Structure-activity relationship study of thiosemicarbazones on an African trypanosome: Trypanosoma brucei brucei

To explore the structure-activity relationships of thiosemicarbazones on African trypanosome: Trypanosoma brucei brucei, a series of thirty-five thiosemicarbazones (1-35) have been synthesized and characterized by their H-1 NMR, C-13 NMR, and FT-IR spectra. All compounds were tested for trypanocidal activity using the method "Lilit alamar blue". The comparison of trypanocidal power of thiosemicarbazones was performed considering their structures. This study that was done using acetophenone thiosemicarbazone (1) as basic model, showed that: (a) the presence of lipophilic substituents in para position on benzene ring, (b) substitution of benzene ring and (c) substitution of hydrogen of thioamide function by a phenyl, strongly influence trypanocidal activity. The various modifications to basic structure (1) allowed the synthesis of 1-(4-chlorophenyl) ethylidene-4-phenyl-thiosemicarbazide (34). With a trypanocidal activity of 3.97 mu M, this compound is the most active of the series.