Heteronuclear double-quantum filtered

The structural connectivity derived from examination of the 111, 13C/DEPT, DQF-COSY, HMQC, and HMBC data (DEPT = distortionless enhancement by polarization transfer DQF = double quantum filtering COSY = correlation spectroscopy HMQC = heteronuclear multiple quantum correlation HMBC = heteronuclear multiple bond correlation) resulted in global reevaluation of sclerophytin B structure and demonstrated that this compound and the related alcohol are not composed of two ether bridges as in the originally formulated structure 37, but share the structural features depicted as 38 <20000L1879>. Comparison of 13C and 111 NMR data of Norte s... 

Traditionally, homonuclear 2D double quantum filtered correlation spectroscopy (DQF-COSY) and total correlated spectroscopy (TOCSY) spectra are valuable in the identification of resonances of individual monosaccharide units. In the presence of small couplings, through space connectivities detected by NOESY/ROESY (nuclear Overhauser effect spectroscopy/ rotational nuclear Overhauser effect spectroscopy) experiments are also useful in completing the resonance assignment. When the H NMR spectra of complex oligosaccharides are too crowded to fully elucidate the structure by homonuclear correlation methods, it is efficient to use 2D heteronuclear correlation methods, such as heteronuclear single quantum correlation... 

The application of three and more gradients is necessary if multiquantum states are to be suppressed as in the double-quantum filtered COSY experiment or if CT pathways in heteronuclear spin systems should be selected in sequences which include magnetization transfer steps. 

A suit of 2D-NMR techniques that include chemical-shift correlation spectroscopy (COSY), double-quantum filtered correlation spectroscopy (DQF-COSY), total correlation spectroscopy (TOCSY), and heteronuclear multiple-quantum coherence spectroscopy (HMQC) have been used for... 

FIGURE 8.2. Flowchart for structure elucidation of purified compounds. DEPT Distortionless Enhancement by Polarization Transfer, HMBC Heteronuclear Multiple Bond Correlation, HSQC Heteronuclear Single Quantum Coherence, HMQC Heteronuclear Multiple Quantum Correlation, DQF-CQSY Double Quantum Filtered Correlated Spectroscopy and NOSEY Nuclear Overhauser effect spectroscopy. 

Fig. 5. HMBC pulse sequence of Bax and Summers (1986). The first 90° pulse serves as a low-pass J-filter (Kogler et al. 1983), as discussed in the text. Heteronuclear multiple-quantum coherence of order zero and two is created by the second 90° pulse. The 180° H pulse interchanges zero- and double-quantum coherences and decouples proton chemical shift evolution during tp Observable proton single-quantum coherence is recreated by the final 90° pulse and detected...

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