Design,Synthesis,and Preliminary Evaluation Of Sulfonyl Fluoride Derivative For PET Imaging β-Amyloid Plaques In Alzheimer’s Disease

Objective:[¹⁸F]BAY-94-9172,[¹⁸F]AV-45,and[¹⁸F]GE-067 were FDA approved positron emission tomography（PET）imaging radiotracer ofβ-amyloid plaques（Aβ）in Alzheimer’s disease（AD）.However,the radiochemical synthesis of the above three probes require multi-step reactions and complex procedure.Moreover,many clinical studies have found that the probes have high non-specific binding in the white matter of the human brain.The aim of this study is to use A novel ¹⁸F labeling method based on sulfuryl fluorine groups to modify the classical skeleton of Aβprobes,so as to obtain Aβ-PET probes with simple and rapid radiochemical synthesis and excellent imaging performance.Methods:The ¹⁸F-labeled Sulfur Fluoride Exchange（Su FEx）method is based on ¹⁹F/¹⁸F isotope exchange of sulfuryl fluoride groups.Three pairs of novel Aβimaging agents,SFA 1-6（Sulfur Fluorideβ-Amyloid）,were designed.Computer simulation was used to perform molecular docking between compounds and Aβprotein to explore their binding modes.The target compounds were synthesized by organic chemistry,and their structures were characterized by ¹H-NMR,¹³C-NMR,¹⁹F-NMR and High-resolution mass spectrometry（HRMS）.The purity of the compounds was identified by High Performance Liquid Chromatography（HPLC）.The ¹⁸F-labeling conditions were verified by manual radiochemical synthesis and optimized,and an automatic synthesis process based on Allin One radiochemical synthesis module was established.The affinity of the probe with Aβwas preliminarily verified by in vitro fluorescence staining experiment and competitive binding experiment of Aβ_1-42 protein based on brain tissue sections of AD transgenic mice.The in vivo biodistribution and Micro-PET/CT imaging of[¹⁸F]SFA 1-6were performed in wild-type mice to verify the ability of[¹⁸F]SFA 1-6 to penetrate the blood-brain barrier and other key pharmacokinetic properties.In vitro autoradiography was used to verify the affinity of the candidate compounds with Aβplaques in AD human brain tissue.Results:In molecular docking,all the six candidate compounds could effectively bind to the Aβprotein,and the binding sites were consistent with the classical probe[¹²⁵I]IMPY.The structure of the compounds was correct after characterization,and the purity of the target compounds was more than 95%verified by HPLC.Manual radiochemical synthesis showed that the ¹⁸F labeling reaction could be quickly completed（30 s）at room temperature（25℃）,and the product purification could be performed using a simple and time-efficient Solid-phase extraction（SPE）method.After optimizing the conditions of labeling reaction,an automatic synthesis process based on Allin One Radiochemical synthesis module was established,and the Radiochemical purity（RCP）of the products was greater than 95%.In vitro fluorescence staining showed that SFA 1-6 could specifically bind to Aβin brain tissue sections of AD transgenic mice.The competitive binding assay based on Aβ_1-42 protein showed high binding potency（3.53±0.39≤K_i≤42.0±4.24 n M）.In vivo biodistribution and Micro-PET imaging showed that[¹⁸F]SFA1-6 could penetrate the blood-brain barrier in wild-type mice.[¹⁸F]SFA 5-6 had higher initial Brain uptake values（3.65±0.9%and 5.07±0.1%ID/g,respectively）and exceptional brain kinetics(Brain uptake_{2 min}/Brain uptake_{60 min}=4.15 and 4.61,respectively).In vitro autoradiography demonstrated the affinity of the[¹⁸F]SFA 5-6 to Aβplaques in AD human brain tissues.Conclusion:The[¹⁸F]SFA series probes are simple,rapid,and easy to purify.They have high affinity with Aβand can effectively pass the blood-brain barrier.[¹⁸F]SFA 5-6 has better pharmacokinetic properties and imaging effect,and may be used as Aβ-PET probes for the detection of AD.