Edited HSQC

Our preferred experiment of this type is the so called DEPT-edited HSQC which is both relatively artefact-free and sensitive. It also has one other major advantage up its sleeve. This experiment is not an absolute value technique like most of the others, but it allows for discrimination between different types of carbons. Methyl and methine carbons give crosspeaks that are phased opposite to the methylene carbons and so the results are best plotted on a colour plotter which can portray this clearly by plotting positive and negative cross peaks in different colors. 

Spectrum 9.3 DEPT-edited HSQC of the morpholine compound. 

In 2006, Milosavljevic and co-workers64 reported a study of the complete 4H and 13C NMR assignment of a new triterpenoid saponin, leucantho-side-A (13), from Cephalaria leucantha L. In the course of determining the structure and assigning the spectra, the authors made extensive use of the normal ensemble of 2D NMR experiments in use for the characterization of natural product structures HSQC, HMBC, DQF-COSY, TOCSY, and NOESY. The authors supplemented the aforementioned list of experiments with 2D /-resolved, DINE-(Double INEPT-Edited)-HSQC, and INADEQUATE spectra. The authors made no mention of the use of the connectivity information derived from the 1,1-ADEQUATE spectrum in the assembly of the triterpene nucleus of the molecule but reported extensive tabulations of the 1,1-ADEQUATE correlations that were used to sequence and assign the saccharide resonances of the tri- and di-saccharide sub-units, 14 and 15, respectively, linked to the triterpene nucleus. 

The order in which various NMR data are acquired is largely one of user preference. Acquisition of the proton reference spectrum will invariably be undertaken first. Whether a user next seeks to establish homo- or heteronuclear shift correlations is where individual preferences come into play. Many spectro-scopists proceed from the proton reference spectrum to either a COSY or a TOCS Y spectrum next, while others may prefer to establish direct proton-carbon chemical shift correlations. This author s preference is for the latter approach. From a multiplicity-edited HSQC spectrum you obtain not only the carbon chemical shifts, which give an indication of the location of heteroatoms, the degree of unsaturation and the like, but also the number of directly attached protons, which eliminates the need for the acquisition of a DEPT spectrum [51, 52]. The statement in the prior sentence presupposes, of course, that there the sensitivity losses associated with the acquisition of multiplicity-edited HSQC data are tolerable. 

NMR (Fig. 17) spectrum for 58 revealed 15 resonances, interpreted from multiplicity-edited HSQC data as eight quaternary, two methine, two methylene, and three methyl carbons. In the H NMR spectrum (Fig. 17)... 

Figure 7-26 Expansions HSQC spectrum (left) and multiplicity-edited HSQC spectrum (right) of T-2 toxin.

The following parametersc re appropriate for edited HSQC experiments ... 

Note that analogous experiments, such as the 13C-edited HSQC—NOESY,72 can be performed on 13C-labeled proteins. For labeled proteins, this latter experiment provides the largest number of conformational restraints for protein structure calculations (see Section 9.09.5.2). The 15N-edited NOESY-HSQC only provides distance information for protons that are close in space to amide protons (since magnetization originates and/or terminates... 

Boyer, R. D., Johnson, R., and Krishnamurthy, K. (2003) Compensation of refocusing inefficiency with synchronized inversion sweep (CRISIS) in multiplicity-edited HSQC. 

D one-bond correlation (with spectrum editing) HMQC or HSQC (with editing) Carbon assignments transposed from proton assignments. Proton spectrum dispersed by C shifts. Carbon multiplicities from edited HSQC (faster than above ID approach). 

Figure 6.19. The multiplicity-edited HSQC spectrum of the disaccharide 6.6 in which positive CH correlations (red) are distinguished from negative CH2...

As mentioned, non-invasive or passive techniques have been added to many multidimensional and multinuclear pulse sequences such as the 2D edited-HSQC up to more complicated 3D and 4D heteronuclear-based NOESYs. The basic principle is to use a relatively long selective pulse to manipulate water. 

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