Synthesis and NMR spectroscopic analysis of acylated pentasaccharide fragments of mycobacterial arabinogalactan
Bibliographic record
Abstract
The mycolyl-arabinogalactan (mAG) complex, a large glycolipid composed of arabinofuranose and galactofuranose monosaccharides and mycolic acid lipids, provides mycobacteria with substantial protection from their environment. It has been proposed that the presence of flexible furanose rings in the mAG facilitates the packing of the hydrophobic mycolic acids, forming a dense protective barrier of low permeability. In a previous article, we probed this "flexible scaffold hypothesis" through the synthesis and NMR analysis of di- and trisaccharide fragments of the mAG acylated with linear fatty acids. However, we saw few conformational changes due to the presence of the acyl chains. We proposed that branched pentasaccharide glycolipids 5-8 might exhibit larger changes due to the presence of more acyl chains, and studies with these compounds are described here. The carbohydrate portion of 5-8 was synthesized in a 1 + 2 + 2 manner. First, the monosaccharide diol was treated with an excess of appropriately protected thioglycoside donor to give a trisaccharide, which, following selective deprotection to a diol, was converted to the pentasaccharide in a one-pot glycosylation. The resulting differentially protected pentasaccharide 20 gave glycolipids 5-8 upon removal of the protecting groups at the primary positions, acylation, and hydrogenolysis. The conformations of 5-8 were probed using NMR spectroscopy, and chemical shift selective filtering 1D-TOCSY spectra allowed for the determination of all the ring coupling constants. It was found that the addition of four fatty acids to the parent pentasaccharide had little effect on the conformation of the compounds in solution.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| 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) | 0.017 | 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".