Department of Chemistry, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
J Mass Spectrom. 2011 Jan;46(1):41-9. doi: 10.1002/jms.1869.
Collision-induced dissociation (CID) of 8-(4''-hydroxyphenyl)-2'-deoxyguanosine and 8-(2''-hydroxyphenyl)-2'-deoxyguanosine was investigated using sequential tandem mass spectrometry. These adducts represent biomarkers of DNA damage linked to phenolic radicals and were investigated to gain insight into the effects of chemical structure of a C-8 modification on fragmentation pathways of modified 2'-deoxyguanosine (dG). CID in MS(2) of the deprotonated molecules of both the isomers generated the same product ion having the same m/z values. CID in MS(3) of the product ion at m/z 242 and CID in MS(4) experiments carried out on the selected product ions at m/z 225 and m/z 218 afford distinct fragmentation patterns. The conformational properties of isomeric product ions from CID showed that the ortho-isomers possess the unique ability to tautomerize through an intramolecular proton transfer between the phenolic OH group and the imine nitrogen (N7). Tautomerization of ortho-isomers to their keto-tautomers led to differences in their system of conjugated double bonds compared with either their enol-tautomer or the para-isomer. The charge redistribution through the N-7 site on the imidazole ring is a critical step in guanosine adduct fragmentation which is disrupted by the formation of the keto-tautomer. For this reason, different reaction pathways are observed for 8-(4''-hydroxyphenyl)-2'-deoxyguanosine and 8-(2''-hydroxyphenyl)-2'-deoxyguanosine. We present herein the dissociation and the gas-phase ion-molecule reactions for highly conjugated ions involved in the CID ion chemistry of the investigated adducts. These will be useful for those using tandem mass spectrometry for structural elucidation of C-8 modified dG adducts. This study demonstrates that the modification at the C-8 site of dG has the potential to significantly alter the reactivity of adducts. We also show the ability of tandem mass spectrometry to completely differentiate between the isomeric dG adducts investigated.
采用串联质谱法研究了 8-(4''-羟苯基)-2'-脱氧鸟苷和 8-(2''-羟苯基)-2'-脱氧鸟苷的碰撞诱导解离（CID）。这些加合物代表与酚基自由基有关的 DNA 损伤生物标志物，研究它们可以深入了解 C-8 修饰的化学结构对修饰的 2'-脱氧鸟苷（dG）的断裂途径的影响。两种异构体的去质子分子在 MS(2)中的 CID 产生了具有相同 m/z 值的相同产物离子。在 m/z 242 的产物离子的 MS(3)中的 CID 和在 m/z 225 和 m/z 218 的选定产物离子的 MS(4)实验中的 CID 提供了不同的断裂模式。CID 中异构体产物离子的构象性质表明，邻位异构体具有通过酚 OH 基团和亚胺氮（N7）之间的分子内质子转移而互变异构的独特能力。邻位异构体到其酮式互变异构体的互变异构导致其共轭双键体系与它们的烯醇互变异构体或对位异构体不同。通过咪唑环上 N-7 位的电荷重排是鸟苷加合物断裂的关键步骤，而酮式互变异构体的形成会破坏这种重排。由于这个原因，对于 8-(4''-羟苯基)-2'-脱氧鸟苷和 8-(2''-羟苯基)-2'-脱氧鸟苷，观察到不同的反应途径。本文介绍了参与所研究加合物 CID 离子化学的高度共轭离子的离解和气相离子-分子反应。这些对于使用串联质谱法对 C-8 修饰的 dG 加合物进行结构阐明将是有用的。这项研究表明，dG 的 C-8 位点的修饰有可能显著改变加合物的反应性。我们还展示了串联质谱法完全区分所研究的 dG 加合物异构体的能力。
