Rotating frame nuclear Overhauser

Sowinski and coworkers40 reported a structure of vacidin A (63), an aromatic hep-taene macrolide antibiotic. The constitution of vacidin A, a representative of the aromatic heptaene macrolide antibiotics, was established on the basis of 13C and H- H double quantum filtered correlated spectroscopy, rotating frame nuclear Overhauser effect spectroscopy, 7-resolved 11 as well as H-13C correlation NMR spectra. The geometry of the polyene chromophore was determined as 22E, 24E, 26E, 28Z, 30Z, 32E, 34E. 

The data from H NMR studies of 63, which included double quantum filtered phase sensitive correlated spectroscopy (DQF-COSY) and rotating frame nuclear Overhauser effect spectroscopy (ROESY) experiments (Figure 12), are collected in Table 17. 

Fattorusso and co-workers identified a component of wormwood called artar-borol. Correlation spectroscopy (COSY) and rotating frame nuclear overhauser effect spectroscopy (ROESY) experiments allowed for deduction of four possible diastereomeric structures of artarborol, 2-5. Low energy conformers of 11-14 were obtained through a molecular mechanics (MM) search. These conformers were screened to identify those having a dihedral angle of around 90 for the C-8 and C-9 protons due to a low coupling constant between these protons. Only conformers of 11 and 13 satisfied this criterion. Next, five low energy conformers, two... 

Conicasterol F Butts and Bifulco were interested in the stracture of conicasterol F (26). Standard NMR analysis led to two possible diasteromers 26a and 26b. The interesting aspect of their approach toward discriminating between these two options was to compare not only the computed and experimental chemical shifts, but also to compare the distances between protons, determined from the optimized structure and the rotating-frame nuclear overhauser effect (ROE). 

Refocused J cross-polarization Rotating frame nuclear Overhauser enhancement Rotating frame nuclear Overhauser enhancement spectroscopy... 

Glc glucose ROESY rotating-frame nuclear Overhauser... 

ROESY, rotating frame nuclear Overhauser enhanced spectroscopy. 

The elucidation of the scalar coupling network by the correlation experiments is, apart from small molecules, not sufficient for the unambiguous, sequential and stereo-specific assignment. The complementary information of spatially adjacent protons is obtained via cross-relaxation experiments, the laboratory-frame nuclear Overhauser enhancement spectroscopy (NOESY) and the rotating-frame nuclear Overhauser effect spectroscopy (ROESY). These experiments provide also the distance restraints for the structure determination and help to recognize exchange processes. 

Rotating Frame Nuclear Overhauser Effect Spectroscopy (ROESY), NMR, a technique that allows exchange processes to be observed when applied to the trimethylam-monium salt of 12 in dichloromethane-rf2, provided evidence for aggregation in solution (Figure 14). Two resonances were observed between 7.0 and 7.5 ppm... 

In contrast, with axle 15 only one orientation is observed at low temperature, even after 70 days. The assignment of the orientation could be obtained by the observation of ROESY (rotating frame nuclear overhauser effect correlation spectroscopy) cross-peaks between C5H CD protons and the 3-methylpyridine site and, conversely, the C3H CD protons with the site containing the disubstituted pyridine. However, increasing the temperature to 343 K equilibration takes place and the two orientations become equally populated, showing that the observed selectivity had a kinetic origin. 

ROESY Rotating frame nuclear Overhauser effect spectroscopy... 

Thus, as illustrated above, one-dimensional rotating frame nuclear Overhauser and exchange spectroscopy (ID-ROESY) experiments may provide a reasonable explanation for significant qualitative and quantitative differences observed in selector-selectand interactions related to chiral CE. This information becomes even... 

ROESY rotating frame nuclear overhauser spectroscopy... 

---