Improved synthesis of 2′-deoxy-2′-[18F]-fluoro-1-β-d-arabinofuranosyl-5-iodouracil ([18F]-FIAU)

An improved synthesis of 2′-[18F]-fluoro-2′-deoxy-1-β-d-arabinofuranosyl-5-iodouracil ([18F]-FIAU) has been developed. The method utilizes trimethylsilyl trifluoromethanesulfonate (TMSOTf) catalyzed coupling of 2-deoxy-2-[18F]-fluoro-1,3,5-tri-O-benzoyl-d-arabinofuranose with 2,4-bis(trimethylsilyloxy)-5-iodouracil to yield the protected dibenzoyl-[18F]-FIAU. Dibenzoyl-[18F]-FIAU was deprotected with sodium methoxide to yield a mixture of α- and β-anomers in a ratio of 1:1, which were purified by HPLC. The procedure described in this article eliminates the need for HBr activation of the sugar prior to coupling with silylated iodouracil and is suitable for automation. The total reaction time was about 110 min, starting from [18F]-fluoride. The average isolated yield of the required β-anomer was 10±6% (decay corrected) with average specific activity of 125 mCi/μmol.