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Updated: Jun 11, 2026
![Radiosynthesis of 1-(2-[18F]Fluoroethyl)-L-Tryptophan using a One-pot, Two-step Protocol](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F63025.jpg&w=3840&q=50)
Radiosynthesis of 1-(2-[18F]Fluoroethyl)-L-Tryptophan using a One-pot, Two-step Protocol
Published on: September 21, 2021
Fluorinated Tryptophan Derivatives for Photo-CIDNP NMR.
Anton Schmidt1, Magdalena J Faber1, Audrey Ayekoi1
1Institute of Physical Chemistry, University of Freiburg, Freiburg 79104, Germany.
Fluorinated amino acids, like fluorinated tryptophan, show promise for protein studies using photochemically induced dynamic nuclear polarization (photo-CIDNP) NMR. This research establishes methods for their use, overcoming previous limitations with specific photosensitizers.
Area of Science:
- Biophysical Chemistry
- Magnetic Resonance Spectroscopy
- Protein Science
Background:
- Fluorinated amino acids offer unique insights into protein environments and radical pair dynamics via Nuclear Magnetic Resonance (NMR).
- Photochemically induced dynamic nuclear polarization (photo-CIDNP) NMR is a powerful technique for studying radical intermediates.
- Limited data exists for fluorinated tryptophan derivatives in photo-CIDNP, unlike fluorinated tyrosine.
Purpose of the Study:
- To establish the utility of fluorinated tryptophan derivatives for photo-CIDNP NMR studies.
- To investigate and overcome challenges associated with using flavin mononucleotide (FMN) as a photosensitizer with fluorinated tryptophans.
- To explore the application of these probes in protein studies.
Main Methods:
- Analysis of photo-CIDNP properties of fluorinated tryptophan derivatives in solution.
- Utilizing geminate photo-CIDNP to probe hyperfine couplings of 1H and 19F nuclei.
- Employing time-resolved photo-CIDNP to study microsecond kinetics of polarization.
- Comparing fluorescein and flavin mononucleotide (FMN) as photosensitizers.
Main Results:
- Identified photochemical reactions between FMN and fluorinated tryptophans causing 19F resonance broadening.
- Demonstrated that fluorescein can be used as an alternative photosensitizer, avoiding broadening.
- Characterized hyperfine couplings for 4-, 5-, 6-, and 7-fluorotryptophan radicals.
- Observed distinct microsecond kinetic evolutions for 19F and 1H polarization in 6-fluorotryptophan radicals due to paramagnetic relaxation differences.
Conclusions:
- Fluorinated tryptophan derivatives are viable probes for photo-CIDNP NMR, with fluorescein as a suitable photosensitizer.
- Understanding radical kinetics and relaxation is crucial for interpreting 19F and 1H photo-CIDNP data.
- This work provides a foundation for incorporating and studying fluorinated tryptophans in proteins using photo-CIDNP NMR.
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