Four triarylantimony(V) carboxylates: syntheses,structural characterization and in vitro cytotoxicities

Four new organoantimony carboxylates, (R–COO)₂SbR′₃ R–COOH = (±)-2-phenoxypropionic acid and R′ = phenyl (1), 4-fluorophenyl (2), 3-fluorophenyl (3), 3,4,5-trifluorophenyl (4)], were synthesized and structurally characterized by elemental analysis, ¹H, ¹³C NMR, IR and X-ray single crystal diffraction. Structural analyses reveal that 1–3 show similar five-coordinate trigonal bipyramidal geometries, binding with three aryl groups and two deprotonated unidentate ligands. Unexpectedly, 4 exhibits pentagonal bipyramidal arrangement accompanied by two Sb–O (carbonyl) coordination bonds. In vitro cytotoxic activities of 1–4 have been determined by the MTT method against four cancer cell lines. Studies reveal that 1–4 have an activity similar to cisplatin on lung cancer cell line A549 and but also exhibit excellent cytotoxicity against cisplatin-insensitive colon cancer cell lines HCT-116, Caco-2 and human promyelocytic leukemia cell line HL-60. Additionally, the results showed that most of these triarylantimony(V) complexes exhibited enhanced cytotoxicity compared with the ligand and four triarylantimony dichloride precursors, which clearly implied a positive synergistic effect. Also interestingly, it was found that 3- or 4- mono-fluoro-substituted triphenylantimony, compounds 2 and 3, exhibit higher in vitro cytotoxicities toward the four cancer cell lines than the tri-3,4,5-trifluoro-substituted and without-fluoro-substituted triphenylantimony complexes. The structure-activity relationship of the cytotoxicity of 1–4 is discussed.