Same, but different: Variations in fragment ions among stereoisomers of a 17α-methyl steroid in gas chromatography/electron ionization mass spectrometry

IF 1.8 3区化学 Q4 BIOCHEMICAL RESEARCH METHODS

Rapid Communications in Mass Spectrometry Pub Date : 2024-11-26 DOI:10.1002/rcm.9934

Jakob Steff, Maria K. Parr

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引用次数: 0

Abstract

Rationale

Gas chromatography/electron ionization mass spectrometry (GC/EI-MS) is a well-established tool for the identification of unknown compounds such as new metabolites of xenobiotics. But it reaches the limits of confident structural assignment if it comes to stereoisomers. This work helps to overcome this difficulty by getting a deeper comprehension of composition of so far unspecific and also characteristic fragment ions in general and comparison among stereoisomers.

Methods

Unit mass resolution mass spectra of various isotopologues of four 17α-methyl steroid diastereomers obtained by selectively introducing [²H₉]-trimethylsilyl (TMS) groups or chemical syntheses were systematically compared. The impact of stereochemistry on variations of relative abundances has been assessed by statistical comparison from repeated measurements. Additionally, characterization of m/z 318 with high-resolution MS using gas chromatography/quadrupole time-of-flight MS (GC/QTOF-MS) was performed.

Results

The formation of fragment ions from TMS-derivatives after cleavage of methyl or TMS groups ([M-CH₃]⁺, [M-TMSOH]^•+, [M-CH₃-TMSOH]⁺, [M-2x90]^•+, [M-2x90-CH₃]⁺) rarely arises from only one position in the molecule and composition of fragment ion signals is highly influenced by the stereochemistry of the A-ring at C3 and C5 of the steroid. Similarly, the formation of the characteristic fragment ion m/z 143 most likely consists of two different ways of formation. A possible structure for fragment ion m/z 318 was postulated.

Conclusions

Stereoisomers showed differing fragmentation behaviors based on their configuration. These observations further illustrate that variations among stereoisomers in EI-MS fragmentation is no random underlying process but instead a pattern which needs to be understood in its complexity. This easily accessible technical approach can be applied on different molecule structures to further investigate the field of isomeric assignment in GC/EI-MS.

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相同，但不同：气相色谱/电离质谱法中 17α 甲基类固醇立体异构体碎片离子的变化

原理气相色谱/电离质谱法（GC/EI-MS）是鉴定未知化合物（如异种生物的新代谢物）的成熟工具。但是，如果涉及到立体异构体，它的结构鉴定能力就会受到限制。本研究通过深入了解迄今为止尚无特异性和特征性的碎片离子的组成以及立体异构体之间的比较，帮助克服了这一困难。通过选择性引入[2H9]-三甲基硅烷基（TMS）基团或化学合成方法，系统地比较了四种 17α-甲基类固醇非对映异构体的不同同位素的质量分辨率质谱。通过重复测量的统计比较，评估了立体化学对相对丰度变化的影响。此外，还利用气相色谱/四极杆飞行时间质谱（GC/QTOF-MS）对 m/z 318 进行了高分辨率质谱分析。结果 TMS 衍生物在甲基或 TMS 基团裂解后形成的碎片离子（[M-CH3]+、[M-TMSOH]-+、[M-CH3-TMSOH]+、[M-2x90]-+、[M-2x90-CH3]+）很少只来自分子中的一个位置，碎片离子信号的组成受甾体 C3 和 C5 的 A 环立体化学的影响很大。同样，特征碎片离子 m/z 143 的形成也很可能包含两种不同的形成方式。还推测了碎片离子 m/z 318 的可能结构。结论立体异构体根据其构型表现出不同的碎片行为。这些观察结果进一步说明，立体异构体之间在 EI-MS 破碎过程中的变化并不是一个随机的基本过程，而是一种需要理解其复杂性的模式。这种简便易行的技术方法可应用于不同的分子结构，以进一步研究 GC/EI-MS 中的异构体分配领域。

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来源期刊

Rapid Communications in Mass Spectrometry 化学-分析化学

CiteScore

4.10

自引率

5.00%

发文量

219

审稿时长

2.6 months

期刊介绍： Rapid Communications in Mass Spectrometry is a journal whose aim is the rapid publication of original research results and ideas on all aspects of the science of gas-phase ions; it covers all the associated scientific disciplines. There is no formal limit on paper length ("rapid" is not synonymous with "brief"), but papers should be of a length that is commensurate with the importance and complexity of the results being reported. Contributions may be theoretical or practical in nature; they may deal with methods, techniques and applications, or with the interpretation of results; they may cover any area in science that depends directly on measurements made upon gaseous ions or that is associated with such measurements.