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Topic: carbohydrate detritylation  (Read 1369 times)

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Offline Humr

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carbohydrate detritylation
« on: April 30, 2023, 08:21:17 AM »
Hello, I am trying to prepare 1,2,3,4-tetra-O-acetyl-α-D-glucopyranoside. My starting compound is glucopyranoside with trityl on primary OH. Has someone any experience with this deprotection?

I tryed textbook conditions for detritylation TFA/DCM (1:10) and i obtained mixture of products. Products are very close on TLC. I am guessing i obtained my product + product with free OH on carbon 4 and acyl on primary OH.
I also tryed to heat my starting material to 80 °C in mixture of chloroform and acetic acid - same mixture.

After some searching in "Protective groups in organic chemistry by Green" i am considering:

a) reduction with hydrogen and Pd/C
b) ZnCl2 in methanol
c) heating it with Montmorilonite K10
d) start column chromatography and let it sit inside column at least for a day

To try all ideas would take a lot of time so i am trying to narrow it down by others opinion.

Offline phth

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Re: carbohydrate detritylation
« Reply #1 on: April 30, 2023, 08:48:09 PM »
Don't you have to acetyl ate first before deprorection ?
a) could work
b) ZnCl2 in methanol probably produces alpha methoxy glycopyranoside
c) heating it with Montmorilonite K10 Should you heat a fragile molecule?
d) start column chromatography and let it sit inside column at least for a day Don't think this will work.

Offline Humr

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Re: carbohydrate detritylation
« Reply #2 on: May 01, 2023, 01:01:35 PM »
Thank you for an answer. You are correct, I just explained myself badly. I start with acetylated compound and do detritylation.

This molecule is fragile, but I meant temperature like 40-50 °C. Considering this clay is only mildly acidic, i thought this can work.

Idea with column chromatography is not from my head. I have read article about deprotection of rtr this way. Problem is that there is a lot of silica gel types.

Offline Babcock_Hall

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Re: carbohydrate detritylation
« Reply #3 on: May 01, 2023, 03:32:39 PM »
Greene and Wuts's book is wonderful, but you might want to consult something like the Handbook of Chemical Glycosylation, edited by Alexei V. Demchenko.

Is it possible that your product now exists as both stereoisomers at C-1?

Offline rolnor

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Re: carbohydrate detritylation
« Reply #4 on: May 05, 2023, 06:32:02 AM »
I have always used 90% HOAc? Its not a very good strategy you have, acetyls are easily deprotected as well. Hydrogenolysis is often sluggish with Trityl, its so bulky.

Offline Humr

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Re: carbohydrate detritylation
« Reply #5 on: May 14, 2023, 08:53:27 AM »
So i tried hydrogenation with hydrogen and Pd/C in ethanol. I observed zero conversion.

Montmorilonite works. It reacts at the room temperature. This reaction is also dependent on solvent.
I observed full conversion of starting compound only in acetic acid. Unfortunatelly i can see on TLC 2 spots with almost identical RF. It looks like one is shadowing another.
In DCM there is only partial conversion, some  another sideproduct and shadowing.
In methanol there are at least 4 products.
THF and DMF provide very low conversion of starting compound.
Toluene provides one sideproduct, no shadowing and quite satisfactory conversion of starting compound.

So i am considering to work up toluene reaction mixture and analyse it, since it is best result i have.

Rolnor, do you use 90% HOAc on this compound, or something else? And can i ask you for exact conditions, please?

Offline rolnor

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Re: carbohydrate detritylation
« Reply #6 on: May 15, 2023, 02:39:00 AM »
I would try 90% acetic acid, no solvent. Dissolve and heat to 50C, if nothing happens heat to 80C. I think you should try another PG-strategy or buy the compound, its probably commersial

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