SiFA‐Modified Phenylalanine: A Key Compound for the Efficient Synthesis of <sup>18</sup>F‐Labelled Peptides
Bibliographic record
Abstract
Abstract Both the racemic and the stereoselective synthesis of the silicon‐modified amino acid p‐(tBu2FSi)C6H4CH2(NH2)COOH (SiFA‐phenylalanine, 6) and its derivatives p‐(tBu2FSi)C6H4CH2(NHBoc)COOH (10) and p‐(tBu2FSi)C6H4CH2(NHFmoc)COOH (11) are reported. The latter two compounds are valuable building blocks for the convenient introduction of silicon‐based fluoride acceptors (SiFAs) into peptides by solid‐phase peptide syntheses (SPPS). As prove of principle, the Tyr3‐octreotate derivatives 12, 13 and 14 were prepared by using standard protocols of the solid‐phase peptide synthesis (SPPS). They were labelled with 18F‐fluorine by isotopic exchange in radiochemical yields of up to 70 % (with radiochemical purity ranging between 92 and 99 %). The incorporation of 18F‐fluorine into the SiFA‐modified amino acid 6 was studied as the latter may also serve as a tracer in PET. After purification, [18F]‐6 showed a remarkable stability in an isotonic solution. Also reported is the molecular structure, as determined by single‐crystal X‐ray diffraction analysis, of p‐(tBu2FSi)C6H4CHCH[C(O)OMe]NHC(O)OCH2Ph (8), which serves as a precursor for the stereoselective synthesis of compound 6.
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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 | 0.001 |
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".