Discrimination between coupling networks of glucopyranosides varying at a single stereocenter using two-dimensional vibrational correlation spectroscopy

A combination of two-dimensional infrared (2DIR) correlation spectroscopy, linear absorption spectroscopy, and density functional theory quantum calculations was used to identify characteristic spectral features of two anomers of acetylated 2-azido-2-deoxy-D-glucopyranose. While the linear absorption spectra for the α and β anomers were distinctive, a substantial difference between them was observed only in the spectral region below 1200 cm−1. The infrared correlation spectra of the two anomers differed significantly, even in regions where their linear absorption spectra were similar. Very substantial differences were found for the NN/CO stretch mode region of the 2DIR correlation spectrum, indicating differences in the anharmonic coupling of the NN stretching mode of the equatorially oriented N3 group with the CO modes when the C1 ester was either in the axial (α anomer) or equatorial (β anomer) orientation. In addition, the energy transport patterns originating from the excited NN stretching mode were found to be different for the two anomers; up to a 1.8-fold difference in the energy transport times was observed for the probed modes of the same type in the two anomers. The results demonstrate the capability of 2DIR and relaxation-assisted 2DIR (RA 2DIR) spectroscopies to provide unique spectroscopic data specific to sugar anomers that vary at a single stereochemical center. These methods identify unique coupling networks within individual sugar stereochemical units and demonstrate the potential to identify a number of stereochemical differences among them.