18F-FAC (1-(2'-deoxy-2'-[18F]fluoro-β-D-arabinofuranosyl)-cytosine) is an important 2'-fluoro-nucleoside-based positron emission tomography (PET) tracer that has been used for in vivo prediction of response to the widely used cancer chemotherapy drug gemcitabine. Previously reported synthetic routes to 18F-FAC have relied on early introduction of the 18F radiolabel prior to attachment to protected cytosine base. Considering the 18F radiochemical half-life (110 min) and the technical challenges of multi-step syntheses on PET radiochemistry modular systems, late-stage radiofluorination is preferred for reproducible and reliable radiosynthesis with in vivo applications. Herein, we report the first late-stage radiosynthesis of 18F-FAC. Cytidine derivatives with leaving groups at the 2'-position are particularly prone to undergo anhydro side-product formation upon heating because of their electron density at the 2-carbonyl pyrimidone oxygen. Our rationally developed fluorination precursor showed an improved reactivity-to-stability ratio at elevated temperatures. 18F-FAC was obtained in radiochemical yields of 4.3–5.5% (n = 8, decay-corrected from end of bombardment), with purities ≥98% and specific activities ≥63 GBq/µmol. The synthesis time was 168 min.
18F-FAC(1-(2'-脱氧-2'-[18F]
氟-β-D-阿糖
呋喃糖基)-
胞嘧啶)是一种重要的基于2'-
氟核苷的正电子发射断层扫描(PET)示踪剂,已用于预测体内对广泛使用的抗癌化疗药物
吉西他滨的反应。先前报道的18F-FAC合成路线依赖于在保护的
胞嘧啶基团连接之前早期引入18F放射性标记。考虑到18F放射
化学半衰期(110分钟)和PET放射
化学模块系统中多步骤合成的技术挑战,优选晚期放射
氟化以实现可重复且可靠的体内应用放射合成。在此,我们报道了18F-FAC的首次晚期放射合成。由于其在2-羰基
嘧啶酮氧上的电子密度,在加热时,在2'-位置具有离去基团的
胞嘧啶衍
生物特别容易发生脱
水副产物的形成。我们合理开发的
氟化前体在升高的温度下显示出改进的反应性-稳定性比。18F-FAC的放射
化学产率为4.3-5.5%(n = 8,从轰击结束衰减校正),纯度≥98%,比活性≥63 GBq/µmol。合成时间为168分钟。