Clotilde Boudot

A series of substituted pyrrolo[2,3-d]pyrimidines was designed, synthesized, and evaluated in vitro against two protozoan parasites: Plasmodium falciparum and Trypanosoma brucei brucei. Pharmacological studies revealed antiprotozoal activity with IC₅₀ values in the submicromolar to micromolar range. Additionally, the in vitro cytotoxicity of these new compounds was assessed using human HepG2 cells. Among them, the pyrrolopyrimidine derivative 1d emerged as the most potent antimalarial compound, exhibiting a selectivity index (SI) of 600.81 against the P. falciparum chloroquine-resistant W2 strain. For the chloroquine-sensitive 3D7 strain, the most notable selectivity index (SI) was observed for pyrrolo[2,3-d]pyrimidine 1c, with a value of approximately 123. Furthermore, compound 1b demonstrated the most interesting activity against Trypanosoma brucei brucei, with an SI of 39.52, marking it as a promising trypanocidal agent. FRET melting assays confirmed that these nitrogen-containing heterocyclic compounds bind to telomeric G-quadruplexes in P. falciparum and Trypanosoma. However, no clear correlation was found between G-quadruplex binding and antiparasitic activity or selectivity, suggesting that G-quadruplex targeting is unlikely to be the main mechanism underlying cytotoxicity.

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).

As 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).

A series of novel 2,9-bis[(substituted-aminomethyl)]-4,7-phenyl-1,10-phenanthroline derivatives was designed, synthesized, and evaluated in vitro against three protozoan parasites (Plasmodium falciparum, Leishmania donovani and Trypanosoma brucei brucei). Pharmacological results showed antiprotozoal activity with IC₅₀ values in the sub and μM range. In addition, the in vitro cytotoxicity of these original molecules was assessed with human HepG2 cells. The substituted diphenylphenanthroline 1l was identified as the most potent antimalarial derivative with a ratio of cytotoxic to antiparasitic activities of 505.7 against the P. falciparum CQ-resistant strain W2. Against the promastigote forms of L. donovani, the phenanthrolines 1h, 1j, 1n and 1o were the most active with IC₅₀ from 2.52 to 4.50 μM. The phenanthroline derivative 1o was also identified as the most potent trypanosomal candidate with a selectivity index (SI) of 91 on T. brucei brucei strain. FRET melting and native mass spectrometry experiments evidenced that the nitrogen heterocyclic derivatives bind the telomeric G-quadruplexes of P. falciparum and Trypanosoma. Moreover, as the telomeres of the parasites P. falciparum and Trypanosoma could be considered to be possible targets of this kind of nitrogen heterocyclic derivatives, their potential ability to stabilize the parasitic telomeric G-quadruplexes have been determined through the FRET melting assay and by native mass spectrometry.

An 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 (T_1/2 > 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.

1H-3-{4-[(3-Dimethylaminopropyl)aminomethyl]phenyl}-2-phenylindole was synthesized via a multi-step pathway starting from 2-iodoaniline. Structure characterization of this new indole compound was achieved by ¹H-NMR, ¹³C-NMR and ESI-MS spectral analysis. The title compound was screened in vitro against three protozoan parasites (Plasmodium falciparum, Leishmania donovani and Trypanosoma brucei brucei). Biological results showed antiparasitic activity with IC₅₀ values in the μM range.