Alternative strategies for the synthesis of [11C]ER176 for PET imaging of neuroinflammation.

Abstract [11C]ER176 is a next generation PET radioligand for imaging 18 kDa translocator protein, a biomarker for neuroinflammation. The goal of this work was to investigate alternative strategies for the radiochemical synthesis, purification, and formulation of [11C]ER176. An optimized tri-solvent high-performance liquid chromatography (HPLC) protocol is described to separate the hydro-de-chlorinated byproduct from [11C]ER176. A newly implemented solid phase extraction work-up efficiently removed HPLC solvent while maintaining chemical purity and overall radiochemical yield and purity. This new HPLC purification and final formulation was completed within 40 minutes, providing 2.7 ± 0.5 GBq of [11C]ER176 at end of synthesis with 1400 ± 300 GBq/μmol molar activity while meeting all specifications for radiopharmaceutical quality control tests for human research use.