Reproducible methods for [18F]radiolabeling of biological vectors are essential for the development of new [18F]radiopharmaceuticals. Molecules such as carbohydrates, peptides and proteins are challenging substrates that often require multi-step indirect radiolabeling methods. With the goal of developing more robust, time saving, and less expensive procedures for indirect [18F]radiolabeling of such molecules, our group has synthesized ethynyl-4-[18F]fluorobenzene ([18F]2, [18F]EYFB) in a single step (14 ± 2% non-decay corrected radiochemical yield (ndc RCY)) from a readily synthesized, shelf stable, inexpensive precursor. The alkyne-functionalized synthon [18F]2 was then conjugated to two azido-functionalized vector molecules via CuAAC reactions. The first ‘proof of principle’ conjugation of [18F]2 to 1-azido-1-deoxy-β-d-glucopyranoside (3) gave the desired radiolabeled product [18F]4 in excellent radiochemical yield (76 ± 4% ndc RCY (11% overall)). As a second example, the conjugation of [18F]2 to matrix-metalloproteinase inhibitor (5), which has potential in tumor imaging, gave the radiolabeled product [18F]6 in very good radiochemical yield (56 ± 12% ndc RCY (8% overall)). Total preparation time for [18F]4 and [18F]6 including [18F]F− drying, two-step reaction (nucleophilic substitution and CuAAC conjugation), two HPLC purifications, and two solid phase extractions did not exceed 70 min. The radiochemical purity of synthon [18F]2 and the conjugated products, [18F]4 and [18F]6, were all greater than 98%. The specific activities of [18F]2 and [18F]6 were low, 5.97 and 0.17 MBq nmol−1, respectively.
可重复的[18F]放射性标记
生物载体方法对于新型[18F]放射性药物的开发至关重要。
碳水化合物、肽和蛋白质等分子是具有挑战性的底物,通常需要多步骤间接放射性标记方法。为了开发更稳健、省时且成本更低的间接[18F]放射性标记方法,我们的研究小组在单一步骤中合成了
乙炔基-4-[18F]
氟苯([18F]2,[18F]EYFB),产率高达14±2%(未经衰变校正的放射
化学产率,ndc RCY),原料易于合成、稳定且成本低廉。然后通过
铜催化的
叠氮-炔环加成反应(Cu
AAC)将功能化的
炔烃前体[18F]2与两个功能化的
叠氮载体分子偶联。首次“原理验证”将[18F]2与1-
叠氮-1-脱氧-β-
D-吡喃葡萄糖苷(3)偶联,得到理想的放射性标记产物[18F]4,放射
化学产率非常优秀(76±4% ndc RCY,总体产率11%)。作为第二个例子,将[18F]2与潜在用于肿瘤成像的基质
金属蛋白酶抑制剂(5)偶联,得到放射性标记产物[18F]6,放射
化学产率非常好(56±12% ndc RCY,总体产率8%)。包括[18F]F−干燥、两步反应(亲核取代和Cu
AAC偶联)、两次高效
液相色谱纯化和两次固相萃取在内的总制备时间不超过70分钟。前体[18F]2及其偶联产物[18F]4和[18F]6的放射
化学纯度均超过98%。[18F]2和[18F]6的比活度较低,分别为5.97和0.17 MBq nmol−1。