Again, thank you all for your responses. I have not resynthesized
this peptide yet but will let you know how it turns out. I will
watch cycles and use different Arg-pbf. I would like to clear up one
misunderstanding though. This
synthesis did not include a double couple or recouple cycle. I had
done that on a previous synthesis that had this problem but not this
one. I, like most of you, very seldom do a recouple. I normally just
go for it, especially on short peptides. I do after-the-fact Kaiser
tests so if there were a problem of any kind, I would have a clue
where to start.
One more time, thanks!
Sandie
>This is very interesting.So,you say that there may be enough base to remove
>the Fmoc group,especially if there is a lengthy treatment?Does this happen
>more with some residue(like Arg),than other?
> Anyway,from day one,after I started using Fmoc chemistry,I stuck to a
>single coupling,though longer with difficult amino acid,such as N-methyl
>ones.
>
>
>
>
>wesdocps@appliedbiosystems.com@aecom.yu.edu> on 02/05/2001 10:54:40 AM
>
>Sent by: Association of Biomolecular Resource Facilities
> <abrf-request@aecom.yu.edu>
>
>
>To: Recipients of ABRF List <abrf@aecom.yu.edu>
>cc: Recipients of ABRF List <abrf@aecom.yu.edu>
>
>Subject: Re: peptide syn
>
>
>
>Hi Sandie:
>
>Your extra Arg is most likely due to a double addition of Arg when you
>performed you "Double Couple" cycle. This can occur when the Fmoc attached
>to the Arg added during the first coupling is prematurely removed prior to
>the introduction of your second dose of Arg. This effect is enhanced when
>there is washing with solvent (NMP or DMF) between the two additions,
>especially if you have old or bad solvent containing high residual amine
>content. My suggestion...do not double couple. If you do, eliminate any
>wash between the two Arg additions for that double couple cycle.
>
>Hope this helps.
>
>Pat Wesdock
>Applied Biosystems
>
>
>
>
>
>
>Sandie Smith <sandie@mail.utexas.edu>@aecom.yu.edu> on 01/31/2001 02:40:10
>AM
>
>Sent by: Association of Biomolecular Resource Facilities
> <abrf-request@aecom.yu.edu>
>
>
>To: Recipients of ABRF List <abrf@aecom.yu.edu>
>cc:
>
>Subject: peptide syn
>
>
>Dear pepsyn gurus
>
> I have just synthesized a peptide: GARRGKGR-NH2. By mass analysis I
>have two species,one is correct, the other has an extra Arg (+156).
>The incorrect one is about 70%. There was nothing to indicate an
>instrumental error. A Kaiser test indicated only that coupling was
>not as efficient at the RR cycles as the other cycles. This has
>happened one time before,two to three months ago, again involving a
>RR sequence. That time I had done a recouple after the first R. I
>redid the synthesis, without a recouple and got the correct mass
>only. I put it down to some unknown, never to be explained, problem,
>with the recouple. Now it's come up again. Please, does anyone have
>a solution to this puzzle?
>
>Thank you,
>Sandie
>Sandra S. Smith
>Research Associate
>Protein Microanalysis Facility
>Institute for Cellular and Molecular Biology
>MBB 1.420
>University of Texas, Austin, Texas 78712
Sandra S. Smith
Research Associate
Protein Microanalysis Facility
Institute for Cellular and Molecular Biology
MBB 1.420
University of Texas, Austin, Texas 78712
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