A Novel Mitragynine Analog with Low-Efficacy Mu Opioid Receptor Agonism Displays Antinociception with Attenuated Adverse Effects

J Med Chem. 2021 Sep 23;64(18):13873-13892. doi: 10.1021/acs.jmedchem.1c01273. Epub 2021 Sep 10.


Mitragynine and 7-hydroxymitragynine (7OH) are the major alkaloids mediating the biological actions of the psychoactive plant kratom. To investigate the structure-activity relationships of mitragynine/7OH templates, we diversified the aromatic ring of the indole at the C9, C10, and C12 positions and investigated their G-protein and arrestin signaling mediated by mu opioid receptors (MOR). Three synthesized lead C9 analogs replacing the 9-OCH3 group with phenyl (4), methyl (5), or 3'-furanyl [6 (SC13)] substituents demonstrated partial agonism with a lower efficacy than DAMGO or morphine in heterologous G-protein assays and synaptic physiology. In assays limiting MOR reserve, the G-protein efficacy of all three was comparable to buprenorphine. 6 (SC13) showed MOR-dependent analgesia with potency similar to morphine without respiratory depression, hyperlocomotion, constipation, or place conditioning in mice. These results suggest the possibility of activating MOR minimally (G-protein Emax ≈ 10%) in cell lines while yet attaining maximal antinociception in vivo with reduced opioid liabilities.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Analgesics, Opioid / adverse effects
  • Analgesics, Opioid / chemical synthesis
  • Analgesics, Opioid / metabolism
  • Analgesics, Opioid / pharmacology*
  • Animals
  • Male
  • Mice, Inbred C57BL
  • Molecular Docking Simulation
  • Molecular Dynamics Simulation
  • Molecular Structure
  • Rats, Sprague-Dawley
  • Receptors, Opioid, mu / agonists*
  • Receptors, Opioid, mu / metabolism
  • Secologanin Tryptamine Alkaloids / adverse effects
  • Secologanin Tryptamine Alkaloids / chemical synthesis
  • Secologanin Tryptamine Alkaloids / metabolism
  • Secologanin Tryptamine Alkaloids / pharmacology*
  • Structure-Activity Relationship


  • Analgesics, Opioid
  • Receptors, Opioid, mu
  • Secologanin Tryptamine Alkaloids
  • mitragynine