Mitragynine

Mitragynine, an indole alkaloid, is the most abundant active alkaloid in the plant Mitragyna speciosa, commonly known as Kratom.

Pharmacology
In small doses its activity is reported to be stimulant-like, while in higher doses more opiate-like. These effects agree with the profile of mitragynine's actions developed by study of its action on the brain. It has been shown to be adrenergic (like some related alkaloids from yohimbe) at lower doses, while at higher doses mitragynine acts on the mu- and delta-opiate receptors. The mu-opiate receptors are responsible for the enjoyable effects of the opiates, analgesia, and physical dependence. Its potential for treating drug addiction, perhaps in combination with ibogaine, is being investigated. It is orally active.

Mitragynine itself acts primarily via μ-opioid receptors, although its oxidation product mitragynine-pseudoindoxyl, which is likely to be a major component of kratom that has been aged or stored for extended periods, acts as a fairly selective δ-opioid agonist with little affinity for μ or κ receptors. Another alkaloid with a major contribution to the μ-opioid activity of the kratom plant is the related compound 7-hydroxymitragynine, which while present in the plant in much smaller quantities than mitragynine, is a much more potent μ-opioid agonist.

Discovery
Mitragynine was isolated in 1907 by D. Hooper, a process repeated in 1921 by E. Field who gave the alkaloid its name. Its structure was first fully determined in 1964 by D. Zacharias, R. Rosenstein and E. Jeffrey.

Structure
It is structurally related to both the yohimbe alkaloids and, more distantly, voacangine. Chemically, mitragynine is 9-methoxy-corynantheidine.

Dose
Dry kratom leaf contains roughly 0.25% mitragynine. A typical dose ranges from 15 mg to 65 mg.

Synthesis
The first total synthesis of mitragynine was reported by Takayama et al. in 1995.

Chemical properties
Physically the freebase is a white, amorphous powder. It is soluble in alcohol, chloroform and acetic acid.