Aspects of 6-[18F]fluoro-L-DOPA preparation: precursor synthesis, preparative HPLC purification and determination of radiochemical purity.

A modified method for the synthesis of the intermediate product N-Boc-3,4-di(Boc-O)-6-iodo-L-phenylalanine ethyl ester of the [18F]FDOPA precursor preparation was developed. With the application of bis-(trifluoroacetoxy)-iodobenzene for the iodination step with elemental iodine the yield of the intermediate can be increased from 12% to 50-60%. By replacing silica-gel-based RP HPLC column by a polymer-based column for semi-preparative purification of [18F]FDOPA from the reaction mixture the radiochemical purity of the final product can be increased up to >99%. For the determination of the radiochemical impurity [18F]fluoride a HPLC method using a column with polymer-based RP material was introduced.