Synthesis of three classes of rhodacyanine dyes and evaluation of their in vitro and in vivo antimalarial activity

Antimalarial activities of benzothiazole analogs: A systematic review

BACKGROUND

Benzothiazole derivatives have been reported to possess a wide range of biological activities, including antimalarial activity. This systematic review aims to summarize and evaluate the antimalarial activities of benzothiazole analogs.

METHODS

We conducted an electronic search using nine databases in October 2017 and subsequently updated in September 2022. We included all original in vitro and in vivo studies that documented the antimalarial activities of compounds containing benzothiazole analogs with no restriction. The risk of bias of each included study was assessed by ToxRTool.

RESULTS

Twenty-eight articles were included in our study, which are in vitro, in vivo, or both. Of these, 232 substances were identified to have potent antiplasmodial activity against various strains of the malaria parasite. Benzothiazole analogs show different antimalarial mechanisms, including inhibition of Plasmodium falciparum enzymes in in vitro studies and inhibition of blood parasites in in vivo studies.

CONCLUSIONS

Benzothiazole derivatives are promising substances for treating malaria. The structure-activity relationship studies suggest that the substitution pattern of the benzothiazole scaffold plays a crucial role in determining the antimalarial activity of the analog.

Synthesis, antiproliferative and antitrypanosomal activities, and DNA binding of novel 6-amidino-2-arylbenzothiazoles

A series of 6-amidinobenzothiazoles, linked via phenoxymethylene or directly to the 1,2,3-triazole ring with a p-substituted phenyl or benzyl moiety, were synthesised and evaluated in vitro against four human tumour cell lines and the protozoan parasite Trypanosoma brucei. The influence of the type of amidino substituent and phenoxymethylene linker on antiproliferative and antitrypanosomal activities was observed, showing that the imidazoline moiety had a major impact on both activities. Benzothiazole imidazoline 14a, which was directly connected to N-1-phenyl-1,2,3-triazole, had the most potent growth-inhibitory effect (IC₅₀ = 0.25 µM) on colorectal adenocarcinoma (SW620), while benzothiazole imidazoline 11b, containing a phenoxymethylene linker, exhibited the best antitrypanosomal potency (IC₉₀ = 0.12 µM). DNA binding assays showed a non-covalent interaction of 6-amidinobenzothiazole ligands, indicating both minor groove binding and intercalation modes of DNA interaction. Our findings encourage further development of novel structurally related 6-amidino-2-arylbenzothiazoles to obtain more selective anticancer and anti-HAT agents.

Exported plasmodial J domain protein, PFE0055c, and PfHsp70-x form a specific co-chaperone-chaperone partnership

Plasmodium falciparum is a unicellular protozoan parasite and causative agent of a severe form of malaria in humans, accounting for very high worldwide fatality rates. At the molecular level, survival of the parasite within the human host is mediated by P. falciparum heat shock proteins (PfHsps) that provide protection during febrile episodes. The ATP-dependent chaperone activity of Hsp70 relies on the co-chaperone J domain protein (JDP), with which it forms a chaperone-co-chaperone complex. The exported P. falciparum JDP (PfJDP), PFA0660w, has been shown to stimulate the ATPase activity of the exported chaperone, PfHsp70-x. Furthermore, PFA0660w has been shown to associate with another exported PfJDP, PFE0055c, and PfHsp70-x in J-dots, highly mobile structures found in the infected erythrocyte cytosol. Therefore, the present study aims to conduct a structural and functional characterization of the full-length exported PfJDP, PFE0055c. Recombinant PFE0055c was successfully expressed and purified and found to stimulate the basal ATPase activity of PfHsp70-x to a greater extent than PFA0660w but, like PFA0660w, did not significantly stimulate the basal ATPase activity of human Hsp70. Small-molecule inhibition assays were conducted to determine the effect of known inhibitors of JDPs (chalcone, C86) and Hsp70 (benzothiazole rhodacyanines, JG231 and JG98) on the basal and PFE0055c-stimulated ATPase activity of PfHsp70-x. In this study, JG231 and JG98 were found to inhibit both the basal and PFE0055c-stimulated ATPase activity of PfHsp70-x. C86 only inhibited the PFE0055c-stimulated ATPase activity of PfHsp70-x, consistent with PFE0055c binding to PfHsp70-x through its J domain. This research has provided further insight into the molecular basis of the interaction between these exported plasmodial chaperones, which could inform future antimalarial drug discovery studies.

Role of the J Domain Protein Family in the Survival and Pathogenesis of Plasmodium falciparum

Plasmodium falciparum has dedicated an unusually large proportion of its genome to molecular chaperones (2% of all genes), with the heat shock protein 40 (Hsp40) family (now called J domain proteins, JDPs) exhibiting evolutionary radiation into 49 members. A large number of the P. falciparum JDPs (PfJDPs) are predicted to be exported, with certain members shown experimentally to be present in the erythrocyte cytosol (PFA0660w and PFE0055c) or erythrocyte membrane (ring-infected erythrocyte surface antigen, RESA). PFA0660w and PFE0055c are associated with an exported plasmodial Hsp70 (PfHsp70-x) within novel mobile structures called J-dots, which have been proposed to be dedicated to the trafficking of key membrane proteins such as erythrocyte membrane protein 1 (PfEMP1). Well over half of the PfJDPs appear to be essential, including the J-dot PfJDP, PFE0055c, while others have been found to be required for growth under febrile conditions (e.g. PFA0110w, the ring-infected erythrocyte surface antigen protein [RESA]) or involved in pathogenesis (e.g. PF10_0381 has been shown to be important for protrusions of the infected red blood cell membrane, the so-called knobs). Here we review what is known about those PfJDPs that have been well characterised, and may be directly or indirectly involved in the survival and pathogenesis of the malaria parasite.

A novel mitochondria-targeted ratiometric fluorescent probe for endogenous sulfur dioxide derivatives as a cancer-detecting tool

A new mitochondria-targeted fluorescent probe RBC, constructed using a coumarin moiety which was selected as the donor and a benzothiazole derivative as the acceptor, for SO₂ derivatives (HSO₃^-/SO₃^2-) was presented. The probe designed on a new FRET platform showed high selectivity and a low detection limit. Importantly, the probe could respond to HSO₃^-/SO₃^2- within 35 s. Furthermore, the probe could target mitochondria and was successfully used for fluorescence imaging of endogenous bisulfite in HepG2 with low cytotoxicity, which significantly assisted in cancer diagnosis.

Structural Activity Relationship and Importance of Benzothiazole Derivatives in Medicinal Chemistry: A Comprehensive Review

:

Benzothiazole (1, 3-benzothiazole) is one of the heterocyclic compounds, which is a weak base having varied biological activities. The unique methine center present in the thiazole ring makes benzothiazole as the most important heterocyclic compound. It is a common and integral structure of many natural and synthetic bioactive molecules. Benzothiazole derivatives show a variety of activities, with less toxic effects and their derivatives showed enhanced activities, which has proven Benzothiazole scaffold as one of the important moieties in medicinal chemistry. Benzothiazole ring containing compounds possess various pharmacological activities such as anti-viral, anti-microbial, antiallergic, anti-diabetic, anti-tumor, anti-inflammatory, anthelmitic and anti-cancer, which makes benzothiazole a rapidly developing and interesting compound in the medicinal chemistry. This review briefly explains the importance, common methods of synthesis of the benzothiazole scaffold and also explains the popular benzothiazole molecules which have applications in various fields of chemistry. A review has been carried out based on various pharmacological activities containing benzothiazole moieties and rationalize the activities based on the structural variations. Literature on benzothiazole derivatives reveals that substitution on the C-2 carbon atom and C-6 are the reasons for a variety of biological activities.

Synthesis and antileishmanial activity of fluorinated rhodacyanine analogues: The 'fluorine-walk' analysis

In a search for potent antileishmanial drug candidates, eighteen rhodacyanine analogues bearing fluorine or perfluoroalkyl substituents at various positions were synthesized. These compounds were tested for their inhibitory activities against Leishmania martiniquensis and L. orientalis. This 'fluorine-walk' analysis revealed that the introduction of fluorine atom at C-5, 6, 5', or 6' on the benzothiazole units led to significant enhancement of the activity, correlating with the less negative reduction potentials of the fluorinated analogues confirmed by the electrochemical study. On the other hand, CF₃ and OCF₃ groups were found to have detrimental effects, which agreed with the poor aqueous solubility predicted by the in silico ADMET analysis. In addition, some of the analogues including the difluorinated species showed exceptional potency against the promastigote and axenic amastigote stages (IC₅₀ = 40-85 nM), with the activities surpassing both amphotericin B and miltefosine.

Facile Synthesis of a Series of Non-Symmetric Thioethers Including a Benzothiazole Moiety and Their Use as Efficient In Vitro anti-Trypanosoma cruzi Agents

A series of 2-benzylsulfanyl benzothiazole (BTA) derivatives were synthesized and fully characterized and in vitro tested against two strains of T. cruzi (NINOA and INC-5), exhibiting good activities at low concentrations.

5-Ene-4-thiazolidinones - An efficient tool in medicinal chemistry

The presented review is an attempt to summarize a huge volume of data on 5-ene-4-thiazolidinones being a widely studied class of small molecules used in modern organic and medicinal chemistry. The manuscript covers approaches to the synthesis of 5-ene-4-thiazolidinone derivatives: modification of the C5 position of the basic core; synthesis of the target compounds in the one-pot or multistage reactions or transformation of other related heterocycles. The most prominent pharmacological profiles of 5-ene derivatives of different 4-thiazolidinone subtypes belonging to hit-, lead-compounds, drug-candidates and drugs as well as the most studied targets have been discussed. Currently target compounds (especially 5-en-rhodanines) are assigned as frequent hitters or pan-assay interference compounds (PAINS) within high-throughput screening campaigns. Nevertheless, the crucial impact of the presence/nature of C5 substituent (namely 5-ene) on the pharmacological effects of 5-ene-4-thiazolidinones was confirmed by the numerous listed findings from the original articles. The main directions for active 5-ene-4-thiazolidinones optimization have been shown: i) complication of the fragment in the C5 position; ii) introduction of the substituents in the N3 position (especially fragments with carboxylic group or its derivatives); iii) annealing in complex heterocyclic systems; iv) combination with other pharmacologically attractive fragments within hybrid pharmacophore approach. Moreover, the utilization of 5-ene-4-thiazolidinones in the synthesis of complex compounds with potent pharmacological application is described. The chemical transformations cover mainly the reactions which involve the exocyclic double bond in C5 position of the main core and correspond to the abovementioned direction of the 5-ene-4-thiazolidinone modification.

Recent developments with rhodanine as a scaffold for drug discovery

INTRODUCTION

Rhodanines, as one of the 4-thiazolidinones subtypes, are recognized as privileged heterocycles in medicinal chemistry. The main achievements include the development of drug-like molecules with numerous biological activities as well as approved drugs. Among rhodanines, 5-ene-rhodanines are of special interest, and are often claimed as pan assay interference compounds due to Michael acceptor functionality. Areas covered: Herein, the synthetic protocols for rhodanines and their transformation are reviewed. Biological activity is briefly discussed as well as biotargets, mode of actions and optimization directions. Furthermore, the utilization of 5-ene-rhodanines in Michael additions are discussed while both pro and contra arguments have been outlined within medicinal chemistry application. Expert opinion: Rhodanines remain privileged heterocycles in drug discovery. They are accessible building blocks for optimization and transformation into related heterocycles, simplified analogues and fused heterocycles with a thiazolidine framework. Michael acceptor functionality, as well as the thesis about low selectivity towards biotargets of rhodanines, must be confirmed experimentally and it cannot be based on just the presence of conjugated α,β-unsaturated carbonyl. Moreover, the positive aspects of Michael acceptors must be considered as well as their multitarget properties. New criteria for target affinity must be found. In conclusion, rhodanines are generally not problematic per se.

A comprehensive review in current developments of benzothiazole-based molecules in medicinal chemistry

Benzothiazole (BTA) and its derivatives are the most important heterocyclic compounds, which are common and integral feature of a variety of natural products and pharmaceutical agents. BTA shows a variety of pharmacological properties, and its analogs offer a high degree of structural diversity that has proven useful for the search of new therapeutic agents. The broad spectrum of pharmacological activity in individual BTA derivative indicates that, this series of compounds is of an undoubted interest. The related research and developments in BTA-based medicinal chemistry have become a rapidly developing and increasingly active topic. Particularly, numerous BTA-based compounds as clinical drugs have been extensively used in practice to treat various types of diseases with high therapeutic potency. This work systematically gives a comprehensive review in current developments of BTA-based compounds in the whole range of medicinal chemistry as anticancer, antibacterial, antifungal, antiinflammatory, analgesic, anti-HIV, antioxidant, anticonvulsant, antitubercular, antidiabetic, antileishmanial, antihistaminic, antimalarial and other medicinal agents. It is believed that, this review article is helpful for new thoughts in the quest for rational designs of more active and less toxic BTA-based drugs, as well as more effective diagnostic agents and pathologic probes.

Cinchona alkaloid derivative-catalyzed enantioselective synthesis via a Mannich-type reaction and antifungal activity of β-amino esters bearing benzoheterocycle moieties

An efficient synthesis of highly functionalized chiral β-amino ester derivatives containing benzothiophene and benzothiazole moieties is developed by a Mannich-type reaction using a cinchona alkaloid-derived thiourea catalyst. The desired products were obtained in good yields and high enantioselectivities (~86% yield, >99% ee) using to the optimized reaction conditions. The synthesized compounds were characterized by 1H-NMR, 13C-NMR, IR, and HREI-MS analyses. The bioassays identified that compound 5dr has excellent antifungal activity, with a 60.53% inhibition rate against F. oxysporum, higher than that of the commercial agricultural fungicide hymexazol, whose inhibition rate was 56.12%.

Optical properties of hemicyanines with terminal amino groups and their applications in near-infrared fluorescent imaging of nucleoli

A cellular dye with properties of long-wave emission, large Stokes shift, water solubility, low cytotoxicity, and good photostability is reported.

Synthesis and anti-TMV activity of dialkyl/dibenzyl 2-((6-substituted-benzo[d]thiazol-2-ylamino)(benzofuran-2-yl)methyl) malonates

Starting from benzofuran-2-methanal, 6-substituted benzothiazole-2-amines and malonic esters, sixteen title compounds were designed and synthesized seeking to introduce anti-TMV activity. The structures of the newly synthesized compounds were confirmed by ¹H-NMR, ¹³C-NMR, IR spectra, and MS (HREI) analysis. The bioassays identified some of these new compounds as having moderate to good anti-TMV activity. The compounds 5i and 5m have good antiviral activity against TMV with a curative rate of 52.23% and 54.41%, respectively, at a concentration of 0.5 mg/mL.

Synthesis and initial evaluation of YM-08, a blood-brain barrier permeable derivative of the heat shock protein 70 (Hsp70) inhibitor MKT-077, which reduces tau levels

The molecular chaperone, heat shock protein 70 (Hsp70), is an emerging drug target for treating neurodegenerative tauopathies. We recently found that one promising Hsp70 inhibitor, MKT-077, reduces tau levels in cellular models. However, MKT-077 does not penetrate the blood-brain barrier (BBB), limiting its use as either a clinical candidate or probe for exploring Hsp70 as a drug target in the central nervous system (CNS). We hypothesized that replacing the cationic pyridinium moiety in MKT-077 with a neutral pyridine might improve its clogP and enhance its BBB penetrance. To test this idea, we designed and synthesized YM-08, a neutral analogue of MKT-077. Like the parent compound, YM-08 bound to Hsp70 in vitro and reduced phosphorylated tau levels in cultured brain slices. Pharmacokinetic evaluation in CD1 mice showed that YM-08 crossed the BBB and maintained a brain/plasma (B/P) value of ∼0.25 for at least 18 h. Together, these studies suggest that YM-08 is a promising scaffold for the development of Hsp70 inhibitors suitable for use in the CNS.

Medicinal significance of benzothiazole scaffold: an insight view

Heterocycles bearing nitrogen, sulphur and thiazole moieties constitute the core structure of a number of biologically interesting compounds. Benzothiazole, a group of xenobiotic compounds containing a benzene ring fused with a thiazole ring, are used worldwide for a variety of therapeutic applications. Benzothiazole and their heterocyclic derivatives represent an important class of compounds possessing a wide spectrum of biological activities. The myriad spectrum of medicinal properties associated with benzothiazole related drugs has encouraged the medicinal chemists to synthesize a large number of novel therapeutic agents. Several analogues containing benzothiazole ring system exhibit significant antitumour, antimicrobial, antidiabetic, anti-inflammatory, anticonvulsant, antiviral, antioxidant, antitubercular, antimalarial, antiasthmatic, anthelmintic, photosensitizing, diuretic, analgesic and other activities. This article is an attempt to present the research work reported in recent scientific literature on different pharmacological activities of benzothiazole compounds.

Identification of new antileishmanial leads from hits obtained by high-throughput screening

A previous screen of ~200,000 compounds from the PubChem database identified 70 compounds possessing 50% effective concentrations (EC(50)s) below 1 μM against Leishmania major promastigotes that were not toxic to mammalian epithelial cancer cells at this concentration (E. Sharlow et al., PLoS Negl. Trop. Dis. 3:e540, 2009). Based on availability and chemical exclusion criteria, 31 of these compounds were purchased from commercial suppliers and evaluated for in vitro activity against intracellular L. donovani and L. amazonensis parasites. Benzothiazole cyanine compounds (PubChem 16196319 and 16196223) displayed potent activity against intracellular amastigotes, prompting a search for commercially available compounds that were structurally related. Pubchem 123859 (the cyanine dye thiazole orange) showed exceptionally potent activity against intracellular L. donovani in vitro (50% inhibitory concentration [IC(50)] = 21 ± 12 nM) and low cytotoxicity against Vero cells (IC(50) = 7,800 ± 200 nM). Administration of 123859 and 16196319 at a dose of 1 mg/kg of body weight intraperitoneally (i.p.) daily for 5 days resulted in 44% ± 4% and 42% ± 3% suppression of liver parasitemia in L. donovani-infected BALB/c mice, respectively, compared to the untreated control group (the reductions in liver parasitemia were 30% ± 5% and 27% ± 4%, respectively, compared to the (2-hydroxypropyl)-β-cyclodextrin solution (HPβCD) vehicle control, which itself displayed some antileishmanial activity). Benzothiazole-containing cyanine dyes are thus potential lead compounds for the discovery of novel antileishmanial agents.

Synthesis and in vitro antiprotozoal activities of 5-phenyliminobenzo[a]phenoxazine derivatives

A series of 5-phenyliminobenzo[a]phenoxazine derivatives were synthesized. The in vitro antiprotozoal activities were evaluated against Plasmodium falciparum K1, Trypanosoma cruzi, Leishmania donovani and Trypanosoma brucei rhodesiense. N,N-Diethyl-5-((4-methoxyphenyl)imino)-5H-benzo[a]phenoxazin-9-amine shows IC(50)=0.040 μmol L(-1) with a selective index of 1425 against Plasmodium falciparum K1.

A, Lu J, Ismail NSM, Wittlin S, Kaiser M, Brun R, Charman SA, Nguyen T, Morizzi J, Itoh I, Ihara M. Discovery of Novel Benzo[a]phenoxazine SSJ-183 as a Drug Candidate for Malaria

Malaria is a serious infectious disease caused by protozoan parasites in tropical and subtropical regions. Even inhabitants of temperate zones are exposed to the danger of malaria infection because of travel and global warming. Novel, effective, safe, and inexpensive drugs are required to treat malaria and contribute to the global goal of eradication. A search for new antimalarial agents has been performed by the synthesis of new benzo[a]phenoxazines, followed by biological evaluations. The derivative SSJ-183 (5), having a 4-aminopyridine group, showed an IC50 value against Plasmodium falciparum of 7.6 nM and a selectivity index of >7300. Cure was achieved by three oral doses of 5 at 100 mg/kg to mice infected with the Plasmodium berghei ANKA strain. The safety of 5 was supported by acute toxicity testing in mice with single doses up to 2000 mg/kg po, chromosome aberration test, in vitro as well as in vivo micronucleus tests, and phototoxicity studies in mice. Thus, 5 is a promising candidate as a new antimalarial agent.

Pharmacodynamics and pharmacokinetics studies of phenoxazinium derivatives for antimalarial agent

In vivo antimalarial drug candidates screening test was carried out on a series of water-soluble 3,7-bis(dialkylamino)phenoxazin-5-ium derivatives. Among them, 3-(diethylamino)-7-(piperidin-1-yl)phenoxazin-5-ium chloride (SSJ-206) showing highest efficacy was chosen for further pharmcodynamics and pharmacokinetics study. It was supported from these data that the phenoxazinium salts, SSJ-206, would be one of hopeful candidates as an oral antimalarial drug.

Synthesis and in vitro antiprotozoal activities of water-soluble, inexpensive 3,7-bis(dialkylamino)phenoxazin-5-ium derivatives

3,7-Bis(dialkylamino)phenoxazinium salts were synthesized and evaluated for in vitro activities against Plasmodium falciparum, Trypanosoma cruzi, T. brucei rhodesiense, and Leishmania donovani. Notably, the compounds showed potent antiprotozoal activities, especially against P. falciparum and T. cruzi. The compounds with alkyl side chains less than three carbons in length possessed good activities with high selective indices.

Synthesis and Antimalarial Property of Orally Active Phenoxazinium Salts

Phenoxazinium salts were found to display good antimalarial efficacy in vivo against Plasmodium berghei. Several compounds provided 100% parasitemia clearance at a dose of 20-30 mg kg-1x4 days (ip) and good survival effects without obvious acute toxicity. They also showed excellent potency by oral administration. A preliminary pharmacokinetic study revealed that the oral availability of 1a was excellent.