The Iboga Alkaloids

5-HT2A Receptor Knockout Mice Show Sex-Dependent Differences following Acute Noribogaine Administration

Noribogaine (noribo) is the primary metabolite from ibogaine, an atypical psychedelic alkaloid isolated from the root bark of the African shrub Tabernanthe iboga. The main objective of this study was to test the hypothesis that molecular, electrophysiological, and behavioral responses of noribo are mediated by the 5-HT2A receptor (5-HT2AR) in mice. In that regard, we used male and female, 5-HT2AR knockout (KO) and wild type (WT) mice injected with a single noribo dose (10 or 40 mg/kg; i.p.). After 30 min., locomotor activity was recorded followed by mRNA measurements by qPCR (immediate early genes; IEG, glutamate receptors, and 5-HT2AR levels) and electrophysiology recordings of layer V pyramidal neurons from the medial prefrontal cortex. Noribo 40 decreased locomotion in male, but not female WT. Sex and genotype differences were observed for IEG and glutamate receptor expression. Expression of 5-HT2AR mRNA increased in the mPFC of WT mice following Noribo 10 (males) or Noribo 40 (females). Patch-clamp recordings showed that Noribo 40 reduced the NMDA-mediated postsynaptic current density in mPFC pyramidal neurons only in male WT mice, but no effects were found for either KO males or females. Our results highlight that noribo produces sexually dimorphic effects while the genetic removal of 5HT2AR blunted noribo-mediated responses to NMDA synaptic transmission.

Reactivity of the Iboga Skeleton: Oxidation Study of Ibogaine and Voacangine

The iboga alkaloids scaffold shows great potential as a pharmacophore in drug candidates for the treatment of neuropsychiatric disorders. Thus, the study of the reactivity of this type of motif is particularly useful for the generation of new analogs suitable for medicinal chemistry goals. In this article, we analyzed the oxidation pattern of ibogaine and voacangine using dioxygen, peroxo compounds, and iodine as oxidizing agents. Special focus was placed on the study of the regio- and stereochemistry of the oxidation processes according to the oxidative agent and starting material. We found that the C16-carboxymethyl ester present in voacangine stabilizes the whole molecule toward oxidation in comparison to ibogaine, especially in the indole ring, where 7-hydroxy- or 7-peroxy-indolenines can be obtained as oxidation products. Nevertheless, the ester moiety enhances the reactivity of the isoquinuclidinic nitrogen to afford C3-oxidized products through a regioselective iminium formation. This differential reactivity between ibogaine and voacangine was rationalized using computational DFT calculations. In addition, using qualitative and quantitative NMR experiments combined with theoretical calculations, the absolute stereochemistry at C7 in the 7-hydroxyindolenine of voacangine was revised to be S, which corrects previous reports proposing an R configuration.

Recycling Upstream Redox Enzymes Expands the Regioselectivity of Cycloaddition in Pseudo-Aspidosperma Alkaloid Biosynthesis

Nature uses cycloaddition reactions to generate complex natural product scaffolds. Dehydrosecodine is a highly reactive biosynthetic intermediate that undergoes cycloaddition to generate several alkaloid scaffolds that are the precursors to pharmacologically important compounds such as vinblastine and ibogaine. Here we report how dehydrosecodine can be subjected to redox chemistry, which in turn allows cycloaddition reactions with alternative regioselectivity. By incubating dehydrosecodine with reductase and oxidase biosynthetic enzymes that act upstream in the pathway, we can access the rare pseudoaspidosperma alkaloids pseudo-tabersonine and pseudo-vincadifformine, both in vitro and by reconstitution in the plant Nicotiana benthamiana from an upstream intermediate. We propose a stepwise mechanism to explain the formation of the pseudo-tabersonine scaffold by structurally characterizing enzyme intermediates and by monitoring the incorporation of deuterium labels. This discovery highlights how plants use redox enzymes to enantioselectively generate new scaffolds from common precursors.

In Vitro and In Silico Antistaphylococcal Activity of Indole Alkaloids Isolated from Tabernaemontana cymosa Jacq (Apocynaceae)

The species of the genus Tabernaemontana have a long tradition of use in different pathologies of infectious origins; the antibacterial, antifungal, and antiviral effects related to the control of the pathologies where the species of this genus are used, have been attributed to the indole monoterpene alkaloids, mainly those of the iboga type. There are more than 1000 alkaloids isolated from different species of Tabernaemontana and other genera of the Apocynaceae family, several of which lack studies related to antibacterial activity. In the present study, four monoterpene indole alkaloids were isolated from the seeds of the species Tabernaemontana cymosa Jacq, namely voacangine (1), voacangine-7-hydroxyindolenine (2), 3-oxovoacangine (3), and rupicoline (4), which were tested in an in vitro antibacterial activity study against the bacteria S. aureus, sensitive and resistant to methicillin, and classified by the World Health Organization as critical for the investigation of new antibiotics. Of the four alkaloids tested, only voacangine was active against S. aureus, with an MIC of 50 µg/mL. In addition, an in silico study was carried out between the four isolated alkaloids and some proteins of this bacterium, finding that voacangine also showed binding to proteins involved in cell wall synthesis, mainly PBP2 and PBP2a.

Recent Advances in Divergent Synthetic Strategies for Indole-Based Natural Product Libraries

Considering the potential bioactivities of natural product and natural product-like compounds with highly complex and diverse structures, the screening of collections and small-molecule libraries for high-throughput screening (HTS) and high-content screening (HCS) has emerged as a powerful tool in the development of novel therapeutic agents. Herein, we review the recent advances in divergent synthetic approaches such as complexity-to-diversity (Ctd) and biomimetic strategies for the generation of structurally complex and diverse indole-based natural product and natural product-like small-molecule libraries.

Small molecules as kinetoplastid specific proteasome inhibitors for Leishmaniasis: a patent review from 1998 to 2021

INTRODUCTION

: Leishmaniasis is a neglected tropical infectious disease. The available limited therapeutic options for leishmaniasis are inadequate due to their poor pharmacokinetic profile, resistance, toxicity, high cost, and compliance problems. This warrants identification of new targets for the development of safer and effective anti-Leishmania therapy. The kinetoplastid specific proteasome (KSP) is a novel validated target to develop drugs against leishmaniasis.

AREA COVERED

: This review focuses on all the published patent applications and granted patents related to the studied small molecules as KSP inhibitors (KSPIs) against Leishmania from 1998 to December 31, 2021.

EXPERT OPINION

: A little amount of work has been done on KSPIs, but the study results are quite encouraging. LXE408 and GSK3494245 are two KSPIs in different phases of clinical trials. Some other small molecules have also shown KSP inhibitory potential, but they are not in clinical trials. The KSPIs are promising next-generation orally active patient compliant drugs against kinetoplastid diseases, including leishmaniasis. However, the main challenge to discover the KSPIs will be the resistance development and their selectivity against the proteasome of eukaryotic cells.

A systematic literature review of clinical trials and therapeutic applications of ibogaine

BACKGROUND

Iboga and its primary alkaloids, ibogaine and noribogaine, have been of interest to researchers and practitioners, mainly due to their putative efficacy in treating substance use disorders (SUDs). For many SUDs, still no effective pharmacotherapies exist. Distinct psychoactive and somatic effects of the iboga alkaloids set them apart from classic hallucinogens like LSD, mescaline, and psilocybin.

AIMS

The study team performed this systematic review focusing on clinical data and therapeutic interventions involving ibogaine and noribogaine.

METHODS

The team conducted a search for all publications up to December 7, 2020, using PubMed and Embase following PRISMA guidelines.

RESULTS

In total, we identified 743 records. In this review, we consider 24 studies, which included 705 individuals receiving ibogaine or noribogaine. This review includes two randomized, double-blind, controlled clinical trials, one double-blind controlled clinical trial, 17 open-label studies or case series (including observational or retrospective studies), three case reports, and one retrospective survey. The published data suggest that ibogaine is an effective therapeutic intervention within the context of SUDs, reducing withdrawal symptoms and craving. Data also point toward a beneficial impact on depressive and trauma-related psychological symptoms. However, studies have reported severe medical complications and deaths, which seem to be associated with neuro- and cardiotoxic effects of ibogaine. Two of these fatalities were described in the 24 studies included in this review.

CONCLUSION

Treatment of SUDs and persisting comorbidities requires innovative treatment approaches. Rapid-onset therapies such as the application of ibogaine may offer novel treatment opportunities for specific individuals. Rigorous study designs within medical settings are necessary to warrant safe application, monitoring, and, possibly, medical intervention.

Efficient Access to the Iboga Skeleton: Optimized Procedure to Obtain Voacangine from Voacanga africana Root Bark

Iboga alkaloids are a group of monoterpenoid indole alkaloids with promising and intriguing biological activities. Ibogaine is the representative member of the series and has become widely known as a potent atypical psychedelic with promising effects to treat substance use disorder. Nowadays, an efficient and scalable enantioselective total synthesis of ibogaine and related iboga alkaloids is still lacking, so direct extraction from natural sources or semi-synthetic schemes are the methods of choice to obtain them in a preparative scale. In particular, ibogaine can be obtained either by a low yielding direct isolation from Tabernanthe iboga or using a semi-synthetic procedure from voacangine, an iboga alkaloid occurring in a higher yield in the root bark of Voacanga africana. In this work, we describe an optimized process to obtain voacangine from V. africana root bark as a precursor of the iboga scaffold. Using a direct acetone-based extraction procedure (0.5 kg of root bark), voacangine was isolated in ∼0.8% of root bark dried weight, while the major alkaloids isolated from the bark were identified as iboga-vobasinyl dimers (∼3.7%) such as voacamine and voacamidine. Since these alkaloids contain the voacangine moiety in their structure, the cleavage of the dimers was further optimized, affording an extra amount of voacangine in ∼50% isolated molar yield. In this manner, the total amount of voacangine obtained by application of the whole procedure to the plant material (extraction and dimer cleavage) could almost duplicate the content originally found in the root bark.

Molecular Human Targets of Bioactive Alkaloid-Type Compounds from Tabernaemontana cymose Jacq

Alkaloids are a group of secondary metabolites that have been widely studied for the discovery of new drugs due to their properties on the central nervous system and their anti-inflammatory, antioxidant and anti-cancer activities. Molecular docking was performed for 10 indole alkaloids identified in the ethanol extract of Tabernaemontana cymosa Jacq. with 951 human targets involved in different diseases. The results were analyzed through the KEGG and STRING databases, finding the most relevant physiological associations for alkaloids. The molecule 5-oxocoronaridine proved to be the most active molecule against human proteins (binding energy affinity average = −9.2 kcal/mol) and the analysis of the interactions between the affected proteins pointed to the PI3K/ Akt/mTOR signaling pathway as the main target. The above indicates that indole alkaloids from T. cymosa constitute a promising source for the search and development of new treatments against different types of cancer.

Rhodium-Catalyzed C-H Alkenylation/Electrocyclization Cascade Provides Dihydropyridines That Serve as Versatile Intermediates to Diverse Nitrogen Heterocycles

Nitrogen heterocycles are present in approximately 60% of drugs, with nonplanar heterocycles incorporating stereogenic centers being of considerable interest to the fields of medicinal chemistry, chemical biology, and synthetic methods development. Over the past several years, our laboratory has developed synthetic strategies to access highly functionalized nitrogen heterocycles with multiple stereogenic centers. This approach centers on the efficient preparation of diverse 1,2-dihydropyridines by a Rh-catalyzed C-H bond alkenylation/electrocyclization cascade from readily available α,β-unsaturated imines and alkynes. The often densely substituted 1,2-dihydropyridine products have proven to be extremely versatile intermediates that can be elaborated with high regioselectivity and stereoselectivity, often without purification or even isolation. Protonation or alkylation followed by addition of hydride or carbon nucleophiles affords tetrahydropyridines with divergent regioselectivity and stereoselectivity depending on the reaction conditions. Mechanistic experiments in combination with density functional theory (DFT) calculations provide a rationale for the high level of regiocontrol and stereocontrol that is observed. Further elaboration of the tetrahydropyridines by diastereoselective epoxidation and regioselective ring opening furnishes hydroxy-substituted piperidines. Alternatively, piperidines can be obtained directly from dihydropyridines by catalytic hydrogenation in good yields with high face selectivity.When trimethylsilyl alkynes or N-trimethylsilylmethyl imines are employed as starting inputs, the Rh-catalyzed C-H bond alkenylation/electrocyclization cascade provides silyl-substituted dihydropyridines that enable a host of new and useful transformations to different heterocycle classes. Protonation of these products under acidic conditions triggers the loss of the silyl group and the formation of unstabilized azomethine ylides that would be difficult to access by other means. Depending on the location of the silyl group, [3 + 2] cycloaddition of the azomethine ylides with dipolarophiles provides tropane or indolizidine privileged frameworks, which for intramolecular cycloadditions yield complex polycyclic products with up to five contiguous stereogenic centers. When different types of conditions are employed, loss of the silyl group can result in either rearrangement to cyclopropyl-fused pyrrolidines or to aminocyclopentadienes. Mechanistic experiments supported by DFT calculations provide reaction pathways for these unusual rearrangements.The transformations described in this Account are amenable to natural product synthesis and drug discovery applications because of the biological relevance of the structural motifs that are prepared, short reaction sequences that rely on readily available starting inputs, high regiocontrol and stereocontrol, and excellent functional group compatibility. For example, the methods have been applied to efficient asymmetric syntheses of morphinan drugs, including the opioid antagonist (-)-naltrexone, which is extensively used for the treatment of drug abuse.

The iboga enigma: the chemistry and neuropharmacology of iboga alkaloids and related analogs

Covering: 2000 up to 2020 Few classes of natural products have inspired as many chemists and biologists as have the iboga alkaloids. This family of monoterpenoid indole alkaloids includes the anti-addictive compound ibogaine as well as catharanthine, a precursor to the chemotherapeutic vinblastine. Despite being known for over 120 years, these small molecules continue to challenge our assumptions about biosynthetic pathways, catalyze our creativity for constructing complex architectures, and embolden new approaches for treating mental illness. This review will cover recent advances in both the biosynthesis and chemical synthesis of iboga alkaloids as well as their use as next-generation neurotherapeutics. Whenever appropriate, we provide historical context for the discoveries of the past decade and indicate areas that have yet to be resolved. While significant progress regarding their chemistry and pharmacology has been made since the 1960s, it is clear that the iboga alkaloids will continue to stoke scientific innovation for years to come.

A Divergent Enantioselective Total Synthesis of Post-Iboga Indole Alkaloids

Divergent enantioselective total syntheses of five naturally occurring post-iboga indole alkaloids, dippinine B and C, 10,11-demethoxychippiine, 3-O-methyl-10,11-demethoxychippiine, and 3-hydroxy-3,4-secocoronaridine, as well as the two analogues 11-demethoxydippinine A and D, are presented for the first time. The enantioenriched aza[3.3.1]-bridged cycle, a common core intermediate to the target molecules, was constructed through an asymmetric phase-transfer-catalyzed Michael/aldol cascade reaction. The challenging azepane ring fused around the indole ring and the [3.3.1]-bridged cycle were installed through an intramolecular S_N 2'-type reaction. These cyclization strategies enabled rapid construction of the [6.5.6.6.7]-pentacyclic core at an early stage. Highlights of the late-stage synthetic steps include a Pd-catalyzed Stille coupling and a highly stereoselective catalyst-controlled hydrogenation to incorporate the side chain at C₂₀ with both R and S configurations in the natural products.

A Single Administration of the Atypical Psychedelic Ibogaine or Its Metabolite Noribogaine Induces an Antidepressant-Like Effect in Rats

Anecdotal reports and open-label case studies in humans indicated that the psychedelic alkaloid ibogaine exerts profound antiaddictive effects. Ample preclinical evidence demonstrated the efficacy of ibogaine, and its main metabolite, noribogaine, in substance-use-disorder rodent models. In contrast to addiction research, depression-relevant effects of ibogaine or noribogaine in rodents have not been previously examined. We have recently reported that the acute ibogaine administration induced a long-term increase of brain-derived neurotrophic factor mRNA levels in the rat prefrontal cortex, which led us to hypothesize that ibogaine may elicit antidepressant-like effects in rats. Accordingly, we characterized behavioral effects (dose- and time-dependence) induced by the acute ibogaine and noribogaine administration in rats using the forced swim test (FST, 20 and 40 mg/kg i.p., single injection for each dose). We also examined the correlation between plasma and brain concentrations of ibogaine and noribogaine and the elicited behavioral response. We found that ibogaine and noribogaine induced a dose- and time-dependent antidepressant-like effect without significant changes of animal locomotor activity. Noribogaine's FST effect was short-lived (30 min) and correlated with high brain concentrations (estimated >8 μM of free drug), while the ibogaine's antidepressant-like effect was significant at 3 h. At this time point, both ibogaine and noribogaine were present in rat brain at concentrations that cannot produce the same behavioral outcome on their own (ibogaine ∼0.5 μM, noribogaine ∼2.5 μM). Our data suggests a polypharmacological mechanism underpinning the antidepressant-like effects of ibogaine and noribogaine.

Ibogaine Administration Modifies GDNF and BDNF Expression in Brain Regions Involved in Mesocorticolimbic and Nigral Dopaminergic Circuits

Ibogaine is an atypical psychedelic alkaloid, which has been subject of research due to its reported ability to attenuate drug-seeking behavior. Recent work has suggested that ibogaine effects on alcohol self-administration in rats are related to the release of Glial cell Derived Neurotrophic Factor (GDNF) in the Ventral Tegmental Area (VTA), a mesencephalic region which hosts the soma of dopaminergic neurons. Although previous reports have shown ibogaine’s ability to induce GDNF expression in rat midbrain, there are no studies addressing its effect on the expression of GDNF and other neurotrophic factors (NFs) such as Brain Derived Neurotrophic Factor (BDNF) or Nerve Growth Factor (NGF) in distinct brain regions containing dopaminergic neurons. In this work, we examined the effect of ibogaine acute administration on the expression of these NFs in the VTA, Prefrontal Cortex (PFC), Nucleus Accumbens (NAcc) and the Substantia Nigra (SN). Rats were i.p. treated with ibogaine 20 mg/kg (I₂₀), 40 mg/kg (I₄₀) or vehicle, and NFs expression was analyzed after 3 and 24 h. At 24 h an increase of the expression of the NFs transcripts was observed in a site and dose dependent manner. Only for I₄₀, GDNF was selectively upregulated in the VTA and SN. Both doses elicited a large increase in the expression of BDNF transcripts in the NAcc, SN and PFC, while in the VTA a significant effect was found only for I₄₀. Finally, NGF mRNA was upregulated in all regions after I₄₀, while I₂₀ showed a selective upregulation in PFC and VTA. Regarding protein levels, an increase of GDNF was observed in the VTA only for I₄₀ but no significant increase for BDNF was found in all the studied areas. Interestingly, an increase of proBDNF was detected in the NAcc for both doses. These results show for the first time a selective increase of GDNF specifically in the VTA for I₄₀ but not for I₂₀ after 24 h of administration, which agrees with the effective dose found in previous self-administration studies in rodents. Further research is needed to understand the contribution of these changes to ibogaine’s ability to attenuate drug-seeking behavior.

Cascade cyclization and intramolecular nitrone dipolar cycloaddition and formal synthesis of 19-hydroxyibogamine

A cascade or domino sequence of condensation of hydroxylamine and an aldehyde to give an oxime, cyclization to a nitrone, and intramolecular 1,3-dipolar cycloaddition has been successfully employed where there is branching at C-4 as a route to the iboga alkaloids. Cyclization occurs with displacement of chloride as a leaving group and intramolecular cycloaddition occurs with an alkene as a dipolarophile. The reaction gives an azabicyclo[2.2.2]octane product containing a fused isoxazolidine as a single stereoisomer and this was converted to an isoquinuclidine that completed a formal synthesis of the alkaloid (±)-19-hydroxyibogamine.

A case report SPECT study and theoretical rationale for the sequential administration of ibogaine and 5-MeO-DMT in the treatment of alcohol use disorder

Ibogaine is a plant-derived alkaloid and dissociative psychedelic that demonstrates anti-addictive properties with several substances of abuse, including alcohol. 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) is a naturally occurring psychedelic known to occasion potent mystical-type experiences and also demonstrates anti-addictive properties. The potential therapeutic effects of both compounds in treating alcohol use disorder require further investigation and there are no published human neuroimaging findings of either treatment to date. We present the case of a 31-year-old male military veteran with moderate alcohol use disorder who sought treatment at an inpatient clinic in Mexico that utilized a sequential protocol with ibogaine hydrochloride (1550mg, 17.9mg/kg) on day 1, followed by vaporized 5-MeO-DMT (bufotoxin source 50mg, estimated 5-MeO-DMT content, 5-7mg) on day 3. The patient received SPECT neuroimaging that included a resting-state protocol before, and 3 days after completion of the program. During the patient's ibogaine treatment, he experienced dream-like visions that included content pertaining to his alcohol use and resolution of past developmental traumas. He described his treatment with 5-MeO-DMT as a peak transformational and spiritual breakthrough. On post-treatment SPECT neuroimaging, increases in brain perfusion were noted in bilateral caudate nuclei, left putamen, right insula, as well as temporal, occipital, and cerebellar regions compared to the patient's baseline scan. The patient reported improvement in mood, cessation of alcohol use, and reduced cravings at 5 days post-treatment, effects which were sustained at 1 month, with a partial return to mild alcohol use at 2 months. In this case, serial administration of ibogaine and 5-MeO-DMT resulted in increased perfusion in multiple brain regions broadly associated with alcohol use disorders and known pharmacology of both compounds, which coincided with a short-term therapeutic outcome. We present theoretical considerations regarding the potential of both psychedelic medicines in treating alcohol use disorders in the context of these isolated findings, and areas for future investigation.

Ibogaine Acute Administration in Rats Promotes Wakefulness, Long-Lasting REM Sleep Suppression, and a Distinctive Motor Profile

Ibogaine is a potent psychedelic alkaloid that has been the focus of intense research because of its intriguing anti-addictive properties. According to anecdotic reports, ibogaine has been originally classified as an oneirogenic psychedelic; i.e., induces a dream-like cognitive activity while awake. However, the effects of ibogaine administration on wakefulness (W) and sleep have not been thoroughly assessed. The main aim of our study was to characterize the acute effects of ibogaine administration on W and sleep. For this purpose, polysomnographic recordings on chronically prepared rats were performed in the light phase during 6 h. Animals were treated with ibogaine (20 and 40 mg/kg) or vehicle, immediately before the beginning of the recordings. Furthermore, in order to evaluate associated motor behaviors during the W period, a different group of animals was tested for 2 h after ibogaine treatment on an open field with video-tracking software. Compared to control, animals treated with ibogaine showed an increase in time spent in W. This effect was accompanied by a decrease in slow wave sleep (SWS) and rapid-eye movements (REM) sleep time. REM sleep latency was significantly increased in animals treated with the higher ibogaine dose. While the effects on W and SWS were observed during the first 2 h of recordings, the decrement in REM sleep time was observed throughout the recording time. Accordingly, ibogaine treatment with the lower dose promoted an increase on locomotion, while tremor and flat body posture were observed only with the higher dose in a time-dependent manner. In contrast, head shake response, a behavior which has been associated in rats with the 5HT_2A receptor activation by hallucinogens, was not modified. We conclude that ibogaine promotes a waking state that is accompanied by a robust and long-lasting REM sleep suppression. In addition, it produces a dose-dependent unusual motor profile along with other serotonin-related behaviors. Since ibogaine is metabolized to produce noribogaine, further experiments are needed to elucidate if the metabolite and/or the parent drug produced these effects.