Synthesis, antitrypanosomal activity and molecular docking studies of pyrimidine derivatives

Structure-based design, optimization of lead, synthesis, and biological evaluation of compounds active against Trypanosoma cruzi

Chagas' disease affects approximately eight million people throughout the world, especially the poorest individuals. The protozoan that causes this disease-Trypanosoma cruzi-has the enzyme cruzipain, which is the main therapeutic target. As no available medications have satisfactory effectiveness and safety, it is of fundamental importance to design and synthesize novel analogues that are more active and selective. In the present study, molecular docking and the in silico prediction of ADMET properties were used as strategies to optimize the trypanocidal activity of the pyrimidine compound ZN3F based on interactions with the target site in cruzipain. From the computational results, eight 4-amino-5-carbonitrile-pyrimidine analogues were proposed, synthesized (5a-f and 7g-h) and, tested in vitro on the trypomastigote form of the Tulahuen strain of T. cruzi. The in silico study showed that the designed analogues bond favorably to important amino acid residues of the active site in cruzipain. An in vitro evaluation of cytotoxicity was performed on L929 mammal cell lines. All derivatives inhibited the Tulahuen strain of T. cruzi and also exhibited lower toxicity to L929 cells. The 5e product, in particular, proved to be a potent, selective (IC50  = 2.79 ± 0.00 μM, selectivity index = 31.3) inhibitor of T. cruzi. The present results indicated the effectiveness of drugs based on the structure of the receptor, revealing the potential trypanocidal of pyrimidines. This study also provides information on molecular aspects for the inhibition of cruzipain.

4-amino-2-phenyl-6-(p-fluorophenyl)-5-carbonitrile-pyrimidine-bis-substituted-loaded liposomes as promising system for cancer treatment

The aim of the present study was to perform in vitro and in vivo assessments of the antineoplastic action of 4-amino-pyrimidine encapsulated in liposomes. Liposomes were prepared and characterized for particle size and drug encapsulation and submitted to long-term stability tests. Cytotoxicity assays were performed in HeLa cells. Antineoplastic activity was investigated using the experimental sarcoma 180 tumor in Swiss albino mice. Encapsulation efficiency was 82.93 ± 0.04% and no significant changes were found with respect to particle size or pH after centrifugation and mechanical agitation tests. The in vitro results at concentration of 20 μg/mL indicated a considerable reduction in cell viability after treatment with encapsulated pyrimidine (75.91%). The in vivo assays using the compounds in encapsulated and free forms and 5-fluorouracil achieved tumor inhibition rates of 66.47 ± 26.8%, 50.46 ± 16.24% and 14.47 ± 9.22%, respectively. Mitotic counts demonstrated a greater reduction in the number of mitoses in animals treated with liposomal pyrimidine (32.15%) compared to those treated with the pyrimidine free (87.69%) and 5-fluorouracil (71.39%). This study demonstrated that the development of liposome formulations containing 4-amino-pyrimidine is a promising alternative for overcoming limitations related to the toxicity of current cancer treatment, ensuring greater therapeutic efficacy.

Structural improvement of new thiazolyl-isatin derivatives produces potent and selective trypanocidal and leishmanicidal compounds

Neglected diseases are a group of transmissible diseases that occur mostly in countries in tropical climates. Among this group, Chagas disease and leishmaniasis stand out, considered threats to global health. Treatment for these diseases is limited. Therefore, there is a need for new therapies against these diseases. In this sense, our proposal consisted of developing two series of compounds, using a molecular hybridization of the heterocyclic isatin and thiazole. The isatin and thiazole ring are important scaffold for several biological disorders, including antiparasitic ones. Herein, thiazolyl-isatin has been synthesized from respective thiosemicarbazone or phenyl-thiosemicarbazone, being some of these new thiazolyl-isatin toxic for trypomastigotes without affecting macrophages viability. From this series, compounds 2e (IC₅₀ = 4.43 μM), 2j (IC₅₀ = 2.05 μM), 2l (IC₅₀ = 4.12 μM) and 2m (1.72 μM) showed the best anti-T. cruzi activity for trypomastigote form presenting a selectivity index higher than Benznidazole (BZN). Compounds 2j, 2l and 2m were able to induce a significantly labelling compatible with necrosis in trypomastigotes. Analysis by scanning electron microscopy showed that T. cruzi trypomastigote cells treated with the compound 2m from IC₅₀ concentrations, promoted changes in the shape, flagella and surface of body causing of the parasite dead. Concerning leishmanicidal evaluation against L. amazonensis and L. infantum, compounds 2l (IC₅₀ = 7.36 and 7.97 μM, respectively) and 2m (6.17 and 6.04 μM, respectively) showed the best activity for promastigote form, besides showed a higher selectivity than Miltefosine. Thus, compounds 2l and 2m showed dual in vitro trypanosomicidal and leishmanicidal activities. A structural activity relationship study showed that thiazolyl-isatin derivatives from phenyl-thiosemicarbazone (2a-m) were, in general, more active than thiazolyl-isatin derivatives from thiosemicarbazone (1a-g). Crystallography studies revealed a different configuration between series 1a-g and 2a-m. The configuration and spatial arrangement divergent between the two sub-series could explain the improved biological activity profile of 2a-m sub-series.

The discovery of novel antitrypanosomal 4-phenyl-6-(pyridin-3-yl)pyrimidines

Human African trypanosomiasis, or sleeping sickness, is a neglected tropical disease caused by Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense which seriously affects human health in Africa. Current therapies present limitations in their application, parasite resistance, or require further clinical investigation for wider use. Our work herein describes the design and syntheses of novel antitrypanosomal 4-phenyl-6-(pyridin-3-yl)pyrimidines, with compound 13, the 4-(2-methoxyphenyl)-6-(pyridine-3-yl)pyrimidin-2-amine demonstrating an IC₅₀ value of 0.38 μM and a promising off-target ADME-Tox profile in vitro. In silico molecular target investigations showed rhodesain to be a putative candidate, supported by STD and WaterLOGSY NMR experiments, however, in vitro evaluation of compound 13 against rhodesain exhibited low experimental inhibition. Therefore, our reported library of drug-like pyrimidines present promising scaffolds for further antikinetoplastid drug development for both phenotypic and target-based drug discovery.