Higher-Rank Correlation NMR Spectra with Spectral Moment Filtering

Higher-rank correlation spectroscopy is introduced as an alternative to 3D Fourier transform (FT) NMR spectroscopy for resonance assignment and molecular structure determination. The method combines standard 2D FT spectra that share a common frequency dimension, such as a 2D C-13-H-1 HSQC and a 2D H-1-H-1 TOCSY spectrum, and constructs higher-rank correlation spectra with ultrahigh spectral resolution. Spectral overlap along a common dimension, in particular, the H-1 dimension, is addressed by a spectral filtering method, which identifies mismatches between the first and second moments of cross-peak profiles. The method, which provides a substantial speed-up over traditional 3D FT spectroscopy while effectively suppressing false peaks, is demonstrated for the triple-rank C-13-H-1 HSQC-TOCSY spectrum of a cyclic decapeptide with different mixing times. Higher-rank correlation spectroscopy is usefully applicable to the analysis of a wide range of NMR spectra of synthetic and natural products.