There has been significant and rapid growth in the development of amino acid-based molecular imaging agents (e.g., peptides, proteins, and antibody constructs) largely due to facile library preparation and high throughput screening. Positron-emitting fluorine-18 (half-life = 109.7 min) has a unique set of properties that match well with the pharmacokinetics of smaller sized constructs. Several indirect fluorine-18 labeling approaches have been developed yet only a few have advanced to human trials. Enzymatically catalyzed radiofluorination utilizing lipoic acid ligase shows promise as a mild site-specific method for coupling fluorine-18-labeled carboxylate substrates with biomolecules. Methods for preparation of two [18F]fluorocarboxylates and their ligation to a specific peptide sequence (LAP peptide) are presented herein.
Keywords: Biomolecule; Enzymatic radiolabeling; Fluorine-18; LAP peptide; Lipoic acid ligase; PET; Peptide; Radiofluorination.