Propargyl 4-[F]fluorobenzoate: A Putatively More Stable Prosthetic group for the Fluorine-18 Labeling of Biomolecules via Click Chemistry

Abstract

Faster and more efficient approaches for radiolabeling biomolecules with short-lived (18)F are in dire need. Herein we report a new (18)F-labeled prosthetic group containing an acetylene function that permits the labeling of biomolecules via click chemistry. This template, propargyl 4-[(18)F]fluorobenzoate ([(18)F]PFB) was synthesized from a quaternary salt precursor in decay-corrected radiochemical yields of 58 +/- 31%. Several model compounds containing an azide moiety-benzyl azide, two lysine derivatives and a transglutaminase-reactive peptide-were labeled using [(18)F]PFB via a click reaction in decay-corrected radiochemical yields of 88 +/- 4%, 79 +/- 33%, 75 +/- 5%, and 37 +/- 31%, respectively. Our results suggest that the novel agent [(18)F]PFB is a potentially useful template for the (18)F-labeling of biomolecules via click chemistry.

Fig. (1)

A typical HPLC profile of the reaction mixture from the synthesis of propargyl 4-[¹⁸F]fluorobenzoate ([¹⁸F]1).

Fig. (2)

Radio thin layer chromatography profile of the reaction mixture from the synthesis of propargyl 4-[¹⁸F]fluorobenzoate ([¹⁸F]1).

Fig. (3)

HPLC of reaction mixture from the preparation of [¹⁸F]1 before and after treatment with polystyrene-bound sulfonic acid. Reaction mixture was reconstituted in THF as described in the text and a 10 :L aliquot was injected onto HPLC (left panel). Then the THF solution was treated with the sulfonic acid derivative for 1 h and 10 :L aliquot was injected again (right panel). Note the disappearance of the peak corresponding to compound 2 pointed out by arrows.

Fig. (4)

HPLC profile of the click reaction between azidohexanoyl-YQSIYVPDI and [¹⁸F]1.

Scheme 1

Synthesis of unlabeled and ¹⁸F-labeled propargyl 4-fluorobenzoate (1) and its quaternary salt precursor, 4-propargyloxycarbonyl N, N, N-trimethylanilinium trifluoromethanesulfonate (3).

Scheme 2

Synthesis of unlabeled and ¹⁸F-labeled (1-benzyl-1H-1,2,3-triazol-4-yl)methyl 4-fluorobenzoate.

Scheme 3

Synthesis of 6-amino-2-(4-azidobenzamido)hexanoic acid (7) and, labeled and unlabeled 1-[4-(5-amino-1-carboxy-pentylcarbamoyl)-phenyl]-1H-[1,2,3]triazol-4-ylmethyl 4-fluorobenzoate (8).

Scheme 4

Synthesis of 6-amino-2-(6-azidohexamido)hexanoic acid (11) and, labeled and unlabeled 1-[5-(5-amino-1-carboxy-pentylcarbamoyl)-pentyl]-1H-[1,2,3]triazol-4-ylmethyl 4-fluorobenzoate (12).

Scheme 5

Synthesis of labeled and unlabeled 14.