Effect of electron withdrawing groups at α-position of nitrophenyl styrene derivatives on nucleophilic aromatic 18F-fluorination

1046 Objectives Several drug entities contain α-carbonyl-β-phenyl styrene moieties and display nM affinity to their target (1-4). Developing PET imaging agents containing such moiety to target disease would be significant. Herein, we explored single-step fluorination in presence of an electron withdrawing group (EWG) at α-position to styrene that is two carbons away from the aromatic ring. Methods Aqueous F-18 eluted from QMA cartridge (K2CO3/K222) was dried azeotropically and reacted with substituted nitro-styrenes containing different electron withdrawing group α-position. The reaction was followed using TLC and HPLC. The reaction kinetics was studied at different reaction temperatures, reaction time, and precursor quantity used. Results The radiochemical yield (RCY) for the select compounds is shown in Table. The RCY were significantly higher for styrene entities containing ethyl ester and ketone as compared to that for the aldehyde, at α- position . In presence of strong EWG such as NO2 at α-position and leaving group either at ortho- or para- position of phenyl group, no product formation was obtained. In addition, no product formation occurred when p-nitrophenyl ester was present at α-position of the styrene. Conclusions We obtained high RCY for three of the test compounds containing EWG at α-positions of styrene. However, this reaction failed when nitro or p-nitrophenyl ester groups were present as EWG at the α-position of styrene. We hypothesize that in such reactions, inductive as well as resonance effects play crucial role. These results suggest further optimization of reaction conditions and perhaps including microwave heating to achieve favorable reaction kinetics.