Two new series of complexes with pyridine-containing Schiff bases, [V^VO(SALIEP)L] and [V^VO(Cl-SALIEP)L] (SALIEP=N-(salicylideneaminato)-2-(2-aminoethylpyridine; Cl-SALIEP=N-(5-chlorosalicylideneaminato)-2-(2-aminoethylpyridine, L=catecholato(2- ) ligand) have been synthesized. Characterization by ¹H and ⁵¹V NMR and UV-vis spectroscopies confirmed that: 1) most complexes form two major geometric isomers in solution, and [V^VO(SALIEP)(DTB)] (DTB=di-tertbutylcatecholato(2- )) forms two isomers that equilibrate in solution; and 2) tert-butyl substituents were necessary to stabilize the reduced V^IV species (EPR spectroscopy and cyclicvoltammetry). The pyridine moiety within the Schiff base ligands significantly changed their chemical properties with unsubstituted catecholate ligands compared with the parent HSHED (N-(salicylideneaminato)-N’-(2-hydroxyethyl)-1,2-ethanediamine) Schiff base complexes. Immediate reduction to V^IV occurred for the unsubstituted-catecholato VV complexes on dissolution in DMSO. By contrast, the pyridine moiety within the Schiff base significantly improved the hydrolytic stability of [V^VO(SALIEP)(DTB)] compared with [V^VO(HSHED)(DTB)] in organic solvent and cell culture media. There was significant cellular uptake of the intact complex by T98g (human glioblastoma) cells and very good anti-proliferative activity (IC₅₀ 6.7+0.9 μM, 72 h), which was five times higher than for the non-cancerous human cell line, HFF-1 (IC₅₀ 34+10 μM). This made it a potential drug candidate for the treatment of advanced gliomas.

Drew Walters

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