Solution conformation of the disaccharide of avermectin B1a examined by NMR spectroscopy and nuclear Overhauser enhancement restrained hard-sphere exo-anomeric effect calculation.

The solution conformation of the disaccharide of avermectin B1a was examined by combining NMR data with theoretical conformational energy calculations. Carbon and proton resonances were assigned unambiguously using high-field, high-resolution 2D NMR correlation spectroscopy. 3JHH coupling constants were determined at 600 MHz. The minimum-energy conformation was attained through an extended hard-sphere exo-anomeric effect (HSEA) approach. The HSEA conformation was refined by considering the experimental nuclear Overhauser enhancement contacts. The resulting three-dimensional structure was confirmed by comparing its glycosidic dihedral angles to those calculated from experimental 3JCOCH coupling constants. Differences has been found in the glycosidic dihedral angles between the solution conformation and the X-ray structure.