Protection against peroxynitrite-mediated nitration reaction by intramolecularly coordinated diorganoselenides

A series of intramolecularly Se center dot center dot center dot X (X = N, O) coordinated diorganoselenides and sulfides are synthesized by using the heteroatom-directed lithiation route and characterized by multinuclear (H-1, C-13, Se-77) NMR, IR spectroscopy, and electrospray mass spectrometry (ES-MS). The intramolecular Se center dot center dot center dot O interactions in diorganoselenides 26-31 have been studied by multinuclear NMR studies in solution and in the solid state by single-crystal X-ray crystallography. The protection against peroxynitrite-mediated nitration reaction (PN assay) by diorganoselenides/-sulfides (with and without intramolecular coordination) has been evaluated. The PN assay data of diorganoselenides reveal that the selenides 20-22, having a basic amino group (sp(3)-N donor) in close proximity of selenium, are more active compared to the diorganoselenides 16-19, having an imino group (sp(2)-N donor), and also show much higher protective action than the unsubstituted diorganoselenides 14 and 15. The diorganoselenides 16-31 were oxidized to corresponding selenoxides 44-59. The redox properties of the selenoxides 13 and 44-59 have been investigated by cyclic voltammetry and potentiometric titration experiments. Two redox potentials for in situ-generated ferrocenyl selenoxides (50, 54-59) were observed. The reduction of selenoxides 13 and 48 to ebselen (2) and selenide 20 with benzenethiol (PhSH) was monitored by ES-MS.