DIFFERENTIATION AMONG THE 4 DIASTEREOMERS OF BENZYLOXYCARBONYL-PROTECTED GAMMA-HYDROXYORNITHINE IN NEGATIVE-ION FAST-ATOM-BOMBARDMENT MASS-SPECTROMETRY

Discrimination among the four gamma-hydroxyornithine diastereomers was studied by fast atom bombardment mass spectrometry (FABMS). It is imp ossible to distinguish among the four diastereomers of this amino acid by positive- and negative-ion FAB and collisionally activated dissoci ation MS, but benzyloxycarbonyl group protection of the alpha- and del ta-amino groups in gamma-hydroxyornithine allows differentiation among the diastereomers in negative-ion FABMS. The negative-ion mass spectr a of benzyloxycarbonyl-protected gamma-hydroxyomithine diastereomers s howed differences among the abundances of the molecule ion [M - H]-, t he dehydrated ion [M - H - H2O]- due to the loss of the gamma-hydroxyl group and the fragment ions formed from both [M - H]- and [M - H - H2 O]- ions. On the other hand, no difference was found between the fragm entations of the benzyloxycarbonyl-protected enantiomers of ornithine in negative-ion FABMS. These results indicate that the orientation of the gamma-hydroxyl group and the existence of two benzene rings in the benzyloxycarbonyl group are important factors which are responsible f or the fragmentations of the four benzyloxycarbonyl-protected gamma-hy droxyornithine diastereomers in negative-ion FABMS. These studies also showed that the negative-ion FABMS for benzyloxycarbonyl-protected ga mma-hydroxyornithine diastereomers is a useful method for determining the configuration of each diastereomer of gamma-hydroxyornithine.