Evaluation of fluorine-18-labeled alkylating agents as potential synthons for the labeling of oligonucleotides

Six fluorine-18-labeled alkylating agents were selected as potentially suitable synthons for the labeling of antisense oligonucleotides. The selected synthons were evaluated in a model reaction with the monomer adenosine 5′-O-thiomonophosphate. Of these synthons, α-bromo-α′-[18F]fluoro-m-xylene and N-(4-[18F]fluorobenzyl)-2-bromoacetamide were found to be the most promising. Labeling with the former synthon was less complicated and time consuming and gave higher uncorrected overall yields. The latter synthon required smaller amounts of the costly precursor to achieve acceptable labeling yields.