El-Aneed Anas, Banoub Joseph, Koen-Alonso Mariano, Boullanger Paul, Lafont Dominique
Biochemistry Department, Memorial University of Newfoundland, St. John's, Newfoundland, Canada.
J Am Soc Mass Spectrom. 2007 Feb;18(2):294-310. doi: 10.1016/j.jasms.2006.09.026. Epub 2006 Nov 7.
In this study we evaluated the fragmentation pattern of 16 novel amphiphilic neoglycolipid cholesteryl derivatives that can be efficiently used to increase cationic liposomal stability and to enhance gene transfer ability. These neoglycolipids bear different sugar moieties, such as D-glucosamine, N-acetyl-D-glucosamine, N-trideuterioacetyl-D-glucosamine, N-acetyllactosamine, L-fucose, N-allyloxycarbonyl-D-glucosamine, and some of their per-O-acetylated derivatives. Regardless of the structure of the tested neoglycolipid, QqToF-MS analysis using electrospray ionization (ESI) source showed abundant protonated [M+H]+ species. We also identified by both QqToF-MS and low-energy collision tandem mass spectrometry (CID-MS/MS) of the [M+H]+ ion, the presence of specific common fingerprint fragment ions: [Cholestene]+, sugar [oxonium]+, [(Sugar-spacer-OH)+H]+, [oxonium-H2O]+, and [(Cholesterol-spacer-OH)+H]+. In addition, we observed a unique ion that could not be rationally explained by the expected fragmentation of these amphiphilic molecules. The structure of this ion was tentatively proposed with that of a C-glycoside species formed by a chemical reaction between the sugar portion and the cholesterol. MS/MS analysis of this unique [C-glycoside]+ confirmed the validity of the proposed structure of this ion. The presence of an amino group at position C-2 and free hydroxyl groups of the sugar motif is crucial for the formation of a "reactive" sugar oxonium ion that can form the [C-glycoside]+ species. In summary, we precisely established the fragmentation patterns of the tested series of neoglycolipid cholesteryl derivatives and authenticated their structure as well; moreover, we speculated on the formation of a C-glycoside with the ESI source under atmospheric pressure and in the collision cell during MS/MS analysis.
在本研究中，我们评估了16种新型两亲性新糖脂胆固醇衍生物的碎片化模式，这些衍生物可有效用于提高阳离子脂质体的稳定性并增强基因转移能力。这些新糖脂带有不同的糖部分，如D-葡糖胺、N-乙酰-D-葡糖胺、N-三氘代乙酰-D-葡糖胺、N-乙酰乳糖胺、L-岩藻糖、N-烯丙氧基羰基-D-葡糖胺，以及它们的一些全-O-乙酰化衍生物。无论所测试新糖脂的结构如何，使用电喷雾电离（ESI）源的QqToF-MS分析均显示出丰富的质子化[M+H]+物种。我们还通过对[M+H]+离子进行QqToF-MS和低能碰撞串联质谱（CID-MS/MS）鉴定，确定了特定常见指纹碎片离子的存在：[胆甾烯]+、糖[鎓离子]+、[(糖-间隔基-OH)+H]+、[鎓离子-H2O]+和[(胆固醇-间隔基-OH)+H]+。此外，我们观察到一种独特的离子，无法通过这些两亲性分子的预期碎片化合理地解释。该离子的结构初步推测为由糖部分与胆固醇之间的化学反应形成的C-糖苷物种。对这种独特的[C-糖苷]+进行MS/MS分析证实了该离子所提出结构的有效性。糖基序在C-2位存在氨基和游离羟基对于形成能够形成[C-糖苷]+物种的“反应性”糖鎓离子至关重要。总之，我们精确地确定了所测试的新糖脂胆固醇衍生物系列的碎片化模式并对其结构进行了验证；此外，我们推测了在大气压下以及MS/MS分析期间在碰撞池中通过ESI源形成C-糖苷的过程。
