Antiprotozoal agents: How have they changed over a decade?

Neglected tropical diseases are a diverse group of communicable diseases that are endemic in low- or low-to-middle-income countries located in tropical and subtropical zones. The number and availability of drugs for treating these diseases are low, the administration route is inconvenient in some cases, and most of them have safety, efficacy, or adverse/toxic reaction issues. The need for developing new drugs to deal with these issues is clear, but one of the most drastic consequences of this negligence is the lack of interest in the research and development of new therapeutic options among major pharmaceutical companies. Positive changes have been achieved over the last few years, although the overall situation remains alarming. After more than one decade since the original work reviewing antiprotozoal agents came to light, now it is time to question ourselves: How has the scenario for the treatment of protozoal diseases such as malaria, leishmaniasis, human African trypanosomiasis, and American trypanosomiasis changed? This review covers the last decade in terms of the drugs currently available for the treatment of these diseases as well as the clinical candidates being currently investigated.

Synthesis and molecular modelling studies of pyrimidinones and pyrrolo[3,4-d]-pyrimidinodiones as new antiplasmodial compounds.

BACKGROUND Malaria is responsible for 429,000 deaths per year worldwide, and more than 200 million cases were reported in 2015. Increasing parasite resistance has imposed restrictions to the currently available antimalarial drugs. Thus, the search for new, effective and safe antimalarial drugs is crucial. Heterocyclic compounds, such as dihydropyrimidinones (DHPM), synthesised via the Biginelli multicomponent reaction, as well as bicyclic compounds synthesised from DHPMs, have emerged as potential antimalarial candidates in the last few years. METHODS Thirty compounds were synthesised employing the Biginelli multicomponent reaction and subsequent one-pot substitution/cyclisation protocol; the compounds were then evaluated in vitro against chloroquine-resistant Plasmodium falciparum parasites (W2 strain). Drug cytotoxicity in baseline kidney African Green Monkey cells (BGM) was also evaluated. The most active in vitro compounds were evaluated against P. berghei parasites in mice. Additionally, we performed an in silico target fishing approach with the most active compounds, aiming to shed some light into the mechanism at a molecular level. RESULTS The synthetic route chosen was effective, leading to products with high purity and yields ranging from 10-84%. Three out of the 30 compounds tested were identified as active against the parasite and presented low toxicity. The in silico study suggested that among all the molecular targets identified by our target fishing approach, Protein Kinase 3 (PK5) and Glycogen Synthase Kinase 3ß (GSK-3ß) are the most likely molecular targets for the synthesised compounds. CONCLUSIONS We were able to easily obtain a collection of heterocyclic compounds with in vitro anti-P. falciparum activity that can be used as scaffolds for the design and development of new antiplasmodial drugs.

Conformational characterization of ipomotaosides and their recognition by COX-1 and 2.

The aerial parts of Ipomoea batatas are described herein to produce four new resin glycosides, designated as ipomotaosides A, B, C, and D. Ipomotaoside A was found to present inhibitory activity on both cyclooxygenases. However, the conformational elucidation of these molecules may be difficult due to their high flexibility. In this context, the current work presents a conformational characterization of ipomotaosides A-D in aqueous and nonaqueous solvents. The employed protocol includes metadynamics evaluation and unrestrained molecular dynamics simulations (MD). The obtained data provided structural models for the ipomotaosides in good agreement with previous ROESY distances measured in pyridine. Accordingly, the most abundant conformation of ipomotaoside A in solution was employed in flexible docking studies, providing a structural basis for the compound's inhibition of COX enzymes. The so-obtained complex supports resin glycosides' role as original scaffolds for future studies, aiming at structural optimization and development of potential new anti-inflammatory agents.

Two series of new semisynthetic triterpene derivatives: differences in anti-malarial activity, cytotoxicity and mechanism of action.

BACKGROUND: The discovery and development of anti-malarial compounds of plant origin and semisynthetic derivatives thereof, such as quinine (QN) and chloroquine (CQ), has highlighted the importance of these compounds in the treatment of malaria. Ursolic acid analogues bearing an acetyl group at C-3 have demonstrated significant anti-malarial activity. With this in mind, two new series of betulinic acid (BA) and ursolic acid (UA) derivatives with ester groups at C-3 were synthesized in an attempt to improve anti-malarial activity, reduce cytotoxicity, and search for new targets. In vitro activity against CQ-sensitive Plasmodium falciparum 3D7 and an evaluation of cytotoxicity in a mammalian cell line (HEK293T) are reported. Furthermore, two possible mechanisms of action of anti-malarial compounds have been evaluated: effects on mitochondrial membrane potential (ΔΨm) and inhibition of ß-haematin formation. RESULTS: Among the 18 derivatives synthesized, those having shorter side chains were most effective against CQ-sensitive P. falciparum 3D7, and were non-cytotoxic. These derivatives were three to five times more active than BA and UA. A DiOC(6)(3) ΔΨm assay showed that mitochondria are not involved in their mechanism of action. Inhibition of ß-haematin formation by the active derivatives was weaker than with CQ. Compounds of the BA series were generally more active against P. falciparum 3D7 than those of the UA series. CONCLUSIONS: Three new anti-malarial prototypes were obtained from natural sources through an easy and relatively inexpensive synthesis. They represent an alternative for new lead compounds for anti-malarial chemotherapy.

The Design of Multi-target Drugs to Treat Cardiovascular Diseases: Two (or more) Birds on One Stone.

Cardiovascular diseases (CVDs) comprise a group of diseases and disorders of the heart and blood vessels, which together are the number one cause of death worldwide, being associated with multiple genetic and modifiable risk factors, and that may directly arise from different etiologies. For a long time, the search for cardiovascular drugs was based on the old paradigm "one compound - one target", aiming to obtain a highly potent and selective molecule with only one desired molecular target. Although historically successful in the last decades, this approach ignores the multiple causes and the multifactorial nature of CVDs. Thus, over time, treatment strategies for cardiovascular diseases have changed, and, currently, pharmacological therapies for CVD are mainly based on the association of two or more drugs to control symptoms and reduce cardiovascular death. In this context, the development of multitarget drugs, i.e., compounds having the ability to act simultaneously at multiple sites, is an attractive and relevant strategy that can be even more advantageous to achieve predictable pharmacokinetic and pharmacodynamics correlations as well as better patient compliance. In this review, we aim to highlight the efforts and rational pharmacological bases for the design of some promising multitargeted compounds to treat important cardiovascular diseases like heart failure, atherosclerosis, acute myocardial infarction, pulmonary arterial hypertension, and arrhythmia.

The long and winding road of designing phosphodiesterase inhibitors for the treatment of heart failure.

Cyclic nucleotide phosphodiesterases (PDEs) are a superfamily of enzymes known to play a critical role in the indirect regulation of several intracellular metabolism pathways through the selective hydrolysis of the phosphodiester bonds of specific second messenger substrates such as cAMP (3',5'-cyclic adenosine monophosphate) and cGMP (3',5'-cyclic guanosine monophosphate), influencing the hypertrophy, contractility, apoptosis and fibroses in the cardiovascular system. The expression and/or activity of multiple PDEs is altered during heart failure (HF), which leads to changes in levels of cyclic nucleotides and function of cardiac muscle. Within the cardiovascular system, PDEs 1-5, 8 and 9 are expressed and are interesting targets for the HF treatment. In this comprehensive review we will present a briefly description of the biochemical importance of each cardiovascular related PDE to the HF, and cover almost all the "long and winding road" of designing and discovering ligands, hits, lead compounds, clinical candidates and drugs as PDE inhibitors in the last decade.

Novel Quinolinyl-pyrrolo[3,4-d]pyrimidine-2,5-dione Derivatives Against Chloroquine-resistant Plasmodium falciparum.

INTRODUCTION: In this work DHPMs were combined with the quinoline nucleus to obtain new quinolinyl-pyrrolo[3,4-d]pyrimidine-2,5-dione compounds with improved antiplasmodial activity as well as decreased cytotoxicity. Nineteen quinolinyl-pyrrolo[3,4-d]pyrimidine-2,5-dione derivatives connected by a linker group to quinolone ring moieties with different substituents were synthesized and assayed against P. falciparum. MATERIALS AND METHODS: Nineteen quinolinyl-pyrrolo[3,4-d]pyrimidine-2,5-dione derivatives connected by a linker group to quinoline ring moieties with different substituents were synthesized and assayed against chloroquine-resistant Plasmodium falciparum, along with the reference drug chloroquine. Among these compounds, the derivatives with two methylene carbon spacers showed the best activity accompanied by low cytotoxicity. RESULTS: The derivative without substituents on the aromatic ring (2a) and the derivative with a chlorine group at position 4 (2d) provided the best results, with IC50 = 1.15 µM and 1.5 µM, respectively. CONCLUSION: Compared to the parent drugs, these compounds presented marked decreases in cytotoxicity, with MDL50 values over 1,000 µM and selectivity indexes of >869.5 and >666.6, respectively. The quinolinyl-pyrrolo[3,4-d]pyrimidine-2,5-dione framework appears to be promising for further studies as an antimalarial for overcoming the burden of resistance in P. falciparum.

Multicomponent Reactions for the Synthesis of Bioactive Compounds: A Review.

Multicomponent reactions (MCRs) are composed of three or more reagents in which the final product has all or most of the carbon atoms from its starting materials. These reactions represent, in the medicinal chemistry context, great potential in the research for new bioactive compounds, since their products can present great structural complexity. The aim of this review is to present the main multicomponent reactions since the original report by Strecker in 1850 from nowadays, covering their evolution, highlighting their significance in the discovery of new bioactive compounds. The use of MCRs is, indeed, a growing field of interest in the synthesis of bioactive compounds and approved drugs, with several examples of commerciallyavailable drugs that are (or can be) obtained through these protocols.

Synthesis of limonene beta-amino alcohol derivatives in support of new antileishmanial therapies.

A series of seven limonene beta-amino alcohol derivatives has been regioselectively synthesised in moderate to good yields. Two of these compounds were found to be significantly effective against in vitro cultures of the Leishmania (Viannia) braziliensis promastigote form in the micromolar range. The activities found for 3b and 3f were about 100-fold more potent than the standard drug, Pentamidine, in the same test, while limonene did not display any activity. This is the first report of antileishmanial activity by limonene beta-amino alcohol derivatives.

Discovery of a Series of Acridinones as Mechanism-Based Tubulin Assembly Inhibitors with Anticancer Activity.

Microtubules play critical roles in vital cell processes, including cell growth, division, and migration. Microtubule-targeting small molecules are chemotherapeutic agents that are widely used in the treatment of cancer. Many of these compounds are structurally complex natural products (e.g., paclitaxel, vinblastine, and vincristine) with multiple stereogenic centers. Because of the scarcity of their natural sources and the difficulty of their partial or total synthesis, as well as problems related to their bioavailability, toxicity, and resistance, there is an urgent need for novel microtubule binding agents that are effective for treating cancer but do not have these disadvantages. In the present work, our lead discovery effort toward less structurally complex synthetic compounds led to the discovery of a series of acridinones inspired by the structure of podophyllotoxin, a natural product with important microtubule assembly inhibitory activity, as novel mechanism-based tubulin assembly inhibitors with potent anticancer properties and low toxicity. The compounds were evaluated in vitro by wound healing assays employing the metastatic and triple negative breast cancer cell line MDA-MB-231. Four compounds with IC50 values between 0.294 and 1.7 µM were identified. These compounds showed selective cytotoxicity against MDA-MB-231 and DU-145 cancer cell lines and promoted cell cycle arrest in G2/M phase and apoptosis. Consistent with molecular modeling results, the acridinones inhibited tubulin assembly in in vitro polymerization assays with IC50 values between 0.9 and 13 µM. Their binding to the colchicine-binding site of tubulin was confirmed through competitive assays.

Improving the thrombin inhibitory activity of glycyrrhizin, a triterpenic saponin, through a molecular simplification of the carbohydrate moiety.

Glycyrrhizin, a saponin, and its aglycone glycyrrhetinic acid are natural products found in the Liquorice (Glycyrrhiza glabra L.) root extract. This saponin is known for its in vitro and in vivo thrombin inhibitory activity. The design and synthesis of five glycyrrhizin derivatives were carried out to improve the natural product activity. Compound 3b, a phthalic ester derivative of glycyrrhizin, presented a more pronounced thrombin inhibition (IC50  = 114.4 ± 1.3 µm) than the saponin (IC50  = 235.7 ± 1.4 µm). Molecular docking simulations performed to investigate the molecular interaction between compound 3b and the enzyme indicate that this product is, as previously determined for glycyrrhizin, an allosteric thrombin inhibitor.

Synthesis and molecular modelling studies of pyrimidinones and pyrrolo[34-d]-pyrimidinodiones as new antiplasmodial compounds

BACKGROUND Malaria is responsible for 429,000 deaths per year worldwide, and more than 200 million cases were reported in 2015. Increasing parasite resistance has imposed restrictions to the currently available antimalarial drugs. Thus, the search for new, effective and safe antimalarial drugs is crucial. Heterocyclic compounds, such as dihydropyrimidinones (DHPM), synthesised via the Biginelli multicomponent reaction, as well as bicyclic compounds synthesised from DHPMs, have emerged as potential antimalarial candidates in the last few years. METHODS Thirty compounds were synthesised employing the Biginelli multicomponent reaction and subsequent one-pot substitution/cyclisation protocol; the compounds were then evaluated in vitro against chloroquine-resistant Plasmodium falciparum parasites (W2 strain). Drug cytotoxicity in baseline kidney African Green Monkey cells (BGM) was also evaluated. The most active in vitro compounds were evaluated against P. berghei parasites in mice. Additionally, we performed an in silico target fishing approach with the most active compounds, aiming to shed some light into the mechanism at a molecular level. RESULTS The synthetic route chosen was effective, leading to products with high purity and yields ranging from 10-84%. Three out of the 30 compounds tested were identified as active against the parasite and presented low toxicity. The in silico study suggested that among all the molecular targets identified by our target fishing approach, Protein Kinase 3 (PK5) and Glycogen Synthase Kinase 3β (GSK-3β) are the most likely molecular targets for the synthesised compounds. CONCLUSIONS We were able to easily obtain a collection of heterocyclic compounds with in vitro anti-P. falciparum activity that can be used as scaffolds for the design and development of new antiplasmodial drugs.

Synthesis and in vitro activity of limonene derivatives against Leishmania and Trypanosoma.

The synthesis and in vitro activity of R(+)-Limonene derivatives against Leishmania and Trypanosoma cruzi strains are reported. Seven compounds have shown better in vitro activity against Leishmania (V.)braziliensis than the standard drug pentamidine. Additionally, we have identified two promising new anti-T. cruzi limonene derivatives.

Synthesis of limonene β-amino alcohol derivatives in support of new antileishmanial therapies

A series of seven limonene β-amino alcohol derivatives has been regioselectively synthesised in moderate to good yields. Two of these compounds were found to be significantly effective against in vitro cultures of the Leishmania (Viannia) braziliensis promastigote form in the micromolar range. The activities found for 3b and 3f were about 100-fold more potent than the standard drug, Pentamidine, in the same test, while limonene did not display any activity. This is the first report of antileishmanial activity by limonene β-amino alcohol derivatives.