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

Two new Pt and Pd complexes of formula [LMCl] (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[24.2.1.0.0]enneicosa-2,4,6,20,22,24,26,28-octaene (L) containing the 2,5-diphenyl [1, 3, 4]oxadiazole as intercalating fragment. M is coordinated in cis-position by the two S atoms of L. The two crystal structures of [LPtCl] and [LPdCl] complexes showed that the M 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 [LPtCl] and [LPdCl], monitored towards a leukemic cellular model (U937), is coherent with their ability to interfere, at different levels, with the DNA structure.