Potential antimalarial activity of indole alkaloids

Oral acute toxicity study and in vivo antimalarial activity of Strychnos lucida R. Br. tablet

ETHNOPHARMACOLOGICAL RELEVANCE

Malaria eradication has been a major goal of the Indonesian government since 2020. Medicinal plants, such as Strychnos lucida R. Br., are empirically used to treat malaria through traditional preparation methods. However, the safety and efficacy of these plants have not yet been confirmed. Therefore, further investigations are necessary to confirm the safety and efficacy of S. lucida as an antimalarial agent.

AIMS OF THE STUDY

To quantify the concentration of brucine in the S. lucida extract, determine the acute oral toxicity of the standardized extract, and evaluate the in vivo antimalarial potency of S. lucida tablet (SLT).

MATERIALS AND METHODS

Acute oral toxicity of S.lucida extract was determined using the Organization for Economic Co-operation and Development 420 procedure, and the analytical method for brucine quantification was validated using high-performance liquid chromatography. In addition, antimalarial activity was determined using the Peter's four-day suppressive method.

RESULTS

Acute toxicity analysis revealed S. lucida as a low-toxicity compound with a cut-off median lethal dose of 2000-5000 mg/kg body weight [BW], which was supported by the hematological and biochemical profiles of the kidneys, liver, and pancreas (p > 0.05). Extract standardization revealed that S. lucida contained 3.91 ± 0.074% w/w brucine, adhering to the limit specified in the Indonesian Herbal Pharmacopeia. Antimalarial test revealed that SLT inhibited the growth of Plasmodium berghei by 27.74-45.27%. Moreover, SLT improved the hemoglobin and hematocrit levels. White blood cell and lymphocyte counts were lower in the SLT-treated group than in the K (+) group (p < 0.05).

CONCLUSION

Histopathological and biochemical evaluations revealed that S. lucida extract was safe at a dose of 2000 mg/kg BW with low toxicity. SLT inhibited Plasmodium growth and improved the hemoglobin, hematocrit, and red blood cell profiles. Additionally, SLT reduced the lymphocyte and WBC counts and increased the monocyte and thrombocyte counts as part of the immune system response against Plasmodium infection.

Alkaloidal Extracts from Avicennia africana P. Beauv. (Avicenniaceae) Leaf: An Antiplasmodial, Antioxidant, and Erythrocyte Viable

Background

The emergence of drug-resistant parasites impedes disease management and eradication efforts. Hence, a reinvigorated attempt to search for potent lead compounds in the mangroves is imperative.

Aim

This study evaluates in vitro antiplasmodial activity, antioxidant properties, and cytotoxicity of A. africana leaf alkaloidal extracts.

Methods

The A. africana leaves were macerated with 70% ethanol to obtain a total crude extract. Dichloromethane and chloroform-isopropanol (3 : 1, v/v) were used to extract the crude alkaloids and quaternary alkaloids from the total crude. The antiplasmodial activities of the alkaloidal extracts were performed against 3D7 P. falciparum chloroquine-sensitive clone via the SYBR Green I fluorescence assay with artesunate serving as the reference drug. The alkaloidal extracts were further evaluated for antioxidant properties via the total antioxidant capacity (TAC), the total glutathione concentration (GSH), the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, and the ferric-reducing antioxidant power (FRAP) methods. The cytotoxic activity of the alkaloidal extracts was tested on erythrocytes using a 3-(4,5-dimethylthiazol-2-yl)-5-diphenyltetrazolium bromide-MTT assay with little modification. The phytocompounds in the alkaloidal extracts were identified via gas chromatography-mass spectrometry (GC-MS) techniques.

Results

The total crude extract showed good antiplasmodial activity (IC50 = 11.890 µg/mL). The crude and quaternary alkaloidal extracts demonstrated promising antiplasmodial effects with IC50 values of 6.217 and 6.285 µg/mL, respectively. The total crude and alkaloidal extracts showed good antioxidant properties with negligible cytotoxicity on erythrocytes with good selectivity indices. The GC-MS spectral analysis of crude alkaloidal extracts gave indole and isoquinoline alkaloids and several other compounds. Dexrazoxane was found to be the main compound predicted, with an 86% peak area in the quaternary alkaloidal extract.

Conclusion

The crude and quaternary alkaloidal extracts exhibited antiplasmodial activities and ability to inhibit oxidative stress with negligible toxicity on erythrocytes. This may be good characteristics to avoid oxidative stress related to Plasmodium infection in the treatment of malaria.

New NADPH Oxidase 2 Inhibitors Display Potent Activity against Oxidative Stress by Targeting p22phox-p47phox Interactions

NADPH oxidase (NOX2) is responsible for reactive oxygen species (ROS) production in neutrophils and has been recognized as a key mediator in inflammatory and cardiovascular pathologies. Nevertheless, there is a lack of specific NOX2 pharmacological inhibitors. In medicinal chemistry, heterocyclic compounds are essential scaffolds for drug design, and among them, indole is a very versatile pharmacophore. We tested the hypothesis that indole heteroaryl-acrylonitrile derivatives may serve as NOX2 inhibitors by evaluating the capacity of 19 of these molecules to inhibit NOX2-derived ROS production in human neutrophils (HL-60 cells). Of these compounds, C6 and C14 exhibited concentration-dependent inhibition of NOX2 (IC₅₀~1 µM). These molecules also reduced NOX2-derived oxidative stress in cardiomyocytes and prevented cardiac damage induced by ischemia-reperfusion. Compound C6 significantly reduced the membrane translocation of p47^phox, a cytosolic subunit that is required for NOX2 activation. Molecular docking analyses of the binding modes of these molecules with p47^phox indicated that C6 and C14 interact with specific residues in the inner part of the groove of p47^phox, the binding cavity for p22^phox. This combination of methods showed that novel indole heteroaryl acrylonitriles represent interesting lead compounds for developing specific and potent NOX2 inhibitors.

Synthetic and Semisynthetic Compounds as Antibacterials Targeting Virulence Traits in Resistant Strains: A Narrative Updated Review

This narrative review paper provides an up-to-date overview of the potential of novel synthetic and semisynthetic compounds as antibacterials that target virulence traits in resistant strains. The review focused on research conducted in the last five years and investigated a range of compounds including azoles, indoles, thiophenes, glycopeptides, pleuromutilin derivatives, lactone derivatives, and chalcones. The emergence and spread of antibiotic-resistant bacterial strains is a growing public health concern, and new approaches are urgently needed to combat this threat. One promising approach is to target virulence factors, which are essential for bacterial survival and pathogenesis, but not for bacterial growth. By targeting virulence factors, it may be possible to reduce the severity of bacterial infections without promoting the development of resistance. We discuss the mechanisms of action of the various compounds investigated and their potential as antibacterials. The review highlights the potential of targeting virulence factors as a promising strategy to combat antibiotic resistance and suggests that further research is needed to identify new compounds and optimize their efficacy. The findings of this review suggest that novel synthetic and semisynthetic compounds that target virulence factors have great potential as antibacterials in the fight against antibiotic resistance.

Geobarrettin D, a Rare Herbipoline-Containing 6-Bromoindole Alkaloid from Geodia barretti

Geobarrettin D (1), a new bromoindole alkaloid, was isolated from the marine sponge Geodia barretti collected from Icelandic waters. Its structure was elucidated by 1D, and 2D NMR (including 1H-15N HSQC, 1H-15N HMBC spectra), as well as HRESIMS data. Geobarrettin D (1) is a new 6-bromoindole featuring an unusual purinium herbipoline moiety. Geobarrettin D (1) decreased secretion of the pro-inflammatory cytokine IL-12p40 by human monocyte derived dendritic cells, without affecting secretion of the anti-inflammatory cytokine IL-10. Thus, compound 1 shows anti-inflammatory activity.

Synthesis and Biological Evaluation of Some New Chalcone Derivatives as Anti-inflammatory Agents

AIM

The present research work aims to prepare a series of 1-(4-(2-(1H-indol-1-yl)-2- oxoethoxy)phenyl)-3-phenylprop-2-en-1-one derivatives.

METHODS

The major compound was achieved by the reaction of indole with chloroacetylchloride in benzene afforded 2-chloro-1-(indoline-1-yl) ethanone which reacts o- hydroxy acetophenone in presence of acetonitrile to form 2-(4-acetylphenoxy)-1-(1H-indol-1-yl)ethan-1-one then goes through aldol condensation to give various final derivatives.

RESULTS AND CONCLUSION

After the synthesis of compounds, the synthesized compounds were characterized by checking their solubility, melting point, thin layer chromatography, IR, 1HNMR spectral data and elemental analysis. All of the prepared derivatives were evaluated for their anti-inflammatory activity on wistar albino rats by following the carrageenan-induced Rat Hind Paw Edema model.

A Review: Meridianins and Meridianins Derivatives

Meridianins are a family of indole alkaloids derived from Antarctic tunicates with extensive pharmacological activities. A series of meridianin derivatives had been synthesized by drug researchers. This article reviews the extraction and purification methods, biological activities and pharmacological applications, pharmacokinetic characters and chemical synthesis of meridianins and their derivatives. And prospects on discovering new bioactivities of meridianins and optimizing their structure for the improvement of the ADMET properties are provided.

Antimalarial Natural Products

Natural products have made a crucial and unique contribution to human health, and this is especially true in the case of malaria, where the natural products quinine and artemisinin and their derivatives and analogues, have saved millions of lives. The need for new drugs to treat malaria is still urgent, since the most dangerous malaria parasite, Plasmodium falciparum, has become resistant to quinine and most of its derivatives and is becoming resistant to artemisinin and its derivatives. This volume begins with a short history of malaria and follows this with a summary of its biology. It then traces the fascinating history of the discovery of quinine for malaria treatment and then describes quinine's biosynthesis, its mechanism of action, and its clinical use, concluding with a discussion of synthetic antimalarial agents based on quinine's structure. The volume then covers the discovery of artemisinin and its development as the source of the most effective current antimalarial drug, including summaries of its synthesis and biosynthesis, its mechanism of action, and its clinical use and resistance. A short discussion of other clinically used antimalarial natural products leads to a detailed treatment of other natural products with significant antiplasmodial activity, classified by compound type. Although the search for new antimalarial natural products from Nature's combinatorial library is challenging, it is very likely to yield new antimalarial drugs. The chapter thus ends by identifying over ten natural products with development potential as clinical antimalarial agents.

An insight in anti-malarial potential of indole scaffold: A review

Malaria is a major parasitic disease in tropical and sub-tropical regions. Pertaining to the sustaining resistance in malarial parasite against the available drugs, novel treatment options are the need of the hour. In this resolve recently, focus has shifted to finding the natural alternatives that possess anti-plasmodial activity for combatting malaria. Drawing on the text written in ancient scriptures and Ayurveda, natural compounds are now being screened for their therapeutic properties. Indole is one such natural compound, present in all living organisms, it displays a range of therapeutic activities including anticancer, anti-inflammatory, antimalarial etc. In this review, we have discussed various indole scaffold as well as the semi-synthetic drugs containing indole moiety that have been synthesized for malaria treatment.

Cheminformatics techniques in antimalarial drug discovery and development from natural products 2: Molecular scaffold and machine learning approaches

A large number of natural products, especially those used in ethnomedicine of malaria, have shown varying in-vitro antiplasmodial activities. Cheminformatics involves the organization, integration, curation, standardization, simulation, mining and transformation of pharmacology data (compounds and bioactivity) into knowledge that can drive rational and viable drug development decisions. This chapter will review the application of two cheminformatics techniques (including molecular scaffold analysis and bioactivity predictive modeling via Machine learning) to natural products with in-vitro and in-vivo antiplasmodial activities in order to facilitate their development into antimalarial drug candidates and design of new potential antimalarial compounds.

Antimalarial Activity of Seed Extracts of Schinus molle Against Plasmodium berghei in Mice

Background.

Malaria is a major public health problem in developing countries. In Ethiopian, the seeds of Schinus molle are used for the management of malaria. Therefore, the current study aimed to evaluate in vivo antimalarial activity of hydro-alcoholic crude extract and solvent fractions of Schinus molle seeds in Plasmodium berghei infected mice.

Methods.

An 80 percent of methanolic crude extract and solvent fractions of Schinus molle seeds were tested for antimalarial activity at 100, 200 and 400 mg/kg doses. The parasitemia level, packed cell volume, body weight, survival of date and rectal temperature were used to evaluate the anti-malarial activity of the extracts. One-way ANOVA followed by post hoc Tukey’s HSD multiple comparison test was employed and the result was expressed in mean ± SEM (standard error of the mean).

Results.

The curative activity of the highest dose of crude extract and aqueous fraction of Schinus molle seeds was 69.86% and 73.82% (p < 0.001), respectively. In the prophylactic test, aqueous fraction had 72.39% (p < 0.001) suppression antimalarial activity. Among solvent fractions, only chloroform fraction was significantly attenuated packed cell volume reduction. The mice treated with crude extract and aqueous fraction had longer survival date than vehicle-treated mice (p < 0.001).

Conclusion.

The experiment finding showed that the crude extract and solvent fractions of Schinus molle seeds had significant curative and prophylaxis anti-plasmodial activity. This result revealed that the Schinus molle seeds extract has promising antimalarial activity against Plasmodium berghei. However, further confirmatory studies, isolation and characterization of the active constituents are recommended.

Anti-Oxidant Potential and Antimalarial Effects of Acanthus polystachyus Delile (Acanthaceae) Against Plasmodium berghei: Evidence for in vivo Antimalarial Activity

BACKGROUND

Malaria is among the most devastating and widespread tropical parasitic diseases which is more prevalent in developing countries. Acanthus polystachyus (Acanthaceae) leaves are traditionally used for the treatment of malaria in Ethiopia. This study aimed to investigate the in vivo antimalarial and in vitro antioxidant activity of the leaves extract of Acanthus polystachyus.

MATERIALS AND METHODS

The leaves part of A. polystachyus were extracted using 80% methanol. The antioxidant effect of Acanthus polystachyus extract was evaluated by using (DPPH) diphenyl-2-picrylhydrazyl assay model. To evaluate the antimalarial effect of the A. polystachyus extract, Plasmodium berghei ANKA strain (chloroquine sensitive) was used to infect the mice in three different experimental protocol: suppressive, curative, and prophylactic test models.

RESULTS

The leaves extract of Acanthus polystachyus significantly (P<0.05-0.0001) suppressed the parasitemia in all experimental protocol. The extract exhibited a chemosupression of 27.64%, 33.67% and 49.25% in 4-day suppressive test; 33.76%, 39.24% and 53.59% in curative test, and 25%, 32.84% and 50% in prophylactic tests at dose of 100, 200, and 400mg/kg, respectively. The extract also extended the mean survival time, prevented the bodyweight loss and body temperature drop, and packed cell volume significantly (P<0.05) as compared to the negative control. Dose-dependent antioxidant activity was shown by the leaf extract of A. polystachyus with an IC50 value of 9.37µg/mL.

CONCLUSION

The current finding showed that the leaves extract of Acanthus polystachyus has revealed promising antimalarial effects. Thus, this finding supports the traditional use of A. polystachyus for the treatment of malaria.

Inhibition of Hemoglobin Degrading Protease Falcipain-2 as a Mechanism for Anti-Malarial Activity of Triazole-Amino Acid Hybrids

BACKGROUND

Novel drug development against malaria parasite over old conventional antimalarial drugs is essential due to rapid and indiscriminate use of drugs, which led to the emergence of resistant strains.

METHODS

In this study, previously reported triazole-amino acid hybrids (13-18) are explored against Plasmodium falciparum as antimalarial agents. Among six compounds, 15 and 18 exhibited antimalarial activity against P. falciparum with insignificant hemolytic activity and cytotoxicity towards HepG2 mammalian cells. In molecular docking studies, both compounds bind into the active site of PfFP-2 and block its accessibility to the substrate that leads to the inhibition of target protein further supported by in vitro analysis.

RESULTS

Antimalarial half-maximal inhibitory concentration (IC50) of 15 and 18 compounds were found to be 9.26 μM and 20.62 μM, respectively. Blood stage specific studies showed that compounds, 15 and 18 are effective at late trophozoite stage and block egress pathway of parasites. Decreased level of free monomeric heme was found in a dose dependent manner after the treatment with compounds 15 and 18, which was further evidenced by the reduction in percent of hemoglobin hydrolysis. Compounds 15 and 18 hindered hemoglobin degradation via intra- and extracellular cysteine protease falcipain-2 (PfFP-2) inhibitory activity both in in vitro and in vivo in P. falciparum.

CONCLUSION

We report antimalarial potential of triazole-amino acid hybrids and their role in the inhibition of cysteine protease PfFP-2 as its mechanistic aspect.

Indole: The After Next Scaffold of Antiplasmodial Agents?

Malaria remains a global public health problem due to the uphill fight against the causative Plasmodium parasites that are relentless in developing resistance. Indole-based antiplasmodial compounds are endowed with multiple modes of action, of which inhibition of hemozoin formation is the major mechanism of action reported for compounds such as cryptolepine, flinderoles, and isosungucine. Indole-based compounds exert their potent activity against chloroquine-resistant Plasmodium strains by inhibiting hemozoin formation in a mode of action different from that of chloroquine or through a novel mechanism of action. For example, dysregulating the sodium and osmotic homeostasis of Plasmodium through inhibition of PfATP4 is the novel mechanism of cipargamin. The potential of developing multi-targeted compounds through molecular hybridization ensures the existence of indole-based compounds in the antimalarial pipeline.

Ruthenium Catalyzed Tandem Pictet-Spengler Reaction

We report a pyridyl-phosphine ruthenium(II) catalyzed tandem alcohol amination/Pictet-Spengler reaction sequence to synthesize tetrahydro-β-carbolines from an alcohol and tryptamine. Our conditions use a Lewis acid cocatalyst, In(OTf)₃, that is compatible with typically base catalyzed amination and an acid catalyzed Pictet-Spengler cyclization. This method proceeds well with benzylic alcohols, heterocyclic carbinols, and aliphatic alcohols. We also show how combining this reaction with a subsequent cycloamination enables a direct synthesis of tetracyclic alkaloids like harmicine.

Indole alkaloids: 2012 until now, highlighting the new chemical structures and biological activities

Indole alkaloids have attracted attention because of their therapeutic properties, being anti-inflammatory, antinociceptive, antitumoural, antioxidant and antimicrobial. These compounds present a wide structural diversity, which is directly related to the genera of the producing plants, as well as the biological activities. Indole alkaloids have attracted attention over the last decade because of this combination of bioactivity and structural diversity. Therefore, this review presented recent (2012-2018) advances in alkaloids, focusing on new compounds, extraction methods and biological activities. As such, approximately 70 articles were identified, which showed 261 new compounds produced by plants of the families Apocynaceae, Rubiaceae, Annonaceae and Loganiaceae. In addition, different extraction methods were identified, and the structures of the new compounds were analysed. In addition to indole molecules, there were mono-indole-, di-indole-, vinblastine-, vimblastine-, gelsedine-, geissospermidine-, koumine-, geissospermidine-, iboga-, perakine-, corynanthe-, vincamine-, ajmaline-, aspidorpema-, strychnos-type, β-carboline alkaloids and indole alkaloid glucosides. The reported biological activities are mainly anticancer, antibacterial, antimalarial, antifungal, antiparasitic, and antiviral, as well as anti-acetylcholinesterase and anti-butyrylcolinesterase properties. This review serves as a guide for those wishing to find the most recently identified alkaloid structures and their associated activities.

A trace alkaloid, oleraisoindole A from Portulaca oleracea L. and its anticholinesterase effect

A new trace alkaloid possessing the lignan structure, named oleraisoindole A, was obtained from the extract of the Portulaca oleracea L.. The structure of oleraisoindole A was elucidated by 1D and 2D NMR and high resolution electrospray ionization time-of-flight mass spectroscopic methods. The compound presented an anticholinesterase effect with the IC₅₀ value of 60.4 μM.

Enhanced Solubility of Alkaloids by Complexation with Polycarboxylic Materials for Controlled Release Formulations: Case of Peschiera fuchsiaefolia

Malaria is a major public health problem with hundreds of thousands of deaths yearly. Extracts of Peschiera fuchsiaefolia (Pf), an Apocynaceae family plant, are used as malaria treatment by several populations. Artemisinin is another effective largely used antimalarial agent but susceptible to generate resistant forms of Plasmodium. To reduce the risk of new resistant strains' appearance, the WHO recommended artemisinin-based combination therapy (ACT) with another bioactive agent, ensuring a long duration of antiplasmodial activity. Pf alkaloids are good candidates for ACT, but their solubility is very low. This research was aimed to improve the solubility of Pf alkaloids by complexation via their amine groups with carboxylate groups of carboxymethylstarch (CMS), an excipient used to formulate oral dosage forms for controlled drug release. It was found that when complexed as CMS-Pf, the solubility of Pf is increased (four to five times in function of dissolution medium). A new specific and faster approach to evaluate the solubility was proposed, measuring the effective saturation concentration of the compound of interest via one of its specific capacities, i.e., absorption capacity at a specific wavelength or antioxidant properties. This approach is more convenient for solubility evaluation of various active agents from complexes or crude extracts, or in heterogeneous samples. Also, the storage stability was markedly improved from 1 week for Pf co-processed with maltodextrin (MD/Pf) to several months for CMS-Pf (in similar controlled temperature and humidity conditions). The co-processing as MD/Pf or complexation as CMS-Pf affected physical properties but not the biological (i.e., antioxidant) activity of Pf.

Triazole derivatives and their antiplasmodial and antimalarial activities

Malaria, caused by protozoan parasites of the genus Plasmodium especially by the most prevalent parasite Plasmodium falciparum, represents one of the most devastating and common infectious disease globally. Nearly half of the world population is under the risk of being infected, and more than 200 million new clinical cases with around half a million deaths occur annually. Drug therapy is the mainstay of antimalarial therapy, yet current drugs are threatened by the development of resistance, so it's imperative to develop new antimalarials with great potency against both drug-susceptible and drug-resistant malaria. Triazoles, bearing a five-membered heterocyclic ring with three nitrogen atoms, exhibit promising in vitro antiplasmodial and in vivo antimalarial activities. Moreover, several triazole-based drugs have already used in clinics for the treatment of various diseases, demonstrating the excellent pharmaceutical profiles. Therefore, triazole derivatives have the potential for clinical deployment in the control and eradication of malaria. This review covers the recent advances of triazole derivatives especially triazole hybrids as potential antimalarials. The structure-activity relationship is also discussed to provide an insight for rational designs of more efficient antimalarial candidates.

In vitro antiplasmodial activity and identification, using tandem LC-MS, of alkaloids from Aspidosperma excelsum, a plant used to treat malaria in Amazonia

ETHNOPHARMACOLOGICAL RELEVANCE

Aspidosperma excelsum Benth. (Apocynaceae), a native tree in the Brazilian Amazonia, is traditionally used to treat various diseases, including malaria.

AIM OF STUDY

To investigate the chemical constitution, antiplasmodial activity and cytotoxicity of samples obtained from A. excelsum trunk bark by different procedures aiming to evaluate their potential as an antimalarial phytomedicine.

MATERIALS AND METHODS

A hydroethanolic extract and alkaloid extracts were prepared and assayed for antiplasmodial activity and cytotoxicity against chloroquine-resistant Plasmodium falciparum (W2 strain) and HepG2 cells, respectively. Taking into account the known occurrence and antimalarial activity of Aspidosperma monoterpene indole alkaloids (MIA), acid-base extractions were carried out and the fractions were assayed for antiplasmodial activity and cytotoxicity. All the samples were analysed by hyphenated chromatographic techniques, such as UPLC-DAD-ESI-MS/MS and HRMS (HPLC-MS MicroTOF), comparing their chemical composition to the literature data.

RESULTS

The hydroethanolic extract disclosed a moderate in vitro activity against chloroquine-resistant Plasmodium falciparum (W2 strain) with IC₅₀ 23.68 ± 3.08 µg/mL), low cytotoxicity to HepG2 cells (> 250 µg/mL) and good SI (> 10.56). A total of 20 known monoterpene indole alkaloids were identified, seven of which are here firstly described for A. excelsum. Known highly active alkaloids, namely demethylaspidospermine, aspidocarpine, and ochrolifuanine are present in active alkaloid fractions and might contribute to their observed antiplasmodial effect. An alkaloid fraction (Ae-Alk2), obtained directly from trunk bark by extraction with dil. aqueous HCl, pointed out for its activity (IC₅₀ 8.75±2.26 µg/mL, CC₅₀ 185.14±1.97 µg/mL, SI 21.16) and should be highlighted as the most promising out of the assayed samples.

CONCLUSION

The present results represent a preliminary support to the alleged antimalarial use of A. excelsum trunk bark and allowed to highlight alkaloid fractions as promising phytomedicines.

Tracking pereirine and flavopereirine in pau-pereira using Raman and SERS spectroscopies

Raman and SERS spectroscopies have been used to identify the bioactive compounds pereirine and flavopereirine from stem bark, ethanolic crude extracts and infusions.

Comparative Analysis of Hydrophilic Ingredients in Toad Skin and Toad Venom Using the UHPLC-HR-MS/MS and UPLC-QqQ-MS/MS Methods Together with the Anti-Inflammatory Evaluation of Indolealkylamines

Toad skin and toad venom, as two kinds of Chinese medicine, are prepared from Bufo bufo gargarizans Cantor and Bufo melanostictus Schneider. However, they display distinct properties in traditional application, and the hydrophilic ingredients are the possible distinguishing chemicals between them. In this work, 36 and 22 hydrophilic components were characterized from toad skin and venom, respectively, by UHPLC-HR-MS/MS, including amino acids, nucleosides, polypeptides, and indolealkylamines (IAAs). Among them, 15 compounds were unambiguously confirmed by comparison with standards. The CID-MS/MS fragmentation behaviors of seven indolealkylamine references were investigated to ascertain three types of structures. Subsequently, 11 high abundance contents of hydrophilic ingredients were determined from 11 batches of toad skin and 4 batches of toad venom by UPLC-QqQ-MS/MS. The quantitative results showed that the content of main IAAs in toad venom was much higher than in skin. In addition, the N-methyl serotonin (free IAA), bufothionine (combined IAA), and total IAAs sample were selected for anti-inflammatory evaluation in lipopolysaccharide (LPS) stimulated zebrafish embryo models. The obvious anti-inflammatory activities of IAAs were observed, especially for the free IAAs. This study illustrated IAAs were the main distinct hydrophilic components that probably lead to the difference between toad skin and toad venom in traditional applications.

Isolation, Chemical Profile and Antimalarial Activities of Bioactive Compounds from Rauvolfia caffra Sond

In this study, the chemical profile of a crude methanol extract of Rauvolfia caffra Sond was determined by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). Column chromatography and preparative thin layer chromatography were used to isolate three indole alkaloids (raucaffricine, N-methylsarpagine and spegatrine) and one triterpenoid (lupeol). The antiplasmodial activity was determined using the parasite lactate dehydrogenase (pLDH) assay. The UPLC-MS profile of the crude extract reveals that the major constituents of R. caffra are raucaffricine (m/z 513.2) and spegatrine (m/z 352.2). Fraction 3 displayed the highest antiplasmodial activity with an IC₅₀ of 6.533 μg/mL. However, raucaffricine, isolated from the active fraction did not display any activity. The study identifies the major constituents of R. caffra and also demonstrates that the major constituents do not contribute to the antiplasmodial activity of R. caffra.

Predictive classifier models built from natural products with antimalarial bioactivity using machine learning approach

In view of the vast number of natural products with potential antiplasmodial bioactivity and cost of conducting antiplasmodial bioactivity assays, it may be judicious to learn from previous antiplasmodial bioassays and predict bioactivity of these natural products before experimental bioassays. This study set out to harness antimalarial bioactivity data of natural products to build accurate predictive models, utilizing classical machine learning approaches, which can find potential antimalarial hits from new sets of natural products. Classical machine learning approaches were used to build four classifier models (Naïve Bayesian, Voted Perceptron, Random Forest and Sequence Minimization Optimization of Support Vector Machines) from bioactivity data of natural products with in-vitro antiplasmodial activity (NAA) using a combination of the molecular descriptors and two-dimensional molecular fingerprints of the compounds. Models were evaluated with an independent test dataset. Possible chemical features associated with reported antimalarial activities of the compounds were also extracted. From the results, Random Forest (accuracy 82.81%, Kappa statistics 0.65 and Area under Receiver Operating Characteristics curve 0.91) and Sequential Minimization Optimization (accuracy 85.93%, Kappa statistics 0.72 and Area under Receiver Operating Characteristics curve 0.86) showed good predictive performance for the NAA dataset. The amine chemical group (specifically alkyl amines and basic nitrogen) was confirmed to be essential for antimalarial activity in active NAA dataset. This study built and evaluated classifier models that were used to predict the antiplasmodial bioactivity class (active or inactive) of a set of natural products from interBioScreen chemical library.

Apocynaceae species with antiproliferative and/or antiplasmodial properties: a review of ten genera

Apocynaceae is a large family of tropical trees, shrubs and vines with most species producing white latex. Major metabolites of species are triterpenoids, iridoids, alkaloids and cardenolides, which are known for a wide range of biological and pharmacological activities such as cardioprotective, hepatoprotective, neuroprotective, anti-inflammatory, anticancer and antimalarial properties. Prompted by their anticancer and antimalarial properties, the current knowledge on ten genera (Allamanda, Alstonia, Calotropis, Catharanthus, Cerbera, Dyera, Kopsia, Nerium, Plumeria and Vallaris) is updated. Major classes of metabolites are described using some species as examples. Species with antiproliferative (APF) and/or antiplasmodial (APM) properties have been identified. With the exception of the genus Dyera, nine genera of 22 species possess APF activity. Seven genera (Alstonia, Calotropis, Catharanthus, Dyera, Kopsia, Plumeria and Vallaris) of 13 species have APM properties. Among these species, Alstonia angustiloba, Alstonia macrophylla, Calotropis gigantea, Calotropis procera, Catharanthus roseus, Plumeria alba and Vallaris glabra displayed both APF and APM properties. The chemical constituents of these seven species are compiled for assessment and further research.

Inverse docking based screening and identification of protein targets for Cassiarin alkaloids against Plasmodium falciparum

Various reports have shown Cassiarin alkaloids, selective in vitro activities against various strains of Plasmodium falciparum with low cytotoxicity, which indicates their possible candidature as antimalarial drug. However, poor recognition of their protein targets and molecular binding behaviour, certainly limits their exploration as antimalarial drug candidature. To address this, we utilises inverse screening, based on three different docking methodologies in order to find their most putative protein targets. In our study, we screened 1047 protein structures from protein data bank, which belongs to 147 different proteins. Our investigation identified 16 protein targets for Cassiarins. In few cases of identified protein targets, the binding site was poorly studied, which encouraged us to perform comparative sequence and structural studies with their homologous proteins, like as in case of Kelch motif associated protein, Armadillo repeats only protein and Methionine aminopeptidase 1b. In our study, we also found Tryptophanyl-tRNA synthetase and 1-Deoxy-D-Xylose-5-phosphate reductoisomerase proteins are the most common targets for Cassiarins.

Design, synthesis, and biological evaluation of 2-substituted-2,3,4,9-tetrahydrospiro-β-carboline-3-carboxylic acid derivatives as first-in-class mast cell stabilizers

Mast cell degranulation plays a momentous role in myriad diseases like asthma, eczema, allergic rhinitis, and conjunctivitis as well as anaphylactic shock; hence, there is an unmet need for developing new mast cells stabilizers. The reported mast cell stabilizers have a heterocyclic moiety and an acidic group. Furthermore, the role of tryptophan in suppression of mast cell activation is established. Hence, we prepared constrained analogs of tryptophan, which are derivatives of 2,3,4,9-tetrahydrospiro-β-carboline-3-carboxylic acid, and evaluated them for ex vivo inhibition of compound 48/80-induced mast degranulation activity. By comparing IC₅₀ (μM) values with that of the standard drug sodium cromoglycate (IC₅₀  = 0.489 ± 0.003 μM), compounds with bulky groups like heptyl (compound 9; IC₅₀  = 0.389 ± 0.015 μM) and octyl (compound 10; IC₅₀  = 0.354 ± 0.023 μM) were found to be of similar potency as sodium cromoglycate. Furthermore, the polar group-containing compounds like the chloropropyl (compound 16; IC₅₀  = 0.382 ± 0.083 μM) and benzoyl derivative (compound 14; IC₅₀  = 00.469 ± 0.032 μM) were also found to be of similar potency as sodium cromoglycate. This is a seminal study of spiro-β-carboline mast cell stabilization having a wider scope in mast cell research; yet, the mechanism of action remains elusive.

In Vivo Antimalarial Activity of the Solvent Fractions of Fruit Rind and Root of Carica papaya Linn (Caricaceae) against Plasmodium berghei in Mice

BACKGROUND

Currently, antimalarial drug resistance poses a serious challenge. This stresses the need for newer antimalarial compounds. Carica papaya is used traditionally and showed in vitro antimalarial activity. This study attempted to evaluate in vivo antimalarial activity of C. papaya in mice.

METHODS

In vivo antimalarial activity of solvent fractions of the plant was carried out against early P. berghei infection in mice. Parasitemia, temperature, PCV, and body weight of mice were recorded. Windows SPSS version 16 (one-way ANOVA followed by Tukey's post hoc test) was used for data analysis.

RESULTS

The pet ether and chloroform fractions of C. papaya fruit rind and root produced a significant (p < 0.001) chemosuppressive effect. A maximum parasite suppression of 61.78% was produced by pet ether fraction of C. papaya fruit rind in the highest dose (400 mg/kg/day). Only 400 mg/kg/day dose of chloroform fraction of C. papaya root exhibited a parasite suppression effect (48.11%). But, methanol fraction of the plant parts produced less chemosuppressive effect.

CONCLUSION

Pet ether fraction of C. papaya fruit rind had the highest antimalarial activity and could be a potential source of lead compound. Further study should be done to show the chemical and metabolomic profile of active ingredients.

Phytochemical and Pharmacological Review of Cryptolepis sanguinolenta (Lindl.) Schlechter

Ethnopharmacological Relevance

Cryptolepis sanguinolenta is a scrambling thin-stemmed shrub found in Africa. Traditionally in West Africa, it is employed in the treatment of malaria, diarrhea, and respiratory conditions. This review discusses the traditional importance as well as the phytochemical, ethnomedical, pharmacological, and toxicological importance of this plant.

Materials and Methods

Excerpta Medica Database, Google Scholar, Springer, and PubMed Central were the electronic databases used to search for and filter primary studies on Cryptolepis sanguinolenta.

Results

The detailed review of various studies conducted on C. sanguinolenta and some of its constituents gives an important body of proof of its potential therapeutic benefits and also of its use as a source of lead compounds with therapeutic potentials.

Conclusion

The review on C. sanguinolenta is important in identifying grey areas in the research on this medicinal plant and also provides comprehensive data thus far to continue research on this plant.

In vitro antiplasmodial activity and prophylactic potentials of extract and fractions of Trema orientalis (Linn.) stem bark

BACKGROUND

Trema orientalis (T. orientalis Linn) has been used in the management of malaria in the western part of Nigeria and despite its application in ethnomedicine, there is dearth of scientific evidence to justify the acclaimed prophylactic antimalarial usage of the plant. The aim of this study is to assess the in vitro antiplasmodial cell-free assay and chemopreventive efficacy of the methanol extract of the stem bark of T. orientalis and its fractions as a prophylactic regimen for malaria prevention. Also, the antimicrobial activities of the extract and the fractions were investigated.

METHOD

Vacuum liquid chromatography was used to obtain dichloromethane, ethylacetate and methanol fractions from the methanol extract of T. orientalis. The fractions were tested for their prophylactic and cell-free antimalarial activity using murine models and β-hematin formation assay respectively. Disc diffusion method was used to determine the antibacterial activity of the extract and its fractions against both Gram-positive and Gram-negative bacteria.

RESULTS

In the prophylactic experiment, dichloromethane (DCMF), methanol fraction (MF) and extract (ME) (in this order) showed significant chemopreventive effects against P. berghei invasion of the red blood cells when compared with both Sulfadoxine-Pyrimethamine (SP) and untreated controls. Results of the in vitro study showed that the DCMF had the highest effect in preventing the formation of β-hematin when compared with other fractions. The DCMF also had the highest percentage inhibition of β-hematin formation when compared with chloroquine. The extract and fractions showed a concentration dependent antibacterial activity. Methanol extract had a pronounced inhibitory effect on Enterobacter cloaca ATCC 13047 and Enterococcus faecalis ATCC 29212. Serratia mercescens ATCC 9986 and Pseudomonas aeruginosa ATCC 19582 were the most susceptible bacteria.

CONCLUSION

The results obtained showed that both extract and fractions of T. orientalis possessed antiplasmodial and antimicrobial activity.

Antimalarial activity of Syzygium guineense during early and established Plasmodium infection in rodent models

BACKGROUND

In Ethiopia, the leaves of Syzygium guineense have been found useful for the prevention and cure of malaria, and demonstrated antiplasmodial activity in vitro. Nevertheless, no scientific study has been conducted to confirm its antimalarial activity in vivo. Therefore, the objective of the study was to evaluate the antimalarial effect of Syzygium guineense leaf extract in mice.

METHODS

Inoculation of the study mice was carried out by using the malaria parasite, Plasmodium berghei. The plant extract was prepared at 200, 400 and 600 mg/kg. Chloroquine and distilled water was administered to the positive and negative control groups respectively. Parameters like parasitaemia, survival time and body weight were determined following standard tests (4-day suppressive, Rane's and repository tests).

RESULTS

Syzygium guineense crude leaf extract displayed considerable (p < 0.05) parasite suppression at doses of 600 and 400 mg/kg in a 4-day suppressive test with chemosuppressive value of 59.39 and 49.09% respectively. S. guineense crude leaf extract also showed dose-dependent schizontocidal activity in both the repository and curative tests. The extract also prevented body weight loss and prolonged survival date of mice significantly (P < 0.05) at the highest dose employed in the study. Qualitative chemical assay for S. guineense methanolic leaf extract revealed that the plant is endowed with different plant secondary metabolites exemplified by terpenoids, alkaloids, triterpenes, flavonoids, anthraquinones, tannins, glycosides, saponins and phenols.

CONCLUSION

Syzygium guineense leaf extract possess antimalarial activity in mice. The test substance was found to be safe with no observable signs of toxicity in the study mice. The results of the present work confirmed the in vitro antiplasmodial finding and traditional claims in vivo in mice. Therefore, Syzygium guineense could be regarded as a potential source to develop safe, effective and affordable antimalarial agent.

Synthesis of New (E)-2-(1H-Indole-3-ylcarbonyl)-3-heteroaryl-acrylonitriles via Microwave-Assisted Knoevenagel Condensation

Given the broad spectrum of biological uses of heteroaryl-acrylonitrile derivatives, it is necessary to find simple methods to synthesize and diversify this family of compounds. We report a stereoselective synthesis of a series of new (E)-2-(1H-indole-3-ylcarbonyl)-3-heteroaryl-acrylonitriles (3a–3i) obtained from 3-(cyanoacetyl)indole and heteroaryl-aldehydes under microwave-assisted Knoevenagel reaction at 300 W of potency and 100°C. The desired derivatives (3a–3i) were obtained with variable yields (30–94%) and time reactions (8–90 min). All the heteroaryl-acrylonitriles were characterized by physicoanalytical techniques such IR, 1H, 13C NMR, and electrospray mass spectrometry.

Natural product inspired design and synthesis of β-carboline and γ-lactone based molecular hybrids

β-Carboline and γ-lactone moieties have been selected by nature as privileged scaffolds and display a wide range of pharmacological properties. Following nature, we envisaged the preparation of new β-carboline and γ-lactone based molecular hybrids incorporating both the pharmacophores. In this regard, a water-assisted In-mediated environmentally benign and easy to execute single-step tandem Barbier type allylation-lactonisation process has been devised in order to afford the targeted molecular architectures. It is anticipated that aqueous medium plays the key role in allylation as well as in the subsequent lactonisation process for the diastereo-selective synthesis of these conjugates. It is believed that water drives the reaction pathway through dual activation, it increases the electrophilic character of formyl and ester functionalities and simultaneously enhances the nucleophilic potential of the hydroxyl group to facilitate the in situ intramolecular condensation. Importantly, during this synthetic strategy no column chromatographic purification was required at any stage.

Prioritization of anti-malarial hits from nature: chemo-informatic profiling of natural products with in vitro antiplasmodial activities and currently registered anti-malarial drugs

BACKGROUND

A large number of natural products have shown in vitro antiplasmodial activities. Early identification and prioritization of these natural products with potential for novel mechanism of action, desirable pharmacokinetics and likelihood for development into drugs is advantageous. Chemo-informatic profiling of these natural products were conducted and compared to currently registered anti-malarial drugs (CRAD).

METHODS

Natural products with in vitro antiplasmodial activities (NAA) were compiled from various sources. These natural products were sub-divided into four groups based on inhibitory concentration (IC50). Key molecular descriptors and physicochemical properties were computed for these compounds and analysis of variance used to assess statistical significance amongst the sets of compounds. Molecular similarity analysis, estimation of drug-likeness, in silico pharmacokinetic profiling, and exploration of structure-activity landscape were also carried out on these sets of compounds.

RESULTS

A total of 1040 natural products were selected and a total of 13 molecular descriptors were analysed. Significant differences were observed among the sub-groups of NAA and CRAD for at least 11 of the molecular descriptors, including number of hydrogen bond donors and acceptors, molecular weight, polar and hydrophobic surface areas, chiral centres, oxygen and nitrogen atoms, and shape index. The remaining molecular descriptors, including clogP, number of rotatable bonds and number of aromatic rings, did not show any significant difference when comparing the two compound sets. Molecular similarity and chemical space analysis identified natural products that were structurally diverse from CRAD. Prediction of the pharmacokinetic properties and drug-likeness of these natural products identified over 50% with desirable drug-like properties. Nearly 70% of all natural products were identified as potentially promiscuous compounds. Structure-activity landscape analysis highlighted compound pairs that form 'activity cliffs'. In all, prioritization strategies for the NAA were proposed.

CONCLUSIONS

Chemo-informatic profiling of NAA and CRAD have produced a wealth of information that may guide decisions and facilitate anti-malarial drug development from natural products. Articulation of the information provided within an interactive data-mining environment led to a prioritized list of NAA.

Exploration of Scaffolds from Natural Products with Antiplasmodial Activities, Currently Registered Antimalarial Drugs and Public Malarial Screen Data

In light of current resistance to antimalarial drugs, there is a need to discover new classes of antimalarial agents with unique mechanisms of action. Identification of unique scaffolds from natural products with in vitro antiplasmodial activities may be the starting point for such new classes of antimalarial agents. We therefore conducted scaffold diversity and comparison analysis of natural products with in vitro antiplasmodial activities (NAA), currently registered antimalarial drugs (CRAD) and malaria screen data from Medicine for Malaria Ventures (MMV). The scaffold diversity analyses on the three datasets were performed using scaffold counts and cumulative scaffold frequency plots. Scaffolds from the NAA were compared to those from CRAD and MMV. A Scaffold Tree was also generated for each of the datasets and the scaffold diversity of NAA was found to be higher than that of MMV. Among the NAA compounds, we identified unique scaffolds that were not contained in any of the other compound datasets. These scaffolds from NAA also possess desirable drug-like properties making them ideal starting points for antimalarial drug design considerations. The Scaffold Tree showed the preponderance of ring systems in NAA and identified virtual scaffolds, which may be potential bioactive compounds.

Metal-free 1,3-dipolar cycloaddition approach towards the regioselective synthesis of β-carboline and isoxazole based molecular hybrids

Nature has nourished β-carboline and isoxazole derivatives as privileged scaffolds and consequently they are ubiquitously found in alkaloids isolated from various sources.

In(OTf)3 catalysed an expeditious synthesis of β-carboline–imidazo[1,2-a]pyridine and imidazo[1,2-a]pyrazine conjugates

β-Carboline containing alkaloids are ubiquitously present in Nature, while an imidazo[1,2-a]pyridine nucleus is incorporated in various synthetic commercial drugs and biologically previliged moieties.

Enantiopure Indolizinoindolones with in vitro Activity against Blood- and Liver-Stage Malaria Parasites

Malaria continues to be a major cause of morbidity and mortality to this day, and resistance to drugs like chloroquine has led to an urgent need to discover novel chemical entities aimed at new targets. Here, we report the discovery of a novel class of potential antimalarial compounds containing an indolizinoindolone scaffold. These novel enantiopure indolizinoindolones were synthesized, in good-to-excellent yields and excellent diastereoselectivities, by cyclocondensation reaction of (S)- or (R)-tryptophanol and 2-acyl benzoic acids, followed by intramolecular α-amidoalkylation. Interestingly, we were able to synthesize for the first time 7,13b-cis indolizinoindolones in a two-step route. The novel compounds showed promising activity against erythrocytic stages of the human malaria parasite, Plasmodium falciparum, and liver stages of the rodent parasite Plasmodium berghei. In particular, an (S)-tryptophanol-derived isoindolinone was identified as a promising starting scaffold to search for novel antimalarials, combining excellent activity against both stages of the parasite's life cycle with low cytotoxicity and excellent metabolic and chemical stability in vitro.

Potential antimalarials from African natural products: A reviw

Malaria remains an overwhelming infectious disease with significant health challenges in African and other endemic countries globally. Resistance to antimalarial drugs has become one of the most momentous challenges to human health, and thus has necessitated the hunt for new and effective drugs. Consequently, few decades have witnessed a surfeit of research geared to validate the effectiveness of commonly used traditionally medicines against malaria fever. The present review work focuses on documenting natural products from African whose activity has been reported in vivo or in vitro against malaria parasite. Literature was collected using electronic search of published articles (Google Scholar, PubMed, Medline, Sciencedirect, and Science domain) that report on antiplasmodial activity of natural products from differernts Africa region. A total of 652 plant taxa from 146 families, 134 isolated antimalarial compounds from 39 plants species, 2 herbal formulations and 4 insect/products were found to be reported in literature from 1996 to 2015. Plants species from family Asteraceae (11.04%), Fababceae (8.128%), Euphorbiaceae (5.52%), Rubiaceas (5.52%), and Apocyanaceae (5.214%), have received more scientific validation than others. African natural products possess remarkable healing properties as revealed in the various citations as promising antimalarial agents. Some of these natural products from Africa demonstrate high, promising or low activities against Plasmodium parasite. This study also shows that natural products from Africa have a huge amount of novel antimalarial compounds that could serve as a leads for the development of new and effective antiplasmodial drugs. However, in a view of bridging the gap in knowledge, clinical validation of these natural products are of paramount importance.

Ethnopharmacological evaluation of medicinal plants used against malaria by quilombola communities from Oriximiná, Brazil

ETHNOPHARMACOLOGICAL RELEVANCE

Malaria is the most important parasitic disease in the world, including in the Amazon region, due to its high incidence. In addition, malaria is difficult to control because of the geographical characteristics of the endemic Amazon region. The quilombola communities of Oriximina, located in remote rainforest areas, have extensive experience with medicinal plants due to their close contact with and dependence on local biodiversity as a therapeutic resource. To search for active bioproducts against malaria, based on in vitro tests using blood culture-derived parasites and plants selected by an ethno-directed approach in traditional quilombola communities of Oriximiná, in the Amazon region of Brazil.

MATERIALS AND METHODS

Ethnobotanical data were collected from 35 informants in the quilombola communities of Oriximiná, Brazil, by a free-listing method for the survey of species locally indicated to be effective against malaria and related symptoms. Data were analyzed by salience index (S) and major use agreement. The activity of extracts from 11 plants, selected based on their Salience values (four plants with S>1; seven plants with S<0.1), was measured in vitro in cultures of W2 clone Plasmodium falciparum parasites resistant to chloroquine.

RESULTS

Thirty-five ethnospecies comprising 40 different plants belonging to 23 botanical families and 37 genera were listed as antimalarials by the ethno-directed approach. Among these, 11 species selected based on their S values were assayed against P. falciparum. The most active plant extracts, with an IC50 as low as 1.6μg/mL, were obtained from Aspidosperma rigidum (Apocynaceae), Bertholletia excelsa (Lecythidaceae) and Simaba cedron (Simaroubaceae), all of which displayed an S value>1.

CONCLUSION

A strong correlation between the consensus of the informants from quilombola communities living in a malaria endemic area and the salience index indicating antiplasmodial activity was observed, where the ethnospecies mostly cited to be effective against malaria produced the most active plant extracts in vitro. It was also evident from the data that these groups approached the treatment of malaria with an holistic view, making use of purgative, depurative, emetic and adaptogen plants.