Hi folks,

i need your help if you're familiar with organic chemistry :D

look at following picture:

I am not sure what do you want. Did you mean to have another protecting rgoup, not Fmoc, or you want to deprotect this animo acid to free the NH2?

no i dont want to free the NH2 ( i know this can be done by piperidine.. etc.)

i want to know if i can "displace" the FMOC ( i dont want the dibenzofulvene part !, the COO part can remain on the NH of the Aminoacid) by some other moiety ( doesnt matter what...)

why? --> i got some other moiety sticking @ dibenzovulvene which is unstable (variates) and i want to see where the fmoc sticks @ the aminoacids...(with ms --> i need the exact mass, but since the moiety variates...)... so i actually need a kind of "Tag" which marks the position of the Aminoacid

hope that it is clearer now^^

greets
Diabloo

or in other words:

can i transesterificate a Proteinprotection group (FMOC, BOC) ?

greets
Diabloo

Maybe you can try boc protection after the deprotection of Fmoc?

hm, but if i would deptrotect it, and add Boc, there's not guarantee that the Boc sticks @ the same position where the fmoc was... thats what i actually want....

Is this an amino acid or a part of more complicated structure? Are there any additional amino groups? If it is an amino acid you can do the deprotection/reprotection with a decent yield. Otherwise, protect the other amine groups first with a different protection group is needed.

its not only 1 aminoacid its a peptide... hm sounds not bad,
so you think i could do this:

takethe peptid(s), adding boc, and then "kick" all Fmoc (with the variating moiety i dont want) and then add the Fmoc i want... -->
would it work with the boc ( or some other proctecting group) to protect all the other aminoacid's (NH2-groups) in a peptide mix ?

btw. thx for your help & ideas :D

No. It is not so easy. You need to first protect any free amine groups with a protecting agent that can be removed under a different condition than that for Fmoc and Boc. Then remove the Fmoc. Followed by Boc protect the newly generated NH2 with Boc anhydride or other Boc reagents, then remove the first protecting group that you used.

It will be easier if the peptide is still on the resin, otherwise, it will be a very, very difficult work ahead. Good luck.

hm, i just thought to use BOC and FMOC only cause:

BOC = unstable under acidic conditions
FMOC = unstable under alkaline conditions.

so i would add BOC to the peptide mixture and then kick the FMOC (alkaline conditions). --> then i won't need a 3rd protecting group... wouldn't that work? ( or plz tell me why you think to need a 3rd kind of protection group)

and plz can you tell me why you think it will be very very difficult? :D

thx,

greets Diablooo

First, you need to tell me if there is free NH2 in this peptide. If so, you need to protected first with a third group or you will have more Boc groups in the peptide than the place(s) that Fmoc occupies and you want to replace, did I get you right?

Peptide modification to completion and subsequent purification can be tricky and its much easier you do it while it is on column.

sry i didn't reveal all; its that way:

i got a protein which is random sticked with FMOC ( so guess there are for sure free NH2's). Now i treated this protein with Trypsin, so i got alot of peptides.
The aim is: to find the Aminoacids where the FMOC is (random) sticked (with the MS). I know it sounds a bit stupid ^^ --> so i don't have a protein sticked to a column...

greets Diabloo