Differentiation among the four diastereomers of benzyloxycarbonyl-protected γ-hydroxyornithine in negative-ion fast atom bombardment mass spectrometry

Discrimination among the four γ‐hydroxyornithine diastereomers was studied by fast atom bombardment mass spectrometry (FABMS). It is impossible to distinguish among the four diastereomers of this amino acid by positive‐ and negative‐ion FAB and collisionally activated dissociation MS, but benzyloxycarbonyl group protection of the α‐ and δ‐amino groups in γ‐hydroxyornithine allows differentiation among the diastereomers in negative‐ion FABMS. The negative‐ion mass spectra of benzyloxycarbonyl‐protected γ‐hydroxyornithine diastereomers showed differences among the abundances of the molecule ion [M – H]‐, the dehydrated ion [M — H — H2O]‐ due to the loss of the γ‐hydroxyl group and the fragment ions formed from both [M — H]‐ and [M — H — H2O]‐ ions. On the other hand, no difference was found between the fragmentations of the benzyloxycarbonyl‐protected enantiomers of ornithine in negative‐ion FABMS. These results indicate that the orientation of the γ‐hydroxyl group and the existence of two benzene rings in the benzyloxycarbonyl group are important factors which are responsible for the fragmentations of the four benzyloxycarbonyl‐protected γ‐hydroxyornithine diastereomers in negative‐ion FABMS. These studies also showed that the negative‐ion FABMS for benzyloxycarbonyl‐protected γ‐hydroxyornithine diastereomers is a useful method for determining the configuration of each diastereomer of γ‐hydroxyornithine.