H2BC: a new technique for NMR analysis of complex carbohydrates

It is demonstrated that the H2BC NMR pulse sequence (J. Am. Chem. Soc. 2005, 127, 6154, Magn. Reson. Chem. 2005, 43, 971–974) offers unambiguous assignments and significant simplification of NMR spectra of large and complex carbohydrates compared to other techniques for the establishment of correlations over more than one bond. H2BC almost exclusively correlates protons and proton-bearing carbon spins separated by two covalent bonds and is independent of occasionally vanishing 2JCH coupling constants, which alleviates the problem of missing two-bond correlations in HMBC spectra. H2BC also solves the problem of distinguishing two- and three-bond correlations in HSQC–TOCSY or HMBC. It is a further asset of H2BC that the experiment is significantly shorter than HMBC and HSQC–TOCSY, and hence less sensitive to transverse relaxation. The H2BC experiment is demonstrated on an approximately 30-residue oligosaccharide from Francisella victoria.