Absolute configuration assignments by experimental and theoretical approaches of <i>ent</i>-labdane- and <i>cis</i>-<i>ent</i>-clerodane-type diterpenes isolated from <i>Croton glabellus</i>
Bibliographic record
Abstract
The bioassay-guided fractionation of the moderately cytotoxic extract from Croton glabellus resulted in the isolation of bioactive compounds, which were characterized as austroinulin (2), 6-O-acetylaustroinulin (3), the acetonide artifact of 2 (4), and 3-O-methylkaempferol (9). In addition, a new natural cis-ent-clerodane lactone diterpene named marrubiagenin (1), trans-dehydrocrotonin (6), the epimeric mixture of cajucarinolide (7/8), and 5,7,3′,4′-tetrahydroxy-3-methoxyflavonoid (10) were also characterized and identified as nonbioactive compounds. The structures of all compounds were determined by analyses of their physical and spectroscopic data and by comparison with those reported in the literature. The absolute configuration assignment of 3 was carried out by means of the modified Mosher method and by the experimental and theoretical circular dichroism method establishing that 3 belongs to the ent-labdane diterpene series. Furthermore, the absolute configuration of 1 was established by analysis of its chiroptical properties concluding that 1 belongs to the cis-ent-clerodane diterpene series.Key words: Croton glabellus, ent-labdane-type diterpenes, cis-ent-clerodane-type diterpenes, circular dichroism, TD-DFT.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.007 | 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".