A facile automated synthesis of N‐succinimidyl 4‐[18F]fluorobenzoate ([18F]SFB) for 18F‐labeled cell‐penetrating peptide as PET tracer

A fully automated synthesis of N‐succinimidyl 4‐¹⁸F]fluorobenzoate (¹⁸F]SFB) was carried out by a convenient three‐step, one‐pot procedure on the modified TRACERlab FX_FN synthesizer, including ¹⁸F]fluorination of ethyl 4‐(trimethylammonium triflate)benzoate as the precursor, saponification of the ethyl 4‐¹⁸F]fluorobenzoate with aqueous tetrapropylammonium hydroxide instead of sodium hydroxide, and conversion of 4‐¹⁸F]fluorobenzoate salt (¹⁸F]FBA) to ¹⁸F]SFB treated with N,N,N′,N′‐tetramethyl‐O‐(N‐succinimidyl)uranium tetrafluoroborate (TSTU). The purified ¹⁸F]SFB was used for the labeling of Tat membrane‐penetrating peptide (containing the Arg‐Lys‐Lys‐Arg‐Arg‐Arg‐Arg‐Arg‐Arg‐Arg‐Arg‐Pro‐Leu‐Gly‐Leu‐Ala‐Gly‐Glu‐Glu‐Glu‐Glu‐Glu‐Glu‐Glu sequence, ¹⁸F]CPP) through radiofluorination of lysine amino groups. The uncorrected radiochemical yields of ¹⁸F]SFB were as high as 25–35% (based on ¹⁸F]fluoride) (n=10) with a synthesis time of～40 min. ¹⁸F]CPP was produced in an uncorrected radiochemical yields of 10–20% (n=5) within 30 min (based on ¹⁸F]SFB). The radiochemical purities of ¹⁸F]SFB and ¹⁸F]CPP were greater than 95%. Copyright © 2010 John Wiley & Sons, Ltd.