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 alpha and beta 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 N equivalent to N/C equivalent to O stretch mode region of the 2DIR correlation spectrum, indicating differences in the anharmonic coupling of the N equivalent to N stretching mode of the equatorially oriented N-3 group with the CO modes when the C-1 ester was either in the axial (alpha anomer) or equatorial (beta anomer) orientation. In addition, the energy transport patterns originating from the excited N equivalent to N 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.