2D selective-TOCSY-DQFCOSY and HSQC-TOCSY NMR experiments for assignment of a homogeneous asparagine-linked...

The assignment of (1)H and (13)C NMR signals of a complex type triantennary asialooligosaccharide was examined using 2D selective-TOCSY-DQFCOSY and HSQC-TOCSY experiments. The 2D selective-TOCSY-DQFCOSY experiment exhibits a 2D DQFCOSY spectrum of an individual monosaccharide in the undecasaccharide, although the NMR signals of several monosaccharides in the triantennary undecasaccharide are heavily overlapped. Selective excitation of each anomeric proton signal and subsequent TOCSY experiment afforded transverse magnetization corresponding to all of the proton signals of the monosaccharide. This magnetization was then developed with the corresponding DQFCOSY pulse sequence to afford the DQFCOSY spectrum of the individual monosugars. In this case, four GlcNAc-b, -e, -j, and -h residues were excited as a mixture. In order to assign (13)C signals, a conventional 2D HSQC-TOCSY spectrum was examined and compared with an unambiguous assignment of 2D selective-TOCSY-DQFCOSY thus obtained. This systematic analysis made it possible to obtain an assignment of the (1)H and (13)C NMR signals of the triantennary undecasaccharide. In addition, these experiments also revealed all of the glycosyl positions in the triantennary undecasaccharide.