Fruteau de Laclos B, Zirrolli J A, Murphy R C
National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206.
Biol Mass Spectrom. 1993 Jan;22(1):9-18. doi: 10.1002/bms.1200220103.
The low-energy collision-induced dissociations (CID) of carboxylate anions derived from pentafluorobenzyl ester, trimethylsilyl ether derivatives of four arachidonic acid metabolites of the 5-lipoxygenase pathway have been determined. These molecules include leukotriene B4 (LTB4), a potent chemotactic factor for the human neutrophil; 20-carboxy-LTB4, an inactive metabolite; 5-hydroxyeicosatetraenoic acid (5-HETE), a useful marker of 5-lipoxygenase activity within cells; and 5-hydroxyeicosanoic acid (5-HEA), which has been previously used for the quantitation of leukotriene E4. The carboxylate anion of 5-HEA (m/z 399) was found to decompose by the loss of trimethylsilanol as well as the loss of 146 u corresponding to the loss of trimethylsilanol followed by acrolein, a process specific for 5-hydroxy-containing saturated fatty acids. The loss of trimethylsilanol by a remote site mechanism is the major transition observed for the 5-HETE carboxylate anion (m/z 391). The ion formed (m/z 301) further decomposes by the loss of CO2 (m/z 257). The loss of trimethylsilanol is also seen at m/z 389 after collisional activation of the carboxylate anion of LTB4 (m/z 479) by a complex charge-driven mechanism, not the remote site fragmentation mechanism as expected. The loss of an olefinic proton possibly from carbon-7 is involved as well as an oxygen atom derived from the carboxylic acid moiety. The loss of two trimethylsilanol neutral molecules gives rise to ions seen at m/z 299. Isotopic labeling studies revealed that two isobaric ions are present at m/z 299. Both of these ions involve the loss of trimethylsilanol from the carbon-12 position according to remote site mechanisms, but only one has lost the olefinic proton at carbon-7 and, therefore, likely originates from the further decomposition of the ion (m/z 389) described above. An additional ion seen at m/z 317 is attributed to the loss of trimethylsilyl ether (TMS-O-TMS) following a charge-driven mechanism involving the oxygen atom at carbon-12. The 20-carboxy-LTB4 carboxylate anion (m/z 689) decomposes primarily through the loss of one and two trimethylsilanol moieties, but the base peak (m/z 491) is due to the loss of pentafluorobenzyl alcohol. This ion, likely a ketene, further gives rise to three ions by the sequential loss of one and two trimethylsilanols and TMS-O-TMS. All collision-induced decompositions of the carboxylate anions of these eicosanoids are characterized by losses of small neutral molecules from the derivatizing groups (TMS and pentafluorobenzyl) and little fragmentation of the carbon backbone.
已确定了源自5-脂氧合酶途径的四种花生四烯酸代谢物的五氟苄酯、三甲基硅醚衍生物的羧酸盐阴离子的低能碰撞诱导解离（CID）。这些分子包括白三烯B4（LTB4），一种对人中性粒细胞有强大趋化作用的因子；20-羧基-LTB4，一种无活性代谢物；5-羟基二十碳四烯酸（5-HETE），细胞内5-脂氧合酶活性的有用标志物；以及5-羟基二十烷酸（5-HEA），其先前已用于白三烯E4的定量。发现5-HEA的羧酸盐阴离子（m/z 399）通过失去三甲基硅醇以及失去146 u（对应于失去三甲基硅醇后再失去丙烯醛）而分解，这是含5-羟基的饱和脂肪酸特有的过程。通过远程位点机制失去三甲基硅醇是5-HETE羧酸盐阴离子（m/z 391）观察到的主要转变。形成的离子（m/z 301）进一步通过失去CO2（m/z 257）而分解。在通过复杂的电荷驱动机制对LTB4的羧酸盐阴离子（m/z 479）进行碰撞活化后，在m/z 389处也观察到了三甲基硅醇的损失，而不是预期的远程位点碎片化机制。可能涉及从碳-7失去一个烯丙基质子以及来自羧酸部分的一个氧原子。失去两个三甲基硅醇中性分子产生了在m/z 299处看到的离子。同位素标记研究表明在m/z 299处存在两个等压离子。这两个离子都根据远程位点机制从碳-12位置失去了三甲基硅醇，但只有一个在碳-7处失去了烯丙基质子，因此可能源自上述离子（m/z 389）的进一步分解。在m/z 317处看到的另一个离子归因于在涉及碳-12处氧原子的电荷驱动机制后失去三甲基硅醚（TMS-O-TMS）。20-羧基-LTB4羧酸盐阴离子（m/z 689）主要通过失去一个和两个三甲基硅醇部分而分解，但基峰（m/z 491）是由于失去了五氟苄醇。这个离子，可能是一个乙烯酮，通过依次失去一个和两个三甲基硅醇以及TMS-O-TMS进一步产生了三个离子。这些类二十烷酸羧酸盐阴离子的所有碰撞诱导分解的特征都是从衍生基团（TMS和五氟苄基）失去小的中性分子，并且碳骨架几乎没有碎片化。
