Synthesis and evaluation of fluoroethyl cyclofenil analogs: Models for potential estrogen receptor imaging agent

Cyclofenil analogs (2a–2f) and their fluorine-containing derivatives (3a–3f) were synthesized and evaluated as candidate ligands for positron emission tomography (PET) imaging of estrogen receptors. Most of them show relatively high binding affinities comparable with estradiol (E2). (4-Fluoroethoxyphenyl)-(4-hydroxyphenyl) methylenecyclopentane (3a) showed both the highest binding affinity for ERs (88.6 for ERβ, 13.8 for ERα) and highest β/α ratio (β/α for 6.4-fold). The radioactive compound [18F]3a was prepared via displacement of the corresponding mesylate precursor 4 with [18F]fluoride (18F: β+; 96.7%, T1/2 = 109.8 min). The biodistribution studies in immature female SD rats demonstrated that the uptake in the uterus and ovaries were 1.358 ± 0.089% ID/g, 1.439 ± 0.214% ID/g, respectively, both of the ratios of uterus/blood and ovaries/blood was less than 2:1. Micro-PET imaging of immature female SD rats has also been reported.