Bis(picolinato) complexes of vanadium and zinc as potential antidiabetic agents: synthesis, structural elucidation and in vitro insulin-mimetic activity study†
Vanadium(V) compounds with 3,5-difluoropicolinic acid (HpicFF) and 3-hydroxypicolinic acid (H2hypic) and zinc(II) compounds with HpicFF, H2hypic and 4-methylhydroxypicolinic acid (HpicCH2OH) in the presence or absence of pyridine (py), 4-(dimethylamino)pyridine (DMAP), and 1,10-phenanthroline (phen) have been synthesized and characterized. The crystal structures of NH4[VO2(picFF)2]·1.6H2O (3·1.6H2O), NH4[VO2(hypic)2]·H2O (4·H2O), [Zn(picFF)2(H2O)2] (5), [Zn(picFF)2(py)2]·py (6·py), [Zn(picFF)2(DMAP)2]·H2O (7·H2O), [Zn(picFF)2(phen)]·2CHCl3 (8·2CHCl3), [Zn(Hhypic)2(MeOH)2] (10), [Zn(Hhypic)2(DMAP)(H2O)] (11) and [Zn(Hhypic)2(phen)] (12) were determined by X-ray crystallography. The spatial arrangement of the vanadium(V) complex 3 possesses carboxylate oxygen atoms in a mutual trans orientation while crystal structure 4 represents the first crystallographic evidence for the formation of an isomer with two picolinato nitrogen atoms in a mutual trans position. Two different spatial arrangements were found in the zinc(II) complexes with trans (5, 10 and 11) and cis (6, 7, 8 and 12) octahedral geometry. Insulin-mimetic activity of the selected VIVO, VVO2 and ZnII complexes was studied by in vitro inhibition of the free fatty acid (FFA) release from isolated rat adipocytes treated with epinephrine. All the studied metal complexes showed insulin-mimetic activity. Vanadium complexes 1–4 exhibit activities similar to VOSO4 with the Hhypic complexes being more active than the picFF ones. The zinc complexes also exhibited some insulin-mimetic activity, with the Hhypic complex (9) being more active than the other two, however, the insulin-mimetic activity of these complexes did not show more potent activity than ZnSO4.