Anti-leishmanial activity of Ni(ii), Pd(ii) and Pt(ii) β-oxodithioester complexes

Abstract

New functionalized planar β-oxodithioester cis-chelate complexes, [M(L)₂] (L = L1, methyl-3-hydroxy-3-(p-bromophenyl)-2-propenedithioate, M = Ni 1, Pd 5, Pt 9; L2, methyl-3-hydroxy-3-(p-fluorophenyl)-2-propenedithioate, Ni 2, Pd 6, Pt 10; L3, methyl-3-hydroxy-3-(naphthyl)-2-propenedithioate, Ni 3, Pd 7, Pt 11; methyl-3-hydroxy-3-(p-methoxyphenyl)-2-propenedithioate, Ni 4, Pd 8, Pt 12), have been synthesized and characterized by elemental analysis, IR, UV-Vis, ¹H and ¹³C NMR spectroscopy; the structures of 2–4, 8 and 11 have been elucidated by X-ray crystallography. In all crystal structures, the metal has four-coordinate slightly distorted square planar geometry with a cis-configuration of the ligands. These complexes have been assessed for their use as anti-leishmanial agents; 7 and 9 showed impressive anti-promastigote and anti-amastigote efficacy with IC₅₀ values of 0.59 ± 0.10 μg mL⁻¹, 0.56 ± 0.10 μg mL⁻¹ and IC₅₀ 0.85 ± 0.27, 1.99 ± 0.08 μg mL⁻¹, respectively. Cytotoxicity assays on both compounds displayed toxicity on the promastigotes but less toxicity against RAW 264.7 cell lines at different concentrations. The Pd and Pt complexes exhibit luminescent characteristics in solution, originating from the intraligand charge transfer state.