Chemical confirmation for the configurations assigned to the indole alkaloids, speciogynine, speciociliatine, mitraciliatine and hirsutine

Temperature and pH-Dependent Stability of Mitragyna Alkaloids

Mitragynine (MG) is the principal psychoactive alkaloid in kratom. The drug produces a variety of dose-dependent effects that appeal to recreational drug users and individuals seeking therapeutic benefits in the absence of medical supervision. In light of documented intoxications, hospitalizations and fatalities, MG and other alkaloids from Mitragyna speciosa are of growing importance to the forensic toxicology community. However, the chemical stability of these compounds has not been thoroughly described. In this report, the stability of MG, 7-hydroxymitragynine (MG-OH), speciociliatine (SC), speciogynine (SG) and paynantheine (PY) are investigated. Short-term stability of the Mitragyna alkaloids was determined over a range of pH (2-10) and temperature (4-80°C) over 8 hours. Liquid chromatography--quadrupole/time-of-flight mass spectrometry was used to estimate half-lives and identify degradation products where possible. The stability of MG and other alkaloids was highly dependent on pH and temperature. All of the Mitragyna alkaloids studied were acid labile. Under alkaline conditions, MG undergoes chemical hydrolysis of the methyl ester to produce 16-carboxymitragynine. MG-OH was the most unstable alkaloid studied, with significant drug loss at 8 hours experienced at temperatures of 40°C and above. No significant drug losses were observed for MG in aqueous solution (pH 2-10) at 4, 20 or 40°C. Diastereoisomers of MG (SC and SG) demonstrated even greater stability. These findings are discussed within the context of the identification of Mitragyna alkaloids in toxicological specimens.

A matter of some sensitivity

The development of sensitive chromatographic and spectroscopic techniques for the isolation and structure determination of natural products has greatly facilitated phytochemical investigations. Chemical investigations of herbarium material have resulted in the isolation of indole, quinoline and isoquinoline alkaloids from a wide number of plants. Examples of novel natural products from higher plants are given and include alkaloids, terpenoids, phenolics and quinones. Some plants investigated have not yielded the types of constituents which would have been predicted from them. Plant tissue cultures provide alternative sources of biologically active compounds and examples investigated include Cinchona, Ailanthus, Brucea and Artemisia for antiprotozoal compounds and Datura for tropane alkaloids. Biological tests are useful for bioassay-guided fractionation of plant extracts and examples of the isolation of a series of natural products with antiprotozoal and cytotoxic activities are given. Chemical and biological investigations into the traditional medicine Dragon's blood (Croton lechleri) from S. America and a Chinese prescription for the treatment of atopic eczema are described. The use of radio-ligand binding assays for the detection of a wide range of biological activities is discussed. Sensitivity of chemical and biological techniques has greatly improved prospects for finding new drug entities from plants and for investigating traditional medicines. Basic phytochemical investigations should continue to be encouraged especially in view of the rapid loss of plant species.

The alkaloids of the leaves of Mitragyna inermis (Willd.) O. Kuntze

The leaves of Mitragyna inermis (Willd.) O. Kuntze have been examined for alkaloids and shown to contain routundifoline, isorotundifoline, rhynchophylline, isorhynchophylline, ciliaphylline, rhynchociline, speciophylline, a small amount of uncarine F, mitraciliatine and traces of a second indole alkaloid which appears to be of the corynanthine type. There is also a polar compound present, Dragendorff positive, which remains on the base line when subjected to thin-layer chromatography with the usual solvent systems used for the mitragyna alkaloids.

The influence of stereochemistry on pKa, rate of quaternization and partition coefficients of corynantheidine-type alkaloids

In alkaloids of the corynantheidine group, the rate of quaternization at N-4 and the pKa values give a measure of the degree of steric hindrance at this site due to the axial hydrogen at C-3 and the ethyl group at C-20. These hinder the availability of the lone pair of electrons on N-4 to electrophiles. Partition coefficients indicate that lipid solubility is associated with planarity of the molecules; this explains why the more planar isomers (allo and normal) are more highly metabolized in microsomes than the less planar isomers (pseudo and epiallo).

Gas-liquid chromatography of heteroyohimbine alkaloids: the effect of methoxy substitution and of configuration

The gas-liquid chromatographic retention times of heteroyohimbine alkaloids on a 1% SE-30 column are in the order pseudo < epiallo < allo < normal. The introduction of one methoxy group into the indole nucleus doubles the retention time while two methoxy groups increase it by a factor of four. Binding of the indole nucleus reinforced by the suitably orientated lone pair electrons of the basic nitrogen to the liquid phase of the column in the important conformers of the various configurations, is used to explain the results.