Facile synthesis of α-<scp>D</scp>-Ara<i>f-</i>(1→5)-<scp>D</scp>-Gal<i>f</i>, the linker unit of the arabinan to the galactan in <i>Mycobacterium tuberculosis</i>
Bibliographic record
Abstract
The arabinogalactan is a crucial constituent of the cell wall of mycobacteria. Both monosaccharides (arabinose and galactose) are found in the furanose configuration, absent in mammals. An efficient synthesis of α-D-Araf-(1→5)-D-Galf, the linker unit of the arabinan to the galactan, is described. The strategy relies on the use of a conveniently substituted D-galactono-1,4-lactone as a precursor of the reducing furanose ring. The glycosylation step was performed by the tin(IV) chloride promoted method using 1,2,3,5-tetra-O-benzoyl-α,β-D-arabinofuranose. The arabinose donor was obtained in a crystalline state in one step by benzoylation of arabinose in hot pyridine. Selective glycosylation of the exocyclic OH-5 was obtained in 75% yield to give 2,3,5-tri-O-benzoyl-α-D-arabinofuranosyl-(1→5)-2,6-di-O-pivaloyl-D-galactono-1,4-lactone. Reduction with disiamylborane gave the disaccharide synthon, useful for further glycosylations. Dec-9-enyl α-D-Araf-(1→5)-β-D-Galf, a convenient substrate for arabinofuranosyl transferases studies, was obtained by the trichloroacetimidate method of glycosylation.Key words: arabinofuranose, galactofuranose, Mycobacterium arabinogalactan, trichloroacetimidate, tin(IV) chloride.
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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) | 0.000 | 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) | 0.001 | 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".