Vanadium and zinc complexes of 5-cyanopicolinate and pyrazine derivatives: synthesis, structural elucidation and in vitro insulino-mimetic activity study†
Vanadium(V) compounds with 5-cyanopicolinato acid (HpicCN), pyrazine-2-carboxylic acid (Hprz) and 3-aminopyrazine-2-carboxylic acid (HprzNH2) and zinc compounds with HpicCN in the presence of 4-aminopyridine (4apy), pyridine (py) and 1,10-phenanthroline (phen) have been synthesized and characterized. The crystal structures of NH4[VO2(picCN)2] (3), NH4[VO2(prz)2] (4), NH4[VO2(przNH2)2]·H2O (5·H2O), [Zn(picCN)2(H2O)2] (6), [Zn(picCN)2(4apy)2]·C7H8 (7·C7H8), [Zn(picCN)2(4apy)] (8), [Zn(picCN)2(py)2] (9) and [Zn(picCN)2(phen)]·C7H8·2MeOH (10·C7H8·2MeOH) were determined by X-ray crystallography. The spatial arrangements of all the vanadium(V) complexes are similar, having carboxylate oxygen atoms in a mutual trans orientation. In the zinc bis(5-cyanopicolinato) complexes three different arrangements were found with trans (6) and a cis (7, 9 and 10) octahedral and square-pyramidal (8) geometries. The insulino-mimetic activity of selected VO(IV), VO2(V) and Zn(II) complexes was studied by in vitro inhibition of the free fatty acid (FFA) release from isolated rat adipocytes treated with epinephrine. All metal complexes showed insulino-mimetic activity and among them the VO(IV)–prz complex 2 was found to have higher insulino-mimetic activity than the positive control. The other vanadium compounds have activities similar to VOSO4. The Zn complexes also exhibited some insulino-mimetic activity. Introduction of the N-donor 4apy to the zinc picCN complex 8 significantly increased inhibition of FFA release compared to 6.