Synthesis And Analysis Of 4-(3-Fluoropropyl)-Glutamic Acid Stereoisomers To Determine The Stereochemical Purity Of (4s)-4-(3-[F-18]Fluoropropyl)-L-Glutamic Acid ([F-18]Fspg) For Clinical Use

(4S)-4-(3-[F-18]Fluoropropyl)-L-glutamic acid ([F-18]FSPG) is a positron emission tomography (PET) imaging agent for measuring the system x(C)(-) transporter activity. It has been used for the detection of various cancers and metastasis in clinical trials. [F-18]FSPG is also a promising diagnostic tool for evaluation of multiple sclerosis, drug resistance in chemotherapy, inflammatory brain diseases, and infectious lesions. Due to the very short half-life (110 min) of F-18 nuclide, [F-18]FSPG needs to be produced on a daily basis; therefore, fast and efficient synthesis and analytical methods for quality control must be established to assure the quality and safety of [F-18]FSPG for clinical use. To manufacture cGMP-compliant [F-18]FSPG, all four nonradioactive stereoisomers of FSPG were prepared as reference standards for analysis. (2S,4S)-1 and (2R,4R)-1 were synthesized starting from protected L- and D-glutamate derivatives in three steps, whereas (2S,4R)-1 and (2R,4S)-1 were prepared in three steps from protected (S)- and (R)-pyroglutamates. A chiral HPLC method for simultaneous determination of four FSPG stereoisomers was developed by using a 3-cm Chirex 3126 column and a MeCN/CuSO4(aq) mobile phase. In this method, (2R,4S)-1, (2S,4S)-1, (2R,4R)-1, and (2S,4R)-1 were eluted in sequence with sufficient resolution in less than 25 min without derivatization. Scale-up synthesis of intermediates for the production of [F-18]FSPG in high optical purity was achieved via stereo-selective synthesis or resolution by recrystallization. The enantiomeric excess of intermediates was determined by HPLC using a Chiralcel OD column and monitored at 220 nm. The nonradioactive precursor with >98% ee can be readily distributed to other facilities for the production of [F-18]FSPG. Based on the above accomplishments, cGMP-compliant [F-18]FSPG met the acceptance criteria in specifications and was successfully manufactured for human use. It has been routinely prepared and used in several pancreatic ductal adenocarcinoma metastasis-related clinical trials.