Department of Chemistry, University of New Orleans, 2000 Lakeshore Drive, New Orleans, Louisiana 70148, USA.
Anal Chem. 2009 Nov 1;81(21):8826-38. doi: 10.1021/ac901341c.
Brevetoxins are a group of natural neurotoxins characterized by polyether ring systems that are found in the blooms of red tide algae. In a conventional water/organic solvent system, without any other additives, deprotonated molecules of brevetoxins do not appear in high abundance in negative mode electrospray mass spectrometry (ES-MS) due to lack of acidic functional groups; thus, they are not well-suited for collision-induced decomposition (CID) experiments in negative mode electrospray. In this study, several anions were tested for their abilities to form anionic adducts by mixing ammonium salts of these anions with brevetoxin-2 and brevetoxin-3. Under CID, M + Cl, M + Br, M + OAc, M + HCOO, and M + NO(3) adducts all produced only the respective anions in CID experiments and thus provided no structural information. In contrast, upon CID, both M + F and M + HCO(3) precursor adducts gave structurally informative fragment peaks that exhibited similarities to those of M - H ions, which indicated that the first step in gas-phase decomposition of these anionic adducts was loss of neutral HF or H(2)CO(3) molecules, respectively, leaving deprotonated brevetoxin (M - H) to undergo consecutive fragmentations. In comparison to bicarbonate, fluoride formed adducts in higher abundance and provided more fragment peaks, thus more structural information, in MS/MS experiments. It is therefore the anion of choice to study brevetoxins in negative mode electrospray mass spectrometry using the anion attachment approach. The detailed fragmentation mechanisms are discussed, and diagnostic product ions are proposed for the brevetoxin-2 side chain (m/z 95, 133, and 151), the brevetoxin-3 side chain (m/z 97, 135, and 153), and the type-B brevetoxin backbone (m/z 725, 739, 741, and 797). To test the developed methodology, a sample of brevetoxin-2 subjected to in vitro microsomal incubation was analyzed, and a reduction product of the substrate was confirmed to have the structure of brevetoxin-3.
短裸甲藻毒素是一组天然神经毒素，其特征为多醚环系统，存在于赤潮藻类的藻华之中。在传统的水/有机溶剂体系中，由于缺乏酸性官能团，不带电荷的短裸甲藻毒素分子在负离子模式电喷雾质谱（ES-MS）中不会以高丰度出现；因此，它们不适合在负离子模式电喷雾的碰撞诱导分解（CID）实验中使用。在这项研究中，通过将这些阴离子的铵盐与短裸甲藻毒素-2 和短裸甲藻毒素-3 混合，测试了几种阴离子形成阴离子加合物的能力。在 CID 下，M + Cl、M + Br、M + OAc、M + HCOO 和 M + NO(3) 加合物在 CID 实验中均只产生各自的阴离子，因此没有提供结构信息。相比之下，在 CID 下，M + F 和 M + HCO(3) 前体加合物均产生具有结构信息的碎片峰，与 M - H 离子的碎片峰相似，这表明这些阴离子加合物在气相中的第一步分解分别是中性 HF 或 H(2)CO(3) 分子的丢失，分别留下去质子化的短裸甲藻毒素 (M - H) 以进行连续的碎片化。与碳酸氢盐相比，氟化物形成的加合物丰度更高，在 MS/MS 实验中提供了更多的碎片峰，从而提供了更多的结构信息。因此，在负离子模式电喷雾质谱中使用阴离子附加方法研究短裸甲藻毒素时，氟化物是首选的阴离子。讨论了详细的碎裂机制，并提出了短裸甲藻毒素-2 侧链（m/z 95、133 和 151）、短裸甲藻毒素-3 侧链（m/z 97、135 和 153）和 B 型短裸甲藻毒素骨架（m/z 725、739、741 和 797）的特征性产物离子。为了测试所开发的方法，对经过体外微粒体孵育的短裸甲藻毒素-2 样品进行了分析，并确认了底物的还原产物具有短裸甲藻毒素-3 的结构。
