Antikinetoplastid SAR study in 3-nitroimidazopyridine series: identification of a novel non-genotoxic and potent anti-T. b. brucei hit-compound with improved pharmacokinetic properties

To study the antikinetoplastid 3-nitroimidazo[1,2-a]pyridine pharmacophore, a structure-activity relationship study was conducted through the synthesis of 26 original derivatives and their in vitro evaluation on both Leishmania spp and Trypanosoma brucei brucei. This SAR study showed that the antitrypanosomal pharmacophore was less restrictive than the antileishmanial one and highlighted positions 2, 6 and 8 of the imidazopyridine ring as key modulation points. None of the synthesized compounds allowed improvement in antileishmanial activity, compared to previous hit molecules in the series. Nevertheless, compound 8, the best antitrypanosomal molecule in this series (EC50 = 17 nM, SI = 2650 & E° = -0.6 V), was not only more active than all reference drugs and previous hit molecules in the series but also displayed improved aqueous solubility and better in vitro pharmacokinetic characteristics: good microsomal stability (T1/2 > 40 min), moderate albumin binding (77%) and moderate permeability across the blood brain barrier according to a PAMPA assay. Moreover, both micronucleus and comet assays showed that nitroaromatic molecule 8 was not genotoxic in vitro. It was evidenced that bioactivation of molecule 8 was operated by T. b. brucei type 1 nitroreductase, in the same manner as fexinidazole. Finally, a mouse pharmacokinetic study showed that 8 displayed good systemic exposure after both single and repeated oral administrations at 100 mg/kg (NOAEL) and satisfying plasmatic half-life (T1/2 = 7.7 h). Thus, molecule 8 appears as a good candidate for initiating a hit to lead drug discovery program

Antikinetoplastid SAR study in 3-nitroimidazopyridine series:identification of a novel non-genotoxic and potent anti-T. b. brucei hit-compound with improved pharmacokinetic properties.

International audienceTo study the antikinetoplastid 3-nitroimidazo[1,2-a]pyridine pharmacophore, a structure-activity relationship study was conducted through the synthesis of 26 original derivatives and their in vitro evaluation on both Leishmania spp and Trypanosoma brucei brucei. This SAR study showed that the antitrypanosomal pharmacophore was less restrictive than the antileishmanial one and highlighted positions 2, 6 and 8 of the imidazopyridine ring as key modulation points. None of the synthesized compounds allowed improvement in antileishmanial activity, compared to previous hit molecules in the series. Nevertheless, compound 8, the best antitrypanosomal molecule in this series (EC50 = 17 nM, SI = 2650 & E° = −0.6 V), was not only more active than all reference drugs and previous hit molecules in the series but also displayed improved aqueous solubility and better in vitro pharmacokinetic characteristics: good microsomal stability (T1/2 > 40 min), moderate albumin binding (77%) and moderate permeability across the blood brain barrier according to a PAMPA assay. Moreover, both micronucleus and comet assays showed that nitroaromatic molecule 8 was not genotoxic in vitro. It was evidenced that bioactivation of molecule 8 was operated by T. b. brucei type 1 nitroreductase, in the same manner as fexinidazole. Finally, a mouse pharmacokinetic study showed that 8 displayed good systemic exposure after both single and repeated oral administrations at 100 mg/kg (NOAEL) and satisfying plasmatic half-life (T1/2 = 7.7 h). Thus, molecule 8 appears as a good candidate for initiating a hit to lead drug discovery program

Synthesis and study of the antikinetoplastid activity of new nitroaromatic derivatives

Les kinétoplastidés sont des protozoaires flagellés responsables de maladies tropicales négligées, pouvant être potentiellement mortelles chez l’Homme, telles que la leishmaniose viscérale (L. donovani et L. infantum), la trypanosomiase humaine africaine (T. brucei) ou la maladie de Chagas (T. cruzi), et pour lesquelles les traitements actuellement disponibles présentent des limitations. Ces dernières années, un regain d’intérêt est porté aux molécules anti-infectieuses nitroaromatiques, à l’image du fexinidazole. L’activité anti-kinétoplastidés de ces composés résulte de leur bioactivation sélective par des nitroréductases parasitaires, conduisant à la formation d’espèces réactives toxiques pour le parasite. Deux hits antileishmaniens et deux hits anti-Trypanosoma, substrats des nitroréductases parasitaires de type 1, ont été précédemment décrits en série 3-nitroimidazo[1,2-a]pyridine. Ces travaux de thèse portent sur la synthèse et l’étude des relations structure-activité de cent-trois dérivés originaux, dont soixante-et-un dérivés sont fonctionnalisés en positions 2, 6 et 8 du pharmacophore 3-nitroimidazo[1,2-a]pyridine, et trente-cinq dérivés sont fonctionnalisés en positions 5 ou 7, via des réactions de SN2, SNAr, ou de couplages pallado-catalysés. Deux dérivés en série 3-nitroimidazo[1,2-b]pyridazine et cinq dérivés 5-nitroimidazoles sont obtenus par miodification structurale. Ainsi, deux nouveaux hits ont été identifiés en série 3-nitroimidazo[1,2-a]pyridine, un premier antileishmanien, et un second anti-Trypanosoma, possédant tous deux de meilleurs paramètres pharmacocinétiques et physicochimiques que les hits précédents.Kinetoplastids are flagellated protozoa responsible for life-threatening neglected tropical diseases in humans, such as visceral leishmaniasis (L. donovani and L. infantum), human African trypanosomiasis (T. brucei), or Chagas disease (T. cruzi), for which currently available treatments have limitations. The antikinetoplastid activity of these compounds results from their selective bioactivation by parasitic nitroreductases, leading to the formation of reactive species toxic to the parasite. Two antileishmanial and two anti-Trypanosoma hits, substrates of type 1 parasitic nitroreductases, have been previously described in 3-nitroimidazo[1,2-a]pyridine series. This thesis work focuses on the synthesis and structure-activity relationships of one hundred and three original derivatives, of which sixty-one derivatives are functionalized at positions 2, 6, and 8 of the 3-nitroimidazo[1,2-a]pyridine pharmacophore, and thirty-five derivatives are functionalized at positions 5 or 7, via SN2, SNAr, or pallado-catalyzed coupling reactions. Two 3-nitroimidazo[1,2-b]pyridazine series derivatives are also obtained from a scaffold-hopping strategy, and five 5-nitroimidazole derivatives are obtained by structural simplification. Thus, two new hits were identified in 3-nitroimidazo[1,2-a]pyridine series, a first one antileishmanial, and a second one anti-Trypanosoma, both showing better pharmacokinetic (microsomal stability, human albumin binding) and physicochemical (water solubility, PAMPA permeability tests) properties than the previous hits

<i>N</i>-[1-(2-Chlorophenyl)-2-{1-methyl-5-nitro-4-[(phenylsulfonyl)methyl]-1<i>H</i>-imidazol-2-yl}ethyl]-4-methylbenzenesulfonamide

In continuation of our research program to develop original synthetic methods using TDAE methodology on nitroheterocyclic substrates, we were able to generate for the first time a stable carbanion in position 2 of the 5-nitroimidazole scaffold. Starting from a 2-chloromethyl-4-phenylsulfonylmethyl-5-nitroimidazole intermediate, prepared by the vicarious nucleophilic substitution of hydrogen (VNS) reaction, we selectively introduced a N-tosylbenzylimine moiety at position 2 without reducing the sulfone at position 4, leading to the formation of N-[1-(2-chlorophenyl)-2-{1-methyl-5-nitro-4-[(phenylsulfonyl)methyl]-1H-imidazol-2-yl}ethyl]-4-methylbenzenesulfonamide in 47% yield. This new synthetic method using TDAE should allow access to new 2-substituted 5-nitroimidazole derivatives with various electrophiles such as carbonyls and other N-tosylbenzylimines

Structural simplification of the 3‐nitroimidazo[1,2‐ a ]pyridine antileishmanial pharmacophore: Design, synthesis, and antileishmanial activity of novel 2,4-disubstituted 5-nitroimidazoles

International audienceAs part of our ongoing antileishmanial structure–activity relationship study, a structural simplification of the 3‐nitroimidazo[1,2‐ a ]pyridine ring to a 5-nitroimidazole moiety was conducted. A series of novel 2,4-disubsituted 5-nitroimidazole derivatives, including the 5-nitroimidazole analog of Hit A and the 4-phenylsulfonylmethyl analog of fexinidazole, were obtained by using the vicarious nucleophilic substitution of hydrogen (VNS) reaction, to substitute position 4, and by using the tetrakis(dimethylamino)ethylene methodology to modulate position 2. The molecular structures of eight novel 5-nitroimidazoles were characterized by 1 H NMR, 13 C NMR, LC/MS, and HRMS. The in vitro antileishmanial activity of these compounds was evaluated against the promastigote form of Leishmania infantum and their influence on cell viability was assessed on the human hepatocyte HepG2 cell line. The 4-phenylsulfonylmethyl analog of fexinidazole showed the best selectivity index of the series, displaying good activity against both the promastigote form of L. infantum (EC 50 = 0.8 µM, SI &gt; 78.1) and the promastigote form of Leishmania donovani (EC 50 = 4.6 µM, SI &gt; 13.6), and exhibiting low cytotoxicity on the HepG2 cell line (CC 50 &gt; 62.5 µM)

Synthesis of New 5- or 7-Substituted 3-Nitroimidazo[1,2-a]pyridine Derivatives Using SNAr and Palladium-Catalyzed Reactions To Explore Antiparasitic Structure–Activity Relationships

International audienceTo study the antikinetoplastid structure–activity relationships in a 3-nitroimidazo[1,2-a]pyridine series, we explored the substitution of positions 5 and 7 of the scaffold, developing nucleophilic aromatic substitution reactions and palladium-catalyzed Suzuki–Miyaura, Sonogashira, and Buchwald–Hartwig cross-coupling reactions that had never been reported at these positions in this series. In four steps from 2-amino(bromo)pyridines, 33 original compounds were obtained, allowing a better definition of the antiparasitic pharmacophore

Diethyl (5-Benzyl-2-(4-(N′-hydroxycarbamimidoyl)phenyl)-5-methyl-4,5-dihydrofuran-3-yl)phosphonate

International audienceAs part of our ongoing research into the antileishmanial properties of amidoxime derivatives, we report a preliminary assessment of the antiparasitic properties of a novel compound, diethyl (5-benzyl-2-(4-(N′-hydroxycarbamimidoyl)phenyl)-5-methyl-4,5-dihydrofuran-3-yl)phosphonate. This compound was evaluated in vitro for the first time against the promastigote form of Leishmania amazonensis. Compounds containing both amidoxime and phosphonyl functional groups in dihydrofuran scaffolds are relatively rare, despite the extensive study of this heterocycle in various biological applications. Therefore, this work makes a valuable contribution to the fight against Leishmania spp. as a neglected disease. The cyclized 4,5-dihydrofuran intermediate scaffold was obtained via a three-step synthetic route that had previously been developed for accessing other derivatives, including the sulfone moiety. This synthesis was performed using a manganese-based free radical oxidative method under microwave irradiation. The intermediary 4,5-dihydrofuran, which included a nitrile group, tolerated the subsequent reaction with hydroxylamine hydrochloride, resulting in the formation of the target product. The target compound showed moderate activity in vitro against the promastigote form of L. amazonensis (IC50 = 91.1 µM)

6-Chloro-3-nitro-8-(phenylthio)-2-[(phenylthio)methyl] imidazo[1,2-<i>a</i>]pyridine

As part of our ongoing antikinetoplastid structure–activity relationship study focused on positions 2 and 8 of the 3-nitroimidazo[1,2-a]pyridine scaffold, we were able to introduce a phenylthioether moiety at both position 2 and position 8 in one step. Using a previously reported synthetic route developed in our laboratory, we obtained 6-chloro-3-nitro-8-(phenylthio)-2-[(phenylthio)methyl]imidazo[1,2-a]pyridine in 74% yield. The in vitro cell viability of this compound was assessed on the HepG2 cell line, and its in vitro activity was evaluated against the promastigote form of L. donovani, the axenic amastigote form of L. infantum and the trypomastigote blood stream form of T. b. brucei. It showed low solubility in HepG2 culture medium (CC50 > 7.8 µM), associated with weak activity against both the promastigote form of L. donovani (EC50 = 8.8 µM), the axenic amastigote form of L. infantum (EC50 = 9.7 µM) and the trypomastigote blood stream form of T. b. brucei (EC50 = 12.8 µM)

6-Chloro-3-nitro-2-[(phenylsulfonyl)methyl]imidazo[1,2-b]pyridazine

International audienceAs part of our ongoing scaffold-hopping work on an antikinetoplastid 3-nitroimidazo[1,2-a]pyridine scaffold, we explored 3-nitroimidazo[1,2-b]pyridazine as a potential new antikinetoplastid series. Using conditions previously described by our lab, we obtained 6-chloro-3-nitro-2-[(phenylsulfonyl)methyl]imidazo[1,2-b]pyridazine with 54% yield. In vitro activity of this compound was evaluated against both the promastigote form of Leishmania donovani, the axenic amastigote form of Leishmania infantum and the trypomastigote blood stream form of Trypanosomabrucei brucei, and its influence on cell viability was assessed on the HepG2 cell line. However, despite good activity against the trypomastigote blood stream form of T. b. brucei (EC50 = 0.38 µM), it showed poor solubility in both HepG2 (CC50 > 7.8 µM) and L. infantum axenic amastigotes (EC50 > 1.6 µM) culture media, associated with a loss of activity against the promastigote form of L. infantum (EC50 > 15.6 µM)

Improving Aqueous Solubility and In Vitro Pharmacokinetic Properties of the 3-Nitroimidazo[1,2-a]pyridine Antileishmanial Pharmacophore

International audienceAn antileishmanial structure–activity relationship (SAR) study focused on positions 2 and 8 of the imidazo[1,2-a]pyridine ring was conducted through the synthesis of 22 new derivatives. After being screened on the promatigote and axenic amastigote stages of Leishmania donovani and L. infantum, the best compounds were tested against the intracellular amastigote stage of L. infantum and evaluated regarding their in vitro physicochemical and pharmacokinetic properties, leading to the discovery of a new antileishmanial6-chloro-3-nitro-8-(pyridin-4-yl)-2-[(3,3,3-trifluoropropylsulfonyl)methyl]imidazo[1,2-a]pyridine hit. It displayed low cytotoxicities on both HepG2 and THP1 cell lines (CC50 > 100 µM) associated with a good activity against the intracellular amastigote stage of L. infantum (EC50 = 3.7 µM versus 0.4 and 15.9 µM for miltefosine and fexinidazole, used as antileishmanial drug references). Moreover, in comparison with previously reported derivatives in the studied series, this compound displayed greatly improved aqueous solubility, good mouse microsomal stability (T1/2 > 40 min) and high gastrointestinal permeability in a PAMPA model, making it an ideal candidate for further in vivo studies on an infectious mouse model