Wan Xunda, Lan Ziqiang, Yang Shushu, Yang Shanzheng, Zhu Yangjian, Wang Feng, Yang Weiran, Chen Jinlong
School of Resources Environmental & Chemical Engineering, Nanchang University, Nanchang, Jiangxi, China.
Paediatrics College, Nanchang University, Nanchang, Jiangxi, China.
Rapid Commun Mass Spectrom. 2022 May 15;36(9):e9269. doi: 10.1002/rcm.9269.
Norpimarane diterpenes possess plentiful bioactivities and are widely distributed in herbs, such as Flickingeria fimbriata. Rapid characterization of these natural products in complicated plant extracts is of great importance, and electrospray ionization tandem mass spectrometry is a powerful tool for chemical constituent profiling. However, limited researches on their fragmentation mechanisms seriously hinder identification via mass spectrometry.
Three norpimarane diterpenes isolated from F. fimbriata via multiple types of column chromatography served as reference compounds, and collision-induced dissociation experiments were performed on them with a series of variable collision energies. Plausible fragmentation pathways were proposed based on product ions. To further validate the fragmentation mechanisms, the proton affinity and product ion energy were simulated by density functional theory at the B3LYP/6-31+G(d, p) level.
Three main cleavage reactions induced skeleton breakage and resulted in characteristic ions, methyl (CH -20) migration, hydrogen arrangement and Retro-Diels-Alder reaction, among which methyl migration was firstly proposed for pimarane diterpenes. A series of common diagnostic ions were identified, such as m/z 133.1012, 121.1012, 119.0805 and 107.0855. Additionally, the constructed fragmentation mechanisms were successfully applied for fragment ion rationalization of previously reported isopimarane diterpenes.
Fragmentation mechanisms of norpimarane diterpenes have been uncovered. Carbocation located at the C ring tends to result in methyl (CH -20) migration which has been rarely reported before. This characteristic dissociation reaction allows multiple diagnostic ions to be rationalized and aids in rationalizing fragmentation patterns of other diterpenes. The uncovered mechanisms also shed light on rapid identification of norpimarane diterpenes.
降海松烷二萜具有丰富的生物活性，广泛分布于如石仙桃等草药中。在复杂植物提取物中快速表征这些天然产物非常重要，而电喷雾电离串联质谱是化学成分剖析的有力工具。然而，对其裂解机制的研究有限，严重阻碍了通过质谱进行的鉴定。
通过多种柱色谱法从石仙桃中分离得到的三种降海松烷二萜作为参考化合物，对其进行了一系列可变碰撞能量的碰撞诱导解离实验。基于产物离子提出了合理的裂解途径。为进一步验证裂解机制，在B3LYP/6 - 31 + G(d, p)水平上通过密度泛函理论模拟了质子亲和力和产物离子能量。
三种主要的裂解反应导致骨架断裂并产生特征离子，甲基（CH - 20）迁移、氢重排和逆狄尔斯 - 阿尔德反应，其中甲基迁移首次被提出用于海松烷二萜。鉴定出了一系列常见的诊断离子，如m/z 133.1012、121.1012、119.0805和107.0855。此外，构建的裂解机制成功应用于先前报道的松香烷二萜的碎片离子合理化分析。
已揭示降海松烷二萜的裂解机制。位于C环的碳正离子倾向于导致甲基（CH - 20）迁移，这在此前鲜有报道。这种特征性解离反应使多个诊断离子得以合理化，并有助于其他二萜裂解模式的合理化分析。所揭示的机制也为降海松烷二萜的快速鉴定提供了线索。
