S J. Braz. Chem. Soc., Vol. 22, No. 2, 352-358, 2011
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J. Braz. Chem. Soc., Vol. 22, No. 2, 352-358, 2011. Printed in Brazil - ©2011 Sociedade Brasileira de Química S 0103 - 5053 $6.00+0.00 Short Report Synthesis and Antileishmanial Activity of New 1-Aryl-1H-Pyrazole-4- Carboximidamides Derivatives Maurício S. dos Santos,a Adriana O. Gomes,a Alice M. R. Bernardino,*,a Marcos C. de Souza,a Misbahul A. Khan,b Monique A. de Brito,c Helena C. Castro,d Paula A. Abreu,d Carlos R. Rodrigues,e Rosa M. M. de Léo,f Leonor L. Leonf and Marilene M. Canto-Cavalheirof aPrograma de Pós-Graduação em Química Orgânica and dLABioMol, GCM - IB, Universidade Federal Fluminense, Outeiro de São João Baptista, 24020-150 Niterói-RJ, Brazil bChemistry Department, The Islamia University of Bahawalpur, 63100 Bahawalpur, Pakistan cLaboratório de Química Medicinal Computacional, Faculdade de Farmácia, Universidade Federal Fluminense, 24241-000 Niterói-RJ, Brazil eFaculdade de Farmácia, ModMolQSAR, Universidade Federal do Rio de Janeiro, 24020-150 Rio de Janeiro-RJ, Brazil fLaboratório de Bioquímica de Tripanosomatídeos, IOC, Fundação Oswaldo Cruz, 21040-900 Rio de Janeiro-RJ, Brazil A quimioterapia para as leishmanioses, doenças causadas por protozoários do gênero Leishmania, ainda permanece ineficiente em diversos tratamentos. Portanto, existe a necessidade de pesquisa por novos fármacos. Nesse trabalho, foram sintetizados derivados 1-aril-1H-pirazol- 4-carboximidamidas, avaliadas as atividades leishmanicida e os efeitos citotóxicos in vitro, e realizado um estudo de relação estrutura-atividade (REA) com a série de compostos. O composto 2 apresentou um perfil de atividade que pode ser melhorado através de estratégias de modificação molecular da química medicinal. Chemotherapy for leishmaniasis, diseases caused by protozoa of the genus Leishmania, remains inefficient in several treatments. So there is a need to search for new drugs. In this work, we have synthesized 1-aryl-1H-pyrazole-4-carboximidamides derivatives and evaluated antileishmanial activities in vitro, as well as cytotoxic effects. Structure-activity relationship (SAR) studies were carried out with all the compounds of the series. Compound 2 showed an activity profile that can be improved through medicinal chemistry strategies. Keywords: synthesis, 1-aryl-1H-pyrazole-4-carboximidamides, leishmaniasis Introduction manifestations occur in four major forms in humans including: i) visceral leishmaniasis (VL) that is usually Leishmaniasis is a group of vector-borne diseases fatal when untreated, ii) muco-cutaneous leishmaniasis caused by species of the genus Leishmania that affects (MCL) that is a mutilating disease, iii) diffuse cutaneous about 12 million people in 88 countries in the world. leishmaniasis (DCL), which is a long-lasting disease due These life-threatening diseases are of medical, social and to a deficient cellular-mediated immune response and, economic importance in endemic areas, particularly in iv) cutaneous leishmaniasis (CL) that is disabling when subtropical and tropical regions. Leishmania parasites there are multiple lesions.3 exist in two forms: amastigote in the mammalian host and The difficulty to control this parasitic disease remains a a flagellated promastigote in the insect vector.1,2 Clinical serious problem mainly due to the diversity of mammalian reservoirs (wild and domestic animals), species of vectors *e-mail: [email protected] and Leishmania species.4 Vol. 22, No. 2, 2011 dos Santos et al. 353 Chemotherapy for leishmaniasis is generally ineffective In the present work, we prepared five new 1-aryl-1H- mainly due to the emergence of drug-resistant strains pyrazole-4-carboximidamides derivatives 1-5 and evaluated and toxicity of the therapeutics agents. The pentavalent their leishmanicidal acitivity, cytotoxicity and theoretical antimonials compounds are widely used as primary profiles (Scheme 1). therapy whereas other drugs such as amphotericin B, pentamidine, paromomycin, azole derivatives and Results and Discussion glucantime are also used.5 Pyrazoles are a class of heterocyclic compounds The key intermediates 1-aryl-1H-pyrazole-4- that exhibit a broad spectrum of biological activities carbonitriles 24-28 were obtained from two alternate such antiinflamatory, antimicrobial and antitumor.6 routes (methods A and B). In method A, 1-aryl-1H- Consequently, a large number of synthetic routes pyrazole-4-carbaldehydes 10-13 were synthesized through to pyrazoles have been reported and summarized in a Vilsmeyer-Haack reaction involving 1-aryl-1H-pyrazoles 7,8 14 some monographs and reviews. These reports have 6-9, dimethylformamide (DMF) and POCl3. The been useful for biologists and chemists engaged in aldehydes formed were converted to key intermediates from the development of new drugs and/or synthetic routes. the “one-pot reaction” with hydroxylamine and methanoic Our group has synthesized pyrazole carbohydrazides acid.15 In method B, arylhydrazine hydrochlorides with anti-Leishmania in vitro9 and in vivo10 activity. 14-18 reacted with ethoxymethylenemalononitrile in Simultaneously, substances containing the amidine group ethanol and the resulting 5-amino-1-aryl-1H-pyrazole-4- and affecting large number of pathogens (i.e., Giardia carbonitriles 19-23 were subjected to aprotic deamination lamblia, Leishmania sp., Pneumocystis carinii, Candida with t-butyl nitrite in tetrahydrofuran to generate the key albicans, Aspargillus sp. and Trypanosoma sp.) have intermediates.16,17 Finally, the targets 1-aryl-1H-pyrazole- been reported,11 as well as some reviews about synthetic 4-carboximidamides derivatives 1-5 were obtained by approaches.12 Pentamidine (Figure 1) is clinically used in the reaction of the key intermediates 24-28 with gaseous the treatment of pneumonia caused by the opportunistic hydrochloric acid followed by treatment with ammonia.18 fungus, Pneumocystis jirovecii, early stage human The compounds 1-5 were identified by proton nuclear african tripanosomiasis (HAT) and when treatment with magnetic resonance (1H NMR), carbon nuclear magnetic pentavalent antimonials or amphotericin B has failed resonance (13C NMR), Fourier transform infrared (FTIR) against Leishmania.5,13 spectroscopies and elementary analysis. Biological and cytotoxity assays The effect of different concentrations (40, 80, 160 and Figure 1. Structural formula of pentamidine. 320 µg mL-1) of the 1-aryl-1H-pyrazole-4-carboximidamides Scheme 1. 354 Synthesis and Antileishmanial Activity J. Braz. Chem. Soc. derivatives against L. amazonensis promastigotes growth adenosine monophosphate) protein kinase (PKA)21 and inhibition was monitored microscopically at the end of the on nitric oxide production by promastigotes and axenic exponential growth phase. Interestingly, an antiproliferative amastigotes forms of L. amazonensis.22 effect was observed for compounds 2 and 3 (IC50 = 105 ± Concerning the 1 - a r y l - 1 H -pyrazole-4- 45 µmol L-1 or 279 ± 12 µg mL-1 and 112 ± 41 µmol L-1 or carboximidamides compounds, the pyrazoles nucleus have 259 ± 12 µg mL-1 respectively) on L .amazonensis in contrast displayed an impressive array of biological activities, among -1 -1 to compounds 1 (IC50 > 1720 µmol L or > 320 µg mL ), which antiprotozoa, anti-malarial, anti-inflammatory, -1 -1 4 (IC50 > 1480 µmol L or > 320 µg mL ) and 5 immunomodulatory, nitric oxide inhibition, cytotoxic and -1 -1 23 (IC50 > 1250 µmol L or > 320 µg mL ) (Figure 2). Despite anti-cancer activities. the lower profile of2 and 3 compared to pentamidine effect -1 (IC50 = 3.6 ± 1.6 µmol L ), their activity is still promising Molecular modeling and Lipinski rule of five studies since new substitutions may be performed to improve it. The major pyrazolic compounds presented a cytotoxicity The minimum energy conformations of 1-5 derivatives, profile better than pentamidine (Figure 2). calculated by the AM1 semiempirical Hamiltonian,24 showed that, as expected, all rings of these compounds are co-planar except for 5 where the two chlorines lead to a rotation of the ring (Figure 3). Despite of this conformational difference, this structural feature did not contribute for a biological activity for 5. Subsequently, a single-point energy ab initio calculation was performed at the 6-311G* level in order to derive electronic properties, such as highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy values, volume, molecular dipole moment (µ), and molecular electrostatic potential (MEP), which could be related to the variation of the antileishmanial 25 Figure 2. Biological features of 1-aryl-1H-pyrazole-4-carboximidamides activity of these compounds. The results showed that, compounds compared with pentamidine. Antiparasitic effect against although the substitution pattern into the 1-aryl-1H- Leishmania amazonensis (left) and cytotoxicity profile against mice pyrazole-4-carboximidamides structures lead to different peritoneal macrophages (right). antileishmanial profiles, the molecular dipole moment, These biological results may suggest that the two volume and TPSA (total polar surface area) values did not amidine groups of the pentamidine (Figure 1) are important present any direct correlation with it, as shown in Table 1 for binding in a non-intercalative way to the minor grove and Figure 3. regions of DNA (kDNA) in the Leishmania.19 Differently, HOMO and LUMO energy values Literature reports described monoamidine derivatives apparently seem to be related to these derivatives biological with three hydrophobic phenyl groups with potential profile since compounds2