Nongenotoxic 3-Nitroimidazo[1,2-a]pyridines Are NTR1 Substrates That Display Potent in Vitro Antileishmanial Activity.

Twenty nine original 3-nitroimidazo[1,2-a]pyridine derivatives, bearing a phenylthio (or benzylthio) moiety at position 8 of the scaffold, were synthesized. In vitro evaluation highlighted compound 5 as an antiparasitic hit molecule displaying low cytotoxicity for the human HepG2 cell line (CC50 > 100 µM) alongside good antileishmanial activities (IC50 = 1-2.1 µM) against L. donovani, L. infantum, and L. major; and good antitrypanosomal activities (IC50 = 1.3-2.2 µM) against T. brucei brucei and T. cruzi, in comparison to several reference drugs such as miltefosine, fexinidazole, eflornithine, and benznidazole (IC50 = 0.6 to 13.3 µM). Molecule 5, presenting a low reduction potential (E° = -0.63 V), was shown to be selectively bioactivated by the L. donovani type 1 nitroreductase (NTR1). Importantly, molecule 5 was neither mutagenic (negative Ames test), nor genotoxic (negative comet assay), in contrast to many other nitroaromatics. Molecule 5 showed poor microsomal stability; however, its main metabolite (sulfoxide) remained both active and nonmutagenic, making 5 a good candidate for further in vivo studies.

Novel 8-nitroquinolin-2(1H)-ones as NTR-bioactivated antikinetoplastid molecules: Synthesis, electrochemical and SAR study.

To study the antiparasitic 8-nitroquinolin-2(1H)-one pharmacophore, a series of 31 derivatives was synthesized in 1-5 steps and evaluated in vitro against both Leishmania infantum and Trypanosoma brucei brucei. In parallel, the reduction potential of all molecules was measured by cyclic voltammetry. Structure-activity relationships first indicated that antileishmanial activity depends on an intramolecular hydrogen bond (described by X-ray diffraction) between the lactam function and the nitro group, which is responsible for an important shift of the redox potential (+0.3 V in comparison with 8-nitroquinoline). With the assistance of computational chemistry, a set of derivatives presenting a large range of redox potentials (from -1.1 to -0.45 V) was designed and provided a list of suitable molecules to be synthesized and tested. This approach highlighted that, in this series, only substrates with a redox potential above -0.6 V display activity toward L. infantum. Nevertheless, such relation between redox potentials and in vitro antiparasitic activities was not observed in T. b. brucei. Compound 22 is a new hit compound in the series, displaying both antileishmanial and antitrypanosomal activity along with a low cytotoxicity on the human HepG2 cell line. Compound 22 is selectively bioactivated by the type 1 nitroreductases (NTR1) of L. donovani and T. brucei brucei. Moreover, despite being mutagenic in the Ames test, as most of nitroaromatic derivatives, compound 22 was not genotoxic in the comet assay. Preliminary in vitro pharmacokinetic parameters were finally determined and pointed out a good in vitro microsomal stability (half-life > 40 min) and a 92% binding to human albumin.

Antileishmanial pharmacomodulation in 8-nitroquinolin-2(1H)-one series.

An antileishmanial pharmacomodulation at position 4 of 8-nitroquinolin-2(1H)-one was conducted by using the Sonogashira and Suzuki-Miyaura coupling reactions. A series of 25 derivatives was tested in vitro on the promastigote stage of Leishmania donovani along with an in vitro cytotoxicity evaluation on the human HepG2 cell line. Only the derivatives bearing a phenyl moiety at position 4 of the quinoline ring displayed interesting biologic profile, when the phenyl moiety was substituted at the para position by a Br or Cl atom, or by a CF3 group. Among them, molecules 17 and 19 were the most selective and were then tested in vitro on the intracellular amastigote stage of both L. donovani and Leishmania infantum, in parallel with complementary in vitro cytotoxicity assays on the macrophage cell lines THP-1 and J774A.1. Molecule 19 showed no activity on the amastigote stages of the parasites and some cytotoxicity on the J774A.1 cell line while molecule 17, less cytotoxic than 19, showed anti-amastigote activity in L. infantum, being 3 times less active than miltefosine but more active and selective than pentamidine. Nevertheless, hit-molecule 17 did not appear as selective as the parent compound.

Discovery of new thienopyrimidinone derivatives displaying antimalarial properties toward both erythrocytic and hepatic stages of Plasmodium.

A preliminary in vitro screening of compounds belonging to various chemical families from our library revealed the thieno[3,2-d]pyrimidin-4(3H)-one scaffold displayed a promising profile against Plasmodium falciparum. Then, 120 new derivatives were synthesized and evaluated in vitro; compared to drug references, 40 showed good activity toward chloroquine sensitive (IC50 35-344 nM) and resistant (IC50 45-800 nM) P. falciparum strains. They were neither cytotoxic (CC50 15-50 µM) toward HepG2 and CHO cells, nor mutagenic. Structure-activity relationships were defined. The lead-compound also appeared active against the Plasmodium liver stages (Plasmodium yoelii IC50 = 35 nM) and a preliminary in vivo evaluation indicated the in vitro activity was preserved (45% reduction in parasitemia compared to untreated infected mice). A mechanistic study demonstrated these molecules do not involve any of the pathways described for commercial drugs and exert a specific activity on the ring and trophozoite stages.

Looking for new antileishmanial derivatives in 8-nitroquinolin-2(1H)-one series.

From a recently identified antileishmanial pharmacophore, a structure-activity relationship study was conducted by introducing various aminated, phenoxy or thiophenoxy moieties at position 4 of the 8-nitroquinolin-2(1H)-one scaffold, using SNAr reactions. Thus a series of 47 derivatives was synthesized and evaluated in vitro on the promastigote stage of Leishmania donovani. In parallel, the cytotoxicity of the active molecules was tested on the human HepG2 cell line. The results we obtained showed that the introduction of a substituent at position 4 of the antileishmanial pharmacophore can either lead to inactive or active derivatives, depending on the nature of the substituent. Aminated moieties appear as very unfavorable toward antileishmanial activity, while phenoxy or thiophenoxy moieties were shown to maintain the in vitro antileishmanial profile, especially when the phenyl ring of these moieties was substituted at the para or ortho position by a halogen atom (except fluorine), a trifluoromethyl group or a methyl group. Most of these derivatives showed a lack of solubility in the culture media which hindered the in vitro determination of both their cytotoxicity and activity against the intracellular amastigoste stage of L. donovani.

Synthesis and in vitro evaluation of 4-trichloromethylpyrrolo[1,2-a]quinoxalines as new antiplasmodial agents.

Thanks to a preliminary in vitro screening of several CCl3-substituted-nitrogen containing heterocycles belonging to our chemical library, the 2-trichloromethylquinoxaline scaffold appeared to be of potential interest for developing new antiplasmodial agents. Then, combining these experimental results to the antimalarial properties reported for various pyrrolo[1,2-a]quinoxaline derivatives, an original series of fifteen 7-substituted-4-trichoromethylpyrrolo[1,2-a]quinoxalines was synthesized in a 4 to 5 reaction steps pathway. All molecules were evaluated in vitro toward both their antiplasmodial activity on the K1 multi-resistant Plasmodium falciparum strain and their cytotoxicity on the HepG2 human cell line. Thus, 3 hit molecules were identified, displaying IC50 values in the micromolar range and low cytotoxicity values, reaching good selectivity indexes, in comparison with the reference drugs chloroquine and doxycycline. Structure-activity relationship studies showed that the pyrrolo[1,2-a]quinoxaline scaffold can support selective antiplasmodial activity when substituted at position 4 by a CCl3 group. However, substitution at position 7 of the same scaffold is neither beneficial for cytotoxicity nor favourable for the solubility in the biological media.

Targeting the human parasite Leishmania donovani: discovery of a new promising anti-infectious pharmacophore in 3-nitroimidazo[1,2-a]pyridine series.

We report herein the discovery of antileishmanial molecules based on the imidazo[1,2-a]pyridine ring. In vitro screenings of imidazopyridines belonging to our chemical library, toward the promastigotes stage of Leishmania donovani, J774A.1 murine and HepG2 human cells, permitted to identify three selective hit-compounds (12, 20 and 28). New derivatives were then synthesized to allow structure-activity and -toxicity relationships analyses, enabling to characterize a lead-compound (44) displaying both a high potency (IC50=1.8 µM) and a good selectivity index, in comparison with three antileishmanial reference drug-compounds (amphotericin B, miltefosine and pentamidine). Moreover, lead-compound 44 also exhibits good in vitro activity against the intracellular amastigote stage of L. donovani. Thus, the 6-halo-3-nitro-2-(phenylsulfonylmethyl)imidazo[1,2-a]pyridine scaffold appears as a new promising selective antileishmanial pharmacophore, especially when substituted at position 8 by a bromine atom.

Discovery of a new antileishmanial hit in 8-nitroquinoline series.

A series of nitrated 2-substituted-quinolines was synthesized and evaluated in vitro toward Leishmania donovani promastigotes. In parallel, the in vitro cytotoxicity of these molecules was assessed on the murine J774 and human HepG2 cell lines. Thus, a very promising antileishmanial hit molecule was identified (compound 21), displaying an IC(50) value of 6.6 µM and CC(50) values ≥ 100 µM, conferring quite good selectivity index to this molecule, in comparison with 3 drug-compounds of reference (amphotericin B, miltefosine and pentamidine). Compound 21 also appears as an efficient in vitro antileishmanial molecule against both Leishmania infantum promastigotes and the intracellular L. donovani amastigotes (respective IC(50) = 7.6 and 6.5 µM). Moreover, hit quinoline 21 does not show neither significant antiplasmodial nor antitoxoplasmic in vitro activity and though, presents a selective antileishmanial activity. Finally, a structure-activity relationships study enabled to define precisely the antileishmanial pharmacophore based on this nitroquinoline scaffold: 2-hydroxy-8-nitroquinoline.

4-Thiophenoxy-2-trichloromethyquinazolines display in vitro selective antiplasmodial activity against the human malaria parasite Plasmodium falciparum.

A series of original quinazolines bearing a 4-thiophenoxy and a 2-trichloromethyl group was synthesized in a convenient and efficient way and was evaluated toward its in vitro antiplasmodial potential. The series revealed global good activity against the K1-multi-resistant Plasmodium falciparum strain, especially with hit compound 5 (IC(50)=0.9 µM), in comparison with chloroquine and doxycycline chosen as reference-drugs. Both the in vitro cytotoxicity study which was conducted on the human HepG2 cell line and the in vitro antitoxoplasmic screening against Toxoplasma gondii indicate that this series presents an interesting selective antiplasmodial profile. Structure-activity- and toxicity relationships highlight that the trichloromethyl group plays a key role in the antiplasmodial activity and also show that the modulation of the thiophenol moiety influences the toxicity/activity ratio.

Targeting the human malaria parasite Plasmodium falciparum: in vitro identification of a new antiplasmodial hit in 4-phenoxy-2-trichloromethylquinazoline series.

From the promising results we previously obtained in quinazoline series and to complete the evaluation of the in vitro antiplasmodial activity of original 2-trichloromethylquinazolines, we synthesized new quinazolines possessing a variously substituted phenoxy group at position 4 through a simple and efficient two-step-synthesis approach. The studies of their activity toward the multi-resistant W2 Plasmodium falciparum strain and of their cytotoxicity on the human hepatocyte HepG2 cell line highlighted a hit compound (molecule 7) displaying a W2 IC(50) value of 1.1 µM and a HepG2 CC(50) value of 50 µM, comparable to chloroquine and doxycycline. Structure-activity- and toxicity relationships indicate that the trichloromethyl group plays a key role in the antiplasmodial activity of such chemical scaffold and also that the phenoxy group substitution as a direct influence on the molecules selectivity. Moreover, molecule 7 displays significant specific activity against the Plasmodium genus in comparison with Toxoplasma and does not show any mutagenic property at the Ames test.

Synthesis and evaluation of original amidoximes as antileishmanial agents.

An original series of amidoxime derivatives was synthesized using manganese(III) acetate, Buchwald-Hartwig and Heck reactions. Two amidoximes (39 and 52) showed interesting in vitro activities toward Leishmania donovani promastigotes, exhibiting 8.3 and 8.8 µM IC(50) values. Moreover, the cytotoxicity of these compounds was evaluated on human THP1 cells, giving access to the corresponding selectivity index. Among the 25 tested compounds, amidoximes 38 and 39 and diamidoximes 50 and 52 exhibited a better selectivity index than pentamidine used as a drug compound reference.

Antimalarial compounds from the aerial parts of Flacourtia indica (Flacourtiaceae).

AIM OF THE STUDY: In the Comoros Islands, the aerial parts of Flacourtia indica are used in traditional medicine to treat malaria. Because of the important use of this plant, the phytochemistry of the aerial parts was investigated. MATERIALS AND METHODS: Three compounds were isolated from the decoction of this plant material, pyrocatechol, homaloside D and poliothrysoside. The in vitro antiplasmodial activity on the chloroquine-resistant strain (W2) of Plasmodium falciparum and the cytotoxicity on two complementary human cell lines (THP1, HepG2), of AcOEt extract obtained after liquid/liquid extraction of the decoction and pure compounds, were evaluated. RESULTS: The poliothrysoside isolated from the AcOEt extract presented a strong antiplasmodial activity (IC(50)=7.4 microM) and a good selectivity index (>28) similar to chloroquine. CONCLUSION: This study reports for the first time antiplasmodial activity for Flacourtia indica, for its AcOEt extract and the three major constituents and confirms its traditional use.

TDAE-assisted synthesis of new imidazo[2,1-b]thiazole derivatives as anti-infectious agents.

A series of new imidazo[2,1-b]thiazoles was prepared in moderate to good yields in a four step synthesis using the TDAE methodology from 6-chloromethyl-5-nitroimidazo[2,1-b]thiazole and keto esters, ketomalonates and ketolactams. All compounds were tested for their antibacterial and antifungal activities against four bacterial strains (two Gram positive and two Gram negative ones) and four yeasts. Among these synthesized 5-nitroimidazo[2,1-b]thiazoles, the compounds 1 and 6 showed potent antimicrobial activities against all candida strains and compound 3e showed an interesting antifungal potential against Candida tropicalis.

Synthesis and antiprotozoal activity of 4-arylcoumarins.

A large series of 4-arylcoumarins was synthesized by Suzuki-Miyaura cross-coupling reaction and evaluated for antiprotozoal activity against Plasmodium falciparum and Leishmania donovani. Several compounds were found to strongly inhibit the proliferation of human cell line and/or parasites. The 4-(3,4-dimethoxyphenyl)-6,7-dimethoxycoumarin exhibit a potent activity on L. donovani amastigotes with a selectivity index (SI=265) twice than amphotericin B (SI=140).

Original quinazoline derivatives displaying antiplasmodial properties.

The multistep synthesis of new quinazoline-derived molecules and their in vitro antiplasmodial evaluation on the W2 chloroquino-resistant Plasmodium falciparum strain is described herein. These molecules have also been studied concerning their in vitro cytotoxicity toward two human cell lines (K652 and HepG2) in order to calculate their respective selectivity indexes (S.I.). Among the fourteen tested molecules, two exhibited both significant antiplasmodial activity (IC(50)=0.95 and 1.3 microM) and low toxicity (IC(50)>100 or 125 microM), compared with two reference drugs: chloroquine and doxycycline. The structure activity relationships establish that the molecular scaffold which exerts the best profile is the 6-nitro-2-(tosylmethyl)-N-(3-substituted-phenyl)-quinazolin-4-amine. The hit molecules were finally investigated regarding their potential action toward two other protozoa, Leishmania donovani and Toxoplasma gondii, showing that these molecules display a selective antiplasmodial activity.

Synthesis and in vitro antiplasmodial evaluation of 4-anilino-2-trichloromethylquinazolines.

To identify a new safe antiplasmodial molecular scaffold, an original series of 2-trichloromethylquinazolines, functionalized in position 4 by an alkyl- or arylamino substituent, was synthesized from 4-chloro-2-trichloromethylquinazoline 1, via a cheap, fast and efficient solvent-free operating procedure. Among the 40 molecules prepared, several exhibit a good profile with both a significant antiplasmodial activity on the W2 Plasmodium falciparum strain (IC(50) values: 0.4-2.2 microM) and a promising toxicological behavior regarding human cells (HepG2/W2 selectivity indexes: 40-83), compared to the antimalarial drug compounds chloroquine and doxycycline. The in vitro antitoxoplasmic and antileishmanial evaluations were conducted in parallel on the most active molecules, showing that these ones specifically display antiplasmodial properties.

Cytotoxic activity of alkaloids isolated from Stephania rotunda [corrected].

Three major alkaloids: cepharanthine (1), tetrahydropalmatine (2) and xylopinine (3) isolated from Stephania rotunda tuber were investigated for their cytotoxic activity in a panel of human cancer cells (HT29, LS174T, SW620 and HepG2) using MTT assay. In the present study, cepharanthine (1) exerted potent cytotoxicity against colon and hepatoma cancer cell lines with IC(50) values between 2.4 and 5.3 microM while tetrahydropalmatine (2) and xylopinine (3) displayed weak cytotoxicity. In addition, the mutagenic activity of cepharanthine (1) was investigated using a modified liquid incubation technique of the Salmonella/microsomal assay. This alkaloid (1) was found to be non-mutagenic for doses up to 8.2 microM.

Antimicrobial activities of 3-amino- and polyaminosterol analogues of squalamine and trodusquemine.

A series of 3-amino- and polyaminosterol analogues of squalamine and trodusquemine were synthesized and evaluated for their in vitro antimicrobial properties against human pathogens. The activity was highly dependent on the structure of the different compounds involved and the best results were obtained with aminosterol derivatives 4b, 4e, 8b, 8e and 8n exhibiting minimum inhibitory concentrations (MICs) against yeasts, Gram positive and Gram negative bacteria at average concentrations of 3.12-12.5 microM.

Synthesis and antiplasmodial activity of new 4-aryl-2-trichloromethylquinazolines.

A series of original 4-aryl-substituted 2-trichloromethylquinazoline derivatives was synthesized using a microwave-assisted Suzuki-Miyaura cross-coupling approach. Antiplasmodial activity was evaluated on both chloroquino-resistant and -sensitive Plasmodium falciparum strains, and the selectivity indexes for THP1 and HepG2 human cells were also calculated, revealing their antiplasmodial potential.

In vitro antimicrobial activity of plants used in Cambodian traditional medicine.

The purpose of the present study was to screen 27 plant species used in the traditional medicine of Cambodia for in vitro antibacterial and antifungal activities. Thirty-three methanolic extracts were tested against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Mycobacterium smegmatis and Candida albicans. Screened by disk diffusion assay, the extracts showed antimicrobial activity especially on Gram-positive bacteria. None of the crude methanolic extracts showed activity against P. aeruginosa. Twenty-five selected extracts were evaluated using a micro-dilution test. Harrisonia perforata (roots) and Hymenodictyon excelsum (bark) exhibited a bactericidal effect against S. aureus at a concentration of 500 microg/ml. Azadirachta indica (bark), Harrisonia perforata (roots and stem) and Shorea obtusa (roots) exhibited a bactericidal effect against M. smegmatis at 250 microg/ml.