Activity of the julocrotine, a glutarimide alkaloid from Croton pullei var. glabrior, on Leishmania (L.) amazonensis

Recent developments in the total synthesis of natural products using the Ugi multicomponent reactions as the key strategy

The total syntheses of selected natural products using different versions of the Ugi multicomponent reaction is reviewed on a case-by-case basis. The revision covers the period 2008-2023 and includes detailed descriptions of the synthetic sequences, the use of state-of-the-art chemical reagents and strategies, as well as the advantages and limitations of the transformation and some remedial solutions. Relevant data on the isolation and bioactivity of the different natural targets are also briefly provided. The examples clearly evidence the strategic importance of this transformation and its key role in the modern natural products synthetic chemistry toolbox. This methodology proved to be a valuable means for easily building molecular complexity and efficiently delivering step-economic syntheses even of intricate structures, with a promising future.

In Vitro Leishmanicidal Activity of Copaiba Oil and Kojic Acid Combination on the Protozoan Leishmania (Leishmania) amazonensis and Host Cell

(1) Background: Leishmaniasis refers to a group of anthropozoonotic diseases caused by Leishmania. The major chemotherapeutic agent used for its treatment is Glucantime®®, but the search continues for new compounds that are economically viable and act on the protozoan without causing damage to the host cell. As an alternative approach, this study used a combination of copaiba oil (CO) and kojic acid (KA) to determine their in vitro action on host cells, on the Leishmania (Leishmania) amazonensis protozoan and its interaction with macrophages. (2) Methods: In vitro culture, analysis of cytokine release and microscopy assays were performed. Statistical analysis was performed with ANOVA (GraphPad Prism). (3) Results: The combination did not induce cytotoxic effects on macrophages after treatment but promoted morphological changes in the protozoan, such as nuclear alterations (apoptotic characteristics), alterations in the cellular body and an increase in the number of electrodense structures and acidocalcisomes, observed mainly at the concentrations of CO20KA50 and CO30KA50 μg/mL. We observed reductions in the intracellular amastigote number and in the production of proinflammatory cytokines, such as IL-6 and TNF-α, after treatment with CO30KA at 50 µg/mL. (4) Conclusions: We report here, for the first time, that the combination of CO and KA may be a promising approach against Leishmania (Leishmania) amazonensis.

Neuroprotective potential of cinnamoyl derivatives against Parkinson's disease indicators in Drosophila melanogaster and in silico models

Parkinson's disease (PD) is a movement disorder resulting from the loss of dopaminergic neurons over time. While there is no cure for PD, available conventional therapies aid to manage the motor symptoms. Natural products (NPs) derived from plants are among the most potent alternative therapies for PD. This study explored the neuroprotective potential of selected cinnamoyl derivatives namely toussaintine A (1), E-toussaintine E (2), asperphenamate (3) and julocrotine (4) against PD indicators using rotenone-challenged Drosophila melanogaster and in silico models. The compounds were first assessed for their toxicity preceding treatment experiments. Adult flies (aged 1-4 days) were exposed to varying concentrations of the compounds for 7 days. During the experiment, the mortality of flies was observed, and the lethal concentration (LC₅₀) of each tested compound was determined. The LC₅₀ values were found to be 50.1, 55.6, 513.5, and 101.0 µM for compounds 1, 2, 3, and 4, respectively. For seven days, we exposed flies to 500 µM of rotenone and co-fed with a chosen dose of 40 µM of each test compound in the diet. Using a negative geotaxis test, rotenone-challenged flies exhibited compromised climbing ability in comparison to control flies, the condition that was reversed by the action of studied compounds. Rotenone exposure also elevated malondialdehyde levels in the brain tissues, as measured by lipid peroxidation, when compared to control flies. In flies exposed to rotenone and co-fed with the compounds, this effect was lessened. In flies exposed to rotenone, mRNA levels of antioxidant enzymes such as superoxide dismutase and catalase were raised but were normalized in flies treated with the investigated compounds. Moreover, in-silico studies examined the inhibitory ability of compounds 1-4 against selected PD molecular targets, revealing the strong power of toussaintine A (1) against Adenosine receptor 2 (A2AR) and monoamine oxidase B. Thus, our findings suggest that cinnamoyl derivatives have neuroprotective potential via reducing the oxidative burden and improving locomotor ability after toxin invectives. In particular, compound 1 at lower doses can simultaneously be a potential inhibitor of A2AR and an anti-oxidative mediator in the development of anti-PD agents.

The Search for Putative Hits in Combating Leishmaniasis: The Contributions of Natural Products Over the Last Decade

Despite advancements in the areas of omics and chemoinformatics, potent novel biotherapeutic molecules with new modes of actions are needed for leishmaniasis. The socioeconomic burden of leishmaniasis remains alarming in endemic regions. Currently, reports from existing endemic areas such as Nepal, Iran, Brazil, India, Sudan and Afghanistan, as well as newly affected countries such as Peru, Bolivia and Somalia indicate concerns of chemoresistance to the classical antimonial treatment. As a result, effective antileishmanial agents which are safe and affordable are urgently needed. Natural products from both flora and fauna have contributed immensely to chemotherapeutics and serve as vital sources of new chemical agents. This review focuses on a systematic cross-sectional view of all characterized anti-leishmanial compounds from natural sources over the last decade. Furthermore, IC50/EC50, cytotoxicity and suggested mechanisms of action of some of these natural products are provided. The natural product classification includes alkaloids, terpenes, terpenoids, and phenolics. The plethora of reported mechanisms involve calcium channel inhibition, immunomodulation and apoptosis. Making available enriched data pertaining to bioactivity and mechanisms of natural products complement current efforts geared towards unraveling potent leishmanicides of therapeutic relevance.

The Dichloromethane Fraction of Croton sonorae, A Plant Used in Sonoran Traditional Medicine, Affect Entamoeba histolytica Erythrophagocytosis and Gene Expression

Intestinal parasites are a global problem, mainly in developing countries. Obtaining information about plants and compounds that can combat gastrointestinal disorders and gastrointestinal symptoms is a fundamental first step in designing new treatment strategies. In this study, we analyzed the antiamoebic activity of the aerial part of Croton sonorae. The dichloromethane fraction of C. sonorae (CsDCMfx) contained flavonoids, terpenes, alkaloids, and glycosides. The ultrastructural morphology of the amoebae treated for 72 h with CsDCMfx was completely abnormal. CsDCMfx reduced erythrophagocytosis of trophozoites and the expression of genes involved in erythrocyte adhesion (gal/galnac lectin) and actin cytoskeleton rearrangement in the phagocytosis pathway (rho1 gtpase and formin1). Interestingly, CsDCMfx decreased the expression of genes involved in Entamoeba histolytica trophozoite pathogenesis, such as cysteine proteases (cp1, cp4, and cp5), sod, pfor, and enolase. These results showed that C. sonorae is a potential source of antiamoebic compounds.

Ethanolic extract of Croton blanchetianus Ball induces mitochondrial defects in Leishmania amazonensis promastigotes

Leishmaniasis is a neglected disease caused by Leishmania. Chemotherapy remains the mainstay for leishmaniasis control; however, available drugs fail to provide a parasitological cure, and are associated with high toxicity. Natural products are promising leads for the development of novel chemotherapeutics against leishmaniasis. This work investigated the leishmanicidal properties of ethanolic extract of Croton blanchetianus (EECb) on Leishmania infantum and Leishmania amazonensis, and found that EECb, rich in terpenic compounds, was active against promastigote and amastigote forms of both Leishmania species. Leishmania infantum promastigotes and amastigotes presented IC50 values of 208.6 and 8.8 μg/mL, respectively, whereas Leishmania amazonensis promastigotes and amastigotes presented IC50 values of 73.6 and 3.1 μg/mL, respectively. Promastigotes exposed to EECb (100 µg/mL) had their body cellular volume reduced and altered to a round shape, and the flagellum was duplicated, suggesting that EECb may interfere with the process of cytokinesis, which could be the cause of the decline in the parasite multiplication rate. Regarding possible EECb targets, a marked depolarization of the mitochondrial membrane potential was observed. No cytotoxic effects of EECb were observed in murine macrophages at concentrations below 60 µg/mL, and the CC50 obtained was 83.8 µg/mL. Thus, the present results indicated that EECb had effective and selective effects against Leishmania infantum and Leishmania amazonensis, and that these effects appeared to be mediated by mitochondrial dysfunction.

Two decades of recent advances of Ugi reactions: synthetic and pharmaceutical applications

Multicomponent reactions (MCRs) are powerful synthetic tools in which more than two starting materials couple with each other to form multi-functionalized compounds in a one-pot process, the so-called “tandem”, “domino” or “cascade” reaction, or utilizing an additional step without changing the solvent, the so-called a sequential-addition procedure, to limit the number of synthetic steps, while increasing the complexity and the molecular diversity, which are highly step-economical reactions. The Ugi reaction, one of the most common multicomponent reactions, has recently fascinated chemists with the high diversity brought by its four- or three-component-based isonitrile. The Ugi reaction has been introduced in organic synthesis as a novel, efficient and useful tool for the preparation of libraries of multifunctional peptides, natural products, and heterocyclic compounds with stereochemistry control. In this review, we highlight the recent advances of the Ugi reaction in the last two decades from 2000–2019, mainly in the synthesis of linear or cyclic peptides, heterocyclic compounds with versatile ring sizes, and natural products, as well as the enantioselective Ugi reactions. Meanwhile, the applications of these compounds in pharmaceutical trials are also discussed.

We highlight the recent advances of the Ugi reaction in the last two decades from 2000–2019, mainly in the synthesis of linear or cyclic peptides, heterocyclic compounds with versatile ring sizes, and natural products, as well as the enantioselective Ugi reactions.

Emerging therapeutic targets for treatment of leishmaniasis

INTRODUCTION

Parasitic diseases that pose a threat to human life include leishmaniasis - caused by protozoan parasite Leishmania species. Existing drugs have limitations due to deleterious side effects like teratogenicity, high cost and drug resistance. This calls for the need to have an insight into therapeutic aspects of disease. Areas covered: We have identified different drug targets via. molecular, imuunological, metabolic as well as by system biology approaches. We bring these promising drug targets into light so that they can be explored to their maximum. In an effort to bridge the gaps between existing knowledge and prospects of drug discovery, we have compiled interesting studies on drug targets, thereby paving the way for establishment of better therapeutic aspects. Expert opinion: Advancements in technology shed light on many unexplored pathways. Further probing of well established pathways led to the discovery of new drug targets. This review is a comprehensive report on current and emerging drug targets, with emphasis on several metabolic targets, organellar biochemistry, salvage pathways, epigenetics, kinome and more. Identification of new targets can contribute significantly towards strengthening the pipeline for disease elimination.

Leishmanicidal Activity of (+)-Phyllanthidine and the Phytochemical Profile of Margaritaria nobilis (Phyllanthaceae)

The effects of the Securinega alkaloid (+)-phyllanthidine on Leishmania (L.) amazonensis and the first chemical investigation of Margaritaria nobilis L.f. (Phyllanthaceae) are described. Treating the parasites with this alkaloid caused a dose-dependent reduction in promastigote growth of 67.68% (IC₅₀ 82.37 μg/mL or 353 µM) and in amastigote growth of 83.96% (IC₅₀ 49.11 μg/mL or 210 µM), together with ultrastructural alterations in the promastigotes. No cytotoxic effect was detected in mammalian cells (CC₅₀ 1727.48 µg/mL or CC₅₀ 5268 µM). Classical chromatographic techniques and spectral methods led to the isolation and identification of betulinic acid, kaempferol, corilagin, gallic acid and its methyl ester, besides (+)-phyllanthidine from M. nobilis leaves and stems. Margaritaria nobilis is another source of the small group of Securinega alkaloids, together with other Phyllanthaceae (Euphorbiaceae s.l.) species. The low toxicity to macrophages and the effects against promastigotes and amastigotes are suggestive that (+)-phyllanthidine could be a promising antileishmanial agent for treating cutaneous leishmaniasis.

In vitro biological action of aqueous extract from roots of Physalis angulata against Leishmania (Leishmania) amazonensis

BACKGROUND

Leishmaniasis is an infectious disease caused by various species of the protozoan parasites of the Leishmania genus and transmitted by phlebotomine sandflies. The protozoa multiply in phagocytic cells, mainly macrophages, which play an important role defending the organism from pathogens. The most effective treatment for leishmaniasis is the chemotherapy and besides the high cost, these drugs are toxic and require a long period of treatment. Currently, some herbal products are considered an important alternative source of a new leishmanicidal agent, which includes the plant Physalis angulata, . We evaluated effects of an aqueous extract from roots of Physalis angulata (AEPa) on Leishmania proliferation, morphology and also determined whether physalins were present in the extract contributing to the knowledge of its pharmacological efficacy.

METHODS

Morphological alterations were determined by light microscopy, transmission and scanning electron microscopy. Host cell viability was evaluated by MTT, and propidium iodide. AEPa were submitted in full HRESITOF analysis.

RESULTS

AEPa promoted a dose-dependent reduction on promastigotes (IC50 = 39.5 μg/mL ± 5.1) and amastigotes (IC50 = 43.4 μg/mL ± 10.1) growth. This growth inhibition was associated with several morphological alterations observed in promastigote forms. No cytotoxic effect in mammalian cells was detected (IC50 > 4000 μg/mL). Furthemore, the presence of physalins A, B, D, E, F, G and H were described, for the first time, in the P. angulata root.

CONCLUSIONS

Results demonstrate that AEPa effectively promotes antileishmanial activity with several important morphological alterations and has no cytotoxic effects on host cells.

In vitro evaluation of (-)α-bisabolol as a promising agent against Leishmania amazonensis

Current treatments for leishmaniasis present some difficulties due to their toxicity, the use of the intravenous route for administration and therapy duration, which may lead to treatment discontinuation. The aim of this study is to investigate new treatment alternatives to improve patients well being. Therefore, we evaluated the inhibitory effect of (-)α-bisabolol, a sesquiterpene alcohol found in various essential oils of different plant species, against the promastigotes and intracellular amastigotes forms of Leishmania amazonensis, as well as the cytotoxic, morphological and ultrastructural alterations of treated cells. Promastigotes forms of L. amazonensis were incubated with (-)α-bisabolol to determine the antileishmanial activity of this compound. The cytotoxicity effect was evaluated by testing against J774.G8 cells. After these tests, the infected and uninfected cells with L. amazonensis were used to determine if the (-)α-bisabolol was able to kill intracellular parasites and to cause some morphological changes in the cells. The (-)α-bisabolol compound showed significant antileishmanial activity against promastigotes with a 50% effective concentration of 8.07 µg/ml (24 h) and 4.26 µg/ml (48 h). Against intracellular amastigotes the IC50 (inhibitory concentration) of (-)α-bisabolol (24 h) was 4.15 µg/ml. The (-)α-bisabolol also showed a cytotoxic effect against the macrophage strain J774.G8. The value of 50% cytotoxic concentration was 14.82 µg/ml showing that (-)α-bisabolol is less toxic to macrophages than to the parasite. Ultrastructural studies of treated promastigotes and amastigotes showed several alterations, such as loss of cytoplasmic organelles, including the nucleus, and the presence of lipid inclusions. This study showed that (-)α-bisabolol has promising antileishmanial properties, as it can act against the promastigote forms and is able to penetrate the cell, and is also active against the amastigote forms. About 69% of the promastigotes forms suffered mitochondrial membrane damage after treatment with IC50 of (-)α-bisabolol, suggesting inhibition of the metabolic activity of parasites. These results open new prospects for research that can contribute to the development of products based on essential oils or isolated compounds from plants for the treatment of cutaneous leishmaniasis.

A novel function for kojic acid, a secondary metabolite from Aspergillus fungi, as antileishmanial agent

Kojic acid (KA) is a fungal metabolite used as a topical treatment skin-whitening cosmetic agent for melasma in humans; however its potential as an anti-leishmanial agent is unknown. Chemotherapy is one of the most effective treatments for Leishmaniasis. However, the drugs available are expensive, invasive, require long-term treatment and have severe side effects. Thus, the development of new effective leishmanicidal agents is a necessity. In this study we investigated the anti-leishmanial effect of KA on L. amazonensis, following in vitro and in vivo infections. KA (50 μg/mL) was found to decrease the growth by 62% (IC₅₀ 34 μg/mL) and 79% (IC₅₀ 27.84 μg/mL) of promastigotes and amastigotes in vitro, respectively. Ultrastructural analysis of KA-treated amastigotes showed the presence of vesicles bodies into the flagellar pocket, and an intense intracellular vacuolization and swelling of the mitochondrion. During the in vitro interaction of parasites and the host cell, KA reverses the superoxide anions (O₂^-) inhibitory mechanism promoted by parasite. In addition, 4 weeks after KA-topical formulation treatment of infected animals, a healing process was observed with a high production of collagen fibers and a decrease in parasite burden. Thus, these results demonstrated the great potential of KA as an anti-leishmanial compound.

Virtualizing the p-ANAPL library: a step towards drug discovery from African medicinal plants

Background

Natural products play a key role in drug discovery programs, both serving as drugs and as templates for the synthesis of drugs, even though the quantities and availabilities of samples for screening are often limitted.

Experimental approach

A current collection of physical samples of > 500 compound derived from African medicinal plants aimed at screening for drug discovery has been made by donations from several researchers from across the continent to be directly available for drug discovery programs. A virtual library of 3D structures of compounds has been generated and Lipinski’s “Rule of Five” has been used to evaluate likely oral availability of the samples.

Results

A majority of the compound samples are made of flavonoids and about two thirds (2/3) are compliant to the “Rule of Five”. The pharmacological profiles of thirty six (36) selected compounds in the collection have been discussed.

Conclusions and implications

The p-ANAPL library is the largest physical collection of natural products derived from African medicinal plants directly available for screening purposes. The virtual library is also available and could be employed in virtual screening campaigns.

Zoghbi M, Araújo IS, Uetanabaro APT, Santos LS, do S. B. Brasil D. Volatiles, a glutarimide alkaloid and antimicrobial effects of Croton pullei (Euphorbiaceae)

Chemical investigation of Croton pullei (Euphorbiaceae) collected in the Brazilian Amazon region was revisited. The chemical composition of the essential oils of leaves and stems was analyzed by GC/MS. It was found that both the oils comprise mainly terpenes, among which linalool was the major one (24.90 and 39.72%, respectively). Phytochemical investigation of the stem methanol extract led to the isolation of a new natural product from the glutarimide alkaloid group named N-[2,6-dioxo-1-(2-phenylethyl)-3-piperidinyl]-acetamide, confirming that C. pullei is a rich source of this class of alkaloids. The hexane and methanol extracts of the stems of C. pullei showed moderate antibacterial and antifungal activity and the highest inhibition was observed when the methanol extract was tested against Staphylococcus aureus CCMB 262 and CCMB 263.

In vitro and in vivo activity of a palladacycle complex on Leishmania (Leishmania) amazonensis

Background

Antitumor cyclopalladated complexes with low toxicity to laboratory animals have shown leishmanicidal effect. These findings stimulated us to test the leishmanicidal property of one palladacycle compound called DPPE 1.2 on Leishmania (Leishmania) amazonensis, an agent of simple and diffuse forms of cutaneous leishmaniasis in the Amazon region, Brazil.

Methodology/Principal Findings

Promastigotes of L. (L.) amazonensis and infected bone marrow-derived macrophages were treated with different concentrations of DPPE 1.2. In in vivo assays foot lesions of L. (L.) amazonensis-infected BALB/c mice were injected subcutaneously with DPPE 1.2 and control animals received either Glucantime or PBS. The effect of DPPE 1.2 on cathepsin B activity of L. (L.) amazonensis amastigotes was assayed spectrofluorometrically by use of fluorogenic substrates. The main findings were: 1) axenic L. (L.) amazonensis promastigotes were destroyed by nanomolar concentrations of DPPE 1.2 (IC50 = 2.13 nM); 2) intracellular parasites were killed by DPPE 1.2 (IC50 = 128.35 nM), and the drug displayed 10-fold less toxicity to macrophages (CC50 = 1,267 nM); 3) one month after intralesional injection of DPPE 1.2 infected BALB/c mice showed a significant decrease of foot lesion size and a reduction of 97% of parasite burdens when compared to controls that received PBS; 4) DPPE 1.2 inhibited the cysteine protease activity of L. (L.) amazonensis amastigotes and more significantly the cathepsin B activity.

Conclusions/Significance

The present results demonstrated that DPPE 1.2 can destroy L. (L.) amazonensis in vitro and in vivo at concentrations that are non toxic to the host. We believe these findings support the potential use of DPPE 1.2 as an alternative choice for the chemotherapy of leishmaniasis.

Leishmaniasis is an important public health problem with an estimated annual incidence of 1.5 million of new human cases of cutaneous leishmaniasis and 500,000 of visceral leishmaniasis. Treatment of the diseases is limited by toxicity and parasite resistance to the drugs currently in use, validating the need to develop new leishmanicidal compounds. We evaluated the killing by the palladacycle complex DPPE 1.2 of Leishmania (Leishmania) amazonensis, an agent of human cutaneous leishmaniasis in the Amazon region, Brazil. DPPE 1.2 destroyed promastigotes of L. (L.) amazonensis in vitro at nanomolar concentrations, whereas intracellular amastigotes were killed at drug concentrations 10-fold less toxic than those displayed to macrophages. L. (L.) amazonensis-infected BALB/c mice treated by intralesional injection of DPPE 1.2 exhibited a significant decrease of foot lesion sizes and a 97% reduction of parasite burdens when compared to untreated controls. Additional experiments indicated the inhibition of the cathepsin B activity of L. (L.) amazonensis amastigotes by DPPE 1.2. Further studies are needed to explore the potential of DPPE 1.2 as an additional option for the chemotherapy of leishmaniasis.

Synthesis of (-)-julocrotine and a diversity oriented Ugi-approach to analogues and probes

An improved total synthesis of (−)-julocrotine in three steps from Cbz-glutamine, in 51% overall yield, is presented. To demonstrate the potential of the heterocyclic moiety for diversity oriented synthesis, a series of (−)-julocrotine analogues was synthesized by employing the heterocyclic precursor as an amino input in Ugi four-component reactions (Ugi-4CR) [1].

Plant derived therapeutics for the treatment of Leishmaniasis

Diseases caused by insect borne trypanosomatid parasites are significant, yet remain a neglected public health problem. Leishmania, a unicellular protozoan parasite is the causative organism of Leishmaniasis and is transmitted by female phlebotamine sandflies affecting millions of people worldwide. In the wake of resistance to pentavalent antimonial drugs, new therapeutic alternatives are desirable. The plant kingdom has in the past provided several affordable compounds and this review aims to provide an overview of the current status of available leishmanicidal plant derived compounds that are effective singly or in combination with conventional anti-leishmanial drugs, yet are non toxic to mammalian host cells. Furthermore, delineation of the contributory biochemical mechanisms involved in mediating their effect would help develop new chemotherapeutic approaches.

Synthesis of N-[(3S)-2,6-dioxo-1-(2-phenylethyl)-3-piperidinyl]-(2S)-2-methylbutanamide ((-)-julocrotine)

The total synthesis of (-)-julocrotine (1) starting from l-glutamic acid in 41% overall yield is described. The methodology utilizes protection, deprotection, and regioselection (carbonyl differentiation via oxazolidinone) protocols, and glutarimide ring formation is the key step.