Identification of Inhibitors to trypanosoma cruzi sirtuins based on compounds developed to human enzymes

Chagas disease is an illness caused by the protozoan parasite Trypanosoma cruzi, affecting more than 7 million people in the world. Benznidazole and nifurtimox are the only drugs available for treatment and in addition to causing several side effects, are only satisfactory in the acute phase of the disease. Sirtuins are NAD+-dependent deacetylases involved in several biological processes, which have become drug target candidates in various disease settings. T. cruzi presents two sirtuins, one cytosolic (TcSir2rp1) and the latter mitochondrial (TcSir2rp3). Here, we characterized the effects of human sirtuin inhibitors against T. cruzi sirtuins as an initial approach to develop specific parasite inhibitors. We found that, of 33 compounds tested, two inhibited TcSir2rp1 (15 and 17), while other five inhibited TcSir2rp3 (8, 12, 13, 30, and 32), indicating that specific inhibitors can be devised for each one of the enzymes. Furthermore, all inhibiting compounds prevented parasite proliferation in cultured mammalian cells. When combining the most effective inhibitors with benznidazole at least two compounds, 17 and 32, demonstrated synergistic effects. Altogether, these results support the importance of exploring T. cruzi sirtuins as drug targets and provide key elements to develop specific inhibitors for these enzymes as potential targets for Chagas disease treatment

Uso das sirtuínas do Trypanosoma cruzi como alvos moleculares no desenvolvimento de fármacos para o tratamento da doença de chagas.

Submitted by Ana Maria Fiscina Sampaio ([email protected]) on 2017-11-13T17:51:30Z No. of bitstreams: 2 Tanira Matutino Bastos Uso das sirtuinas do Trypanosoma....pdf: 10155145 bytes, checksum: a90da7d8f4e7011cd7f64029594890d1 (MD5) Tanira Matutino Bastos Uso das sirtuinas do Trypanosoma....pdf: 10155145 bytes, checksum: a90da7d8f4e7011cd7f64029594890d1 (MD5)Approved for entry into archive by Ana Maria Fiscina Sampaio ([email protected]) on 2017-11-13T17:59:27Z (GMT) No. of bitstreams: 2 Tanira Matutino Bastos Uso das sirtuinas do Trypanosoma....pdf: 10155145 bytes, checksum: a90da7d8f4e7011cd7f64029594890d1 (MD5) Tanira Matutino Bastos Uso das sirtuinas do Trypanosoma....pdf: 10155145 bytes, checksum: a90da7d8f4e7011cd7f64029594890d1 (MD5)Made available in DSpace on 2017-11-13T17:59:27Z (GMT). No. of bitstreams: 2 Tanira Matutino Bastos Uso das sirtuinas do Trypanosoma....pdf: 10155145 bytes, checksum: a90da7d8f4e7011cd7f64029594890d1 (MD5) Tanira Matutino Bastos Uso das sirtuinas do Trypanosoma....pdf: 10155145 bytes, checksum: a90da7d8f4e7011cd7f64029594890d1 (MD5) Previous issue date: 2017CAPES, CNPq, FAPESB, FAPESPFundação Oswaldo Cruz. Instituto Gonçalo Moniz. Salvador, BA, BrasilINTRODUÇÃO: A doença de Chagas, causada pelo protozoário flagelado Trypanosoma cruzi, afeta em torno de 6 a 7 milhões de pessoas mundialmente. O benznidazol e o nifurtimox, medicamentos utilizados no tratamento da doença, apresentam eficácia limitada, e estão associados com a presença de efeitos colaterais graves. Portanto, torna-se necessária a identificação de novos alvos farmacológicos para a seleção de moléculas com boa eficácia contra o parasito e baixa toxicidade. Neste contexto, devido ao fato de atuarem em processos celulares vitais, as sirtuínas têm atraído interesse como potenciais alvos farmacológicos para o tratamento de diferentes doenças, incluindo a doença de Chagas. OBJETIVO: O objetivo deste estudo foi caracterizar as sirtuínas de T. cruzi, TcSir2rp1 e TcSir2rp3, como alvos farmacológicos para a identificação de novas drogas para o tratamento da doença de Chagas. METODOLOGIA: As TcSir2rp1 e TcSir2rp3 recombinantes foram produzidas utilizando sistema de expressão em bactérias e purificadas para posterior validação da atividade biológica das enzimas e triagem de 48 moléculas sintéticas e isoladas de produtos naturais. As moléculas que apresentaram atividade inibitória para as enzimas foram investigadas para avaliar o potencial em inibir as formas tripomastigota e amastigota do parasito, além da toxicidade em fibroblastos humanos. Além disso, foi investigada a propriedade antiparasitária in vivo de outros compostos que, apesar de não inibirem as sirtuínas do parasito, apresentaram atividade antiparasitária nos ensaios de triagem em sistema de High Content Screening padronizado para atividade tripanocida. RESULTADOS: As sirtuínas recombinantes produzidas apresentam atividade de lisina desacetilase NAD+ dependente, sendo demonstrado, pela primeira vez, a atividade biológica de TcSir2rp1 em ensaio funcional. Dentre os 48 compostos que foram triados, 10 apresentaram atividade inibitória de sirtuínas do parasito, sendo 3 inibidores de TcSir2rp1 (compostos 14, 17 e 40), 5 deles inibidores de TcSir2rp3 (compostos 10, 12, 13, 33 e 35) e 2 inibidores de ambas as sirtuínas do parasito (compostos 43 e 44). Foi verificada atividade antiparasitária de todos os compostos selecionados no ensaio de triagem com as enzimas recombinantes. Porém, o ensaio de toxicidade em fibroblasto humano indica que a atividade destes compostos não é seletiva. Dentre os compostos que não inibiram as sirtuínas de T. cruzi, mas apresentaram atividade antiparasitária potente e seletiva (compostos 45, 46, 47 e 48), 2 deles foram selecionados para o ensaio de atividade em camundongo (compostos 45 e 48) e apesar do tratamento in vivo causar a redução da parasitemia, os animais vieram ao óbito, com sinais de toxicidade. CONCLUSÕES: Este trabalho reforça o uso das sirtuínas do parasito como alvos farmacológicos, com a identificação de diferentes compostos que podem ser otimizados através da química medicinal com o intuito de identificar moléculas mais seletivas e potentes para serem usadas no tratamento da doença de Chagas.INTRODUCTION: Chagas disease, caused by protozoa parasite Trypanosoma cruzi, affects around 6 to 7 million people worldwide. Nifurtimox and benznidazol, the drugs used in the treatment of the disease, have limited efficacy and have been associated with severe side effects. Thus, there is an urgent need to find new biotargets for the identification of compounds with good efficacy against the parasite and low toxicity. In this context, due to their biological function on vital cellular processes, sirtuins have attracted interest as potential pharmacological targets for the treatment of different diseases, including Chagas disease. OBJECTIVE: The objective of this study was to characterize T. cruzi sirtuins, TcSir2rp1 and TcSir2rp3, as pharmacological targets for the identification of new drugs for the treatment of Chagas disease. METHODOLOGY: For this, recombinant TcSir2rp1 and TcSir2rp3 were produced, using expression system in bactéria, and purified for subsequent validation of biological activity of enzymes and screening of 48 synthetic molecules or isolated from natural products. The molecules that presented inhibitory activity for enzymes were investigated to assess the potential to inhibit the trypomastigote and amastigote forms of the parasite, and the toxicity effect in human fibroblasts. In addition, we also investigated the antiparasitic effects in vivo of other compounds which, although did not inhibit the sirtuin activity, showed anti-T. cruzi activity when screened in vitro using the High Content Screening System. RESULTS: The recombinant sirtuins produced presented NAD + dependent lysine desacetilase activity, being the first time this is shown for TcSir2rp1 in a functional test. Among the 48 compounds screened, 10 showed inhibitory activity of T. cruzi sirtuins, being 3 TcSir2rp1 inhibitors (compounds 14, 17 and 40), 5 of them anti-TcSir2rp3 (compounds 10, 12, 13, 33 and 35) and 2 inhibitors of both sirtuins of the parasite (compounds 43 and 44). Antiparasitic activity was found in all compounds selected in screening assays with recombinant enzymes. However, the toxicity test in human fibroblasts indicates that the activity of these compounds is not selective. Among the compounds that did not inhibit the sirtuins of T. cruzi, but showed potent and selective antiparasitic activity (compounds 45, 46, 47 and 48). Two of them (compounds 45 and 48) were tested in vivo in T. cruzi-infected mice, and although they caused a reduction of parasitemia, mortality was seen associated with signs of drug toxicity. CONCLUSIONS: This study reinforces the use of the sirtuins of the parasite as pharmacological targets, with the identification of different compounds that can be optimized through the medicinal chemistry in order to identify more selective and potent molecules to be used in the treatment of Chagas diseas

Anti-Trypanosoma cruzi activity of nicotinamide

Submitted by Ana Maria Fiscina Sampaio ([email protected]) on 2014-08-11T19:30:51Z No. of bitstreams: 1 Soares MB Anti-Trypanosoma....pdf: 1207763 bytes, checksum: 69f837370e5c46f7e1843460c2bd4154 (MD5)Made available in DSpace on 2014-08-11T19:30:51Z (GMT). No. of bitstreams: 1 Soares MB Anti-Trypanosoma....pdf: 1207763 bytes, checksum: 69f837370e5c46f7e1843460c2bd4154 (MD5) Previous issue date: 2012Fundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, BrasilFundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, BrasilFundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, BrasilFundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, BrasilFundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, BrasilLaboratory of Molecular Parasitology, Microbiology. Dpt, Hellenic Pasteur Institute. Athens, GreecePontifícia Universidade Católica do Rio Grande do Sul – PUCRS. Faculdade de Biociências. Instituto Nacional de Ciência e Tecnologia em Tuberculose-CNPq. Laboratório de Bioquímica Estrutural. Porto Alegre, RS, Brasil / Pontifícia Universidade Católica do Rio Grande do Sul. Porto Alegre, RS, BrasilInhibition of Trypanosoma brucei and Leishmania spp. sirtuins has shown promising antiparasitic activity, indicating that these enzymes may be used as targets for drug discovery against trypanosomatid infections. In the present work we carried out a virtual screening focused on the C pocket of Sir2 from Trypanosoma cruzi. Using this approach, the best ligand found was nicotinamide. In vitro tests confirmed the anti-T. cruzi activity of nicotinamide on epimastigote and trypomastigote forms. Moreover, treatment of T. cruzi-infected macrophages with nicotinamide caused a significant reduction in the number of amastigotes. In addition, alterations in the mitochondria and an increase in the vacuolization in the cytoplasm were observed in epimastigotes treated with nicotinamide. Analysis of the complex of Sir2 and nicotinamide revealed the details of the possible ligand–target interaction. Our data reveal a potential use of TcSir2 as a target for anti-T. cruzi drug discovery

Indirubin derivatives are potent and selective anti-Trypanosoma cruzi agents

Current treatment for combatting Chagas disease, a life-threatening illness caused by the kinetoplastid protozoan parasite Trypanosoma cruzi is inadequate, and thus the discovery of new antiparasitic compounds is of prime importance. Previous studies identified the indirubins, a class of ATP kinase inhibitors, as potent growth inhibitors of the related kinetoplastid Leishmania. Herein, we evaluated the inhibitory activity of a series of 69 indirubin analogues screened against T. cruzi trypomastigotes and intracellular amastigotes. Seven indirubins were identified as potent T. cruzi inhibitors (low μΜ, nM range). Cell death analysis of specific compounds [3'oxime-6-bromoindirubin(6-BIO) analogues 10, 11 and 17, bearing a bulky extension on the oxime moiety and one 7 substituted analogue 32], as evaluated by electron microscopy and flow cytometry, showed a different mode of action between compound 32 compared to the three 6-BIO oxime- substituted indirubins, suggesting that indirubins may kill the parasite by different mechanisms dependent on their substitution. Moreover, the efficacy of four compounds that show the most potent anti-parasitic effect in both trypomastigotes and intracellular amastigotes (10, 11, 17, 32), was evaluated in a mouse model of T. cruzi infection. Compound 11 (3ʹpiperazine-6-BIO) displayed the best in vivo efficacy (1/6 mortality, 94.5% blood parasitaemia reduction, 12 dpi) at a dose five times reduced over the reference drug benznidazole (20 mg/kg vs100 mg/kg). We propose 3ʹpiperazine-6-BIO as a potential lead for the development of new treatments of Chagas disease

Chemical Constituents of <i>Anacardium occidentale</i> as Inhibitors of <i>Trypanosoma cruzi</i> Sirtuins

Benznidazole and nifurtimox, the only drugs available for the treatment of Chagas disease, have limited efficacy and have been associated with severe adverse side effects. Thus, there is an urgent need to find new biotargets for the identification of novel bioactive compounds against the parasite and with low toxicity. Silent information regulator 2 (Sir2) enzymes, or sirtuins, have emerged as attractive targets for the development of novel antitrypanosomatid agents. In the present work, we evaluated the inhibitory effect of natural compounds isolated from cashew nut (Anacardium occidentale, L. Anacardiaceae) against the target enzymes TcSir2rp1 and TcSir2rp3 as well as the parasite. Two derivates of cardol (1, 2), cardanol (3, 4), and anacardic acid (5, 6) were investigated. The two anacardic acids (5, 6) inhibited both TcSir2rp1 and TcSir2rp3, while the cardol compound (2) inhibited only TcSir2rp1. The most potent sirtuin inhibitor active against the parasite was the cardol compound (2), with an EC50 value of 12.25 &#181;M, similar to that of benznidazole. Additionally, compounds (1, 4), which were inactive against the sirtuin targets, presented anti-T. cruzi effects. In conclusion, our results showed the potential of Anacardium occidentale compounds for the development of potential sirtuin inhibitors and anti-Trypanosoma cruzi agents

Physalins B and F, seco-steroids isolated from Physalis angulata L., strongly inhibit proliferation, ultrastructure and infectivity of Trypanosoma cruzi.

Submitted by Ana Maria Fiscina Sampaio ([email protected]) on 2014-07-07T19:07:08Z No. of bitstreams: 1 Meira CS Physalins B and F....pdf: 573771 bytes, checksum: 2e9ab6264149abbb0df24fafaa90c499 (MD5)Made available in DSpace on 2014-07-07T19:07:08Z (GMT). No. of bitstreams: 1 Meira CS Physalins B and F....pdf: 573771 bytes, checksum: 2e9ab6264149abbb0df24fafaa90c499 (MD5) Previous issue date: 2013Fundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, BrasilFundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, Brasil / Universidade do Estado da Bahia. Departamento de Ciências da Vida. Salvador, BA, BrasilFundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, BrasilFundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, BrasilFundação Oswaldo Cruz. Instituto de Tecnologia em Fármacos (Farmanguinhos). Rio de Janeiro, RJ, BrasilFundação Oswaldo Cruz. Instituto de Tecnologia em Fármacos (Farmanguinhos). Rio de Janeiro, RJ, BrasilHospital São Rafael. Centro de Biotecnologia e Terapia Celular. Salvador, BA, BrasilFundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, Brasil / Hospital São Rafael. Centro de Biotecnologia e Terapia Celular. Salvador, BA, BrasilWe previously observed that physalins have immunomodulatory properties, as well as antileishmanial and antiplasmodial activities. Here, we investigated the anti-Trypanosoma cruzi activity of physalins B, D, F and G. We found that physalins B and F were the most potent compounds against trypomastigote and epimastigote forms of T. cruzi. Electron microscopy of trypomastigotes incubated with physalin B showed disruption of kinetoplast, alterations in Golgi apparatus and endoplasmic reticulum, followed by the formation of myelin-like figures, which were stained with MDC to confirm their autophagic vacuole identity. Physalin B-mediated alteration in Golgi apparatus was likely due to T. cruzi protease perturbation; however physalins did not inhibit activity of the trypanosomal protease cruzain. Flow cytometry examination showed that cell death is mainly caused by necrosis. Treatment with physalins reduced the invasion process, as well as intracellular parasite development in macrophage cell culture, with a potency similar to benznidazole. We observed that a combination of physalins and benznidazole has a greater anti-T. cruzi activity than when compounds were used alone. These results indicate that physalins, specifically B and F, are potent and selective trypanocidal agents. They cause structural alterations and induce autophagy, which ultimately lead to parasite cell death by a necrotic process

Nitro/nitrosyl ruthenium complexes are potent and selective anti-Trypanosoma cruzi agents causing autophagy and necrotic parasite death

Submitted by Ana Maria Fiscina Sampaio ([email protected]) on 2014-09-15T16:28:22Z No. of bitstreams: 1 Bastos TM Nitro nitrosyl....pdf: 1279385 bytes, checksum: c422c1bbb8ce7f4412e1f081213091fe (MD5)Approved for entry into archive by Ana Maria Fiscina Sampaio ([email protected]) on 2014-09-15T16:28:44Z (GMT) No. of bitstreams: 1 Bastos TM Nitro nitrosyl....pdf: 1279385 bytes, checksum: c422c1bbb8ce7f4412e1f081213091fe (MD5)Made available in DSpace on 2014-09-15T17:29:28Z (GMT). No. of bitstreams: 1 Bastos TM Nitro nitrosyl....pdf: 1279385 bytes, checksum: c422c1bbb8ce7f4412e1f081213091fe (MD5) Previous issue date: 2014Fundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, BrasilUFSCAR. Departamento de Química. São Carlos, SP, BrasilUFSCAR. Departamento de Química. São Carlos, SP, BrasilUFSCAR. Departamento de Química. São Carlos, SP, BrasilFundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, BrasilFundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, Brasil / UNEB. Departamento de Ciências da Vida. Salvador, BA, BrasilUSP. Instituto de Física de São Carlos. São Carlos, SP, BrasilFundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, Brasil / Centro de Biotecnologia e Terapia Celular. Hospital São Rafael. Salvador, BA, BrasilUFSCAR. Departamento de Química. São Carlos, SP, BrasilFundação Oswaldo Cruz. Centro de Pesquisa Gonçalo Moniz. Salvador, BA, Brasil / Centro de Biotecnologia e Terapia Celular. Hospital São Rafael. Salvador, BA, BrasilThe cis–[RuCl(NO2)(dppb)(5,5’–mebipy)] (1), cis–[Ru(NO2)2(dppb)(5,5’–mebipy)] (2), ct– [RuCl(NO)(dppb)(5,5’–mebipy)](PF6)2 (3) and cc–[RuCl(NO)(dppb)(5,5’–mebipy)]PF6 (4) complexes, where 5,5’–mebipy = 5,5’–dimethyl–2,2’-bipyridine and dppb = 1,4–bis(diphenylphosphino)butane, were synthesized and characterized. The structure of the cis–[Ru(NO2)2(dppb)(5,5’–mebipy)] (2) complex was determined by X ray crystallography. These complexes exhibited a higher anti-T. cruzi activity than benznidazole, the current antiparasitic drug. Complex (3) was the most potent, displaying EC50 = 2.1±0.6 μM against trypomastigotes and IC50 = 1.3±0.2 μM against amastigotes, while it displayed a CC50 of 51.4±0.2 μM in macrophages. It was observed that the nitrosyl complex (3), but not its analog lacking the nitrosyl group, releases nitric oxide into parasite cells. This release has a diminished effect on the trypanosomal protease cruzain, but induces substantial parasite autophagy, which is followed by a series of irreversible morphological impairments to the parasites and finally results in cell death by necrosis. In infected mice, orally administered complex (3) (5 x 75 μmol/kg) reduced blood parasitemia and increased the survival rate of the mice. Combination index analysis of complex (3) indicated that its in vitro activity against trypomastigotes is synergic with benznidazole. In addition, drug combination enhanced efficacy in infected mice, suggesting that ruthenium- nitrosyl complexes are potential constituents for drug combinations

Antioxidant, antibacterial, leishmanicidal and trypanocidal activities of extract and fractions of Manilkara rufula stem bark

Submitted by Ana Maria Fiscina Sampaio ([email protected]) on 2019-08-12T16:20:17Z No. of bitstreams: 1 Anny, Carolinny Antioxidant, antibacterial....pdf: 413750 bytes, checksum: b9d851bdf0baf25e4f030bdc3dcebb9a (MD5)Approved for entry into archive by Ana Maria Fiscina Sampaio ([email protected]) on 2019-08-12T16:31:05Z (GMT) No. of bitstreams: 1 Anny, Carolinny Antioxidant, antibacterial....pdf: 413750 bytes, checksum: b9d851bdf0baf25e4f030bdc3dcebb9a (MD5)Made available in DSpace on 2019-08-12T16:31:05Z (GMT). No. of bitstreams: 1 Anny, Carolinny Antioxidant, antibacterial....pdf: 413750 bytes, checksum: b9d851bdf0baf25e4f030bdc3dcebb9a (MD5) Previous issue date: 2019Fundação de Amparo a Pesquisa do Estado da Bahia (FAPESB) and Conselho Nacional de Desenvolvimento Científico Tecnológico (CNPq).State University of the Southwest of Bahia. Department of Biological Sciences. Jequié, BA, Brazil.Fundação Oswaldo Cruz. Instituto Gonçalo Moniz. Salvador, BA, Brasil.Fundação Oswaldo Cruz. Instituto Gonçalo Moniz. Salvador, BA, Brasil.Fundação Oswaldo Cruz. Instituto Gonçalo Moniz. Salvador, BA, Brasil.Fundação Oswaldo Cruz. Instituto Gonçalo Moniz. Salvador, BA, Brasil.Fundação Oswaldo Cruz. Instituto Gonçalo Moniz. Salvador, BA, Brasil.State University of the Southwest of Bahia. Department of Sciences and Technologies. Jequié, BA, Brazil.State University of the Southwest of Bahia. Department of Sciences and Technologies. Jequié, BA, Brazil.University of São Paulo. Faculty of Animal Science and Food Engineering. Pirassununga, SP, Brazil.State University of the Southwest of Bahia. Department of Natural Sciences. Vitória da Conquista, BA, Brazil.Manilkara rufula belongs to family Sapotaceae and has received little attention regarding its pharmacological properties and chemical composition. Therefore, our objective was to determine the farmacological activities and preliminary chemical profile of the stem bark from M. rufula. The plant stem bark of M. rufula was collected and ethanolic extract and fractions were prepared. The antioxidant activity was determined by •DPPH and ABTS•+ scavenger methods and inhibition of β-carotene oxidation. The minimum inhibitory and bactericidal concentrations were estimated through the broth microdilution method against gram positive and negative bacteria. Cytotoxicity, antioxidant and cytoprotection potential were investigated on culture macrophages. Antiproliferative activity was evaluated by Alamar Blue method. The in vitro arginase activity from Leishmania amazonensis was determined in presence of the samples. In addition, their effects on survival of L. amazonensis and Trypanosoma cruzi amastigotes in mice macrophages were assessed. The preliminary phytochemical profile was evaluated by qualitative methods of classical phytochemistry, infrared spectroscopy, LC-MS/MS and CG-MS. The samples presented antioxidant, bactericidal, leishmanicidal and trypanocidal properties without toxic characteristics on normal cells. Triterpenes were observed in the hexane fraction, while glycosides, aromatic rings, fatty esters, proanthocyanidin dimers and trimers, catechin and various terpenes were observed in the other fractions

Production of Highly Active Antiparasitic Compounds from the Controlled Halogenation of the Arrabidaea brachypoda Crude Plant Extract

AbstractUHPLC-PDA-ELSD-MS analyses of the halogenation reactions at the analytical scale and NMR, and HRMS data of the isolated compound

Structural isomerism of Ru(II)-carbonyl complexes : synthesis, characterization and their antitrypanosomal activities.

New complexes with the general formula [RuCl(CO)(dppb)(diimine)]PF6, [dppb = 1,4-bis(diphenylphosphino) butane; diimine = 2,20-bipyridine (bipy) or 1,10-phenanthroline (phen)], were prepared. Thus, the complexes ct-[RuCl(CO)(dppb)(bipy)]PF6 (1), ct-[RuCl(CO)(dppb)(phen)]PF6 (2), tc-[RuCl(CO)(dppb)(bipy)]PF6 (3), tc-[RuCl(CO)(dppb)(phen)]PF6 (4), cc-[RuCl(CO)(dppb)(bipy)]PF6 (5) and cc-[RuCl(CO)(dppb)(phen)]PF6 (6) were obtained and characterized. In this case, the first letter in the prefixes indicates the position of CO with respect to the chlorido ligand and the second one is related to the phosphorus atoms. The compositions of the complexes were confirmed by analytical techniques and an octahedral environment around the ruthenium was confirmed by single-crystal X-ray diffraction of the complexes ct-[RuCl(CO)(dppb)(bipy)]PF6 and cc-[RuCl(CO)(dppb)(phen)]PF6. The oxidation potentials of the complexes were determined by cyclic voltammetry and it was found that they vary according to the CO position in the complexes. In order to obtain information on the stability of the ct, tc and cc-[RuCl(CO)(dppb)(bipy)]PF6 (1), (3) and (5) isomers, computational studies were carried out, and they showed large differences between the HOMO/LUMO energies. As monitored by 13C NMR, the stability of the complexes with respect to CO displacement, for at least 72 h, in DMSO-d6 solution, is independent of the CO position in the complexes. Pharmacological evaluation of the complexes against the Trypanosoma cruzi parasite revealed the structure?activity relationships, showing that the presence and position of the CO ligand in the complexes are relevant for the antiparasitic activity of the compounds. The most active compound, the tc-[RuCl(CO)(dppb)(bipy)]PF6 isomer, presented potent antiparasitic activity, which was achieved by causing oxidative stress followed by parasite cell death through necrosis. Thus, the findings presented here demonstrate that the use of a carbonyl ligand provides stability and pharmacological properties to ruthenium/diphosphine/diimine complexes