Abstract
If oligopeptides contain a free and acidic α-amino acid at the N-terminal, the B/E linked scan sputtered ion mass spectrometry (SIMS) technique is useful, without derivatization, as a general method not only to distinguish each pair of α- and ω-isomers but also to elucidate some of their structures. Ten pairs of such glutamyl oligopeptides (1-10, 11-20) and five pairs of aspartyl dipeptides (28-37) were examined in order to prove the usefulness and generality of the technique. γ-Linkage of the terminal acidic amino acid in naturally occurring norophthalmic acid (17) and glutathione (21) could be identified easily by using this method. Spectra of a pair of acetylated glutamyl dipeptides (21, 23), and two pairs of esters (24-27) of glutamic acid were also measured for comparison.
