Syntheses, structures, and insulin-like activities of oxovanadium(IV) complexes with tetra- and penta-dentate histidine derivatives

[VO(H-pm)(ClO4)], [VO(HeY)], and [VO(((pm)2)H)](ClO4) were prepared by reactions of VOSO4 and H-pm (N-2-pyridylmethyl-(S)-histidine), HeY (N,N'-ethylene-(S)-histidine-(S)-tyrosine) and ((pm)2)H (N,N-bis(2-pyridylmethyl)-(S)-histidine) respectively, and followed with Ba(ClO4)(2). X-ray structure analysis of [VO(HeY)] showed that a pentadentate ligand and an oxoanion were coordinated with a vanadium(IV) ion, thereby forming a distorted octahedral geometry. In in vitro evaluation using isolated rat adipocytes, a tetradentate complex [VO(H-pm) (ClO4)] (IC50 = 0.762 mM) was found to be more active at lower concentration than VOSO4 (IC50 = 3.56 mM) in term of IC50 value, a 50% inhibition concentration of FFA release from the adipocytes. On the other hand, two VO complexes of pentadentate (HeY and ((pm)2)H) ligands were found to be inactive for insulin-like activities.