Diazaphenoxazines and Diazaphenothiazines: Synthesis of the “Correct” Isomers Reveals They Are Highly Reactive Radical-Trapping Antioxidants

Abstract

The preparation of 2,4-diazaphenothiazines and 2,4-diazaphenoxazines via a copper-catalyzed intramolecular amination is described. Literature approaches which utilize easily accessed (2′-aminophenyl) 4-pyri(mi)dyl sulfides undergo a Smiles rearrangement that gives rise to the 1,3-diaza derivatives instead, confirmed by X-ray crystallography. Inversion of the polarity of the cyclization avoids the rearrangement and affords the desired products. Preliminary kinetic studies suggest that 2,4diazaphenothiazines and diazaphenoxazines, but not the 1,3-diaza isomers, are remarkably potent radical-trapping antioxidants.

Temperature-dependence of radical-trapping activity of phenoxazine, phenothiazine and their aza-analogues clarifies the way forward for new antioxidant design

“…Both approaches have been described elsewhere. 24 Electrochemical measurements confirmed that the azaanalogues of PNX and PTX are less oxidizable than the parent compounds (data are summarized in Table 1). Reversible cyclic voltammograms were obtained for the 1-aza and 4-aza isomers of each, revealing shifts of 50 mV for 1-and 4-azaPNX relative to PNX and 120 and 80 mV for 1-and 4-azaPTZ, respectively, relative to PTZ.…”

“…kPBD-BODIPY = 5310 M -1 s -1 in dioxane/PhCl (Figure 3A). 12,24 The rate constant for reaction of the RTAs with chain-carrying peroxyl radicals (kinh) can be derived from the initial rate of PBD-BODIPY consumption by Eq 1, while the stoichiometry (n) of the reaction is related to the duration of the inhibited period by Eq 2 (Figure 3B). Dioxane was strategically employed as a substrate for autoxidation because hydrogen-bonding of the PNX and PTZ derivatives to dioxane slows their reactions sufficiently to enable determination of highly reproducible rate constants, kinh, for their reactions with chain-carrying radicals (Figure 3C).…”

The Potency of Diarylamine Radical-Trapping Antioxidants as Inhibitors of Ferroptosis Underscores the Role of Autoxidation in the Mechanism of Cell Death

“…Fer-1, Lip-1, arylamines 1 – 14 , ,, PBD-BODIPY and STY-BODIPY, RSL-3, and Erastin were synthesized according to literature procedures. Egg phosphatidylcholine, MeOAMVN, MEM with/without phenol red, DMEM with/without phenol red, Dulbecco’s phosphate-buffered saline (DPBS), fetal bovine serum (FBS), penicillin-streptomycin, Aquabluer, and reagents for synthesis were purchased from commercial sources and used as received.…”

“…, engine lubricants, fuels, and rubbers) due to a catalytic reactivity wherein the diarylamine is regenerated from an oxidation product in situ using the substrate as the stoichiometric reductant. , Given that the inherent reactivity of Fer-1 and Lip-1 toward peroxyl radicals ( k = 3.5 and 2.4 × 10 5 M –1 s –1 , respectively, at 37 °C in chlorobenzene) is similar to that of common industrial antioxidants (4,4′-dialkyldiphenylamines, for which k = 1.8 × 10 5 M –1 s –1 under the same conditions), we wondered if these industrial additives would be similarly potent inhibitors of ferroptosis. Moreover, we wondered if heterocyclic diarylamineswhich we have shown to be up to 2000-fold more reactive than 4,4′-dialkyldiphenylamines ,, would be even more potent. Such a realization would not only provide alternative, and perhaps better, leads to preventive and/or therapeutic agents than Fer-1 and Lip-1, but would also contribute to resolving the relevance of autoxidation in the execution of ferroptosis.…”

Recent Insights on Hydrogen Atom Transfer in the Inhibition of Hydrocarbon Autoxidation

“…Our efforts to demonstrate this point were protracted; although the synthesis of diazaphenothiazines had some precedent in the literature, we discovered that they were incorrectly identified as reaction products. 13 For example, 2,4-diazaphenothiazines (see Figure 2C, X = S) that had been allegedly synthesized in 2008 were found instead to be disulfides of the Smiles rearrangement products of the starting material. Optimization of the reaction conditions lead to cyclization to the 1,3-diazaphenothiazine, but inversion of the polarity of the cyclization by switching the positions of the amine and bromide substituents on the pyrimidyl and phenyl rings was necessary to access the desired 2,4-diazaphenothiazines (and 2,4-diazaphenoxazines).…”