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Ascorbigen A-NMR identification.

Vladimír Sychrovský1, David Šaman1, Radovan Fiala2

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|July 2, 2019
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Summary

This study unambiguously determined the atomic connectivity of ascorbigen A for the first time using advanced NMR techniques. The confirmed structure aligns with previous suggestions, advancing our understanding of this important metabolite.

Keywords:
13C NMR13C-13C coupling constants13C-1H coupling constants1H NMR1H-1H coupling constantsNMRNOEnatural productrotamersstereochemistry

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Area of Science:

  • Organic Chemistry
  • Metabolomics
  • Structural Elucidation

Background:

  • Ascorbigen A is an important metabolite with an incompletely defined structure.
  • Previous structural suggestions for ascorbigen A were made in 1966.
  • Unambiguous determination of ascorbigen A's atomic connectivity is crucial for understanding its biological role.

Purpose of the Study:

  • To unambiguously determine the complete atomic connectivity of ascorbigen A.
  • To confirm the stereochemistry of ascorbigen A using spectroscopic and computational methods.
  • To validate the previously proposed structure of ascorbigen A.

Main Methods:

  • Two-dimensional Nuclear Overhauser Effect SpectroscopY (2D INADEQUATE) for carbon-carbon connectivity.
  • Correlation SpectroscopY (COSY) and gradient Heteronuclear Single Quantum Coherence (gHSQC) for C-C and C-H bond identification.
  • Proton Nuclear Magnetic Resonance (1H NMR) and Density Functional Theory (DFT) calculations for structural and stereochemical analysis.

Main Results:

  • Complete atomic connectivity of ascorbigen A was established for the first time.
  • The derived structure, 3-((1H-indol-3-yl)methyl)-3,3a,6-trihydroxytetrahydrofuro[3,2-b]furan-2(5H)-one, confirmed the 1966 proposal.
  • DFT calculations and Nuclear Overhauser Effect (NOE) measurements helped elucidate the stereochemistry, identifying two potential isomers, with one excluded on synthetic grounds.
  • Rotational flexibility and solvent model limitations impacted detailed DFT NMR interpretation.

Conclusions:

  • The structure of ascorbigen A has been unambiguously determined and confirmed.
  • The study provides a detailed stereochemical assignment for ascorbigen A.
  • This work enhances the understanding of ascorbigen A's chemical structure and properties.