α-Azido Esters in Depsipeptide Synthesis: C–O Bond Cleavage during Azido Group Reduction
Bibliographic record
Abstract
α-Azido esters, when treated with dithiothreitol (DTT)/diisopropylethylamine (DIPEA), undergo both azido group reduction to give α-amino esters and C–O bond cleavage to give triazoles. The extent of triazole formation depends upon leaving group ability. Some C–O bond cleavage via triazole formation was also found to occur when a resin-bound peptide, which contained a terminal α-azido ester group, was treated with DTT/DIPEA. C–O bond cleavage also took place when this peptide was treated with PPh 3, PBu 3, or PMe 3; however, in these cases, C–O bond cleavage occurred via either triazole formation and/or hydrolysis of the ester bond in the iminophosphorane intermediate to give betaines. The mechanism that dominated for C–O bond cleavage depended upon the phosphine that was used for azido group reduction. C–O bond cleavage during reduction of the azido group in the peptide was minimized by performing the reduction with PBu 3 in the presence of a symmetric anhydride derived from an amino acid in dry THF followed by the addition of water. Surprisingly, these conditions provided the amine as the major product, while the expected amide was formed as a minor product. These conditions were employed in an improved synthesis of an analogue of the cyclic lipodepsipeptide antibiotic daptomycin.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.000 | 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 teacher head, 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".