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At 11:06 15.09.99
I was hoping to find out some information concerning removal of the
>F-moc group from a peptide that has already been cleaved off the resin.
Is
>it possible? The literature I have reviewed only discusses removal of
the
>Fmoc while it is still attached to the resin. The peptide in question
is a
>14mer with the following sequence . . . K Q K A F E R A I A G D E H.
Any
>help with this matter would be greatly appreciated. Thanks in advance.
>
>Rachel Pulver
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Dear Rachel,
I have used a mixture of 20% piperidine in DMF a couple of times and it
worked quite well. Using DMF solution you can precipitate your peptide
afterwards as usual with Et2O and use the normal workup procedure.
Somebody also posted a message in this group that neat piperidine will
also
work. I tried this and it cleaved; unfortunately not only the Fmoc group
but the complete peptide into small pieces, so please be careful with
this
kind of recipe.
Just for curiosity: Is the peptide still completely Fmoc protected or do
you just want to remove the remainings of an incomplete deprotection
step?
If the latter one is the case, how did you determine the Fmoc content?
In
my experience e.g. MALDI-MS usually shows a horrible amount of uncleaved
Fmoc-peptide (sometimes 50% or even more) while in fact (according to
HPLC
at 215 nm) it is most likely below 5%. This is probably due to an very,
very much better desorption of the Fmoc-peptide (maybe because of an
extremly efficient energy transfer upon the Fmoc group (comments
appreciated...)? Fmoc cleavage can be monitored by UV absorption between
300 and 320 nm , the N2-laser has a wavelength of 337 nm...).
Marcus Macht
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50% diethylamine in DMSO for 1 hour at rt rotovap to ~1/2 volume
precipitate at -20 C with 10 volumes of diethyl ether
Henry Wolfe
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