Synthesis, characterization and antiamoebic activity of new indole-3-carboxaldehyde thiosemicarbazones and their Pd(II) complexes.

In continuation of our research on thiosemicarbazones and their metal complexes as antiamoebic agents, a new series of indole-3-carboxaldehyde thiosemicarbazones (TSC) 1-7 were prepared by condensing indole-3-carboxaldehyde with cycloalkylaminothiocarbonyl hydrazines. Their palladium(II) complexes of the [Pd(TSC)Cl2] type, were synthesized upon coordination with [Pd(DMSO)2Cl2]. The chemical structures of all the compounds were established by elemental analyses, electronic, IR, (1)H NMR and (13)C NMR spectral data. The structure of the complexes was further established by thermogravimetric analysis and FAB MS. Spectroscopic data revealed that thiosemicarbazones act as bidentate ligands, making use of thione sulphur and azomethine nitrogen atom for coordination to the Pd(II) ion. Among all the compounds evaluated for antiamoebic activity using HM1:IMSS strain of Entamoeba histolytica, all palladium complexes were found to be more active than their respective ligands. Moreover, ligand 5 and complexes 1a-3a, 5a and 7a showed antiamoebic activity, at lower IC(50) doses when compared to the reference drug metronidazole with IC(50)=1.81 microM.