# Ionic Liquid Aided [11C]CO Fixation for Synthesis of 11C‐carbonyls

## TL;DR

A new ionic liquid helps capture radioactive carbon-11 for making PET imaging tracers more efficiently.

## Contribution

A novel method using an ionic liquid to improve [11C]CO fixation for radiotracer synthesis is introduced.

## Key findings

- The ionic liquid [P4442][Pen] effectively traps [11C]CO for radiotracer synthesis.
- The method enables automated radiosynthesis of Bruton's tyrosine kinase inhibitors like [11C]evobrutinib and [11C]ibrutinib.
- The approach facilitates the preparation of 11C-labeled amides, ureas, and carbamates.

## Abstract

Tributyl(ethyl)phosphonium oxopentenolate ([P4442][Pen]) is an ionic liquid developed to capture CO and has shown ability to catalyze carbonylation reactions in organic chemistry. Carbon‐11 (11C, t1/2=20.4 min) labeled CO is a highly versatile building block for the synthesis of positron emission tomography (PET) radiotracers that are applied for medical imaging. The use of [11C]CO is limited by its low solubility in organic solvents. Herein, we report a proof‐of‐concept study evaluating a new method to prepare 11C‐labeled amides, ureas and carbamates via reaction of [11C]CO in [P4442][Pen] and applied for fully automated radiosyntheses of Bruton's tyrosine kinase inhibitors, [11C]evobrutinib and [11C]ibrutinib.

Tributyl(ethyl)phosphonium oxopentenolate ([P4442][Pen]) is an ionic liquid used in a proof‐of‐concept study evaluating its utility to trap carbon‐11 (t1/2=20.4 min)‐labeled CO for preparation of amides, ureas and carbamates.