Synthesis and Preliminary Biological Evaluation of ¹⁸F Labeled Styryl Pyrimidine Derivatives as Aβ-Imaging Agents for Alzheimer’s Disease

Two styryl pyrimidine derivatives substituted by p-tosyloxymethyl, Boc-SPm2-OTs and Boc-SPm5-OTs, were designed and successful synthesized, which were labeled by ¹⁸F to prepared ¹⁸F-SPm2 and ¹⁸F-SPm5 by nucleophilic substitution. The radiochemical purities of both ¹⁸F-SPm2 and ¹⁸F-SPm5 were more than 99%. Both ¹⁸F-SPm2 and ¹⁸F-SPm5 had ideal lipophilicity (LogP=1-2.5) and can maintaining stability in normal saline for over 3 h and can bind to Aβ selectively, but both ¹⁸F-SPm2 and ¹⁸F-SPm5 displayed less binding affinity (the K_i values were 246.6 nmol/L and 318.2 nmol/L, respectively). The results of biodistribution in mice demonstrated that both ¹⁸F-SPm2 and ¹⁸F-SPm5 showed relatively high initial brain uptake, with slow washout from normal brain and obvious defluorination in vivo. In conclusion, both ¹⁸F-SPm2 and ¹⁸F-SPm5 might not be ideal Aβ imaging agents, and further modifications were needed to improve the disadvantages.