Alkaloid Synthesis: Crispine A (Zhou), Cermizine C (Zhang), Tangutorine (Poupon), FR901483 (Kerr), Serratezomine A (Johnston)
Bibliographic record
Abstract
Enantioselective hydrogenation of enamides is a well-established transformation. The corresponding reduction of enamines has been elusive. Qi-Lin Zhou of Nankai University designed (J. Am. Chem. Soc. 2009, 131, 1366) an Ir catalyst that reduced 2 to the Carpus alkaloid Crispine A 3 in high ee. Direct conversion of C-H to C-C bonds is a powerful synthetic transformation. Liming Zhang, now at the University of California, Santa Barbara, observed (J. Am. Chem. Soc. 2009, 131, 8394) that a gold catalyst converted the N-oxide of 4 into 5, that was then deoxygenated to give Cermizine C 6. The gold catalyst and the N-oxide combined to convert the alkyne into an α-keto carbene, in the process reducing the N-oxide back to the amine. The carbene then abstracted a hydride from the carbon adjacent to the amine, generating an intermediate that collapsed to give 5 with high diastereocontrol. Tangutorine 10, isolated from the leaves of Nitraria tangutorum, affects the morphology of human colon cancer cells. In a biomimetic approach, Erwan Poupon of the Université Paris-Sud stirred (Organic Lett . 2009, 11, 1891) glutaraldehyde 7 with bicarbonate to give an unstable carbocyclic dimer. Addition of tryptamine in acetic acid delivered the pentacyclic product 9, that was reduced with borohydride to give the crystalline Tangutorine 10. FR901483, a potent immunosuppressive isolated from a Cladobotyrum fermentation broth, presents an challenging array of stereogenic centers in its tricyclic skeleton. Michael A. Kerr of the University of Western Ontario prepared (Organic Lett. 2009, 11, 777) the activated cyclopropane 11, then effected intramolecular dipolar opening with an intermediate imine, yielding the tricyclic 12. The Lycopodium alkaloid Serratezomine A 21 presents a similarly challenging array of stereogenic centers in its tetracyclic structure. Jeffrey N. Johnston of Vanderbilt University constructed (J. Am. Chem. Soc. 2009, 131, 3470) the pyrrolidine ring of 15 using the imine free radical acceptor that he had previously developed. Having the alkene-Sn bond in place then enabled coupling with the acid chloride 16. Oxidative deprotection of 17 freed the enamine, that added in a conjugate sense to the unsaturated ester, kinetically setting the axial branch of 18.
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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) | 0.001 | 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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.007 | 0.003 |
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".