Abstract
The use of radiolabeled non-natural amino acids can provide high contrast SPECT/PET metabolic imaging of solid tumors. Among them, radiohalogenated tyrosine analogs (i.e., [123I]IMT, [18F]FET, [18F]FDOPA, [123I]8-iodo-L-TIC(OH), etc.) are of particular interest. While radioiodinated derivatives, such as [123I]IMT, are easily available via electrophilic aromatic substitutions, the production of radiofluorinated aryl tyrosine analogs was a long-standing challenge for radiochemists before the development of innovative radiofluorination processes using arylboronate, arylstannane or iodoniums salts as precursors. Surprisingly, despite these methodological advances, no radiofluorinated analogs have been reported for [123I]8-iodo-L-TIC(OH), a very promising radiotracer for SPECT imaging of prostatic tumors. This work describes a convenient synthetic pathway to obtain new radioiodinated and radiofluorinated derivatives of TIC(OH), as well as their non-radiolabeled counterparts. Using organotin compounds as key intermediates, [125I]5-iodo-L-TIC(OH), [125I]6-iodo-L-TIC(OH) and [125I]8-iodo-L-TIC(OH) were efficiently prepared with good radiochemical yield (RCY, 51–78%), high radiochemical purity (RCP, >98%), molar activity (Am, >1.5–2.9 GBq/µmol) and enantiomeric excess (e.e. >99%). The corresponding [18F]fluoro-L-TIC(OH) derivatives were also successfully obtained by radiofluorination of the organotin precursors in the presence of tetrakis(pyridine)copper(II) triflate and nucleophilic [18F]F− with 19–28% RCY d.c., high RCP (>98.9%), Am (20–107 GBq/µmol) and e.e. (>99%).
Highlights
acid transporters (AATs) have been included in the Solute Carrier (SLC) superfamily of transporter systems [7,8,9]
AATs are currently included in 11 SLC families, with at least 66 different members
Because of the key functional role played by AATs in biological processes, expression alterations or dysfunctions have been linked with several human pathologies, such as neurodegenerative disorders, chronic kidney disease and cancer [10,11]
Summary
Pharmaceuticals 2022, 15, 162 and a high proliferation rate, supported by increased AATs express [12,13] This characteristic, leading to an intensive accumulation of A compared with normal cells, has been largely exploited in diagnosti. Of primary cancer lesions and uncontrolled distant metastases high proliferation rate, supported by increased AATs expression and/or activity [12,13] This characteristic, leading to an intensive accumulation of AAs in cancer cells compared most upregulated in cancer is the LAT1 system Its half-life (109.8 min) is long enough to a tinely produced at the multi-Curie level on widely implemented biomedical cyclotrons, using the well-characterized (p, n) nuclear reaction on ankinetic oxygen-18-enriched imaging protocols, facilitating studies water and target high-quali with a relatively low-energy proton beam (e.g., 18 MeV). Since radiolabeling are common in iodine all iodine radioisotopes and considering relativelylow lowcost costofofiodine-125 iodinecommon in all radioisotopes and considering thethe relatively model for our radioiodination protocols
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