Synthesis, structure and cytotoxicity of a series of Dioxidomolybdenum(VI) complexes featuring Salan ligands

Abstract

Seven hexacoordinated cis-dioxidomolybdenum(VI) complexes [MoO2L1-7] (1-7) derived from various tetra dentate diamino bis(phenolato) ``salan'' ligands, N,N'-dimethyl-N,N'-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminoethane {(X = Br, Y = Me, Z = H (H2L1); X = Me, Y=Cl, Z = H (H2L2); X = Pr-i, Y = Cl, Z = Me (H2L3)} and N,N'-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminopropane {(X = Y = Bu-t, Z = H (H2L4); X = Y = Me, Z = H (H2L5); X = Pr-i, Z = Me (H2L6); X = Y = Br, Z = H (H2L7)} containing O--N donor atoms, have been isolated and structurally characterized. The formation of cis-dioxidomolybdenum(VI) complexes was confirmed by elemental analysis, IR, UV vis and NMR spectroscopy, ESI-MS and cyclic voltammetry. X-ray crystallography showed the O2N2 donor set to define an octahedral geometry in each case. The complexes (1-7) were tested for their in vitro antiproliferative activity against HT-29 and HeLa cancer cell line. IC50 values of the complexes in HT-29 follow the order 6 < 7 < < 1 < 2 < 5 < < 3 < 4 while the order was 6 < 7 < 5 < 1 < < 3 < 4 < 2 in HeLa cells. Some of the complexes proved to be as active as the clinical referred drugs, and the greater potency of 6 and 7 (IC50 values of 6 are 2.62 and 10.74 mu M and that of 7 is 11.79 and 30.48 mu M in HT-29 and HeLa cells, respectively) may be dependent on the substituents in the salan ligand environment coordinated to the metal.