Addressing Chirality in the Structure and Synthesis of [<sup>18</sup>F]5‐Fluoroaminosuberic Acid ([<sup>18</sup>F]FASu)
Bibliographic record
Abstract
Abstract An increasing number of positron emission tomography (PET) radiotracers are being developed that are modelled on various amino acids to better understand disease in a manner that is complementary to traditional glycolysis‐targeting [18F]‐fluorodeoxyglucose. Since chiral centers are ubiquitous in amino acids, generating an optically pure radiolabeled amino acid is important for patient dose, image quality and understanding the physiology behaviour. Past studies on the radiosynthesis of amino acid radiotracers seldom address the impact of reaction conditions on their chirality. The amino acid PET tracer, [18F]5‐fluoroaminosuberic acid ([18F]FASu), has two chiral centers at the 2‐ and 5‐positions and is being developed as a specific tracer for the cystine transporter (system xC−), a biomarker for oxidative stress. Herein we report a method for synthesizing pure 2S,5R/S‐FASu. We have resolved the 5‐position configuration by applying Mosher's method combined with 2D NMR, which has enabled the synthesis of 18FASu with fully known configuration. Our study serves as an example of a systematic method to identify and characterize amino acid tracers with chiral centers.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".