The adduct could be the HMP (hydroxymethylphenyl)linker mass 106.1. An
additional long shot guess and interesting side reaction to be aware of
could be the C-terminal cysteine forming a 3-(1-piperidyl)alanine adduct
+51 and you may still have one t-butyl group +56.1 present on your molecule
(Letters in Peptide Science Vol.3 (1996) pp.157-166). This would add up
close to your observed mass. I have see the piperidyl alanine formation
before on C-terminal acid peptides using the Cys(Trt)Wang resin but
successfully made them using the Cys(Trt)2-Cl(trt)resin.
Hope this helps
Darryl Hardie (dhardie@uvic.ca)
UVic Protein Chemistry Centre
Victoria,B.C, Canada
http://proteincentre.dhs.org
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://proteincentre.dhs.org