Hello colleagues,

I am looking for help from those of you who work in peptide synthesis. I am preparing a peptide containing the following amino acids: HO-Cys(SAcm)- Asp(OtBu)-Pro-Gly-Lys(Boc)-NH2, by HRMS (mobile phase H2O/ACN + 0.1% FA) I observe a signal M=690.3, which corresponds to the desired peptide that lost a tBu protecting group from Asp. However, there is another signal with M=585.3, do you have any ideas of what it can be?