Synthesis and decarboxylation of Δ<sup>2</sup>-cephem-4,4-dicarboxylic acids
Why this work is in the frame
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Bibliographic record
Abstract
Penicillin V was converted in 14 steps into Δ 2 -cephems having hydrogen at C-3, hydrogen or ethyl at C-2, and two methoxycarbonyl, two benzyloxycarbonyl, or one methoxycarbonyl and one benzyloxycarbonyl substituent at C-4. Deprotection of these Δ 2 -cephem-4,4-dicarboxylic acid esters by alkaline hydrolysis (in the case of methyl esters) or hydrogenolysis (in the case of benzyl esters) led in all cases to rapid decarboxylation of the Δ 2 -cephem-4,4-dicarboxylic acid or Δ 2 -cephem-4,4-dicarboxylic acid monoester. With hydrogen at C-2, hydrolysis of the dimethyl ester with 1 equiv of base produced a Δ 2 -cephem. With 2 equiv of base, and with all compounds having methyl at C-2, hydrolysis or hydrogenolysis afforded 4α-substituted-Δ 2 -cephems. In contrast, simpler benzyl or methyl acetamidomalonates could be deprotected without difficulty to afford stable malonic acids. Reasons for the differences in ease of decarboxylation were examined using semiempirical (AM1) and ab initio (3-21G) molecular orbital calculations. The decarboxylation barriers of unionized cephem or acetamido malonic acids were found to be high (3540 kcal mol 1 ). Although the monoanion of acetamidomalonic acid retained a high barrier, the epimeric monoanions of a Δ 2 -cephem malonic acid decarboxylated with barriers of only 2 kcal mol 1 .Key words: mercaptoazetidinone, bromomalonate esters, MO calculations, sulfoxides, hydrogenolysis.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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 it