Application of unsymmetrical indirect covariance NMR methods to the computation of the 13C↔15N HSQC-IMPEACH and 13C↔15N HMBC-IMPEACH correlation spectra

Utilization of long-range 1H-15N heteronuclear chemical shift correlation has continually grown in importance since the first applications were reported in 1995. More recently, indirect covariance NMR methods have been introduced followed by the development of unsymmetrical indirect covariance processing methods. The latter technique has been shown to allow the calculation of hyphenated 2D NMR data matrices from more readily acquired non-hyphenated 2D NMR spectra. We recently reported the use of unsymmetrical indirect covariance processing to combine 1H-13C GHSQC and 1H-15N GHMBC long-range spectra to yield a 13C-15N HSQC-HMBC chemical shift correlation spectrum that could not be acquired in a reasonable period of time without resorting to 15N-labeled molecules. We now report the unsymmetrical indirect covariance processing of 1H-13C GHMBC and 1H-15N IMPEACH spectra to afford a 13C-15N HMBC-IMPEACH spectrum that has the potential to span as many as six to eight bonds. Correlations for carbon resonances long-range coupled to a protonated carbon in the 1H-13C HMBC spectrum are transferred via the long-range 1H-15N coupling pathway in the 1H-15N IMPEACH spectrum to afford a much broader range of correlation possibilities in the 13C-15N HMBC-IMPEACH correlation spectrum. The indole alkaloid vincamine is used as a model compound to illustrate the application of the method.