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The non-natural cyclic amino acids (1S,3R,4S)-1-amino-3-fluoro-4-(fluoro-18F)cyclopentane-1-carboxylic acid ([18F]9) and (1S,3S,4R)-1-amino-3-fluoro-4-(fluoro-18F)cyclopentane-1-carboxylic acid ([18F]28) have been prepared in 10% and 1.7% decay corrected radiochemical yield, respectively, and in greater than 99% radiochemical purity. Cell assays in rat 9L glio-sarcoma, human U87 ∆EGFR glioblastoma, and human DU145 androgen-independent prostate carcinoma tumor cells indi-cated that both compounds are substrates for amino acid transport primarily by system L, with some transport taking place via system ASC. In rats with 9L gliosarcoma, [18F]9 and [18F]28 provided high tumor to normal brain tissue ratios, with maximal ratios of 3.5 and 4.1, respectively. Biodistribution studies in healthy rats confirmed that both compounds are BBB permeable, and that bladder accumulation is low until at least 5 minutes post injection.

The non-natural cyclic amino acids (1

The non-natural amino acids (R)- and (S)-2-amino-3-fluoro-2-methylpropanoic acid 5 and (R)- and (S)-3-fluoro-2-methyl-2-N-(methylamino)propanoic acid 8 were synthesized in shorter reaction sequences than in the original report starting from enantiomerically pure (S)- and (R)-α-methyl-serine, respectively. The reaction sequence provided the cyclic sulfamidate precursors for radiosynthesis of (R)- and (S)-[18F]5 and (R)- and (S)-[18F]8 in fewer steps than in the original report. (R)- and (S)-[18F]5 and(R)- and (S)-[18F]8 were synthesized by no-carrier-added nucleophilic [18F]fluorination in 52−66% decay-corrected yields with radiochemical purity over 99%. The cell assays showed that all four compounds were substrates for amino acid transport and enter 9L rat gliosarcoma cells in vitro at least in part by system A amino acid transport. The biodistribution studies demonstrated that in vivo tumor to normal brain ratios for all compounds were high with ratios of 20:1 to115:1 in rats with intracranial 9L tumors....

Both enantiomers of 2-amino-2-methyl-4-iodo-3-(E)-butenoic acid (IVAIB, 5) were radioiodoinated in 65-72% yield. (S)-IVAIB entered 9L gliosarcoma cells primarily via A-type transport in vitro with higher uptake than (R)-IVAIB. Biodistribution studies in rats with 9L gliosarcoma brain tumors demonstrated higher tumor to brain ratios with (S)-IVAIB (75:1 at 1 h) than (R)-IVAIB (7.7:1). In this model, (S)-IVAIB is superior to (R)-IVAIB and is a promising radiotracer for brain tumor imaging.