Mild, Fast, and General Biocatalytic Deprotection Strategies for Automated Fluorine-18 Positron Emission Tomography Radiotracer Synthesis

Positron emission tomography (PET) has become an essential tool in nuclear medicine, driving the continuous development of new radiotracers. Owing to the short half-life of fluorine-18 (110 min), radiotracer production requires fast, robust, and fully automated synthetic protocols. Reactive functional groups present on precursor molecules must be protected to prevent competition during radiofluorination, with deprotection typically achieved under harsh chemical conditions that may compromise automation and lead to partial molecular degradation. Herein, we report a general biocatalytic deprotection strategy based on porcine liver esterase (PLE) as a mild and efficient alternative to conventional chemical methods. Three protecting groups (valerate, pivaloyloxymethyl and pivaloyl ethylidene carbamate) were selected to enable the PLE-deprotection of a broad range of functional groups found in radiotracers and drugs (alcohols, phenols, carboxylic acids, amines, anilines, sulfonamides). The PivEC protective group of amines, anilines and sulfonamides was specifically developed for allowing an esterase deprotection. This approach was validated across a broad substrate scope and was successfully automated on ORA-Neptis modules for clinically relevant PET tracers, including [18F]FMISO, [18F]CABS13, and [18F]Nifene. This work establishes enzymatic deprotection as a versatile and practical strategy for PET scan application.