Novel Method for Radiolabeling and Dimerizing Thiolated Peptides Using ¹⁸F-Hexafluorobenzene

Abstract

Hexafluorobenzene (HFB) reacts with free thiols to produce a unique and selective perfluoroaromatic linkage between two sulfurs. We modified this chemical reaction to produce dimeric 18F-RGD-tetrafluor-obenzene (TFB)-RGD, an integrin αvβ3 receptor ligand. 18F-HFB was prepared by a fluorine exchange reaction using K18F/K2.2.2 at room temperature. The automated radiofluorination was optimized to minimize the amount of HFB precursor and, thus, maximize the specific activity. 18F-HFB was isolated by distillation and subsequently reacted with thiolated c(RGDfk) peptide under basic and reducing conditions. The resulting 18F-RGD-TFB-RGD demonstrated integrin receptor specific binding, cellular uptake, and in vivo tumor accumulation.18F-HFB can be efficiently incorporated into thiol-containing peptides at room temperature to provide novel imaging agents.

Arylation Chemistry for Bioconjugation

“…Cysteine perfluoroarylation was also explored for introducing 18 Fr adiolabels into biomolecules.I n2 015, Chen synthesized perfluoroaryl-linked dimers of an integrin-binding peptide using 18 F-hexafluorobenzene generated from an 18 Fe xchange with an on-radiolabeled hexafluorobenzene ( Figure 18). [125] The 18 F-hexafluorobenzene reacted with at hiol-containing cyclic peptide (cyclo(RGDfK)) that binds to cell surface integrin. After a2 0min reaction at room temperature,a pproximately 50 %c onversion to the desired 18 F-labeled peptide was observed.…”

Using 19F NMR and two‐level factorial design to explore thiol‐fluoride substitution in hexafluorobenzene and its application in peptide stapling and cyclisation

“…In principle, the extent of substitution can be ordered by careful control of the reagents nucleophilicity and the reaction conditions and is summarized in Figure 1. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] In general, there are few approaches reported to selectively afford mono-substitution of HFB, while disubstitution is generally obtained under mild conditions at room temperature. Stronger bases, longer reaction times, higher temperatures and a greater concentration of thiols can orient the reaction toward tetrasubstitution while hexa-substitution can be achieved with even harsher conditions and a larger excess of thiols.…”

Novel chemoselective 18F-radiolabeling of thiol-containing biomolecules under mild aqueous conditions

“…1 The incorporation of a 18 F label into peptides and proteins is most commonly achieved by modifications of lysine (Lys) or cysteine (Cys) residues using a prosthetic group approach. 2 Prosthetic groups are small, bifunctional molecules, which can be readily radiolabeled with 18 F and subsequently conjugated selectively to the molecule of interest. In comparison to Lys, Cys residues are found less abundant in proteins, which permits conjugation chemistry in a more controlled fashion.…”