Labeling of peptides and proteins with ¹⁸F via click chemistry using a novel prosthetic group 4-[¹⁸F]fluoro-N-methyl-N-(prop-2-ynyl)benzenesulfonamide

Ziel/Aim:

The radiolabeling of peptides or proteins with the short-lived positron emitter ¹⁸F requires rapid and mild reaction conditions compatible with the structural and functional integrity of these biopolymers. Over the last two years several approaches have been published focusing on the application of copper(I)-mediated 1,3-dipolar [3+2]cycloaddition of azides and alkynes for labeling peptides with ¹⁸F. The peptides were functionalized with an azide- or alkyne group to be reacted with an appropriately ¹⁸F-labeled azide or alkyne, respectively. We report on the radiosynthesis of a novel alkine containing ¹⁸F-labeled prosthetic group having the advantage of a stable aromatic ¹⁸F-label and low lipophilicity caused from the sulfonamide backbone. First applications for click chemistry by labeling azide-functionalized phosphopeptides and human serum albumin (HSA) are demonstrated.

Methodik/Methods:

Two labeling precursors containing different leaving groups (nitro- and trimethylammoniumtriflate) and the reference substance were prepared by the reaction of N methylpropargylamine with the corresponding sulfonic acid chlorides. Radiofluorination was performed in a single step on an automated synthesizer. After purification on semi-preparative HPLC click reaction was performed with a phosphopeptide and the HSA protein. Peptide and protein have been modified with an azide linker. Click reaction occurs in the presence of copper(I) salts and in combination with different copper-chelating ligand systems.

Ergebnisse/Results:

The radiolabeled sulfonamide can be obtained in radiochemical yields of 19 % (d. c.) in high radiochemical purity of > 99 % after HPLC purification within 84 min. First promising results in labeling an azide modified phosphopeptide and protein via click chemistry gave labeling yields about 42 % for posphopeptides after semi-preparative HPLC and about 31 % for HSA after size exclusion chromatography.

Schlussfolgerungen/Conclusions:

The novel prosthetic group 4-[¹⁸F]fluoro-N-methyl-N-(prop-2-ynyl)benzenesulfonamide for peptide and protein labeling with ¹⁸F via click chemistry can be prepared in reasonable radiochemical yields and high radiochemical purity. Moreover, by this method for the first time click chemistry was successfully applied to the ¹⁸F-labeling of a phosphopeptide and a protein. The radiopharmacological investigation of the ¹⁸F-labeled phoshopeptides and HSA including metabolic stability, biodistribution and cell uptake studies is in progress.