18 F-Trifluoromethylation of Unmodified Peptides with 5- 18 F-(Trifluoromethyl)dibenzothiophenium Trifluoromethanesulfonate.

The 18 F-labeling of 5-(trifluoromethyl)-dibenzothiophenium trifluoromethanesulfonate, commonly referred to as the Umemoto reagent, has been accomplished applying a halogen exchange 18 F-fluorination with 18 F-fluoride, followed by oxidative cyclization with Oxone and trifluoromethanesulfonic anhydride. This new 18 F-reagent allows for the direct chemoselective 18 F-labeling of unmodified peptides at the thiol cysteine residue.