Collision‐induced dissociations of deprotonated peptides, dipeptides and tripeptides with hydrogen and alkyl α groups. An aid to structure determination

The characteristic collision‐induced dissociations of [M  H]− ions of dipeptides and tripeptides involve proton transfer to the carboxylate centre as a prelude to fragmentation. Dipeptides show the process NH2CH(R1)CONHCH(R2)CO2− → NH2C(R1)CONHCH(R2)CO2H → −NHCH(R2)CO2H + NH2C(R1)CO (R = H or alkyl) while tripeptides show the analogous processes NH2CH(R1)CONHCH(R2)CONHCH(R3)CO2− → NH2CH(R1)CONHC(R2)CONHCH(R3)CO2− → NHCH(R3)CO2H + NH2CH(R1)CONHC(R2)CO and NH2CH(R1)CONHCH(R2)CONHCH(R3)CO2− → NH2C(R1)CONHCH(R2)CONHCH(R3)CO2H → −NHCH(R2)CONHCH(R3)CO2H + NH2C(R1)CO. These fragmentations provide ready identification of the peptide.