Pd(II) and Pt(II) complexes with a thio-aza macrocycle ligand containing an intercalating fragment: Structural and antitumor activity studies

Two new Pt(II) and Pd(II) complexes of formula [LMCl2] (M=Pt, Pd) were synthesized and characterized both in solution and solid state. They were obtained using the thio-aza macrocycle 9,18-dimethyl-12,17dithia-9,18,27,28-tetraaaza-29-oxatetracyclo[24.2.1.0(2,7).0(20,25)]enneicosa-2,4,6,20,22,24,26,28(1)-octaene (L) containing the 2,5-diphenyl [1, 3, 4]oxadiazole as intercalating fragment. M(II) is coordinated in cis-position by the two S atoms of L. The two crystal structures of [LPtCl2] and [LPdCl2] complexes showed that the M(II) ion is located outside the macrocyclic cavity. The square planar coordination sphere is fulfilled by two chloride anions in a cisplatin-like arrangement with the chloride leaving groups exposed to the environment. The biological activity of both [LPtCl2] and [LPdCl2], monitored towards a leukemic cellular model (U937), is coherent with their ability to interfere, at different levels, with the DNA structure.