The Reaction of Thiyl Radical with Methyl Linoleate: Completing the Picture,Journal of the American Chemical Society

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The Reaction of Thiyl Radical with Methyl Linoleate: Completing the Picture
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2017-03-21 , DOI: 10.1021/jacs.6b11320
Chryssostomos Chatgilialoglu ₁ , Carla Ferreri ₁ , Maurizio Guerra ₁ , Abdelouahid Samadi ₂ , Vincent W. Bowry ₃

Affiliation

Cis lipids can be converted by thiols and free radicals into trans lipids, which are therefore a valuable tell-tale for free radical activity in the cell's lipidome. Our previous studies have shown that polyunsaturated lipids are isomerized by alkanethiyl radicals (S•) in a cycle propagated by reversible double-bond addition and terminated by radical H-abstraction from the lipid. A critical flaw in this picture has long been that the reported lipid abstraction rate from radiolysis studies is faster than addition-isomerization, implying that the "cycle" must be terminating faster than it is propagating! Herein, we resolved this longstanding puzzle by combining a detailed product analysis, with reinvestigation of the time-resolved kinetics, DFT calculations of the indicated pathways, and reformulation of the radical-stasis equations. We have determined thiol-coupled products in dilute solutions arise mainly from addition to the inside position of the bisallylic group, followed by rapid intramolecular H• transfer, yielding allylic radicals (LZZ + S• ⇄ SL• → SL'•) that are slowly reduced by thiol (SL'• + SH → SL'H + S•). The first-order grow-in rate of the L-H• signal (kexp280nm) may therefore be dominated by the addition-H-translocation rather than slower direct H•-abstraction. Steady-state kinetic analysis of the new mechanism is consistent with products and the rates and trends for polyunsaturated fatty acids (PUFAs), monounsaturated fatty acids (MUFAs), and mixtures, with and without physiological [O2]. Implications of this new paradigm for the thiol-ene reactivity fall in an interdisciplinary research area spanning from synthetic applications to metabolomics.

中文翻译：

硫基自由基与亚油酸甲酯的反应：完成图片

顺式脂质可以通过硫醇和自由基转化为反式脂质，因此这是细胞脂质组中自由基活性的重要指标。我们之前的研究表明，多不饱和脂质在一个循环中被烷烃基自由基 (S•) 异构化，该循环通过可逆双键加成传播，并由脂质中的自由基 H-抽象终止。长期以来，这张图片中的一个关键缺陷是，据报道，辐射分解研究中的脂质提取率比加成异构化更快，这意味着“循环”的终止速度必须比传播速度快！在此，我们通过将详细的产品分析与时间分辨动力学的重新研究、指示途径的 DFT 计算以及自由基停滞方程的重新表述相结合，解决了这个长期存在的难题。我们已经确定稀溶液中的硫醇偶联产物主要来自于双烯丙基内部位置的加成，然后是快速的分子内 H• 转移，产生缓慢的烯丙基自由基 (LZZ + S• ⇄ SL• → SL'•)被硫醇还原（SL'• + SH → SL'H + S•）。因此，LH• 信号(kexp280nm) 的一阶增长速率可能受加成H• 易位而不是较慢的直接H• 抽象支配。新机制的稳态动力学分析与产品以及多不饱和脂肪酸 (PUFA)、单不饱和脂肪酸 (MUFA) 和混合物的速率和趋势一致，无论是否含有生理 [O2]。这种新范式对硫醇-烯反应性的影响属于跨学科研究领域，从合成应用到代谢组学。

更新日期：2017-03-21

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