13C-15N connectivity networks via unsymmetrical indirect covariance processing of 1H-13C HSQC and 1H-15N IMPEACH spectra

Long-range H-1-N-15 heteronuclear shift correlation methods at natural abundance to facilitate the elucidation of small molecule structures have assumed a role of growing importance over the past decade. Recently, there has also been a high level of interest in the exploration of indirect covariance NMR methods. From two coherence transfer experiments, A -> B and A -> C, it is possible to indirectly determine B <-> C. We have shown that unsymmetrical indirect covariance methods can be employed to indirectly determine several types of hyphenated 2D NMR data from higher sensitivity experiments. Examples include the calculation of hyphenated 2D NMR spectra such as 2D GHSQC-COSY and GHSQC-NOESY from the discrete component 2D NMR experiments. We now wish to report the further extension of unsymmetrical indirect covariance NMR methods for the combination of H-1-C-13 GHSQC and H-1-N-13 long-range (GHMBC, IMPEACH-MBC, CIGAR-HMBC, etc.) heteronuclear chemical shift correlation spectra to establish C-13-N-15 correlation pathways.