Benzaldehyde thiosemicarbazone complexes of platinum: Syntheses, structures and cytotoxic properties

Abstract

The reaction of 4-R-benzaldehyde thiosemicarbazones (denoted in general as H2L-R, where H2 stands for the two dissociable protons and R (R = OCH3, CH3, H, Cl and NO2) for the substituent on the phenyl ring) with [Pt(PPh3)2Cl2] in the presence of NEt3 afforded a family of organometallic complexes of platinum(II) of the type [Pt(PPh3)(L-R)]. Reaction of the same group of ligands with K2[PtCl4] in the presence of NEt3 afforded complexes of the type [Pt(HL-R)2]. The crystal structure of [Pt(PPh3)(L-CH3)] and [Pt(HL-CH3)2] have been determined. In the [Pt(PPh3)(L-R)] complexes, the benzaldehyde thiosemicarbazones are coordinated to platinum as dianionic tridentate C,N,S-donors. In the [Pt(HL-R)2] complexes, the benzaldehyde thiosemicarbazones are coordinated to the metal center as bidentate N,S-donors, forming five-membered chelate rings, and with reference to the structure of the uncoordinated thiosemicarbazone ligand, this coordination mode is associated with a change in stereochemistry around the Cdouble bondN bond. All the [Pt(PPh3)(L-R)] and [Pt(HL-R)2] complexes display intense absorptions in the visible and ultraviolet regions. The cytotoxic effects of these complexes, examined on the human leukemia cell line HL-60 and human lymphoma cell line U-937, have shown that all the [Pt(PPh3)(L-R)] and [Pt(HL-R)2] complexes are cytotoxic in nature and their IC50 values indicate their potential use as antitumor agents.