Evaluation of glucose-linked nitroxide radicals for use as an in vivo spin-label probe

Synthesis and in vitro phantom NMR and MRI studies of fully organic free radicals, TEEPO-glucose and TEMPO-glucose, potential contrast agents for MRI

“…As linking nitroxides to glucose seems to have a slight effect on the stability of the compounds, 22 radical stabilities of TEMPO-Glc and TEEPO-Glc were studied by T 1 -measurements as a function of time elapsed from the sample preparation. Human blood plasma was considered to be reasonable matrix to mimic in vivo conditions.…”

Synthesis and Characterization of a Magnetically Active 19F Molecular Beacon

“…Additionally, while stabilized nitroxide radicals are still relatively unstable, especially in an uncontrolled cellular environment where they are subject to reduction by radical scavengers, multiple studies have demonstrated use of nitroxide radicals as contrast agents for in vivo imaging. 22,32,33 These studies showed that pyrroline-based nitroxide radicals can remain stable for at least 20–30 minutes in vivo, which is sufficient time for injection, target hybridization, and imaging, though longer stability may be achieved by gadolinium chelates. 21 It has also been shown previously that molecular beacons can be modified for greater stability and resistance to nuclease degradation in cellular environments using 2′-o-methyl bases, peptide nucleic acids, locked nucleic acids, or phosphorothioate.…”

“…This compound was chosen for its stability in buffered systems, simple attachment chemistry to the oligonucleotide beacon, and the unique configuration of its single unpaired electron, which has a nearly isotropic g tensor that eliminates other paramagnetic effects like pseudocontact shifts. 18,22 With the oligonucleotide in its hairpin conformation, the radical is held within 6−12 Å of the fluorine compound, which enables PRE broadening of the 19 F resonance. However, in the linearized DNA conformation, the moieties have ∼100 Å separation, causing the effects of PRE to become negligible.…”

“…PRE is distance-dependent, exhibiting analogous behavior to fluorescent quenching, with a maximum effective distance of 35 Å. , Several of the “on–off” 19 F probes previously mentioned use gadolinium, a paramagnetic lanthanide widely used as an MRI contrast agent, to generate this PRE effect. ,,, However, in this work, PRE-mediated on–off signaling is achieved with a stabilized pyrroline-based nitroxide radical. This compound was chosen for its stability in buffered systems, simple attachment chemistry to the oligonucleotide beacon, and the unique configuration of its single unpaired electron, which has a nearly isotropic g tensor that eliminates other paramagnetic effects like pseudocontact shifts. , With the oligonucleotide in its hairpin conformation, the radical is held within 6–12 Å of the fluorine compound, which enables PRE broadening of the 19 F resonance. However, in the linearized DNA conformation, the moieties have ∼100 Å separation, causing the effects of PRE to become negligible.…”