July 04, 2022, 08:49:31 AM
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Topic: FMOC deprotection and work-up  (Read 2510 times)

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Offline Babcock_Hall

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FMOC deprotection and work-up
« on: February 24, 2022, 06:13:28 PM »
Our functional groups are tertiary-butylester, vinyl sulfone and FMOC-protecting group on nitrogen.  Our goal is to remove the FMOC group and then couple with an amino acid, derivative as the N-hydroxysuccinimide ester.  We plan to use diethyl amine to remove the FMOC group, which two groups have used in the presence of a vinyl sulfone.*  One of the groups purified by HPLC but did not provide the column, the loading, or the solvent.  The other group removed the volatiles but did not do any further purification before moving on to a coupling reaction.  I have to wonder whether or not the fulvene adduct with diethyl amine will be volatile enough to remove.  I don't have any experience with purifying amines over silica, but I have read that sometimes triethylamine is used in the solvent.  Does anyone have any suggestions on the best way to proceed?
*there is one paper that indicated when an electron-withdrawing group is bound to the sulfur of the sulfone, that addition into the vinyl group can happen.

Offline rolnor

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Re: FMOC deprotection and work-up
« Reply #1 on: February 25, 2022, 04:55:55 AM »
No, the fulvene is to large. Yes 1-5% TEA in the eluent is usefull. Pack the column without the TEA. Is there a risk of 1,4-addition of diethyl amine to the vinylsulphone? Maybe use tertiary amine instead? DBU?

Offline Babcock_Hall

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Re: FMOC deprotection and work-up
« Reply #2 on: February 25, 2022, 10:06:34 AM »
I have also heard that dibenzofulvene can polymerize; therefore, one should not let the mixture sit around indefinitely.  I think that the addition is more of a problem when one has a compound with a S-pyridyl group.
EDT
I have also heard that toluene can help with the removal of the remaining diethyl amine in rotary evaporation.
« Last Edit: February 25, 2022, 11:21:47 AM by Babcock_Hall »

Offline rolnor

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Re: FMOC deprotection and work-up
« Reply #3 on: February 25, 2022, 02:30:49 PM »
Diethyl amine has low bp. No problem. If you use cromatoghraphy these things solve themselves.

Offline Babcock_Hall

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Re: FMOC deprotection and work-up
« Reply #4 on: March 01, 2022, 02:58:48 PM »
We used diethyl amine and followed by TLC.  Then we removed the volatiles.  The solvent we were going to use to move dibenzofulvene through the silica column is 40/60 ethyl acetate and hexanes.  The product is insoluble in it.  The product can be suspended in DCM, but I would not call it a true solution.  Any thoughts about the best way to proceed?

Offline rolnor

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Re: FMOC deprotection and work-up
« Reply #5 on: March 01, 2022, 03:25:24 PM »
Use DCM/MeOH

Offline Babcock_Hall

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Re: FMOC deprotection and work-up
« Reply #6 on: March 01, 2022, 08:44:52 PM »
When we used TLC, we initially thought that 99:1 EtOAc/TEA was sufficient to move the product.  DCM/MeOH was more successful; thank you.

Offline Babcock_Hall

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Re: FMOC deprotection and work-up
« Reply #7 on: March 03, 2022, 03:09:14 PM »
Is there any reason why chloroform might work better than DCM in terms of solubilizing the amine?  I have run columns to purify phosphonates in both solvents previously.
« Last Edit: March 03, 2022, 03:49:23 PM by Babcock_Hall »

Offline wildfyr

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Re: FMOC deprotection and work-up
« Reply #8 on: March 04, 2022, 12:07:02 PM »
No, they are quite similar, though DCM is a bit more polar. I seldom have met small molecules where it dissolved in one but not the other.

Offline rolnor

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Re: FMOC deprotection and work-up
« Reply #9 on: March 04, 2022, 01:17:34 PM »
You have EtOH as stabilizer in chloroform, this can be a problem if to polar. I think they are similar as wildfyr says. Maybe you need to test this in small scale.

Offline Babcock_Hall

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Re: FMOC deprotection and work-up
« Reply #10 on: March 16, 2022, 10:02:08 AM »
From the silica column we obtained two small pools of products, neither one of which is our compound of interest.  We cannot account for all of the mass that we put onto the column.  Back to the drawing board.

Offline rolnor

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Re: FMOC deprotection and work-up
« Reply #11 on: March 16, 2022, 05:05:45 PM »
Do you see any ethyl groups that could come from 1,4-addition? Do you see double bond?

Offline Babcock_Hall

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Re: FMOC deprotection and work-up
« Reply #12 on: March 16, 2022, 05:31:26 PM »
I did not see a double bond.  I also did not see the CH3SO2 group.

Offline rolnor

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Re: FMOC deprotection and work-up
« Reply #13 on: March 16, 2022, 11:58:44 PM »
Maybe you did get 1,4-addition and this product is so polar that it did not elute.

Offline rolnor

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Re: FMOC deprotection and work-up
« Reply #14 on: March 17, 2022, 05:27:47 AM »
I suggest you try 1eq. DBU att 0°C. Its a poor nuchleophile and strong base. Also run in a NMR-tube, you will get signals from DBU but the double-bond should be visible and the deprotection possible to monitor.

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