[18F]FTC-146 was introduced as a very potent and selective sigma-1 receptor radioligand, which has shown promising application as an imaging agent for neuropathic pain with positron emission tomography. In line with a multi-laboratory project on animal welfare, we chose this radioligand to investigate its potential for detecting neuropathic pain and tissue damage in tumor-bearing animals. However, the radiochemical yield (RCY) of around 4–7% was not satisfactory to us, and efforts were made to improve it. Herein, we describe an improved approach for the radiosynthesis of [18F]FTC-146 resulting in a RCY, which is sevenfold higher than that previously reported. A tosylate precursor was synthesized and radio-fluorination experiments were performed via aliphatic nucleophilic substitution reactions using either K[18F]F-Kryptofix®222 (K2.2.2)-carbonate system or tetra-n-butylammonium [18F]fluoride ([18F]TBAF). Several parameters affecting the radiolabeling reaction such as solvent, 18F-fluorination agent with the corresponding amount of base, labeling time, and temperature were investigated. Best labeling reaction conditions were found to be [18F]TBAF and acetonitrile as solvent at 100°C. The new protocol was then translated to an automated procedure using a FX2 N synthesis module. Finally, the radiotracer reproducibly obtained with RCYs of 41.7 ± 4.4% in high radiochemical purity (>98%) and molar activities up to 171 GBq/μmol.
[18F]FTC-146是一种非常有效且具有选择性的sigma-1受体放射性
配体,它作为正电子发射断层扫描神经病理性疼痛成像剂的应用前景广阔。为了配合一个有关动物福利的多实验室项目,我们选择了这种放射性
配体来研究它在检测肿瘤动物的神经病理性疼痛和组织损伤方面的潜力。然而,4-7%左右的放射
化学收率(RCY)并不能令我们满意,因此我们一直在努力改进。在此,我们介绍了一种改进的[18F]FTC-146 辐射合成方法,其 RCY 比以前报道的方法高出七倍。我们合成了一种
对甲苯磺酸盐前体,并使用 K[18F]F-Kryptofix®222 (K2.2.2)-carbonate 体系或[18F]
氟化四正丁基
铵([18F]TBAF)通过脂肪族亲核取代反应进行了放射性
氟化实验。研究了影响放射性标记反应的几个参数,如溶剂、18F-
氟化剂与相应量的碱基、标记时间和温度。结果发现,[18F]TBAF 和
乙腈作为溶剂,温度为 100°C,是最佳的标记反应条件。然后,使用 FX2 N 合成模块将新方案转化为自动程序。最后,放射性示踪剂以高放射
化学纯度(>98%)和最高 171 GBq/μmol 的摩尔活度重复获得,RCYs 为 41.7 ± 4.4%。