetrapeptides DALDA (H-Tyr-D-Arg-Phe-Lys-NH₂ and [Dmt¹]DALDA (H-Dmt-D-Arg-Phe-Lys-NH₂; Dmt = 2',6'-dimethyltyrosine) and their enantiomers (mirror-image isomers) were synthesized and pharmacologically characterized in vitro. Three pairs of enantiomeric cyclic peptides with both mirror-image isomers having equipotent MOR binding affinities but different binding affinities at the δ and κ opioid receptors were identified. The cyclic peptide enantiomers c[-D-Arg-Phe-Lys-Tyr-] (1) and c[-Arg-D-Phe-D-Lys-D-Tyr-] (2) showed nearly identical MOR binding affinity (1 - 2 nM) and equipotent MOR antagonist activity. The results of a MOR docking study indicated a very similar binding mode of the two enantiomers with nearly complete spatial overlap of the peptide ring structures and side chain interactions with the same MOR residues. Compounds 1 and 2 represent the first pair of enantiomeric G-protein-coupled receptor (GPCR) ligands having multiple chiral centers, with both optical antipodes showing equal, low nanomolar receptor binding affinity.

In silico design of novel probes for the atypical opioid receptor MRGPRX2

The primate-exclusive MRGPRX2 G protein-coupled receptor (GPCR) has been suggested to modulate pain and itch. Despite putative peptide and small molecule MRGPRX2 agonists, selective nanomolar potency probes have not yet been reported. To identify a MRGPRX2 probe, we first screened 5,695 small molecules and found many opioid compounds activated MRGPRX2, including (−)- and (+)-morphine, hydrocodone, sinomenine, dextromethorphan and the prodynorphin-derived peptides, dynorphin A, dynorphin B, and α- and β-neoendorphin. We used these to select for mutagenesis-validated homology models and docked almost 4 million small molecules. From this docking, we predicted ZINC-3573, which represents a potent MRGPRX2-selective agonist, showing little activity against 315 other GPCRs and 97 representative kinases, and an essentially inactive enantiomer. ZINC-3573 activates endogenous MRGPRX2 in a human mast cell line inducing degranulation and calcium release. MRGPRX2 is a unique atypical opioid-like receptor important for modulating mast cell degranulation, which can now be specifically modulated with ZINC-3573.

A Cyclic Tetrapeptide ("Cyclodal") and Its Mirror-Image Isomer Are Both High-Affinity μ Opioid Receptor Antagonists

Head-to-tail cyclization of the μ opioid receptor (MOR) agonist [Dmt¹]DALDA (H-Dmt-d-Arg-Phe-Lys-NH₂ (9; Dmt = 2',6'-dimethyltyrosine) resulted in a highly active, selective MOR antagonist, c[-d-Arg-Phe-Lys-Dmt-] (1) ("cyclodal"), with subnanomolar binding affinity. A docking study of cyclodal using the crystal structure of MOR in the inactive form showed a unique binding mode with the two basic residues of the ligand forming salt bridges with the Asp¹²⁷ and Glu²²⁹ receptor residues. Cyclodal showed high plasma stability and was able to cross the blood-brain barrier to reverse morphine-induced, centrally mediated analgesia when given intravenously. Surprisingly, the mirror-image isomer (optical antipode) of cyclodal, c[-Arg-d-Phe-d-Lys-d-Dmt-] (2), also turned out to be a selective MOR antagonist with 1 nM binding affinity, and thus, these two compounds represent the first example of mirror image opioid receptor ligands with both optical antipodes having high binding affinity. Reduction of the Lys-Dmt peptide bond in cyclodal resulted in an analogue, c[-d-Arg-Phe-LysΨ[CH₂NH]Dmt-] (8), with MOR agonist activity.

Applications of Palladium-Catalyzed C-N Cross-Coupling Reactions

Pd-catalyzed cross-coupling reactions that form C–N bonds have become useful methods to synthesize anilines and aniline derivatives, an important class of compounds throughout chemical research. A key factor in the widespread adoption of these methods has been the continued development of reliable and versatile catalysts that function under operationally simple, user-friendly conditions. This review provides an overview of Pd-catalyzed N-arylation reactions found in both basic and applied chemical research from 2008 to the present. Selected examples of C–N cross-coupling reactions between nine classes of nitrogen-based coupling partners and (pseudo)aryl halides are described for the synthesis of heterocycles, medicinally relevant compounds, natural products, organic materials, and catalysts.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 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 (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 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 (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).