Fluorine‐18 labelling of oligonucleotides: Prosthetic labelling at the 5′‐end using the N‐(4‐[18F]fluorobenzyl)‐2‐bromoacetamide reagent

Labelled oligonucleotides are new imaging tools to study gene expression at the nucleic acid and protein levels. We have previously developed a universal method to label oligonucleotides at their 3′-end with radiohalogens and particularly with fluorine-18, the most widely used positron-emitter, t1/2: 109.8 min. Using the same strategy, we herein report the fluorine-18 labelling of oligonucleotides at their 5′-end. A 18-mer 2′O-methyl modified oligoribonucleotide, bearing a phosphorothioate group at its 5′-end, was conjugated to our fluorine-18-labelled reagent N-(4-[18F]fluorobenzyl)-2-bromoacetamide. The whole synthetic procedure yielded up to 1 GBq of fluorine-18-labelled oligonucleotide with a specific radioactivity of 37–74 GBq/μmol in 160 min. Copyright © 2003 John Wiley & Sons, Ltd.