18F-fluorothiols:: A new approach to label peptides chemoselectively as potential tracers for positron emission tomography

[F-18]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 F-18-fluorothiols. The preparations of (3- [F-18] fluoropropylsulfanyl)triphenylmethane, (2-12- [2-(2- [F-18] fluoroethoxy)ethoxy]ethoxy}ethylsulfanyl)triphenylmethane, and 4-[F-18]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 CICH2C(O)-LysGlyPheGlyLys. The corresponding radiochemical yields of F-18-labeled isolated model peptide, decay-corrected to F-18 fluoride, were 10%, 32%, and 1%, respectively. These results indicate a considerable potential of F-18-fluorothiols for the chemoselective labeling of peptides as tracers for positron emission tomography (PET).