Accurate and precise measurement of heteronuclear long-range couplings by a gradient-enhanced two-dimensional multiple-bond correlation experiment

We propose a phase-sensitive gradient-enhanced two-dimensional heteronuclear multiple-bond correlation (psge-2D HMBC) experiment for speedy, accurate, and precise measurement of (2)J(CH) and (3)J(CH). The experiment does not suppress one-bond correlations. Rather, the value of a desired long-range J(CH) is Obtained from the pertinent cross-peak pattern in the HMBC spectrum, using the corresponding (1)J(CH) correlation pattern as reference. The application of the proposed experiment is illustrated for the trisaccharide raffinose. (C) 1998 Academic Press.