Metabolite Profiling of Antiaddictive Alkaloids from Four Mexican Tabernaemontana Species and the Entheogenic African Shrub Tabernanthe iboga (Apocynaceae)

Ibogaine is a monoterpenoid indole alkaloid (MIA) of the ibogan subclass that has been investigated for anti-addictive properties in animal models and used in diverse therapeutic and traditional contexts despite regulatory restrictions in many countries. Previous work has identified ibogaine and related ibogan-type alkaloids such as coronaridine, ibogamine and voacangine across species of the Apocynaceae family, notably Tabernanthe iboga from Central Africa and members of the pantropical Tabernaemontana genus. Interest in alternative sources of these alkaloids has grown because most ibogaine in circulation originates from plant material rather than total synthesis, and rising demand has raised concerns about sustainability and adulteration of T. iboga root bark. This study set out to compare quantitatively the alkaloid profiles of root and stem barks from four Mexican Tabernaemontana species (T. alba, T. amygdalifolia, T. arborea, T. donnell‑smithii) with root bark from Tabernanthe iboga. Using a microextraction protocol coupled with gas chromatography–mass spectrometry (GC/MS) and principal component analysis (PCA), Krengel and colleagues aimed to characterise interspecific and intraspecific variation in monoterpenoid indole alkaloid contents, evaluate the predominance of key ibogan-type compounds, and assess the potential of Mexican Tabernaemontana as alternative sources of anti‑addictive alkaloids.

Plant material comprised root and stem bark samples collected from individual plants of four Mexican Tabernaemontana species and Tabernanthe iboga. Specifically, five T. alba, three T. amygdalifolia, one T. arborea, and four T. donnell‑smithii plants were sampled around Los Tuxtlas (Veracruz) and Yucatán, Mexico in 2017; T. iboga root bark samples were purchased from a Western Cameroon distributor, a Gabonese Pygmy village, and a commercial Gabonese farm. Taxonomic identification and voucher deposition were performed and reported. Alkaloid extraction used a small‑scale protocol adapted from Kim et al. For each individual sample, 100 mg of dried pulverised bark (inner, outer, whole root or stem bark as applicable) was placed in a 2 ml tube with degreased cotton wool, dichloromethane (1.5 ml) and ammonium hydroxide (50 µl). Tubes were vortexed, sonicated for 30 minutes, centrifuged, and the supernatant recovered through the cotton wool; this cycle was repeated five times and extracts stored at −20 °C. Analytical characterisation employed gas chromatography–mass spectrometry (GC/MS) to obtain total ion chromatograms (TICs). Only quantifiable TIC peaks that could be identified as monoterpenoid indole alkaloids were retained for statistical analysis. Principal component analysis (PCA) was used to explore patterns of quantitative variation across samples; before PCA, three alkaloids (ajmalicine, reserpiline and yohimbine) that were detected only in a single outlier T. iboga sample were removed from the raw data. The methods as extracted do not specify further details such as instrument models, detection limits, or the exact identification/quantification criteria applied in GC/MS.

Principal component analysis indicated that quantitative differences in four structurally related ibogan‑type alkaloids—ibogamine, coronaridine, voacangine and ibogaine—drove separation among samples. The authors grouped these as the ‘CIVI‑complex’ and found it predominant across the five species. Tabernanthe iboga samples were distinguishable from the Tabernaemontana clusters mainly by much higher ibogaine concentrations. Within the Mexican Tabernaemontana species, distinct chemotypes emerged. T. alba root bark segregated into two groups: one resembling T. amygdalifolia with predominance of coronaridine and ibogamine, and another resembling T. arborea with strong voacangine association and, to a lesser extent, ibogaine. T. arborea and T. donnell‑smithii showed closer similarity to each other than to T. amygdalifolia. Across all four Tabernaemontana species, major alkaloid concentrations were generally higher in root than in stem bark. Two outliers were noted in the scores plot: a T. amygdalifolia stem bark sample containing only trace amounts of the main MIAs, and one market‑purchased T. iboga sample that lacked the ibogan MIAs detected in other samples and instead contained ajmalicine, reserpiline and yohimbine. Quantitative yields reported for key compounds showed that the highest voacangine detected in Tabernaemontana samples was 0.95% of root bark dry weight. Measured ibogaine in T. alba and T. arborea root bark reached 0.22% and 0.27% respectively, giving combined ibogaine plus voacangine concentrations of about 1.17–1.22% in those samples. One T. iboga sample from a Gabonese farm (14r) contained 1.17% ibogaine, while another T. iboga sample (15r) from a Pygmy community showed a much higher ibogaine content of 4.75% per dry weight, indicating substantial intraspecific variability. T. amygdalifolia produced modest ibogaine but substantial ibogamine (0.76–0.95%) and coronaridine (1.09–1.38%), with outer root bark reaching 2.05% ibogamine in one measurement. Several minor alkaloids (vobasine, apparicine, 10‑hydroxycoronaridine, quebrachamine-related compounds, ibogaline) were identified as potentially species‑ or organ‑specific markers but had lesser influence on PCA outcomes. The authors also observed organ-level differences consistent with a biosynthetic progression: in some species outer root bark accumulated more of the non‑esterified (later-stage) MIAs while inner bark retained more esterified forms. The extracted text does not provide full statistical metrics (e.g. variance explained by PCA components, confidence intervals, or formal tests) nor detailed GC/MS identification parameters.

Krengel and colleagues interpret the predominance of the CIVI‑complex across Tabernaemontana and Tabernanthe as evidence of phytochemical and taxonomic proximity between the two genera. They note that the structural relationships among ibogamine, coronaridine, voacangine and ibogaine, together with recent transcriptomic evidence identifying enzymes (ibogamine 10‑hydroxylase and noribogaine‑10‑O‑methyltransferase), support a plausible biosynthetic pathway that their organ‑specific distributions (inner versus outer root bark) appear to reflect. From a practical perspective, the study corroborates prior suggestions that Mexican Tabernaemontana species—particularly T. alba and T. arborea—could serve as alternative sources of anti‑addictive ibogan alkaloids. Reported combined yields of ibogaine plus voacangine in some Tabernaemontana root barks approached those measured in a commercial T. iboga sample, and individual variability suggests that selection of high‑yielding chemotypes and controlled cultivation could increase yields further. The authors propose that separating inner and outer root bark before extraction might enhance isolation of non‑esterified MIAs. The authors also stress safety and sustainability concerns. Large intraspecific variability in T. iboga ibogaine content—one sample containing 4.75% and another 1.17%—underscores dosing difficulties when using crude plant material or extracts, with potential for stimulant, entheogenic, or cardiotoxic effects depending on dose and patient risk factors. Market pressures and the plant’s long harvest cycle have encouraged unregulated exploitation and adulteration; the outlier market sample lacking ibogan MIAs illustrates the risk of mislabelling and substitution with other Apocynaceae species. Limitations acknowledged in the extracted text include substantial sample‑to‑sample variability and uncertainty about whether some commercial T. iboga samples were composed of single plants or pooled material. The authors recommend further work to characterise intraspecific chemical diversity, to select high‑yielding genotypes, and to apply careful processing methods to reduce risks associated with traditional and therapeutic uses of ibogan‑containing botanical materials.