Copper(II) complexes with substituted thiosemicarbazones of thiophene-2-carboxaldehyde: synthesis, characterization and antiamoebic activity against E. histolytica.

In an effort to develop potent antiamoebic agents, a series of thiosemicarbazone (TSC) ligands 1-5 derived from thiophene-2-carboxaldehyde and N4-substituted thiosemicarbazides has been prepared and characterized using various spectroscopic techniques. Treatment of the ligands with cupric chloride produced the copper(II) complexes [Cu(TSC)2Cl2] 1a-5a where ligand bind through thionic sulfur and the azomethine nitrogen. The possible geometries of the complexes were assigned on the basis of magnetic moment, electronic and thermal patterns as well as infrared spectral studies. The thiosemicarbazones and their copper complexes were tested for their in vitro antiamoebic activity against HK-9 strain of Entamoeba histolytica and showed significant growth inhibition. The results revealed that these complexes are effective chemicals in inhibiting amoebal growth, with compound 5 (having -N(CH3)(C6H5) substituent at N4) and complexes 1a-5a being more effective than the commercial antiamoebic drug, metronidazole, based on IC50 values. These data also indicated that the compounds 3a and 5a are most effective among the complexes studied (IC50=0.26 microM of 3a and IC50=0.21 microM of 5a versus IC50=1.81 microM of metronidazole).