Synthesis and activity of new triphenylphosphonium derivatives of betulin and betulinic acid against Schistosoma mansoni in vitro and in vivo

Therapeutic Potential of Natural Products in the Treatment of Schistosomiasis

It is estimated that 250 million people worldwide are affected by schistosomiasis. Disease transmission is related to the poor sanitation and hygiene habits that affect residents of impoverished regions in tropical and subtropical countries. The main species responsible for causing disease in humans are Schistosoma Mansoni, S. japonicum, and S. haematobium, each with different geographic distributions. Praziquantel is the drug predominantly used to treat this disease, which offers low effectiveness against immature and juvenile parasite forms. In addition, reports of drug resistance prompt the development of novel therapeutic approaches. Natural products represent an important source of new compounds, especially those obtained from plant sources. This review compiles data from several in vitro and in vivo studies evaluating various compounds and essential oils derived from plants with cercaricidal and molluscicidal activities against both juvenile and adult forms of the parasite. Finally, this review provides an important discussion on recent advances in molecular and computational tools deemed fundamental for more rapid and effective screening of new compounds, allowing for the optimization of time and resources.

Bifunctionalized Betulinic Acid Conjugates with C-3-Monodesmoside and C-28-Triphenylphosphonium Moieties with Increased Cancer Cell Targetability

A convenient synthesis is presented for a new class of bioactive bifunctionalized conjugates of lupane-type triterpenoids with triphenylphosphonium (TPP) and glycopyranosyl targeting moieties. The main synthesis steps include glycosylation of haloalkyl esters of the triterpene acid at the C-3 position by the imidate derivatives of glycopyranose followed by the product modification at the C-28 position with triphenylphosphine. The conjugates of betulinic acid (BetA) with TPP and d-glucose, l-rhamnose, or d-mannose moieties were thus synthesized as potential next-generation BetA-derived anticancer compounds. LC-MS/MS analysis in glucose-free physiological solution indicated that the glycosides showed better accumulation in PC-3 prostate cancer cells than both BetA and TPP-BetA conjugate, while the transporting effect of monosaccharide residues increased as follows: d-mannose < l-rhamnose ≈ d-glucose. At saturated concentrations, the glycosides caused a disturbing effect on mitochondria with a more drastic drop in transmembrane potential but weaker overproduction of mitochondrial reactive oxygen species (ROS) compared to TPP-BetA conjugate. Cytotoxicity of the glycosides in culture medium was comparable with or higher than that of the nonglycosylated conjugate, depending on the cancer cell line, whereas the compounds were less active toward primary fibroblasts. Glycosylation tended to increase pro-apoptotic and decrease pro-autophagic activities of the BetA derivatives. Cytotoxicity of the synthesized glycosides was considered in comparison with the summarized data on the natural and modified BetA glycosides. The results obtained are important for the development of bifunctionalized conjugates of triterpenoids with an increased cancer cell targetability.

Design, Synthesis and Preliminary Evaluation of the Cytotoxicity and Antibacterial Activity of Novel Triphenylphosphonium Derivatives of Betulin

For several decades, natural products have been widely researched and their native scaffolds are the basis for the design and synthesis of new potential therapeutic agents. Betulin is an interesting biologically attractive natural parent molecule with a high safety profile and can easily undergo a variety of structural modifications. Herein, we describe the synthesis of new molecular hybrids of betulin via covalent linkage with an alkyltriphenylphosphonium moiety. The proposed strategy enables the preparation of semi-synthetic derivatives (28-TPP^&oplus; BN and 3,28-bisTPP^&oplus; BN) from betulin through simple transformations in high yields. The obtained results showed that the presence of a lipophilic cation improved the solubility of the tested analogs compared to betulin, and increased their cytotoxicity. Among the triphenylphosphonium derivatives tested, analogs 7a (IC₅₀ of 5.56 µM) and 7b (IC₅₀ of 5.77 µM) demonstrated the highest cytotoxicity against the colorectal carcinoma cell line (HCT 116). TPP^&oplus;-conjugates with betulin showed antimicrobial properties against Gram-positive reference Staphylococcus aureus ATCC 25923 and Staphylococcus epidermidis ATCC 12228 bacteria, at a 200 µM concentration in water. Hence, the conjugation of betulin's parent backbone with a triphenylphosphonium moiety promotes transport through the hydrophobic barriers of the mitochondrial membrane, making it a promising strategy to improve the bioavailability of natural substances.

New quaternized pyridinium derivatives of betulin: Synthesis and evaluation of membranotropic properties on liposomes, pro- and eukaryotic cells, and isolated mitochondria

The present study describes the synthesis of pyridinium derivatives of betulin, including new 4-methyl- and 3,5-methyl-pyridinium analogs, their effect on artificial membrane systems (liposomes), cytotoxicity in models of prokaryotic (E. coli K-12 MG1655) and eukaryotic cells (rat thymocytes), as well as their effect on the functioning of membrane systems of rat liver mitochondria. We have shown that the presence of methyl groups in the pyridine ring of compounds determines the ability of the derivatives to effectively permeabilize the artificial membrane of lecithin liposomes for the fluorescent probe sulforhodamine B. The 4-methyl- and 3,5-methyl-pyridinium analogs inhibit the growth of E. coli K-12 MG1655 and, at the same time, did not have a cytotoxic effect on rat thymocytes. However, in the latter case, we noted a decrease in the mitochondrial potential of cells. The studied compounds reduced the functional activity of mitochondria, suppressing the activity of complexes of the respiratory chain and reducing the membrane potential. In addition, compounds containing methyl groups in the p- and m-positions of the pyridine ring were also able to permeabilize the inner membrane of mitochondria, causing them to swell. In this case, the most lipophilic compound containing two methyl substituents at the m-position of the pyridine fragment was most effective and had a protonophore effect on mitochondria. The paper discusses the dependence of the membranotropic and biological actions of the quaternized pyridine derivatives of betulin on their structure and lipophilicity.

Molecular Structure, In Vitro Anticancer Study and Molecular Docking of New Phosphate Derivatives of Betulin

A series of 30-diethylphosphate derivatives of betulin were synthesized and evaluated for their in vitro cytotoxic activity against human cancer cell lines, such as amelanotic melanoma (C-32), glioblastoma (SNB-19), and two lines of breast cancer (T47D, MDA-MB-231). The molecular structure and activities of the new compounds were also compared with their 29-phosphonate analogs. Compounds 7a and 7b showed the highest activity against C-32 and SNB-19 cell lines. The IC₅₀ values for 7a were 2.15 and 0.91 μM, and, for 7b, they were 0.76 and 0.8 μM for the C-32 and SNB-19 lines, respectively. The most potent compounds, 7a and 7b, were tested for their effects on markers of apoptosis, such as H3, TP53, BAX, and BCL-2. For the whole series of phosphate derivatives, a lipophilicity study was performed, and the ADME parameters were calculated. The most active products were docked to the active site of the EGFR protein. The relative binding affinity of selected phosphate betulin derivatives toward EGFR was compared with standard erlotinib on the basis of ChemScore and K_DEEP score. Positively, all derivatives docked inside the cavity and showed significant interactions. Moreover, a molecular dynamics study also reveals that ligands 7a,b form stable complexes and the plateau phase started after 7 ns.

In vitro activities of crude extracts and triterpenoid constituents of Dichapetalum crassifolium Chodat against clinical isolates of Schistosoma haematobium

Dichapetalum crassifolium Chodat (Dichapetalaceae) is widely distributed in Africa, Tropical Asia and Latin America. As part of our quest for potential bioactive lead compounds for various neglected tropical diseases, we report the anti-schistosomal potential of the crude extracts and chemical constituents of the stems and roots of Dichapetalum crassifolium. Column chromatography of extracts of the stems and roots led to the isolation and identification of three oleanane-type triterpenoids, friedelan-3β-ol (1), friedelan-3-one (2), and maslinic acid (3); the ursane-type tritepenoid, pomolic acid (4) and the dammarane-type tetracyclic triterpenoids, dichapetalin A (5) and dichapetalin M (6). Dichapetalin A was isolated from only the roots. Isolated compounds were identified by comparison of their physico-chemical and spectral data with published data. The highest in vitro anti-schistosomal activity (IC₅₀) of the crude extracts against clinical isolates of Schistosoma haematobium (Bilharz 1852) was 248.6 μg/ml for the ethyl acetate extract of the root while dichapetalin A gave the highest activity at 151.1 μg/ml among the compounds compared with the 15.5 μg/ml for the standard drug, praziquantel. The rest of the compounds showed activities in the order 177.9, 191.0, and 378.1 μg/ml respectively for mixture of β-sitosterol/stigmasterol, dichapetalin M and friedelan-3-one. The least active extract was the methanol extract of the stem (893.7 μg/ml). The constituents of D. crassifolium showed activity against the S. haematobium that are below praziquantel. It is envisaged that the presence of multiple layers and the minute sizes of pores in the egg shells, may preclude penetration of eggs by the compounds.

Effect of a newly synthesized quinoline-based compound (PPQ-8) on murine schistosomiasis mansoni

Schistosomiasis represents a public health problem and praziquantel is the only drug used for treatment of all forms of the disease. Thus, the development of new anti-schistosomal agents is of utmost importance to increase the effectiveness, reduce side effects and delay the emergence of resistance. The present study was conducted to report the therapeutic efficacy of PPQ-8, a new synthetic quinoline-based compound against Schistosoma mansoni. Mice were treated with PPQ-8 at day 49 post infection using two treatment regimens (20 and 40 mg/kg). Significant reductions were recorded in hepatic (62.9% and 83.6%) and intestinal tissue egg load (57.4% and 73.5%), granuloma count (75.4% and 89.1%) and diameter (26.2% and 47.3%), in response to the drug regimens, respectively. In addition, both treatment regimens induced significant decrease in liver (23.3% and 32.8%) and spleen (37.5% and 45.3%) indices. Also, there were significant reductions in mature ova, total worm and female count, which were more prominent with the higher dose. The reduction in the level of nitric oxide in the liver by both therapeutic regimens to 22.5% and 47.2% indicates the anti-oxidant activity of PPQ-8. Bright field microscopic examination of worms recovered from infected and PPQ-8-treated mice showed nearly empty intestinal caeca with no observable changes in the tegument. Our findings hold promise for the development of a novel anti-schistosomal drug using PPQ-8, but further in vitro and in vivo studies are needed to elucidate the possible mechanism/s of action and to study the effect of PPQ-8 on other human schistosomes.

One-pot Synthesis of Betulin Triterpenoid Quaternized Pyridine Derivatives and their Antimicrobial Activity

Background:

A wide range of biological activity, relatively low toxicity and multiple pharmacological effects of triterpenoids are major advantages of these compounds in the prevention and treatment of various diseases. They include the lupane- type triterpenoids that proved to be a promising platform for the synthesis of analogs with a wide range of biological activities, including anti-inflammatory, antitumor, antiparasitic and antiviral properties. The main disadvantage complicating the use of all known derivatives of lupane acids in medical practice is low bioavailability associated with poor solubility in biologic fluids, limiting their effective interaction with the biological targets.

Objective:

The objective of this study is the synthesis of new amphiphilic betulin derivatives on the base of pyridinium salts with antifungal and antibacterial activity.

Methods:

In this study we have developed an effective one-pot method for the preparation of new quaternized pyridine derivatives 4-6 of the betulinic series based on the reaction of the initial triterpenes 1-3 with the Tempo+Br3 - reagent in the pyridine. The synthesized and initial compounds were tested for their antimicrobial and antifungal activity.

Results:

The data presented in this document indicate that all synthesized compounds 4-6 exhibited high activity against both gram-positive Staphylococcus aureus bacteria and gram-negative Pseudomonas aeruginosa strains, as well as Candida albicans and Cryptococcus neoformans fungi with the >90% coverage of the inhibition zone. The best result in a series of compounds 4-6 was found for the derivative 6 at the minimum inhibitory concentration of 1 µg/ml against S. aureus bacteria, C. albicans and C. neoformans fungi at the concentration of 8 µg/ml.

Conclusion:

Thus, we have demonstrated the first example of the pyridine quaternization using the betulin triterpenoids as the lipophilic substrates and Tempo+Br3 - cation. The obtained quaternized pyridine analogs of betulin triterpenes showed high antibacterial and antifungal activity in comparison with the initial compounds.

Triphenylphosphonium Analogues of Betulin and Betulinic Acid with Biological Activity: A Comprehensive Review

Naturally occurring pentacyclic lupane triterpenoids such as betulin (1) or betulinic acid (2) and their synthetic derivatives display a broad spectrum of biological activities and, therefore, have been the subject of great interest. However, the use of these compounds as potential therapeutic agents is limited by their low bioavailability, high hydrophobicity, and insufficient intracellular accumulation. In this context, research on modifications of the parent structures that will improve their pharmacokinetic properties is particularly important. In the past few years, methods of synthesis as well as cytotoxic and antiparasitic properties of a series of lupane triterpenoids modified by introducing one or two triphenylphosphonium moieties at the C-2, C-3, C-28, or C-30 positions by carbon-carbon or ester bonds have been described. The presence of triphenylphosphonium groups affects not only physical properties but also the mechanism of action of a potential drug. This review summarizes published findings on synthetic methods and biological properties of the triphenylphosphonium derivatives of betulin and betulinic acid.

Betulin and its derivatives as novel compounds with different pharmacological effects

Betulin (B) and Betulinic acid (BA) are natural pentacyclic lupane-structure triterpenoids which possess a wide range of pharmacological activities. Recent evidence indicates that B and BA have several properties useful for the treatment of metabolic disorders, infectious diseases, cardiovascular disorders, and neurological disorders. In the current review, we discuss B and BA structures and derivatives and then comprehensively explain their pharmacological effects in relation to various diseases. We also explain antiviral, antibacterial and anti-cancer effects of B and BA. Finally, we discuss the delivery methods, in which these compounds most effectively target different systems.

Recent Developments in the Functionalization of Betulinic Acid and Its Natural Analogues: A Route to New Bioactive Compounds

Betulinic acid (BA) and its natural analogues betulin (BN), betulonic (BoA), and 23-hydroxybetulinic (HBA) acids are lupane-type pentacyclic triterpenoids. They are present in many plants and display important biological activities. This review focuses on the chemical transformations used to functionalize BA/BN/BoA/HBA in order to obtain new derivatives with improved biological activity, covering the period since 2013 to 2018. It is divided by the main chemical transformations reported in the literature, including amination, esterification, alkylation, sulfonation, copper(I)-catalyzed alkyne-azide cycloaddition, palladium-catalyzed cross-coupling, hydroxylation, and aldol condensation reactions. In addition, the synthesis of heterocycle-fused BA/HBA derivatives and polymer‒BA conjugates are also addressed. The new derivatives are mainly used as antitumor agents, but there are other biological applications such as antimalarial activity, drug delivery, bioimaging, among others.

Neuroprotective Effects of Betulin in Pharmacological and Transgenic Caenorhabditis elegans Models of Parkinson's Disease

Parkinson’s disease (PD) is the second most common degenerative disorder of the central nervous system in the elderly. It is characterized by progressive loss of dopaminergic neurons in the substantia nigra pars compacta, as well as by motor dysfunction. Although the causes of PD are not well understood, aggregation of α-synuclein (α-syn) in neurons contributes to this disease. Current therapeutics for PD provides satisfactory symptom relief but not a cure. Treatment strategies include attempts to identify new drugs that will prevent or arrest the progressive course of PD by correcting disease-specific pathogenic process. Betulin is derived from the bark of birch trees and possesses anticancer, antimicrobial, and anti-inflammatory properties. The aim of the present study was to evaluate the potential for betulin to ameliorate PD features in Caenorhabditis elegans (C. elegans) models. We demonstrated that betulin diminished α-syn accumulation in the transgenic C. elegans model. Betulin also reduced 6-hydroxydopamine-induced dopaminergic neuron degeneration, reduced food-sensing behavioral abnormalities, and reversed life-span decreases in a pharmacological C. elegans model. Moreover, we found that the enhancement of proteasomes activity by promoting rpn1 expression and downregulation of the apoptosis pathway gene, egl-1, may be the molecular mechanism for betulin-mediated protection against PD pathology. Together, these findings support betulin as a possible treatment for PD and encourage further investigations of betulin as an antineurodegenerative agent.

Combination of betulinic acid with diazen-1-ium-1,2-diolate nitric oxide moiety donating a novel anticancer candidate

Background

Betulinic acid (BA) is a complex lupane triterpenoid with unique antineoplastic activity. However, its antiproliferative activity is far from satisfaction. In order to improve its anticancer efficacy, betulinic acid was conjugated with a nitric oxide (NO)-releasing moiety to get a novel hybrid, BA-78.

Methods

The antiproliferative activity of BA-78 against 6 cell lines and the ability of releasing nitric oxide were determined. The pro-apoptosis mechanism of BA-78 was investigated as well.

Results

BA-78 exhibited time-dependent release of NO, and it displayed higher antiproliferative potential than BA through increasing apoptosis and inducing cell cycle arrest at G1 phase. Western blotting results showed that BA-78 increased the expression of Bax, Bid, Bad and cytochrome C and reduced the level of anti-apoptosis proteins including Bcl-2 and Bcl-xl.

Conclusion

Our study revealed that novel compound BA-78, possessing betulinic acid and nitric oxide (NO)-releasing moiety, could be developed as an antitumor agent.

Antischistosomal agents: state of art and perspectives

Praziquantel has remained the drug of choice for schistosomiasis chemotherapy for almost 40 years. The pressing need to develop a new antischistosomal drug may necessitate exploring and filtering chemotherapeutic history to search for the most promising ones. In this context, this review attempts to summarize all progress made in schistosomiasis chemotherapy from the early 20th century (mid-1910s) to 2016. We gathered almost 100 compounds providing information on therapeutic action, specifically covering at least first in vivo studies in animal model and in vitro. Pharmacokinetic and toxicity profiles of antischistosomal agents were also described. Preclinical studies indicate a handful of promising future candidates.

Schistosomiasis: Drugs used and treatment strategies

Neglected tropical diseases (NTDs) affect millions of people in different geographic regions, especially the poorest and most vulnerable. Currently NTDs are prevalent in 149 countries, seventeen of these neglected tropical parasitic diseases are classified as endemic. One of the most important of these diseases is schistosomiasis, also known as bilharzia, a disease caused by the genus Schistosoma. It presents several species, such as Schistosoma haematobium, Schistosoma japonicum and Schistosoma mansoni, the latter being responsible for parasitosis in Brazil. Contamination occurs through exposure to contaminated water in the endemic region. This parasitosis is characterized by being initially asymptomatic, but it is able to evolve into more severe clinical forms, potentially causing death. Globally, more than 200 million people are infected with one of three Schistosome species, including an estimated 40 million women of reproductive age. In Brazil, about 12 million children require preventive chemotherapy with anthelmintic. However, according to the World Health Organization (WHO), only about 15% of the at-risk children receive regular treatment. The lack of investment by the pharmaceutical industry for the development and/or improvement of new pharmaceutical forms, mainly aimed at the pediatric public, is a great challenge. Currently, the main forms of treatment used for schistosomiasis are praziquantel (PZQ) and oxaminiquine (OXA). PZQ is the drug of choice because it presents as a high-spectrum anthelmintic, used in the treatment of all known species of schistosomiasis and some species of cestodes and trematodes. OXA, however, is not active against the three Schistosome species. This work presents a literature review regarding schistosomiasis. It addresses points such as available treatments, the role of the pharmaceutical industry against neglected diseases, and perspectives for treatment.

Controlling schistosomiasis with praziquantel: How much longer without a viable alternative?

The current approach of morbidity control of schistosomiasis, a helminth disease of poverty with considerable public health and socioeconomic impact, is based on preventive chemotherapy with praziquantel. There is a pressing need for new drugs against this disease whose control entirely depends on this single drug that has been widely used over the past 40 years. We argue that a broader anthelminthic approach supplementing praziquantel with new antischistosomals targeting different parasite development stages would not only increase efficacy but also reduce the risk for drug resistance. Repositioning drugs already approved for other diseases provides a shortcut to clinical trials, as it is expected that such drugs rapidly pass the regulatory authorities. The antischistosomal properties of antimalarial drugs (e.g., semisynthetic artemisinins, synthetic trioxolanes, trioxaquines and mefloquine) and of drugs being developed or registered for other purposes (e.g., moxidectin and miltefosin), administered alone or in combination with praziquantel, have been tested in the laboratory and clinical trials. Another avenue to follow is the continued search for new antischistosomal properties in plants. Here, we summarise recent progress made in schistosomiasis chemotherapy, placing particular emphasis on repositioning of existing drugs against schistosomiasis.

Antiparasitic evaluation of betulinic acid derivatives reveals effective and selective anti-Trypanosoma cruzi inhibitors

Betulinic acid is a pentacyclic triterpenoid with several biological properties already described, including antiparasitic activity. Here, the anti-Trypanosoma cruzi activity of betulinic acid and its semi-synthetic amide derivatives (BA1-BA8) was investigated. The anti-Trypanosoma cruzi activity and selectivity were enhanced in semi-synthetic derivatives, specially on derivatives BA5, BA6 and BA8. To understand the mechanism of action underlying betulinic acid anti-T. cruzi activity, we investigated ultrastructural changes by electron microscopy. Ultrastructural studies showed that trypomastigotes incubated with BA5 had membrane blebling, flagella retraction, atypical cytoplasmic vacuoles and Golgi cisternae dilatation. Flow cytometry analysis showed that parasite death is mainly caused by necrosis. Treatment with derivatives BA5, BA6 or BA8 reduced the invasion process, as well as intracellular parasite development in host cells, with a potency and selectivity similar to that observed in benznidazole-treated cells. More importantly, the combination of BA5 and benznidazole revealed synergistic effects on trypomastigote and amastigote forms of T. cruzi. In conclusion, we demonstrated that BA5 compound is an effective and selective anti-T. cruzi agent.

Ameliorative effect of betulin from Betula platyphylla bark on scopolamine-induced amnesic mice

Alzheimer’s disease (AD) is a neurodegenerative disease induced by cholinergic neuron damage or amyloid-beta aggregation in the basal forebrain region and resulting in cognitive disorder. We previously reported on the neuroprotective effects of Betula platyphylla bark (BPB) in an amyloid-beta-induced amnesic mouse model. In this study, we obtained a cognitive-enhancing compound by assessing results using a scopolamine-induced amnesic mouse model. Our results show that oral treatment of mice with BPB and betulin significantly ameliorated scopolamine-induced memory deficits in both passive avoidance and Y-maze tests. In the Morris water maze test, administration of BPB and betulin significantly improved memory and cognitive function indicating the formation of working and reference memories in treated mice. Moreover, betulin significantly increased glutathione content in mouse hippocampus, and the increase was greater than that from betulinic acid treatment. We conclude that BPB and its active component betulin have potential as therapeutic, cognitive enhancer in AD.

Trypanocidal action of bisphosphonium salts through a mitochondrial target in bloodstream form Trypanosoma brucei

Lipophilic bisphosphonium salts are among the most promising antiprotozoal leads currently under investigation. As part of their preclinical evaluation we here report on their mode of action against African trypanosomes, the etiological agents of sleeping sickness. The bisphosphonium compounds CD38 and AHI-9 exhibited rapid inhibition of Trypanosoma brucei growth, apparently the result of cell cycle arrest that blocked the replication of mitochondrial DNA, contained in the kinetoplast, thereby preventing the initiation of S-phase. Incubation with either compound led to a rapid reduction in mitochondrial membrane potential, and ATP levels decreased by approximately 50% within 1 h. Between 4 and 8 h, cellular calcium levels increased, consistent with release from the depolarized mitochondria. Within the mitochondria, the Succinate Dehydrogenase complex (SDH) was investigated as a target for bisphosphonium salts, but while its subunit 1 (SDH1) was present at low levels in the bloodstream form trypanosomes, the assembled complex was hardly detectable. RNAi knockdown of the SDH1 subunit produced no growth phenotype, either in bloodstream or in the procyclic (insect) forms and we conclude that in trypanosomes SDH is not the target for bisphosphonium salts. Instead, the compounds inhibited ATP production in intact mitochondria, as well as the purified F₁ ATPase, to a level that was similar to 1 mM azide. Co-incubation with azide and bisphosphonium compounds did not inhibit ATPase activity more than either product alone. The results show that, in T. brucei, bisphosphonium compounds do not principally act on succinate dehydrogenase but on the mitochondrial F_oF₁ ATPase.

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Bisphosphonium salts display highly promising antiprotozoal activity.

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It has been reported that, in Leishmania, they act on the mitochondrial SDH complex.

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We show that in Trypanosoma brucei SDH is not essential and not the drug target.

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Instead, we present strong evidence that the F1F0 ATPase is the target.

Natural products with antischistosomal activity

In recent years, natural product groups have been gaining prominence as possible sources of new drugs for schistosomiasis. This review attempts to update the antischistosomal natural compounds, or natural product-derived compounds, from the mid-1980s. Some of the main metabolites obtained from plants (e.g., terpenes, alkaloids, phenolic compounds and peptides) with in vitro and/or in vivo antischistosomal properties are discussed. Less thoroughly, due to scarcity of data in the literature, molecules from animals (e.g., peptides) are also described. Special mention of the anthelmintic activity against different parasitic stages of schistosomes is made; the mechanism of action of most of the metabolites is discussed, and a number of bioassay procedures are listed.