The invention relates to a process for preparation of radiopharmaceutical precursors, and in particular protected amino acid derivatives which are used as precursors for production of radiolabelled amino acids for use in in vivo imaging procedures such as positron emission tomography (PET). Particularly, the invention relates to a process for preparation of a precursor of the [18F]-1-amino-3-fluorocyclobutanecarboxylic acid ([18F] FACBC) PET agent, ensuring that the reaction efficiently goes to completion.
