Antitumor activity of copper(II) complexes with Schiff bases derived from N'-tosylbenzene-1,2-diamine.

The electrochemical oxidation of anodic metal copper in a solution of the ligands N-[(5-tert-butyl-2-hydroxyphenyl)methylidine]-N'-tosylbenzene-1,2-diamine [HL] and N-[(3,5-di-tert-butyl-2-hydroxyphenyl)methylidine]-N'-tosylbenzene-1,2-diamine, [HL] afforded homoleptic [CuL] compounds or solvate [CuLS] complexes. The addition to the electrochemical cell of coligands (L') such as 2,2'-bipyridine (2-bpy), 4,4'-bipyridine(4-bpy) or 1,10-phenanthroline (phen) allowed the synthesis, in one step, of heteroleptic [CuLL'] compounds, namely [CuL(HO)] (1), [CuL(2,2'-bpy)]⋅CHCN (2), [CuL(phen)]·HO (3), [CuL(4,4'-bpy)] (4), [CuL(CHOH)] (5), [CuL(2,2'-bpy)] (6), [CuL(phen)] (7) and [CuL(4,4'-bpy)] (8). The crystal structures of both ligands, HL, HL, and those of the complexes (2), (4), (5), (6) and (7) have been determined by X-ray diffraction techniques. Coordination polyhedron around metal atom is square planar for [CuL(CHOH)] (5) and [CuL(4,4'-bpy)] (4) and square pyramid for the other complexes with additional chelating ligands. The cytotoxic activity of this new series of copper(II) complexes against the SH-SY5Y neuroblastoma cell line and U87-MG and U373-MG glioblastoma cell lines has been investigated. Most of the test compounds showed higher activity than cisplatin in the three cell lines. Among this series, compound [CuL(phen)] (3) displayed the highest activity with IC equal to 1.77 μM on SH-SY5Y whereas compound [CuL(4.4'-bpy)] (4) resulted the most potent compounds on U87 MG and U373 MG glioblastoma cell lines. Studies on the cytotoxic activity of these derivatives suggest that these compounds induce cell death by a mechanism other than apoptosis.