Catalyst-free thia-Diels-Alder click reaction for the labeling of peptides for imaging applications

Abstract

A thia-Diels-Alder reaction between a phosphonodithioester and a highly reactive exocyclic diene for the chemoselective labeling of peptides under catalyst-free mild conditions is described. An efficient method to introduce the dithioester function into a model tripeptide was first developed and then applied to two bioactive peptides, PSMA and apelin-13. The tripeptide-dithioester was used to optimize the cycloaddition with dienes bearing fluorine-18 or a fluorophore. Then, the cycloaddition of the PSMA-dithioester with the ¹⁸F-diene led to a new PSMA-radiotracer, which was used for in vivo Positron Emission Tomography (PET) imaging. In the same way, a fluorescent apelin-13 probe was obtained from the apelin-dithioester and a squaraine-linked diene before beingused for in cellulo optical imaging.

GRAPHICAL ABSTRACT

Keywords:

• Click chemistry
• peptides
• dithioesters
• thia-Diels-Alder
• fluorine-18
• fluorophores

Acknowledgments

This work is part of the Interdisciplinary Thematic Institutes IMS and InnoVec, ITI 2021-2028 program of the University of Strasbourg, CNRS, and Inserm, supported by IdEx Unistra (ANR-10-IDEX-0002) and SFRI-STRAT’US project (ANR-20-SFRI-0012). T.M. was supported by a fellowship from the ENS Paris-Saclay. We thank Dr. Nicolas Humbert (LBP, UMR 7021) for his expertise on the spectrophotometers and fluorometers, and the platforms PACSI (GDS 3670), PIQ-QuESt (Faculty of Pharmacy, Strasbourg), and CYRCé for technical support.