Synthesis of a new π‐deficient phenylalanine derivative from a common 1,4‐diketone intermediate and study of the influence of aromatic density on prolyl amide isomer population
Bibliographic record
Abstract
Abstract magnified image Enantiopure (2S)‐N‐(Boc)‐3‐(6‐methylpyridazinyl)alanine (14) has been synthesized to serve as a phenylalanine analog lacking significant π‐donor capability. Two approaches were developed to furnish the target compound from L‐aspartic acid as chiral educt in respectively six and nine steps and 13% and 12% yields. In both routes, a key homoallylic ketone intermediate was synthesized by a copper‐catalyzed cascade addition of vinylmagnesium bromide to a carboxylic ester. Dipeptide models Ac‐Xaa‐Pro‐NHMe (21a–c) were prepared and the relative populations of prolyl cis‐ and trans‐amide isomers were measured in chloroform, dimethylsulfoxide, and water by proton NMR spectroscopy in order to assess the significance of the electron density of the neighboring aromatic residue on the prolyl amide geometry. © 2006 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 88: 290–299, 2007. This article was originally published online as an accepted preprint. The ‘Published Online’ date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
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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".