5-Carboxy-5-methyl-1-pyrroline N-oxide: a spin trap for the hydroxyl radical
作者:Pei Tsai、Martyna Elas†、Adrian D. Parasca、Eugene D. Barth、Colin Mailer、Howard J. Halpern、Gerald M. Rosen
DOI:10.1039/b101945g
日期:——
The in vivo in situ detection of hydroxyl radical (HO˙) in real time has been one of the great challenges of free radicals in biology. While we have been able to identify this free radical as a secondary biomarker of HO˙, the discovery that 5-carboxy-5-methyl-1-pyrroline N-oxide 2 can specifically spin trap HO˙ at the expense of superoxide (O2˙−) opens new avenues of research. In particular, nitrone 2 will allow us to detect HO˙ from low doses of radiation in animal tumors in real time.
The free radical trapping properties of eight 5-alkoxycarbonyl-5-methyl-1-pyrroline N-oxide (EMPO) type nitrones and those of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) were evaluated for trapping of superoxide anion radicals in the presence of 2,6-di-O-methyl-β-cyclodextrin (DM-β-CD). 1H-NMR titrations were performed to determine both stoichiometries and binding constants for the diamagnetic nitroneâDM-β-CD equilibria. EPR titrations were then performed and analyzed using a two-dimensional EPR simulation program affording 1 : 1 and 1 : 2 stoichiometries for the nitroxide spin adducts with DM-β-CD and the associated binding constants after spin trapping. The nitroxide spin adducts associate more strongly with DM-β-CD than the nitrones. The ability of the nitrones to trap superoxide, the enhancement of the EPR signal intensity and the supramolecular protection by DM-β-CD against sodium L-ascorbate reduction were evaluated.
Synthesis and spin trapping behavior of three novel DMPO derivatives, namely 5-hydroxymethyl-5-methyl-pyrroline N-oxide (HMMPO), 5-(2-furanyl)-oxymethyl-5-methyl-pyrroline N-oxide (FMMPO), and 5-(2-pyranyl)-oxymethyl-5-methyl-pyrroline N-oxide (PMMPO) towards different oxygen- and carbon-centered radicals are described. The stabilizing effect of a series of cyclodextrins on the superoxide adducts was
Strain-promoted cycloadditions of cyclic nitrones with cyclooctynes for labeling human cancer cells
作者:Craig S. McKay、Jessie A. Blake、Jenny Cheng、Dana C. Danielson、John Paul Pezacki
DOI:10.1039/c1cc13808a
日期:——
Strain-promotedcycloadditions of cyclic nitrones with cyclooctynes proceed with rate constants up to 3.38 +/- 0.31 M(-1) s(-1) in CD(3)CN, or 59 times faster than the analogous reaction of azides. This highly specific modular labeling strategy can be applied for direct labeling of proteins and for live cell imaging of cancer cells.
Kinetics studies of rapid strain-promoted [3 + 2]-cycloadditions of nitrones with biaryl-aza-cyclooctynone
作者:Craig S. McKay、Mariya Chigrinova、Jessie A. Blake、John Paul Pezacki
DOI:10.1039/c2ob07165g
日期:——
Strain-promoted cycloadditions of cyclic nitrones with biaryl-aza-cyclooctynone (BARAC) proceed with rate constants up to 47.3 M−1 s−1, this corresponds to a 47-fold rate enhancement relative to reaction of BARAC with benzyl azide and a 14-fold enhancement over previously reported strain promoted alkyne–nitrone cycloadditions (SPANC). Studies of the SPANC reaction using the linear free energy relationship defined by the Hammett equation demonstrated that the cycloaddition reaction has a rho value of 0.25 ± 0.04, indicating that reaction is not sensitive to substituents and thus should have broad applicability.