Friedrich Leon M, Lütjohann Clemens, Hartke Bernd, Lindhorst Thisbe K
Otto Diels Institute of Organic Chemistry, Christiana Albertina University of Kiel, Otto-Hahn-Platz 3-4, 24118, Kiel, Germany.
Institute for Physical Chemistry, Christiana Albertina University of Kiel, Max-Eyth-Straße 2, 24118, Kiel, Germany.
Chemistry. 2024 Nov 26;30(66):e202403117. doi: 10.1002/chem.202403117. Epub 2024 Oct 31.
para-Nitrophenyl (PNP) ethers of glycosides are important building blocks en route to functional carbohydrates. They are stable in neutral media, however, under basic conditions such as during the Zemplén deacylation of sugars, aryl migration is frequently observed. We have employed a library of O-PNP-substituted methyl glycosides of the manno-, galacto-, gluco- and altro-series to study the kinetics of aryl migration in MeOH/sodium methoxide using NMR spectroscopy revealing that migration between cis-oriented OH groups is faster than between trans-oriented ones. The rate constants of migration decrease in the order of Alt>Man>Gal>Glc and are related to the energy barriers of chair conformation inversion. The energy profile of the 3 to 4-PNP migration in methyl mannoside was calculated using DFT methods suggesting the Meisenheimer complex is an intermediate of PNP migration and that coordination of the sodium cation has a major impact on the energy profile.
糖苷的对硝基苯基（PNP）醚是通往功能性碳水化合物途中的重要结构单元。它们在中性介质中稳定，然而，在碱性条件下，如在糖的泽普伦脱酰过程中，经常观察到芳基迁移。我们使用了甘露糖、半乳糖、葡萄糖和阿卓糖系列的O-PNP取代甲基糖苷库，通过核磁共振光谱研究了甲醇/甲醇钠中芳基迁移的动力学，结果表明顺式取向的羟基之间的迁移比反式取向的羟基之间的迁移更快。迁移速率常数按阿卓糖>甘露糖>半乳糖>葡萄糖的顺序降低，并且与椅式构象反转的能垒有关。使用密度泛函理论方法计算了甲基甘露糖苷中3到4-PNP迁移的能量分布，表明迈森海默络合物是PNP迁移的中间体，并且钠阳离子的配位对能量分布有重大影响。
