Coordination Chemistry and Insulin-Enhancing Behavior of Vanadium Complexes with Maltol C6H6O3 Structural Isomers

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Abstract
Syntheses of vanadium complexes using the naturally occurring ligands isomaltol (Hima) and allomaltol (Hama), as well as a newly synthesized, potentially tetradentate diaminodipyrone [H2(en(ama)2], are reported. Complete characterization of the resulting compounds [trans-VO(ima)2(H2O), VO(ama)2, V(ima)3, V(ama)3 and VO(en(ama)2)], including X-ray crystallography analyses for trans-VO(ima)2(H2O) and V(ima)3, are presented herein. Potentiometric titrations (25°C, I = 0.16 M NaCl) were used to measure stability constants in the V(IV)−Hima system; these data were compared to previous data collected on the V(IV)−L (L = Hma, Hama) systems. The in vivo efficacy of these compounds to lower the blood glucose levels of STZ-diabetic rats was tested; all but VO(en(ama)2) produced significant decreases in plasma glucose levels. The results were compared to those of the benchmark compound BMOV [VO(ma)2, bis(maltolato)oxovanadium(IV)], a known insulin-enhancing agent.