Synthesis, cytotoxicity and antimalarial activities of thiosemicarbazones and their nickel (II) complexes
A series of Schiff base metal complexes with the formulations [Ni(L1)2] (4), [Ni(L2)2] (5) and [Ni(L3)2] (6), (where 1 or L1 = fluorene-2-carboxaldehyde thiosemicarbazone, 2 or L2 = fluorene-2-carboxaldehyde-4-methyl-thiosemicarbazone and 3 or L3 = fluorene-2-carboxaldehyde-4-ethyl-thiosemicarbazone) have been synthesised. The compounds were characterised by FT-IR, 1H NMR, 13C NMR, and single crystal X-Ray diffraction. The results suggested that the thiosemicarbazone ligands behaved as bidentate ligands which were coordinated to the Ni(II) ion via their N,S atoms. Among the six compounds tested, two of the nickel complexes which are complexes 5 and 6 exhibited moderate in vitro antimalarial activity with IC50 of 23.79 and 2.29 μM, respectively. It is noteworthy that as the size of the substituent group increases, the antimalarial activity of the compound increases. Complex 6 exhibited the highest antimalarial activity. In addition, ligand 3 and complex 4 showed higher cytotoxic activity against HCT 116 human colorectal carcinoma cell line than cisplatin with IC50 of 0.69 and 3.36 μM, respectively.