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Organic Chemistry, Compound Detection 493

FIGURE 16 COSY NMR spectrum of stevioside (contour plot).

a decade since Moon and Richards at California Insti- serve only those protons that are attached to the labeled
tute of Technology and Hoult at Oxford demonstrated that carbons.
31
FT– P NMR spectroscopy is an effective probe of the in
vivo generation and utilization of phosphate-bond energy.
1
FTNMR spectroscopy has since been applied to the study J. H NMR “Polarimetry”
of many diverse systems, progressing from intact cells to
Optical purity of enantiomers is of great importance in
perfused organs to animals and man. In vivo FTNMR is
the chemistry of natural products, especially in the fields
noninvasive, and thus event-induced changes in the con-
of flavors, fragrances, and pheromones. Since odor recep-
centration of metabolites can be followed over a time pe- tors in mammals and in insects can discriminate between
riod. 31 P is by far the most widely used nucleus for bio-
enantiomers, it is important to know the enantiomeric
chemical FTNMR determinations, as the key metabolite,
composition of chiral molecules that impinge on these
ATP, adenosine diphosphate (ADP), creatine phosphate,
receptors.
and sugar phosphates, for example, all contain phospho-
Determination of the enantiomeric composition of nat-
rus. The NMR sensitivity of phosphorus is high (100%) ural semiochemicals by H NMR spectroscopy using a
1
13
and offers selectivity not obtained with nuclei such as C chiral lanthanide shift reagent is a rapid, accurate, and ion-
1
or H because it is not ubiquitous, but rather occurs pri-
destructive technique. It is also a quantitative method for
marily in cellular metabolites. Metabolic pathways are detection of adulteration of essential oils and oleoresins
now being followed by 31 P FTNMR. Techniques using
by synthetic racemic chemicals.
whole animals (or humans) require that the NMR mea-
surements be localized to a particular organ or to a certain
portion of the body. More recently is the application of K. Supersonic Jet Spectroscopy
FTNMR in the study of the metabolism of 13 C-labeled
drugs. The fate of the labeled carbons can be followed as Capillary column gas chromatography (GC) is the high-
a function of time using 13 C NMR spectroscopy. Also est resolution separation technique, but it is ultimately
new pulse sequences have now been developed to ob- limited by the volatility of the molecules in the sample.