Synthesis and antiprotozoal activity of cationic 1,4-diphenyl-1H-1,2,3-triazoles

Antiprotozoal activity of dicationic 3,5-diphenylisoxazoles, their prodrugs and aza-analogues

Fifty novel prodrugs and aza-analogues of 3,5-bis(4-amidinophenyl)isoxazole and its derivatives were prepared. Eighteen of the 24 aza-analogues exhibited IC₅₀ values below 25 nM against Trypanosoma brucei rhodesiense or Plasmodium falciparum. Six compounds had antitrypanosomal IC₅₀ values below 10 nM. Twelve analogues showed similar antiplasmodial activities, including three with sub-nanomolar potencies. Forty-four diamidines (including 16 aza-analogues) and the 26 prodrugs were evaluated for efficacy in mice infected with T. b. rhodesiense STIB900. Six diamidines cured 4/4 mice at daily 5 mg/kg intraperitoneal doses for 4 days, giving results far superior to pentamidine and furamidine. One prodrug attained 3/4 cures at daily 25 mg/kg oral doses for 4 days.

Synthesis and antiprotozoal activity of dicationic 2,6-diphenylpyrazines and aza-analogues

Dicationic 2,6-diphenylpyrazines, aza-analogues and prodrugs were synthesized; evaluated for DNA affinity, activity against Trypanosoma brucei rhodesiense (T. b. r.) and Plasmodium falciparum (P. f.) in vitro, efficacy in T. b. r. STIB900 acute and T. b. brucei GVR35 CNS mouse models. Most diamidines gave poly(dA-dT)2 ΔTm values greater than pentamidine, IC50 values: T. b. r. (4.8-37nM) and P. f. (10-52nM). Most diamidines and prodrugs gave cures for STIB900 model (11, 19a and 24b 4/4 cures); 12 3/4 cures for GVR35 model. Metabolic stability half-life values for O-methylamidoxime prodrugs did not correlate with STIB900 results.

Diamidines versus Monoamidines as Anti-Pneumocystis Agents: An in Vivo Study

Some compounds articulated around a piperazine or an ethylenediamine linker have been evaluated in vitro to determine their activity in the presence of a 3T6 fibroblast cell line and an axenic culture of Pneumocystis carinii, respectively. The most efficient antifungal derivatives, namely N,N′-bis(benzamidine-4-yl)ethane-1,2-diamine (compound 6, a diamidine) and N-(benzamidine-4-yl)-N′-phenylethane-1,2-diamine (compound 7, a monoamidine), exhibited no cytotoxicity and were evaluated in vivo in a rat model. Only the diamidine 6 emerged as a promising hit for further studies.

Synthesis and antiprotozoal activity of dicationic m-terphenyl and 1,3-dipyridylbenzene derivatives

4,4″-Diamidino-m-terphenyl (1) and 36 analogues were prepared and assayed in vitro against T rypanosoma brucei rhodesiense , Trypanosoma cruzi , Plasmodium falciparum , and Leishmania amazonensis . Twenty-three compounds were highly active against T. b. rhodesiense or P. falciparum. Most noteworthy were amidines 1, 10, and 11 with IC50 of 4 nM against T. b. rhodesiense, and dimethyltetrahydropyrimidinyl analogues 4 and 9 with IC50 values of ≤ 3 nM against P. falciparum. Bis-pyridylimidamide derivative 31 was 25 times more potent than benznidazole against T. cruzi and slightly more potent than amphotericin B against L. amazonensis. Terphenyldiamidine 1 and dipyridylbenzene analogues 23 and 25 each cured 4/4 mice infected with T. b. rhodesiense STIB900 with four daily 5 mg/kg intraperitoneal doses, as well as with single doses of ≤ 10 mg/kg. Derivatives 5 and 28 (prodrugs of 1 and 25) each cured 3/4 mice with four daily 25 mg/kg oral doses.

Novel amidines and analogues as promising agents against intracellular parasites: a systematic review

Parasitic protozoa comprise diverse aetiological agents responsible for important diseases in humans and animals including sleeping sickness, Chagas disease, leishmaniasis, malaria, toxoplasmosis and others. They are major causes of mortality and morbidity in tropical and subtropical countries, and are also responsible for important economic losses. However, up to now, for most of these parasitic diseases, effective vaccines are lacking and the approved chemotherapeutic compounds present high toxicity, increasing resistance, limited efficacy and require long periods of treatment. Many of these parasitic illnesses predominantly affect low-income populations of developing countries for which new pharmaceutical alternatives are urgently needed. Thus, very low research funding is available. Amidine-containing compounds such as pentamidine are DNA minor groove binders with a broad spectrum of activities against human and veterinary pathogens. Due to their promising microbicidal activity but their rather poor bioavailability and high toxicity, many analogues and derivatives, including pro-drugs, have been synthesized and screened in vitro and in vivo in order to improve their selectivity and pharmacological properties. This review summarizes the knowledge on amidines and analogues with respect to their synthesis, pharmacological profile, mechanistic and biological effects upon a range of intracellular protozoan parasites. The bulk of these data may contribute to the future design and structure optimization of new aromatic dicationic compounds as novel antiparasitic drug candidates.

Triazolbenzo[d]thiazoles: efficient synthesis and biological evaluation as neuroprotective agents

A number of (1H-1,2,3-triazol-1-yl)benzo[d]thiazoles were synthesized utilizing a versatile Cu-catalyzed azide-alkyne click reaction (CuAAC) on tautomeric benzo[4,5]thiazolo[3,2-d]tetrazole (1) and 2-azidobenzo[d]thiazole (2) starting materials. Moreover, one of the resulting products of this investigation, triazolbenzo[d]thiazole 22, was found to possess significant neuroprotective activity in human neuroblastoma (SH-SY5Y) cells.

Synthesis, DNA binding and antileishmanial activity of low molecular weight bis-arylimidamides

The effects of reducing the molecular weight of the antileishmanial compound DB766 on DNA binding affinity, antileishmanial activity and cytotoxicity are reported. The bis-arylimidamides were prepared by the coupling of aryl S-(2-naphthylmethyl)thioimidates with the corresponding amines. Specifically, we have prepared new series of bis-arylimidamides which include 3a, 3b, 6, 9a, 9b, 9c, 13, and 18. Three compounds 9a, 9c, and 18 bind to DNA with similar or moderately lower affinity to that of DB766, the rest of these compounds either show quite weak binding or no binding at all to DNA. Compounds 9a, 9c, and 13 were the most active against Leishmania amazonensis showing IC(50) values of less than 1 μM, so they were screened against intracellular Leishmania donovani, showing outstanding activity with IC(50) values of 25-79 nM. Despite exhibiting little in vitro cytotoxicity these three compounds were quite toxic to mice.

Isothermal microcalorimetry, a new tool to monitor drug action against Trypanosoma brucei and Plasmodium falciparum

Isothermal microcalorimetry is an established tool to measure heat flow of physical, chemical or biological processes. The metabolism of viable cells produces heat, and if sufficient cells are present, their heat production can be assessed by this method. In this study, we investigated the heat flow of two medically important protozoans, Trypanosoma brucei rhodesiense and Plasmodium falciparum. Heat flow signals obtained for these pathogens allowed us to monitor parasite growth on a real-time basis as the signals correlated with the number of viable cells. To showcase the potential of microcalorimetry for measuring drug action on pathogenic organisms, we tested the method with three antitrypanosomal drugs, melarsoprol, suramin and pentamidine and three antiplasmodial drugs, chloroquine, artemether and dihydroartemisinin, each at two concentrations on the respective parasite. With the real time measurement, inhibition was observed immediately by a reduced heat flow compared to that in untreated control samples. The onset of drug action, the degree of inhibition and the time to death of the parasite culture could conveniently be monitored over several days. Microcalorimetry is a valuable element to be added to the toolbox for drug discovery for protozoal diseases such as human African trypanosomiasis and malaria. The method could probably be adapted to other protozoan parasites, especially those growing extracellularly.

The impact of click chemistry in medicinal chemistry

INTRODUCTION

The copper(I)-catalyzed 1,3-dipolar cycloaddition of alkynes and azides to form 1,2,3-triazoles is the most popular reaction in click chemistry. This reaction is also near-perfect, in terms of its robustness, due to the high degree of reliability and complete specificity. Furthermore, this reaction has been used increasingly in drug discovery, because the formed 1,2,3-triazole can act as both a bioisostere and a linker.

AREAS COVERED

This review provides an overview of a most important click reaction, 1,3-dipolar cycloadditions of alkynes and azides, in the drug discovery.

EXPERT OPINION

Click chemistry is a very powerful tool, in the drug discovery, because it is very efficient in the creation of compound libraries through combinatorial methodology. However, the 1,2,3-triazole ring itself is not a commonly used pharmacophore and has rarely been found in marketed drugs, demonstrating that there are still some limitations during the use of 1,2,3-triazole in the molecules of drug candidates. Hopefully, in the next decade, we will witness the emergence of 1,2,3-triazole-bearing drugs on the market as this click reaction is used more and more widely in the drug discovery.

New insights in staging and chemotherapy of African trypanosomiasis and possible contribution of medicinal plants

Human African trypanosomiasis (HAT) is a fatal if untreated fly-borne neuroinflammatory disease caused by protozoa of the species Trypanosoma brucei (T.b.). The increasing trend of HAT cases has been reversed, but according to WHO experts, new epidemics of this disease could appear. In addition, HAT is still a considerable burden for life quality and economy in 36 sub-Saharan Africa countries with 15-20 million persons at risk. Following joined initiatives of WHO and private partners, the fight against HAT was re-engaged, resulting in considerable breakthrough. We present here what is known at this day about HAT etiology and pathogenesis and the new insights in the development of accurate tools and tests for disease staging and severity monitoring in the field. Also, we elaborate herein the promising progresses made in the development of less toxic and more efficient trypanocidal drugs including the potential of medicinal plants and related alternative drug therapies.

Synthesis and anti-protozoal activity of novel dihydropyrrolo[3,4-d][1,2,3]triazoles

1,2,4-Oxadiazole and 1,2,3-triazole containing heterocyclic compounds continue to gain interest in synthesis of chemical entities and exhibit various biological activities as anti-protozoal and anti-cancer agents. By using the principle of bioisosterism, a series of novel oxadiazolyl pyrrolo triazole diones; namely, (3aS,6aR)-1-((3-(4-substituted phenyl)-1,2,4-oxadiazol-5-yl)methyl)-5-phenyl-1,6a-dihydropyrrolo[3,4-d][1,2,3] triazole-4,6(3aH,5H)-diones (5a-k) was designed and synthesized by the 1,3-dipolar cycloaddition reaction of novel 5-azidomethyl 3-aryl substituted 1,2,4-oxadiazoles (4a-k) with N-phenyl maleimide. The structures of all the cycloadducts were elucidated by means of spectroscopic methods and physical characteristics. The in vitro anti-protozoal and cytotoxic activities of these novel heterocyclic compounds were investigated.

Synthesis and antimalarial activities of a diverse set of triazole-containing furamidine analogues

Four different series of triazole diamidines have been prepared by the Pinner method from the corresponding triazole dinitriles. Copper-catalyzed "click chemistry" was used for the synthesis of 1,4- and 4,5-substituted triazoles, aryl magnesium acetylide reagents for the 1,5-substituted triazoles, with a thermal dipolar addition reaction employed for the 2,4-substituted triazoles. In vitro antimalarial activity against two different PfCRT-modified parasite lines (Science 2002, 298, 210-213) of Plasmodium falciparum and inhibition of hemozoin formation were determined for each compound. Several diamidines with potent nanomolar antimalarial activities were identified, and selected molecules were resynthesized as their diamidoxime triazole prodrugs. One of these prodrugs, OB216, proved to be highly potent in vivo with an ED50 value of 5 mg kg(-1) (po) and an observed 100 % cure rate (CD100) of just 10 mg kg(-1) by oral (po) administration in mice infected with P. vinckei.

Neglected disease - african sleeping sickness: recent synthetic and modeling advances

Human African Trypanosomiasis (HAT) also called sleeping sickness is caused by subspecies of the parasitic hemoflagellate Trypanosoma brucei that mostly occurs in sub-Saharan Africa. The current chemotherapy of the human trypanosomiases relies on only six drugs, five of which have been developed more than 30 years ago, have undesirable toxic side effects and most of them show drug-resistance. Though development of new anti-trypanosomal drugs seems to be a priority area research in this area has lagged far behind. The given review mainly focus upon the recent synthetic and computer based approaches made by various research groups for the development of newer anti-trypanosomal analogues which may have improved efficacy and oral bioavailability than the present ones. The given paper also attempts to investigate the relationship between the various physiochemical parameters and anti-trypanosomal activity that may be helpful in development of potent anti-trypanosomal agents against sleeping sickness.

Structures, targets and recent approaches in anti-leishmanial drug discovery and development

Recent years have seen a significant improvement in available treatment options for leishmaniasis. Two new drugs, miltefosine and paromomycin, have been registered for the treatment of visceral leishmaniasis (VL) in India since 2002. Combination therapy is now explored in clinical trials as a new treatment approach for VL to reduce the length of treatment and potentially prevent selection of resistant parasites. However there is still a need for new drugs due to safety, resistance, stability and cost issues with existing therapies. The search for topical treatments for cutaneous leishmaniasis (CL) is ongoing. This review gives a brief overview of recent developments and approaches in anti-leishmanial drug discovery and development.

Exploration of larger central ring linkers in furamidine analogues: synthesis and evaluation of their DNA binding, antiparasitic and fluorescence properties

The effects of replacing the central furan ring of furamidine with indole and benzimidazole on their DNA binding affinity, antiparasitic activity and fluorescence are reported. The bis-cyanophenylindoles required to make the corresponding amidines were prepared by sequential Stille and/or Suzuki coupling reactions. The bis-cyanophenylbenzimidazoles were obtained by coupling 4-cyanobenzaldehydes with the appropriate cyano substituted phenylenediamine. The bis-nitriles were converted to the diamidines by reaction with LiN[Si(CH(3))(3)](2) or by Pinner methodology. Specifically, we have prepared new series of 2,6- and 2,5-diaryl indoles (6a,b, 12 and 17a-d) and the related benzimidazoles (24, 30 and 35). The new compounds bind in the DNA minor groove in DNA AT base pair sequences and eight of the ten new analogues exhibit ΔT(m) values comparable to or higher than that of furamidine. Six of ten of the new compounds exhibit lower IC(50) values against Trypanosoma brucei rhodesiense (T. b. r.) and eight of ten exhibit lower IC(50) values against Plasmodium falciparum (P. f.) than furamidine. Four of the ten show greater efficacy than furamidine in the rigorous T. b. r. STIB900 mouse model for African trypanosomiasis. Generally, the fluorescence properties of the new analogues are similar to that of DAPI.

Regioselective [3+2] cycloaddition of chalcones with a sugar azide: easy access to 1-(5-deoxy-D-xylofuranos-5-yl)-4,5-disubstituted-1H-1,2,3-triazoles

[3+2] Cycloaddition of 5-azido-5-deoxy-1,2-O-isopropylidene-alpha-d-xylofuranose with 1,3-diphenyl-prop-3-enones, followed by oxidation of the intermediate triazolines in a tandem manner, led to the regioselective formation of 4-benzoyl-1-(5-deoxy-1,2-O-isopropylidene-alpha-d-xylofuranos-5-yl)-5-phenyl-1H-1,2,3-triazoles in moderate to good yields.