Synthesis and application of <scp>L</scp>-<i>N</i>-Boc-<i>N</i>-methyl-β-hydroxyvaline in the preparation of a depsipeptide
Bibliographic record
Abstract
Enantiopure (>99% ee) L-N-tert-butyloxycarbonyl-N-methyl-β-hydroxyvaline (2) was synthesized in six steps and 43% overall yield from D-serine methyl ester (5). Methyl (4S)-N-(9-phenylfluoren-9-yl)-oxazolidine-4-carboxylate (7) was prepared in two steps and 73% yield by N-phenylfluorenation of 5 followed by cyclization of N-(PhF)amino alcohol 6 with formaldehyde and catalytic p-toluenesulfonic acid (PhF = 9-phenylfluoren-9-yl). The addition of MeLi to oxazolidine carboxylate 7 produced the tertiary alcohol 8 in 91% yield. Oxazolidines 8 equilibrated with oxazolidine 9 under acidic conditions. Reduction of pure 8 or the mixture of oxazolidines 8 and 9 with NaCNBH 3 and hydrochloric acid in anhydrous dioxane afforded N-methyl amino diol 11 in 86%92% yields. Attempts to selectively oxidize N-(PhF)amino diol 11 were unsuccessful; however, hydrogenation of 11 in the presence of di-tert-butyl dicarbonate gave the corresponding N-(Boc)amino diol 12 in 82% yield. Selective oxidation of diol 12 was performed using a cocktail containing TEMPO free radical, NaClO 2 , and NaOCl to give L-N-Boc-N-methyl-β-hydroxyvaline (2) in 87% yield. Coupling of β-hydroxyvaline 2 and (S)-2-hydroxy-3-methylbutanoate (15) was accomplished by using the methodology of Mitsunobu to provide depsipeptide Boc-(S)-HOMeVal-(R)-Hmb (4) for use as a building block in the synthesis of the cyclic antifungal depsipeptide aureobasidin B.Key words: N-methylated amino acid, serine, depsipeptide, aureobasidin.
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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 | 0.001 |
| 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".