Natural product analysis, nuclear magnetic resonance

Within the past two decades, the importance of nuclear magnetic resonance (n.m.r.) spectroscopy has enlarged tremendously. Its advantages over other methods in the structural and conformational analysis of such complex molecules as natural products, and particularly with regard to the still-increasing importance of medical investigations using n.m.r. techniques, is abundantly evident. Because destruction of the sample is avoided, different n.m.r. experiments can be performed repeatedly, and... 

Progress in photochemistry could only be made following progress in spectroscopy and, in particular, the interpretation of spectra in at least semiquantitative terms, but history has shown that this was not enough. The arrival of new methods of analysis which permit determination of small amounts of products, the development of flash photolysis, nuclear magnetic resonance, and electron spin resonances which can yield valuable information about the natures of intermediate excited states, as well as of atoms and radicals, all have permitted the photochemist to approach the truly fundamental problem of photochemistry What is the detailed history of a molecule which absorbs radiation ... 

Use of an integrated system incorporating CCC separation, PDA detector, and LC-MS proved to be a valuable tool in the rapid identification of known compounds from microbial extracts.6 This collection of analytical data has enabled us to make exploratory use of advanced data analysis methods to enhance the identification process. For example, from the UV absorbance maxima and molecular weight for the active compound(s) present in a fraction, a list of potential structural matches from a natural products database (e.g., Berdy Bioactive Natural Products Database, Dictionary of Natural Products by Chapman and Hall, etc.) can be generated. Subsequently, the identity of metabolite(s) was ascertained by acquiring a proton nuclear magnetic resonance ( H-NMR) spectrum. 

From a medicinal chemist s perspective, nuclear magnetic resonance (NMR) was still the analytical tool of choice, whereas mass spectrometry, infrared (IR), and elemental analyses completed the necessary ensemble of analytical structure confirmation. Synthesis routines were capable of generating several milligrams of product, which is more than adequate for proton and carbon NMR experiments. For analyses that involved natural products, metabolites, or synthetic impurities, time-consuming and often painstaking isolation methods were necessary, followed by expensive scale-up procedures, to obtain the necessary amount of material for an NMR experiment. In situations that involved trace-mixture analysis, radiolabeling approaches were often used in conjunction with various formats of chromatographic separation. 

In 2002, through the use of nuclear magnetic resonance (NMR) and mass spectrometry/mass spectrometry (MS/MS) analysis, the planar and partial stereostructure of a SAAF from the egg-conditioning medium of C. intestinalis w s elucidated to be a previously uncharacterized sulfated steroid 3,4,7,26-tetrahydroxycholestane-3,26-disulfate (30).73 Its structure was deduced from only 4p.g (6 nmol) of sample. Thus, SAAF may represent the smallest amount of sample used in the structure elucidation of novel nonpeptidic or nonoligosaccharide natural products.74... 

In general, any analytical equipment or procedure used in the field of natural products chemistry and environmental engineering is also helpful in aroma analysis 64,65 The history and principles of such art are described in detail elsewhere and will not be featured here. Gas chromatography (GC), GC-mass spectrometry (MS), and nuclear magnetic resonance (NMR) are the most frequently used techniques along with rather specialized setups such as proton transfer reaction-mass spectrometry66 (PTR-MS) used in retronasal aroma analysis (see Chapters 9.02, 9.06, 9.10-9.11). 

The solid catalyst was recovered by filtration on fritted glass and washed with ethyl acetate. The solution was analyzed by gas phase chromatography, and the nature of the final products was confirmed by a complete spectroscopic analysis (infrared, nuclear magnetic resonance, mass spectrometry). 

Yang Z. Online hyphenated liquid chromatography-nuclear magnetic resonance spectroscopy-mass spectrometry for drug metabolite and nature product analysis. J Pharm Biomed Anal 2006 40 516-527. 

Miraziridine A 7 is a pentapeptide natural product isolated from the marine sponge Theonella aff. mirabilis in Japan in 2000 [3], It was also isolated 12 years later from the red sea sponge Theonella swinhoei [4], Miraziridine A inhibits cathepsin B with an IC50 value of 1.4 pg/ml. The sequencing of the amino acid residues and the absolute stereochemistry of each residue were achieved by a combination of Marfey analysis and nuclear magnetic resonance (NMR) data and resulted in the following sequence (2/ ,3J )-aziridine-2,3-dicarboxylic acid (Azd) (CO)/L-leucine (Leu) (NH), Leu (CO)/(35,45)-statine (Sta) (NH), Sta (CO)/(5)-a-aminobutyric acid... 

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