NOE interactions

Figure 5.43 A typical NOESY spectrum the off-diagonal cross-peaks represent the nOe interactions between various nuclei.

The ROESY spectrum affords homonuclear transverse nOe interactions as cross-peaks between the various dipolarly coupled hydrogens. This... 

Assuming a y3-orientation of the C-1 methine proton (8 4.8), the stereochemistry at other centers can be assigned. For instance, )8-orientation of the C-2 methine proton (8 3.2) is confirmed by nOe interaction between C-2 and C-1 protons. Selective irradiation of C-1 proton (8... 

The modification of the physical properties of some molecules as consequence of complexation with CDs is well known. Kongo et al.126 studied the TB-p-CD/porphyrine complex and observed a drastic change in the photochemical and photophysical properties of porphyrine. The conformational analysis by NMR revealed strong NOE interactions between the ligand and the internal part of the CD, in agreement with a deep insertion of the porphyrine analogue into the CD s cavity. The NOE data provided structural information to propose the 3D model of 1 2 inclusion complexes. 

In the HMBC spectrum this NH proton exhibited 3/(CH) correlation to the C3" (5174.15) and 2/(CH) interaction to the C13 (5165.48) carbonyl, the latter in turn showing 2/(CH) interaction with H12(56.05). Thus it became clear that a carboxamide group linked the conjugated triene and the cyclopentenone unit. A 2/(CH) coupling of the triene terminus H7 to C4 (5jj/5c 5.86/71.20) established the point of attachment of the triene unit to C4. An observed NOE interaction between the H7 and H5 lent further support to this attachment and was suggestive of proximal orientation of the trans-A1 bond to the epoxy unit in the most preferred conformation. The absolute configuration at C4 was not established. 

Mele, A., Romano, G., Giannone, M. et al.. The local structure of ionic liquids Cation-cation NOE interactions and internuclear distances in neat [bmim][BF4] and [bdmim][ BFJ, Angew. Chem. Int. Ed., 45,1123, 2006. 

High resolution multidimensional NMR experiments can provide the dendrimer chemist with a wealth of additional information extending far beyond the determination of the molecular structure. In the interpretation of (2D)-NOESY (NOESY=nuclear Overhauser enhancement spectroscopy) spectra, a knowledge of the spatial interrelationships between protons in different parts of the dendrimer scaffold can be acquired from proton-proton NOE interactions. At the same time, the prevailing conformation of the dendritic branches in the solvent used can be deduced from this information. Furthermore, studies of dendrimer/sol-vent interactions and the influence of solvent on the spatial structure of the dendrimer are also possible [22]. Thus the information content of such NMR experiments resembles that of small-angle scattering experiments on dissolved dendrimers (see Section 7.6). 

The structure of the dimer was elucidated using ROESY NMR measurements performed in DMSO-c/V, with the guanidioniocarbonyl group appearing to be in an orientation in which the adjacent carbonyl group is in plane with the pyrrolic NH, as only NOE interactions observed with the pyrrolic CH. The orientation of the amino acid arm could not be determined due to the presence of various NOE interactions along the chain. 

Conformational analyses of JOM-13 and [L-Ala3]DPDPE have proven to be critical for the determination of the bioactive conformation of enkephalin-like peptides at the delta receptor. H-NMR studies of JOM-13 in aqueous solution revealed that this tetrapeptide exists in two distinct conformations on the NMR time scale as evidenced by two sets of resonances [63]. Large differences in the observed chemical shifts and coupling constants for the D-Cys2 residue in the two conformers suggested that the major differences between the two NMR conformers reside in the disulfide portion of the molecule however, a paucity of conformationally informative nuclear Overhauser enhancement (NOE) interactions precluded the development of a detailed structural model from the NMR studies. In order to develop such a model a thorough conformational analysis of JOM-13 was undertaken, in which the NMR data were complemented by x-ray diffraction results and by molecular mechanics calculations [64]. The results indicate that the 11-... 

The other anomer of glucose, in contrast, has its anomeric proton (/31) in the axial position. In the preferred chair conformation of glucose, protons occupy all of the other axial positions leading to presumed diaxial interactions between H-l (/31) and H-3 (/33) and between H-l (/31) and H-5 (/35).The ROESY spectrum reveals three interactions with the anomeric proton, /SI, at 4.67 ppm. The H-2 COSY interaction is, of course, present, and the two-diaxial NOE interactions to H-3 (/33) and H-5 (/S5) are quite evident. 

The other connectivity can be established by way of the NOE interaction between the aspartic acid N—H and the two glycine H-2 s. There is no ambiguity or overlap in this correlation thus proving the sequence given in Problem 7.6A. An interesting aside worth noting is the NOE correlation between the aspartic acid N—H and only one of the two diastereotopic methylene protons of aspartic acid... 

NOES Y and ROESY (Fig. 10.13) correlate protons with other protons via their homonuclear NOE interactions. A NOESY spectrum looks very much like a COSY, except that the crosspeaks correspond to pairs of protons that are close in space (<5 A) and not necessarily close in the bonding network. The intensities of crosspeaks are roughly proportional to 1/r6, where r is the direct through-space distance between the two protons correlated by the crosspeak. 

In Chapter 5 we observed NOE interactions by ID NOE difference, measuring the steady-state NOE resulting from a long (several seconds), low-power continuous-wave irradiation of one nucleus. The modern selective (DPFGSE) ID NOE experiment... 

In cholesterol we can see nearly all of the 1,3-diaxial and 1,2 axial-equatorial NOE interactions, whether they are H-H or H-CH3 relationships. One should take great care, however, in establishing regiochemistry or stereochemistry by NOE experiments. Even in a small ring (4-6 members), the difference in the H-H distance between a cis 1,2 (vicinal) relationship and a trans relationship is small. For an ideal cyclohexane chair conformation, for example, the vicinal distances are 2.54 A for equatorial-equatorial (trans), 2.48 A for... 

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