Unusual conformational behavior of trisaccharides containing N-acetylglucosamine

Protected trisaccharides containing N-acetylglucosamine can adopt unexpected conformations through the formation of hydrogen bonds involving the amide group. This conformational behavior was observed by NMR spectroscopy when three protected trisaccharides were dissolved in deuterated chloroform and to a lesser extent in deuterated dichloromethane. In contrast, NMR spectra of the same analogues acquired in the hydrogen bond-accepting solvents deuterated acetonitrile and dimethylsulfoxide showed that the N-acetylglucosamine residues adopted the expected ⁴C₁ conformation.