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NMR Spectrum and 13C Label

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I need some help with this challenging question:
13C-NMR spectroscopy was used to detect (13)C-label accumulation in cerebral metabolites following the intravenous infusion of [1,6-(13)C]-glucose (Glc). The (1)H- [(13)C]-NMR method yielded high-quality (1)H-[(13)C]-NMR spectra. As a result, the (13)C labeling of [4-(13)C]-glutamate (Glu) and [4-(13)C]-glutamine (Gln) could be detected. The formation of [n-(13)C]-Glu, [n-(13)C]-Gln (n = 2 or 3), [2-(13)C]-aspartate
(Asp), [3-(13)C]-Asp, [3-(13)C]-alanine (Ala), and [3-(13)C]-lactate (Lac) was also
observed to be reproducible. For 2 of the above metabolites (your choice), show by means of tracing the path of the 13C label, that the NMR results are biochemically plausible.

Reference for this Problem: (Magn. Reson. Med., 49(1):37-46, 2003 - available online as a tool. I found this to help explain NMR spec).

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Solution Preview

13C-NMR spectroscopy was used to detect (13)C-label accumulation in cerebral
metabolites following the intravenous infusion of [1,6-(13)C]-glucose (Glc).

The (1)H- [(13)C]-NMR method yielded high-quality (1)H-[(13)C]-NMR spectra. As a result, the (13)C labeling of [4-(13)C]-glutamate (Glu) and [4-(13)C]-glutamine (Gln) could be detected.

The formation of [n-(13)C]-Glu, [n-(13)C]-Gln (n = 2 or 3), [2-(13)C]-aspartate
(Asp), [3-(13)C]-Asp, [3-(13)C]-alanine (Ala), and [3-(13)C]-lactate (Lac) was also
observed to be reproducible.

For 2 of the above metabolites (your choice), show by means of tracing the path of the 13C label, that the NMR results are biochemically plausible.

===========================================

Response:

First of all, this question is a lot simpler than it looks. All the nmr mumbo-jumbo is not all that relevant. The real issue is the labelling and tracing of labelled carbons. That's what's relevant. Therefore, that's all we focus on, okay?

Let's start with a simple one.

How to go from glucose to ...

Solution Summary

This in-depth solution explains the transformation of glucose to alanine and glucose to lactate through the labeling of 13C in cerebral metabolites. All steps are clearly explained.

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See Also This Related BrainMass Solution

13C NMR and 1H NMR Equivalency of Carbons and Protons

Please see the attached file for the complete problems.

1. For the compound below tell how many signals you would expect the molecule to have in its normal, broadband decoupled 13C NMR spectra.

2. Identify the indicated sets of protons as unrelated, homotopic, enantiotopic, or diastereotopic.

3. For the compounds below tell how many types of nonequivalent protons there are.

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