Structure revision of mitragynaline, an indole alkaloid in Mitragyna speciosa

Phytochemistry and biological activities of corynanthe alkaloids

Medicinal plants constitute a source for designing clinically useful drugs targeting diseases through various mechanisms. Plant secondary metabolites can be used as lead compounds of drugs. Corynanthe alkaloids are highly abundant natural bioactive substances of various core structures possessing important properties such as nerve excitation and antimalarial and analgesic effects. In this review, we summarize and review the state-of-the-art corynanthe-type alkaloid research focusing on phytochemistry, pharmacology, and structural chemistry. Approximately 120 articles reporting 231 alkaloids classified into simple corynanthe, yohimbine, oxindole corynanthe, mavacurane, sarpagine, akuammiline, strychnos, and ajmaline-type groups were compiled. Relevant biological properties discussed include antiviral, antibacterial, anti-inflammatory, antimalarial, muscle-relaxant, vasorelaxant, and analgesic activities and activities affecting the main nervous and cardiac systems, as well as NF-κB inhibitory and Na⁺-glucose cotransporter inhibitory properties. This review provides insights and a reference for future studies, thus paving the way for the discovery of drugs based on corynanthe alkaloids.

In silico investigation of mitragynine and 7-hydroxymitragynine metabolism

Objective

Mitragynine is the main active compound of Mitragyna speciose (Kratom in Thai). The understanding of mitragynine derivative metabolism in human body is required to develop effective detection techniques in case of drug abuse or establish an appropriate dosage in case of medicinal uses. This in silico study is based upon in vivo results in rat and human by Philipp et al. (J Mass Spectrom 44:1249–1261, 2009).

Results

Gas-phase structures of mitragynine, 7-hydroxymitragynine and their metabolites were obtained by quantum chemical method at B3LYP/6-311++G(d,p) level. Results in terms of standard Gibbs energies of reaction for all metabolic pathways are reported with solvation energy from SMD model. We found that 7-hydroxy substitution leads to changes in reactivity in comparison to mitragynine: position 17 is more reactive towards demethylation and conjugation with glucuronic acid and position 9 is less reactive towards conjugation with glucuronic acid. Despite the changes, position 9 is the most reactive for demethylation and position 17 is the most reactive for conjugation with glucuronic acid for both mitragynine and 7-hydroxymitragynine. Our results suggest that 7-hydroxy substitution could lead to different metabolic pathways and raise an important question for further experimental studies of this more potent derivative.

Electronic supplementary material

The online version of this article (10.1186/s13104-019-4461-3) contains supplementary material, which is available to authorized users.

Development and validation of a UPLC-MS/MS method for the determination of 7-hydroxymitragynine, a μ-opioid agonist, in rat plasma and its application to a pharmacokinetic study

A simple, sensitive and specific ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed and validated to determine the concentrations of 7-hydroxymitragynine in rat plasma. Following a single-step liquid-liquid extraction of plasma samples using chloroform, 7-hydroxymitragynine and the internal standard (tryptoline) were separated on an Acquity UPLC(TM) BEH C18 (1.7 µm, 2.1 × 50 mm) column using an isocratic elution at a flow rate of 0.2 mL/min. The mobile phase consisted of 0.1% acetic acid in water and 0.1% acetic acid in acetonitrile (10:90, v/v). The run time was 2.5 min. The analysis was carried out under the multiple reaction-monitoring mode using positive electrospray ionization. Protonated ions [M + H](+) and their respective product ions were monitored at the following transitions: 415 → 190 for 7-hydroxymitragynine and 173 → 144 for the internal standard. The calibration curve was linear over the range of 10-4000 ng/mL (r(2) = 0.999) with a lower limit of quantification of 10 ng/mL. The extraction recoveries ranged from 62.0 to 67.3% at concentrations of 20, 600 and 3200 ng/mL). Intra- and inter-day assay precisions (relative standard deviation) were <15% and the accuracy was within 96.5-104.0%. This validated method was successfully applied to quantify 7-hydroxymitragynine in rat plasma following intravenous administration.

Computational Study on the Conformations of Mitragynine and Mitragynaline

A conformational search on mitragynine and mitragynaline, natural products isolated from the leaves of Mitragyna speciosa, was performed using the MMFF94s force field and the quantum mechanical B3LYP method. The main difference for the mitragynine conformers is caused by the position of the lone pair of the nitrogen shared by rings 3 and 4. Specifically, the lone pair can be syn or anti to the exocylic ethyl group on ring 4. Syn was found to be lower in energy than anti, because of less steric hindrance between the ethyl and the methylene group adjacent to the N in ring 3. The geometrical parameters for the lowest energy conformer of mitragynine are in excellent agreement with the published X-ray crystal structure's geometry. Because it has one more double bond, mitragynaline has less conformational freedom than mitragynine. The main possible conformational choice in mitragynaline is for orientational flexibility of a C-C single bond in ring 3. The finding of two low energy conformers of mitragynaline differing in ring 3 conformation matches reported X-ray crystal structural data.

New procedure to mask the 2,3-pi bond of the indole nucleus and its application to the preparation of potent opioid receptor agonists with a Corynanthe skeleton

Treatment of indole alkaloids with hypervalent iodine in the presence of ethylene glycol provides 2,3-ethylene glycol bridged adducts that could be converted into the original indoles under mild reductive conditions. This procedure, which involves masking of the reactivity of the indole nucleus at the beta-position, was utilized for the modification of the benzene ring of the indoline derivative and was applied to the preparation of potent opioid receptor agonists with the Corynanthe skeleton. [reaction: see text]

Chemistry and pharmacology of analgesic indole alkaloids from the rubiaceous plant, Mitragyna speciosa

The leaves of a tropical plant, Mitragyna speciosa KORTH (Rubiaceae), have been traditionally used as a substitute for opium. Phytochemical studies of the constituents of the plant growing in Thailand and Malaysia have led to the isolation of several 9-methoxy-Corynanthe-type monoterpenoid indole alkaloids, including new natural products. The structures of the new compounds were elucidated by spectroscopic and/or synthetic methods. The potent opioid agonistic activities of mitragynine, the major constituent of this plant, and its analogues were found in in vitro and in vivo experiments and the mechanisms underlying the analgesic activity were clarified. The essential structural features of mitragynines, which differ from those of morphine and are responsible for the analgesic activity, were elucidated by pharmacological evaluation of the natural and synthetic derivatives. Among the mitragynine derivatives, 7-hydroxymitragynine, a minor constituent of M. speciosa, was found to exhibit potent antinociceptive activity in mice.

A New 9-Methoxyyohimbine-Type Indole Alkaloid from Mitragyna africanus

A new yohimbine-type indole alkaloid (1). was isolated from the stem bark of Mitragyna africanus (WILLD.) collected in Nigeria, along with known seven Corynanthe-type oxindole alkaloids, two secoiridoids, three lignans, and a quinovic acid derivative. Their structures were elucidated by spectroscopic analyses.

First total synthesis of a novel monoterpenoid isoquinoline alkaloid, (+/-)-alangine

The structure including the stereochemistry of a novel monoterpenoid isoquinoline alkaloid, alangine, was confirmed by total synthesis via N-acyliminium cyclization to construct the isoquinoline skeleton and reductive cleavage of vinyl epoxide with Pd(0) catalyst.

Formation of an unusual dimeric compound by lead tetraacetate oxidation of a corynanthe-type indole alkaloid, mitragynine

Lead tetraacetate oxidation of a Corynanthe-type indole alkaloid, mitragynine, produced mainly 7-acetoxyindolenine derivative (2) together with a dimeric compound (4) as a minor product. The novel structure having a bridge between the C-11' and C-7 positions in the respective indolenine parts and its formation mechanism were studied.

A new type of lycopodium alkaloid, lycoposerramine-A, from Lycopodium serratum Thunb

A novel alkaloid, lycoposerramine-A (1), which has a 1,2,4-oxadiazolidin-5-one residue in the molecule, was isolated from the club moss Lycopodium serratum Thunb. The structure was determined by spectroscopic and X-ray analyses. [structure: see text]