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

(18)F labeled natural amino acids have been introduced as promising tumor imaging agents. A novel [(18)F]fluoro amino acid analog 1-[(18)F]fluoroethyl-L-tryptophan (1-[(18)F]FETrp) was designed and synthesized by a two-pot three-step procedure, including the synthesis of 1-[(18)F]fluoro-2- (tosyloxy)ethane, the [(18)F]fluoroethylation of the precursor N-Boc-L-tryptophan ethyl ester and following the deprotection of the tert-butoxycarbonyl and ethyl ester protecting groups. 1-[(18)F]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-[(18)F]FETrp was 95-97%. The radiosynthetic method needs to be further optimized to get a satisfying radiochemical yield.