Phase-sensitive NOESY

HSQC NOESY phase-sensitive HSQC-NOESY with discrimination of direct CH correlations from CH NOE correlations [23]... 

HSQC edited NOESY phase-sensitive HSQC-NOESY mixed phase, no additional information... 

Phase-sensitive NOESY spectra are generally significantly superior in resolution to absolute-mode spectra. As in phase-sensitive COSY spectra. 

Figure 5.44 (a) Phase-sensitive absorption-mode NOESY spectrum of bovine phos-... 

The reason for this is that our experiments are phase-sensitive. What do we mean by this You will remember that in the DEPT and APT spectra the CH/CHj and CH2 peaks are in one case positive (up) and in the other negative (down), which we also refer to as in opposite phase. Here in COSY and NOESY our experiments include such phase information, which is read off from the way the signals look in the plot. 

Aryl derivatives of thieno[3,2-f]pyridines, 36 and 37, have been the subject of two-dimensional (2-D) NMR studies. Phase-sensitive nuclear Overhauser enhancement spectroscopy (NOESY) and correlation spectroscopy (COSY) experiments confirm the nonplanar conformation of the two aromatic ring systems <1999SAA1035>. 

Notably, two isomeric products can be generated. The usual infrared (IR) and mass spectra as well as H and 13C NMR chemical shifts could not define which isomer was formed. The authors used different NMR techniques, such as 2-D heteronuclear multiple bond correlation (HMBC) experiments and phase-sensitive nuclear overhauser enhancement spectroscopy (NOESY) measurements to elucidate the product s structure. 

The spectra were acquired with 2048 t2 complex data points and 256 ri increments in the phase sensitive mode with quadrature detection using the method described by States et al. (25). Water resonance was supressed during the 1.5s relaxation period used in the NOESY, DQF-COSY and TOCSY experiments and the mixing period of the NOESY experiments by irradiating continuously at its resonance frequency. The amide exchange experiments were carried out by... 

Since the pulse sequence is the same for EXSY and NOESY, NOESY (or ROESY) cross peaks might be mistaken for EXSY cross peaks. They can be distinguished in the phase-sensitive experiment, since EXSY and ROESY peaks have opposite phases, as do EXSY and NOESY peaks in the fast motion regime. For example, two resolved OH or NH resonances may exhibit EXSY cross peaks from slow proton exchange. These peaks could be mistakenly taken to be NOESY peaks and interpreted incorrectly in terms of stereochemistry. 

Chemical and conformational exchange effects are observed in NOESY spectra, but they are not usually troublesome if the experiment is performed in the phase-sensitive mode. If these exchange processes occur on the same time scales that have been discussed here, the same NOESY parameters can be used for EXSY experiments, but Tm now is the average time of the exchange process under investigation. The following parameters are appropriate for NOESY experiments ... 

Finally, the nuclear Overhauser effect can be utilized to construct a 2D spectrum where cross-peaks correspond to protons close in space (phase-sensitive NOESY spectrum). 

Fig. (3). Phase-sensitive NOESY spectrum of saponarioside C from Saponaria officinalis (the mixing time was 600 msec). Note that both the inter-residue (bold labeled) and intra-residue NOEs were observed. For the a-D-galactose moiety, the only intra-residue NOE noted is between H, and H2. For all other sugar units, the intra-residue NOEs between H,/H3 and H,/H5 are observed.

Fig. (4). The calculated preferred conformation (part) of mimusopin and NOEs observed from phase-sensitive NOESY.

Assignments are based on COSY, HOHAHA, DEPT, HETCOR, phase-sensitive NOESY, and HMBC experiments. 

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