In-situ Preparation of a chemically bonded chiral stationary phase for the separation of aromatic α-amino acid enantiomers

[18F]fluoro-beta-fluoromethylene-m-tyrosine analogs, potential PET agents for presynaptic dopamine terminals: synthesis and spectroscopic characterization

18F-labeled (E)-beta-fluoromethylene-DL-m-tyrosine (FMMT) was prepared by the direct reaction of FMMT with [18F]acetylhypofluorite (AcOF) resulting into three product isomers. Extensive 1H, 13C and 19F-NMR spectroscopic analysis identify these products to be 2-fluoro, 6-fluoro-FMMT and 2,6-difluoro-FMMT. The HPLC isolated radiochemical EOB yields of these products were 22, 25 and 14%, respectively, based on starting [18F]AcOF. The specific activity at the end of a synthesis time of an hour was ca 200 mCi/mmol. With the possible advantage of "metabolic trapping" in dopamine nerve terminals via covalent binding to MAO and reduced metabolite formation, [18F]F-FMMT may potentially be the optimal PET tracer for CNS dopamine nerve terminals.

Production of 6-[18F]fluoro-L-dopa and its metabolism in vivo--a critical review

This report critically appraises methods for the synthesis of 6-[18F]fluoro-L-3,4-dihydroxyphenylalanine (6-FDOPA) that are based on labelling by non-regioselective electrophilic fluorination, regioselective fluorodemetalation or nucleophilic substitution. Recommendations for the standardization of labelling procedures, the optimization of radiochemical yield and the assurance of product quality and safety are given. Studies of the metabolism of 6-FDOPA in vivo are also reviewed to emphasize the importance of the biochemical component of the development of this tracer for positron emission tomography (PET).

Ligand-exchange chromatography of alpha-trifluoromethyl-alpha-amino acids on chiral sorbents

The chromatographic behaviour of some alpha-trifluoromethyl-alpha-aminoacids on L-proline- and L-hydroxyproline sorbents was studied. The retention and selectivity parameters of the separation of amino acid enantiomers on the sorbents were determined. The introduction of a CF3 [corrected] group led to an increased selectivity in the separation of amino acid enantiomers on a proline sorbent and to a decreased selectivity on a hydroxyproline sorbent.

Synthesis of radiofluorinated analogs of m-tyrosine as potential L-dopa tracers via direct reaction with acetylhypofluorite

The direct electrophilic radiofluorination of m-tyrosine using [18F]acetylhypofluorite was investigated. Results showed that this reaction was both rapid and efficient with recovered decay corrected yield of 71% radiofluorinated m-tyrosines based on starting [18F]acetylhypofluorite. Specific activity of the product obtained in this study was 100-200 mCi/mmol although 1-5 Ci/mmol are easily achievable with our improved production of [18F]AcOF. Three positional isomers were found and identified by 19F-NMR to be 2-, 4-, 6-fluoro-m-tyrosine with a distribution of 36:11:52, respectively. This measured distribution allowed the assignment of the radio-HPLC peaks. Biological studies are currently underway in our laboratory using these fluoro-m-tyrosines to determine which isomer would be most suited for the evaluation of the dopamine system by positron tomography.

A new route for the synthesis of [18F]fluoroaromatic substituted amino acids: no carrier added L-p-[18F]fluorophenylalanine

L-p-[18F]fluorophenylalanine was designed as a potential marker for probing protein synthesis in the human brain by positron emission tomography. This radiotracer has been synthesized using nucleophilic displacement of the activated nitro group of p-nitrobenzaldehyde by NCA 18F- obtained from the 18O (p, n) reaction on enriched water. The L-form of the [18F]fluoroamino acid can be separated on an analytical scale chiral column. A typical production run of 22.2 GBq (600 mCi) of 18F obtained after a 10 microA.h bombardment of 18 MeV protons on 99.8% 18O-enriched water leads to a batch of 1.11 GBq (30 mCi) of NCA L-p-[18F]fluorophenylalanine after a total synthesis time of 120 min.