Sinomenine Hydrochloride Protects IgA Nephropathy Through Regulating Cell Growth and Apoptosis of T and B Lymphocytes.

Purpose: Sinomenine hydrochloride (SH) is used to treat chronic inflammatory diseases such as rheumatoid arthritis and may also be efficacious against Immunoglobulin A nephropathy (IgAN). However, no trial has investigated the molecular mechanism of SH on IgAN. Therefore, this study aims to investigate the effect and mechanism of SH on IgAN. Methods: The pathological changes and IgA and C3 depositions in the kidney of an IgAN rat model were detected by periodic acid-Schiff (PAS) and direct immunofluorescence staining. After extracting T and B cells using immunomagnetic beads, we assessed their purity, cell cycle phase, and apoptosis stage through flow cytometry. Furthermore, we quantified cell cycle-related and apoptosis-associated proteins by Western blotting. Results: SH reduced IgA and C3 depositions in stage 4 IgAN, thereby decreasing inflammatory cellular infiltration and mesangial injury in an IgAN model induced using heteroproteins. Furthermore, SH arrested the cell cycle of lymphocytes T and B from the spleen of IgAN rats. Regarding the mechanism, our results demonstrated that SH regulated the Cyclin D1 and Cyclin E1 protein levels for arresting the cell cycle and it also regulated Bax and Bcl-2 protein levels, thus increasing Cleaved caspase-3 protein levels in Jurkat T and Ramos B cells. Conclusion: SH exerts a dual regulation on the cell cycle and apoptosis of T and B cells by controlling cell cycle-related and apoptosis-associated proteins; it also reduces inflammatory cellular infiltration and mesangial proliferation. These are the major mechanisms of SH in IgAN.

Morphinan Evolution: The Impact of Advances in Biochemistry and Molecular Biology.

Morphinan-based opioids, derived from natural alkaloids like morphine, codeine and thebaine, have long been pivotal in managing severe pain. However, their clinical utility is marred by significant side effects and high addiction potential. This review traces the evolution of the morphinan scaffold in light of advancements in biochemistry and molecular biology, which have expanded our understanding of opioid receptor pharmacology. We explore the development of semi-synthetic and synthetic morphinans, their receptor selectivity and the emergence of biased agonism as a strategy to dissociate analgesic properties from undesirable effects. By examining the molecular intricacies of opioid receptors and their signaling pathways, we highlight how receptor-type selectivity and signaling bias have informed the design of novel analgesics. This synthesis of historical and contemporary perspectives provides an overview of the morphinan landscape, underscoring the ongoing efforts to mitigate the problems facing opioids through smarter drug design. We also highlight that most morphinan derivatives show a preference for the G protein pathway, although detailed experimental comparisons are still necessary. This fact underscores the utility of the morphinan skeleton in future opioid drug discovery.

Recent Advances in the Therapeutic Potential of Sinomenine for Cancer Treatment.

BACKGROUND: Cancer is a major cause of death worldwide. Although modern medicine has made strides in treatment, a complete cure for cancer remains elusive. SUMMARY: Utilization of medicinal plants in traditional medicine for the treatment of multiple diseases, including cancer, is a well-established practice. Sinomenine is an alkaloid extracted from a medicinal plant and has a diverse range of biological properties, including anti-oxidative, anti-inflammatory, and antibacterial effects. Sinomenine exhibits inhibitory effects on various types of tumor cells, including breast, lung, and liver cancers. The anticancer properties of sinomenine are believed to involve stimulation of apoptosis and autophagy as well as suppression of cell proliferation, invasion, and metastasis. KEY MESSAGE: This review summarizes the current research on sinomenine's potential as an anticancer agent, which may contribute to the discovery of more effective cancer treatments.

Bioactivities and Mechanisms of Action of Sinomenine and Its Derivatives: A Comprehensive Review.

Sinomenine, an isoquinoline alkaloid extracted from the roots and stems of Sinomenium acutum, has been extensively studied for its derivatives as bioactive agents. This review concentrates on the research advancements in the biological activities and action mechanisms of sinomenine-related compounds until November 2023. The findings indicate a broad spectrum of pharmacological effects, including antitumor, anti-inflammation, neuroprotection, and immunosuppressive properties. These compounds are notably effective against breast, lung, liver, and prostate cancers, exhibiting IC50 values of approximately 121.4 nM against PC-3 and DU-145 cells, primarily through the PI3K/Akt/mTOR, NF-κB, MAPK, and JAK/STAT signaling pathways. Additionally, they manifest anti-inflammatory and analgesic effects predominantly via the NF-κB, MAPK, and Nrf2 signaling pathways. Utilized in treating rheumatic arthritis, these alkaloids also play a significant role in cardiovascular and cerebrovascular protection, as well as organ protection through the NF-κB, Nrf2, MAPK, and PI3K/Akt/mTOR signaling pathways. This review concludes with perspectives and insights on this topic, highlighting the potential of sinomenine-related compounds in clinical applications and the development of medications derived from natural products.

Proposal for the classification of sinomenine alkaloids.

The chemical structure of sinoacutine is formed by a phenanthrene nucleus and an ethylamine bridge. Because it has a similar parent structure to morphine, it is subdivided into morphinane. At present, all reports have pointed out that the basic skeleton of morphine alkaloids is salutaridine (the isomer of sinoacutine), which is generated by the phenol coupling reaction of (R)-reticuline. This study shows that the biosynthetic precursors of sinoacutine and salutaridine are different. In this paper, the sinoacutine synthetase (SinSyn) gene was cloned from Sinomenium acutum and expressed SinSyn protein. Sinoacutine was produced by SinSyn catalyzed (S)-reticuline, according to the results of enzyme-catalyzed experiments. The optical activity, nuclear magnetic resonance, and mass spectrum of sinoacutine and salutaridine were analyzed. The classification and pharmacological action of isoquinoline alkaloids were discussed. It was suggested that sinoacutine should be separated from morphinane and classified as sinomenine alkaloids.

Discovery of sinomenine/8-Bis(benzylthio)octanoic acid hybrids as potential anti-leukemia drug candidate via mitochondrial pathway.

Traditional Chinese medicine Qingfengteng primarily acquired from the dried canes of Sinomenium acutum (Thunb.) Rehd. et Wils. var. cinereum Rehd. et Wils. and S. acutum (Thunb.) Rehd. et Wils. For the therapeutic treatment of rheumatism, acute arthritis, and rheumatoid arthritis based on Qingfengteng, sinomenine hydrochloride was recently made the principal active ingredient in various dosage forms. 8-Bis(benzylthio)octanoic acid (CPI-613) was an orphan medicine that the FDA and EMA approved orphan for the treatment of certain resistant malignancies. Its unique mode of action and minimal toxicity toward normal tissues made for an apt pharmacophore. In order to expand the field of sinomenine anticancer structures, sinomenine/8-Bis(benzylthio)octanoic acid derivatives were designed and synthesized. Among them, target hybrids e4 stood out for having notable cytotoxic effects against cancer cell lines, especially for K562 cells, with IC50 values of 2.45 µM and high safety. In-depth investigations demonstrated that e4 caused apoptosis by stopping the cell cycle at G1 phase, and doing so by altering the morphology of the nucleus and causing membrane potential of the in mitochondria to collapse. These results indicated e4 exerted an antiproliferative effect through apoptosis induction via mitochondrial pathway.

Pharmacological mechanisms of sinomenine in anti-inflammatory immunity and osteoprotection in rheumatoid arthritis: A systematic review.

BACKGROUND: Sinomenine (SIN) is the main pharmacologically active component of Sinomenii Caulis and protects against rheumatoid arthritis (RA). In recent years, many studies have been conducted to elucidate the pharmacological mechanisms of SIN in the treatment of RA. However, the molecular mechanism of SIN in RA has not been fully elucidated. PURPOSE: To summarize the pharmacological effects and molecular mechanisms of SIN in RA and clarify the most valuable regulatory mechanisms of SIN to provide clues and a basis for basic research and clinical applications. METHODS: We systematically searched SciFinder, Web of Science, PubMed, China National Knowledge Internet (CNKI), the Wanfang Databases, and the Chinese Scientific Journal Database (VIP). We organized our work based on the PRISMA statement and selected studies for review based on predefined selection criteria. OUTCOME: After screening, we identified 201 relevant studies, including 88 clinical trials and 113 in vivo and in vitro studies on molecular mechanisms. Among these studies, we selected key results for reporting and analysis. CONCLUSIONS: We found that most of the known pharmacological mechanisms of SIN are indirect effects on certain signaling pathways or proteins. SIN was manifested to reduce the release of inflammatory cytokines such as Tumor necrosis factor-α (TNF-α), Interleukin-6 (IL-6), and IL-1ß, thereby reducing the inflammatory response, and apparently blocking the destruction of bone and cartilage. The regulatory effects on inflammation and bone destruction make SIN a promising drug to treat RA. More notably, we believe that the modulation of α7nAChR and the regulation of methylation levels at specific GCG sites in the mPGES-1 promoter by SIN, and its mechanism of directly targeting GBP5, certainly enriches the possibilities and the underlying rationale for SIN in the treatment of inflammatory immune-related diseases.

Protection of pancreatic islets from oxidative cell death by a peripherally-active morphinan with increased drug safety.

OBJECTIVE: Dextromethorphan (DXM) is a commonly used antitussive medication with positive effects in people with type 2 diabetes mellitus, since it increases glucose tolerance and protects pancreatic islets from cell death. However, its use as an antidiabetic medication is limited due to its central nervous side effects and potential use as a recreational drug. Therefore, we recently modified DXM chemically to reduce its blood-brain barrier (BBB) penetration and central side effects. However, our best compound interacted with the cardiac potassium channel hERG (human ether-à-go-go-related gene product) and the µ-opioid receptor (MOR). Thus, the goal of this study was to reduce the interaction of our compound with these targets, while maintaining its beneficial properties. METHODS: Receptor and channel binding assays were conducted to evaluate the drug safety of our DXM derivative. Pancreatic islets were used to investigate the effect of the compound on insulin secretion and islet cell survival. Via liquor collection from the brain and a behavioral assay, we analyzed the BBB permeability. By performing intraperitoneal and oral glucose tolerance tests as well as pharmacokinetic analyses, the antidiabetic potential and elimination half-life were investigated, respectively. To analyze the islet cell-protective effect, we used fluorescence microscopy as well as flow cytometric analyses. RESULTS: Here, we report the design and synthesis of an optimized, orally available BBB-impermeable DXM derivative with lesser binding to hERG and MOR than previous ones. We also show that the new compound substantially enhances glucose-stimulated insulin secretion (GSIS) from mouse and human islets and glucose tolerance in mice as well as protects pancreatic islets from cell death induced by reactive oxygen species and that it amplifies the effects of tirzepatide on GSIS and islet cell viability. CONCLUSIONS: We succeeded to design and synthesize a novel morphinan derivative that is BBB-impermeable, glucose-lowering and islet cell-protective and has good drug safety despite its morphinan and imidazole structures.

Analysis of non-volatile metabolites and quantitation of the anti-arthritic alkaloid sinomenine from blood fruit (Haematocarpus validus (Miers) Bakh.f. ex Forman).

Haematocarpus validus (Miers) Bakh. f. ex Forman, a lesser-known fruit and medicinal plant of high nutraceutical and medicinal value, is used as anti-arthritic, hepatoprotective, and anti-inflammatory agents in ethnomedicine. Metabolome studies in H. validus are a virgin area of research and here we report the spectra of non-volatiles present in the methanolic leaf and fruit extract, using high-resolution liquid chromatography-mass spectrometry. Furthermore, the alkaloid sinomenine was quantified using high-performance thin layer chromatography spectrodensitometric analysis owing to its pharmacological importance as anti-arthritic and anti-inflammatory drug. Electrospray ionization with protonation in positive mode was selected for the analysis and the spectral data was interrogated using MassHunter software. A total of 40 compounds were identified from leaf and fruit samples and the major classes of compounds identified were alkaloids, terpenoids, steroids, tripeptides, vitamins, and related compounds. For separation and quantitation of sinomenine, chloroform:methanol:water (60:30:6.5, v/v) was used as the mobile phase and sinomenine hydrochloride as reference compound. The analysis confirmed the presence of sinomenine in both non-defatted and defatted methanolic leaf extract with quantities 45.73 and 26.02 mg/100 g dry weight, respectively. H. validus is a non-conventional source of sinomenine, the anti-arthritic and anti-inflammatory alkaloid. Sinomenine detected in this study supports the ethnomedicinal uses of H. validus as an anti-arthritic agent. Further study is needed to elucidate the underlying molecular mechanism of its anti-arthritic attributes as well as the corresponding structure-activity relationships.

A review on pharmacokinetics of sinomenine and its anti-inflammatory and immunomodulatory effects.

Autoimmune diseases (ADs), with significant effects on morbidity and mortality, are a broad spectrum of disorders featured by body's immune responses being directed against its own tissues, resulting in chronic inflammation and tissue damage. Sinomenine (SIN) is an alkaloid isolated from the root and stem of Sinomenium acutum which is mainly used to treat pain, inflammation and immune disorders for centuries in China. Its potential anti-inflammatory role for treating immune-related disorders in experimental animal models and in some clinical applications have been reported widely, suggesting an inspiring application prospect of SIN. In this review, the pharmacokinetics, drug delivery systems, pharmacological mechanisms of action underlying the anti-inflammatory and immunomodulatory effects of SIN, and the possibility of SIN as adjuvant to disease-modifying anti-rheumatic drugs (DMARDs) therapy were summarized and evaluated. This paper aims to reveal the potential prospects and limitations of SIN in the treatment of inflammatory and immune diseases, and to provide ideas for compensating its limitations and reducing the side effects, and thus to make SIN better translate to the clinic.

[Development of a Simple and Sensitive Enzyme-linked Immunosorbent Assay for Sinomenine].

Sinomenine (SIN) is a major component contained in extracts of the Chinese medicinal herb Sinomenium acutum. SIN has various pharmacological properties, including cytoprotection, immunosuppression and anti-inflammation effects. Furthermore, recent studies have reported that SIN has anti-tumor and antidepressant effects, which has created a strong need for SIN kinetic studies. This paper reports a simple and sensitive competitive enzyme-linked immunosorbent assay (ELISA) for the pharmacokinetic evaluation of SIN. Anti-SIN serum was obtained by immunizing mice with an antigen conjugated with bovine serum albumin and carboxylic modified SIN using the N-succinimidyl ester method. Enzyme labeling of SIN with horseradish peroxidase was similarly performed using carboxylic modified SIN. Under optimized conditions, this ELISA shows a linear detection range from 40 to 5000 pg/mL, and a limit of detection of 12.1 pg/mL for 50-µL samples. This assay was specific for SIN and showed very slight cross-reactivity with dextromethorphan (0.45%), dimemorfan (0.22%) and codeine (0.01%), but no cross-reactivity with 2-methoxycyclohex-2-enone (<0.001%). Using this ELISA, SIN levels were easily determined in the blood of mice after oral administration of Kampo medicine, Boiogito. The ELISA may be a valuable tool for studies of the biological and pharmacological properties of SIN.

Role for µ-opioid receptor in antidepressant effects of δ-opioid receptor agonist KNT-127.

Previous pharmacological data have shown the possible existence of functional interactions between µ- (MOP), κ- (KOP), and δ-opioid receptors (DOP) in pain and mood disorders. We previously reported that MOP knockout (KO) mice exhibit a lower stress response compared with wildtype (WT) mice. Moreover, DOP agonists have been shown to exert antidepressant-like effects in numerous animal models. In the present study, the tail suspension test (TST) and forced swim test (FST) were used to examine the roles of MOP and DOP in behavioral despair. MOP-KO mice and WT mice were treated with KNT-127 (10 mg/kg), a selective DOP agonist. The results indicated a significant decrease in immobility time in the KNT-127 group compared with the saline group in all genotypes in both tests. In the saline groups, immobility time significantly decreased in MOP-KO mice compared with WT mice in both tests. In female MOP-KO mice, KNT-127 significantly decreased immobility time in the TST compared with WT mice. In male MOP-KO mice, however, no genotypic differences were found in the TST after either KNT-127 or saline treatment. Thus, at least in the FST and TST, the activation of DOP and absence of MOP had additive effects in reducing measures of behavioral despair, suggesting that effects on this behavior by DOP activation occur independently of MOP.

Sinococuline, a bioactive compound of Cocculus hirsutus has potent anti-dengue activity.

Dengue virus (DENV) infection has increased worldwide, with over 400 million infections annually, and has become a serious public health concern. Several drug candidates, new and repurposed, have failed to meet the primary efficacy endpoints. We have recently shown that Aqueous Extract of the stem of Cocculus hirsutus (AQCH) was effective in vitro and in vivo against DENV and was safe in humans. We now report that an active ingredient of AQCH, Sinococuline, protects against the antibody-mediated secondary-DENV infection in the AG129 mouse model. DENV infection markers were assessed, viz. serum viremia and vital organs pathologies-viral load, proinflammatory cytokines and intestinal vascular leakage. The treatment with Sinococuline at 2.0 mg/kg/day; BID (twice a day), was the most effective in protecting the severely DENV-infected AG129 mice. Also, this dose effectively reduced serum viremia and tissue-viral load and inhibited the elevated expression levels of proinflammatory cytokines (TNF-α and IL-6) in several vital organs. Based on these findings, it could be explored further for pre-clinical and clinical developments for the treatment of dengue.

Sinomenine attenuated dextran sulfate sodium-induced inflammatory responses by promoting 14-3-3θ protein and inhibiting NF-κB signaling.

ETHNOPHARMACOLOGICAL RELEVANCE: The rhizome of Chinese medical plant QingTeng (scientific name: Sinomenium acutum (Thunb.) Rehd. et Wils.) is widely used by traditional medical doctors for anti-inflammation and immunoregulatory in China and other Asian countries. AIM OF THE STUDY: The purpose of this study was to evaluate the effects and possible mechanisms of sinomenine resistance against DSS-induced inflammation in vitro and in vivo. MATERIALS AND METHODS: The UC model was induced by treating female mice with 3% DSS in vivo and human colonic epithelial cells (Hcoepic) with 0.8 mg/ml DSS in vitro. The mice and Hcoepic were then treated with sinomenine. Inflammatory factors were detected using ELISA and qRT-PCR. Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65 and 14-3-3θ were analyzed by bioinformatic analysis and verified by western blotting, immunofluorescent staining or immunohistochemistry. RESULTS: DSS-induced Hcoepic underwent high inflammation and oxidative stress conditions, whereas sinomenine reduced the uncontrolled immune microenvironment by suppressing NF-κB signaling and targeting 14-3-3θ. Knockdown of 14-3-3θ decreased the protective effect of sinomenine against DSS-induced inflammation in vitro. Moreover, sinomenine promoted 14-3-3θ protein expression and inhibited NF-κB p65 signaling in DSS-induced mice. CONCLUSION: These findings suggest that 14-3-3θ plays an important role in sinomenine against DSS treatment, and sinomenine could be considered a potential drug for the treatment of UC.

Towards Better Sinomenine-Type Drugs to Treat Rheumatoid Arthritis: Molecular Mechanisms and Structural Modification.

Sinomenine is the main component of the vine Sinomenium acutum. It was first isolated in the early 1920s and has since attracted special interest as a potential anti-rheumatoid arthritis (RA) agent, owing to its successful application in traditional Chinese medicine for the treatment of neuralgia and rheumatoid diseases. In the past few decades, significant advances have broadened our understanding of the molecular mechanisms through which sinomenine treats RA, as well as the structural modifications necessary for improved pharmacological activity. In this review, we summarize up-to-date reports on the pharmacological properties of sinomenine in RA treatment, document their underlying mechanisms, and provide an overview of promising sinomenine derivatives as potential RA drug therapies.

Characterization of a Potential KOR/DOR Dual Agonist with No Apparent Abuse Liability via a Complementary Structure-Activity Relationship Study on Nalfurafine Analogues.

Discovery of analgesics void of abuse liability is critical to battle the opioid crisis in the United States. Among many strategies to achieve this goal, targeting more than one opioid receptor seems promising to minimize this unwanted side effect while achieving a reasonable therapeutic profile. In the process of understanding the structure-activity relationship of nalfurafine, we identified a potential analgesic agent, NMF, as a dual kappa opioid receptor/delta opioid receptor agonist with minimum abuse liability. Further characterizations, including primary in vitro ADMET studies (hERG toxicity, plasma protein binding, permeability, and hepatic metabolism), and in vivo pharmacodynamic and toxicity profiling (time course, abuse liability, tolerance, withdrawal, respiratory depression, body weight, and locomotor activity) further confirmed NMF as a promising drug candidate for future development.

SLL-627 Is a Highly Selective and Potent κ Opioid Receptor (KOR) Agonist with an Unexpected Nonreduction in Locomotor Activity.

Undue central nervous system (CNS) side effects including dysphoria and sedation remain to be a challenge for the development of κ opioid receptor (KOR) agonists as effective and safe analgesics. On the basis of our previous work on morphinan-based KOR agonists, a series of 7α-methyl-7ß-substituted northebaine derivatives were designed, synthesized, and biologically assayed. Among others, compound 4a (SLL-627) has been identified as a highly selective and potent KOR agonist both in vitro and in vivo, and its molecular basis was also examined and discussed. Besides low liability to conditioned place aversion (CPA) test, treatment of SLL-627 was associated with a nonreduction in locomotor activity, compared to most of the other arylacetamide- or morphinan-based KOR agonists which generally exhibited apparently sedative effects. This unexpected finding provides new insights to dissociate analgesia from sedation for future discovery of innovative KOR agonists.

Anti-breast cancer sinomenine derivatives via mechanisms of apoptosis induction and metastasis reduction.

Sinomenine, a morphinane-type isoquinoline-derived alkaloid, was first isolated from stems and roots of Sinomenium diversifolius (Miq.) in 1920. Later discovery by researchers confirmed various essential biological efficacy sinomenine exerted in vitro and in vivo. In this study, a series of 15 sinomenine/furoxan hybrid compounds were designed and synthesised in search of a TNBC drug candidate. Some of the target compounds exhibited strong antiproliferative activities against cancer cell lines, especially for TNBC cells, compared to positive controls. Among them, hybrid 7Cc exerted superior cytotoxic effects on cancer cell lines with exceptionally low IC50 (0.82 µM) against MDA-MB-231 cells with the highest safety index score. Further studies in mechanism displayed that 7Cc could induce an S phase cell cycle arrest, stimulate apoptosis in MDA-MB-231 cells, disrupt mitochondrial membrane potential and exert a genotoxic effect on DNA in cancer cells. In addition, 7Cc also notably inhibited MDA-MB-231 cells in both migration, invasion and adhesion.

Modulatory apoptotic effects of sinomenine on Mycoplasma pneumonia through the attenuation of inflammation via ERK/JNK/NF-κB signaling pathway.

Mycoplasma pneumoniae (MPP) induced pneumonia is a common disease of children. Sinomenine (SIN) is an isoquinoline mainly sequestered from Sinomenium acutum. It is a promising drug for treating arthritis, lung, colon, liver and gastric cancer. Hence, the present study investigated the role and mechanism of SIN treatment in MPP induced pneumonia in experimental in-vivo mice model. The BALB/c male mice were separated into four groups (n = 6 mice/group): normal, MPP, MPP + SIN (20 mg/kg bw), and SIN (20 mg/kg bw) alone. Results were expressed as mean ± SD. Data were analyzed using one way Analysis of Variance (ANOVA) with the Dunnett's post hoc test using SPSS v 18.0. P value < 0.05 was considered significant. The total protein, cell count, inflammatory cytokines, MP-IgM, Monocyte chemo attractant protein-1 (MCP-1), and MP-DNA were measured. The protein expressions of Bax/Bcl-2, ERK, JNK, NF-κB were analyzed and histopathology of lungs was examined. SIN treatment significantly (p < 0.05) reduced the total proteins, cell counts in BALF, inflammatory cytokines, MP-IgM, MCP-1, MP-DNA and reversed the histological alterations. SIN attenuated the apoptotic pathway through the modulation of Bax/Bcl-2 expression. SIN alleviated pulmonary inflammatory mediators and apoptosis in MPP-infected mice via suppression of ERK/JNK/NF-κB signaling. SIN administration diminished inflammation and lung fibrosis by inhibiting apoptosis in MPP mice. Hence, SIN is a potential natural protective remedy for MPP.

Diels-Alder Adducts of Morphinan-6,8-Dienes and Their Transformations.

6,14-ethenomorphinans are semisynthetic opiate derivatives containing an ethylene bridge between positions 6 and 14 in ring-C of the morphine skeleton that imparts a rigid molecular structure. These compounds represent an important family of opioid receptor ligands in which the 6,14-etheno bridged structural motif originates from a [4 + 2] cycloaddition of morphinan-6,8-dienes with dienophiles. Certain 6,14-ethenomorphinans having extremely high affinity for opioid receptors are often non-selective for opioid receptor subtypes, but this view is now undergoing some revision. The agonist 20R-etorphine and 20R-dihydroetorphine are several thousand times more potent analgesics than morphine, whereas diprenorphine is a high-affinity non-selective antagonist. The partial agonist buprenorphine is used as an analgesic in the management of post-operative pain or in substitution therapy for opiate addiction, sometimes in combination with the non-selective antagonist naloxone. In the context of the current opioid crisis, we communicated a summary of several decades of work toward generating opioid analgesics with lesser side effects or abuse potential. Our summary placed a focus on Diels-Alder reactions of morphinan-6,8-dienes and subsequent transformations of the cycloadducts. We also summarized the pharmacological aspects of radiolabeled 6,14-ethenomorphinans used in molecular imaging of opioid receptors.