Formulation and method of synthesis

A method of preparation of a PET tracer composition in a cassette system having an end of synthesis (EOS) radiochemical purity (RCP) of at least 95%, comprising

• (a) reacting in a reaction vessel of the cassette system a source of 18F-fluoride with a precursor compound of Formula I:
• wherein:
• LG is a leaving group;
• PG1 is a carboxy protecting group;
• and, PG2 is an amine protecting group;
• wherein said reacting step is carried out in acetonitrile;
• to obtain a reaction mixture comprising a compound of Formula II:
• wherein PG1 and PG2 are as defined for Formula I;
• (b) transferring said reaction mixture comprising said compound of Formula II out of said reaction vessel onto a reversed phase solid phase cartridge of the cassette system and carrying out removal of PG1 to obtain a reaction mixture comprising a compound of Formula III:
• wherein PG1 is as defined for Formula I;
• (c) applying heat to said reaction vessel to remove residual solvent from the reaction vessel at the same time as carrying out removal of PG1 on the reversed phase solid phase cartridge;
• (d) transferring said reaction mixture comprising said compound of Formula III from the reversed phase solid phase cartridge back into said reaction vessel and carrying out removal of PG2 to obtain a reaction mixture comprising 18F-FACBC;
• (e) purifying said reaction mixture comprising 18F-FACBC by passing it through a hydrophilic lipophilic balanced (HLB) solid phase, wherein said purifying does not comprise passing the reaction mixture comprising 18F-FACBC through an alumina solid phase, wherein the purified reaction mixture is obtained in steps (c) or (e) with citrate buffer, wherein said composition comprises no more than 5.0 μg/mL dissolved aluminium (Al) and no more than 25 μg/mL acetonitrile (MeCN).