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Topic: Contaminant after removal of acetyl groups  (Read 2020 times)

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Offline Babcock_Hall

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Contaminant after removal of acetyl groups
« on: September 18, 2023, 11:13:48 AM »
We deprotected a tetra-acetylated glycopyranoside using sodium methoxide in methanol.  There is an extra signal in the H-1 NMR spectrum, that may be sodium formate.  The peak is at 8.45 ppm, and the SDBS site indicates 8.525 ppm.  We are also obtaining C-13 data.  I am still working on confirming its identity.  We have another deprotection to do soon.

One, sodium formate might have arisen from either methoxide or methanol.  We can use fresh sodium methoxide and fresh methanol, or we can buy premade sodium methoxide in methanol, or we can make our own from sodium metal.  Any thoughts on the best choice?

Two, we may need to remove sodium formate from our sample.  One could try exchanging sodium for a proton and using reduced pressure to remove formic acid.  Or one could try reverse phase purification of some sort.    Because I would like to avoid using an acidic ion-exchange resin out of concern for the glycosidic linkage, I favor the latter idea, but I am not set on it.  Thoughts?

« Last Edit: September 18, 2023, 02:48:11 PM by Babcock_Hall »

Offline rolnor

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Re: Contaminant after removal of acetyl groups
« Reply #1 on: September 19, 2023, 04:40:47 AM »
You could use weak acidic ion-exchange, the carboxylic-acid type, (Amberlite I think) not the sulphonic acid (Amberlyst?) type? You have used RP-cromatography now, the formate will run very fast on a column so that is another option.

Offline Babcock_Hall

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Re: Contaminant after removal of acetyl groups
« Reply #2 on: October 11, 2023, 06:56:53 PM »
We used some C18-coated silica and methanol/water.  My first look at the H-1 NMR suggested to me that the contaminant was removed.  Sodium formate, if it was indeed the contaminant, should have eluted much earlier.

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