[18F] Azadibenzocyclooctyne ([18F]ADIBO): A biocompatible radioactive labeling synthon for peptides using catalyst free [3+2] cycloaddition

N-Terminally azido-modified peptides were labeled with the novel prosthetic labeling synthon [F-18]azadibenzocyclooctyne ([F-18]ADIBO) using copper-free azide-alkyne [3+2]-dipolar cycloaddition in high radiochemical yields (RCYs). F-18-Labeled [F-18]ADIBO was prepared by nucleophilic substitution of the corresponding tosylate in 21% overall RCY (EOB) in a fully automated synthesis unit within 55 min. [F-18]ADIBO was incubated with azide-containing peptides at room temperature in the absence of toxic metal catalysts and the formation of the triazole conjugate was confirmed. Finally, the azide-alkyne [3+2]-dipolar cycloaddition was shown to proceed with 95% radiochemical yield in ethanol within 30 min, allowing for a development of a kit-like peptide labeling approach with [F-18]ADIBO. (C) 2011 Elsevier Ltd. All rights reserved.