Department of Chemistry and Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, Tennessee 37235, USA.
J Am Chem Soc. 2010 Dec 15;132(49):17490-500. doi: 10.1021/ja106503a. Epub 2010 Nov 19.
Free radical co-oxidation of polyunsaturated lipids with tyrosine or phenolic analogues of tyrosine gave rise to lipid peroxide-tyrosine (phenol) adducts in both aqueous micellar and organic solutions. The novel adducts were isolated and characterized by 1D and 2D NMR spectroscopy as well as by mass spectrometry (MS). The spectral data suggest that the polyunsaturated lipid peroxyl radicals give stable peroxide coupling products exclusively at the para position of the tyrosyl (phenoxy) radicals. These adducts have characteristic (13)C chemical shifts at 185 ppm due to the cross-conjugated carbonyl of the phenol-derived cyclohexadienone. The primary peroxide adducts subsequently undergo intramolecular Diels-Alder (IMDA) cyclization, affording a number of diastereomeric tricyclic adducts that have characteristic carbonyl (13)C chemical shifts at ~198 ppm. All of the NMR HMBC and HSQC correlations support the structure assignments of the primary and Diels-Alder adducts, as does MS collision-induced dissociation data. Kinetic rate constants and activation parameters for the IMDA reaction were determined, and the primary adducts were reduced with cuprous ion to give a phenol-derived 4-hydroxycyclohexa-2,5-dienone. No products from adduction of peroxyls at the phenolic ortho position were found in either the primary or cuprous reduction product mixtures. These studies provide a framework for understanding the nature of lipid-protein adducts formed by peroxyl-tyrosyl radical-radical termination processes. Coupling of lipid peroxyl radicals with tyrosyl radicals leads to cyclohexenone and cyclohexadienone adducts, which are of interest in and of themselves since, as electrophiles, they are likely targets for protein nucleophiles. One consequence of lipid peroxyl reactions with tyrosyls may therefore be protein-protein cross-links via interprotein Michael adducts.
多不饱和脂质与酪氨酸或酪氨酸的酚类类似物的自由基协同氧化，在水胶束和有机溶剂中生成脂质过氧化物-酪氨酸（酚）加合物。通过 1D 和 2D NMR 光谱以及质谱（MS）对新型加合物进行了分离和表征。光谱数据表明，多不饱和脂质过氧自由基仅在酪氨酸（苯氧基）自由基的对位生成稳定的过氧化物偶联产物。这些加合物由于来自苯酚衍生的环己二烯酮的交叉共轭羰基，具有特征的（13）C 化学位移在 185 ppm。随后，初级过氧化物加合物经历分子内 Diels-Alder（IMDA）环化，生成多种具有特征羰基（13）C 化学位移在~198 ppm 的非对映立体选择性三环加合物。所有的 NMR HMBC 和 HSQC 相关都支持主要和 Diels-Alder 加合物的结构分配，MS 碰撞诱导解离数据也是如此。确定了 IMDA 反应的动力学速率常数和活化参数，并将初级加合物用亚铜离子还原，得到苯酚衍生的 4-羟基环己-2,5-二烯酮。在初级或亚铜还原产物混合物中均未发现过氧自由基在酚类邻位加成的产物。这些研究为理解通过过氧-酪氨酸自由基-自由基终止过程形成的脂质-蛋白质加合物的性质提供了一个框架。脂质过氧自由基与酪氨酸自由基的偶联导致环己烯酮和环己二烯酮加合物的形成，这些加合物本身就是有趣的，因为作为亲电试剂，它们可能是蛋白质亲核试剂的靶标。因此，脂质过氧反应与酪氨酸的一个后果可能是通过蛋白质间迈克尔加合物形成蛋白质-蛋白质交叉连接。
