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

Target fishing reveals PfPYK-1 and PfRab6 as potential targets of an antiplasmodial 4-anilino-2-trichloromethylquinazoline hit compound

We present investigations about the mechanism of action of a previously reported 4-anilino-2-trichloromethylquinazoline antiplasmodial hit-compound (Hit A), which did not share a common mechanism of action with established commercial antimalarials and presented a stage-specific effect on the erythrocytic cycle of P. falciparum at 8 < t < 16 h. The target of Hit A was searched by immobilising the molecule on a solid support via a linker and performing affinity chromatography on a plasmodial lysate. Several anchoring positions of the linker (6,7 and 3') and PEG-type linkers were assessed, to obtain a linked-hit molecule displaying in vitro antiplasmodial activity similar to that of unmodified Hit A. This allowed us to identify the PfPYK-1 kinase and the PfRab6 GTP-ase as potential targets of Hit A.

Functional analyses of Toxoplasma gondii dihydroorotase reveal a promising anti-parasitic target

Toxoplasma gondii relies heavily on the de novo pyrimidine biosynthesis pathway for fueling the high uridine-5'-monophosphate (UMP) demand during parasite growth. The third step of de novo pyrimidine biosynthesis is catalyzed by dihydroorotase (DHO), a metalloenzyme that catalyzes the reversible condensation of carbamoyl aspartate to dihydroorotate. Here, functional analyses of TgDHO reveal that tachyzoites lacking DHO are impaired in overall growth due to decreased levels of UMP, and the noticeably growth restriction could be partially rescued after supplementation with uracil or high concentrations of L-dihydroorotate in vitro. When pyrimidine salvage pathway is disrupted, both DHOH35A and DHOD284E mutant strains proliferated much slower than DHO-expressing parasites, suggesting an essential role of both TgDHO His35 and Asp284 residues in parasite growth. Additionally, DHO deletion causes the limitation of bradyzoite growth under the condition of uracil supplementation or uracil deprivation. During the infection in mice, the DHO-deficient parasites are avirulent, despite the generation of smaller tissue cysts. The results reveal that TgDHO contributes to parasite growth both in vitro and in vivo. The significantly differences between TgDHO and mammalian DHO reflect that DHO can be exploited to produce specific inhibitors targeting apicomplexan parasites. Moreover, potential DHO inhibitors exert beneficial effects on enzymatic activity of TgDHO and T. gondii growth in vitro. In conclusion, these data highlight the important role of TgDHO in parasite growth and reveal that it is a promising anti-parasitic target for future control of toxoplasmosis.

Dichloro{4-(4-chlorophenoxy)phthalazin-1-yl} methylphosphonic dichloride

As part of our ongoing scaffold-hopping work on an antiplasmodial 2-trichloromethylquinazoline scaffold, we aimed to explore the 1-trichloromethylphthalazine scaffold as a potential new antimalarial series. Using previously chlorination conditions described by our lab to obtain a trichloromethyl group from a methyl group, we did not obtain the target compound; instead, we obtained a dichloro methylphosphonic dichloride side product 3. The nature of this compound was then characterized by NMR, HRMS and X-ray crystallography. The same issue was previously reported by Kato et al., starting from the 2-methyl-3-nitropyridine. Finally, compound 3, although not cytotoxic, was not active against P. falciparum, the parasite responsible for human malaria.

Evaluation of the Anti-Leishmania mexicana and -Trypanosoma brucei Activity and Mode of Action of 4,4'-(Arylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)

Trypanosomiasis and leishmaniasis are neglected infections caused by trypanosomatid parasites. The first-line treatments have many adverse effects, high costs, and are prone to resistance development, hence the necessity for new chemotherapeutic options. In line with this, twenty five 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols) derivatives were synthesized and evaluated in vitro for their anti-trypanosomatid activity. Ten and five compounds from this series showed IC50 ≤ 10 µM against the promastigote and the bloodstream stage of Leishmania mexicana and Trypanosoma brucei brucei, respectively. Overall, derivatives with pyrazole rings substituted with electron-withdrawing groups proved more active than those with electron-donating groups. The hits proved moderately selective towards L. mexicana and T. brucei (selectivity index, SI, compared to murine macrophages = 5−26). The exception was one derivative displaying an SI (>111−189) against T. brucei that surpassed, by >6-fold, the selectivity of the clinical drug nifurtimox (SI = 13−28.5). Despite sharing a common scaffold, the hits differed in their mechanism of action, with halogenated derivatives inducing a rapid and marked intracellular oxidative milieu in infective T. brucei. Notably, most of the hits presented better absorption, distribution, metabolism, and excretion (ADME) properties than the reference drugs. Several of the bioactive molecules herein identified represent a promising starting point for further improvement of their trypanosomatid potency and selectivity.

2-Phenoxy-3-Trichloromethylquinoxalines Are Antiplasmodial Derivatives with Activity against the Apicoplast of Plasmodium falciparum

The malaria parasite harbors a relict plastid called the apicoplast. Although not photosynthetic, the apicoplast retains unusual, non-mammalian metabolic pathways that are essential to the parasite, opening up a new perspective for the development of novel antimalarials which display a new mechanism of action. Based on the previous antiplasmodial hit-molecules identified in the 2-trichloromethylquinoxaline series, we report herein a structure–activity relationship (SAR) study at position two of the quinoxaline ring by synthesizing 20 new compounds. The biological evaluation highlighted a hit compound (3i) with a potent PfK1 EC₅₀ value of 0.2 µM and a HepG2 CC₅₀ value of 32 µM (Selectivity index = 160). Nitro-containing (3i) was not genotoxic, both in the Ames test and in vitro comet assay. Activity cliffs were observed when the 2-CCl₃ group was replaced, showing that it played a key role in the antiplasmodial activity. Investigation of the mechanism of action showed that 3i presents a drug response by targeting the apicoplast and a quick-killing mechanism acting on another target site.

Synthesis and Antiplasmodial Evaluation of 4-Carboxamido- and 4-Alkoxy-2-Trichloromethyl Quinazolines

From three previously identified antiplasmodial hit compounds (A–C) and inactive series (D), all based on a 2-trichloromethylquinazoline scaffold, we conducted a structure-activity relationship (SAR) study at position four of the quinazoline ring by synthesizing 42 novel derivatives bearing either a carboxamido- or an alkoxy-group, to identify antiplasmodial compounds and to enrich the knowledge about the 2-trichloromethylquinazoline antiplasmodial pharmacophore. All compounds were evaluated in vitro for their cytotoxicity towards the HepG2 cell line and their activity against the multiresistant K1 P. falciparum strain, using doxorubicin, chloroquine and doxycycline as reference drugs. Four hit-compounds (EC₅₀ K1 P. falciparum ≤ 2 µM and SI ≥ 20) were identified among 4-carboxamido derivatives (2, 9, 16, and 24) and two among 4-alkoxy derivatives (41 and 44). Regarding the two most potent molecules (16 and 41), five derivatives without a 2-CCl₃ group were prepared, evaluated, and appeared totally inactive (EC₅₀ > 50 µM), showing that the 2-trichloromethyl group was mandatory for the antiplasmodial activity.

Looking for new antiplasmodial quinazolines: DMAP-catalyzed synthesis of 4-benzyloxy- and 4-aryloxy-2-trichloromethylquinazolines and their in vitro evaluation toward Plasmodium falciparum

A DMAP catalyzed synthesis of new 4-benzyloxy- and 4-aryloxy-2-trichloromethylquinazolines was studied, in a view to react 4-chloroquinazolines with poorly nucleophilic alcohols such as benzylic alcohols, via a simple and cheap SNAr reaction approach. A fast (1 h) general operating procedure, affording good reaction yields, was achieved under microwave irradiation. Thus, a series of 35 molecules was obtained and evaluated in vitro on the K1 multi-resistant Plasmodium falciparum strain, in parallel with a cytotoxicity assessment on the human HepG2 cell line. 5 hit-molecules were identified, presenting both promising antiplasmodial activity (1.5 μM < IC50 < 2 μM) and low cytotoxicities (25 μM < CC50 < 45 μM). Apart for 2 molecules, the global series displayed a satisfying solubility in the aqueous biological media. Structure-activity relationships showed that the molecules presenting a benzyloxy moiety were less cytotoxic than the ones bearing a phenoxy moiety at position 4 of the quinazoline ring. It also appeared that the introduction of a heteroaryl moiety afforded inactive compounds. Finally, the most active and selective molecules (Selectivity Index = 22-27) were the ones presenting either an unsubstituted benzyloxy group or a phenoxy group, this last bearing a p-bromo or an o-acetyl substituent.

Hexachlorocyclotriphosphazene (HCCP)-mediated direct formation of thioethers and ethers from quinazolin-4(3H)-ones

A hexachlorocyclotriphosphazene (HCCP)-mediated direct formation of quinazoline (thio)ethers from quinazolin-4(3H)-ones has been developed. Treatment of quinazolin-4(3H)-ones with HCCP, diisopropylethylamine (DIPEA), and thiophenols resulted in formation of the corresponding 4-arylthioquinazoline derivatives in moderate to excellent yields. This method has also been utilized to prepare 4-aryloxyquinazoline and 4-alkoxyquinazoline derivatives using phenols and sodium alkoxides as the nucleophiles.

A new synthetic route to original sulfonamide derivatives in 2-trichloromethylquinazoline series: a structure-activity relationship study of antiplasmodial activity

We report herein a simple and efficient two-step synthetic approach to new 2-trichloromethylquinazolines possessing a variously substituted sulfonamide group at position 4 used to prepare new quinazolines with antiparasitic properties. Thus, an original series of 20 derivatives was synthesized, which proved to be less-toxic than previously synthesized hits on the human HepG2 cell line, but did not display significant antiplasmodial activity. A brief Structure-Activity Relationship (SAR) evaluation shows that a more restricted conformational freedom is probably necessary for providing antiplasmodial activity.