Observation and characterization of a specific vibrational circular dichroism band in phenyl glycosides

Application of vibrational circular dichroism (VCD) spectroscopy to structural analysis of carbohydrates has recently progressed. However, few studies on glycoconjugates VCD have thus far been reported, despite the fact that naturally occurring carbohydrates exist as various glycoconjugates. To further explore the application of the VCD technique, we have measured a series of aromatic glycosides and found that axial aromatic glycosides exhibited a negative band at around 1230 cm(-1) while equatorial ones showed flat features in this region. This is the first structure-spectra relationship on glycoconjugate VCD that distinguishes the stereochemistry of the sugar anomers. Several model compounds were prepared and their vibrational properties calculated by using the density functional theory (DFT) method, which assigned the vibrational mode of this band based on the stretching motion of the glycosidic oxygen and aromatic carbon. This concept that aglycan parts can reflect stereochemical information of sugar moieties may encourage further VCD studies on glycoconjugates to realize practical structural analysis of carbohydrates.