Direct synthesis of C3-mono-functionalized oxindoles from N-unprotected 2-oxindole and their antileishmanial activity

Spiro heterocycles bearing piperidine moiety as potential scaffold for antileishmanial activity: synthesis, biological evaluation, and in silico studies

New spiro-piperidine derivatives were synthesised via the eco-friendly ionic liquids in a one-pot fashion. The in vitro antileishmanial activity against Leishmania major promastigote and amastigote forms highlighted promising antileishmanial activity for most of the derivatives, with superior activity compared to miltefosine. The most active compounds 8a and 9a exhibited sub-micromolar range of activity, with IC50 values of 0.89 µM and 0.50 µM, respectively, compared to 8.08 µM of miltefosine. Furthermore, the antileishmanial activity reversal of these compounds via folic and folinic acids displayed comparable results to the positive control trimethoprim. This emphasises that their antileishmanial activity is through the antifolate mechanism via targeting DHFR and PTR1. The most active compounds showed superior selectivity and safety profile compared to miltefosine against VERO cells. Moreover, the docking experiments of 8a and 9a against Lm-PTR1 rationalised the observed in vitro activities. Molecular dynamics simulations confirmed a stable and high potential binding to Lm-PTR1.

Natural-Product-Inspired Microwave-Assisted Synthesis of Novel Spirooxindoles as Antileishmanial Agents: Synthesis, Stereochemical Assignment, Bioevaluation, SAR, and Molecular Docking Studies

Leishmaniasis is a neglected tropical disease, and there is an emerging need for the development of effective drugs to treat it. To identify novel compounds with antileishmanial properties, a novel series of functionalized spiro[indoline-3,2'-pyrrolidin]-2-one/spiro[indoline-3,3'-pyrrolizin]-2-one 23a-f, 24a-f, and 25a-g were prepared from natural-product-inspired pharmaceutically privileged bioactive sub-structures, i.e., isatins 20a-h, various substituted chalcones 21a-f, and 22a-c amino acids, via 1,3-dipolar cycloaddition reactions in MeOH at 80 °C using a microwave-assisted approach. Compared to traditional methods, microwave-assisted synthesis produces higher yields and better quality, and it takes less time. We report here the in vitro antileishmanial activity against Leishmania donovani and SAR studies. The analogues 24a, 24e, 24f, and 25d were found to be the most active compounds of the series and showed IC₅₀ values of 2.43 µM, 0.96 µM, 1.62 µM, and 3.55 µM, respectively, compared to the standard reference drug Amphotericin B (IC₅₀ = 0.060 µM). All compounds were assessed for Leishmania DNA topoisomerase type IB inhibition activity using the standard drug Camptothecin, and 24a, 24e, 24f, and 25d showed potential results. In order to further validate the experimental results and gain a deeper understanding of the binding manner of such compounds, molecular docking studies were also performed. The stereochemistry of the novel functionalized spirooxindole derivatives was confirmed by single-crystal X-ray crystallography studies.

Hierarchical Clustering and Target-Independent QSAR for Antileishmanial Oxazole and Oxadiazole Derivatives

Leishmaniasis is a neglected tropical disease that kills more than 20,000 people each year. The chemotherapy available for the treatment of the disease is limited, and novel approaches to discover novel drugs are urgently needed. Herein, 2D- and 4D-quantitative structure–activity relationship (QSAR) models were developed for a series of oxazole and oxadiazole derivatives that are active against Leishmania infantum, the causative agent of visceral leishmaniasis. A clustering strategy based on structural similarity was applied with molecular fingerprints to divide the complete set of compounds into two groups. Hierarchical clustering was followed by the development of 2D- (R2 = 0.90, R2pred = 0.82) and 4D-QSAR models (R2 = 0.80, R2pred = 0.64), which showed improved statistical robustness and predictive ability.

Metabolic Pathways of Leishmania Parasite: Source of Pertinent Drug Targets and Potent Drug Candidates

Leishmaniasis is a tropical disease caused by a protozoan parasite Leishmania that is transmitted via infected female sandflies. At present, leishmaniasis treatment mainly counts on chemotherapy. The currently available drugs against leishmaniasis are costly, toxic, with multiple side effects, and limitations in the administration route. The rapid emergence of drug resistance has severely reduced the potency of anti-leishmanial drugs. As a result, there is a pressing need for the development of novel anti-leishmanial drugs with high potency, low cost, acceptable toxicity, and good pharmacokinetics features. Due to the availability of preclinical data, drug repurposing is a valuable approach for speeding up the development of effective anti-leishmanial through pointing to new drug targets in less time, having low costs and risk. Metabolic pathways of this parasite play a crucial role in the growth and proliferation of Leishmania species during the various stages of their life cycle. Based on available genomics/proteomics information, known pathways-based (sterol biosynthetic pathway, purine salvage pathway, glycolysis, GPI biosynthesis, hypusine, polyamine biosynthesis) Leishmania-specific proteins could be targeted with known drugs that were used in other diseases, resulting in finding new promising anti-leishmanial therapeutics. The present review discusses various metabolic pathways of the Leishmania parasite and some drug candidates targeting these pathways effectively that could be potent drugs against leishmaniasis in the future.

Recent Progress in the Development of Indole-Based Compounds Active against Malaria, Trypanosomiasis and Leishmaniasis

Human protozoan diseases represent a serious health problem worldwide, affecting mainly people in social and economic vulnerability. These diseases have attracted little investment in drug discovery, which is reflected in the limited available therapeutic arsenal. Authorized drugs present problems such as low efficacy in some stages of the disease or toxicity, which result in undesirable side effects and treatment abandonment. Moreover, the emergence of drug-resistant parasite strains makes necessary an even greater effort to develop safe and effective antiparasitic agents. Among the chemotypes investigated for parasitic diseases, the indole nucleus has emerged as a privileged molecular scaffold for the generation of new drug candidates. In this review, the authors provide an overview of the indole-based compounds developed against important parasitic diseases, namely malaria, trypanosomiasis and leishmaniasis, by focusing on the design, optimization and synthesis of the most relevant synthetic indole scaffolds recently reported.

Highly diastereoselective cascade [5 + 1] double Michael reaction, a route for the synthesis of spiro(thio)oxindoles

The first diastereoselective synthesis of spirothiooxindoles is reported via the Michael reaction between thiooxindoles and dibenzalacetones. The reaction was conducted without any catalyst or additive under green conditions, i.e., ethanol as the solvent and at room temperature. In addition, the described robust method benefits from scalability, simple work-up, and column chromatography-free purification. This work demonstrates the art of governing regio- and stereoselectivity, which has been discussed in the light of Density Functional Theory calculations. Our method represents the first synthesis of spiro[cyclohexanone-thiooxindoles] with the relative configuration of the aryl moieties at the cyclohexanone ring as cis. The obtained cis-spirothiooxindoles, can be used to afford cis-spirooxindoles, which their synthesis had not been explored before. According to our molecular docking studies, cis-spirooxindoles demonstrate higher binding affinities than corresponding trans-spirooxindoles for the OPRT domain of the Leishmania donovani uridine 5′-monophosphate synthase (LdUMPS). Thus, the reported method may eventually be utilized to develop new hit compounds for leishmaniasis treatment.

Discovery of highly potent and selective antiparasitic new oxadiazole and hydroxy-oxindole small molecule hybrids

A series of highly active hybrids were discovered as novel antiparasitic agents. Two heterocyclic scaffolds (1,2,4-oxadiazole and 3-hydroxy-2-oxindole) were linked, and the resulting compounds showed in vitro activities against intracellular amastigotes of two protozoan parasites, Trypanosoma cruzi and Leishmania infantum. Their cytotoxicity was assessed using HFF-1 fibroblasts and HepG2 hepatocytes. Compounds 5b, 5d, 8h and 8o showed selectivity against L. infantum (IC₅₀ values of 3.89, 2.38, 2.50 and 2.85 μM, respectively). Compounds 4c, 4q, 8a and 8k were the most potent against T. cruzi, exhibiting IC₅₀ values of 6.20, 2.20, 2.30 and 2.20 μM, respectively. Additionally, the most potent anti-T. cruzi compounds showed in vitro efficacies comparable or superior to that of benznidazole. These easy-to-synthesize molecules represent novel chemotypes for the design of potent and selective lead compounds for Chagas disease and leishmaniasis drug discovery.

Synthesis and Anti-HIV Profile of a Novel Tetrahydroindazolylbenzamide Derivative Obtained by Oxazolone Chemistry

A new tetrahydroindazolylbenzamide derivative has been synthesized, characterized, and evaluated as HIV-inhibitor. The biological data revealed the ability to inhibit HIV proliferation with low cytotoxicity allowing for significant selectivity (EC₅₀ 2.77 μM; CC₅₀ 118.7 μM; SI = 68). The compound did not inhibit the viral integrase as demonstrated by in vitro studies. QPCR experiments showed that the block of viral replication occurred at early replication steps, prior to integration, profiling it as a late reverse transcription inhibitor. An efficient multistep strategy was adopted for the synthesis of the scaffold, consisting of a sequential ring-opening reaction of oxazol-5-(4H)-one with 1,3-diketone, followed by cyclocondensation with hydrazine and hydrolysis of the nitrile to the desired carboxamide.

Anti-leishmanial effect of spiro dihydroquinoline-oxindoles on volume regulation decrease and sterol biosynthesis of Leishmania braziliensis

Diverse spiro dihydroquinoline-oxindoles (JS series) were prepared using the BF₃•OEt₂-catalyzed imino Diels-Alder reaction between ketimine-isatin derivatives and trans-isoeugenol. Ten spiro-oxiindole derivatives were selected and evaluated at different stages of the life cycle of Leishmania braziliensis parasites, responsible for cutaneous leishmaniasis in South America. Among them, the 8'-ethyl-4'-(4-hydroxy-3-methoxyphenyl)-3'-methyl-3',4'-dihydro-1'H-spiro[indoline-3,2'-quinolin]-2-one called JS87 was able to inhibit the growth of promastigotes without affecting the mammalian cells viability, and to decrease the number of intracellular amastigotes of L. braziliensis. This spiro compound was found to act through the alteration of parasite internal regulation by disrupting the regulatory volume decrease (RVD), and to affect the sterol biosynthetic pathway at level of squalene epoxidase (SE) enzyme. These results revealed that the spiro annulation between quinoline and oxindole scaffolds enhances the anti-leishmanial activity, and could assist in the development of potent quinoline-oxindole hybrids against Leishmania braziliensis, the main etiological agent of cutaneous leishmaniasis in South America.

Discovery of benzimidazole-based Leishmania mexicana cysteine protease CPB2.8ΔCTE inhibitors as potential therapeutics for leishmaniasis

Chemotherapy is currently the only effective approach to treat all forms of leishmaniasis. However, its effectiveness is severely limited due to high toxicity, long treatment length, drug resistance, or inadequate mode of administration. As a consequence, there is a need to identify new molecular scaffolds and targets as potential therapeutics for the treatment of this disease. We report a small series of 1,2-substituted-1H-benzo[d]imidazole derivatives (9a-d) showing affinity in the submicromolar range (K_i  = 0.15-0.69 μM) toward Leishmania mexicanaCPB2.8ΔCTE, one of the more promising targets for antileishmanial drug design. The compounds confirmed activity in vitro against intracellular amastigotes of Leishmania infantum with the best result being obtained with derivative 9d (IC₅₀  = 6.8 μM), although with some degree of cytotoxicity (CC₅₀  = 8.0 μM on PMM and CC₅₀  = 32.0 μM on MCR-5). In silico molecular docking studies and ADME-Tox properties prediction were performed to validate the hypothesis of the interaction with the intended target and to assess the drug-likeness of these derivatives.

"Click" on PLGA-PEG and hyaluronic acid: Gaining access to anti-leishmanial pentamidine bioconjugates

Pentamidine (Pent), an antiparasitic drug used for the treatment of visceral leishmaniasis, has been modified with terminal azide groups and conjugated to two different polymer backbones (PLGA-PEG [PP] copolymer and hyaluronic acid [HA]) armed with alkyne end-groups. The conjugation has been performed by Copper Catalyzed Azido Alkyne Cycloaddition (CuAAC) using CuSO₄ /sodium ascorbate as metal source. The novel PP-Pent and HA-Pent bioconjugates are proposed, respectively, as non-targeted and targeted drug delivery systems against Leishmania infections. Moreover, Pent has been encapsulated into PP nanoparticles by the oil-in-water emulsion method, with the aim to compare the biological activity of the bioconjugates with that of the classical drug-loaded delivery system that physically entraps the therapeutic agent. Biological assays against Leishmania infantum amastigote-infected macrophages and primary macrophages revealed that Pent, either covalently conjugated with polymers or loaded into polymeric nanoparticles, turned out to be more potent and less toxic than the free Pent. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2778-2785, 2018.

Chemoselective Double Michael Addition: Synthesis of 2,6-Diarylspiro[Cyclohexane-1,3′-Indoline]-2′,4-Diones via Addition of Indolin-2-One to Divinyl Ketones

Seventeen examples of 2,6-diarylspiro[cyclohexane-1,3′-indoline]-2′4-diones were efficiently prepared by the Cs2CO3-catalysed chemoselective double Michael additions of indolin-2-one to divinyl ketones. This method has the advantage of high chemoselectivity, mild reaction conditions, high yield and atom- and step-economy.

A Novel Spirooxindole Derivative Inhibits the Growth of Leishmania donovani Parasites both In Vitro and In Vivo by Targeting Type IB Topoisomerase

Visceral leishmaniasis is a fatal parasitic disease, and there is an emergent need for development of effective drugs against this neglected tropical disease. We report here the development of a novel spirooxindole derivative, N-benzyl-2,2'α-3,3',5',6',7',7α,α'-octahydro-2methoxycarbonyl-spiro[indole-3,3'-pyrrolizidine]-2-one (compound 4c), which inhibits Leishmania donovani topoisomerase IB (LdTopIB) and kills the wild type as well as drug-resistant parasite strains. This compound inhibits catalytic activity of LdTopIB in a competitive manner. Unlike camptothecin (CPT), the compound does not stabilize the DNA-topoisomerase IB cleavage complex; rather, it hinders drug-DNA-enzyme covalent complex formation. Fluorescence studies show that the stoichiometry of this compound binding to LdTopIB is 2:1 (mole/mole), with a dissociation constant of 6.65 μM. Molecular docking with LdTopIB using the stereoisomers of compound 4c produced two probable hits for the binding site, one in the small subunit and the other in the hinge region of the large subunit of LdTopIB. This spirooxindole is highly cytotoxic to promastigotes of L. donovani and also induces apoptosis-like cell death in the parasite. Treatment with compound 4c causes depolarization of mitochondrial membrane potential, formation of reactive oxygen species inside parasites, and ultimately fragmentation of nuclear DNA. Compound 4c also effectively clears amastigote forms of wild-type and drug-resistant parasites from infected mouse peritoneal macrophages but has less of an effect on host macrophages. Moreover, compound 4c showed strong antileishmanial efficacies in the BALB/c mouse model of leishmaniasis. This compound potentially can be used as a lead for developing excellent antileishmanial agents against emerging drug-resistant strains of the parasite.

Alterations in Red Blood Cell Functionality Induced by an Indole Scaffold Containing a Y-Iminodiketo Moiety: Potential Antiproliferative Conditions

We have recently proposed a new erythrocyte-based model of study to predict the antiproliferative effects of selected heterocyclic scaffolds. Starting from the metabolic similarity between erythrocytes and cancer cells, we have demonstrated how the metabolic derangement induced by an indolone-based compound (DPIT) could be related to its antiproliferative effects. In order to prove the validity of our biochemical approach, in the present study the effects on erythrocyte functionality of its chemical precursor (PID), whose synthesis we reported, were investigated. The influence of the tested compound on band 3 protein (B3), oxidative state, ATP efflux, caspase 3, metabolism, intracellular pH, and Ca²⁺ homeostasis has been evaluated. PID crosses the membrane localizing into the cytosol, increases anion exchange, induces direct caspase activation, shifts the erythrocytes towards an oxidative state, and releases less ATP than in normal conditions. Analysis of phosphatidylserine externalization shows that PID slightly induces apoptosis. Our findings indicate that, due to its unique features, erythrocyte responses to exogenous molecular stimuli can be fruitfully correlated at structurally more complex cells, such as cancer cells. Overall, our work indicates that erythrocyte is a powerful study tool to elucidate the biochemical/biological effects of selected heterocycles opening considerable perspectives in the field of drug discovery.

Oxindole: A chemical prism carrying plethora of therapeutic benefits

Oxindole has emerged as a valuable scaffold in medicinal chemistry possessing diverse range of pharmacological activities. Its value has further been increased by its natural occurrence as alkaloids in variety of plants. It was first extracted from the cat claw's plant Uncaria tomentosa found in the Amazon rainforest and other tropical areas of South and Central America. Traditionally as well as present emerging therapeutic potential of oxindole nucleus has captured the interest of medicinal chemists to synthesize novel oxindole derivatives. In the present review the authors have integrated its chemistry and synthetic strategies developed after 1945. Also the information of naturally occurring oxindole alkaloids has been incorporated. The detailed pharmacological activities including anti-cancer, anti-HIV, antidiabetic, antibacterial, antioxidant, kinase inhibitory, AChE inhibitory, anti-leishmanial, β3 adrenergic receptor agonistic, phosphatase inhibitory, analgesic, spermicidal, vasopressin antagonists, progesterone antagonists, neuroprotection, and NMDA blocker activities of oxindole derivatives alongwith their SAR has also been discussed in detail. Additionally, information regarding the oxindole derivatives in clinical trials has been incorporated. Thus, this review will provide insights for the synthetic as well as medicinal chemist for the designing and synthesis of novel oxindole derivatives with novel improved range of pharmacological implications.

Decorated 6,6′,7,7′-tetrahydro-1H,1′H-2,3′-biindole scaffold as promising candidate for recognition of the CDK2 allosteric site

Decorated 6,6′,7,7′-tetrahydro-1H,1′H-2,3′-biindoles, such as DPIT, targeting CDK2 seem to be an attractive scaffold for development of useful anticancer drugs.

A new erythrocyte-based biochemical approach to predict the antiproliferative effects of heterocyclic scaffolds: The case of indolone

BACKGROUND

The indole core is a key structural feature of many natural products and biomolecules with broad spectrum chemotherapeutic properties. Some of us have recently synthesized a library of biologically promising indolone-based compounds. The present study focuses on the effects of one of them, namely DPIT, on human erythrocytes.

METHODS

We have examined the influence of DPIT on band 3 protein, intracellular ATP concentration and transport, caspase 3 activation, metabolic adaptation and membrane stability.

RESULTS

Our study elucidates that DPIT, intercalated into the phospholipid bilayer, decreases the anion transport, the intracellular ATP concentration and the cytosolic pH, inducing a direct activation of caspase 3.

CONCLUSIONS

Starting from the metabolic similarity between erythrocytes and cancer cells, we investigate how the metabolic derangements and membrane alterations induced by selected heterocycles could be related to the antiproliferative effects.

GENERAL SIGNIFICANCE

Our work aims to propose a new model of study to predict the antiproliferative effects of heterocyclic scaffolds, pointing out that only one of the listed conditions would be unfavorable to the life cycle of neoplastic cells.

Synthesis, Crystal Structure, and Biological Activity ofcis/transAmide Rotomers of (Z)-N′-(2-Oxoindolin-3-ylidene)formohydrazide

(Z)-N′-(2-Oxoindolin-3-ylidene)formohydrazide (2) was synthesized by the reaction of (Z)-3-hydrazonoindolin-2-one (1) with formic acid under reflux. The structure of2was characterized by IR, Mass,1H NMR, and X-ray crystal structure determination. Interestingly, compound2appeared in DMSO-d6ascisandtransamide rotomers in 25% and 75%, respectively. The X-ray analysis showed theZgeometrical isomer of2around –C=N– forcisandtransamide rotomers. The crystal of2belongs to monoclinic, space groupP21/c, witha=4.5206(1) Å,b=22.4747(7) Å,c=17.3637(5) Å,β=103.752(1)°,Z=8,V=1713.57(8) Å3,Dc=1.467 Mg m−3,μ=0.11 mm−1,F(000)=784,R=0.047, andwR=0.123for 3798 observed reflections withI>2σ(I). Compound2exhibited a moderate activity in its antimicrobial evaluation againstE. coliandP. aeruginosaand a good activity againstS. aureusclose to that of the standard drug ciprofloxacin. Thein vitroanticancer activity of2was evaluated against two human tumor cell lines, namely, HepG2 hepatocellular carcinoma and MCF-7 breast cancer. HepG2 cancer cell line was more susceptible to compound2than MCF-7.