COLLISION-INDUCED DISSOCIATIONS OF DEPROTONATED DIPEPTIDE METHYL-ESTERS CONTAINING H, ALKYL OR BENZYL ALPHA-SIDE-CHAINS

The mass spectra of(M - H)- ions derived from dipeptide methyl esters are not as useful from an analytical viewpoint as those of the underivatised peptides in that they lack the characteristic backbone cleavage which provides the primary sequencing data. Instead, major fragmentation occurs through the ester group, viz. competitive losses of MeOH and HCO(2)Me are noted. Specific fragmentations differentiate between dipeptide methyl esters containing C- and N-terminal Phe. Deuterium labelling and product ion studies have aided this investigation.