Studies On The Bioactivity Of 4’-amino-Substituted Thebaine Analogues

Opioid analgesics are the most commonly used analgesic prescription drugs.Opioid drugs play an analgesic effect by binding with opioid receptors.Opioid receptors are mainly distributed in central nervous system,peripheral nervous system and gastrointestinal tract.Opioid receptor is a member of the G protein-coupled receptor(GPCR)family,and there are mainly three subtypes of μ 8 and κ opioid receptors.Each subtype has about 60%homology and mediates different physiological effects.Traditional opioid analgesics,such as fentanyl,morphine,codeine,heroin,etc.,are mostly complete agonists of μ opioid receptors or μ/δ opioid receptors.Traditional μopioid analgesics have many side effects,such as dependence,addiction,tolerance,respiratory depression,constipation and so on.These increasingly serious public health hazards make the current analgesics face great challenges in clinical practice.Among opioid receptors,κ opioid receptors have high homology with μ opioid receptors,but the difference between them is that κopioid receptors not only have good analgesic effect,but also do not produce the side effects of typical μ opioid receptors.Therefore,the design and synthesis of κ opioid receptor agonists with low affinity for μ opioid receptor and 8 opioid receptor,high affinity for κ opioid receptor,good analgesic effect and little side effects is a promising direction for the development of effective and safe potential analgesic drugs.Based on this research purpose,17 4’-amino-substituted bendibane-like compounds designed and synthesized by pharmaceutical chemists were selected as the main research objects.The specific binding of κ opioid receptor was used as the entry point,and[3H]competitive binding test was used to screen the series of compounds.The compounds with low affinity of μ opioid receptor and 8 opioid receptor and high affinity of κ opioid receptor were screened out.The activation ability of these compounds on G proteins of different opioid receptor subtypes was evaluated by[35S]GTPγS functional test.To study the analgesic effect in vivo we used analgesic animal models,and hope to obtain the effective and safe κ opioid receptor agonist for analgesia.In this study,the pharmacological activities of 4’-amino-substituted bendibane-like compounds were evaluated by screening in vitro and overall animal level.In radioactive-receptor ligand binding experiments,we found that compound 4j has a high affinity for κ opioid receptor,but a low affinity for μ opioid receptor and δ opioid receptor,indicating that compound 4j has a selective high affinity for κ opioid receptor.The representative compounds 4a,4b,4g,4i,4j,4m,DAMGO,DPDPE and U50,488 were selected for the[35S]GTPyS binding assay to test the ability of these compounds to bind to the receptor G protein.In vitro functional activity[35S]GTPγS assay showed that the potential compound 4j could completely excite κ opioid receptors,but the excitability of 4j was weak.In order to farther study the pharmacological properties of compound 4j,we selected two analgesic animal models,namely hot plate model and acetic acid torsion model,to evaluate the analgesic effect of compound 4j.Compound 4j showed relatively weak analgesic effect in hot plate test and acetic acid writhing test,and the maximum analgesic effect was 50%.These results were consistent with the evaluation results of functional activity of compound 4j.According to the results of pharmacodynamics experiments,compound 4j is still far from being a clinically effective and safe new analgesic drug.Evaluation of its side effects has not been carried out,and whether compound 4j has adverse reactions and central side effects of traditional opioid analgesics remains to be further verified.We built the model using molecular docking technology and found compound 4j aryl acetamide amide N hydrogen atoms can with κ opioid receptors predominate in the second extracellular region C210 hydrogen bond formation,and more flexible connection chains.We speculated that this might be the reason for compound 4j’s high κ opioid receptor affinity and selectivity,which also provides a useful reference for further structural optimization of the compound.We developed a drug screening system to evaluate potential opioid analgesics at the in vitro and in vivo level.It provides a new idea for the development of new analgesic K-opioid receptor agonists.