13C isotope effects on 1H chemical shifts: NMR spectral analysis of 13C-labelled D-glucose and some 13C-labelled amino acids

The one- and two-bond C-13 isotope shifts, typically -1.5 to -2.5 ppb and -0.7 ppb respectively, in non-cyclic aliphatic systems and up to -4.4 ppb and -1.0 ppb in glucose cause effects that need to be taken into account in the adaptive NMR spectral library-based quantification of the isotopomer mixtures. In this work, NMR spectral analyses of some C-13-labelled amino acids, D-glucose and other small compounds were performed in order to obtain rules for prediction of the C-13 isotope effects on H-1 chemical shifts. It is proposed that using the additivity rules, the isotope effects can be predicted with a sufficient accuracy for amino acid isotopomer applications. For glucose the effects were found strongly non-additive. The complete spectral analysis of fully C-13-labelled D-glucose made it also possible to assign the exocyclic proton signals of the glucose. Copyright (C) 2009 John Wiley & Sons, Ltd.