Differences in the formation and fragmentation of sodium adduct ions between tertiarybutoxycarbonyl-protected prolylproline diastereomers in fast atom bombardment mass spectrometry

The effect of Na+ ions on the fragmentation of tertiarybutoxycarbonyl (Boc) protected prolylproline (Pro-Pro) diastereomers, Boc-Pro-Pro and Boc-D-Pro-Pro, was studied in positive-ion fast atom bombardment (FAB) and tandem mass spectrometry. The formation of the [M+Na](+) ion for Boc-D-Pro-Pro was more predominant than that for Boc-Pro-Pro on the addition of sodium chloride in positive-ion FAB mass spectrometry, suggesting that Boc-D-Pro-Pro has a stronger Na+ ion affinity than Boc-Pro-Pro. In the collisional-activated decomposition mass spectra of the [M+Na](+) ions, the abundance of the [M+Na-C(CH3)(3)+H](+) ion, which is due to the loss of a tertiarybutyl group from the [M+Na](+) ion for Boc-D-Pro-Pro, was higher than that for Poe-pro-Pro. These results indicate that the interaction of the Naf ion with Boc-Pro-Pro is different from that with Boc-D-Pro-Pro in the FAB condition, and these diastereomers are distinguished by the addition of a Na+ ion in FAB and tandem mass spectrometry.