Dear Cami:
Possible solutions to your problem are:
i) re-synthesize peptide using Boc-chemistry (if you can "afford" it);
otherwise, incorporate Hmb-Ile before your first Asp as well.
ii) I can't recall any report on regio-specific aspartimide ring
cleavage. Normally, it proceeds regioselectively (ca. 2:1) in favor of
wrong opening product, the beta-Asp peptide. Termination of Edman
sequencing you observe I take as indication that aspartimide ring is
intact in your product (MS?). If so, you should try to convert it to the
mixture of regioisomers with partial recovery of functional properties.
Try pH 8.5 overnight and add guanidinium hydrochloride in case of
precipitation. You even may be lucky to resolve regioisomers using HR
IEC, but chances are poor.
Good luck!
Igor Rodionov
Laboratory of Peptide Chemistry
Branch of Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry
6 Science Avenue, Pushchino, Moscow Region
142292, Russian Federation
rodionov@fibkh.serpukhov.su
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