Spin-edited 2D HSQC-TOCSY experiments for the measurement of homonuclear and heteronuclear coupling constants: application to carbohydrates and peptides.

Simple modifications of the sensitivity-improved HSQC-TOCSY pulse sequence are proposed for the easy determination of the sign and the magnitude of homonuclear and heteronuclear coupling constants. Whereas in well-resolved regions, a clean two-component E.COSY-like pattern allows a direct measurement from a single 2D spectrum, separate acquisition of equivalent single-component TROSY/anti-TROSY spectra becomes highly interesting when spectral crowding complicates the spectral analysis. It is also demonstrated that an additional restricted planar mixing element after the isotropic TOCSY process completely retains all spin-editing features and permits the accurate measurement of the sign and the size of the corresponding homonuclear proton-proton coupling constants. Among others, the proposed techniques are particularly suited for molecules presenting a great number of CH and NH spin systems. Examples and practical details of the implementation of these techniques on standard carbohydrates and peptides at 13C and 15N natural abundance are provided.