Homonuclear long‐range correlation spectra from HMBC experiments by covariance processing

Abstract

We present a new application of covariance nuclear magnetic resonance processing based on 1H--13C-HMBC experiments which provides an effective way for establishing indirect 1H--1H and 13C--13C nuclear spin connectivity at natural isotope abundance. The method, which identifies correlated spin networks in terms of covariance between one-dimensional traces from a single decoupled HMBC experiment, derives 13C--13C as well as 1H--1H spin connectivity maps from the two-dimensional frequency domain heteronuclear long-range correlation data matrix. The potential and limitations of this novel covariance NMR application are demonstrated on two compounds: eugenyl-beta-D-glucopyranoside and an emodin-derivative.

Multistep correlations via covariance processing of COSY/GCOSY spectra: opportunities and artifacts

“…[4 -7] It is important to recall, however, that covariance NMR-processing methods can also be advantageously applied to individual 2D NMR spectra. [8,9] Brüschweiler et al have demonstrated the acquisition of 2D NMR spectra with minimal datasets [10] as well as the use of covariance processing methods with TOCSY spectra to extract individual component spectra from a mixture. [11,12] We now report the application of covariance NMRprocessing methods to observe multistep long-range correlations in COSY spectra acquired with modest numbers of increments of the evolution period, t 1 .…”

Using indirect covariance spectra to identify artifact responses in unsymmetrical indirect covariance calculated spectra

“…Titrating the sample with d 6 -benzene demonstrated that aromatic solvent induced shifts (ASIS) [12] could remove the degeneracy and eliminate the artifact response. Perhaps more importantly, it was also shown that the indirect covariance processed GHSQC spectrum (icv-HSQC hereafter) showed off-diagonal responses that predicted the location and identity of the O-methyl artifact response in the 13 C-15 N icv-HSQC-HMBC spectrum. On that basis, we wanted to explore the possibility of using off-diagonal responses in the icv-HSQC spectrum to identify artifact responses in icv-13 C-13 C-COSY correlation plots derived by indirect covariance processing of GHSQC-TOCSY spectra as well as artifact responses in icv-HSQC-COSY/-TOCSY spectra derived by unsymmetrical indirect covariance coprocessing of gradient or nongradient HSQC and either COSY or TOCSY spectra.…”

“…[1] A footnote in that 2004 report mentioned the possibility of proton resonance overlap causing artifacts in the icv-13 C-13 C-COSY connectivity plots but the authors did not elaborate further on that observation. Using several model compounds, in 2005 the present authors reported the analysis of two types of artifacts in icv- 13 C-13 C-COSY connectivity plots derived from indirect covariance processing of inverted direct response (IDR)-GHSQC-TOCSY spectra. [2] In an effort to eliminate artifact responses, the indirect covariance processing algorithm was modified to allow two 2D NMR data matrices to be coprocessed.…”

“…Examples have included: coprocessing 1 H-13 C GHSQC and GHMBC spectra to yield the equivalent of an m,n-ADEQUATE spectrum [3] ; coprocessing GHSQC and GCOSY spectra to yield icv-HSQC-COSY spectra [4,5] ; coprocessing GHSQC and nuclear Overhauser effect spectroscopy (NOESY) data to produce the equivalent of icv-HSQC-NOESY spectra [6] ; and coprocessing 1 H- 13 long-range correlation spectra to derive icv- 13 C-15 N HSQC-HMBC (the notation HSQC-HMBC defines the heteronuclides involved, 13 C in the case of the HSQC portion of the acronym and 15 N for the HMBC portion) heteronuclear shift correlation spectra. [7 -9] It should be noted that the unsymmetrical indirect covariance processing method is not restricted to gradient-based experiments with perhaps the sole exception of 1 H-15 N long-range correlation experiments, which cannot be reasonably performed without resorting to gradients.…”

Unsymmetrical indirect covariance processing of hyphenated and long‐range heteronuclear 2D NMR spectra ‐ Enhanced visualization of 2JCH and 4JCH correlation responses

“…In a similar fashion, 1 H-13 C direct and 1 H-13 C long-range correlation experiments can be co-processed to afford the equivalent of m,n-ADEQUATE spectra [5,6]. 1 processed to afford various types of 13 C-15 N heteronuclear correlation spectra [7][8][9].…”