Radiosynthesis of 1-[18F]fluoroethyl-L-tryptophan as a novel potential amino acid PET tracer

18F labeled natural amino acids have been introduced as promising tumor imaging agents. A novel [18F]fluoro amino acid analog 1-[18F]fluoroethyl-L-tryptophan (1-[18F]FETrp) was designed and synthesized by a two-pot three-step procedure, including the synthesis of 1-[18F]fluoro-2- (tosyloxy)ethane, the [18F]fluoroethylation of the precursor N-Boc-L-tryptophan ethyl ester and following the deprotection of the tert-butoxycarbonyl and ethyl ester protecting groups. 1-[18F]FETrp was resulted in 0.9±0.2% (n=5) radiochemical yields (no decay corrected) by HPLC purification, within a total synthesis time of 65 min. The radiochemical purity of 1-[18F]FETrp was 95–97%. The radiosynthetic method needs to be further optimized to get a satisfying radiochemical yield.

► We designed and synthesized the novel amino acid analog 1-[19F]FETrp.
► We radiosynthesized 1-[18F]FETrp using the two-pot three-step procedure.
► The total synthesis time was 65 min and the yield was very low.
► The synthetic strategy via [18F]FCH2CH2OTs needs to be optimized or changed.