Inhibitory activity of marine sponge-derived natural products against parasitic protozoa

Michellamines A6 and A7, and further mono- and dimeric naphthylisoquinoline alkaloids from a Congolese Ancistrocladus liana and their antiausterity activities against pancreatic cancer cells

Michellamines A₆ (1) and A₇ (2) are the first dimers of 5,8′-coupled naphthylisoquinoline alkaloids with cis-configured stereocenters in both tetrahydroisoquinoline subunits. They were isolated from the leaves of a recently discovered, yet unidentified Congolese Ancistrocladus liana that shares some morphological characteristics with Ancistrocladus likoko. Two further new dimeric analogs, michellamines B₄ (3) and B₅ (4), were obtained, along with two previously likewise unknown monomers, ancistrobonsolines A₁ (5) and A₂ (6), which, besides one single known other example, are the only naphthyldihydroisoquinolines with an M-configured biaryl axis and R-configuration at C-3. Moreover, five compounds earlier reported from other Ancistrocladus species were identified, ancistroealaine C (7), korupensamines A (8a) and B (8b), and michellamines A₂ (9) and E (10). Their complete structural elucidation succeeded due to the fruitful interplay of spectroscopic, chemical, and chiroptical methods. Chemotaxonomically, the stereostructures of the metabolites clearly delineate this Congolese Ancistrocladus liana from all known related species, showing that it might be a new taxon. Ancistrobonsolines A₁ (5) and A₂ (6) exhibited strong preferential cytotoxicities against human PANC-1 pancreatic cancer cells under nutrient-deprived conditions, without displaying toxicity in normal, nutrient-rich medium. Against cervical HeLa cancer cells, the dimeric alkaloids michellamines A₆ (1) and E (10) displayed the highest cytotoxic activities, comparable to that of the standard agent, 5-fluorouracil. Furthermore, ancistrobonsolines A₁ (5) and A₂ (6) showed weak-to-moderate antiprotozoal activities.

The first dimers of 5,8′-coupled naphthylisoquinolines with two 1,3-cis-configured tetrahydroisoquinoline portions and their cytotoxicities against cancer cells are described.

Acid-Induced Rearrangement of Epoxygermacranolides: Synthesis of Furanoheliangolides and Cadinanes from Nobilin

The acid-induced rearrangement of three epoxyderivatives of nobilin 1, the most abundant sesquiterpene lactone in Anthemisnobilis flowers, was investigated. From the 1,10-epoxyderivative 2, furanoheliangolide 5 was obtained, while the 4,5-epoxy group of 3 did not react. Conversely, when the 3-hydroxy function of nobilin was acetylated (12), the 4,5-epoxy derivative did cyclize into cadinanes (15 and 16) under Lewis acid catalysis. The reactivity of the 4,5- and 1,10-epoxy derivatives of nobilin (2 and 3) was compared with that of parthenolide, and rationalized on the basis of quantum chemical calculations. All isolated reaction products were fully characterized by spectroscopic and computational methods, and their in vitro anti-protozoal activity was evaluated. The paper could provide new insights into the biosynthesis of this class of natural products.

Hippeastrum reticulatum (Amaryllidaceae): Alkaloid Profiling, Biological Activities and Molecular Docking

The Amaryllidaceae family has proven to be a rich source of active compounds, which are characterized by unique skeleton arrangements and a broad spectrum of biological activities. The aim of this work was to perform the first detailed study of the alkaloid constituents of Hippeastrum reticulatum (Amaryllidaceae) and to determine the anti-parasitological and cholinesterase (AChE and BuChE) inhibitory activities of the epimers (6α-hydroxymaritidine and 6β-hydroxymaritidine). Twelve alkaloids were identified in H. reticulatum: eight known alkaloids by GC-MS and four unknown (6α-hydroxymaritidine, 6β-hydroxymaritidine, reticulinine and isoreticulinine) by NMR. The epimer mixture (6α-hydroxymaritidine and 6β-hydroxymaritidine) showed low activity against all protozoan parasites tested and weak AChE-inhibitory activity. Finally, a molecular docking analysis of AChE and BuChE proteins showed that isoreticulinine may be classified as a potential inhibitory molecule since it can be stabilized in the active site through hydrogen bonds, π-π stacking and hydrophobic interactions.

Jozilebomines A and B, Naphthylisoquinoline Dimers from the Congolese Liana Ancistrocladus ileboensis, with Antiausterity Activities against the PANC-1 Human Pancreatic Cancer Cell Line

Two new naphthylisoquinoline dimers, jozilebomines A (1a) and B (1b), were isolated from the roots of the Congolese plant Ancistrocladus ileboensis, along with the known dimer jozimine A₂ (2). These compounds are Dioncophyllaceae-type metabolites, i.e., lacking oxygen functions at C-6 and with an R-configuration at C-3 in their tetrahydroisoquinoline moieties. The dimers 1a and 1b consist of two 7,1'-coupled naphthylisoquinoline monomers linked through an unprecedented 3',6″-coupling in the binaphthalene core and not, as in 2, via the C-3-positions of the two naphthalene units. Thus, different from the C₂-symmetric jozimine A₂ (2), the new jozilebomines are constitutionally unsymmetric. The central biaryl axis of each of the three dimers is rotationally hindered, so that 1a, 1b, and 2 possess three consecutive chiral axes. The two jozilebomines have identical constitutions and the same absolute configurations at all four stereogenic centers, but differ from each other in their axial chirality. Their structural elucidation was achieved by HRESIMS, 1D and 2D NMR, oxidative degradation, and experimental and calculated ECD data. They exhibited distinct and specific antiplasmodial activities. All dimers showed potent cytotoxicity against HeLa human cervical cancer cells and preferential cytotoxicity against PANC-1 human pancreatic cancer cells under nutrition-deprived conditions. Furthermore, these dimers significantly inhibited the colony formation of PANC-1 cells, even when exposed to noncytotoxic concentration for a short time. Jozilebomines A (1a) and B (1b) and jozimine A₂ (2) represent novel potential candidates for future drug development against pancreatic cancer.

Antiprotozoal Linear Furanosesterterpenoids from the Marine Sponge Ircinia oros

Chemical investigation of the marine sponge Ircinia oros yielded four linear furanosesterterpenoids, including the known metabolites ircinin-1 (1) and ircinin-2 (2) and two new compounds, ircinialactam E (3) and ircinialactam F (4). Their chemical structures were elucidated by using a combination of [α]_D, NMR, HRMS, and FT-IR spectroscopy. The absolute configuration of C-18 in compounds 1-3 was identified as R by electronic circular dichroism (ECD) spectroscopy coupled with time-dependent density functional theory calculations. Compounds 1-4 showed moderate leishmanicidal, trypanocidal, and antiplasmodial activities (IC₅₀ values 28-130 μM). This is the second report of rare glycinyl lactam derivatives 3 and 4 from the genus Ircinia.

Alkaloid Constituents of the Amaryllidaceae Plant Amaryllis belladonna L

The plant family Amaryllidaceae is well-known for its unique alkaloid constituents, which exhibit a wide range of biological activities. Its representative, Amaryllis belladonna, has a geographical distribution covering mainly southern Africa, where it has significant usage in the traditional medicine of the native people. In this study, A. belladonna samples collected in Brazil were examined for alkaloid content. Alkaloid profiles of A. belladonna bulbs were generated by a combination of chromatographic, spectroscopic and spectrometric methods, including GC–MS and 2D NMR. In vitro screening against four different parasitic protozoa (Trypanosoma cruzi, T. brucei rhodesiense, Leishmania donovani and Plasmodium falciparum) was carried out using the A. belladonna crude methanol extract, as well as three of its alkaloid isolates. Twenty-six different Amaryllidaceae alkaloids were identified in the A. belladonna bulb samples, and three of them were isolated. Evidence for their respective biosynthetic pathways was afforded via their mass-spectral fragmentation data. Improved data for 1-O-acetylcaranine was provided by 2D NMR experiments, together with new ¹H-NMR data for buphanamine. The crude extract and 3-O-acetylhamayne exhibited good antiprotozoal activity in vitro, although both with a high cytotoxic index.

Antiplasmodial Ealapasamines A-C,'Mixed' Naphthylisoquinoline Dimers from the Central African Liana Ancistrocladus ealaensis

Three unusual heterodimeric naphthylisoquinoline alkaloids, named ealapasamines A-C (1-3), were isolated from the leaves of the tropical plant Ancistrocladus ealaensis J. Léonard. These 'mixed', constitutionally unsymmetric dimers are the first stereochemically fully assigned cross-coupling products of a 5,8'- and a 7,8'-coupled naphthylisoquinoline linked via C-6' in both naphthalene portions. So far, only two other West and Central Ancistrocladus species were known to produce dimers with a central 6,6″-axis, yet, in contrast to the ealapasamines, usually consisting of two 5,8'-coupled monomers, like e.g., in michellamine B. The new dimers 1-3 contain six elements of chirality, four stereogenic centers and the two outer axes, while the central biaryl axis is configurationally unstable. The elucidation of the complete stereostructures of the ealapasamines was achieved by the interplay of spectroscopic methods including HRESIMS, 1D and 2D NMR (in particular ROESY measurements), in combination with chemical (oxidative degradation) and chiroptical (electronic circular dichroism) investigations. The ealapasamines A-C display high antiplasmodial activities with excellent half-maximum inhibition concentration values in the low nanomolar range.

Furanoterpene Diversity and Variability in the Marine Sponge Spongia officinalis, from Untargeted LC-MS/MS Metabolomic Profiling to Furanolactam Derivatives

The Mediterranean marine sponge Spongia officinalis has been reported as a rich source of secondary metabolites and also as a bioindicator of water quality given its capacity to concentrate trace metals. In this study, we evaluated the chemical diversity within 30 S. officinalis samples collected over three years at two sites differentially impacted by anthropogenic pollutants located near Marseille (South of France). Untargeted liquid chromatography—mass spectrometry (LC–MS) metabolomic profiling (C18 LC, ESI-Q-TOF MS) combined with XCMS Online data processing and multivariate statistical analysis revealed 297 peaks assigned to at least 86 compounds. The spatio-temporal metabolite variability was mainly attributed to variations in relative content of furanoterpene derivatives. This family was further characterized through LC–MS/MS analyses in positive and negative ion modes combined with molecular networking, together with a comprehensive NMR study of isolated representatives such as demethylfurospongin-4 and furospongin-1. The MS/MS and NMR spectroscopic data led to the identification of a new furanosesterterpene, furofficin (2), as well as two derivatives with a glycinyl lactam moiety, spongialactam A (12a) and B (12b). This study illustrates the potential of untargeted LC–MS metabolomics and molecular networking to discover new natural compounds even in an extensively studied organism such as S. officinalis. It also highlights the effect of anthropogenic pollution on the chemical profiles within the sponge.

A new antifungal and antiprotozoal bibenzyl derivative from Gavilea lutea

A new bibenzyl derivative (4), together with two glycosylated flavonoids (1 and 2), batatasin III (3) and the phenanthrene isohircinol (5) were isolated from the aerial parts of Gavilea lutea. Their structures were elucidated on the basis of spectroscopic studies including 1D and 2D NMR, UV, IR and HRESIMS. All isolated compounds were evaluated for their antifungal activity towards Candida albicans. The new compound 4 showed inhibitory activity with a MIQ of 50 μg. In addition, compound 4 exhibited a selective activity (IC₅₀ = 2.3 μg/mL) against Leishmania donovani.

Dioncophyllines C2, D2, and F and Related Naphthylisoquinoline Alkaloids from the Congolese Liana Ancistrocladus ileboensis with Potent Activities against Plasmodium falciparum and against Multiple Myeloma and Leukemia Cell Lines

Dioncophylline F (1), the first 5,8'-coupled dioncophyllaceous alkaloid (i.e., lacking an oxygen function at C-6 and possessing an R-configuration at C-3), was isolated from the recently described Congolese liana Ancistrocladus ileboensis. Two further, likewise Dioncophyllaceae-type, alkaloids, the dioncophyllines C₂ (2) and D₂ (3), were identified, along with the Ancistrocladaceae-type compound ancistrocladisine B (4), which is oxygenated at C-6 and S-configured at C-3. The structures of the new compounds were determined by spectroscopic, chemical, and chiroptical methods. The stereostructure of 1 was further confirmed by total synthesis. As a consequence of the lack of a methyl group ortho to their biaryl axes, both dioncophylline F (1) and the 7,8'-coupled dioncophylline D₂ (3) occur as pairs of configurationally semistable and, thus, slowly interconverting atropo-diastereomers, whereas dioncophylline C₂ (2), with its 5,1'-linkage, is configurationally stable at the axis. Eight further known naphthylisoquinolines were isolated from A. ileboensis, among them dioncophylline A (P-10), its 4'-O-demethyl analogue P-11, and 5'-O-methyldioncophylline D (7), which were found to display strong cytotoxic activities against multiple myeloma INA-6 cells (P-10 even stronger than the standard drug melphalan) and against drug-sensitive acute lymphoblastic CCRF-CEM leukemia cells and their multidrug-resistant subline, CEM/ADR5000. Moreover, the dioncophyllines 1, 3, and 7 showed high-and specific-activities against the malaria parasite Plasmodium falciparum.

Antiprotozoal Activity-Based Profiling of a Dichloromethane Extract from Anthemis nobilis Flowers

A dichlomethane extract of Anthemis nobilis flower cones showed promising in vitro antiprotozoal activity against Trypanosoma brucei rhodesiense and Leishmania donovani, with IC₅₀ values of 1.43 ± 0.50 and 1.40 ± 0.07 μg/mL, respectively. A comprehensive profiling of the most active fractions afforded 19 sesquiterpene lactones, including 15 germacranolides, two seco-sesquiterpenes, one guaianolide sesquiterpene lactone, and one cadinane acid. Of these, 13 compounds were found to be new natural products. The compounds were characterized by extensive spectroscopic data analysis (1D and 2D NMR, HRMS, circular dichroism) and computational methods, and their in vitro antiprotozoal activity was evaluated. The furanoheliangolide derivative 15 showed high potency and selectivity in vitro against T. b. rhodesiense bloodstream forms (IC₅₀ 0.08 ± 0.01 μM; SI 63). In silico calculations were consistent with the drug-like properties of 15.

Synthesis and activity of nucleoside-based antiprotozoan compounds

Parasitic protozoa employ a salvage pathway to synthesize purines and generate essential active nucleotides, whereas mammals are capable of their de novo biosynthesis. This difference provides opportunity for the design of potential new antiprotozoan compounds. A series of 47 adenosine analogues was prepared with modifications at the 2-, 6- and 5'-positions, based on the hypothesis that such compounds would serve as substrates for protozoan nucleoside salvage enzymes, while remaining refractory in mammalian cells. The nucleosides were designed to produce toxic metabolites upon cleavage to the corresponding purine base by the parasite. Three 7-deazaguanosine derivatives were prepared with similar objectives. All of these compounds were tested in vitro against T. brucei (African sleeping sickness), T. cruzi (Chagas' disease), L. donovani (leishmaniasis) and P. falciparum (malaria). In order to determine the therapeutic selectivity indices (SI) of the antiprotozoan nucleosides, their cytotoxicities toward a rat myoblast cell line were also determined. One adenosine derivative proved highly effective against P. falciparum (IC₅₀=110nM and SI=1010, while a modified guanosine displayed potent activities against L. donovani (IC₅₀=60nM, SI=2720) and T. brucei (IC₅₀=130nM, SI=1250), as well as moderate activity against T. cruzi (IC₅₀=3.4µM, SI=48). These results provide proof of concept for the nucleoside-based antiprotozoan strategy, as well as potential lead compounds for further optimization and validation.

Ceylonins A-F, Spongian Diterpene Derivatives That Inhibit RANKL-Induced Formation of Multinuclear Osteoclasts, from the Marine Sponge Spongia ceylonensis

Six new spongian diterpene derivatives, ceylonins A-F (1-6), were isolated from the Indonesian marine sponge Spongia ceylonensis along with spongia-13(16),14-dien-19-oic acid (7). They contained three additional carbons in ring D to supply an ether-bridged bicyclic ring system. Their structures were elucidated by analyzing NMR spectroscopic data and calculated ECD spectra in comparison to experimental ECD spectra. The bicyclic ring system may be derived from the major metabolite 7 and a C₃ unit (an acrylic acid equivalent) through an intermolecular Diels-Alder reaction, which was experimentally supported by the formation of 1-6 from 7 and acrylic acid. The inhibitory effects of the isolated compounds on the RANKL-induced formation of multinuclear osteoclasts in RAW264 macrophages were examined.

Purpureone, an antileishmanial ergochrome from the endophytic fungus Purpureocillium lilacinum

The ethyl acetate extracts prepared from the mycelia of three endophytic fungi Purpureocillium lilacinum, Aspergillus sp., and Fusarium sp., isolated from the roots of Rauvolfia macrophylla (Apocynaceae) were screened for their antiprotozoal activity in vitro against Plasmodium falciparum (NF54), Leishmania donovani, Trypanosoma brucei rhodesiense, and Trypanosoma cruzi. Amongst these extracts, the one from P. lilacinum showed potent antileishmanial activity against L. donovani (IC50 value of 0.174 μg mL−1) with good selectivity (SI=94.9) toward the L6 cell line, whereas the other extracts were inactive and not selective. The fractionation and purification of the active extract from P. lilacinum by column chromatography over silica gel yielded a new ergochromone derivative (1), together with six known compounds: (22E,24R)-stigmasta-5,7,22-trien-3-β-ol (2), (22E,24R)-stigmasta-4,6,8(14),22-tetraen-3-one (3), emodin (4), chrysophanol (5), aloe-emodin (6), and palmitic acid, whose structures were elucidated spectroscopically. Compound 1 was tested in vitro for its antiparasitic activities against the above listed parasites and for its antimicrobial activity against Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes, Escherichia coli, Providencia stuartii, Klebsiella pneumoniae, and Pseudomonas aeruginosa. The compound displayed potent antileishmanial activity against L. donovani with an IC50 value of 0.63 μg mL−1 (0.87 μm) with good selectivity (SI=49.5) toward the L6 cell line. It also exhibited good antibacterial activity against three of the tested microbial strains B. cereus, E. coli ATCC879, and P. stuartii ATCC29916 with minimum inhibitory concentrations below 62.6 μg mL−1. Compound 1 is thus a promising active compound that could be investigated for antileishmanial and antimicrobial drug development.

Nitrotriazole-based acetamides and propanamides with broad spectrum antitrypanosomal activity

3-Nitro-1H-1,2,4-triazole-based acetamides bearing a biphenyl- or a phenoxyphenyl moiety have shown remarkable antichagasic activity both in vitro and in an acute murine model, as well as substantial in vitro antileishmanial activity but lacked activity against human African trypanosomiasis. We have shown now that by inserting a methylene group in the linkage to obtain the corresponding propanamides, both antichagasic and in particular anti-human African trypanosomiasis potency was increased. Therefore, IC50 values at low nM concentrations against both T. cruzi and T. b. rhodesiense, along with huge selectivity indices were obtained. Although several propanamides were active against Leishmania donovani, they were slightly less potent than their corresponding acetamides. There was a good correlation between lipophilicity (clogP value) and trypanocidal activity, for all new compounds. Type I nitroreductase, an enzyme absent from the human host, played a role in the activation of the new compounds, which may function as prodrugs. Antichagasic activity in vivo was also demonstrated with representative propanamides.

Antitrypanosomal activity of 5-nitro-2-aminothiazole-based compounds

A small series of 5-nitro-2-aminothiazole-based amides containing arylpiperazine-, biphenyl- or aryloxyphenyl groups in their core were synthesized and evaluated as antitrypanosomatid agents. All tested compounds were active or moderately active against Trypanosoma cruzi amastigotes in infected L6 cells and Trypanosoma brucei brucei, four of eleven compounds were moderately active against Leishmania donovani axenic parasites while none were deemed active against T. brucei rhodesiense. For the most active/moderately active compounds a moderate selectivity against each parasite was observed. There was good correlation between lipophilicity (clogP value) and antileishmanial activity or toxicity against L6 cells. Similarly, good correlation existed between clogP values and IC50 values against T. cruzi in structurally related subgroups of compounds. Three compounds were more potent as antichagasic agents than benznidazole but were not activated by the type I nitrorectusase (NTR).

Molecular mechanisms of endocrine and metabolic disruption: An in silico study on antitrypanosomal natural products and some derivatives

The VirtualToxLab is an in silico technology for estimating the toxic potential - endocrine and metabolic disruption, as well as aspects of carcinogenicity and cardiotoxicity - of drugs, chemicals and natural products. The technology is based on an automated protocol that simulates and quantifies the binding of small molecules towards a series of currently 16 proteins, known or suspected to trigger adverse effects. The simulations are conducted at the atomic level and explicitly allow for a mechanistic interpretation of the results (in real-time 3D/4D), thereby complying with the Setubal principles put forward in 2002 for computational approaches to toxicology. Moreover, the underlying "ab-initio" protocol is independent from any training data and makes the approach universal with respect to the applicability domain. The VirtualToxLab runs in client-server mode and is freely available to academic and non-profit organizations. As the underlying technology yields a thermodynamic estimate of the binding affinity, the associated ligand-protein complexes have been challenged by molecular-dynamics simulations to probe their kinetic stability. Human African trypanosomiasis is a neglected tropical disease caused by two subspecies of Trypanosoma brucei. The control of this parasitic infection relies on a few chemotherapeutic agents, most of which were discovered decades ago and pose many challenges including adverse side effects, poor efficacy, and the occurrence of drug resistances. Natural products, on the other hand, offer a high potential for the discovery of new drug leads due to their chemical diversity. In this in silico study, we analyze a series of 89 natural products and derivatives displaying anti-trypanosomal activity for their potential to trigger adverse effects. Our results indicate a moderate potential for a number of those compounds to bind to nuclear receptors and thereby ease the development of endocrine disregulation. A few others would seem to inhibit enzymes of the cytochrome P450 family and, hence, sustain drug-drug interactions.

The Laurencia Paradox: An Endless Source of Chemodiversity

Nature, the most prolific source of biological and chemical diversity, has provided mankind with treatments for health problems since ancient times and continues to be the most promising reservoir of bioactive chemicals for the development of modern drugs. In addition to the terrestrial organisms that still remain a promising source of new bioactive metabolites, the marine environment, covering approximately 70% of the Earth's surface and containing a largely unexplored biodiversity, offers an enormous resource for the discovery of novel compounds. According to the MarinLit database, more than 27,000 metabolites from marine macro- and microorganisms have been isolated to date providing material and key structures for the development of new products in the pharmaceutical, food, cosmeceutical, chemical, and agrochemical sectors. Algae, which thrive in the euphotic zone, were among the first marine organisms that were investigated as sources of food, nutritional supplements, soil fertilizers, and bioactive metabolites.Red algae of the genus Laurencia are accepted unanimously as one of the richest sources of new secondary metabolites. Their cosmopolitan distribution, along with the chemical variation influenced to a significant degree by environmental and genetic factors, have resulted in an endless parade of metabolites, often featuring multiple halogenation sites.The present contribution, covering the literature until August 2015, offers a comprehensive view of the chemical wealth and the taxonomic problems currently impeding chemical and biological investigations of the genus Laurencia. Since mollusks feeding on Laurencia are, in many cases, bioaccumulating, and utilize algal metabolites as chemical weaponry against natural enemies, metabolites of postulated dietary origin of sea hares that feed on Laurencia species are also included in the present review. Altogether, 1047 secondary metabolites, often featuring new carbocyclic skeletons, have been included.The chapter addresses: (1) the "Laurencia complex", the botanical description and the growth and population dynamics of the genus, as well as its chemical diversity and ecological relations; (2) the secondary metabolites, which are organized according to their chemical structures and are classified into sesquiterpenes, diterpenes, triterpenes, acetogenins, indoles, aromatic compounds, steroids, and miscellaneous compounds, as well as their sources of isolation which are depicted in tabulated form, and (3) the biological activity organized according to the biological target and the ecological functions of Laurencia metabolites.

The effects of a thermophile metabolite, tryptophol, upon protecting shrimp against white spot syndrome virus

White spot syndrome virus (WSSV) is a shrimp pathogen responsible for significant economic loss in commercial shrimp farms and until now, there has been no effective approach to control this disease. In this study, tryptophol (indole-3-ethanol) was identified as a metabolite involved in bacteriophage-thermophile interactions. The dietary addition of tryptophol reduced the mortality in shrimp Marsupenaeus japonicus when orally challenged with WSSV. Our results revealed that 50 mg/kg tryptophol has a better protective effect in shrimp than 10 or 100 mg/kg tryptophol. WSSV copies in shrimp were reduced significantly (P < 0.01) when supplemented with 50 mg/kg tryptophol, indicating that virus replication was inhibited by tryptophol. Consequently, tryptophol represents an effective antiviral dietary supplement for shrimp, and thus holds significant promise as a novel and efficient therapeutic approach to control WSSV in shrimp aquaculture.

3-Nitrotriazole-based piperazides as potent antitrypanosomal agents

Novel linear 3-nitro-1H-1,2,4-triazole-based piperazides were synthesized and evaluated as antitrypanosomal agents. In addition, some bisarylpiperazine-ethanones which were formed as by-products were also screened for antiparasitic activity. Most 3-nitrotriazole-based derivatives were potent and selective against Trypanosoma cruzi parasites, but only one displayed these desired properties against Trypanosoma brucei rhodesiense. Moreover, two 3-nitrotriazole-based chlorophenylpiperazides were moderately and selectively active against Leishmania donovani. Although the bisarylpiperazine-ethanones were active or moderately active against T. cruzi, none of them demonstrated an acceptable selectivity. In general, 3-nitrotriazole-based piperazides were less toxic to host L6 cells than the previously evaluated 3-nitrotriazole-based piperazines and seven of 13 were 1.54- to 31.2-fold more potent antichagasic agents than the reference drug benznidazole. Selected compounds showed good ADMET characteristics. One potent in vitro antichagasic compound (3) was tested in an acute murine model and demonstrated antichagasic activity after a 10-day treatment of 15 mg/kg/day. However, neither compound 3 nor benznidazole showed a statistically significant P value compared to control due to high variability in parasite burden among the untreated animals. Working as prodrugs, 3-nitrotriazole-based piperazides were excellent substrates of trypanosomal type I nitroreductases and constitute a novel class of potentially effective and more affordable antitrypanosomal agents.

Antiprotozoal Activity Profiling of Approved Drugs: A Starting Point toward Drug Repositioning

Neglected tropical diseases cause significant morbidity and mortality and are a source of poverty in endemic countries. Only a few drugs are available to treat diseases such as leishmaniasis, Chagas’ disease, human African trypanosomiasis and malaria. Since drug development is lengthy and expensive, a drug repurposing strategy offers an attractive fast-track approach to speed up the process. A set of 100 registered drugs with drug repositioning potential for neglected diseases was assembled and tested in vitro against four protozoan parasites associated with the aforementioned diseases. Several drugs and drug classes showed in vitro activity in those screening assays. The results are critically reviewed and discussed in the perspective of a follow-up drug repositioning strategy where R&D has to be addressed with limited resources.

Highly antiplasmodial non-natural oxidative products of dioncophylline A: synthesis, absolute configuration, and conformational stability

Four new compounds, the monomeric dioncotetralones A (6 a) and B (6 b) and the dimeric compounds jozimine A3 (7) and jozimine A4 (9), were semi-synthesized from the natural product dioncophylline A (4) and its 5'-O-demethylated derivative (5), respectively, under phenol oxidative reaction conditions. Dioncotetralones A (6 a) and B (6 b) possess an unprecedented Z-configured double bond, in contrast to the classic biaryl axis that is present in the precursor dioncophylline A (4), and an additional stereogenic center at the C2' atom was generated due to the dearomatization. The resulting steric repulsion forced the expected planar double bond into a helical distorted conformation. The homocoupling of 5 yielded compounds 7 and 9, the latter of which is the first sp(3) -sp(2) coupled product of a monomeric naphthylisoquinoline with a reduced one and, thus, contains a newly generated stereogenic center. The full stereostructures of 6 a, 6 b, 7, and 9 were successfully elucidated by the interplay of spectroscopic methods (1D/2D NMR and electronic circular-dichroism spectroscopy) in combination with quantum-chemical calculations. In addition, compounds 6 a and 7 exhibited high antiplasmodial activities with excellent half-maximal inhibitory concentration values.

Novel 3-nitrotriazole-based amides and carbinols as bifunctional antichagasic agents

3-Nitro-1H-1,2,4-triazole-based amides with a linear, rigid core and 3-nitrotriazole-based fluconazole analogues were synthesized as dual functioning antitrypanosomal agents. Such compounds are excellent substrates for type I nitroreductase (NTR) located in the mitochondrion of trypanosomatids and, at the same time, act as inhibitors of the sterol 14α-demethylase (T. cruzi CYP51) enzyme. Because combination treatments against parasites are often superior to monotherapy, we believe that this emerging class of bifunctional compounds may introduce a new generation of antitrypanosomal drugs. In the present work, the synthesis and in vitro and in vivo evaluation of such compounds is discussed.

(2R,1'S,2'R)- and (2S,1'S,2'R)-3-[2-Mono(di,tri)fluoromethylcyclopropyl]alanines and their incorporation into hormaomycin analogues

Efficient and scalable syntheses of enantiomerically pure (2R,1'S,2'R)- and (2S,1'S,2'R)-3-[2-mono(di,tri)fluoromethylcyclopropyl]alanines 9a–c, as well as allo-D-threonine (4) and (2S,3R)-β-methylphenylalanine (3), using the Belokon' approach with (S)- and (R)-2-[(N-benzylprolyl)amino]benzophenone [(S)- and (R)-10] as reusable chiral auxiliaries have been developed. Three new fluoromethyl analogues of the naturally occurring octadepsipeptide hormaomycin (1) with (fluoromethylcyclopropyl)alanine moieties have been synthesized and subjected to preliminary tests of their antibiotic activity.

Characterisation of taxlllaids A-G; natural products from Xenorhabdus indica

Six new lipodepsipeptides and an additional linear derivative named taxlllaids A-G (1-7) have been identified in the entomopathogenic bacterium Xenorhabdus indica. The structures of the main compounds have been solved by detailed NMR spectroscopic analysis and the structures of minor derivatives were elucidated by a combination of labelling experiments and detailed MS experiments. The absolute configuration of the taxlllaids was deduced by using the advanced Marfey method and analysis of the biosynthesis gene cluster showing the presence of epimerisation domains, which was subsequently proved to be correct by solid-phase peptide synthesis of all taxlllaids. The exchange of a single amino acid in the adenylation domain was shown to be responsible for substrate promiscuity of the third A domain, resulting in the incorporation of leucine, phenylalanine or tyrosine. Bioactivity testing revealed the taxlllaids to be weakly active against Plasmodium falciparum and against a number of eukaryotic cell lines.

Antitrypanosomal quinoline alkaloids from the roots of Waltheria indica

Chemical investigation of the dichloromethane root extract of Waltheria indica led to the isolation and characterization of 10 quinoline alkaloids, namely, 8-deoxoantidesmone (1), waltheriones E-L (2-9), and antidesmone (10). Among these, compounds 2-9 have not yet been described in the literature. Their chemical structures were established by means of spectroscopic data interpretation including (1)H and (13)C NMR, HSQC, HMBC, COSY, and NOESY experiments and UV, IR, and HRESIMS. The absolute configurations of the compounds were established by comparison of experimental and TDDFT-calculated ECD spectra. In addition, the isolated constituents were evaluated for their in vitro antitrypanosomal activity. Compounds 4, 5, and 8 showed potent and selective growth inhibition toward Trypanosoma cruzi with IC50 values between 0.02 and 0.04 μM. Cytotoxicity for mouse skeletal L-6 cells was also determined for these compounds.

Quinone-amino acid conjugates targeting Leishmania amino acid transporters

The aim of the present study was to investigate the feasibility of targeting Leishmania transporters via appropriately designed chemical probes. Leishmania donovani, the parasite that causes visceral leishmaniasis, is auxotrophic for arginine and lysine and has specific transporters (LdAAP3 and LdAAP7) to import these nutrients. Probes 1–15 were originated by conjugating cytotoxic quinone fragments (II and III) with amino acids (i.e. arginine and lysine) by means of an amide linkage. The toxicity of the synthesized conjugates against Leishmania extracellular (promastigotes) and intracellular (amastigotes) forms was investigated, as well their inhibition of the relevant amino acid transporters. We observed that some conjugates indeed displayed toxicity against the parasites; in particular, 7 was identified as the most potent derivative (at concentrations of 1 µg/mL and 2.5 µg/mL residual cell viability was reduced to 15% and 48% in promastigotes and amastigotes, respectively). Notably, 6, while retaining the cytotoxic activity of quinone II, displayed no toxicity against mammalian THP1 cells. Transport assays indicated that the novel conjugates inhibited transport activity of lysine, arginine and proline transporters. Furthermore, our analyses suggested that the toxic conjugates might be translocated by the transporters into the cells. The non-toxic probes that inhibited transport competed with the natural substrates for binding to the transporters without being translocated. Thus, it is likely that 6, by exploiting amino acid transporters, can selectively deliver its toxic effects to Leishmania cells. This work provides the first evidence that amino acid transporters of the human pathogen Leishmania might be modulated by small molecules, and warrants their further investigation from drug discovery and chemical biology perspectives.

Xenortide Biosynthesis by Entomopathogenic Xenorhabdus nematophila

The biosynthesis gene cluster of the xenortides and a new derivative, xenortide D, which is produced in only trace amounts, was identified in Xenorhabdus nematophila. The structure of xenortide D was elucidated using a combination of labeling experiments followed by MS analysis and was confirmed by synthesis. Bioactivity tests revealed a weak activity of tryptamine-carrying xenortides against Plasmodium falciparum and Trypanosoma brucei.

Indole alkaloids from marine sources as potential leads against infectious diseases

Indole alkaloids comprise a large and complex class of natural products found in a variety of marine sources. Infectious diseases remain a major threat to public health, and in the absence of long-term protective vaccines, the control of these infectious diseases is based on a small number of chemotherapeutic agents. Furthermore, the emerging resistance against these drugs makes it urgently necessary to discover and develop new, safe and, effective anti-infective agents. In this regard, the aim of this review is to highlight indole alkaloids from marine sources which have been shown to demonstrate activity against infectious diseases.

Investigation of indolglyoxamide and indolacetamide analogues of polyamines as antimalarial and antitrypanosomal agents

Pure compound screening has previously identified the indolglyoxylamidospermidine ascidian metabolites didemnidine A and B (2 and 3) to be weak growth inhibitors of Trypanosoma brucei rhodesiense (IC₅₀ 59 and 44 μM, respectively) and Plasmodium falciparum (K1 dual drug resistant strain) (IC₅₀ 41 and 15 μM, respectively), but lacking in selectivity (L6 rat myoblast, IC₅₀ 24 μM and 25 μM, respectively). To expand the structure–activity relationship of this compound class towards both parasites, we have prepared and biologically tested a library of analogues that includes indoleglyoxyl and indoleacetic “capping acids”, and polyamines including spermine (PA3-4-3) and extended analogues PA3-8-3 and PA3-12-3. 7-Methoxy substituted indoleglyoxylamides were typically found to exhibit the most potent antimalarial activity (IC₅₀ 10–92 nM) but with varying degrees of selectivity versus the L6 rat myoblast cell line. A 6-methoxyindolglyoxylamide analogue was the most potent growth inhibitor of T.brucei (IC₅₀ 0.18 μM) identified in the study: it, however, also exhibited poor selectivity (L6 IC₅₀ 6.0 μM). There was no apparent correlation between antimalarial and anti-T. brucei activity in the series. In vivo evaluation of one analogue against Plasmodium berghei was undertaken, demonstrating a modest 20.9% reduction in parasitaemia.

Drug discovery and human African trypanosomiasis: a disease less neglected?

Human African trypanosomiasis (HAT) has been neglected for a long time. The most recent drug to treat this disease, eflornithine, was approved by the US FDA in 2000. Current treatments exhibit numerous problematic side effects and are often ineffective against the debilitating CNS resident stage of the disease. Fortunately, several partnerships and initiatives have been formed over the last 20 years in an effort to eradicate HAT, along with a number of other neglected diseases. This has led to an increasing number of foundations and research institutions that are currently working on the development of new drugs for HAT and tools with which to diagnose and treat patients. New biochemical pathways as therapeutic targets are emerging, accompanied by increasing numbers of new antitrypanosomal compound classes. The future looks promising that this collaborative approach will facilitate eagerly awaited breakthroughs in the treatment of HAT.

Novel 3-nitro-1H-1,2,4-triazole-based compounds as potential anti-Chagasic drugs: in vivo studies

BACKGROUND

Chagas disease is caused by the parasite Trypanosoma cruzi, is endemic in Latin America and leads to an estimated 14,000 deaths per year and around 100 million people at risk of infection. Drugs currently used in the treatment of Chagas are old, partially effective and have numerous side effects.

METHODOLOGY

We have previously reported that 3-nitro-1H-1,2,4-triazole-based compounds demonstrate significant and selective activity against T. cruzi amastigotes in infected L6 cells via activation of a type I nitroreductase, specific to trypanosomatids. In the present work we evaluated in vivo 13 of these compounds based on their high in vitro potency against T. cruzi (IC50 < 1 µM) and selectivity (SI: toxicity to L6 cells/toxicity against T. cruzi amastigotes > 200). Representative compounds of different chemical classes were included. A fast luminescence assay with transgenic parasites that express luciferase, and live imaging techniques were used. A total of 11 out of 13 compounds demonstrated significant antichagasic activity when administered intraperitoneally for 5-10 days at relatively small doses. The best in vivo activity was demonstrated by amides and sulfonamide derivatives. ADMET studies were performed for specific compounds.

CONCLUSION

At least three compounds were identified as effective, non-toxic antichagasic agents suitable for further development.

Two trypanocidal dipeptides from the roots of Zapoteca portoricensis (Fabaceae)

Zapoteca portoricensis (Jacq) HM Hernández is used with remarkable efficacy in ethnomedicinal management of tonsillitis in the Eastern part of Nigeria. Previous pharmacological studies have validated the antiinflammatory and antimicrobial activities of the crude extract. In this study, two dipeptides, saropeptate (aurantiamide acetate) and anabellamide, were isolated from the methanol root extract of Zapoteca portoricensis and their chemical structures deduced by one dimensional and two dimensional NMR and mass spectrometry. These compounds were isolated for the first time from this plant, and no report has been found on their previous isolation from the genus Zapoteca. Evaluation of their trypanocidal activity showed that compound 1 exhibited potent activity against Trypanosoma brucei rhodesiense with an IC₅₀ value of 3.63 µM and selectivity index of 25.3.

Antiparasitic chaiyaphumines from entomopathogenic Xenorhabdus sp. PB61.4

A new class of four depsipentapeptides called chaiyaphumines A-D (1-4) was isolated from Xenorhabdus sp. PB61.4. Their structures were elucidated by detailed 1D and 2D NMR experiments and by a Marfey's analysis following flash hydrolysis of the peptide. Verification of the structure was achieved by three-dimensional modeling using NOE-derived distance constraints, molecular dynamics, and energy minimization. Chaiyaphumine A (1) showed good activity against Plasmodium falciparum (IC50 of 0.61 μM), the causative agent of malaria, and was active against other protozoal tropical disease causing agents.