NOESY technique

NOESY NMR spectroscopy is a homonuclear two-dimensional experiment that identifies proton nuclei that are close to each other in space. If one has already identified proton resonances in one-dimensional NMR spectroscopy or by other methods, it is then possible to determine three dimensional structure through NOESY. For instance, it is possible to determine how large molecules such as proteins fold themselves in three-dimensional space using the NOESY technique. The solution structures thus determined can be compared with solid-state information on the same protein obtained from X-ray crystallographic studies. The pulse sequence for a simple NOESY experiment is shown in Figure 3.23 as adapted from Figure 8.12 of reference 19. 

The double-selective TOCSY-ROESY and TOCSY-NOESY techniques are particularly useful. They allow one to measure NOE and ROE correlations in spectra with high degree of overlap as often found in carbohydrates. In addition to the DANTE, DANTE-Z [66], and Gaussian pulses as described earlier for selective excitation, self-refocusing shaped pulses such as BURP (EBURP and UBURP) [67] have also been used for this purpose [64]. 

An example of the complex set of spectroscopic information required in natural products research is afforded by the mixture of hydroperoxides 207, 208, the endoperoxide 209 and other minor products, obtained by photosensitized addition of O2 to phytol (206), according to Scheme 10. The scheme is complicated by the fact that 208 is a mixture of the E and Z isomers. After separation by HPLC, each fraction can undergo characterization by FTIR, H and NMR, also applying the HSQC, HMBC, H- H COSY and NOESY techniques, and EI-MS . ... 

Cylindramide (90) is a cytotoxic compound isolated from Halichondria cylindrata (7.10 s % wet wt.), but very likely of bacterial origin [148]. The structure was deduced from spectroscopic analysis, the relative stereochemistry (only) of the bicyclo[3.3.0]octene unit by NOESY techniques, and the absolute stereochemistry of the amino acid of the tetramic acid ring (25,35) from the recovery of erythtro-L-(3-hydroxyomithine from oxidative degradation of 90. It showed cytotoxicity to B16 melanoma cells (IC50 0.8 (ig/ml). 

Intramolecular dynamics of 1,5-dihydronaphtho[l,8-(s/][l,2,3]trithiocine 16 in solutions was studied by 2-D nuclear Overhauser enhancement spectroscopy (NOESY) technique <2003AMR97> and interpreted based on the... 

NMR experiments, involving iH-lH-COSY, DQC-COSY, 1H- 3C-HETCOR, 1H-13C-COLOC and iR-lH-NOESY techniques, have been used in order to determine unambiguously the swainsonine structure and its 1,2,8-triacetate [162]. Four methylene and four methyne protons are evident in the spectrum of swainsonine in its IH- C-HETCOR NMR spectrum, the most downfield carbon resonance (5 75.23) is the methyne carbon connected to nitrogen (C-8a), and the chemical shift of the attached proton (H-8a) is observed at 5 1.89 (dd, J= 10.4 Hz). H-8a is coupled to H-8 (6 3.77, ddd, J= 11, 10, 4 Hz), as well as to H-1 (8... 

Hindered rotation at the exocyclic B— N bond in a 1,3-diborolane (6) could be shown by H and C NMR spectra, using the 2D-NOESY techniques <930M2433>. 

Unlike steady-state NOEs calculated from difference spectra, the transient NOEs determined using the ID gradient NOESY technique have some attributes associated with responses that are worthy of mention. Responses are sensitive to mixing time choices and may vary markedly as a function of this parameter choice. 

On the basis of semiempirical molecular modelling data, the total unreactivity of the primary alcohol group in l-(l-deoxy-P-D-psicofuranosyl)thymine (3) has been ascribed to hydrogen bonding with the base moiety as shown. The H- and C-n.m.r. spectra of ribofliranose in D2O have been fully assigned by use of 2D techniques. The C-n.m.r. spectra of methyl tri-O-acetyl-a- and -P-L-arabinofuranosides are referred to in Part 4 below, 2D H NOESY techniques were used to ascertain the anomeric configuration of several purine deoxyribonucleosides and the chemical shift values allowed differentiation between 7- and 9-A linked isomers. The anomeric configurations of the C-nucleosides 4, obtained in... 

In order to investigate the intermolecular interactions responsible for the miscibility in polybutadiene/polyisoprene blends above the glass-transition temperature Tg), the NOESY technique was applied under MAS [12]. The results showed the existence of weak intermolecular interactions between the vinyl side chain of the polybutadiene and the polyisoprene methyl group, thus confirming that intermolecular associations can indeed be probed using this technique. 

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