Nitroindazolinone derivatives: assessing the impact of the nitro group location on the activity against Trypanosoma cruzi

Abstract In the last decades, different 5-nitroindazole-based compounds have been synthesized and proposed as potential agents for treating the infection caused by Trypanosoma cruzi , i.e. Chagas disease. In previous works, the 1,2-disubstituted 5-nitroindazolinone system has been identified as a promising scaffold to design compounds, among which derivatives with a benzyl moiety at N-2 stand out. Now, we have synthesized 4-, 6- and 7-nitroindazolin-3-ones ( 19 – 24 ), analogues of the previously studied 2-benzyl-1-methyl-5-nitroindazolinone ( 1 ) and 2-benzyl-5-nitro-1-propylindazolinone ( 2 ), to explore the impact of the nitro group position on their trypanocidal activity. These 8 nitro derivatives were in silico predicted to have good oral bioavailability and no toxicity risks. In vitro assays over bloodstream trypomastigotes (Y strain, DTU TcII) showed an improvement in the lytic profile of 2-benzyl-1-propyl derivatives, when the NO 2 group is moved to position 6 of the indazole ring: EC 50 = 34.55 µM ( 23 ) versus EC 50 > 50 µM ( 2, 22 and 24 ). Regarding the assays on amastigotes (Tulahuen strain, DTU TcVI), 4-, 6- and 7-nitroindazoles did not display better activity (EC 50 from 3.82 to > 20 µM) than 5-nitroindazoles, with EC 50 = 2.34 ( 1 ) and 3.03 µM ( 2 ). The lack of cytotoxicity over cardiac (CC 50 > 200 µM) and L929 cells (CC 50 > 170 µM) supports selective action, particularly of 5-nitroindazolinones towards intracellular forms: SI > 85.47 ( 1 ) and 56.53 ( 2 ). Altogether, data indicate that the anti- T. cruzi activity of 4-, 6- and 7-nitroindazolinones is not better than that of 1 and 2 , not presenting significant advantages over these two 5-nitroindazolinones.