Nguan Hock-Seng, Chen Jien-Lian, Ni Chi-Kung
Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei 10617, Taiwan.
Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan.
J Phys Chem A. 2024 May 16;128(19):3812-3820. doi: 10.1021/acs.jpca.4c00640. Epub 2024 May 1.
Structural determination of carbohydrates using mass spectrometry remains challenging, particularly, the differentiation of anomeric configurations. In this work, we studied the collision-induced dissociation (CID) mechanisms of sodiated α- and β-l-fucose using an experimental method and quantum chemistry calculations. The calculations show that α-l-fucose is more likely to undergo dehydration due to the fact that O1 and O2 are on the same side of the sugar ring. In contrast, β-l-fucose is more prone to the ring-opening reaction because more OH groups are on the same side of the sugar ring as O1. These differences suggest a higher preference for the dehydration reaction in sodiated α-l-fucose but a lower preference for ring-opening compared to that of β-l-fucose. The calculation results, which are used to assign the CID mass spectra of α- and β-l-fucose separated by high-performance liquid chromatography, are supported by the fucose produced from the CID of disaccharides Fuc-β-(1 → 3)-GlcNAc and Fuc-α-(1 → 4)-GlcNAc. This study demonstrates that the correlation of cis- and trans-configurations of O1 and O2 to the relative branching ratios of dehydration and cross-ring dissociation in CID, observed in aldohexose and ketohexose in the pyranose form, can be extended to deoxyhexoses for anomericity determination.
利用质谱法进行碳水化合物的结构测定仍然具有挑战性，尤其是在区分异头构型方面。在这项工作中，我们使用实验方法和量子化学计算研究了钠化α-和β-L-岩藻糖的碰撞诱导解离（CID）机制。计算结果表明，α-L-岩藻糖由于O1和O2位于糖环的同一侧，更有可能发生脱水反应。相比之下，β-L-岩藻糖更容易发生开环反应，因为与O1位于糖环同一侧的羟基更多。这些差异表明，钠化α-L-岩藻糖对脱水反应的偏好更高，但与β-L-岩藻糖相比，对开环反应的偏好较低。通过对二糖Fuc-β-(1→3)-GlcNAc和Fuc-α-(1→4)-GlcNAc进行CID产生的岩藻糖，支持了用于指定通过高效液相色谱分离的α-和β-L-岩藻糖的CID质谱的计算结果。这项研究表明，在吡喃糖形式的醛己糖和酮己糖中观察到的O1和O2的顺式和反式构型与CID中脱水和跨环解离的相对分支比之间的相关性，可以扩展到脱氧己糖用于异头物的测定。
