Unusual Odd-Electron Fragments from Even-Electron Protonated Prodiginine Precursors Using Positive-Ion Electrospray Tandem Mass Spectrometry
Unusual Odd-Electron Fragments from Even-Electron Protonated Prodiginine Precursors Using Positive-Ion Electrospray Tandem Mass Spectrometry
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DOI：
10.1016/j.jasms.2008.08.002
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发表时间：
2008-12-01
影响因子：
3.2
通讯作者：
Cole, Richard B.
中科院分区：
文献类型：
--
作者：
Chen, Kan;Rannulu, Nalaka S.;Cole, Richard B.
抗癌和免疫抑制特性的报道最近引起了对细菌产生的前体素的兴趣。我们使用电喷雾串联质谱（ES-MS/MS）来研究灵菌红素，十一烷基灵，和链脲菌素B（丁基-间-环庚基灵），并探讨其裂解途径，以解释不寻常的甲基自由基损失和连续的碎片离子，占主导地位的低能量碰撞诱导解离（CID）质谱。偶电子离子和自由基离子的形成之间的竞争进行了详细研究。理论计算用于优化结构，并使用Gaussian 03程序计算反应物和产物的能量。结果表明，质子化发生在最初没有氢的氮原子上，从而允许形成伪七元环，构成最稳定的基态[M + H]（+）结构。从这个前体，实验数据表明，甲基自由基的损失具有最低的表观阈值，但作为替代，甚至电子碎片离子可以形成由甲醇分子的损失。计算模型表明，甲基自由基损失是在这种竞争中的吸热过程，但较低的表观阈值与甲基自由基损失点较低的动力学障碍。另外，来自每个前体的甲基自由基的这种特征和不寻常的损失（与较弱的甲醇损失组合）可用于进行恒定的中性损失扫描，以快速和有效地鉴定复杂生物混合物中的所有前体，而无需任何清理或纯化。这种方法的可行性已被证明，通过鉴定一个新的，低丰度灵菌红素类似物Hahella chejuensis。（J Am Soc Mass Spectrom 2008，19，1856-1866）（c）2008年美国质谱学会
Reports of anticancer and immunosuppressive properties have spurred recent interest in the bacterially produced prodiginines. We use electrospray tandem mass spectrometry (ES-MS/MS) io investigate prodigiosin, undecylprodiginine, and streptorubin B (butyl-meta- cycloheptylprodiginine) and to explore their fragmentation pathways to explain the unusual methyl radical loss and consecutive fragment ions that dominate low-energy collision-induced dissociation (CID) mass spectra. The competition between the formation of even-electron ions and radical ions is examined in detail. Theoretical calculations are used to optimize the structures and calculate the energies of both reactants and products using the Gaussian 03 program. Results indicate that protonation occurs on the nitrogen atom that initially held no hydrogen, thus allowing formation of a pseudo-seven-membered ring that constitutes the most stable ground state [M + H](+) structure. From this precursor, experimental data show that methyl radical loss has the lowest apparent threshold but, alternatively, even-electron fragment ions can be formed by loss of a methanol molecule. Computational modeling indicates that methyl radical loss is the more endothermic process in this competition, but the lower apparent threshold associated with methyl radical loss points to a lower kinetic barrier. Additionally, this characteristic and unusual loss of methyl radical (in combination with weaker methanol loss) from each prodiginine is useful for performing constant neutral loss scans to quickly and efficiently identify all prodiginines in a complex biological mixture without any clean-up or purification. The feasibility of this approach has been proven through the identification of a new, low-abundance prodigiosin analog arising from Hahella chejuensis. (J Am Soc Mass Spectrom 2008, 19, 1856-1866) (c) 2008 American Society for Mass Spectrometry