<i>Bis</i>- and <i>tris</i>(pyridyl)amine-oxidovanadium complexes: characteristics and insulin-mimetic potential

Two novel vanadium complexes, [VIVO(bp-O)(HSO4)] (1) and [VIVO(bp-OH)Cl2]•CH3OH (2•CH3OH), where bp-OH is 2-{[bis(pyrid-2-yl)methyl]amine}methylphenol, were prepared and structurally characterised. EPR spectra of methanol solutions of 2 suggest exchange of Cl- for CH3OH and partial conversion to [VO(bp-OH)(CH3OH)3]2+. Speciation studies on the VO2+-bpOH system in a water/dmso mixture (4:1 v/v) revealed [VO(bp-O)(H2O)n]+ as the dominating species in the pH range 2–7. The insulin-mimetic properties of 1 and 2, [VIVO(SO4)tpa] (3), [VIVO(pic-trpMe)2] (5) and the new mixed-ligand complexes [VVO(pic-trpH)tpa]Cl2 (4Cl2) and [VVO(pic-OEt)tpa]Cl2 (6Cl2), tpa = tris(pyrid-2-yl)methylamine, picH-trpH = 2-carboxypyridine-5-(L-tryptophan)carboxamide (picH-trpMe is the respective tryptophanmethyl ester), pic-OEt = 5-carboethoxypyridine-2-carboxylic acid, were evaluated with rat adipocytes, employing two lipolysis assays (release of glycerol and free fatty acids (FFA)), respectively and a lipogenesis assay (incorporation of glucose into lipids). The IC50 values for the inhibition of lipolysis in the FFA assay vary between 0.41 (±0.03) (5) and 21.2 (±0.6) mM (2), as compared to 0.81 (±0.2) mM for VOSO4