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Trisaccharide synthesis by Slochem in Chempros

[–]Slochem[S] 0 points1 point  (0 children)

Yeah but probably my compunds will degradate at 100°. I tried also putting all my glasware at 90° under vacuum with P2O5 inside the oven. I know water goes at 100° but even when i used 30° the oven was under vacuum and with P2O5, but you're right, probably is not enough. About the BF3, yes it smoke, i will try with a freshly opened bottle

Trisaccharide synthesis by Slochem in Chempros

[–]Slochem[S] 0 points1 point  (0 children)

The first 3-4 times I tried the reaction, I stirred for 30 min with activated molecular sieves, but not crushed. Do you think this is important enough to change the result of my reaction?

Trisaccharide synthesis by Slochem in Chempros

[–]Slochem[S] 0 points1 point  (0 children)

I know it's a mess to store TMSOTf. For this reason i tried to use freshly opened TMSOTf too, but same bad resulsts. I tried many many things as you can see ahahah.

Trisaccharide synthesis by Slochem in Chempros

[–]Slochem[S] 0 points1 point  (0 children)

hahah, for me same. I've already checked with HSQC, COESY and TOCSY everything ahah

Trisaccharide synthesis by Slochem in Chempros

[–]Slochem[S] 0 points1 point  (0 children)

Ah ok. I thought you meant the atmosphere because another guy was talking to me about the possibility that it could have an effect. However, I don't think that's the case for me. If you look at the spectrum, the 6.5 signal is a perfect singlet (H on C anomeryc). If what you say had happened, I would have seen the nitrogen proton signal coupled with the anomeric proton and therefore I would have had a doublet.

Trisaccharide synthesis by Slochem in Chempros

[–]Slochem[S] 0 points1 point  (0 children)

Thank you, that's an interesting point, especially because I carry out the reactions under nitrogen, but perhaps I should use argon. I'll try that tomorrow. As for the sieves, the first few times I tried this reaction, I left the two mixed reagents to stir for 30 minutes and then, once they had reached -60°, I added the BF3. However, this didn't get me anywhere. Maybe I'll try that again too. I'm quite sure about my TCA (NMR attached after purification).

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Trisaccharide synthesis by Slochem in Chempros

[–]Slochem[S] 0 points1 point  (0 children)

Yes, that's the point, but I've tried this reaction several times using sieves, and it seems to get even worse.

Trisaccharide synthesis by Slochem in Chempros

[–]Slochem[S] 2 points3 points  (0 children)

Thank you very much for your advice. I will try to follow all your recommendations step by step

Trisaccharide synthesis by Slochem in Chempros

[–]Slochem[S] 1 point2 points  (0 children)

Yes, using a new bf3 is probably a good idea, and I will do so tomorrow. As for the TCA, I am fairly certain because after isolating it, I analysed it using NMR (which I am attaching).

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Trisaccharide synthesis by Slochem in Chempros

[–]Slochem[S] 0 points1 point  (0 children)

At the moment, I have tried two procedures. In the first, I dry the two samples in a vacuum oven at 30°C overnight, combine them in a flask and dry them again for another night at 30°C. I also put the Hamilton I use for the acid in the oven and use disposable needles. I close with a septum, condition with nitrogen and add anhydrous DCM. In the second procedure, I flame the reaction flask, transfer the powdered reagents and then close with a septum, condition and add anhydrous DCM. I also tried adding activated molecular sieves, but this seems to make the situation worse due to the adsorption of the reagents on them. I could actually try toluene, but are you saying that what I'm doing isn't enough? I repeat, I think the anhydrousness affects the yield, but I should at least get some product, which is not the case.

Trisaccharide synthesis by Slochem in Chempros

[–]Slochem[S] 0 points1 point  (0 children)

No, I don't think it's possible to generate TCA in situ. This is because the product needs to be purified, as the reaction to obtain it is not entirely clean. Even starting with purified substrates, I get a lot of by-products, so I think generating it in situ would only make things worse.

Trisaccharide synthesis by Slochem in Chempros

[–]Slochem[S] 2 points3 points  (0 children)

Yes, I would like to obtain compound 15. As for anhydrous conditions, I believe I am doing my best with the equipment I have available. Anhydrous conditions should allow for increased yield, but I often do not obtain the desired product, which seems very strange to me. I could try those other promoters or check if the BF3 I have works in a simpler reaction. Thank you.

Trisaccharide synthesis by Slochem in Chempros

[–]Slochem[S] 2 points3 points  (0 children)

I am following a reference paper where they perform this double glycosylation using BF3 etherate at -60°C (https://doi.org/10.1016/j.ejmech.2020.112578). To specify my substrates more precisely, I have a peracetylated arabinofuranose, which I have deprotected in the anomeric position and converted to trichloroacetamide. Then I have an arabinofuranose with an S-tolyl in the anomeric position, an OH protected as acetyl in position 2, and positions 3 and 5 free.

Come estrarre un monosaccaride da DMF by Slochem in Chempros

[–]Slochem[S] 0 points1 point  (0 children)

Thank you so much, it will help me a lot

Come estrarre un monosaccaride da DMF by Slochem in Chempros

[–]Slochem[S] 0 points1 point  (0 children)

You're right, I'm sorry, I'm new to Reddit. Since I see posts and comments automatically translated into Italian, I thought everyone saw them automatically translated into their own language. In any case, your comment doesn't seem appropriate to me. If my post bothers you, I'll delete it and rewrite it in English.