Module-assisted one-pot synthesis of [18F]SFB for radiolabeling proteins

The need of reliable production of N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB), a versatile 18F-labeled prosthetic group for protein labeling, has increased dramatically due to the easy availability of proteins or their engineered derivatives for targeted molecular imaging. A module-assisted radiosynthesis of [18F]SFB was developed using a three-step, one-pot procedure and ethyl 4-(trimethylammonium)benzoate triflate (1) as the starting material. The radiochemical transformations were carried out in a general-purpose, custom-made module and streamlined by an anhydrous deprotection strategy using t-BuOK/DMSO. After HPLC-purification, [18F]SFB was synthesized in radiochemical yields of 20–30% (n > 10, not decay-corrected) and excellent radiochemical and chemical purities (>98%). The total synthesis and purification time required is ~90 min. Using the purified [18F]SFB, three 18F-labeled proteins, bovine serum albumin (BSA), chicken egg albumin (CEA) and transferrin, were synthesized in yields of 61.0–79.5%. The 18F-Annexin V for apoptosis imaging was also produced in 5% radiolabeling yield and >95% radiochemical purity.