NMR structural elucidation

The primary function of this section is to organize data to faalitate NMR structure elucidation of organofluonne compounds Selectively fluonnated aliphatics are emphasized, whereas fluonnated aromatics are covered m less detail Inorganic nitrogen, phosphorus, silicon, and sulfur fluondes are not included, although compounds containing these and other heteroatoms attached to CF3 are the focus of multmuclear data presented later (see Table 16)... 

According to the ICH guidelines, any impurity greater than 0.1% of UV intensity by HPLC has to be characterized and identified. Traditionally, the individual impurities have to be isolated by preparative LC, and then subjected to NMR structure elucidation. The disadvantages... 

Computer control of NMR instruments has led to great advances in both data acquisition and processing and has given rise to advanced NMR structural elucidation techniques. One of the the first of these was two-dimensional... 

Franck, U., Neszmelyi, A., and Wagner, H., 2D-NMR structure elucidation of a procyanidin from... 

Balas, L., Vercauteren, J., and Laguerre, M., 2D NMR structure elucidation of proanthocyanidins the special case of the catechin-(4a-8)-catechin-(4a-8)-catechin trimer, Magn. Reson. Chem., 33, 85, 1995. 

An initially pursued strategy consisting of an acetonitrile extraction, followed by a classical column chromatographic work-up, and subsequential comprehensive off-line NMR structural elucidation, proved to be unsuitable for two reasons on the one hand, mostly sub-fractions of asterosaponins were... 

NMR Structure elucidation depends on the NMR experiments required and the purity of the isolated material. With more than 95% pure material, several hundreds of micrograms may be sufficient for NMR experiments however, for NMR experiments, several milligrams may be necessary. The reader is cautioned that NMR experiments are often required for a complete proof-of-structure. 

Isolation of a sufficient amount of pure analyte for NMR structure elucidation. 

Isolate the impurity from the drug product in sufficient quantity and purity for NMR structure elucidation, including the acquisition of C data. 

Molecular weight and proposed structures based on LC/MS analysis expedite the NMR structure elucidation. 

Homonuclear NMR Structural elucidation becomes much more difficult as spectral complexity increases. Under these circumstances, proton NMR spectroscopy has benefited considerably from the use of 2D NMR techniques. For example, homonuclear correlation spectroscopy (COSY) identifies spin-coupled pairs of nuclei as well as spin-coupled networks of nuclei in a molecule, even without prior structural information. The 2D /-resolved spectroscopy method permits even highly overlapping resonances to be resolved into readily interpretable multiplets. This enables chemical shift assignments to be made in a very straightforward manner. Both of... 

Xie X, Wallwey C, Matuschek M, Steinbach K, Li S-M (2011) Eormyl migration product of chanoclavine-I aldehyde in the presence of the old yellow enzyme FgaOx3 from Aspergillus fumigatus. a NMR structure elucidation. Magn Reson Chem 49 678-681... 

M. alba fruits (28) and C soldandla (29), respectively, shows that the opposite chirahty may occur in different plants. Caution with absolute configuration assignment is therefore advised after only NMR structure elucidation. All cal5rstegines and other di- or trihydroxynortropane alkaloids are hydrophilic their octanol-water partition coefficient is well below zero (Table 1). In liquid-liquid extraction s5rstems between water and organic phase they will remain in the aqueous phase, even if the pH is elevated above 7. This property prevented their detection in former times, as classical alkaloid analysis includes liquid extraction of free alkaloid bases by organic solvents from an alkaline water extract. 

Yuste, F., Barrios, H., Diaz, E., Enriquez, R.G., Gonzalez-Gutierrez, L., Ortiz, B., Sanchez-Obregon, R., and Walls, F., The ultraviolet irradiation of isoperezone acetate. 2D NMR structure elucidation, Nat. Prod. Lett., 8, 181, 1996. 

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