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Fragmentation of typical sulfonamide drugs via heterolytic bond cleavage and stepwise rearrangement

机译：典型的磺酰胺药物通过杂合键裂解和逐步重排而断裂

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Although many experiments have been carried out to elucidate the fragmentation of typical sulfonamide drugs, little effort has been devoted to understanding the reaction process theoretically. Herein, the characteristic fragmentation pathways were investigated by performing density functional theory calculations. Employing sulfamethoxazole as a representative sulfonamide, the structure of the molecular ion was initially examined. The site of protonation was found to be located at the nitrogen atom of the isoxazole ring, which could facilitate energy minimization by forming a hydrogen bond. The fragment ion A at m/z 156 was then recognized as the result of heterolytic S-N bond cleavage with the energy requirement of 50.25 kcal mol(-1). This result could be supported by analyzing the S-N bond nature and by the energy comparison of different reaction pathways. Formation of the fragment ion B at m/z 108 was attributed to a stepwise rearrangement reaction. Heterolytic C-S bond cleavage was the rate-limiting step of the overall reaction, with an energy barrier of 31.93 kcal mol(-1). This is in good agreement with the Fukui function and spin density analysis. The fragment ion C(T) at m/z 92 was also obtained from the heterolytic C-S bond cleavage of A, with the energy requirement of 29.98 kcal mol(-1). The results in this work suggested that formation of the fragment ions B and C(T) were competitive reactions with the major difference being the degree of the heterolytic C-S bond cleavage.
机译：尽管已经进行了许多实验来阐明典型的磺酰胺药物的片段化，但是在理论上很少致力于了解反应过程。在此，通过进行密度泛函理论计算来研究特征性的断裂途径。以磺胺甲基恶唑为代表的磺酰胺，首先检查了分子离子的结构。发现质子化的位点位于异恶唑环的氮原子上，这可以通过形成氢键促进能量的最小化。然后，识别出m / z 156处的碎片离子A是S-N键杂合裂解的结果，能量需求为50.25 kcal mol（-1）。通过分析S-N键的性质以及通过不同反应途径的能量比较，可以支持该结果。 m / z 108处碎片离子B的形成归因于逐步重排反应。杂合C-S键裂解是整个反应的限速步骤，其能垒为31.93 kcal mol（-1）。这与Fukui函数和自旋密度分析非常吻合。还可以通过A的杂化C-S键裂解获得m / z 92处的碎片离子C（T），其能量需求为29.98 kcal mol（-1）。这项工作的结果表明，碎片离子B和C（T）的形成是竞争性反应，主要区别在于杂合C-S键的裂解程度。

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