Antimalarial Activities of Alkyl Cyclohexenone Derivatives Isolated from the Leaves of Poupartia borbonica

Undescribed Cyclohexene and Benzofuran Alkenyl Derivatives from Choerospondias axillaris, a Potential Hypoglycemic Fruit

The fruit of Choerospondias axillaris (Anacardiaceae), known as south wild jujube in China, has been consumed widely in several regions of the world to produce fruit pastille and leathers, juice, jam, and candy. A comprehensive chemical study on the fresh fruits led to the isolation and identification of 18 compounds, including 7 new (1-7) and 11 known (8-18) comprised of 5 alkenyl (cyclohexenols and cyclohexenones) derivatives (1-5), 3 benzofuran derivatives (6-8), 6 flavonoids (9-14) and 4 lignans (15-18). Their structures were elucidated by extensive spectroscopic analysis. The known lignans 15-18 were isolated from the genus Choerospondias for the first time. Most of the isolates exhibited significant inhibitory activity on α-glucosidase with IC50 values from 2.26 ± 0.06 to 43.9 ± 0.96 μM. Molecular docking experiments strongly supported the potent α-glucosidase inhibitory activity. The results indicated that C. axillaris fruits could be an excellent source of functional foods that acquire potential hypoglycemic bioactive components.

Access to Functionalized Cyclohex-2-enones from a Multicomponent Cascade Reaction of Readily Available Alkynes, Ketones, and Ethyl Acetoacetate

The synthesis of cyclohex-2-enone derivatives is a topic of current interest in organic chemistry. A novel three-component cascade reaction of alkynes with ketones and ethyl acetoacetate has been uncovered. This process provides di- and trisubstituted cyclohex-2-enones in good yields with excellent functional group tolerance. A variety of terminal alkynes and a wide range of aryl, alkyl, and cyclic ketones are viable in this transformation. Successful scale-up preparation and synthetic transformations have demonstrated the potential of this simple operating protocol.

Poly(N-methyl-N-vinylacetamide): A Strong Alternative to PEG for Lipid-Based Nanocarriers Delivering siRNA

Lipid-based nanocarriers have demonstrated high interest in delivering genetic material, exemplified by the success of Onpattro and COVID-19 vaccines. While PEGylation imparts stealth properties, it hampers cellular uptake and endosomal escape, and may trigger adverse reactions like accelerated blood clearance (ABC) and hypersensitivity reactions (HSR). This work highlights the great potential of amphiphilic poly(N-methyl-N-vinylacetamide) (PNMVA) derivatives as alternatives to lipid-PEG for siRNA delivery. PNMVA compounds with different degrees of polymerization and hydrophobic segments, are synthesized. Among them, DSPE (1,2-distearoyl-sn-glycero-3-phosphoethanolamine)-PNMVA efficiently integrates into lipoplexes and LNP membranes and prevents protein corona formation around these lipid carriers, exhibiting stealth properties comparable to DSPE-PEG. However, unlike DSPE-PEG, DSPE-PNMVA24 shows no adverse impact on lipoplexes cell uptake and endosomal escape. In in vivo study with mice, DSPE-PNMVA24 lipoplexes demonstrate no liver accumulation, indicating good stealth properties, extended circulation time after a second dose, reduced immunological reaction, and no systemic pro-inflammatory response. Safety of DSPE-PNMVA24 is confirmed at the cellular level and in animal models of zebrafish and mice. Overall, DSPE-PNMVA is an advantageous substitute to DSPE-PEG for siRNA delivery, offering comparable stealth and toxicity properties while improving efficacy of the lipid-based carriers by minimizing the dilemma effect and reducing immunological reactions, meaning no ABC or HSR effects.

Stereospecific Synthesis of Cyclohexenone Acids by [3,3]-Sigmatropic Rearrangement Route

Herein we report a modular synthetic method for the preparation of diaryl-substituted cyclohexenone acids starting from phenyl pyruvate and suitable enones. When the reaction is carried out in alkaline tert-butanol or toluene solutions in microwave-assisted conditions mainly anti configuration products are obtained with up to 86% isolated yield. However, when the reaction is carried out in alkaline water, a mixture of products with anti and syn conformations is obtained with up to 98% overall isolated yield. Mechanistically the product with anti conformation forms by a hemiketal-oxy-Cope type [3,3]-sigmatropic rearrangement-intramolecular aldol condensation route and syn product by an intermolecular aldol condensation-electrocyclization (disrotatory type) route.

Poly(vinyl pyrrolidone) derivatives as PEG alternatives for stealth, non-toxic and less immunogenic siRNA-containing lipoplex delivery

The recent approval of Onpattro® and COVID-19 vaccines has highlighted the value of lipid nanoparticles (LNPs) for the delivery of genetic material. If it is known that PEGylation is crucial to confer stealth properties to LNPs, it is also known that PEGylation is responsible for the decrease of the cellular uptake and endosomal escape and for the production of anti-PEG antibodies inducing accelerated blood clearance (ABC) and hypersensitivity reactions. Today, the development of PEG alternatives is crucial. Poly(N-vinyl pyrrolidone) (PNVP) has shown promising results for liposome decoration but has never been tested for the delivery of nucleic acids. Our aim is to develop a series of amphiphilic PNVP compounds to replace lipids-PEG for the post-insertion of lipoplexes dedicated to siRNA delivery. PNVP compounds with different degrees of polymerization and hydrophobic segments, such as octadecyl, dioctadecyl and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE), were generated. Based on the physicochemical properties and the efficiency to reduce protein corona formation, we showed that the DSPE segment is essential for the integration into the lipoplexes. Lipoplexes post-grafted with 15% DSPE-PNVP30 resulted in gene silencing efficiency close to that of lipoplexes grafted with 15% DSPE-PEG. Finally, an in vivo study in mice confirmed the stealth properties of DSPE-PNVP30 lipoplexes as well as a lower immune response ABC effect compared to DSPE-PEG lipoplexes. Furthermore, we showed a lower immune response after the second injection with DSPE-PNVP30 lipoplexes compared to DSPE-PEG lipoplexes. All these observations suggest that DSPE-PNVP30 appears to be a promising alternative to PEG, with no toxicity, good stealth properties and lower immunological response.

Dimeric polyphenols to pave the way for new antimalarial drugs

Because of the threat of resistant Plasmodium sp., new orally active antimalarials are urgently needed. Inspired by the structure of ellagic acid, exhibiting potent in vivo and in vitro antiplasmodial effects, polyphenolic structures possessing a similar activity-safety profile were synthesized. Indeed, most exhibited a marked in vitro effect (IC50 < 4 μM) on resistant P. falciparum, without any detrimental effects reported during the toxicity assays (hemolysis, cytotoxicity, in vivo). In addition, they possessed a greater hydrosolubility (from 7 μM to 2.7 mM) compared to ellagic acid. Among them, 30 is the most promising for antimalarial purposes since it displayed a significant parasitaemia reduction after oral administration in mice (50 mg kg-1) compared to the orally ineffective ellagic acid. In conclusion, our investigations led to the identification of a promising scaffold, which could bring new insights for malaria treatment.

Bioactive Clerodane Diterpenoids from the Leaves of Casearia coriacea Vent

Casearia coriacea Vent., an endemic plant from the Mascarene Islands, was investigated following its antiplasmodial potentialities highlighted during a previous screening. Three clerodane diterpene compounds were isolated and identified as being responsible for the antiplasmodial activity of the leaves of the plant: caseamembrin T (1), corybulosin I (2), and isocaseamembrin E (3), which exhibited half maximal inhibitory concentrations (IC₅₀) of 0.25 to 0.51 µg/mL. These compounds were tested on two other parasites, Leishmania mexicana mexicana and Trypanosoma brucei brucei, to identify possible selectivity in one of them. Although these products possess both antileishmanial and antitrypanosomal properties, they displayed selectivity for the malaria parasite, with a selectivity index between 6 and 12 regarding antitrypanosomal activity and between 25 and 100 regarding antileishmanial activity. These compounds were tested on three cell lines, breast cancer cells MDA-MB-231, pulmonary adenocarcinoma cells A549, and pancreatic carcinoma cells PANC-1, to evaluate their selectivity towards Plasmodium. This has not enabled us to establish selectivity for Plasmodium, but has revealed the promising activity of compounds 1-3 (IC₅₀ < 2 µg/mL), particularly against pancreatic carcinoma cells (IC₅₀ < 1 µg/mL). The toxicity of the main compound, caseamembrin T (1), was then evaluated on zebrafish embryos to extend our cytotoxicity study to normal, non-cancerous cells. This highlighted the non-negligible toxicity of caseamembrin T (1).

Stereoselective N-Heterocyclic-Carbene-Catalyzed Formal [4 + 2] Cycloaddition: Access to Chiral Heterocyclic Cyclohexenones

The present study reports an asymmetric NHC-catalyzed formal [4 + 2] cycloaddition of heterocyclic alkenes containing a polarized double bond with an azolium-dienolate intermediate generated from α-bromo-α,β-unsaturated aldehydes without external oxidation of the Breslow intermediate. Heterocyclic cyclohexenones were produced in good isolated yields (typically about 90%) with good stereochemical outcomes (in most cases, dr > 20/1, and ee = 70-99%). The synthetic utility of the protocol was exemplified by the scope of heterocyclic alkenes.

Unveiling antiplasmodial alkaloids from a cumulative collection of Strychnos extracts by multi-informative molecular networks

Malaria, a disease known for thousands of years and caused by parasites of the Plasmodium genus, continues to cause many deaths throughout the world today, particularly due to the emergence of parasite resistance to the current therapeutic arsenal. Plants of the Strychnos genus, remarkable due to their multiple traditional uses as well as their alkaloid content, are promising candidates to develop new antimalarial treatments. Indeed, previous research on this plant group has shown promising (≤ 5 µg/ml) or good (between 5 and 15 µg/ml) antiplasmodial activities. Using the chloroquine-sensitive strain of Plasmodium falciparum (3D7), and artemisinin as positive control, a screening of antiplasmodial activities from 43 crude methanolic extracts from 28 species of the Strychnos genus was carried out in three independent assays. A total of 12 extracts had good (6 extracts) or promising (6 extracts) antiplasmodial activities. These results allowed both to confirm known activities but also to detect new ones. These extracts were then analyzed by HPLC-ESI(+)-Q/TOF, and the processed MS/MS data allowed to generate a molecular network in which the antiplasmodial activities were implemented as metadata. The exploration of the molecular network revealed the presence of alkaloids still unknown, and potentially active against malaria, in particular alkaloids close to usambarensine and its derivatives. This study shows that the emergence of molecular networking offers new leads for identifications of alkaloids from the Strychnos genus. The presence of unknown alkaloids potentially active against malaria confirms all the interest to continue in studying the Strychnos genus. Bioassay- and mass-guided fractionations as well as various dereplication tools would allow to identify and characterize these interesting alkaloids further.

Biological Activities of Some Isoquinoline Alkaloids from Fumaria schleicheri Soy. Will

Fumaria schleicheri Soy. Will. is a species belonging to the Papaveraceae family, being widespread in East-Central and Southern Europe. As with numerous other species of the genus, it is used in traditional medicine for the treatment of hepatobiliary and digestive disorders. The aim of the present study consisted of the evaluation of its alkaloid content and the assessment of its in vitro antioxidant, anti-cholinesterase and cytotoxic potential. Total alkaloid content in the composition of the species was quantified by a spectrophotometrical method and they were individually identified and quantified by HPLC-DAD. The antioxidant capacity was investigated by the DPPH and FRAP methods, while the anti-cholinesterase activity was assessed by an adapted Ellman's method. The in vitro cytotoxic activity was evaluated on BJ human fibroblasts and DLD-1 human colon adenocarcinoma cell lines. Results showed the presence of bicuculline, protopine, chelidonine, stylopine and sanguinarine, among which bicuculline, protopine, stylopine and sanguinarine were quantified, while the antioxidant and anti-cholinesterase assays showed valuable potentials. No cytotoxic effect was observed on BJ cell lines and selective cytotoxicity was expressed towards tumoral cells. In this context, F. schleicheri appears as an important medicinal species with significant potential of substitution with the officinal species.

Potential of Caffeic Acid Derivatives as Antimalarial Leads

Background:

Background Malaria remained one of the deadliest infectious diseases in 2021. Indeed, this infection, mostly caused by a protozoan called Plasmodium falciparum, is responsible for more than 200 million cases and around 400 000 related deaths annually, mainly in Africa. Despite the availability of efficient drugs, an increase of patients has occurred since 2015, which could be due to the development of resistances from the parasite, but also from its vectors, Anopheles mosquitoes. Consequently, it is necessary to search for new alternative treatments.

Methods:

Methods Polyphenols, and more precisely small phenolic acids, could represent a good starting point for new antimalarials. Indeed, these molecules, including caffeic acid (1), possess several pharmacological activities and an interesting pharmacokinetic profile. Therefore, we have developed several small derivatives of this scaffold to define the potential pharmacophore responsible for the antiplasmodial properties

Results:

Results A good to low activity on Plasmodium falciparum (IC50 = 16-241 µM) was observed, especially for the small ester derivatives (2-6). These molecules were good antiplasmodials compared to their mother compound (IC50 = 80 µM) and showed selectivity against human cells. These structures have also highlighted the need for catechol and carboxyl moieties in the anti-Plasmodium effect.

Conclusion:

Conclusion None of the synthetic caffeate derivatives reported here seemed sufficiently effective to become a potential antimalarial (IC50 < 1 µM). However, the significant increase of their efficacy on the malarial agent and the selectivity to human cells, highlighted their potential as new leads for future developments

Natural-Product-Based Solutions for Tropical Infectious Diseases

About half of the world's population and 80% of the world's biodiversity can be found in the tropics. Many diseases are specific to the tropics, with at least 41 diseases caused by endemic bacteria, viruses, parasites, and fungi. Such diseases are of increasing concern, as the geographic range of tropical diseases is expanding due to climate change, urbanization, change in agricultural practices, deforestation, and loss of biodiversity. While traditional medicines have been used for centuries in the treatment of tropical diseases, the active natural compounds within these medicines remain largely unknown. In this review, we describe infectious diseases specific to the tropics, including their causative pathogens, modes of transmission, recent major outbreaks, and geographic locations. We further review current treatments for these tropical diseases, carefully consider the biodiscovery potential of the tropical biome, and discuss a range of technologies being used for drug development from natural resources. We provide a list of natural products with antimicrobial activity, detailing the source organisms and their effectiveness as treatment. We discuss how technological advancements, such as next-generation sequencing, are driving high-throughput natural product screening pipelines to identify compounds with therapeutic properties. This review demonstrates the impact natural products from the vast tropical biome have in the treatment of tropical infectious diseases and how high-throughput technical capacity will accelerate this discovery process.

Cytotoxicity of Poupartone B, an Alkyl Cyclohexenone Derivative from Poupartia borbonica, against Human Cancer Cell Lines

Poupartia borbonica is an endemic tree from the Mascarene Islands that belongs to the Anacardiaceae family. The leaves of this plant were phytochemically studied previously, and isolated alkyl cyclohexenone derivatives, poupartones A - C, demonstrated antiplasmodial and antimalarial activities. In addition to their high potency against the Plasmodium sp., high toxicity on human cells was also displayed. The present study aims to investigate in more detail the cytotoxicity and pharmacological interest of poupartone B, one of the most abundant derivatives in the leaves of P. borbonica. For that purpose, real-time live-cell imaging of different human cancer cell lines and normal fibroblasts, treated or not treated with poupartone B, was performed. A potent inhibition of cell proliferation associated with the induction of cell death was observed. A detailed morphological analysis of different adherent cell lines exposed to high concentrations of poupartone B (1 - 2 µg/mL) demonstrated that this compound induced an array of cellular alterations, including a rapid retraction of cellular protrusions associated with cell rounding, massive cytoplasmic vacuolization, loss of plasma membrane integrity, and plasma membrane bubbling, ultimately leading to paraptosis-like cell death. The structure-activity relation of this class of compounds, their selective toxicity, and pharmacological potential are discussed.

Phomaligols F-I, polyoxygenated cyclohexenone derivatives from marine-derived fungus Aspergillus flavus BB1

By tracing the ¹³C NMR resonances for carbonyls and enols, four new oxidized phomaligol derivatives, phomaligols F-I (1-4), along with seven known compounds (5-11) were isolated from the culture of the fungus Aspergillus flavus BB1 isolated from the marine shellfish Meretrix meretrix collected on Hailing Island, Yangjiang, China. The chemical structures and the absolute configurations of the new compounds were elucidated by MS, NMR, ECD, optical rotation, and ¹³C NMR calculations. Compounds 1 and 2 represent the first examples of phomaligol derivatives that contain an unusual bicyclic skeleton. All isolated compounds were tested for their cytotoxic activity. Among them, sporogen-AO 1 (8) showed potent inhibitory activity against the cancer cell lines A549, H1299, SK-BR-3, and HCT116 with IC₅₀ values of 0.13, 0.78, 1.19, and 1.32 μM, respectively. Phomaligol G (2) displayed cytotoxic activity against the A549 and H1299 cell lines with IC₅₀ values of 46.86 and 51.87 μM respectively. Additionally, phomaligol H (3) demonstrated cytotoxic activity against the A549 cell line with an IC₅₀ value of 65.53 μM. Mechanistic studies of compound 8 showed that it induced apoptosis of HCT116 cells in a dose-dependent manner.

Polyhydroxybenzoic acid derivatives as potential new antimalarial agents

With more than 200 million cases and 400,000 related deaths, malaria remains one of the deadliest infectious diseases of 2021. Unfortunately, despite the availability of efficient treatments, we have observed an increase in people infected with malaria since 2015 (from 211 million in 2015 to 229 million in 2019). This trend could partially be due to the development of resistance to all the current drugs. Therefore, there is an urgent need for new alternatives. We have, thus, selected common natural scaffolds, polyhydroxybenzoic acids, and synthesized a library of derivatives to better understand the structure-activity relationships explaining their antiplasmodial effect. Only gallic acid derivatives showed a noticeable potential for further developments. Indeed, they showed a selective inhibitory effect on Plasmodium (IC₅₀ ~20 µM, SI > 5) often associated with interesting water solubility. Moreover, this has confirmed the critical importance of free phenolic functions (pyrogallol moiety) for the antimalarial effect. Methyl 4-benzoxy-3,5-dihydroxybenzoate (39) has, for the first time, been recognized as a potential lead for future research because of its marked inhibitory activity against Plasmodium falciparum and its significant hydrosolubility (3.72 mM).

Mechanistic evaluation of a novel cyclohexenone derivative's functionality against nociception and inflammation: An in-vitro, in-vivo and in-silico approach

The synthesis of a novel cyclohexanone derivative (CHD; Ethyl 6-(4-metohxyphenyl)-2-oxo-4-phenylcyclohexe-3-enecarboxylate) was described and the subsequent aim was to perform an in vitro, in vivo and in silico pharmacological evaluation as a putative anti-nociceptive and anti-inflammatory agent in mice. Initial in vitro studies revealed that CHD inhibited both cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) enzymes and it also reduced mRNA expression of COX-2 and the pro-inflammatory cytokines TNF-α and IL-1β. It was then shown that CHD dose dependently inhibited chemically induced tonic nociception in the abdominal constriction assay and also phasic thermal nociception (i.e. anti-nociception) in the hot plate and tail immersion tests in comparison with aspirin and tramadol respectively. The thermal test outcomes indicated a possible moderate centrally mediated anti-nociception which, in the case of the hot plate test, was pentylenetetrazole (PTZ) and naloxone reversible, implicating GABAergic and opioidergic mechanisms. CHD was also effective against both the neurogenic and inflammatory mediator phases induced in the formalin test and it also disclosed anti-inflammatory activity against the phlogistic agents, carrageenan, serotonin, histamine and xylene compared with standard drugs in edema volume tests. In silico studies indicated that CHD possessed preferential affinity for GABAA, opioid and COX-2 target sites and this was supported by molecular dynamic simulations where computation of free energy of binding also favored the formation of stable complexes with these sites. These findings suggest that CHD has prospective anti-nociceptive and anti-inflammatory properties, probably mediated through GABAergic and opioidergic interactions supplemented by COX-2 and 5-LOX enzyme inhibition in addition to reducing pro-inflammatory cytokine expression. CHD may therefore possess potentially beneficial therapeutic effectiveness in the management of inflammation and pain.

A critical review on the use of DP4+ in the structural elucidation of natural products: the good, the bad and the ugly. A practical guide

Covering: 2015 up to the end of 2020Even in the golden age of NMR, the number of natural products being incorrectly assigned is becoming larger every day. The use of quantum NMR calculations coupled with sophisticated data analysis provides ideal complementary tools to facilitate the elucidation process in challenging cases. Among the current computational methodologies to perform this task, the DP4+ probability is a popular and widely used method. This updated version of Goodman's DP4 synergistically combines NMR calculations at higher levels of theory with the Bayesian analysis of both scaled and unscaled data. Since its publication in late 2015, the use of DP4+ to solve controversial natural products has substantially grown, with several predictions being confirmed by total synthesis. To date, the structures of more than 200 natural products were determined with the aid of DP4+. However, all that glitters is not gold. Besides its intrinsic limitations, on many occasions it has been improperly used with potentially important consequences on the quality of the assignment. Herein we present a critical revision on how the scientific community has been using DP4+, exploring the strengths of the method and how to obtain optimal results from it. We also analyze the weaknesses of DP4+, and the paths to by-pass them to maximize the confidence in the structural elucidation.

Toxicological Evaluation of Novel Cyclohexenone Derivative in an Animal Model through Histopathological and Biochemical Techniques

Toxicity studies were conducted to provide safety data of potential drug candidates by determining lethal and toxic doses. This study was designed for pre-clinical evaluation of novel cyclohexenone derivative with respect to the acute and sub-acute toxicity along with the diabetogenic potential. Acute and sub-acute toxicity were assessed after intraperitoneal (i.p) injection of the investigational compound through selected doses for 21 days. This was followed by assessment of isolated body organs (liver, kidney, heart and pancreas) via biochemical indicators and histopathological techniques. No signs of toxicity were revealed in the study of acute toxicity. Similarly, a sub-acute toxicity study showed no significant difference in biochemical indicators on 11th and 21st days between treated and control groups. However, in blood urea nitrogen (BUN) and random blood glucose/sugar (RBS) values, significant differences were recorded. Histopathological evaluation of liver, kidney, pancreas and heart tissues revealed mild to severe changes in the form of steatosis, inflammation, fibrosis, necrosis and myofibrillary damages on 11th and 21st days of treatment. In conclusion, the median lethal dose of the tested compound was expected to be greater than 500 mg/kg. No significant change occurred in selected biomarkers, except BUN and RBS levels, but a histopathological study showed moderate toxic effect on liver, kidney, pancreas and heart tissues by the cyclohexenone derivative.

Phytochemical Investigation and Biological Activities of Lantana rhodesiensis

Lantana rhodesiensis Moldenke is a plant widely used to treat diseases, such as rheumatism, diabetes, and malaria in traditional medicine. To better understand the traditional uses of this plant, a phytochemical study was undertaken, revealing a higher proportion of polyphenols, including flavonoids in L. rhodesiensis leaf extract and moderate proportion in stem and root extracts. The antioxidant activity of the extracts was also determined using three different assays: the radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity, the FRAP method (Ferric-reducing antioxidant power) and the β-carotene bleaching test. The anti-malarial activity of each extract was also evaluated using asexual erythrocyte stages of Plasmodium falciparum, chloroquine-sensitive strain 3D7. The results showed that the leaf extract exhibited higher antioxidant and anti-malarial activities in comparison with the stem and root extracts, probably due to the presence of higher quantities of polyphenols including flavonoids in the leaves. A positive linear correlation was established between the phenolic compound content (total polyphenols including flavonoids and tannins; and total flavonoids) and the antioxidant activity of all extracts. Furthermore, four flavones were isolated from leaf dichloromethane and ethyl acetate fractions: a new flavone named rhodescine (5,6,3',5'-tetrahydroxy-7,4'-dimethoxyflavone) (1), 5-hydroxy-6,7,3',4',5'-pentamethoxyflavone (2), 5-hydroxy-6,7,3',4'-tetramethoxyflavone (3), and 5,6,3'-trihydroxy-7,4'-dimethoxyflavone (4). Their structures were elucidated by 1H, 13CNMR, COSY, HSQC, HMBC, and MS-EI spectral methods. Aside from compound 2, all other molecules were described for the first time in this plant species.

Seasonal Effect on the Chemical Composition, Insecticidal Properties and Other Biological Activities of Zanthoxylum leprieurii Guill. & Perr. Essential oils

This study focused, for the first time, on the evaluation of the seasonal effect on the chemical composition and biological activities of essential oils hydrodistillated from leaves, trunk bark and fruits of Zanthoxylum leprieurii (Z. leprieurii), a traditional medicinal wild plant growing in Côte d'Ivoire. The essential oils were obtained by hydrodistillation from fresh organs of Z. leprieurii growing on the same site over several months using a Clevenger-type apparatus and analyzed by gas chromatography-mass spectrometry (GC/MS). Leaf essential oils were dominated by tridecan-2-one (9.00 ± 0.02-36.80 ± 0.06%), (E)-β-ocimene (1.30 ± 0.50-23.57 ± 0.47%), β-caryophyllene (7.00 ± 1.02-19.85 ± 0.48%), dendrolasin (1.79 ± 0.08-16.40 ± 0.85%) and undecan-2-one (1.20 ± 0.03-8.51 ± 0.35%). Fruit essential oils were rich in β-myrcene (16.40 ± 0.91-48.27 ± 0.26%), citronellol (1.90 ± 0.02-28.24 ± 0.10%) and geranial (5.30 ± 0.53-12.50 ± 0.47%). Tridecan-2-one (45.26 ± 0.96-78.80 ± 0.55%), β-caryophyllene (1.80 ± 0.23-13.20 ± 0.33%), ?-humulene (4.30 ±1.09-12.73 ± 1.41%) and tridecan-2-ol (2.23 ± 0.17-10.10 ± 0.61%) were identified as major components of trunk bark oils. Statistical analyses of essential oil compositions showed that the variability mainly comes from the organs. Indeed, principal component analysis (PCA) and hierarchical cluster analysis (HCA) allowed us to cluster the samples into three groups, each one consisting of one different Z. leprieurii organ, showing that essential oils hydrodistillated from the different organs do not display the same chemical composition. However, significant differences in essential oil compositions for the same organ were highlighted during the studied period, showing the impact of the seasonal effect on essential oil compositions. Biological activities of the produced essential oils were also investigated. Essential oils exhibited high insecticidal activities against Sitophilus granarius, as well as antioxidant, anti-inflammatory and moderate anti-plasmodial properties.

Unraveling Plant Natural Chemical Diversity for Drug Discovery Purposes

The screening and testing of extracts against a variety of pharmacological targets in order to benefit from the immense natural chemical diversity is a concern in many laboratories worldwide. And several successes have been recorded in finding new actives in natural products, some of which have become new drugs or new sources of inspiration for drugs. But in view of the vast amount of research on the subject, it is surprising that not more drug candidates were found. In our view, it is fundamental to reflect upon the approaches of such drug discovery programs and the technical processes that are used, along with their inherent difficulties and biases. Based on an extensive survey of recent publications, we discuss the origin and the variety of natural chemical diversity as well as the strategies to having the potential to embrace this diversity. It seemed to us that some of the difficulties of the area could be related with the technical approaches that are used, so the present review begins with synthetizing some of the more used discovery strategies, exemplifying some key points, in order to address some of their limitations. It appears that one of the challenges of natural product-based drug discovery programs should be an easier access to renewable sources of plant-derived products. Maximizing the use of the data together with the exploration of chemical diversity while working on reasonable supply of natural product-based entities could be a way to answer this challenge. We suggested alternative ways to access and explore part of this chemical diversity with in vitro cultures. We also reinforced how important it was organizing and making available this worldwide knowledge in an "inventory" of natural products and their sources. And finally, we focused on strategies based on synthetic biology and syntheses that allow reaching industrial scale supply. Approaches based on the opportunities lying in untapped natural plant chemical diversity are also considered.

Using the Cancer Dependency Map to Identify the Mechanism of Action of a Cytotoxic Alkenyl Derivative from the Fruit of Choerospondias axillaris

An extract prepared from the fruit of Choerospondias axillaris exhibited differential cytotoxic effects when tested in a panel of pediatric cancer cell lines [Ewing sarcoma (A-673), rhabdomyosarcoma (SJCRH30), medulloblastoma (D283), and hepatoblastoma (Hep293TT)]. Bioassay-guided fractionation led to the purification of five new hydroquinone-based metabolites, choerosponols A-E (1-5), bearing unsaturated hydrocarbon chains. The structures of the natural products were determined using a combination of 1D and 2D NMR, HRESIMS, ECD spectroscopy, and Mosher ester analyses. The purified compounds were evaluated for their antiproliferative and cytotoxic activities, revealing that 1, which contains a benzofuran moiety, exhibited over 50-fold selective antiproliferative activity against Ewing sarcoma and medulloblastoma cells with growth inhibitory (GI50) values of 0.19 and 0.07 μM, respectively. The effects of 1 were evaluated in a larger panel of cancer cell lines, and these data were used in turn to interrogate the Project Achilles cancer dependency database, leading to the identification of the MCT1 transporter as a functional target of 1. These data highlight the utility of publicly available cancer dependency databases such as Project Achilles to facilitate the identification of the mechanisms of action of compounds with selective activities among cancer cell lines, which can be a major challenge in natural products drug discovery.

Antiplasmodial natural products: an update

Background

Malaria remains a significant public health challenge in regions of the world where it is endemic. An unprecedented decline in malaria incidences was recorded during the last decade due to the availability of effective control interventions, such as the deployment of artemisinin-based combination therapy and insecticide-treated nets. However, according to the World Health Organization, malaria is staging a comeback, in part due to the development of drug resistance. Therefore, there is an urgent need to discover new anti-malarial drugs. This article reviews the literature on natural products with antiplasmodial activity that was reported between 2010 and 2017.

Methods

Relevant literature was sourced by searching the major scientific databases, including Web of Science, ScienceDirect, Scopus, SciFinder, Pubmed, and Google Scholar, using appropriate keyword combinations.

Results and Discussion

A total of 1524 compounds from 397 relevant references, assayed against at least one strain of Plasmodium, were reported in the period under review. Out of these, 39% were described as new natural products, and 29% of the compounds had IC₅₀ ≤ 3.0 µM against at least one strain of Plasmodium. Several of these compounds have the potential to be developed into viable anti-malarial drugs. Also, some of these compounds could play a role in malaria eradication by targeting gametocytes. However, the research into natural products with potential for blocking the transmission of malaria is still in its infancy stage and needs to be vigorously pursued.

Flavonoid Analysis and Antioxidant Activities of the Bryonia alba L. Aerial Parts

Bryonia alba L. is the only Bryonia species found in Romanian flora, being known as a remedy for inflammatory pathologies or for its hepatoprotective and adaptogen activities. The present investigation studied the flavonoid composition and antioxidant activities of the aerial parts of this species. Flavonoid profile was evaluated by HPLC coupled with Diode Array Detection (DAD), while antioxidant capacity was assessed by various methods, testing different antioxidant mechanisms: DPPH (2,2-diphenyl-1-picrylhydrazyl), CUPRAC (cupric reducing antioxidant capacity), FRAP (ferric reducing ability of plasma), TEAC (Trolox equivalent antioxidant capacity), EPR (electron paramagnetic resonance method) and SNPAC (silver nanoparticles antioxidant capacity). Cytotoxicity was tested on human cancerous and healthy cell lines. Anti-plasmodial tests were performed on two strains of Plasmodium falciparum. Whole organism toxicity was assessed on zebrafish larvae. The HPLC-DAD analysis proved the presence of lutonarin, saponarin, isoorientin, and isovitexin as the major flavonoids in the composition of tested samples. Significant results were obtained for all antioxidant capacity assays. The cytotoxicity tests proved the absence of cellular and parasitic toxicity and these results were confirmed by the lack of toxicity on the zebrafish larvae model. This study proves a promising potential of the aerial parts of Bryonia alba L. as antioxidant agents.

Flavonoid composition, cellular antioxidant activity and (myelo)peroxidase inhibition of a Bryonia alba L. (Cucurbitaceae) leaves extract

OBJECTIVES

The aim of the present study consisted in the isolation of flavonoids from the leaves of Bryonia alba L. and evaluation of their antioxidant activity and inhibition on peroxidase-catalysed reactions.

METHODS

Flavonoids were isolated by preparative HPLC-DAD and their structures were elucidated by MS and NMR. Inhibitory effect was tested by the horseradish peroxidase and the myeloperoxidase assays. Cellular antioxidant assays consisted in testing the inhibitory activity on the reactive oxygen species released upon activation of neutrophils freshly isolated ex vivo from equine blood and of human monocytes-derived macrophages in vitro. Whole organism toxicity was assessed on zebrafish larvae.

KEY FINDINGS

Four flavonoids (lutonarin, saponarin, isoorientin and isovitexin) were isolated. The performed assays showed significant antioxidant activity and inhibition for the peroxidase-catalysed reactions. Absence of cellular and zebrafish toxicity was confirmed.

CONCLUSIONS

Bryonia alba L. leaves are particularly interesting for their flavonoids content and showed significant inhibitory effect on peroxidase-catalysed oxidation of substrates (Amplex Red and L012), as well as antioxidant/antiradical activity, proving that this species has a medicinal potential. Moreover, the present study highlights the absence of the toxicity of these leaves and offers though a novel perspective on the species, previously known as being toxic.

Antiplasmodial, anti-chikungunya virus and antioxidant activities of 64 endemic plants from the Mascarene Islands

Vector-borne diseases cause more than 1 million deaths annually. The research into new medicines is urgent, especially as there is currently no specific treatment. In this study, the authors have selected 64 endemic plants from the Mascarene Islands based on their endemism, their medicinal use and their registration in the French Pharmacopeia to evaluate the antiplasmodial, anti-chikungunya and antioxidant activities. The list of these 64 plants including their local name, population, data of collection and voucher number are available in the Supporting Information. Forty active extracts were identified from the 38 species: 22 responded positively to the antiplasmodial activity, 8 to the anti-chikungunya activity and 8 to the antioxidant activity. Six plants demonstrated high antiplasmodial activity (concentration inhibiting 50% of parasitic growth (IC₅₀) <5 µg/mL): Casearia coriaceae, Monimia rotundifolia, Poupartia borbonica, Psiadia retusa, Vernonia fimbrillifera and Zanthoxylum heterophyllum; and five showed high anti-chikungunya activity (IC₅₀<20 µg/mL): Aphloia theiformis, Stillingia lineata, Croton mauritianus, Indigofera ammoxylum, and Securinega durissima. Eight plants displayed an important antioxidant activity, with values of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP) or oxygen Radical Absorbance Capacity (ORAC) >2000 µM of Trolox equivalent per mg/mL of extract: Bertiera borbonica, Erythroxylon laurifolium, Erythroxylon sideroxyloides, I. ammoxylum, P. borbonica, Scolopia heterophylla, Sophora denudata, and Terminalia bentzoe. Some data obtained tend to corroborate the reported traditional use of the plant, such as Z. heterophyllum (antiplasmodial), A. theiformis (anti-chikungunya), and E. laurifolium (antioxidant).

G-Quadruplex Identification in the Genome of Protozoan Parasites Points to Naphthalene Diimide Ligands as New Antiparasitic Agents

G-quadruplexes (G4) are DNA secondary structures that take part in the regulation of gene expression. Putative G4 forming sequences (PQS) have been reported in mammals, yeast, bacteria, and viruses. Here, we present PQS searches on the genomes of T. brucei, L. major, and P. falciparum. We found telomeric sequences and new PQS motifs. Biophysical experiments showed that EBR1, a 29 nucleotide long highly repeated PQS in T. brucei, forms a stable G4 structure. G4 ligands based on carbohydrate conjugated naphthalene diimides (carb-NDIs) that bind G4’s including hTel could bind EBR1 with selectivity versus dsDNA. These ligands showed important antiparasitic activity. IC₅₀ values were in the nanomolar range against T. brucei with high selectivity against MRC-5 human cells. Confocal microscopy confirmed these ligands localize in the nucleus and kinetoplast of T. brucei suggesting they can reach their potential G4 targets. Cytotoxicity and zebrafish toxicity studies revealed sugar conjugation reduces intrinsic toxicity of NDIs.