Direct and efficient analysis on monosaccharide composition of polysaccharides from various sources by GEMSTONE–TOCSY NMR spectroscopy

NMR spectroscopy is a powerful spectroscopic technique that permits the detailed study of the molecular structure elucidation and mixture component analysis, especially in the identification of complex mixtures. However, the conventional 1 H NMR generally suffers from crowded resonances when measuring and identifying carbohydrates of polysaccharide hydrolysis systems, which contain various chemically similar compounds and even multiple isomeric monosaccharides. Herein we describe the application of a targeted detection NMR approach, gradient-enhanced multiplet-selective targeted-observation NMR experiment GEMSTONE–TOCSY, exploited for studying polysaccharide hydrolysis mixtures by spectroscopically targeting the desired compounds in separate 1D NMR spectra. There are six model mixtures of natural bioactive polysaccharide hydrolysis (including 11 monosaccharides) and three real reaction systems (carob seed polysaccharide, tremella polysaccharide and stachyose hydrolysis), which are tested by GEMSTONE–TOCSY NMR showing satisfactory performance in monosaccharide identification and structure analysis even when proton signals are crowded and overlapped in conventional 1 H NMR. Moreover, GEMSTONE–TOCSY NMR uses a fast, single-scan method that allows selective excitation of the signals of a single proton multiplet and available for highly efficient analysis. The results demonstrate that GEMSTONE–TOCSY NMR technique is robust and reliable to analyze and identify monosaccharide composition of various polysaccharides from mixture systems, even providing efficient analysis tool for detecting the polysaccharide hydrolysis process.