Conformational Differences Between O- and C-Glycosides: The α-O-Man-(1→1)-β-Gal/α-C-Man-(1→1)-β-Gal Case- A Decisive Demonstration of the Importance of the exo-Anomeric Effect on the Conformation of Glycosides

The conformational behavior of α‐O‐Man‐(1→1)‐β‐Gal (1) and its C‐analogue (2) has been studied using J/NOE NMR data, molecular mechanics, molecular dynamics, and ab initio calculations. The population distribution around the glycosidic linkages of 1 and 2 is rather different, especially for the α‐Man linkage. A lower limit for the exo‐anomeric effect in water has been experimentally determined. El comportamiento conformacional del α‐O‐Man‐(1→1)‐β‐Gal (1) y su análogo C‐glicosídico 2 se ha estudiado utilizando una combinación de datos experimentales de RMN y cálculos de mecánica y dinámica molecular y ab initio. La distribución de poblaciones en torno a los enlaces glicosídicos de 1 y 2 es muy distinta, especialmente para el enlace α‐Man. Además, se ha determinado experimentalmente un límite inferior para el efecto exo‐anomérico en disolución acuosa. First experimental estimation of theexo‐anomeric effect in water solution could be given by the comparison of NMR data for the C‐/O‐glycoside pair 1 and 2. Tar‐MD simulations unequivocally demonstrated the distinct conformational behavior of O‐ and C‐glycosides.