Two‐dimensional POMMIE J(CH)‐resolved 13C NMR spectrum editing. Application to peptide and carbohydrate derivatives

Abstract A pulse sequence has been implemented for two‐dimensional POMMIE J(CH)‐resolved 13C NMR spectroscopy and has been used to explore three methods for the automated acquisition of data for two‐dimensional spectrum editing. In the first two methods, sets of three two‐dimensional data matrices are acquired in either sequential or interleaved modes, by use of three values, π = ϕ/6, π/2 and 5π/6, for the phase shift of the multiple quantum read pulse. Computation of linear combinations of these three data matrices by use of a Pascal program that had been written earlier for two‐dimensional DEPT spectrum editing yielded two‐dimensional POMMIE J(CH)‐resolved CH, CH2 and CH3 subspectra. In the third method, these subspectra are constructed directly during acquisition, by rotation of the phase shifts of the multiple quantum read pulse and the receiver. Selected small peptides and carbohydrate derivatives were used as model compounds for this study, and their 1H and 13C NMR assignments were confirmed by two‐dimensional COSY and heteronuclear CH chemical shift correlation techniques. The results show that if appropriate equipment is available, the two‐dimensional POMMIE method is easier to implement for J(CH)‐resolved spectral editing than the two‐dimensional DEPT technique. However, these methods are comparable in their ability to suppress residual signals.