Synthesis of a tetranitrosyl iron complex with unique structure and properties as an inhibitor of phosphodiesterases.

A novel neutral tetranitrosyl iron complex {[Fe(HO)][FeR(NO)]}·4HO (1) with R = 5-(3-pyridyl)-4-1,2,4-triazole-3-thiolyls (CHNS), which is a supramolecular ensemble, has been synthesized and studied. As follows from X-ray diffraction analysis, this is an octahedral Fecomplex (Lewis acid) with two monoanionic dinitrosyl groups [FeR(NO)] (Lewis base) and 4 water molecules as the ligands. As follows from Mössbauer spectra, the coordinating Fe ion is in a low-spin state = 0, and the dinitrosyl Fe ion is in a low-spin state = 1/2. According to the data of EPR spectroscopy, mass-spectrometry and amperometry, complex 1 in solution forms dinitrosyl particles of [Fe(CHNS-H)(NO)] composition, which are responsible for NO generation. In addition, complex 1 was shown to be a 5-6 times more efficient phosphodiesterase (PDE) inhibitor at 5 × 10 M and 10 M concentrations than its thioligand. Probable binding sites of the [FeR(NO)] ligand for the bovine PDE1B model have been determined by molecular docking and quantum-chemical calculations.