title: Synthesis of nitroxyl radicals for Overhauser-enhanced magnetic resonance imaging.
abstract: Non-invasive measurement and visualization of free radicals in vivo would be important to clarify their roles in the pathogenesis of free radical-associated diseases. Nitroxyl radicals can react with free radicals and be derivatized to achieve specific cellular/subcellular localizing capabilities while retaining the simple spectral features useful in imaging. Overhauser-enhanced magnetic resonance imaging (OMRI), which is a double resonance technique, creates images of free radical distributions in small animals by enhancing the water proton signal intensity via the Overhauser Effect. In this study, we synthesized various nitroxyl probes having (15)N nuclei and deuterium, and measured the enhancement factor for Overhauser-enhanced magnetic resonance imaging experiments. (15)N-D-4-Oxo-2,2,6,6-tetramethylpiperidine-1-oxyl ((15)N-D-oxo-TEMPO) has the highest enhancement factor compared with other nitroxyl probes. The proton signal enhancement was higher for (15)N-labeled nitroxyl probes when compared to the (14)N-labeled analogues because of the reduced spectral multiplicity of the I=1/2 nucleus. Furthermore, this enhancement is proportional to the line width and number of electron spin resonance lines of nitroxyl radicals. Finally, we compared the Overhauser-enhanced magnetic resonance image of (15)N-labeled, deuterated 4-Oxo-2,2,6,6-tetramethylpiperidine-1-oxyl with that of (14)N-H-TEMPOL. These results suggested that the selective deuteration of the nitroxyl probes enhanced the signal-to-noise ratio and thereby improved spatial and temporal resolutions.
authors.affiliation: Department of Bio-function Science, Faculty of Pharmaceutical Sciences, Kyushu University, Maidashi, Fukuoka, Japan.
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Yamada
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Kinoshita
authors.forename: Toshihide
authors.initials: T
authors.lastname: Yamasaki
authors.forename: Hiromi
authors.initials: H
authors.lastname: Sadasue
authors.forename: Fumiya
authors.initials: F
authors.lastname: Mito
authors.forename: Mika
authors.initials: M
authors.lastname: Nagai
authors.forename: Shingo
authors.initials: S
authors.lastname: Matsumoto
authors.forename: Mariko
authors.initials: M
authors.lastname: Aso
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Suemune
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Sakai
authors.forename: Hideo
authors.initials: H
authors.lastname: Utsumi
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry; D007202:Indicators and Reagents; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009589:Nitrogen Oxides / Q000138:chemical synthesis*; D019047:Phantoms, Imaging
chemical_list: D005609:Free Radicals; D007202:Indicators and Reagents; D009589:Nitrogen Oxides; C039900:nitroxyl