Nine new vanadium complexes, with tridentate Schiff base ligand based on 3,5-di-tertbutyl-2-hydroxybenzaldehyde and different hydrazides, are described and characterized. The X-ray crystal structure of complex 8 shows distorted octahedral geometry of vanadium, with ONO ligand in equatorial position. The tridentate Schiff base ligand forms six membered and five-membered chelate rings at the V(V) acceptor center, with the corresponding bite angles being 82.97(9)˚ and 74.48(9)˚. The molecules are gathered by means of intermolecular OH...N hydrogen bond and layered by π...π interactions involving the pyridine and phenolate rings. Such interactions expand the structure along the crystallographic a axis. The complexes were characterized by the elemental analyses, IR, UV-Vis, EPR spectroscopy, cyclic voltammetry, thermogravimetry and magnetic susceptibility measurements. The stabilization role of co-ligands is discussed. The cytotoxicity versus HepG2 hepatocytes and inhibition of human recombinant PTP1B was studied.
Recent research on the action of vanadium compounds shows its important effect on adipogenesis processes and adipocyte function. On the basis of previous screening tests in cellular models, the novel vanadium complex (N′-[(E)-(5-bromo-2-oxophenyl)methylidene]4-methoxybenzohydrazide)oxido(1,10-phenanthroline)vanadium(IV) was selected for this study. This complex exhibits potent inhibition of tyrosine phosphatases, and differences in the degree of inhibition were observed particularly for phosphatases. A significant increase in intracellular lipid accumulation and proliferative effect on 3T3-L1 preadipocytes confirmed the ability of this complex to enhance adipogenesis. The insulinomimetic activity of the tested complex was also demonstrated in fully differentiated 3T3-L1 adipocytes, in which glucose utilization was potentiated. The obtained results support the hypothesis that vanadium complexes show promising possibilities for use as new therapeutic strategies for the treatment of type 2 diabetes.
In this study, 110 newly synthesized vanadium complexes from different structural groups were screened in three cell-based models representing the main target tissues for anti-diabetic drugs. In glucose utilization in C2C12 myocyte experiments, 93% of vanadium complexes were shown to have equal or greater activity than bis(maltolato)oxovanadium(IV) (BMOV), the methyl analog of bis(ethylmaltolato)oxovanadium(IV) (BEOV) which has been tested in clinical trials. Moreover, 49% and 50% of these complexes were shown to have equal or greater activity than BMOV in lipid accumulation in 3T3-L1 adipocytes and insulin secretion in RINm5F beta cell experiments, respectively. These results were the basis for the selection of compounds for the subsequent steps in the characterization of anti-diabetic properties. This study provides strong support for the application of screening cell-based assays with a phenotypic approach for the discovery of novel anti-diabetic drugs from the vanadium complex class. This is especially desirable due to the multiple and not fully defined mechanisms of action vanadium compounds.
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