Synthesis, Characterisation, and Preliminary In Vitro Studies of Vanadium(IV) Complexes with a Schiff Base and Thiosemicarbazones as Mixed Ligands

Abstract

[VO(Sal-<i>L</i>-tryp)(H₂O)] <b>1</b> (where sal-<i>L</i>-tryp = <i>N</i>-salicylidene-<i>L</i>-tryptophanate) was used as a precursor to produce the novel complexes, [VO(Sal-<i>L</i>-tryp)(MeATSC)].1.5C₂H₅OH <b>2</b> (where MeATSC = 9-Anthraldehyde-N(4)-methylthiosemicarbazone), [VO(Sal-<i>L</i>-tryp)(<i>N</i>-Ethhymethohcarbthio)].H₂O <b>3</b> (where <i>N</i>-Ethhymethohcarbthio = (<i>E</i>)-<i>N</i>-ethyl-2-(4-hydroxy-3-methoxybenzylidene)hydrazinecarbothioamide), and [VO(Sal-<i>L</i>-tryp)(acetylethTSC)].C₂H₅OH <b>4</b> (where acetylethTSC = (<i>E</i>)-<i>N</i>-ethyl-2-(1-(thiazol-2-yl)ethylidene)hydrazinecarbothioamide), by reaction with the respective thiosemicarbazone. The chemical and structural properties of these ligands and complexes were characterised by elemental analysis, ESI MS, FT-IR, UV-visible, ESR, ¹H and ¹³C NMR spectroscopy, and X-ray crystallography. DMSO and DMSO-d₆ solutions of compounds <b>1-4</b> were oxidised in air to produce vanadium(V) species which were verified by ESI MS and ⁵¹V NMR spectroscopy. Anti-cancer properties of compounds <b>2-4</b> were examined with three colon cancer cell lines, HTC-116, Caco-2, and HT-29, and also with non-cancerous colonic myofibroblasts, CCD18-Co. Compounds <b>2-3</b> exhibited less inhibitory effects in the CCD-18Co cells, indicating a possible cytotoxic selectivity towards colon cancer cells. In general, those compounds which exhibited anti-proliferative activity on cancer cells, but did not affect non-cancerous cells, may have a potential in chemotherapy.