Nuclear Overhauser Enhancement cross peaks

Nuclear Overhauser enhancement spectroscopy (NOESY) experiments play a very important role in structural studies in quinolizidine derivatives. For instance, the endo-type structure of compound 28 was proven by the steric proximity of the H-3a and H-12a protons according to the NOESY cross peak, while the spatial proximity of the H-6f3 and H-8/3 protons reveals that tha A/B ring junction has a /ra t-stereochemistry. Similarly, compound 28 could be distinguished from its regioisomer 29 on the basis of the NOESY behavior of its H-13 atom <1999JST153>. 

The latter, in contrast to nuclear Overhauser enhancement and exchange spectroscopy (NOESY), always feature positive NOEs (negative cross-peaks with respect to diagonal), eliminating known problems of NOEs vanishing or spin diffusion, depending on correlation time, when high field spectrometers are used for measurements of medium-size compounds. 

The double quantum fdtering correlation spectroscopy (DQF-COSY) assignment, and observance of diagnostic cross-peaks between R-CH2 of the 2-aminoethyl and the CH2 adjacent to the cyanuryl residue, in the nuclear Overhauser enhancement spectroscopy (NOESY) H NMR of 376 indicated the major rotamer to be the trans-isomer, identical to that of the crystal structure (Figure 44). 

NOESY (nuclear Overhauser enhancement spectroscopy) plot for the aromatic region before phosphorylation of (GVGIP)i6(r-Fn3 (GRGDSP- RGYSLG)-(GVGIP) , contains many cross-peaks, many proton-proton con-... 

There are several other sources of cross peaks in the 2D EXSY experiment. Dipolar coupling with nearby nuclei (nuclear Overhauser effects) produces cross peaks, as observed in standard Nuclear Overhauser Enhancement Spectroscopy, NOESY. These can be identified because exchange usually has a larger temperature dependence than dipolar coupling. Scalar coupling interferes with 2D EXSY by producing so-called J cross peaks that can be eliminated by phase cycling. ... 

Two-dimensional nuclear Overhauser enhancement spectroscopy (2D-NOESY) provided qualitative information about spatial proximities of protons in a molecule. The unimer micelle of poly(A/l-Np(60)) (poly(A/l-Np(x)) where x = 60 mol%) in D2O gave cross-peaks between the aromatic and aliphatic protons owing to dipolar interactions, whereas the same polymer showed no such cross-peaks in DMF-rfv [29], This is indicative of a highly compact conformation of the unimer micelle in water. 

The conformation of the mixed p agonist/5 antagonist H-Tyr-c[-D-Orn-2-Nal-D-Pro-Gly-] in comparison to that of H-Tyr-c[-D-Orn-Phe-D-Pro-Gly-] was studied in DMSO-d6 by NMR spectroscopy and by molecular mechanics calculations [62,64]. Neither peptide showed nuclear Overhauser effects between C H protons or chemical exchange cross peaks in spectra obtained by total correlation and rotating frame Overhauser enhance-... 

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