JOURNAL OF MAGNETIC RESONANCE 97,4 1 l-4 18 ( 1992) New Methods for Measurement of Long-Range Proton-Carbon Coupling Constants in O ligosaccharides

The geometry about the glycosidic l inkage plays a crucial role in the conformational analysis of oligosaccharides. Currently, most interglycosidic constraints are obtained from proton-proton NOE measurements. However, as has been pointed out ( 1, 2)) these spectral parameters can often be interpreted in terms of more than one set of conformer populations. Additional experimental constraints are therefore needed in order to allow for a more accurate description of saccharide conformations. The use of interglycosidic heteronuclear coupling constants ( 3Jn,.coc. and 3Jn,,coc,.) to determine the values of torsion angles Cp and + about the glycosidic l inkage is well known (3)) but their measurement (4, 5) has been lim ited by the low natural abundance of 13C and its low sensitivity. The introduction of inverse experi-ments, with the corresponding gain in sensitivity, has resulted in much wider interest in the measurement and interpretation of “J cn coupling constants (6-13). Most of the proposed experiments are, however, designed for the structural analysis of proteins (8-13) and usually performed on isotopically enriched samples. Recently, two different one-dimensional inverse-detected schemes for the evaluation of nJCH coupling con