Indolomonoterpenic Alkaloid Research Articles

Comparative molecular networking analysis of a Rauwolfia plant powder and biological matrices in a fatal ingestion case

Identifying xenobiotics involved in deaths remains a challenge in toxicology, especially when they are missing from the usual suspect databases. The tool development for the rapid processing of untargeted screening data is a valuable asset. In recent years, the molecular networking has been developed in various fields, including toxicology, because of its ability to graphically display and compare complex data acquired from tandem mass spectrometry. Here, we report a case of fatal poisoning by ingestion of an unknown powder (labelled as Tabernanthe iboga) and apply molecular networking to tentatively identify the plant involved in a woman’s death. The supposedly ingested powder, an authentic Tabernanthe iboga root powder and postmortemed biological samples (peripheral blood and bile) were extracted and analyzed according to a screening method using high resolution liquid chromatography hyphenated to tandem mass spectrometry (Q-Exactive®). Analysis of these four matrices by molecular networking revealed a cluster of nodes composed of indolomonoterpenic alkaloids, a characteristic of the Apocynaceae family (ibogaine, ibogamine, ajmaline, reserpiline, yohimbine). Analysis of the spectral annotations of the supposedly ingested powder also shows a majority of occurrences related to the genus Rauwolfia, which differed from the authentic Tabernanthe iboga root powder. Molecular networking allowed us to discard the Tabernanthe iboga identification hypothesis and suggest an alternate Apocynaceae species, most likely belonging to the Rauwolfia genus. In addition, eleven putative compounds could be detected by the molecular networking, many of which seemed to be metabolites of the major components in the Rauwolfia genus.

Corrigendum] Isostrychnopentamine, an indolomonoterpenic alkaloid from Strychnos usambarensis, with potential anti-tumor activity against apoptosis-resistant cancer cells.

After the publication of the article, the authors noted that they had made an error regarding certain data in their manuscript. The error relates to the statistical analysis performed for the data illustrated in Fig. 4A: On page 963 of our article, line 17 of the left-handed column, we identified an erroneous statistical result with respect to the data illustrated in Fig. 4A. The initial statistical value of 'p<0.01' must be corrected to '(p=0.06 when compared to control; Fig. 4A)'.

Dimeric bisindole alkaloids from the stem bark of Strychnos nux-vomica L.

Strychnos nux-vomica L. (Loganiaceae) is famous for its monomeric alkaloid content, such as strychnine, a convulsant poison. The stem bark of the tree is traditionally used to treat intermittent fever in South East Asia. In various studies, it appeared that dimeric indolo-monoterpenic alkaloids possess a promising activity on Plasmodium falciparum. Three bisindolomonoterpenic alkaloids together with strychnochrysine, previously identified in the root bark of S. nux-vomica, were isolated from the stem bark. The structures of these compounds were established using NMR spectroscopy and mass spectrometry. Stereochemistry of the compounds was confirmed by molecular modelling. This then allowed the structural determination of strychnoflavine, a coloured bisindole alkaloid previously isolated from the root bark of the tree. Moreover, the conformational inversion in alkaloids possessing an ether bond in the strychnane moiety could be easily predicted by specific δ (13)C NMR values. These longicaudatine-type alkaloids were found to display in vitro antiplasmodial activity against a chloroquine resistant strain and a chloroquine sensitive strain. The most interesting was strychnochrysine showing an IC(50) value at around 10 μM.

A novel indolomonoterpenic alkaloid from processed Strychnos nux-vomica

A novel indolomonoterpenic alkaloid, 4-hydroxy-19-methyl-16,19-seco-12,24-seco-strychnidine-10,16-dione (1), together with three known compounds 2–4 (vomicine, strychnine, and brucine), have been isolated from processed Strychnos nux-vomica. Its structure was determined by detailed spectral analysis (1H NMR,13C NMR, 1H–1H COSY, HMBC, and HR-ESI-MS).

New alkaloids from the seeds of Strychnos nux-vomica

Eight new trace indolomonoterpenic alkaloids (1–8) were isolated from the seeds of Strychnos nux-vomica. Their structures and absolute configurations were determined by extensive analysis of MS, NMR, CD, and ECD. The skeleton of compound 1 is an unprecedented 6/5/6/5/6/6/7 heptacyclic ring system. Compound 2 possesses a 2-pyridone moiety, and has not yet been found in strychnos alkaloids. Compounds 6 and 7 showed neuroprotective activities on PC12 cells with IE 50 values of 0.68–4.81μM and 0.54–6.50μM, respectively. The biosynthetic pathway of 1 was also postulated.

Isostrychnopentamine, an indolomonoterpenic alkaloid from Strychnos usambarensis, with potential anti-tumor activity against apoptosis-resistant cancer cells

Isostrychnopentamine (ISP) is an indolomonoter-penic alkaloid that is present in the leaves of Strychnos usambarensis, an East African small tree. We have reported previously pro-apoptotic effects induced in vitro by ISP in the human HCT-116 colon cancer cell line, a model that displays relative sensitivity to apoptosis. In the present study, we observed that the in vitro growth inhibitory activities of ISP are similar in cancer cells that display sensitivity versus resistance to apoptosis. We made use of the U373 glioblastoma and the A549 non-small cell lung cancer (NSCLC) cell lines as models relatively resistant to apoptosis, and the human PC-3 prostate cancer cell line as a model relatively sensitive to apoptosis. While ISP induced transient decreases in [ATP]i and apoptosis in human U373 GBM cells, it did not provoke such features in A549 NSCLC cells. It thus seems that ISP-induced anti-cancer activity can lead to pro-apoptotic effects as a consequence, while apoptosis seems not to be the main cause by which ISP induces cancer cell death. ISP is a compound that merits further investigations in order to: i) identify the mechanism(s) of action by which it kills cancer cells, and ii) hemisynthesize novel ISP derivatives aiming to overcome, at least partly, the resistance of metastatic cancers to apoptosis.

Pharmacological effects of Catharanthus roseus root alkaloids in acetylcholinesterase inhibition and cholinergic neurotransmission

The leaves of Catharanthus roseus constitute the only source of the well known indolomonoterpenic alkaloids vincristine and vinblastine. In this work we studied the biological potential of the roots, which are used in several countries as decocts or hot water extracts for the treatment of a number of conditions. The aqueous extract strongly inhibited acetylcholinesterase (AchE) in an in vitro microassay, an effect ascribable mainly to serpentine (IC(50) = 0.775 microM vs physostigmine IC(50) = 6.45 microM) as assessed with the pure compound. Pure alkaloids were tested for muscarinic and nicotinic antagonism using rat ex-vivo preparations, namely, ileum and diaphragm/phrenic-nerve, respectively. Serpentine competitively blocked muscarinic receptors with a pA(2) of 5.2, whereas the precursor ajmalicine up to 80 microM was undistinguishable from control, and catharanthine exhibited an unsurmountable muscarinic antagonism at greater than 10 microM concentrations. Nicotinic receptor mediated diaphragm contractions were fully inhibited by catharanthine (IC(50) = 59.6 microM) and ajmalicine (IC(50) = 72.3 microM), in a reversible but non-competitive manner, unlike the more potent nicotinic antagonist tubocurarine (IC(50) = 0.35 microM) whose competitive blockade was overcome by a physostigmine-induced increase in acetylcholine. Serpentine up to 100 microM did not change diaphragm contractions suggesting reduced affinity for neuromuscular nicotinic receptors. Despite strong in vitro AchE inhibition, serpentine failed to restore diaphragm contractions upon submaximal tubocurarine blockade, suggesting that poor tissue penetration may prevent serpentine from inhibiting AchE in deep neuromuscular synapses in the ex-vivo preparation. To our knowledge, the present study is the first to assess the effect of C. roseus root extracts, as well as of serpentine, ajmalicine and catharanthine on AchE. The results described herein suggest that the currently overlooked C. roseus roots may constitute a promising source of compounds with pharmaceutical interest. Moreover, given serpentine's potent in vitro AchE inhibitory activity and low cholinergic receptor affinity, it is conceivable that minor structural modifications may yield a potent and selective AchE inhibitor, potentially useful for the pharmacological management of conditions such as Alzheimer's disease and/or myasthenia gravis.

Simple and reproducible HPLC–DAD–ESI-MS/MS analysis of alkaloids in Catharanthus roseus roots

Catharanthus roseus is one of the most important medicinal plants worldwide. The leaves of this species are the only source of the indolomonoterpenic alkaloids vincristin (leurocristine) and vinblastin (vincaleucoblastine), whose anticancer activity represents powerful therapeutics to many diseases, such as Hodgkin lymphoma. Usually, the remaining plant parts go to waste. Here we describe a phytochemical study on this species roots. Alkaloids in aqueous extracts, the usual form of consumption of this matrix, were studied using HPLC–DAD–ESI-MS/MS, which allowed the identification of 19- S-vindolinine, vindolinine, ajmalicine and an ajmalicine isomer, tabersonine, catharanthine, serpentine and a serpentine isomer. Quantification of the identified compounds revealed that serpentine and its isomer were predominant (64.7%) over the other alkaloids, namely vindolinine and its isomer (23.9%), catharanthine (7.7%) and ajmalicine (3.8%). The used procedure revealed to be simple, sensitive and reproducible.

Natural Compounds: Leads or Ideas? Bioinspired Molecules for Drug Discovery

In this article, we compare drugs of natural origin to synthetic compounds and analyze the reasons why natural compounds occupy a place of choice in the current pharmacopoeia. The observations reported here support the design of synthetic compounds inspired from plant alkaloids and their biosynthetic pathway. Our reasoning leads to very efficient syntheses of compounds which complexity matches that of indolomonoterpenic alkaloids.

Study of the interaction of antiplasmodial strychnine derivatives with the glycine receptor

Strychnos icaja Baill. (Loganiaceae) is a liana found in Central Africa known to be an arrow and ordeal poison but also used by traditional medicine to treat malaria. Recently, many dimeric or trimeric indolomonoterpenic alkaloids with antiplasmodial properties have been isolated from its rootbark. Since these alkaloids are derivatives of strychnine, it was important, in view of their potential use as antimalarial drugs, to assess their possible convulsant strychnine-like properties. In that regard, their interaction with the strychnine-sensitive glycine receptor was investigated by whole-cell patch-clamp recordings on glycine-gated currents in mouse spinal cord neurons in culture and by [ 3H]strychnine competition assays on membranes from adult rat spinal cord. These experiments were carried out on sungucine (leading compound of the chemical class) and on the antiplasmodial strychnogucine B (dimeric) and strychnohexamine (trimeric). In comparison with strychnine, all compounds interact with a very poor efficacy and only at concentrations > 1 μM with both [ 3H]strychnine binding and glycine-gated currents. Furthermore, the effects of strychnine and protostrychnine, a monomeric alkaloid (without antiplasmodial activity) also isolated from S. icaja and differing from strychnine only by a cycle opening, were compared in the same way. The weak interaction of protostrychnine confirms the importance of the G cycle ring structure in strychnine for its binding to the glycine receptor and its antagonist properties.

In vitro and in vivo antimalarial properties of isostrychnopentamine, an indolomonoterpenic alkaloid from Strychnos usambarensis.

Isostrychnopentamine (ISP) is an asymmetric indolomonoterpenic alkaloid isolated from the leaves of Strychnos usambarensis. The in vitro antiplasmodial activities against five Plasmodium falciparum cell lines were evaluated: ISP possessed an in vitro IC (50) near 0.1 microM against all P. falciparum cell lines tested (chloroquine-resistant and chloroquine-sensitive lines) and showed antiplasmodial selectivity compared to cytotoxicity on human cell lines. The stage-dependent susceptibility to a short exposure of ISP was then investigated. The ring stage was shown to be the most sensitive one, but all stages were affected by ISP treatment. By means of fluorescence microscopy, it was shown that ISP was not accumulated inside the food vacuole of the parasite. Finally, the in vivo antimalarial activities against the P. berghei NK173 and P. vinckei petteri murine strains were determined. The ED (50) in vivo was about 30 mg/kg/day by the intraperitoneal route (after 4 days treatment).

Indolomonoterpenic alkaloids from Strychnos icaja roots

In the course of our search for new antiplasmodial alkaloids from Strychnos icaja, we have isolated five alkaloids: three monomers, protostrychnine and genostrychnine, previously described in Strychnos nux-vomica, pseudostrychnine, already found in the leaves of the plant, a new bisindolic alkaloid, named strychnogucine C, and the first naturally occurring trimeric indolomonoterpenic alkaloid: strychnohexamine. This latter trimeric alkaloid presented an antiplasmodial activity against the FCA Plasmodium falciparum line near 1 μM.

Isostrychnopentamine, an indolomonoterpenic alkaloid from Strychnos usambarensis, induces cell cycle arrest and apoptosis in human colon cancer cells.

Isostrychnopentamine (ISP) is an indolomonoterpenic alkaloid that is present in the leaves of Strychnos usambarensis, a well known African shrub or little tree. The roots contain quaternary alkaloids, which are used to make a curare-like arrow poison. However, tertiary alkaloids isolated from the same plant possess cytotoxic activities against mammalian cells and protozoa. The effect of ISP has been investigated on the growth and viability of HCT-116 colon cancer cells during their exponentially growing phase. ISP induced apoptotic cell death as shown by the translocation of phosphatidylserine from the inner layer to the outer layer of the plasma membrane, chromatin condensation, DNA fragmentation, and caspase-3 and -9 activation. ISP provoked also cell cycle arrest in the G(2)-M phase. We also showed that the expression of p53 was not modified in ISP-treated cells, but that p21 was induced in a p53-independent manner. Finally, we demonstrated that ISP did not affect the catalytic activity of human topoisomerases I and II. In conclusion, ISP, which promotes cell death by a p53-independent apoptotic pathway, could be an interesting lead for cancer chemotherapy.

Strychnohexamine from Strychnos icaja, a naturally occurring trimeric indolomonoterpenic alkaloid

A reinvestigation of Strychnos icaja roots has resulted in the isolation, from the EtOAC extract, of one tertiary trisindole alkaloid, named strychnohexamine. Its structure has been investigated by means of spectroscopic data interpretation (UV, IR, HRESIMS, 1D and 2D NMR). This is the first time that a natural trimeric indolomonoterpenic alkaloid has been isolated directly from a plant species. This compound is one of the largest alkaloids ever discovered.