Synthesis and insulin-mimetic activities of metal complexes with 3-hydroxypyridine-2-carboxylic acid

Metal complexes of 3-hydroxypyridine-2-carboxylic acid (H(2)hpic), Co(Hhpic)(2)(H(2)O)(2)] (1), Fe(Hhpic)(2)(H(2)O)(2)] (2), Zn(Hhpic)(2)(H(2)O)(2)] (3), Mn(Hhpic)(2)(H(2)O)(2)] (4), and Cu(Hhpic)(2)] (5) have been synthesized and characterized by mass spectrometry, elemental analysis, magnetic susceptibility, infrared, electronic absorption and electron paramagnetic resonance (EPR) spectroscopies. The solid-state structure of 1 has been established by X-ray crystallography. The EPR spectra of 4 and 5 displayed six and four-line hyperfine splitting patterns, respectively, due to coupling of the unpaired electron with the (55)Mn (I=5/2) nucleus and the (63)Cu (I=3/2) nucleus. In the EPR spectrum of 5, an additional five-line super-hyperfine splitting pattern was observed at 77 K, caused by additional interaction of the unpaired electron with ligand nitrogen atoms (I=1), indicating that the structure of 5 was retained in dimethyl sulfoxide solution. The insulin-mimetic activity of these complexes was evaluated by means of in vitro measurements of the inhibition of free fatty acid (FFA) release from epinephrine-treated, isolated rat adipocytes. Complex 5 was found to exhibit the most potent insulin-mimetic activity among the complexes examined in this study.