18F-Fluorothiols: A New Approach To Label Peptides Chemoselectively as Potential Tracers for Positron Emission Tomography

[18F]Fluorothiols are a new generation of peptide labeling reagents. This article describes the preparation of suitable methanesulfonyl precursors and their use in no-carrier-added radiosyntheses of 18F-fluorothiols. The preparations of (3-[18F] fluoropropylsulfanyl)triphenylmethane, (2-{2-[2-(2-[18F]fluoroethoxy)ethoxy]ethoxy}ethylsulfanyl)triphenylmethane, and 4[18F]fluoromethyl-N-[2-triphenylmethanesulfanyl)ethyl]benzamide starting from the corresponding methanesulfonyl precursors were investigated. Following the removal of the triphenylmethane protecting group, the 18F-fluorothiols were reacted with the N-terminal chloroacetylated model peptide ClCH2C(O)-LysGlyPheGlyLys. The corresponding radiochemical yields of 18Flabeled isolated model peptide, decay-corrected to 18F fluoride, were 10%, 32%, and 1%, respectively. These results indicate a considerable potential of 18F-fluorothiols for the chemoselective labeling of peptides as tracers for positron emission tomography (PET).