Sandy,
We had encountered a problem with our Pioneer where we began to see +98
adducts strongly from all the peptides where the Fmoc was removed from the
N-terminus. Sue Hantman of PE BioSystems was sharp enough to pick up on the
problem and point it out to us via this discussion group. When using
uronium salts (HATU, HBTU, TBTU) to do the activation you can get
tetramethylguanidium salts (+98) if the activator is delivered to the
synthesis column in excess or before the amino acid. In our case, it was
due to a bad valve allowing activator to leak to the column during the final
Fmoc removal.
I don't know if this may apply to your situation, but if you think it might
check out your valves to be sure there are no leaks (or have service
engineer in) and be sure you do not have activator in excess of your amino
acid.
Randy Wilhelm
Sr. Research Chemist
Mallinckrodt, Inc
Discovery Research Peptide Team
Phone (314)654-3965
Fax (314)654-8911
rrwilhe@mkg.com
> ----------
> From: Sandy Kielland[SMTP:kielland@uvic.ca]
> Sent: Thursday, January 13, 2000 3:06 PM
> To: Recipients of ABRF List
> Subject: PepSyn: Origin and removal of +98 adducts
>
> Peptide Synthesis members,
>
> I have been making Tryptophan(Boc) and Arginine(Pbf) containing peptides
> but have been seeing +98 adducts by Fab-MS. I initially thought they were
> phosphate clusters as in Chowdhury and Chait's "Origin and Removal of
> Adducts..." JASMS paper. Barium acetate precipitation did not improve the
> MS results. The cleavage cocktail used was 95% TFA,2.5% TIS and 2.5%
> water. Can this be a Trp sulfonation problem from the Arg(Pbf) group as
> seen with the older Pmc protecting group? Or as Dr.Stewart suggested in
> an
> older post could it be trifluoracetaldehyde attaching to the indole ring?
> I will be trying his suggestion of addition of indole to the TFA before
> cleavage to see if the adducts decrease.
>
> Any observations or suggestions would be appreciated.
>
> Thanks
>
> Darryl
> Hardie
>
>
>
> Sandy Kielland
> Victoria Protein Microchemistry Centre
> Department of Biochemistry and Microbiology
> University of Victoria
> Victoria B.C. CANADA
> phone: (250) 7218884
> FAX (250) 7218855
> Email Kielland@UVic.ca
> Webpage http://www.proteincentre.com
>
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