Abstract
Nitroxides are broadly used as molecular probes and labels in biophysics, structural biology, and biomedical research. Resistance of a nitroxide group bearing an unpaired electron to chemical reduction with low-molecular-weight antioxidants and enzymatic systems is of critical importance for these applications. The redox properties of nitroxides are known to depend on the ring size (for cyclic nitroxides) and electronic and steric effects of the substituents. Here, two highly strained nitroxides, 5-(tert-butyl)-5-butyl-2,2-diethyl-3-hydroxypyrrolidin-1-oxyl (4) and 2-(tert-butyl)-2-butyl-5,5-diethyl-3,4-bis(hydroxymethyl)pyrrolidin-1-oxyl (5), were prepared via a reaction of the corresponding 2-tert-butyl-1-pyrroline 1-oxides with butyllithium. Thermal stability and kinetics of reduction of the new nitroxides by ascorbic acid were studied. Nitroxide 5 showed the highest resistance to reduction.
Highlights
Nitroxides are broadly used as molecular probes and labels in biophysics, structural biology, and biomedical research [1,2,3,4,5,6]
It has been demonstrated later that the signal belongs to paramagnetic impurities [29], presumably to radical ions of the dinitrones [30]
We again demonstrated that the addition of organolithium compounds to cyclic α-tert-butyl nitrones is an efficient method of the synthesis of highly strained nitroxides
Summary
Nitroxides are broadly used as molecular probes and labels in biophysics, structural biology, and biomedical research [1,2,3,4,5,6]. One can assume that a further increase in the steric demand of Molecules 2020, 25, 845; doi:10.3390/molecules25040845 www.mdpi.com/journal/molecules nitroxide of the 2,5-dihydroimidazole series, 3, with tert-butyl and n-butyl substituents at position 5 of the imidazole ring via the reaction of corresponding cyclic α-tert-butylnitrone with n-butyllithium (n-BuLi). This nitroxide appears to be thermally unstable, rapidly decomposing at 80 °C via tert-butyl radical abstraction [21].
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