I posted the method for using neat piperidine, which we have used on
different occasions. We did not notice fragmentation by ES-MS
afterwards, and the peptide weight afterwards corresponded to the
quantification obtained using FMOC. However, each peptide, as we know,
behaves differently, so I would agree to be careful and try on a small
ammount of peptide first. It would be interesting to know if there are
particular AA sequences that are particularly sensitive to these
conditions.
Bye ALex
Marcus Macht ha scritto:
>
> At 11:06 15.09.99 -0400, you wrote:
> >Hi everybody,
> >
> > 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
>
> 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...).
>
> Yours sincerely,
> Marcus Macht
>
> **************************************************************************
> Dr. Marcus Macht
> University of Cologne
> Centre for molecular medicine - Service laboratory
> Joseph-Stelzmann-Str. 52
> 50931 Cologne, Germany
> Tel.: +49 221 478-6995
> Fax: +49 221 478-6977
> e-mail: Marcus.Macht@uni-koeln.de
> **************************************************************************