# Development of an Efficient 18F labeling technology based on tetrazine trans-cyclooctene ligation

> **NIH NIH R01** · UNIV OF NORTH CAROLINA CHAPEL HILL · 2024 · $643,360

## Abstract

Abstract:
Proposed is the development of readily available tools for radiochemistry based on tetrazine ligation— a
bioorthogonal reaction with rapid kinetics that has been studied for over a decade as a uniquely powerful tool for
radiochemical labeling of biomolecules. Limitations in accessing tetrazine and trans-cyclooctene (TCO) labeling
precursors with appropriate kinetic and physicochemical properties have prevented the broader application of
this technology. This proposal builds on several technological innovations in reaction chemistry that have been
developed in the groups of PIs, including a methodology for introducing 18F into aromatic molecules via
photocatalysis via C-H activation or aromatic substitution, a new methodology for the practical and scalable
synthesis of trans-cyclooctenes with favorable kinetic and physiochemical properties, and new methodologies
for the preparation of functionalized tetrazines. Through this collaborative technology proposal, our groups will
leverage these methodologies for the development of new tools for the efficient radiolabeling of proteins in site-
selective fashion and the application of these tools in vitro. In Aim 1, we will develop improved methods for the
synthesis of 18F-labeled trans-cyclooctenes with balanced reactivity, hydrophilicity and stability. Late-stage
photoisomerization will also be used to obtain highly reactive 18F-TCOs, and we will develop methodology for
the site-selective attachment to the C-terminus of cancer-targeting proteins. In Aim 2, a rapid and mild method
for the preparation of 18F-labeled tetrazine reporters will be developed using photoredox radiofluorination
reactions for PET probe construction. In Aim 3, we will validate the newly developed 18F-TCOs and 18F-tetrazines
using the hydrophilic FAPI ligand, the hydrophobic SR142948A, and proteins. The brain permeability of the 18F-
TCO/tetrazine reporters will also be evaluated in normal rats. Because this application focuses solely on the
development of 18F-labeling technologies, the studies in Aim 3 are primarily intended to provide important
feedback to Aims 1-2, which will result in the design of 18F-TCOs and 18F-tetrazines of high utility to the broader
radiolabeling community (in other words, comprehensive evaluation/characterization of specific probes will not
be performed in this application). In summary, we are developing a general labeling toolbox to generate 18F
labeled PET agents. We aim to develop labeling precursors that can be readily commercialized, so that the
developed technologies will be widely used as efficient and simple labeling methods to modify biologically active
small molecules/peptides/proteins/drugs, which could have a significant impact on medical imaging, drug
discovery and development.

## Key facts

- **NIH application ID:** 10788977
- **Project number:** 1R01CA287184-01
- **Recipient organization:** UNIV OF NORTH CAROLINA CHAPEL HILL
- **Principal Investigator:** JOSEPH M FOX
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $643,360
- **Award type:** 1
- **Project period:** 2023-12-05 → 2027-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10788977

## Citation

> US National Institutes of Health, RePORTER application 10788977, Development of an Efficient 18F labeling technology based on tetrazine trans-cyclooctene ligation (1R01CA287184-01). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10788977. Licensed CC0.

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