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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