Proton resonance assignments in oligosaccharides containing multiple monosaccharide residues of the same type.

A technique is described for assisting the resonance assignment process in oligosaccharide proton NMR spectra, where multiple residues of the same type generate extreme resonance overlap in the spectrum. The approach involves the modification of a conventional HOHAHA experiment with constant-time acquisition in t1, which effectively proton decouples the C-1 protons of residues whose resonances overlap, thus affording a significant increase in effective resolution in that dimension. For a sufficiently long spin-lock time, complete one-dimensional subspectra are obtained essentially free of cross talk from adjacent resonances. Further simplification of the assignment process is illustrated by incorporation of the constant-time modification into a three-dimensional HOHAHA-HOHAHA experiment.