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Topic: Boc Deprotection  (Read 386 times)

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Offline Bertrand

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Boc Deprotection
« on: May 15, 2020, 10:09:06 AM »
Hello everyone!
Does anyone have an appropriate and effective approach to suppress the Boc group?
I have tried the mixture DCM/TFA/Anisol 10/1/1... However, nothing happened.
Thanks in advance for your suggestions... I have attached the reaction

Offline Babcock_Hall

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Re: Boc Deprotection
« Reply #1 on: May 15, 2020, 10:27:20 AM »
By "suppress," do you mean remove?  Offhand, your conditions look reasonable.  How long did you let the reaction proceed, and how did you follow the reaction?

Offline wildfyr

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Re: Boc Deprotection
« Reply #2 on: May 15, 2020, 01:25:45 PM »
There are a lot of ways to remove boc. I suggest checking "Protecting Groups in organic Synthesis" by Greene and Wuts.

Offline Bertrand

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Re: Boc Deprotection
« Reply #3 on: May 15, 2020, 06:49:05 PM »
Here is the detailed procedure I used.

Manual removal of the N-terminal Boc-group can be accomplished by placing the resin in a round bottom flask and washing with DCM/TFA/Anisol 10:1:1 at 0C for 15 minutes with constant mixing.

Precipitate the product by addition of cold Et2O, store at -20C 1 h Decant.
dissolve the residue in RT MeOH, precipitate again by cold Et2O (1 h -20C).


Thanks for the recommended book

Offline kriggy

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Re: Boc Deprotection
« Reply #4 on: May 16, 2020, 02:20:46 PM »
I used 20% TFA in DCM at room temp. Got rid of it pretty much instantly.

Offline Bertrand

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Re: Boc Deprotection
« Reply #5 on: May 17, 2020, 04:27:40 AM »
Do you think the disulfide bond will remain intact?

Offline rolnor

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Re: Boc Deprotection
« Reply #6 on: May 17, 2020, 05:44:18 AM »
Is this solid-phase chemistry? How do you monitor the reaction?

Offline kriggy

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Re: Boc Deprotection
« Reply #7 on: May 18, 2020, 09:08:31 AM »
Do you think the disulfide bond will remain intact?

Yeah I think so. Im not really into this kind of chemistry but my wife was breaking some disulfide bonds and afaik it required reducing agents such as PPh3.

Also, if its solid phase chemistry, dont forget TFA cleaves your product from resin. Dont know what are exact procedures in your group but ours "SPSists" cleave with TFA, filter the residual resin, wash few times with DCM and purify on HPLC or with common collumn chromatography.

Futhermore, based on your first post and description of the procedure "nothing happened" is quite broad steatement. Is there no reaction? Or no precipitation by ether? You might also be getting some intramolecular amidation. Seems likely since it formes 6-membered diketopiperazine

Offline Bertrand

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Re: Boc Deprotection
« Reply #8 on: May 23, 2020, 04:27:34 AM »
Hello everyone and thanks for your suggestions. It is not a solid-phase synthesis.

I also faced difficulties with monitoring the reaction and I found a trick for. Fortunately, The compound is UV visible. 
I just followed the procedure that posted earlier... Normally, I should have obtained a precipitate after adding cold Et2O into the reaction mixture. However, I didn't get a precipitate. Maybe the Et2O wasn't cold enough.

I will repeat the procedure during the coming week with colder Et2O and I will let you know the results   

Offline rolnor

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Re: Boc Deprotection
« Reply #9 on: May 23, 2020, 09:34:20 AM »
You should monitor the reaction in some way, the precipitate is not a good way to do this. You can evaporate and run NMR.

Offline Babcock_Hall

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Re: Boc Deprotection
« Reply #10 on: May 23, 2020, 10:00:22 AM »
By TLC there should be a substantial change in Rf values.  If the compound is UV-active, then fluorescent TLC plates would seem like a good way to proceed.  If the product is a primary amine, it should also be detectable by ninhydrin.  A long time ago I may have read of a method to remove the BOC group after running a TLC plate (perhaps by heat).  That would mean that you could also use ninhydrin for the starting material.

Offline wildfyr

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Re: Boc Deprotection
« Reply #11 on: May 24, 2020, 10:27:05 AM »
Boc is heat unstable by how great the enthalpy and entropy of turning a solid/liquid into CO2 and 2-butene is once you can get over the activation barrier.

Offline Bertrand

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Re: Boc Deprotection
« Reply #12 on: May 24, 2020, 03:08:51 PM »
Hello Everyone!

Thank you so much for your suggestions

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